Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  


2/1/2000 2:56 PM
Mark Hammer
Okay, so we have the tube sound fuzz (TSF), Stellan's and my mods to it, the Hot Harmonics, the E-H Hot Tubes, and the Insanity Box. CMOS inverter tone seems to be here to stay. On a completely different front, we have the Anderton/PAiA Quadrafuzz, which is intended to reduce intermodulation distortion and make chords come out with a bit more definition.  
So, why not marry the two technologies and move towards CMOS distortion that's good with chords, since we have 6 inverter stages to dink around with on a 4049 anyways? Why not use selected series and feedback loop caps to effectively band-distort the signal along 2 or 3 different channels? The input gain stage employed in the IB, HT, and modified TSF's serves as a buffer so you can conveniently split the signal (albeit crudely) along 2 or 3 paths (hi/lo or hi/mid/lo; I'm assuming here that one wants to use two inverters for each distortion path since that would retain signal phase). You could use different feedback resitor values to set the drive for each channel appropriately. Moreover, for tone control and output volume, all you would need would be level controls for each channel feeding a final op-amp mixer stage. Now that I finally got myself a breadboard, I might try this out.
And now, a word from our sponsors:

2/1/2000 3:31 PM

Have you tried the Mini-Tubes preamp from AMZ? It has been getting rave reviews on Aron's bbs.  
I am collecting components to try this one myself since it supposed to sound different from any other distortion.
2/1/2000 6:46 PM
Roger -  
I have a Minipre up on the Breadboard and it is fun and has potential to be a great device (at least in my semi-capable hands) but Mark is barking up a quite different tree here - the idea of dividing the signal into frequency bands before clipping isn't new but has much upside IMHO.  
- The Ape  
2/1/2000 8:22 PM

but you need a good distortion circuit to start with before dividing it into bands. i've never had much luck with cmos but i admit that i have not tried the Insanity. maybe that should be my next project.  
Roger K.
2/1/2000 8:34 PM
I have yet to try any cmos devices. The Minitubes has quite the amplike sound and does smack of marshall, whick is fun for me being an ampeg freak and a bass player primarily. The sustain factor of the Mini is great - pretty near endless yet not nearly as weirded out as the big muff, f'rinstance.  
Too Many Pedals! Arrrrghh!  
- Ape
2/2/2000 6:58 PM
Mark Hammer
Band splitting, and the mini-tubes design
I'm waiting for my J201's to arrive so the jury is out in my town with respect to the mini-tubes preamp.  
Actually, what I described is a little different than the divide and clip strategy, since each gain stage also acts as a filter. The upper and lower ends of the pass-band in the standard CMOS inverter are set by input caps, and feedback loop caps. The Tube Screamer applies a similar kind of logic: shape the clipping tone by virtue of the passband being clipped. In this case, two successive stages sharpen the passband, but since the frequency content in the second stage (and concommitant tone shaping) depends on output of the first, the tone shaping needs to be a little different in the second stage. For instance, if one were to use a two-way split (bass/treble channels), the second bass stage ought to use a higher value cap in the feedback loop to keep the high end from snowballing. Etc, etc.  
The objective here is to get both "edge" and "definition" with chords. Sometimes, one wants the sonic chaos of ringing open chords with a pedal that erodes note definition, but sometimes note definition in multi-note situations is *exactly* what you want. The multi-band approach is intended to get closer to that.  
Still, I'm eager to hear Jack's design. Readers of tube amp schematics will recognize the familiar stage structure of many amps. To this I would add the Bassman 6G6-A. This is a CBS-era Bassman whose Bass pre-amp channel was configured as follows: gain stage, gain stage, bass and volume control, gain stage, gain stage, treble control. This comes very close to the ideal of having pre *and* post gain EQ, with the volume and bass controls providing the "oomph", and the post-gain treble control providing the harmonic tailoring. I always wondered what this amp sounded like, and in truth this promising pre-amp design could have been compromised by any of a number of things like output tube plate voltage, bad speaker compliment, etc. Still, I wonder whether the same logic could be applied to the mini-tubes, which also has 4 gain stages and a Fender tone-stack.
2/3/2000 12:27 AM
Frank Clarke

Let's say we take the Stellan Equalizer Fuzz and split the outputs of the tone controls to 3x (2-stage CD4049) units, then mix the inveter outputs to the output opamp.  
A hybrid of this:  
and that modified TSF thing.  
I assume this is what you mean Mark, to reduce intermodulation distortion. Actually not much more complicated than the MHMTSF to build. Am I close?

  Page 1 of 5 Next> Last Page>>