TNT-Audio Readers' Corner
Monthly section devoted to your letters, positive and negative feedback about everything related to Audio and HiFi.

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February 2010

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PSU for Virtue amps
Dear Nick,
It's the Slate guy again...Happy belated New Year (although we celebrate New Year's for 15 days). I didn't realize you were so talented as a DIY guy. I love reading your articles. On the subject of an alternate to a SMPS, I bought an Audio Art power cord, plugged that into the SMPS and into a Xantrex 800 watt emergency power supply. When I did this, I heard the Winsome Labs Mouse come on to its full glory: better bass, top end more airy, and the T-amp sound, which runs to dryness became more musical. I run a Musical Fidelity Phono with a MF PSU but I haven't tried that with the Mouse. The best thing I did was dust off my old Audio Designs MC step-up to give the Denon Dl-301 Mk.2 more output and the result was a totally more engaging presentation.
I have a question, Mr. good with a soldering iron, how can I add a powered sub (HSU) to my setup? The Mouse has only 1 set of I buy a Behringer active cross over?
Thanks, and keep up the great work...TNT Audio is a must read for me, every week...
Sincerely yours,
Bow - E-mail: bow_160 (at)

Hi Bow,
Happy New Year to you as well.
I think because the class-T amps use a single rail supply, we have a very wide choice of PSU's to choose from. Obviously manufacturers are competing at a price level and many will choose to go with the most cost-effective wall-wart. Fortunately, the class-T's tend to sound quite good even with a basic PSU.
But any power amp is very much dependent on its power supply. Think about it, what we get out of a power amp is a tiny signal mixed with a lot of power from the power supply. So the latter is as critical as the quality of the signal.
I am not familiar with the Winsome Labs Mouse, but I am guessing that it is based on the Tripath 2050 chip, which would make it similar to the Virtue amps that I tested the linear power supplies with. If so, I am not surprised at your findings with the better power supply arrangement as there is obviously a lot of potential in these amps.
I'm afraid that there isn't an easy answer to your question about running a power sub with the Mouse. Unless you want to be altering the volume of the powered sub each time that you change the volume level on the Mouse, you need to tap into the signal after it has gone through the pot in the Mouse. It wouldn't be too hard to take some wires from the output of the pot to a pair of sockets on the back of the Mouse's case (if there is enough room).
If it is a powered sub, you should have a filter in there too so it is just a question of adding some interconnects. If you can fit a summing circuit inside the Mouse, you will need only one IC. The Virtue amps already have a sub output socket fitted.
I hope this helps.
Nick Whetstone

Class D amps
Hi, my name is George and I'm from Greece.
I was intrigued by the T-amp amplifier and by your review for that, but I do have some questions and some blank point that I don't get...

  1. To what type of speakers can i connect that.. cause i'm a little unfamiliar with the technical terms of Ohms and so on.. even though what they represent... i mean, can i just use my hi-fi speakers and replace my typical hi-fi amplifier? or should i use some everyday small speakers, some small YAMAHA's that i use for media-pc use...? For example now, i have a pair of COMET stereo speakers i don't use.. they say 8 Ohms, 20-150Watts.. are they suitable?
  2. Is a jack input enough or the appropriate kind of input to support CDs/radio and so on devices? for all i know, most amplifiers use RCAs...
  3. after a short research on some sites, i saw that there quite many T-amps on the market.. using the T-amp chip.. does this means that they all are great? the chip is the basic requirement, so to have a good sound result?
  4. The pre-amp is kind-of expensive comparing, don't you think... i speak comparatively..
Sorry for my amateur questions and thank you for your time.
George - E-mail: plithos (at)

Dear George,
choosing the right speakers for the T-Amp is easy, just have a look at the tech specs, namely at the sensitivity datum. If it's above 90 dB/w/m they could be worth a try. And I'm referring to standard HiFi speakers, of course, not cheap multimedia stuff. Klipsch speakers, for example, might be good partners.
The minijack input can be easily converted into a pair of RCA's, you just need a minijack/RCA adapter. As for other Class D amps...yes, the TA2024 is a very good sounding chip but it is not the only one. If you want better results and even good connectors, have a look at the Scythe SDA-1000 amp or the latest SDA-1100. They use a Yamaha Class D chipset that is as good as the TA2024.
Anyway, the chipset isn't everything!
Finally, a preamp isn't strictly necessary, if you use just one source. A good option, even for phono, is the T-Preamp.
Lucio Cadeddu

CD test
An interesting review of the Denon CD. There is a good free to download test cd at this url
David - E-mail: halzia (at)

Dear David,
many thanks for your feedback! That page is extremely useful, indeed!
There are many other free test tracks available on the net. There's even an application/software to build your own CD test tracklist here. Unfortunately it's in Italian.
Lucio Cadeddu

T-Amp reboxing
I am wanting to rebox my t amp similar to the mods you did on this page. I was wondering what value of pot was used. I noticed you can get several values. ie. 25k, 100k, etc. If you have any info on this I would greatly appreciate it.
Thanks, and I love your site.
Ryan - E-mail: ryanmhook (at)

Hi Ryan,
Good to hear you hear you are going to rebox your amp; it makes it much more convenient to use. The value I used was 50K (it's there somewhere in my report). Go for a separate power supply if you can and sensitive speakers for best results. I'm using an unmodified T-Amp with a separate 13.8 V power supply to amplify ITunes into some sensitive 4ohm Grundig speakers from the 60s, and the sound is very open and enjoyable.
Thanks for your kind words about our site.
David Holgate

Phono preamps
Dear Mr. Kohli,
I read with great interest your phono preamp shoot out. I commend you on the well thought out reviewing process. It is refreshing to read the reviews and DIY projects here at TNT-Audio. I am a regular subscriber to Stereophile, TAS and other so called high end mags but they do not hold my attention as does TNT.
The reason for this letter besides expressing my admiration of you and TNT is the phono preamps. I need an entry level preamp and you seemed to like the Cambridge 640p. Many others also seem to like the 640p, but I have read most owners end up modding this device. I must buy without listening and can't and don't want to do any mods. So I ask you, do you still recommend the 640p, I noticed in your review that you were going to purchase one. I have a MM cart. now but would like the flexibilty of MC stage also. Like I said I don't have the opportunity to audition.
Thank you so much Arvind for the time, I am open to any and all suggestions or advice you might have.
Best regards,
Jeffrey - E-mail: jlnordi (at)

Thanks for your kind words. I did buy the 640P for myself and am still using it, but keep in mind I have not gotten around to comparing anymore phono stages since then.
If I was to look into some more phono stages it would definitely include some of the battery operated models, they have my curiosity piqued. The caveat there is that while the concept may sound superior or there may be many accolades for a product, it doesn't always guarantee a worthwhile product - there is no substitute for thorough testing and comparisons. But of the 5 phono stages I have used, the 640P is definitely the one to pick.
Hope that helps.
Arvind Kohli

Good day! My name is Sergey. I live in Russia, I came across an article about your DAC to 4X TDA 1543, I have little experience to be precise, it had never done anything like that, but really want to make a DIY DAC, help me. Send details printed circuits, parts list and where I can order them, I will be very grateful if you can help me.
Sergey - E-mail: rem.perm (at)

Dear Sergey,
unfortunately we don't have printed circuit boards nor further informations besides the ones already published in the series of the Convertus DAC project articles. Let me tell you that building such a DAC isn't an easy task and I wouldn't recommend it to an absolute beginner. You'd be safer starting with something easier like many DIY DACs you can find on the market, ready to be assebled (DIY Paradise Monica, ScottNixon and others).
Hope this helped,
Lucio Cadeddu

TC preamp power supply
Dear Mr. Cadeddu,
This is in regards to your 2005 review of the TC-754 phono preamp. They now offer other preamps along with the TC-754. I have great respect for TNT-Audio and you Lucio. I have looked at many phono preamps in the T's price range and above and decided for the money to give the T's a shot. The reason for this letter is to ask for the power supply that I should use. They all come with 12 volt 200mA wall wart power supply.
I would like to replace with something as you would say beefier. I am from the USA so do not have access to the power supplies that you mention in your 2005 review HP 143 and 145. Could you please advise what to look for specifically in a power supply, be it battery or regulated AC adapter. I thank you for the time and look so very forward to your reply.
Best regards,
Jeffrey - E-mail: jlnordi (at)

Dear Jeffrey,
all you need is a standard 12 Volts (DC) adapter with enough current output. 200 mA is definitely too low, I'd go for 1000mA (that is, 1 A) at least. Even better if it is of the regulated and filtered kind. These adapters can be easily found almost anywhere, starting from Radioshack and other online stores. Considering this should be a low-budget solution do not choose something too expensive, I'm pretty sure the T-Preamp performance can be upgraded by just adding more current capacity and some filtering. Also, some befefit can be obtained by using a long umbilical PSU cable, so that the adapter can be placed very far from the phono preamp.
Of course, if you need to power more than one 12V device (e.g. a Class-T amp) you might decide to go for a beefier (read: more amperes!) adapter, so to use just one power supply for all your devices.
Hope this helped,
Lucio Cadeddu

Music for tests
Great website as ever. Hope you can help.
I listen to a wide variety of music from classical to jazz, both fm and cd.
I have been into my HiFi for over 30 years now and as is the way often change things around, remove or add items in the never ending search for perfection, and I'm not there yet as you know.
What I need is a piece of music, any kind, I like it all the same, which will show me if I am going in the right direction or not. Perhaps a jazz cd will be the best?
All the HiFi press when testing use this piece or that as a test piece of music when reviewing an amplifier or speakers etc.
All I need is a cd that can be used to evaluate the kit I am trying out.
Any thoughts would be appreciated. I may already have it in my collection.
Many thanks,
Alan - E-mail: Ag250449 (at)

Dear Alan,
it is very hard to pick up one single CD and use it to test everything. A record can be good for testing timbre, another for imaging, another one for dynamics etc. Anyway, one I currently use that helps me understanding many different aspects of the performance of any HiFi component is Keb Mo debut album and even the subsequent Just like you. Even on CD these albums sound just great: powerful bass, imaging, timbre, presence etc. it's all in there. I particularly love this track (below its acoustic unplugged live version). Play iy absolutely live and hope your system survives.

Lucio Cadeddu

Re: Differences between Class T amps?
Hi Nick,
Thank you for your excellent reply. I look forward to your review of different power supplies.
I have been a sound systems enthusiast since the late 1970s and grew up understanding that Class A amps was the way to go for the most refined sound due to their bias towards 2nd instead of 3rd harmonic distortion when driven hard. I have not tried any of the new Class D and now Class T digital switching amps, and so I am learning if they might be more sensitive therefore re any standard variations in the manufacturing quality of the components supporting the main ICs.
My reading re Class T amps seems to point towards the direction of "more input power available, more output power to the speakers" for these amps, and also that if driven hard, distortion rises much more dramatically than the more traditional Class A/B amps.
I have two more questions. I read that a 2 channel amp "cannot have a shared ground return between the loudspeakers", so how would a similar unit designed for headphone connection work (since there is only one ground for the two channels)?
Also I am confused about a statement where it was stated that it was possible to use a 4-channel Class T amp "in parallel" to get more power. How is that supposed to be wired, positive speaker output of channel 1 into negative speaker output of channel 2 and the remaining free connectors of channels 1 and 2 connected to a loudspeaker; does it double the available power?
Kris - E-mail: skris88 (at)

Hi Kris,
I am not an electronics engineer, and don't have a good grasp of the class-T technology. From what I have been told, it depends on the configuration of the class-T amp as to whether the output is already paralleled (internally) or not as to whether the outputs can be paralleled.
I do not know if any class-T amps are wired to have a headphone output. For more information, there are always the Tripath datasheets, or the 'experts' on the diyAudio forum etc. As regards more power, a lot depends on the type of speakers that you intend to drive. I find even with easy-to-drive speakers, I prefer the class-T amps using higher input voltages, eg The Virtue V1/V2. (If you want to experiment, similar modules are sold on Ebay for very little although you will need to build one into a complete amp). Even with those, it is noticeable that they sound better with a 30v supply instead of 24v.
Class-A amps as you say, are renowned for their smoothness, but the class-T technology is also very smooth, and uses far less power. It will always be a question of what each listener prefers but I would certainly urge anybody to try an amplifier like the V1/V2 with a decent power supply.
Nick Whetstone

Feedback on last month's letters
Franco Dinatale's problem with his SDA-1100 shutting down from vinyl sounds like he has a rumble problem. Most reflex speakers have 4ohm or less impedance at low bass and significant cone flap will be drawing a lot of current.
David Winarso asking about used record decks in Indonesia: in neighbouring Malaysia I find rubber and foam components perish very quickly in the tropical climate. It is important to check the belt and suspension is not rotted. Putting french chalk or talc on the belt stops it sticking to the pulleys and failing too soon.
Getting spares out here is almost impossible. I am suspicious of MDF platters in this climate, but there is a local source of acrylic platters for the Rega P2.
David - E-mail: halzia (at)

Dear David, thanks for the precious feedback and first-hand infos, highly appreciated!
Lucio Cadeddu

Differences between Class T amps?
Hi Nick,
I am coming to the Class-T mini-amp field a little late, but perhaps better late than never.
I read your review and have a question.
Can you do another review with several copies of the same brand/model amp and note if there are differences? My thinking is that if you had 3 similar 'standard' Class A/B amps from say Yamaha, they should all sound alike when compared directly with one another.
My concern is that the variations you heard in the review (above) may be a 'flaw' of class-T amps in general and not the changes between internal components used by different brands.
Kris - E-mail: skris88 (at)

Hi Kris,
Thank you for writing to TNT. Are you suggesting that the differences that we hear between different brands of class-T amps and more likely down to variations in the sound of amps coming from the same production batch?
If so that would be most unlikely. Given that those amps all have the same components, it will be almost impossible to hear any difference between them. There is no reason why they should sound different, no more so than a batch of class A/B amps.
The main factors in these different brands of class-T amps sounding different would be: component choice, particularly any capacitors that the signal passes through, circuit layout - yes it does matter, and choice of power supply.
The PSU is a big factor in how any piece of hi-fi sounds. I know that Virtue Audio auditioned something like 50 SMPS before choosing the two that they eventually supplied with their V1 and V2 amps. I'm currently writing a forth-coming article for TNT about three different linear power supplies for the Virtue amps, and trust me, they all sound quite different.
I am not sure why you suggest that there would be 'flaw' in class-T amps that makes them vary in their sound quality. I think if there was, we would probably see less consistency in the reviews of class-T amps in the various publications.
I remember doing one of my first reviews, that was a comparison of class-T amps, and I had several emails from people who had also heard the same amps, and come to the same conclusions as I had.
And in years of reading popular hi-fi forums such as diyAudio, I have not seen it mentioned that class-T amps from the same source vary in performance.
Nick Whetstone

Phono stages
I know you did a review about comparing 3 entry level phono stage after your entry level analog turntables reviews. *cambridge, parasound, creek * But I was wondering about the bellari VP129 that you used in your first review (Music Hall 2.1; Bellari VP129).
I know that Micheal Fremer did a big review about it but I'm also considering the Cambridge.
Since I've no dealer that sells both, I cannot do a listening comparison!
Mario - E-mail: mario_garon (at)

Hello Mario,
Unfortunately I never did compare the Bellari directly to any of the other units, but the Cambridge impressed me so much even when compared to the much costlier Graham Slee that I have been using it ever since.
Hope this helped,
Arvind Kohli

DIY loudspeakers
Dear Mark,
I wish to build loudspeaker cabinets using birch plywood as you recommend in your articles for tnt-audio.
The cabinet will be bass reflex loaded:

The woofer and tweeter are coaxial, without a crossover, and are of 160mm diameter. I plan to use 12mm birch plywood for the walls and double thickness for the baffle (24mm).
Do you think this will be good, or is the thickness of the birch plywood too much for this little cabinet?
I look forward to your reply,
Andea - E-mail: andreamg (at)

Hi Andrea
This thickness of plywood for the sides and bafle would be perfect for a cabinet of this size. Remember the BBC LS3/5a is similarly proportioned using 12mm birch plywood and most commentators attribute its success to this cabinet. The LS3/5a used the same bass-mid drivers (Kef B110) as many inexpensive speakers of the time but achieved a sound quality loved by many today even in otherwise exotic high end systems.

Do mount the coaxial driver on the front surface of the baffle, not the back to avoid 'tunnel effect' colouration from the narror aperture (the LS3/5a used the crssover to equalise for this, rather unsuccessfully in my opinion) and make sure that thick baffle is either radiused or notched at the back of the driver openning to avoid pressure build up at certain frequencies immediately behind the driver.

I also recommend you radius the baffle edges (you have plenty of scope with 24mm) to minimise diffraction effect and maximise dispersion. Rebating the driver flange into the baffle is also important in this respect.

Unless the coaxial tweeter is a 'whizzer' cone glued to the edge of the voice coil of the bass-mid cone, I expect this 2-way driver has a hidden crossover in the form of a series capacitor on the tweeter terminal. It might be worth investigating if it does and upgrading it to an audiophile equivalent mounted away from the tweeter.

Finally, do not forget that you need to use your measurements on the INSIDE dimensions of the cabinet to ensure you have the correct cabinet volume for your driver.
Happy speaker building, this may be the first of many...
Mark Wheeler

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