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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: 11/8/2005
Hi,

 morricab wrote:
You may be right.  It would perhaps be worthwhile to look into "better" transformers but I am not sure that an advantage can be found over just going RCA to XLR adaptor into the balanced inputs and thereby bypassing the transformer altogether.  What do you think?


I think that a transformer needs an actual reason for being used instead of a piece of wire.

At the very best the transformer can approach the piece of wire closely, very closely indeed, it cannot really improve on the piece of wire, though it may resolve other problems elsewhere in ways the wire could not and lead thusly to improved sound.

But usually, if you can use a piece of wire use it.

If you need a transformer or perhaps another device whose function could be gainfully substituted by a transformer (example - linestage with cathode follower and feedback vs. the same linestage valve without follower and feedback and using a parallelefeed stepdown linetransformer to lower gain and output impedance) the transformer may be the better choice.

For example, you may be interrested to build a copy of the "final euridice" linestage to see if can outperform the silvaweld.

The advantages are that you have Balanced or SE inputs and outputs any which way you like, around 20db very linear gain and around 150 Ohm output Impedance and loads  of available output Voltage (certainly +14dbu @ 20Hz for the TX-101, likely more with the more recent upgraded core materials - that is around 4V @ 20Hz) with negligable distortion.

MY PERSONAL current realisation (where I to build one) would look like this:

1) S&B TX-102 as volume control, with suitable switch

2) 2V Lithium Battery negative pole to the grid of the Valve, bypassed with good non-magnetic silver mica capacitor and in series with a small, low q retardation coil, here for killing oscillation

3) C3g (it is currently "best sound for money" in the application) postal pentode wired as triode, many alternatives exist, the russian 6S3, 6S4, 6S45, 6E5 triode wired, EC8010, EC8020, E55L triode wired, E180F triode wired, WE 417A, WE 437A, 3A/167M and so on....

4) Anode load inductor for C3g, I would use the S&B 120H/12mA 40% Nickel item

5) Mundorf Silver (or other to taste) Parallelfeed Capacitor 3.9uF

6) S&B TX-101 MKII as parallelefeed output transformer, wired for 4:1 stepdown

7) Valve rectified (GZ34/37) and Valve Regulated (O2A X 2, EF86 X 2, 6AS7) powersupply, around 130V @ 12mA X 2 for both Channels, AC for C3g heaters. The +B is besically adjusted for around 10 - 12mA current through the linestage valve.

I am not going to make any claims like "takes the Lamb to the slaughter" or "takes all the nine lives of the CAT" or "Cuts off Conrad's Johnson" (though I believe the Music First Passive Preamp did something like that at the recent HiFi News Awards to the nearly ten times as expensive CJ ACT II) and so on.

But it is a most excellent linestage and what I would choose, IF I needed a linestage with gain, which I don't and which is why I use a copper TX-102 based passive line stage.

Ciao T

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