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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

revatio

revatio ttcop.com
Hi,

 morricab wrote:
As to the best transformers souding more transparent than the best resistors, I'll believe it when I (don't?) hear it.  You claim to have heard this but I most certainly haven't. 

 
Well, the claim is not just mine.

Martin Colloms compared the Music First Audio Passive Magnetic Preamp to a Vishay Resistor version of the Audio Synthesis "Passion". He commented along these lines:

"More sense of drama and dynamic expression"
"Firmer and deeper bass"
"Impression of more detail"
"more delicatly subtle and transparent"
"not quiet as open and perfectly neutral as the passion"

while he noticed the passion had:

"slightly larger stereo images"

(maybe blown up stereo image as sometimes notable with Vishay Bulk foil resistors, also maybe the "look here how great I sound" obnoxious pushing forward of detail the vishay resistors do account for that? I agree with the relative assessment BTW, but personally have slightly different weighting on the impressions)

He also noted much less variability of the MFA PMP with cables and sources, compared to the Vishay Passion. He scored the MFA PMP slightly higher than the Passion (36 vs. 33) on his highly arbitrary scale, but in a region where only very little gear ever makes it.

At any extent, the hundert series transformers from S&B derive from the 101 whch was designed to be as close to a straight wire in terms of measured and subjective performance as was possible. The subsequent 102 & 103 have shown that in most applications they live up to this "close to a piece of wire" aim, even if they still fall slightly short. Other manufacturers of transformers may not have this goal of "nothing but the music" in mind while designing, voicing and making their products.

 morricab wrote:
Based on theoretical arguments the noninductive metal film resistor is certainly more linear and less frequency dependent of the two devices. 


Maybe, I will readily argue that once a system is considered this may nevertheless turn out the opposite way. The MK II version of the TX-102 had a completely unneccarily wide bandwidth for audio (measured flat up to 3MHz, there the generator ends, we suspect 10MHz+ would have been on the cards) which showed up as a problem when coupled with much gear, the current MK III has been designed as a deliberate bandpass device with 10Hz-40KHz ruler flat (remember the rule of the 400000). 

A resistor attenuator BTW shows a LOT MORE variability with setting and load capacitance where frequency response is concerened, so one may argue that a resistor attenuator is in fact the by far more frequency dependent device!!!

 morricab wrote:
I am not so sure the NAF amp has a typical 845 sound (I have heard only a couple of others that were handily outperformed by the NAF with not nearly its openness and speed) but perhaps it has a sound that is a function of the type and size transformers that are required for such an output tube??


I routinely find myself prefering the 211 over the 845 among the "big" triodes. I think it is more down to a mixture of the anode curves of the 211 vs. 845 (the 211 seems to have less variability of Mu with signal levels) and the much lower bias voltage of the 211 which means it is easier to make a linear driver stage.

In terms of output transformer size and design there is not much to choose between 211 & 845, except the 211 really needs well above 10KOhm load impedance while the 845 manages with 5-6k which is what is often used.

 morricab wrote:
Perhaps the "family" sound that one hears from the Audio Note amps is due to the use of their proprietary silver transformers? 


Maybe, but the "Kondo Sound" is still there in the copper transformer versions. I think it has more to do with the valves and circuits used, plus a few tricks not normally illustrated in the schematics that are in public domain. I find it interesting that the "Kondo Sound" is pretty consitent across preamplifiers and also between Push-Pull and SE Amplifiers from Kondo.

 morricab wrote:
Again then we would be back to the sound of the transformer affecting the overall "character" of the amp.


You need to realise that the physically larger a Transformer becomes the narrower the available bandwidth for a given construction. Due to the need to handle a lot of "magnetic bias" SE Output transformers become very large, physically, and have invariably problems on one or the other (or both) ends of the spectrum, even if extreme measures are taken. Transformers problems expand expeonentially as size goes up. However, this means comparably small line level devices (or MC level ones) can be made to levels of perfection that appear incredible in the light of the performance of generic tube amp output transformers. 

 morricab wrote:
As to the Silvaweld input and output transformers:  You may be right but their literature says they are using high quality nickel alloy transformers.


That may be so. However my experience is that truely broadcast level quality (in the definition of the german radio/tv networks) transformers are sonically very transparent. If you find the transformers used not transparent to an EXTREMELY HIGH degree, then I must suggest that in the terms I subscribe to they are not "broadcast quality", which to me translates to "Pro" or "High Quality". This may be of course entierly intentional on the part of the manufacturer, who in fact may feel a certain addition/subtraction from neutrality desirable. Past that Nickel Alloy comes in a wide range of mixtures, from 5% to > 78% Nickel. Formal designations for these Mixtures vary, "Permalloy" and "Radiometal" are generally the lower nickel content designation, with "Superpermalloy" and "Mu-Metal" being the designations for high nickel content alloys, but the use is not consistent, as these old expired tradenames and not formal designations.

 morricab wrote:
I still doubt it would be better than no transformers.


I do not believe in adding transformers for adding a transformer's sake. However, I do feel that there are specific applications where a well designed transformer is a preferable solution.

 morricab wrote:
If you look at the design and parts used they did not cut corners on this design so I find it hard to believe they stuck just any old transformer in there.


Well, the OEM pricing of a pair of "onehundert series" S&B Transformers is several 100% that of anything seemingly comparable based on standard cans and lams. At this point very few OEM's use them and virtually only use them for passive preamplifiers in the form of the 102, with only three users of any other of the 100's and Msuic First being one of them. The reasons are cost and size, most potential OEM customers (including some that make VERY expensive equipment) find the cost too much for their accountants to put up with.

 morricab wrote:
Interesting that you are so enamoured with a moded EL34 based amp.


I am not enmoured and to call it "modded" is being modest. It is in effect a groundup re-build that retains only the key mechanical components. I tend to prefer the Amplifier BTW with KT-88's fitted, but at home keep SE Amp's (as I have them ;-) ).

 morricab wrote:
I imagine it is possible, with proper attention to make a spectacular sounding amp with these tubes and the push-pull concept.  Tell me are you using it as a triode or are you still going "ultralinear"?


The Amplifier is switchable Pentode, Ultralinear or Triode, Class Ab1 operation with class A to around 2 Watt. While triode operation sound marginally better, the differences are quite small. This is attained simply by using tons of negative feedback, which normally is a no-no. But the old Citation Gear had actually found a way to apply this without the usual sonic problems, something which worked out well.

Together with some other tricks (including arguably at least one or two swiped from Kondo and another one or two abstracted from Ken Shindo - not much original work in there I must admit) I managed to design/construct a high feedback PP Amplifier with good compatibility to normal speakers (when compared to a 2A3 or 45 SE Amplifier) while retaining what at least to me makes SE sound so attratcive, that is the purity, immediacy and lack of a feel of mechanism in the music reproduction.

Most funny is that even in pentode mode for the output stage this Amp sounded more "SET" then my IT coupled zero feedback push-pull DHT amplifier (the IT was a high nickel S&B prototype), sounding more direct and immediate and harmonically more complete.

Anyway, it was a fun challenge to make it work like that.

Ciao T

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