A collection of DIY Hi-Fi Audio Projects for Audiophiles.
300B Single-Ended-Triode Amplifier

300B Single-Ended-Triode (SET) Amplifier Project

The DIY 300B triode amplifier shown below was completed by Stamou Tasos (Greece).  The 300B triode amplifier was built following the 300B single-ended (SE) tube amplifier schematic by J.C. Morrison.


DIY 300B Single-Ended-Triode Hi-Fi Amplifier

DIY 300B Single-Ended-Triode Hi-Fi Amplifier

For this single-ended (SE) 300B triode amplifier build Stamou has used premium parts, Lundahl audio output transformers and a DIY chassis. The 300B Single-Ended-Triode (SET) amplifier circuit uses a direct coupled 6SN7 driver stage. The output stage is a SE 300B triode and the maximum power output is about 8 Watts per channel. A pair of reasonably sensitive (~91 dB+) loudspeakers will be required with this 300B SET amplifier. 


300B Single-Ended-Triode Amplifier - Point-to-Point Construction

300B Single-Ended-Triode Amplifier - Point-to-Point Construction

The 300B SET amplifier was built using point-to-point construction.  The chassis for the 300B triode amplifier was also built by Stamou.  The frame is made from 20 mm thick MDF wood which was finished with spray primer and paint. The top plate is made from a 4 mm thick aluminum plate and the bottom plate from a 2 mm thick aluminum plate.   Your enclosure will require good ventilation.  "This is a great sounding 300B triode amplifier that I am sure DIYers will find to be very rewarding."  For the full 300B SET amplifier project details see the DIY 300B Single-Ended-Triode (SET) Hi-Fi Amplifier project page.


More 300B Triode Amplifiers


4S Universal Preamplifier for 12A_7 Tubes
The 4S Universal preamp is a Super Simple Single Stage (4S) line stage preamp that works well with the entire range of 12A_7 tubes - 12AU7, 12AV7, 12AY7, 12AT7, 12AZ7, and 12AX7. You can change the tube type to vary the gain of the preamplifier by quite a large margin. 

4S Universal Preamp for 12A_7 Tubes
4S Universal Preamp for 12A_7 Tubes
The preamp uses a 6CA4 tube rectified power supply which is very quiet. The preamplifier is built using point-to-point construction techniques and into a die cast aluminum enclosure from Pomona.  The attenuation control is on the output of the preamp.

4S Universal Preamp with 6V6 Lacewood Amp
4S Universal Preamp with 6V6 Lacewood Amp
The 4S Universal is a preamp that can be adapted to the task at hand simply by swapping tubes. It also allows some tube rolling to compare various tubes in your stash. The 4S Universal preamp is a great little unit to really bring out the most in your power amps.  For full details see the 4S Universal Preamplifier Project pageComments and questions about this project are welcome in the 4S Universal Tube Preamp Project (12A*7) thread.

Super Simple Single Stage (4S) preamp with Genalex Gold Lion 12AU7
Super Simple Single Stage (4S) preamp with Genalex Gold Lion 12AU7
The photo above is one of Mark's Super Simple Single Stage (4S) preamplifier builds.  For more information see Mark's 4S Universal Preamplifier for 12A?7 Valves.
Cheap Open Baffle Speakers (COBIES)
Bruce has put together a pair of Cheap Open Baffle Speakers - the COBIES.  Relative to most DIY speakers this open baffle project will be quite easy to build.  One of the main design goals for Bruce was to keep the total parts cost under $150US.  The open baffle speaker project was inspired by the "Big Air" open baffle system by Jim Strasser.  

Cheap Open Baffle Speakers
COBIES - Cheap Open Baffle Speakers
Each open baffle uses a GRS 12PF-8 woofer and two Goldwood GT-25 paper cone tweeters.  One tweeter is mounted on the rear of the baffle pointed upwards about 45 degrees.

Rear Mounted Goldwood GT-25 Tweeter
Rear Mounted Goldwood GT-25 Tweeter
Bruce experimented with various crossover points settling on 3.6 kHz finding that lower crossover points put too much of a demand on the GT-25 tweeters.  Using a calibrated microphone and RTA the in-room response from 100 Hz to 10 kHz was quite smooth and free of any large irregularities. Response below 100 Hz was affected by room nodes but quite good down to 40 Hz.  Above 10 kHz was certainly excellent (up to about 18 kHz).  The overall speaker system sensitivity is estimated at 93 dB / 1 watt at one meter. Bruce uses a pair of 5 watt (each) tube mono block amplifiers (EL84 PP) with the open baffle speakers. 

"The sound is something you will either love or hate. As I said earlier open baffle speaker systems are bi-polar. I really like it, some individuals will not. The speakers have an excellent overall sound. They have a lot of ambiance and provide a good listening experience. Bass is quite clean and robust ..."

Full details are available on the  COBIES (Cheap Open Baffle Speakers) project page.  Comments and questions about this project are welcome in the Open Baffle Speaker Project thread.
DIY Nearfield Monitor Speakers with Fostex FE103En

Fostex FE103En DIY Bass Reflex Bookshelf Speakers

These small computer desktop speakers were built using the in-expensive Fostex FE103En fullrange speaker drivers following the bass reflex enclosure box plans that were provided with the FE103En datasheet.  The enclosure volume is noted as 6 L and tuned to 95 Hz but the the gross volume was calculated to be 6.9 L and the box tuning frequency to be about 97 Hz.  The Fostex FE103En drivers are 100 mm in diameter and have a rated sensitivity of about 89 dB / 1 W / 1 m.  There are a couple of easy modifications that can be made to improve the FE103En drivers which are described in detail on the modifications and tweaks for the small Fostex fullrange speaker drivers information page.  A photograph of the stock Fostex FE103En drivers is shown below.

Fostex FE103En Fullrange Speaker Driver
The speaker cabinets are built from 15 mm thick Baltic birch (11 ply multiplex) plywood.  Acousta-Stuf fiber fill is used inside the speaker enclosure to dampen the rear wave from the driver and to reduce standing waves and internal reflections.  The finished speakers are shown below with the computer.  Since this position the speakers are used in the nearfield, there is no need for a baffle step compensation filter.  The  Fostex FE103En DIY Bass Reflex Bookshelf Speakers project page has full details regarding baffle step compensation for farfield use and pairing the speakers with a subwoofer.

DIY Bass Reflex Monitor Speakers with Fostex FE103En  
These little speakers have bee in use with the desktop computer in the office for a few months now and I am quite pleased with the end results.  With no crossover or filters the speakers deliver wonderful playback full with rich details.  For full project details see the Fostex FE103En DIY Bass Reflex Bookshelf Speakers (Nearfield Monitor) project page.

6DJ8 Tube Headphone Amp
We are always on the lookout for good headphone amplifiers and here is a great simple tube design that will work with a wide range of headphones.  This tube headphone amplifier design comes to us from Bruce Heran.  The tube headphone amplifier is designed along the lines of the Oddwatt power amplifiers with the exception that this headamp does not require a driver stage. The headphone amplifier uses only one 6DJ8 tube per channel in a push-pull configuration.  All the circuit gain is in the single output stage. A constant current source (CCS) is used on the cathodes to force class-A operation. The headphone amplifier circuit has no coupling capacitors and no feedback loops.  There are a total of only 7 components including the tube in each channel.  The output stage is transformer coupled and the two transformer choices will accommodate most headphones with an impedance between 32 and 600 ohms.

6DJ8 (ECC88) Valve Headphone Amplifier - Inside
6DJ8 (ECC88) Tube Headphone Amplifier - Finished
The frequency response at the 50 mW level is from 20 Hz to 28 kHz within 0.5 dB and the wide band signal-to-noise is at -84 dB. Power consumption of the headphone amplifier is approximately 20 Watts (W).  Bruce reports excellent results with his Koss Pro4AAT (250 ohms) and Sennheiser HD-280 PRO (64 ohms) headphones.  "there was no audible noise or hum and the response was rich and clean"  For full project details, see the DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project page.

More DIY Headphone Amplifier Projects:
Push-Pull EL84 Mono Block Amps

 Mono Block Ultra-Linear Class-A Push-Pull EL84 Tube Amplifier Project

Recently Bruce has been enjoying his PoddWatt amplifier and the EL84 tube sound that he has revisited the original OddWatt amplifier project, tweaked it and put together an improved EL84 push-pull amplifier.  Like the previous EL84 projects the Mini Block amplifiers use a EL84 self-inverting push-pull output stage that is biased into class-A operation.  The big difference is that the amplifiers are built as mono blocks.

Mini Block Push-Pull EL84 (6BQ5) Valve Amplifiers

Interior - Mini Block EL84 Push-Pull Amplifiers
The input circuit is a 5751 SRPP.  The ouput uses the ultra-linear connection and output power was 5.8 W @ 2% distortion and less than 0.25%  at 1 W.  The measured frequency response was 10 Hz to 44 kHz within 0.2 dB.   Bruce reports that the Mini Blocks have slightly more output power than the Poddwatts and seem to have more detail while retaining all the good characteristics of the stereo Poddwatt amps.  Full details are available on the Mini Block Ultra-Linear Class-A Push-Pull EL84 (6BQ5) Valve (Tube) Amplifier Project page.


More Mono Block Tube Amplifier Projects

Fostex FE206En Double Bass-Reflex Speakers

Fostex FE206En Double Bass-Reflex Speakers

Fans of low power tube amps love high-sensitivity full-range drivers like the 200 mm Fostex FE206En and with good reason.  The drivers are relatively inexpensive, they sound good and they do not require a crossover.  The main reason for the fan fare is because of their high sensitivity (96 dB / 1 W / 1m), which makes them ideal for use with very low power amplifiers.  However, the high sensitivity and wide frequency bandwidth of the driver come at a cost - a very low mass paper cone and a tiny excursion (Xmax=0.8 mm).  This adds up to mean that extracting bass from the Fostex FE206En is often a challenge.  The common solution to this challenge is a large back-loaded horn type enclosure.


Fostex FE206En Back-Loaded Horn Speaker Enclosures 
The problem is that these elaborate back-loaded horn type enclosures often require a skilled woodworker to construct.  The Fostex FE206En driver datasheet also include a recommended enclosure plan for a suitable bass-reflex type enclosure which is far easier to construct.  Mark has built a couple sets of the Fostex FE206En double bass-reflex speakers and reports that the simple enclosure works well with the FE206En full-range driver.


Fostex FE206En Double Bass-Reflex Speakers 
Since Mark will be using the speakers as part of his home theater setup, undercoating paint was used for a stipple like flat black and non-reflective finish.  Mark reports that the speakers are an excellent mate for use with his 6EM7 SET amp.  Full details are available on the Fostex FE206En Double Bass-Reflex Speaker project page.


More Single Driver DIY Speaker Projects



DIY Stepped Attenuator Volume Control
The latest project to be added to the site is a DIY passive volume control which is made using a switched attenuator.  A stepped attenuator operates by switching to different resistors at each of switch settings.  The benefit of a stepped attenuator is that it can use low noise metal film resistors making them quieter than typical hot formed carbon and conductive plastic potentiometers.  The volume control uses a stereo 100k 24-position stepped attenuator which comes fully assembled for $18US from 8 Audio-Mall.  The attenuator uses 1% precision metal film resistors on a "make before break" multi-position switch.  A photo of the stepped attenuator is shown below. 

stereo 100k  24-position stepped attenuator
stereo 100k  24-position stepped attenuator
The stepped attenuator is housed in a small wooden enclosure with aluminum top and bottom plates.  A knob, RCA jacks and a 4 Pole Double Throw (4PDT) switch round out the DIY volume control.

DIY Stepped Attenuator Volume Control
DIY Stepped Attenuator Volume Control
Matt reports that he is pleased with the results of the stepped attenuator volume control as it is significantly quieter than any of the carbon and conductive plastic potentiometer he has used.  The attenuator was measured to have a noise figure which is about 26dB lower than a typical PEC hot molded carbon potentiometer of the same value.  For full project details, see the DIY Switched (Stepped) Attenuator Passive Volume Control project page.


More DIY Volume Controls
DIY Direct Drive Turntable
Our first DIY Turntable project comes to us from Hungary by a talented DIYer, Nandor.  His DIY turntable project uses the platter and the direct drive motor and control assembly from a Dual 701 record player as the starting point.  The plinth of the turntable is built-up using three pieces of plywood that are stacked and glued together.  This improved plinth results in better dynamics in the lower registers and a firmer mid band.
DIY Record Player with Dual 701 Drive
DIY Record Player with Dual 701 Drive
The tonearm is a 3 month DIY project in itself, constructed using a trial and error approach.  The custom tonearm is suspended in air by magnets and a single mono-filament thread is used as an alignment guide and the pivot point.  The result is a custom built tonearm which minimized friction.
Magnetically Stabilized Record Player Tonearm
Magnetically Stabilized Record Player Tonearm
DIY Turntable
DIY Turntable
Nandor goes over the details required to make a great looking turntable using common items.  With the fantastic new tonearm and improved plinth has this old Dual 701 sounding better than ever.  For full project details see the  DIY Turntable project page.

More Phono Projects
DIY Shielded RCA Interconnect Cables
Tom has put together an easy to follow guide showing the construction of simple line-level RCA interconnect cables. The very simple cable recipe uses shielded instrument wire and good quality RCA plugs which you should be able to find at your local instrument shop.  Tom used Sommer SC-Tricone MKII wire and Rean RCA plugs, and you can use your favorite brands.  Tom's finished DIY shielded RCA interconnect cables are shown below. 

DIY Shielded RCA Interconnect Cables
The cables are very simple to construct requiring only basic soldering skills.  The required parts are easy to source and a pair of these shielded RCA cables can be built in about one hour and for as little as $10. Tom indicates that these simple DIY cables are a great upgrade over typical stock and other inexpensive interconnects.  See the project page, DIY Shielded RCA Interconnect Cables for full details.

More DIY Cable Projects
Cello Speakers - Lawrence Audio - CES 2012
CES 2012 doesn't officially kick off until tomorrow, but today I decided to check out the layout of the High-Performance Audio floors at the Venetian.  All the exhibitors were very busy setting up their exhibit rooms and it was nice to chat to them before the large crowds arrive tomorrow.  Secretly my real intent of visiting the show a day before the official start was that I was hoping to get some private listening opportunities.  While walking down one of the hallways the seductive voice of Rebecca Pidgeon pulled me into the Lawrence Audio room who are based out of Taiwan.  Just my luck, their system was ready to play and my private listening session was just moments away.  While it was the voice of Rebbeca that initially caught my attention, I was immediately struck the unique looking speakers on display and the wonderful sound emanating from them.


Lawrence Audio Cello and Violin Speakers at CES 2012
In the photo above are the new Cello speakers (larger, inside) and the Violin speakers (smaller, outside).  The Violin ($7500US) speakers won an Innovations award at CES last year and this year the Cello ($20,000) speaker have received an Innovations award this year.  The unique looking speakers resemble the instrument that they are named after which really is a refreshing change from typical boxy speaker designs.  The Cello speakers each use five drivers to make a 3.5-way floor standing loudspeaker.  The loudspeaker employs an air motion tweeter and an air motion mid-treble.  The woofer and subwoofer units are 8-inch aluminum framed drivers with a non-woven carbon fiber cone.  There is also a rear firing ribbon tweeter which I quickly identified as an Aurum Cantis G2Si.  The crossover frequencies are set at 700Hz, 1.7kHz, 2.6kHz and 9kHz with preimum crossover components used throughout.  The speakers have a nominal impedance of 4 ohms (3.2 ohms minimum) with a frequency response noted as 32Hz to 40kHz and a sensitivity of 90dB.  The loudspeaker enclosures are vented at the bottom.  Shown below with the Cello speaker is Lawrence Liao who is the acoustic designer and founder of Lawrence Audio.


Lawrence Liao of Lawrence Audio with Cello Speakers
The private listening session with Rebbeca Pidgeon and the Cello speakers was wonderful.  I am very familiar The Raven recording and the Cello speakers did a fabulous job reproducing this excellent Rebbeca Pidgeon recording.  The Cello speakers produced a very wide and deep soundstage.  Most impressive was the focus and the deep bass.  With closed eyes one can distinctly pick out all the instruments in the recording.  With it's unique looks and excellent sound reproduction, I'm sure many will be wrting about these speakers at CES 2012.    For more information see the Cello Loudspeaker at Lawrence Audio


More CES 2012 Show Coverage

CES 2012
I hope that all our readers had a great holiday season and best wishes for the new year.  We are kicking off 2012 with a bang - a trip to Las Vegas and attendance at CES 2012.  While I have been to Las Vegas many times, this will be my first time attending CES.  Thumbing through the exhibitors list it certainly looks like almost all the Hi-Fi manufacturers will be represented at the show. The high-performance audio exhibits will be located at the Venetian Hotel.  Floor plans for the High-Performance Audio suites are shown below (click floor plan images to enlarge). 


Floor 29 - High-Performance Audio Exhibitors at CES 2012
Floor 30 - High-Performance Audio Exhibitors at CES 2012
Floor 31 - High-Performance Audio Exhibitors at CES 2012
Floors 34 and 35 - High-Performance Audio Exhibitors at CES 2012
As you can see, the show is huge, so naturally I won't be able to provide complete coverage from all the exhibitors.  We will try check out most of the exhibitors and we will report back on the DIY parts suppliers in attendance and also on some of the new and interesting commercial hi-fi products on display.  Updates and coverage from CES 2012 will be posted on this blog and also in the 2012 CES, Las Vegas - diyAudioProjects.com Show Coverage thread on the forum.  I'm looking forward to hearing some very expensive Hi-Fi setups.  It will be interesting to compare the sound from the high-end systems to that of my modest and predominately DIY system.  


More CES 2012 Show Coverage
Informal Comparison of Six Phono Preamps
This is a project that sort of evolved from an interest to see how good a particular phonograph preamplifier was. Not the one I designed, but one from a DIY kit. If I would have known how difficult and possibly inconclusive it would become, I might have not done it. As it was, the experience was valuable in several ways. First let it be clear in everyones mind that this comparison is largely subjective and based on what I hear or can measure. It was concerned with only those preamps that I had available at the time and your thoughts and results could be quite different. The comparison demonstrated that without a top notch system nearly any preamp might be OK. The flip side was also true that in a top notch system, many preamps would be unacceptable. Another thing that came from the listening and testing is that compliance with RIAA equalization varies from company to company but in many cases might not be audible. My method for comparison had two parts. The first was to listen to various selections of music with each preamp and then score them on various things I felt meaningful. The second was to check various parameters with my test gear. The following six phonograph preamps were the ones compared:
Left top, Moon LP3, left middle TC 750, left bottom Jaycar KC5433,
Right top, Groove, right middle K303, right bottom DH101
General
The various phonograph preamps cover a wide range of designs and prices. The lowest cost ones are approximately $50 (TC750) and the most costly more than 10 times as much (LP3). One has an undetermined price at this time (Groove) and is likely to be above the upper end of the group even in kit form. Design variations range from entirely IC to all tube. Some use single ended configurations on the active devices, one uses fully complementary differential style (DH101) and one SRPP (Groove). All are designed as stand alone devices with the exception of the DH101 which is a complete preamp. All are MM/MI compatible with the LP3 also covering MC applications. All, but one, are solid state devices. There will be two phases, bench testing and listening.

Equipment Used For The Listening Portion 
  • Pro-ject Debut III turntable with acrylic platter and Speedbox 
  • Dynavector 10X5 high output MC cartridge (re-tipped with ruby cantilever by Sound Smith) 
  • 80-Step Passive preamp (1% precision resistors) 
  • Oddwatt KT88 Monoblock valve power amplifiers 
  • Martin Logan Vista electrostatic speakers (operating full range) 
  • Marchand electronic crossover (50 Hz low pass / 24 dB per octave to subs only) 
  • AudioSource Amp 100 dual 50 watt RMS solid state power amplifier (for the sub) 
  • Custom designed 7 cubic foot subwoofers, 15" drivers (F3 = 22 Hz) 
  • APC H10 AC line power conditioner
Listening Tests
Listening tests were performed first to avoid prejudging performance based on what the test measurements might indicate. Music selections consisted of new and older records. The music selected was varied and covered a wide range of genre. Different selections might have provided different results, but I tried to span a wide range. There were acoustic stringed instruments, male and female vocals (duets too), classic rock music, music with keyboards, solo jazz singers and big band. Each preamplifier was played in turn with the order mixed up with the same selection.

The listening performance was subjective and the various ratings are solely those of the tester. Scoring was as follows: Numeric grade of 1 to 10 with 10 being the best. 10 = among the best I have ever heard, 8 = excellent performance, 6 = average performance, 5 = minor deficiencies, below 5 increasing levels of unsatisfactory performance. Areas rated were: Signal to noise both hum and / or background noise (only in bench testing unless one is obviously deficient during the listening tests), treble response, mid range response, base response, image centering, low level detail, sound stage width, and overall involvement of the sound.
(click to enlarge)
(click to enlarge)
(click to enlarge)
Listening Test Results
It seems that price and to a certain degree complexity matters. The three most pricy or complex designs were clearly better than the lower cost three. All of the top three excelled in some areas. There is a different flavor to each that shows up in how they rendered the different musical tracks. The Groove was a clear standout in the bass region. Solid, deep and well controlled bass was noted in all cases. Other preamps occasionally got into the sub 50 Hertz range, but none with such authority. The LP3 was second in this area and was clean and well controlled, but not nearly as authoritative. The DH101 had deeper bass than the LP3, but it was not as clean and well controlled. At the opposite end of the range, the LP3 had a slight edge on all others in treble presentation. The Groove was a close second and often they were tied. In the areas of inner detail, imaging and sound stage width the differences were often linked to the particular music being reproduced. It was largely a toss up between the LP3 and Groove with the edge going to the Groove. The primary difference between the top two preamps is one of flavor. The LP3 has a crisp clean leaning toward neutral sound and the Groove a warmer more delicate sound. Either would be satisfactory in many systems. The DH101 fell slightly short of the performance of the top two, but was in most areas a rather nice sounding preamp. The three preamps in the budget category were sort of a mixed bunch. They clearly were in a different category from the top performers. In some cases they would be good entry level preamps for someone just starting in vinyl. The TC750 even with upgraded components was at the bottom of the group. It performed in what I would generally characterize as less than average manner. It really has no place in a quality system. The other two (Jaycar KC5433 and the K303) are fairly well matched. Each is slightly above the average level, but well short of the top performers. Generally their shortcomings were by omission and not commission. They are characterized by things such as less detail, less response in various parts of the spectrum and the like. They did exhibit some sibilants and edgy sounding behavior on various selections, but were mostly listenable. I felt that the level of listening involvement suffered from the omissions. I would not recommend them for use in systems above the rather modest level. It must be noted that the two are diy kit based and low cost and would not be expected to compete in the same arena as the top performers. For entry level systems they might be a reasonable option. The K303 has two gain options and the recommended setting (less gain) resulted in an output significantly below all the other preamps. I changed the setting to the higher level and the output them was approximately equal to the other preamps.
(click to enlarge)
(click to enlarge)
Equipment For The Bench Testing
  • HP 331A distortion analyzer
  • Velleman PCSD 1000 PC based digital storage oscilloscope
  • Tenma  digital storage oscilloscope
  • Tenma precision signal generator
  • Circuit Specialists MS8040 true RMS multi-meter
  • B&K 290 electronic analog multi-meter
  • APC H10 AC line power conditioner
Bench Testing
All six phonograph preamps were bench checked with my typical set up of equipment. My results may or may not agree with results by other individuals, but are consistent among themselves. A long standing issue in my workshop is a relatively high level of electronic noise. All my equipment is fitted into a fairly small area and a lot of it generates noise. The noise floor in the shop is typically -91 to -95 dBv. This necessarily limits my ability to test really quiet equipment. This was the case with two of the preamps. On the day of the tests the noise floor was -91 dBv. The Moon LP3 measured -91 dBv and the Groove at - 89.9. All those results can tell me is that both units are very quiet. The specification for the Moon is -106 dBv and the Groove has been previously measured consistently right at the noise floor (-90 to -91). The remaining 4 preamps did measure within the capability of my equipment. They ranged from as low as -81 dBv to a high of -84 dBv (more negative is better).

The gain of the preamps ranged from a low of 34 dBv (DH101) to 44.2 dBv (Groove). The remaining 4 units were all clustered around 40 dBv. Initially the K303 was about 2 dB lower than all the others (at an estimated 32 dB) and I made the kit indicated modification for additional gain. In my opinion the original gain would be insufficient for many systems especially those using passive preamps.

For signal to noise level I used a combination of the noise floor and the gain. It might be better called effective difference between the level of output and the noise floor for a given input signal. That way it would provide an indication of how quiet a preamp would seem in any particular system. The more output you have from a preamp the less follow on gain you will need to use for a comfortable listening level. Then turning down of the system gain will apparently lower the noise floor of the entire system. The opposite is equally valid. An apparently excellent noise floor could be offset by low gain with the result being an apparent higher overall noise level in the final sound level from the system. The results here favored the Groove with its higher gain; however the Moon would probably be better if the actual noise level could have been measured. Both are extremely quiet in use. The remaining units were within a 5 dB span with the DH101 with the lowest apparent signal to noise ratio. None however exhibited sufficient noise to detract from the listening experience.

Distortion levels were measured at 1000 Hertz at the 1 volt RMS level into a 10k-ohms resistive load. Capacitance was minimal at approximately 100pF due primarily to the short cables used in the test set up. Deviating from my usual procedures, I used a battery powered signal generator. This eliminated a number of possible noise sources that would be considered by my distortion analyzer as distortion. For it anything that is not the fundamental is considered distortion. The penalty in doing this is that the residual distortion in the generator was 0.44%. However, since all preamps were tested the same the results while not definitive do provide a comparison. It should be noted that doing a complete test of the distortion levels and subsequent matching to the RIAA standard is a very time consuming process and was not the focus of this comparison. The actual distortion levels ranged from 0.65% for the Moon to 2.3% for the Jaycar. As noted in the listening tests there were no specific instances of audible distortion, but rather some less than stellar performances. Of particular note were issues with the TC750. In testing it was discovered that it had a very low output capability. It was unable to deliver over 1.75 volts RMS at low to mid frequencies and above approximately 10 kHz it could not deliver over 0.5 volts RMS without visible distortion of the wave form. All other preamps were able to deliver over 5 volts output at any frequency easily.

To determine basic compliance with the RIAA standard, I used 5 separate frequencies. All preamps were tested at the one volt output level except the TC750 that was unable to deliver that level and it was tested at the 0.5 volt level. The chosen frequencies were picked as they are the ones where the worst performance could be expected. This is at the upper and lower extremes of the audio band in comparison to the 1000 Hertz reference. My experience has been that nearly any phono preamp can come reasonably close to the standard between the limits of 100 Hertz and 10,000 Hertz. There is some disparity in what various manufacturers do at frequencies below 50 Hertz and above 15,000 Hertz. Some either flatten the curves there or in some cases actually intentionally reduce response there. The thinking behind this is most likely that there is little musical content there and there are possible benefits to the signal to noise and cancellation of rumble and low frequency resonances. In my opinion, the preamplifier should reproduce whatever signal it is fed and problems with noise should be handled at the source. As noted in earlier paragraphs, the measurements I made might or might not be the same as someone else would get, but all units were tested the same and the results allow for some comparisons. There really was no perfect fit. However the Groove, Jaycar and (surprise) TC750 were closest. The Moon was excellent on the high end, but for some reason demonstrated a reduction at 50 Hertz (only a dB) and a rapid reduction in response at 20 Hertz (3 dB). The K303 was significantly off at 50 and 20 Hertz and I can speculate it was because of its high sensitivity to the load. This was evident when a quick check of each preamp was done with a 5 k-ohm load in place of the standard 10k one. The only preamp that demonstrated a significant drop in output was the K303. The reduction was approximately 3 dB at mid band. This factor may limit its application to only systems with relatively high input impedance (the test system was approximately 50 k-ohms).
Electrical Test Data (click to enlarge)
Summary and Conclusions
Since the comparison was largely subjective with some bench testing used to verify or at least establish some relationships between the preamps, the conclusions necessarily are also subjective. None of the three budget preamps should be considered anything but entry level devices. The TC750 is at best a marginal one even in that group. The K303 and Jaycar are fairly well matched, but have slightly different sonic signatures. In modest and undemanding systems they would probably be adequate. I would not use the K303 without the modification for higher gain. The notation in its instructions that the extra gain would allow it to be used with low output moving coil cartridges is suspect. With the extra gain it was right in the middle of the group for moving magnet / moving iron cartridges. I would also not use it systems in which the following equipment had an impedance lower than 10K ohms and preferably with ones above 50K. The DH101 was a surprisingly good performer considering it was included primarily as a comparison of older technology, granted one with some exceptional design features. It would have fared better with more gain, but since it is actually part of a complete preamplifier it is entirely likely that the shortage in gain was compensated for in later stages. The remaining two preamps are both excellent and quite different in many respects. Both are extremely quiet. They have low distortion and with the exception of the curious bass reduction in the Moon, match the RIAA curves well. They both sound excellent, but different. The Moon is articulate and the Groove robust. Each is a product of its technology. The Moon is all solid state IC based. The Groove is an all valve design. The end choice is likely to be whether you prefer solid state sound or valve sound. I will not argue for either case as both are valid at the personal level. My personal preference is for the sound of the Groove, but I could, and have listened happily to the Moon for nearly a year while designing and perfecting the Groove.

Good listening,
Bruce Heran
Knock-Down Birch Speaker Cabinets
Speaker building is a lot of fun and there are many who would love to try it out but can't due to some common woodworking hurdles.  You may not have the space, tools or skills necessary to build a good loudspeaker enclosure.  For others sawdust or climate (winter) could be the problem.  Fortunately there are some great solutions that can eliminate much of the woodworking necessary to build a speaker box.  For a number of years Dayton Audio has been producing pre-made speaker enclosures like the Dayton pre-made curved speaker cabinets which make it real simple to put together a great looking finished speaker.  Perhaps the only downside to the great looking ready-made cabinets is that they eliminate too much DIY and they are bulky to ship.

Enter these great Knock-Down Birch Cabinets from Parts Express.  The cabinets are CNC-cut and made from seven-ply, 1/2" birch panels.  The cabinets have dadoed top, bottom, sides and braces to maximize the gluing surface.  The knock-down speaker cabinets are unfinished leaving you with many different finishing options.

Knock-Down Birch Speaker Cabinets
Shown in the photo above is the Knock-Down Birch 5.1 Home Theater Cabinet Package and a Knock-Down Birch 0.60 cu ft Monitor Cabinet.  The YouTube video below shows just how simple it is to put together the knock-down birch speaker cabinets.


With the CNC birch knock-down cabinets it is easy even for the beginner to end up with amazing finished results without the need for expensive tools or access to a woodshop.  There are a number of cabinet sizes to choose from.  See the Knock-Down Birch Cabinets for a full selection.

More DIY speaker kits and cabinets
Groovewatt Tube RIAA Phono Preamp
The latest project from Bruce's workbench is the Groovewatt, a tube based RIAA phono preamplifier.  The Groovewatt is the result of over one year of work and several build iterations.  Bruce set some pretty high performance requirements for the tube preamp and he is very pleased with the results. 

Second Groovewatt Build 
The Groovewatt uses a symmetrical SRPP (12AX7) input stage which feeds a passive RIAA equalization network. The second gain stage is nearly identical to the input stage and is direct coupled to the third stage which is a cathode follower (12AT7).  Bruce used Gold Pin JJ ECC83S for the SRPP stages and half of a ECC81 for each side of the cathode follower.  The power supply is solid state and DC is used for the tube heaters.  Total gain of the RIAA phono preamp is about 45 dB which should be sufficient for use with a high output MC cartridge.

Inside View - Third Groovewatt Build
Third Groovewatt Build
The measured performance of the Grovewatt is excellent and noted in the project page.  Bruce reports excellent results with the Groovewatt in place in his system.  For the full details of the Groovewatt, see the DIY Vacuum Tube (Valve) RIAA Phono Preamp project page.

 
More Hi-Fi Vacuum Tube Projects by Bruce
BK-12m Folded Horn Kit - Fostex FE126En
There is a new high-sensitivity folded horn speaker kit being offered by Madisound.  The new BK-12m is a single-driver folded horn speaker kit that follows in the lineage of the BK-16 and BK-20 designs.  The BK-12m uses the Fostex FE126En full-range speaker driver in a custom folded horn enclosure while the driver is run full range with no filters whatsoever.  The Fostex FE126En driver is 4.7" (120 mm) in diameter with a rated sensitivity of 93dB/W(m).  This high-sensitivity means that the BK-12m speakers will be suitable for use with low powered amplifiers.

BK-12m Folded Horn Kit - Fostex FE126En
The enclosure panels are made using high quality 5/8" (16 mm) thick Baltic Birch multiplex cut using a CNC machine and bundled as a flat pack.  Once completed the speaker cabinets have overall dimensions of 31-5/8" x 7-1/4 x 14-1/2" (800 x 185 x 370 mm).  The Birch plywood is unfinished so you can finish the speakers how you like.

The BK-12m speaker kit includes:
  • 2 x Fostex FE126En 4.5" Full Range Drivers;
  • 2 x Unassembled, unfinished Baltic Birch Cabinets;
  • 3 oz. Acousta-Stuff internal damping material;
  • 5 ft Supra Classic 1.6 15 AWG speaker wire;
  • 4 x QC187 Quick Connects (2 red, 2 black);
  • 8 x 8X1 Socket Head Wood Screws (8x Philips Head wood screws also included);
  • Assembly Instructions.
To put the kit together you will need just a screwdriver, wood glue, sand paper, bar clamps and binding posts.  An inside view of the folded horn speaker enclosure is shown in the photo below.
 
Inside - BK-12m Horn Speaker Kit - Fostex FE126En
 The BK-12m kit is available from Madisound for $315US + shipping.  For full details about the BK-12m speaker kit see the product page at Madisound.


More single-driver speaker kits and projects:
DIY 2-Way Tower Speakers - Ion
Adam has put together a fantastic looking pair of tower loudspeakers and he has shared his design with us.  The speaker design uses a Tang Band 25-1372SC 1" inverted titanium dome tweeter combined with a pair of Audax HM170CO 6" woven carbon fiber mid-woofers and used in a TMM configuration.

DIY 2-Way Tower Speakers Audax HM170CO Tang Band 25-1372SC

The loudspeaker enclosures are constructed using 1.5" thick MDF with solid oak side panels. The overall dimensions of the tower speakers are 37.5" x 8.5" x 11.5" with each weighing about 60 pounds.  The MDF is painted with a textured graphite spray and the side oak panels are stained.

Speaker Box Assembly with Straps
Test Fitting the Drivers
A 2-Way passive crossover dividing network consisting of a 3rd order Butterworth filter at 4000 Hz is used along with an impedance correction network.  The nominal impedance of the speakers is noted at 4 ohms and the loudspeaker covers a frequency range of about 60 Hz to 20 kHz.  In-room you will get some additional bass extension (shown on the in-room measurements).  The total cost for the pair of tower loudspeakers was about $900 US.

Adam reports that the Ion speaker build is his favorite so far.  "The Audax HM170CO woofers produce very warm natural tones up through the upper midrange. With the TangBand 25-1372SC tweeter the highs are crystal clear, detailed but far from harsh.  The Ion speaker is a very challenging build but it comes with a huge payoff! These have quickly become my favorite loudspeakers."  Great work Adam and thanks for sharing your work.

Boozhound Labs JFET RIAA Phono Preamp Kit Review
After building a few diy versions of the Boozhound Labs / Le Pacific JFET RIAA phono preamps,  Mark decided to try the actual $79US Boozhound Laboratories (BHL) JFET RIAA phono preamplifier kit. In Mark's diy versions of the phono preamp he used polypropylene capacitors.

DIY JFET Phono Preamp on Stripboard
On the other hand, the BHL phono preamp kit comes with fabulous looking vintage new old stock (NOS) Russian military paper-in-oil (PIO) capacitors. PIO capacitors made in this fashion are quite respected and sought after for their sonic qualities.  The BHL phono preamp kit comes with a PCB, the circuit parts and detailed building instructions. The kit builder will need to supply a 24VDC power supply (linear, regulated or battery will work), a chassis to house the preamp and various miscellaneous hardware items like connectors and switches.

Finished JFET Phono Preamplifier Kit PCB with PIO Capacitors
For his kit build, Mark used AA cell batteries for a noise free power supply and he housed the preamplifier circuit and battery power supply in the 19-inch 1U chassis shown below.

Inside View - JFET Phono Preamp
Mark reports that this is his best phono preamplifier build so far.  For full details about this project, see Mark's review of the Boozhound Laboratories JFET RIAA phono preamplifier kit.

More Phono Projects
Fundamental Amplifier Techniques with Electron Tubes: Book Review
Late last year Elektor released their most recent publication on the increasingly popular subject of hi-fi tube audio, Fundamental Amplifier Techniques with Electron Tubes by Rudolf Moers.  The new book is actually the English translation of "Fundamentele versterkertechniek met elektronenbuizen" (ISBN 978-90-5381-226-6) authored earlier in Dutch by Rudolf Moers.  The thick hard bound book is 834 pages and seemingly covers what appears to be just about every topic on the subject of audio amplifier design with vacuum tubes.  I recently had an opportunity to read the book and here is my overview of the new electron tube book. 
Fundamental Amplifier Techniques with Electron Tubes - Rudolf Moers
The thick book is divided into ten chapters. At just a few pages each, the first two chapters, (1) Introduction and (2) Principles of Electron Emission are very small relative to the remaining chapters and book.  These very short introductory chapters provide only a very brief overview and assume that the reader has a reasonable background in electronics.  The meat of the book begins with chapters 3, 4, 5 and 6 which each respectively go on to cover the basic electron tube types: diode, triode, tetrode and pentode.  For each of the basic tube types the chapters generally include information on tube construction techniques, the tube characteristics, all the typical tube applications and several design examples.  The chapter subsections are quite detailed and will for example get into the formulas and calculations of AC ripple that can be expected in a C-L-C pi-filter and calculating gain of as common cathode amplifier.  Over 200 pages are dedicated towards the pentode and over 250 pages are spent on the tridode.  The book also contains many technical questions which the reader can work through, much like the questions that would be found in a science text book.  A detailed solution accompanies each of the questions and this makes the book a very good learning tool for those interested in audio theory and design.  Frequency Dependent Behavior is covered in the 88 page Chapter 7.  The chapter goes into details regarding linear distortions for the various components that make up an amplifier.  Non-Linear Distortions and Noise are discussed in Chapter 8 and the various types of Negative Feedback is the topic for Chapter 9.  The final chapter (10) pertains to the construction of electron tube amplifiers.  As a builder of amplifiers I found interest in this chapter as it contained good practical information on electronics components, various construction techniques, crosstalk, heat / cooling issues, grounding, shielding and safety.  Also included in Chapter 10 are additional details of Rudolf's parallel push-pull 300B monoblock tube amplifiers among other of his amplifier builds.

The full table of contents for Fundamental Amplifier Techniques with Electron Tubes is available from Elektor's website [PDF - 163kB].

The book which is written in a technical format with plenty of theory, math and graphs will be primary suited towards advanced hobbyists with a strong understanding of analogue electronics and towards students and professionals involved electrical engineering and audio design.  Those without a good background in electrical science may not find the text and formulas all that easy to follow.  The carefully written book is a significant undertaking and provides plenty of accurate and valuable theoretical information on numerous subjects related to understanding and designing electron tube amplifiers.  Congratulations to Mr. Moers and his colleagues for the excellent learning tool and resource that they have compiled.  I will continue to find value in this book as a reference resource in my workshop.
The book Fundamental Amplifier Techniques with Electron Tubes, by Rudolf Moers (ISBN 978-0-905705-93-4) is available for $104.90US (plus shipping) from Elektor.

More DIY Audio Books
How to Solder - Comic Book Guide
There are a number of great soldering tutorials already available via the internet in the form of videos and webpages and today I came across another great soldering guide - this one packaged in a comic book format (see below for PDF download link).


The great new seven page comic book guide about how to solder has been put together by Mitch Altman (Cornfield Electronics) , Andie Nordgren and Jeff Keyzer (Mighty Ohm).  The comic book guide is based on the popular one-page soldering guide below that Andie and Mitch made last year. (Click image to enlarge)

 
The Soldering Is Easy comic book guide is easy to follow and informative.  The guide is published under a Creative Commons License and the link to the PDF version of the soldering guide is below.

Soldering Is Easy - Here's How To Do It

Feastrex NF-5 and NF-5ex Drivers at SSI 2011
We are big fans of single full-range driver loud speakers so we were excited to check out the Feastrex drivers. Michael Tang of Mike Tang Audio is importing the Japanese Feastrex NF-5 and NF-5EX drivers into Canada and had them on display at the show.


The 5" Feastrex NF-5 ($2000CDN, shown above) uses a large Alnico magnet.  The handmade cones are made from Japanese Washi paper (a higher density fibrous paper) which is impressed in a spiral pattern with embossed ridges.  The drivers surround is made from lamb skin.


The 5" Feastrex NF-5ex ($3000CDN, shown above) uses the same Washi paper cone and a lambskin surround, but with a motor that uses a field-coil magnet (electromagnet).  The field-coil magnet can be operated between 10 and 17V dc.  Changing the voltage allows you to change the damping of the driver.  Michael uses a 12V car battery for the field-coil magnet.  16 ohms, 95 dB, 35 to 25,000 Hz (+/- 3dB).


A Mastersound Compact 845 SET powered the 5" Feastrex NF-5 drivers which were housed in a bass reflex enclosure (enclosure plans from Feastrex, shown below), no passive filters were used.  The speakers sounded excellent, wide soundstage and impressive depth.  The single drivers delivered superb clarity with vocals to die for. 

 
Michael indicated that he is working on a transmission line enclosure design for use with the Feastrex NF-5 and NF-5ex drivers which he plans to have ready for the TAVES (Toronto Audio and Video Entertainment Show) this fall.

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Voxativ Ampeggio Horn Speakers at SSI 2011
There were a number of ultra high-end Hi-Fi systems at the Montreal show and like last year, my favorite Hi-Fi systems at the show was once again a low powered single-ended tube amp matched with high sensitivity fullrange drivers.  My favorite this year were the new German made Voxativ Ampeggio single-driver rear-loaded horn speakers.  The hand built rear-loaded horn enclosures are built in a collaboration between Voxativ and the famous German piano factory Schimmel Pianos. The cabinet surface is finished with a minimum of 13 applications of hand polished lacquer covered in real piano lacquer. The finish on the loudspeakers was simply amazing.



The product literature lists the following specifications for the Ampeggio:

Frequency Response: 38 - 20,000 Hz
Sensitivity: 101 dB / 1w / 1m
Impedance: 10 ohms
Dimensions (W x H x D): 16" x 43" x 14" (40 x 110 x 35 cm)
Weight: 121 lbs (55 kg)
Cost: $29,750US



The lone transducer used in the Ampeggio is the Voxativ AC-3X, which is their largest neodymium driver and unavailable for purchase.  The drivers suspension is made from goat leather.  The loudspeaker systems does not use any crossover components.


A Don Garber Fi WE421A ($3275) single-ended triode amplifier  (a single dual triode), putting out just 5 watts per channel was used to drive the Ampeggio speakers.  With a sensitivity of 101dB it was plenty loud.  The high sensitivity and easy 10 ohm loads means these speakers will mate very well with low power SET amplifiers.  The Ampeggio speakers sounded every bit as wonderful as they looked.  Open, dynamic, excellent clarity and plenty of detail.

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The AuDIYo.com room at SSI 2011
Like last year, the AuDIYo.com room was displaying a number of high-end audio accessories, cables, audio connectors, tweaks and DIY parts from Furutech, Mundorf, DACT, TentLabs, 1877Phono and others.




The AuDIYo show setup was focused around the recently introduced Furutech GT40 USB DAC with phono stage - $495.  The Furutech GT40 USB DAC with phono stage was previously used with a computer to make vinyl rips into 24bits/96kHz lossless digital files.  The digital files were then played back through the DAC which fed a vintage Dynaco ST-70 tube amplifier, which in turn drove a pair of Klaro speakers.  The quality of the vinyl rips was excellent and if you were not paying attention you would think that you are listening to a record as the recording preserved all the surface noise, pops and clicks one would expect from vinyl.  The Furutech GT40 USB DAC also features a very good headphone amplifier and a pair of Sennheiser HD598 headphones were on hand to audition the head amp section.




The vintage Dynaco ST-70 tube amplifier on had been upgraded with Mundorf high voltage filter capacitors and M-Caps were used upgrade the signal and coupling caps.  Simon Au of AuDIYo indicated that they are working on printed circuit boards and customizable kits that can be used to upgrade ST70 amplifiers.  We will post an update when we get word that the upgrade kits are available.


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Solen.ca DIY Speaker Kit - SSI 2011
On display on the Solen.ca room was a new DIY bookshelf speaker kit that is currently being developed and should be available soon.

 
The DIY speaker kit will use a pre-finished curved Dayton Audio 0.38 ft^3 speaker enclosure.  The drivers are from Airborne, a 120 mm wood cone driver with a 25 mm voice coil (HR124B8-10L) and the high-end is covered by a Air Motion Ribbon Tweeter (RT-20021).  The kit will use a 2-way passive crossover which has yet to be finalized.  No word on when exactly the DIY speaker kit will be available but Solen indicated that that the price of the kit will be about $550.  As more details come available about the kit we will post an update.

Also on display were a number of drivers, amplifiers, connectors and feet for you DIY speakr projects.

Little Horn Speakers - SSI 2011
The unique looking "Little Horn Speakers" caught my eye and I was particularly excited to see they use a familiar transducer, the Fostex FE108E Sigma.  While their size is far from what most would describe as a little speaker, they are little for a horn.  [Click on the images to enlarge]


The custom handcrafted speakers are produced by Specimen Products from Chicago.  The enclosure (base) is made using Baltic birch plywood and this acts as the compression chamber.  The horn is cast using a heavy-duty resin and both the base and horn are finished with lacquer.

The overall height is 36" (915 mm) and the bell of the horn is 14" (355 mm) across.  The base is an 8" (200 mm) cube.  The impedance is noted as 8 ohms with a sensitivity of 90 dB.  The frequency response is listed as 77Hz to 23kHz.  The speakers are well suited for use with low power tube amplifiers.

 
The Little Horn Speakers delivered a surprising large soundstage and you get the single-driver finesse and detail that FE108E Sigma is known to deliver.  The speakers retail for $2400 / pair are available in a number of colors.  More information and photographs are available from Specimen Products website

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