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Old 28th October 2006, 11:45 AM   #1
G is offline G  United States
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Default Aikido PCB and AC filaments.

Hi all. Thinking seriously of buying a Aikido octal stereo board and building an Aikido. I've got my PSU designed but was curious if anyone is using AC heating with their Aikido board and have there been any problems with it? I was just going to bias the filaments to about 40v above DC- and go with it. I have also considered using a 12v SMPS for the heaters. Thoughts?
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Old 28th October 2006, 09:46 PM   #2
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bump.
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Old 29th October 2006, 01:19 AM   #3
jayme is offline jayme  United States
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I've got AC heaters, and I just got everything working right tonight. No more hum, no more buzz.

Proper grounding is definitely key to achieving a hum-free design. Pay VERY close attention to your star grounds, and I highly recommend separate star grounds for signal and power supply.

This was my first DIY project, and it was really rather straightforward. I accomplished a lot with just a DVM, a solder gun, and standard tools.

In terms of the sound...it is truely an excellent sounding linestage.
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Old 29th October 2006, 01:49 AM   #4
Bill*B is offline Bill*B  United States
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Default AC heaters

My own Akido was "homebrew" without the currently available board - BUT I used AC on the heaters, and there is NO audible hum. Just twist the heater wires together. Going the DC heater route adds considerable complexity, and I - for one - am skeptical of the need.
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Old 29th October 2006, 10:08 PM   #5
jayme is offline jayme  United States
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I agree...use a drill to twist your heater wires, and mount the resistor body for the grid and cathod resistors (the 300R to 500R resistors) as close to the tube socket pins as possible to eliminate any resistor leads from picking up noise.

Once I cleaned up my grounds, I now have zero hum. No noise...not even tube rush!

I do have to mention that PSU separation is helpful, so I would suggest the mono Aikido boards and dual-runs for the last stage in your PSU. When I had a single B+ for both channels, I had crosstalk between channels (evident with a microphonic tube). When I separated the B+ in the last stage of the PSU and paralleled it...the microphonic tube signal was isolated to just that channel.

The sound....is VERY clean and clear. Fast, musical, and not fatiguing at all. Trumpets sound real....something I haven't heard on anything in my price-range in the commercial market.
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Old 30th October 2006, 01:34 AM   #6
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Thank you all for your replies. AC it is. Biased to about 75 volts above the negative rail.
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Old 30th October 2006, 08:36 PM   #7
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Quote:
Originally posted by jayme
I agree...use a drill to twist your heater wires, and mount the resistor body for the grid and cathod resistors (the 300R to 500R resistors) as close to the tube socket pins as possible to eliminate any resistor leads from picking up noise.

Once I cleaned up my grounds, I now have zero hum. No noise...not even tube rush!

I do have to mention that PSU separation is helpful, so I would suggest the mono Aikido boards and dual-runs for the last stage in your PSU. When I had a single B+ for both channels, I had crosstalk between channels (evident with a microphonic tube). When I separated the B+ in the last stage of the PSU and paralleled it...the microphonic tube signal was isolated to just that channel.

The sound....is VERY clean and clear. Fast, musical, and not fatiguing at all. Trumpets sound real....something I haven't heard on anything in my price-range in the commercial market.

I agreee about everything said here so far but I do have a question about noise. I also have AC heaters and do not hear any hum but I do here some very faint hiss coming out of my 93dB speakers when I go up close. Its not bad but I was wondering if this is normal or do I have a bad layout/soldering technique? My layout is P-P, no PBC (yet). Anyone else noticed any hiss in their Aikidos?
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