Harmonic Distortion Generator

Mlewis

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Jul 5, 2005
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London, England
anybody had a look at this?

http://www.pmillett.com/etf_sod.htm

i've been interested in a diy line level tube distortion box a la culture vulture for a while. the distortion doesn't seem variable on this (fixed at 5%THD i think). i confess to know little about tube stuff but do any tube guys here know if it looks promising or useful for creative distortion purposes in the studio?

The culture vulture uses a 6AS6 instead of a 6BN6 but it seems to be similar in operation. there's a tube overdrive section in the culture vulture too but that's easy enough to put on the front or the back of this isn't it?

anybody interested in such a box?

thanks
 

blandman74

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Aug 4, 2005
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Washington, DC
mlewis:

Hello from the other thread. I did something like this using, IIRC, a triode-pentode-triode arrangement, with the first triode a mu-amp, the pentode having various changes, and the last triode a cathode follower. My knowledge of tube theory isn't the best so there were some problems which made set the thing aside as I learned more, but I could dig up the schematic. I have been planning to return to it anyway, so if you want to review it and make suggestions, I can make the changes and report back on how it sounds. It, too, was inspired by a description I read of the culture vulture.
 

Mlewis

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hello!

yeah.. i'd love to have a look but i'm afraid the only tubes i've truely got to grips with contain toothpaste, so it's worth taking this into account if i suggest anything!!

be great if you could post it here for the group to see/discuss.

thanks... Mark.
 

PRR

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> the distortion doesn't seem variable on this (fixed at 5%THD i think).

No, 5% at rated input: CD-player level though the trim-pots.

THD will decrease to zero for super-small inputs.

THD will increase if you feed it more.

The beam tube is neat. You only really need the tube and an output buffer, with some way to control levels and the bias voltage (all those trimpots).

You can make most any low-order (musically useful) distortion with a long-tail pair. Adjust the input level for desired bentness. Un-balance the pair to shift from odd-order to even-order. You can do it with JFETs.
 

synthi

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Jun 9, 2004
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Madrid (SPAIN)
I was looking for a kind of thermion*c vulture distortion box and now when have a circuit as starting point! :thumb:

Synthi
 

Mlewis

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Jul 5, 2005
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144
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London, England
thank you very much for the responses, as ever...

i found an old long-tail pair amp here:

http://www.dogstar.dantimax.dk/tubestuf/4x4howit.htm

obviously the high power output stage would need to be changed.

there's also some stuff over at aiken amps:

http://www.aikenamps.com/LongTailPairDesign.htm

so to do it the long-tail pair way we'd just need a line output buffer that can switch 6db to take care of the change between ballanced and unballanced depending on whether even or odd order distortion was required, then an input attenuator (with fully un-attenuted +4dBu or -10dBV as the maximum distortion level) to take care of the drive/distortion amount? sounds quite neat.

that would mean only even OR odd order distortion though wouldn't it?

how are the various types of distortion (in particular even AND odd order) produced in the beam tube circuit? i don't really fully understand the circuit yet.

thanks for taking the time to look at this

Mark.
 
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