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KT 19th February 2006 04:10 AM

Unity gain buffer in front of or behind TVC?

I've been very interested in wiring up a TVC like the S&B TX-102 or the Dan Slagle AVC, but I'm concerned about comments I've been seeing about a slight lack of drive and impact using these units unaided (since they are passive).

I'm going to try the TVC by itself first, of course, to see if I notice this effect. But if I do, would adding a buffer help out? I realize there will be other trade-offs by adding an active stage.

Also, if I do add a buffer, is there a general consensus as to which is preferable: before or after the TVC?


moamps 19th February 2006 12:36 PM

Re: Unity gain buffer in front of or behind TVC?
Hi KT:

I had a chance to listen to both the S&B and Sowther TVC and must say I could not hear any drive-related irregularities. IMO, such problems occur when the source has a high output impedance. So, when using a buffer, it should be placed before the TVC. The TVC, unlike other passive attenuators, does not exhibit any issues relating to output impedance.

In case you're interested, I have designed an autotransformer volume control, which I am currently using in my system. I tried the version with and without the buffer (ECC86-based) and did not notice any significant differences (nor did my friends). You may check out the TVCs at my web site.


KT 19th February 2006 02:33 PM

Hi Milan,

I'm interested in taking a look. What is your website?


moamps 19th February 2006 02:37 PM

Hit the www button below. Or just go to ;)


Nordic 19th February 2006 02:38 PM

KT, look below his post, you will see a button that says WWW... click it

Nice stuff on there, whish there was a translated version...

KT 19th February 2006 06:11 PM

Ahhh... thanks. Didn't know about the www button.

I'll have a look.


wilbur-x 22nd February 2006 01:29 PM

Very interesting those TVCs !

I would like to wind a TVC myself.
It would be great if you are willing to share the necessary information.

moamps 22nd February 2006 11:09 PM

Hi wilbur-x:

It's not so difficult to wind an ATVC. All you need is time and patience, and perhaps a good quality transformer core. If you have a couple of old transformer laying around that you can use for building your own ATVC, you can send me a picture and their dimensions and I'll do the calculations for you.


Peter Daniel 26th March 2006 09:59 PM

2 Attachment(s)
I finally finilized my Integrated amp with TVC front end and can definitely state that it sounds better without a buffer in front. As and integrated solution, it also does not seem to need a buffer behind.

As a source, I was using my NOS DAC with passive I/V and 0.1uF coupling caps. I tried it with a buffer and I was loosing immediacy and adding coloration.

The buffer, OTOH, worked very well with a resistor devider based volume control in front of the same amp.

Peter Daniel 26th March 2006 10:02 PM

2 Attachment(s)
The amp below has bridged output, the TVC also works as phase splitter. I prefer it with single primary.

The volume is remote controlled.

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