Mimicking tube amp transformer compression

[vansinn]

Well.. I don't think there are too many really easy ways of achieving the same type of soft knee limiting/compression as what takes place when the output transformer gets loaded into saturation.

But missing it is damn annoying, so I tried using an old ADR Gemini Compact dual/stereo compressor/limiter.
Had to repair it, as it blew the rectifier diodes and voltage regulator on first startup after fifteen years in storage - culprit was the 470uF main filter capacitor gone bad ;)
It's a fully discrete thingy, using a FET and a build-together lamp-fotodiode component, plus a bunch of transistors.

Anyways, when set as a limiter with 1.5:1 ratio and somewhat fast reaction time, it sortof semi-emulates the tranny action. Sortof ;)
Mmnn.. not quite real, but still quite decent. Sortof..

Any other ideas?

[MarshallJMP]

When you go into saturation, you get harmonic distortion which will sound quite different from the sound you get from a comp/ lim .So I don't think you can mimic that sound with a comp/lim.

[vansinn]

I fully agree on the harmonics, AKA intermodulation products.
However, I still do end up with something akin to the soft-knee compression in the loaded output transformer.

Hmnn.. I could try installing a small-signal transformer in the compressor, and use a germanium transistor to drive it into saturation.. :dunno:

[MarshallJMP]

Clipping is a sort of compression but with added harmonics.

[Kim]

How hard would it be to build a very small poweramp circuit to drive the snot out of for this application?  Something with just one 12xx7 tube. 
And then....maybe something based on the Ampulator?

I know I sure would like to have something like this in my home studio.  :thumb-up:

[MarshallJMP]

Voila Kim solved your problem, get a ampulator 

[vansinn]

Hahaha, this is what we have a forum for ;)
Yeah, a single 12AT7 could serve as a stereo triode class-A micro amp, coupled with a small transformer and a few passive components plus a ready-made switch mode psu, and there you go..

Oh oh oh, me thinks I'll just go poke my Behringer MIC100 tube preamp. These things costs next to nothing, and has all that's needed, incl transformers. Only the limiter needs to be modded, as it is kicking-in too abrupt, like going poof-compress, if you get my drift..
(oh well, these ideas at least made me repair my old ADR, so..)

EDIT: Mistakingly wrote 'incl transformers', which is not the case; I ws thinking of the Ultra-G speaker emulator..
Anyways, there should be enough space for a small'ish power transformer in there; just had it opened.

[rnolan]

Go Van, sounds like your having some fun  :thumb-up: