• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Raleigh Audio Preamp - somebody heard ?

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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