6V6/12AX7 Project Question/Help

[Skitch72]

I am working on a tinker/junkbox project and am getting a little over my head. Its really my first scratch build so be nice, I have built a lot of kits and I know just enough to get in trouble and certainly don't mind throwing it together to see what happens!

I am working off of the attached schematic that I put together stealing bits and pieces from other projects I have seen.

An externally hosted image should be here but it was not working when we last tested it.

And am looking at adding in a stereo to mono summing stage in front of this setup. I found this on the aikenamps page:

An externally hosted image should be here but it was not working when we last tested it.

I'm not sure how to determine if this will work with my B+ or not, but I think I am going to throw it together and see. This is going to drive a small mono system from an iPod to just a mom speaker or a paralleled pair of speakers for a desktop type system.

Thoughts, comments, suggestions?

Thanks!

Tim

 

[Tom Bavis]

Assuming you have enough gain already, you just need two resistors for the summing function - one per channel, joined at the input. Value should be several times the output impedance of the iPod - 1K or more should do.

 

[Cassiel]

Why not use a proven schematic? If you're output transformers are cheap best one is RH84. It works with the 6v6 just as well. Kitic's design sounds good with cheap parts - others don't. Anyway, if you insist going your way you'll need a feedback loop for that pentode and the 6v6 cathode resistor should be around 470 Ohms.

 

[Skitch72]

Thanks for the info on the summing, I was really stretching for a use for the other half of the 12ax7 and just thought I would give it a try.

The RH84 project does look pretty interesting, I might bench that up first and see how it sounds with the iron I have on hand.

Thanks

 

[mashaffer]

You could run the two sides of the 12AX7 in parallel to provide more drive. You could also run the 6V6 in triode mode if the output level would be high enough to suit your needs. This would allow you to avoid the need for feedback (simpler) and would give you a use for some of the excess gain of the 12AX7 to drive the higher voltage swing requirements of the triode mode. Just a thought.