Valve buffered GC project

[Lilja]

I am planning to build valve buffered GC and looking for some more inspiration for the design of the circuit. I have already looked at the project on Decibel Dungeon and Joe Rasmussen & JLTi pages. Very nice constructions by the way! How ever, this will be my first construction with a valve involved and would appreciate some tips on the way.

Questions:

1. How many VA should the transformer for the valves have?
2. What about using a common transformer for the whole amp (both the valves and the GC-part)?

// Lilja

[thomgun_lc]

What is the best buffer using 6922 design??

[Franz G]

1. How many VA should the transformer for the valves have?

Not many VA. Because the tube is working in Class-A, the current will not vary alot and does not need a "big" reservoir.

So, every tranny with more than 10VA is O.K. for the anode voltage for a stereoamp (cathode follower a la Joe Rasmussen, one triode per channel).

For the filament, you can calculate the VA by the needed current of the tubes by multiplying the voltage with the current and adding some 20 to 30%.

I already heated valves with small print-trannies.

2. What about using a common transformer for the whole amp (both the valves and the GC-part)?

No problem, but you need separate windings for the separate voltages. And every winding and the cumulated total must fullfill the VA requirements, of course.

BTW: for the anode voltage, you easy could consider the use of a voltage doubler circuit (Greinacher), it works very well and is more easy, to find a suitable tranny.

And if you build the DIY version from Joes site: use higher anode voltage than suggested (dangerous!!).

I run the buffer (E88CC) with about 130VDC.

Success!
Franz

[Lilja]

Thanks a lot for the help!

[pete.a]

Hi Franz and all,

Would it be possible to use the circuit that you mention (Joe Ramm's) on a Non inverting Lm3886 amp. Iv'e just looked at Nuuks site and noticed it's configured for inverting ... Would i be right in thinking that the + 35v and - 35v change with respect to the + or - input to the chip ..hope i make sence it's late and dark in here

[Franz G]

Would it be possible to use the circuit that you mention (Joe Ramm's) on a Non inverting Lm3886 amp.

It is possible, but a noninverting LM-Chip does not really need a buffer in front of it.

Would i be right in thinking that the + 35v and - 35v change with respect to the + or - input to the chip

No! The anode will be driven by the positive voltage, the cathode by the negative voltage in every case.

Franz