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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: 11/4/2005

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Hi,

 morricab wrote:
Thanks for the info about transformers.  It is as I expected, however, that these passive devices are not passive sonically at all. I agree with you that the higher quality of the transformers should lessen the effects I noted (if not eliminate them) but the same can be said for active preamps as well.


I agree. I have to note that even in active preamp I/We (the we are friends from the London Live DIY Circle) tend to prefer TVC's over resistors. An S&B TVC Input and S&B parallelfeed output transformer preamp adornes the system that contains the various "true OTL" PP Amplifiers (with 2A3, 300B and 845 units) which drive ESL pannels directly...

 morricab wrote:
I would imagine the character of the output transformer is even greater (much more wire involved and bigger magnetic fluxes). 


Maybe up to a degree, the key in a transformer are the so called "BH" curves. The result is that transformers are non-linear. A steelcored transformer with no magnetic bias distorts a lot. Add an airgap ana decent amount of magnetic bias and things become much more linear.

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!).

 morricab wrote:
Perhaps you are reacting to the fact that these amps are not SETs but push pull?
 

Thats possible, hard to be sure. If I find the tyme (or is that parsley, sage Rosmarin & thyme) I want to try a SE OTL similar to what Bruce Rosenblit does, but with a single valve. Sadly my current drivers are 4R @ ~ 98db/W/m, definitly not SE OTL material.

 morricab wrote:
String up 8 6c33C tubes in parallel gives you 10 ohms output impedance and probably enough power (about 14 watts).
  

PARALLEL TUBES. Me no like way they sound.... ;-)

 morricab wrote:
Have you heard such an amp before?


Nope, I might look at using one of these "super 300B's" operated at low voltage and high current for the follower job. Maybe we can coax a watt out of 65 Watt anode dissipation?

On second thought, nah, I think I'll better get a Nickel Core Parallelfeed Output made for my upcomming 10Y Amp (3W out for 12W Anode dissipation)...

Ciao T ;-)

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