[Peter Clements]

Am I missing something here? Please put me straight.
A TVC as we know wants low input impedance very high outut impedance and low signal volts. What then is the best course of action for a tube phono stage? Most have a very high output impedance, say 1M and puting a buffer in adds insult, and volts. As I see it at the moment , one course of action is available. Build a custom phono stage using low Rp tubes and a huge cap infront of the TVC to control the inductance in the TVC. What do others do?

[John Chapman]

Hello!

>Am I missing something here? Please put me straight.

It's not my usual way to 'put you straight' but I think the missing link is that the impedances in any source are nothing like 1M. That high an impedance would never show up in a source as it would have issues with any type of pre-amp and also with even modest (short) lengths of cable.

I have 2 tubed phono stages here and have experience with others as well. The two I have here are the K&K kit and the Haggerman Trumpet. Both really good stages from great tube audio circuit designers - I'd say about as good as anything out there. The Trumpet is listed as 750 ohms output impedance and the K&K (from memory) is a similar output impedance. Both work extremely well with the tx102 - no issues at all. I have also used a tx102 on an 834P tubed phono stage with good results but don't know the specs on that one. Myself and many others have used Audio Note Tubed DAC's. They are a really good match for the tx102 - and have a highish output impedance - at the upper end of what you'd find in most any commercially availiable sources. I could go on - I guess I already did.......

I have heard mention of some vintage tube stages with impedances of something like 10K but have not had the chance to try any. I think that would be above the limit of what any passive device would be happy with and even in an active environment carefull attention to cable lengths and other issues would come into play.

I hope this helps clear it up a bit.  
 
Many Thanks!

John Chapman
www.bentaudio.com

[Peter Clements]

Hi John,
Well the 1M is on the high side of a lot of tubed phono stages. What I was after is that a lot are high impedance on the output. More than would be "best" for preformance. Also the high primary inductance  results in a resonant circuit well above the best spot for vinyl. Is this a problem? Or do we just carry on.
Cheers,
Peter.

[Peter Clements]

Hi John,
Well the 1M is on the high side of a lot of tubed phono stages. What I was after is that a lot are high impedance on the output. More than would be "best" for preformance. Also the high primary inductance  results in a resonant circuit well above the best spot for vinyl. Is this a problem? Or do we just carry on.
Cheers,
Peter.

[John Chapman]

Hello!

Having not run into any of these ultra high output impedance phono stages I don't know if I can help a lot. If you have a specific model you can point me too I'll dig into it and see if I can sort it out further. The recomended max output impedance feeding the tx102 is something like 1K to 2K and virtually all commercially availiable sources are far lower than this so it does not come up very much. As mentioned above if the output impedance is anything like 1M it would be unsuitable for any passive pre-amp. I'd suggest for such a source the only course of action would be to build the pre-amp into the phono stage (too keep the signal path very short) and to make the input impedance of the 'pre-amp stage' very very high (several M ohms). Basically the pre-amp becomes the output buffer for the high impedance phono stage. Trying to drive a cable and an amp input from a 1M Ohm source would not be ideal (actually it'd be a disaster!)  so at some place in between a buffer would be needed.

Many Thansk!

John Chapman
www.bentaudio.com