Aikido - alive and kicking butt (not mine!) - diyAudio
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Old 20th December 2006, 12:57 AM   #1
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Join Date: Oct 2006
Default Aikido - alive and kicking butt (not mine!)

Finally, I got the Aikido preamp working in synergy with my main system.

I owe a huge debt to Sy who looked over my circuit diagrams for PSU and inspected a poor quallity photo of my layout. With his recommendations, the amp is now hum-free, except for very minor hum from the transformer which is not getting into the signal.

I am incredibly revieved.

So, I learned a few things:

1. Bias the heaters to 25% of B+ to the center-tap of the heater AC transformer.
2. Mount the volume pot to the chassis
3. Ensure that the signal wiring avoids the proximity of any AC wiring.

I do now need to buy a good stepped attenuator and then move my good quality jacks and source selector from my passive-preamp to Aikido.

Again, I want to thank Sy for his help, and metion that this forum really benefits from his expertise and experience.

Regards,
Charlie
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Old 20th December 2006, 01:41 AM   #2
jayme is offline jayme  United States
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Join Date: Sep 2005
Glad you are now enjoying the aikido circuit. My 6SN7-based aikido brings a smile every time I switch it on...it is just so darn musical...

One comment about the stepped attenuator. I have a cheap Alpha pot, and a nice ladder stepped attenuator. Honestly, the Alpha pot sounded more lively than the stepped, altho it was a bit thin. I swapped it out for the stepped, which sounded dull and rolled off.

In the end, I switched to a shunt-style setup, using a single resistor in the signal path, with just the wiper and the shunt resistors from the stepped providing a path to ground. That proved to be the ticket.

If I were to do it all over again, I would forget about dropping in the stepped, and just using the Alpha pot in shunt form.

All you need is 2 resistors which are the same value resistance as the pot. Start with that, first...
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