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Old 15th April 2008, 03:53 AM   #1
wonsup is offline wonsup  United States
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Default Aikidos Headphone with Output Transformers?

I've been enjoying my Aikido headphone amp for a while now with AKG K701s and Grado SR225. They sound very clean, neutral and detailed.

Unfortunately my tweak-itch has started again and I want to update the amp with a Electra-Print custom wound OPTs, so I can bypass the crappy 470 uF electrolytic caps.

What is the best way to mod the amp to accomplish this and also what impedence should I be looking at for the OPTs, assuming I want to use 62 and 32 ohm headphones? I am running 6CG7 for output and 6922 for inputs.

This thread shows the schematic, but I wasn't sure if that was Sowter OPT specific design or something else?

Aikido as a headphone amplifier (Output transformer groupbuy)
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Old 15th April 2008, 04:09 AM   #2
wonsup is offline wonsup  United States
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OK, I found a page on the tubecad site that described this:

I will probably try out the first option with the coupling capactors. Still need some help around picking the right type of transformer and the winding ratios...
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Old 15th April 2008, 08:24 AM   #3
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Since you are effectively going Parafeed, you can try using Mains toroidals as output transformers. I have them in my headphone amp (PP ECL82 with plate to grid feedback). These are probably the best output transformers in that application - and they are cheap, and if you don't like them you can splash the cash later for custom wounds when the benefits are realised.
Try something like a 12V:110V or a 24V:110V.

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Old 15th April 2008, 09:05 AM   #4
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Originally posted by Shoog
Since you are effectively going Parafeed, you can try using Mains toroidals as output transformers.
Yes, along with Shoog's suggestion, try the smaller transformers, as the larger ones can cut the HF too much.

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Old 15th April 2008, 05:34 PM   #5
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Assuming parafeed, I'll third the toroid suggestion with the caveat that it is only if you are looking for a budget solution. Jack's parafeeds will outperform the toroids -- I've used both.

But, to answer your actual question about impedance ratios, the secondary should match your phones. For the primary, the higher, the smaller the coupling cap you can use, but the more voltage you give up. If you have more than enough gain, then a primary Z of 10K is a good target (this is something like a 220:12V toroid -- if there are dual primaries, you want them in series for the higher inductance.)

If you want to use the gapped version, then I'd talk to Jack and send him the schematic as he'll be able to give the best advice.
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