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jayme 24th October 2006 11:00 PM

choosing cap values for aikido
 
My aikido-based preamp has some low-freq resonance in the B+ (probably due its high Q-factor). There appears to be a 0.1V ripple around 12 hertz or so.

Anyways, my question isn't how to fix the PSU...it's how to block it from hitting my outputs.

http://tubecad.com/2005/January/25/Aikido_Amplifier.png

In the above schematic, I have the top cap at 0.1uF as specified in the schematic. Can this be adjusted to deal with B+ resonance?

My output coupling cap is 0.47uF, which gives me a cutoff of ~3Hz. Is the best idea to reduce that to 0.1uF to increase the cutoff to ~15Hz? If I did that, how would I compute the signal dB down point at 20Hz to see how that affects my signal response?

AND...I get a HUGE voltage spike at turnoff...up to 20V on the outputs. Will reducing that coupling cap reduce the output voltage, or is that spike due to the B+ dropping rapidly when the power is cut?


Sorry for all the questions. I'm learning...but slowly...

Thanks,
Jayme

SY 25th October 2006 01:15 AM

Quote:

Anyways, my question isn't how to fix the PSU...it's how to block it from hitting my outputs.
Fix the PSU.

Increasing the output rolloff frequency to 15 Hz will well and truly ruin the bass- the phase shifts are very significant.

jayme 25th October 2006 02:09 AM

Quote:

Originally posted by SY


Fix the PSU.

Increasing the output rolloff frequency to 15 Hz will well and truly ruin the bass- the phase shifts are very significant.

I am working on that....the resonance was 0.4V AC at 15Hz yesterday...so I am improving the PSU...But, I actually learn more about how the signal circuit functions and overall PSU design from my mistakes with the PSU circuit.

Hence, my questions above. They are more for my overall understanding of how the aikido-based signal circuits work, which then helps me refine my understanding and make it better.

Any thoughts? Especially about that first cap that shunts AC noise to the lower half of the output stage...


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