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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Raleigh Audio Preamp - somebody heard ?

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I built a version of it - used IXYS anode load, and 5676 DHTs, with a LL1540 transformer. It sounded very good indeed - very detailed and immediate sound. Very impressive - I'd recommend it thoroughly.

The parafeed cap is critical. I tried a whole lot of caps and the best by some way were the Russian teflon caps. I had to use quite a few 0.1uFs in parallel - I think I settled on 15 making up 1.5uF. Took up a lot of space, though I used the 200v versions.

This circuit is ideal for the RAKK DAC, which is what I was using, and the total output was just a fraction over line level, hence the LL1540 didn't overload, which it would do with more voltage into it.
 
I've built two different versions of this. One is a preamp that uses cinemag input transformers, Magnequest outputs, and a quad of 12a4 tubes, and auricaps for the parafeed caps. It sounds pretty good -- actually, it sounds pretty nothing in that it seems to have almost no sonic impact at all. If anything, it might be a little flatish sounding, but bumping the current through the tubes seems to help that a bit. Biggest influence on the sound seems to be the auricap.

The other is as an output stage to a pcm1794 based dac. That one uses the Lundahl transformers on the output, a quad of triode strapped 6688's for the tubes, and Mundorf silver oil caps for parafeed.

It's a nice design, but not one you'll likely be happy with if you want a typical SET sound. I go back and forth between this dac and a ad1865n-k based nos dac as to which I prefer.
 

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