|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
In Reply to: Re: Looking for a GOOD 211 / VT4-C Schematic posted by Paul Barker on July 19, 2003 at 01:27:49:
Paul,I really appreciate your help. At the moment i'm trying to order the CD archive 'Sound Practices' to educate me more on DIY hifi.
Preamp drives 2v RMS. Actually, it is Nelson Pass's SS "Balanced Line Stage" pre-amp i've built 2 years ago. My friend uses the same preamp to drive his 300B amp and we couldn't believe the improvement over a regular passive pot. But to go back, I made this preamp mainly because it was fully balanced to match my power amp (with XLR inputs). However, this particular pre-amp also serves as a converter from XLR to RCA or vice-versa. This is another area I wouldn't mine looking at - why... almost all tube circuits i've seen are not balanced? The response I get is "fewer parts in a tube amp... the better the sound". But what if the tube amp could benefit from reduced noise by CMRR in balanced circuits?
If you can spare some time for me in getting a schematic for me - I would be greatly in debt to you. I'm still not experienced enough to make from scratch, a la my-own-design.
Follow Ups:
Balanced? Main benefit is in low level stages, once you've amplified signal to 2vrms maybe the benefits do nopt outweight the added complexity. That said Steve Bench has an 845 circuit which is push pull up to the 845 and then single ended. This could be adapted to retain your balanced topology right up to the 211, but it would be a lot easier to stay single ended.2vrms is quite good, 2.828v peak.
I was wrong about power out. It takes greater voltage swing than I thought. That's working with the 212 for you, it's clouded my judgement. Take the standard high voltage operating point of 1250v 60 mA into your 10k load. You can develop 13 watts from a grid drive of 60v peak (theoretical maximum just under 20 watts from 75v peak drive)
To develop 60 volts from 2.828v requires a voltage gain of 21. It's no use saying good the 6sn7 idea will get us there, because you will necver develop a voltage gain equal to the mu of the valve, and not many 6sn7's you test will actually have a mu of 20. I think you must select a valve that has a little more gain in the first place.
It's now becoming clear why the 6c45pe is populare for this application but it's not the only option, and it isn't pressed into service without some care in application (parasitic oscilation around the 6c45pe can make the resultant amp sound quite solid state like).
That said the circuits already exist and hand it to you on a plate. Buiuld it on a bread board and see how you like the sound, then try something else, to see if it can be improved upon.
This post is made possible by the generous support of people like you and our sponsors: