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In the Forum: Audio Discussions
In the Thread: Passive transformer based preamp
Post Subject: Re: Better among worst?Posted by Thorsten on: 11/7/2005

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Hi,

 morricab wrote:
Hmmm....I guess I can't really see that unless you are enjoying a particular coloration you are getting from the TVC.
 

Nope. On this you are wrong. Based on direct bypass tests the TVC's I USE (that is the specific Items, not the genre) are MORE TRANSPARENT than a pair of good quality resistors, such as the Vishay Bulk Foils used in the AUdio Synthesis passion.

Luckily enough there are a number of reviews in existence now that compare the Music First Audio Passive Magnetic Preamp (a baby at whose birth I helped somewhat and yes, I use what is in effect the MK III spec of this myself, in copper I may add) to some of the best active and resistor based passive preamps. Others exist of devices by other makers using the retail versions of the same transformers (MFA uses a slightly different spec OEM unit). You may wish to peruse these various ones.

 morricab wrote:
Afterall, as you mentioned the behavior of a transformer is non-linear whereas the behavior of a resistor (a good one) is linear, lower in distortion, and has no hysterisis (I think the same cannot be said for a transformer). 
 

As it so happens, I was writing about specific products. But yes, transformers distort, it is a job for the designer to address this in his design. The S&B units do this by using a rather more linear than usual core material and loads of it (simple as that, honest, it is merely a question of cost). If you actually measure the distortion you will find that it is in the region of the noisefloor of most analysers and not materially differnet from the distortion measurable in resistor attenuators. 

FWIW, the TX-102 clocks in at < 0.0002% for the highest harmonic (3rd) @ 2V/1KHz with a 600 Ohm Source, THD stays basically flat down to around 100Hz at 5V (depends on level, at levels below 5V the "knee" slides down further in frequency and distortion is of course also lower), where it rises with a first order function.  

Other manufacturers may be unable to get the core material and cans S&B uses (simply because S&B paid for the tooling!!!!) and may even choose to use not just smaller core sizes but also inferior grades of core material (all the way doen to nasty generic steel) in order to lower their cost, whith obvious results on sound quality. As part of the development of the MFA units we had attempted to add some steel laminations to both increase level handling and give possibly a "better tone" Even just 10% of the whole core replaced by highest grade stell laminations resulted in an unacceptable loss of sound quality.

 morricab wrote:
Resistors as a passive attenuator for sure lose dynamics but they don't affect the signal in the ways I heard from the TVC or the transformers in my Silvaweld preamp (which are good ones). 
 

Sorry, but if the transformers in the Silvaweld preamp effect the sound as you say your conclusion that they are "good ones" may be erronous and driven by company propaganda and assumption, compared to actual fact.

 morricab wrote:
I have not heard too many parallel SETs but what I heard was pretty impressive. For example the New Audio Frontiers parallel SET 845 monoblocks are one of the very best amps I have heard.  Also, the Audio Note (kondo not UK) Kegon KSL is phenomenally good and is a parallel SET also.  Of course I have heard great SETs also.  I have heard great PP (Allen Wright's DPA300b being one of the best I have heard).  Yet I find the OTL sound to be less colored overall and more dynamic (especially in the microdynamic department.)
 

Of those that you mentioned I have heard the NAF Amp's and found them typhical "845" Amp's, terminating any point for me. I have had the chance to compare a wide range of Kondo (ANJ) Amplifiers in a friends system, note that these are pre KSL/BFA units. We had both early Wilson Watt/Puppies (3/2 IIRC) and Avant Garde Trio's as well as Gaku-On, Ongaku, Kegon, Baransu and Neiro there.

While all units shared a certain family sound, when driving speakers where the power levels where of no concern (trio's) the best of the lot was the Single 300B Baransu, with Ongaku second and Neiro third, then Kegon and Gaku-On. This was reversed on the WP's, where Gaku-On took the lead followed by Kegon, simply because the others run out of steam. But the PSE Amplifiers substantially lost imediacy and transparency to the (otherwise very much identical) SE units.

 morricab wrote:

 Thorsten wrote:
"I cannot really say more, but I have a PP Amp (sorta commercial) that sounds to most that hear it a LOT like a really good SE Amp (and that from a high feedback EL34 class AB push pull design!).

"
What is it?  Just curious maybe I have heard it or something close to it.


You have not heard it. It is a rebuild of the Shanling SP-80, only available in the UK and so far with only 6 Pairs made. I can say that is shares many of the principles embodied in the Harman Kardon Citation 2 Amplifier, plus some tricks of my onw, all of which combine to provide a PP Amplifier that has all the hallmarks of an SE Amplifier in terms of low level resolution, tonality and immediacy, while not loosing the advantages of the PP Principle, to wit large output power and low harmonic distortion at high power.

If a current commercial venture gets off the ground well you may very well see a further optimised (using the existing shanling chassis and iron limits the achievable quality somewhat) unit based on the same principles in wider circulation.

A review of a system including these Amplifiers (but really of a system in whose assembly I had more than a small influence and which included basically all my own designs/modifications except speakers) is here:

http://www.realhi-fi.com/pdf/hfcreview2.pdf

Ciao T

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