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Aikido valve ampbuilders, please respond

post #1 of 5
11/13/09 at 5:50pm
Thread Starter 
Hi guys, i am planning to build an Aikido all in one valve amp kit. I would love to build in in a balanced version but I'm a bit worried the gain will be way too high. Is it as simple as buying two kits and building it to a balanced spec or would i need to tweak the existing design to suit my needs? I have recently built a balanced b22 and the gain setting was a matter of using specific resistors but i'm not sure how this would be on a valve amp.
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post #2 of 5
11/13/09 at 7:10pm
The 6CG7 input tube yields a gain of 10, balanced will be 20. You may need to source a lower gain variety - the amp seems to be highly tweakable, you may be able to find a substitute.
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post #3 of 5
11/13/09 at 7:55pm
The Aikido can use just about any triode, a 12AU7 or 12BH7 would give even lower gain than the 6CG7. John Broskie provides a list of tubes and resistor values for various B+ values that all yield different gain. I'm sure he has a user guide pdf posted somehwere on his site specifically for the LSA/HPA board, but I could only find the All in One 9-pin guide right now. The tube chart is at the end of the user guide.
http://tubecad.com/2009/03/13/Aikido...20in%20One.pdf
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post #4 of 5
11/13/09 at 9:08pm
"Aikido Balanced" boards were mentioned at some point by Mr. Broskie and I've seen at least a pair being sold in the 2nd hand market but I can't seem to find them in his shop now.
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post #5 of 5
11/14/09 at 7:17am
Thread Starter 
I actually sent a message to John asking him about the balanced option, here was the reply.

Hi Mark,
The big fear I have of the balance approach is that the coupling capacitors will have to be twice the value of the single ended output, two 40µF, instead of one 20µF. also, the output impedance is doubled. Additionally, I worry about the even distortion harmonics falling out of the mix, leaving only the harsh odd harmonics. You see the problem with balanced drive is that doubles the potential voltage swing, but not the current swing, as the amplifier is severely current limited. Balanced drive is great in a electrostatic headphone amplifier, as lots of voltage swing is needed and most amplifier are voltage limited. But with dynamic drivers, lots of current is needed, not voltage. Thus, paralleling up two triodes would double the current swing, whereas placing two in series (in a balanced setup) doesn’t improve the current delivery potential.

Which headphones to plan on driving?
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