Euphoric valve distortion for synths!

NATDBERG

Member
2006-11-25 4:52 pm
Hi

I'm looking for a circuit design to push valves into distortion to over-emphasise 2nd order harmonics (variable) as an effect-box for synths (line level?) ..

What I'd like to kind of recreated is the distortion I've experienced with a valve hifi pre-amp when it was over driven by a CD player's 2V when it was designed for older gear at probably 250mV. It has this kind of ultra-smooth, over emphasised treble that sounded like a palpable, very very fine smoke in fine focus (if you can imagine that visual to describe sound!). Euphoric in other words.

I would also like to then be able to push it further into distortion to get the beginnings of a dirty sound but not going too far into it.

All the while being able to adjust output (attenuate?) to feed either a mixer or directly to A/D convertor. I guess that's the same as DI.

My other requirement would be to fit it in a small box of a kind of 1U, half width size (I have an old 80s wireless mic receiver box for it).

Would be great if it could use a 12AU7 as I know where to find one for free in an old theatre prop (old lab gear)! Hybrid is fine too...


Can anyone point to anything similar out there? Thanks !
 

NATDBERG

Member
2006-11-25 4:52 pm
Thanks for the replies..

Not looking for a proper distortion as one normally uses it other than at it's limits, much much more subtle type of distortion for the main part - 2nd harmonic distortion kind of thing rather than clipping.

More akin to tape saturation
 

benb

Member
2010-04-24 1:52 am
As far as schematics, look for tube distortion boxes for guitar, as already suggested. There's likely something like what you want already on the market.

There were several models of cheap "tube" mic preamps a decade or two back, the popular name I remember was the "Art Tube Pre." These used mostly solid state circuitry with a single tube (12AX7 or similar dual triode) run at a starved-plate voltage of 40V or so, for its effect. These are probably XLR input only, but a DI box/audio transformer can surely drive it from a synth.

A single stage (or two stages with the second having a larger signal than the first) will distort one polarity of the waveform more than the other, giving largely second harmonic distortion. A push-pull stage (such as a power output stage) will distort both polarities (mostly) equally, more like tape saturation. And of course these sound different, but either way, you surely mean/want "soft clipping" rather than the hard clipping of a high-feedback stage.

If you do the single-stage thing, you might also want a polarity inverter switch (which passes on either the original signal or the signal through an opamp inverter circuit) before the distorting stage, as your original waveform may be asymmetrical, and thus give a different sound depending on polarity.
 

NATDBERG

Member
2006-11-25 4:52 pm
Tape saturation is likely to be mainly 3rd, not 2nd.

Did you really mean "euphoric" or perhaps 'euphonic'?

Really? 3rd is considered to be unpleasant, tape saturation is considered to be pleasing. Perhaps a bad comparison then.

Euphoric in the context of my opening post, a description of the kind of sound I wanted to replicate, that generated by a valve pre-amp I have when fed a CD player output when it is seemingly designed for lower level outputs.

The English language doesn't have much for describing sounds specifically so I am using a common usage of "euphoric" within the realms of hifi equipment reviews and other equipment related sonic description.

But anyway, more akin to rather than sounding like tape saturation - akin in the depth of the effect and akin in terms of the result being pleasing and not like clipping distortion as a tube screamer peddal (the context of my reference to tape saturation) would give.
 
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NATDBERG

Member
2006-11-25 4:52 pm
As far as schematics, look for tube distortion boxes for guitar, as already suggested. There's likely something like what you want already on the market.

There were several models of cheap "tube" mic preamps a decade or two back, the popular name I remember was the "Art Tube Pre." These used mostly solid state circuitry with a single tube (12AX7 or similar dual triode) run at a starved-plate voltage of 40V or so, for its effect. These are probably XLR input only, but a DI box/audio transformer can surely drive it from a synth.

A single stage (or two stages with the second having a larger signal than the first) will distort one polarity of the waveform more than the other, giving largely second harmonic distortion. A push-pull stage (such as a power output stage) will distort both polarities (mostly) equally, more like tape saturation. And of course these sound different, but either way, you surely mean/want "soft clipping" rather than the hard clipping of a high-feedback stage.

If you do the single-stage thing, you might also want a polarity inverter switch (which passes on either the original signal or the signal through an opamp inverter circuit) before the distorting stage, as your original waveform may be asymmetrical, and thus give a different sound depending on polarity.

Thanks for that - Art Tube MP is the current one, £32 or so... hmm.
 
NATDBERG said:
The English language doesn't have much for describing sounds specifically so I am using a common usage of "euphoric" within the realms of hifi equipment reviews and other equipment related sonic description.
Really? I didn't realise that "euphoric" is now misused by "hifi" equipment reviews - maybe that is because I haven't read any for a while, and would probably stop reading if I saw such misuse of language. Anyway, how does "euphoric" misused in a sound reproduction context relate to "euphoric" in the completely different world of sound production?

English does have some words for describing sound, but people seem to prefer to adopt Alice's policy: words mean whatever they want them to mean.

3rd is considered to be unpleasant, tape saturation is considered to be pleasing.
Saturation/compression necessarily involves odd order distortion, as only odd order distortion can produce products at the original signal frequency which partly cancel the incoming signal. If you like saturation/compression then you like 3rd order, even if you didn't realise this.
 

NATDBERG

Member
2006-11-25 4:52 pm
Saturation/compression necessarily involves odd order distortion, as only odd order distortion can produce products at the original signal frequency which partly cancel the incoming signal. If you like saturation/compression then you like 3rd order, even if you didn't realise this.

A confusing analogy by me there then, sorry. I meant that the effect I was looking for would be slow onset and be subtle, akin to the way that tape compression is. In contrast to say a very obvious valve based, clipping distortion which people like for guitar etc.
 
If you are after even order harmonic distortion it's basically about asymmetric distortion of the waveform. Asymmetric clipping, or just harmonic distortion in general, generates even order harmonics whole odd order harmonics are created by symmetric distortion process.

Higher order harmonics are generated by "hardness" of clipping or overall magnitude of distortion. Basically, the more evident the distortion is, the more higher order harmonics it contains. Despite the popular myth that claims high order harmonic distortion sound hideous those added harmonics are essential for certain types of distortion effects, like modern "high gain" guitar tones for example. But what works for that probably wouldn't work in a mic preamp or alike.

And despite what popular myths try to claim neither even vs. odd harmonic distortion sounds better than the other. When you evaluate distortion in context of generating a musical special effect just ignore everything what "HiFi guys" write about it.

Oh, and don't forget about intermodulation distortion: In intermodulation harmonic distortion - of complex waveform consisting of many frequency components - will create sum and difference frequencies of each frequency present in the signal. So even if the harmonic distortion could be all even order the intermodulation process itself is bound to generate odd order distortion.


IMD is also much easier to hear than plain harmonic distortion and therefore even very "transparent" amount of harmonic distortion can turn everything into incomprehensible mud because it quickly elevates magnitude of intermodulation distortion. So in essence, due to IMD, below certain thresholds soft clipping can create mores distortion than hard clipping would. So soft clipping is always not that good for each and every application.
 
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milkshake

Member
2016-02-06 11:51 am
To get 2th harmonics, you can use a "ringmodulator". https://en.wikipedia.org/wiki/Ring_modulator
The simplest is a real ringmodulator with tranies and diodes.
They are very easy and dirt cheap to make, about $10 and sound great.

Ringmodulator_as_downmixer.gif

Build instructions here:
http://http://www.cgs.synth.net/modules/cgsrr.html

To get 2th harmonics, you need to insert the original signal into 2 nodes, the other node then outputs the 2th harmonics. You then need to mix this with the original signal.

You can also make higher harmonics by cascading more ringmodulators with the original signal/outputs of ringmodulators.