• 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.

Passive RIAA with tubes

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Joe Tritschler had a very nice article in October 2003 AudioXpress "Borberly's RIAA Amp with Tubes". He is now offering a kit of stereo boards on his website - and it should be much easier to work with as he has modified it for the 6DJ8

http://tpadevices.com/hifiproducts.html

for $49 a pair of boards it would seem to be a good deal !

fwiw, here's what the schematic for the original design looks like on the SIM:

An externally hosted image should be here but it was not working when we last tested it.
 
well I got a pair of boards from Titschler -- the results are shown below.

the boards which were delivered were quite a bit different from the design published in AudioXpress (and that's not a bad thing, 417A's or 5842's are expensive).

In the stock design 100nF/400V coupling caps were used -- and you can see the droopy LF -- so I inserted a 1.0 uF/ 400V WIMA PP and the results are much better.

I show comparison with the Audio Research SP8 and Koren phonoamp stages modeled in SPICE:

An externally hosted image should be here but it was not working when we last tested it.
 
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