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Topics - QReuCk

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Preamps and Effects / Clipping theory - a nice find this week
« on: May 31, 2013, 03:33:59 AM »
Hi guys!

I stumbled across this article earlier this week:
https://ccrma.stanford.edu/~dtyeh/papers/yeh07_dafx_distortion.pdf
So I though that was somewhat enlightening and I would share the link here.
It is more of a numeric modelisation project, but the approch they used to understand the behaviour of real life analog devices is interesting, me think.

For instance, look at the sine wave signal response they obtain for the Boss DS1 and for the Tube Screamer.
Typically, pieces of information you find on the interweb tell you that the diode arangement of the DS1 is hard clipping, which is often represented with a perfectly truncated sine wave where it hits the voltage limitation of the diodes. They measured the real device through oscilloscope + fourier analysis and what did they found? Both the OP amp and the diodes are distorting the signal, and both these devices do have a different real life behaviour than the typical representation. The resulting wave form is nowhere near what people usually asume for such devices, and the tone setting parts do not explain such behaviour if you model them as pure linear filters.

I don't exactly know if it really fits in there as the electrical behaviour of each component and arrangement is pretty blured in this "block box" approach. But as it deals with stompboxes, I might be in the correct forum to gather your thoughts about "real life" devices vs "how we assume it should work".

Thoughts anyone?

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The Newcomer's Forum / Some noob questions.
« on: June 21, 2012, 06:47:47 AM »
Hi all.
I'm new here and would like to ask some questions you may have answers to:
I've got an old 15W mono chanel SS combo. The brand name is Avenger and the model name is FA15. I've found no schematics or even serious review of this amp, nor any info on the brand.
Features are simplistic: A gain knob, a Volume knob, a master know, and a 3 band EQ. There is a 6' small speaker in it (closed back).
I also own a Peavey Envoy 110 Sheffield, which I consider a great sounding amp, but cannot obtain with it the beautifull crunch I am able to hear with the avenger. I've read numerous times that SS amps are supposedly unable to produce a good sounding clean, but I swear this little low end thing sounds just as good and dynamic as a Fender Blues Junior as far as light crunch is what you want to hear. There are a few problems though:
1° the gain know is unusable: Adds a lot of harshness. More harshness than distortion I think, so this amp is limittated to various slight overdrive tones. My feeling is that this works as designed (poorly, but as designed).
2° the volume know is good for settings from clean to average overdrive. Only trouble is that the range on the pot is not optimal: volume at 0: no sound, volume at 0,5: clean, volume at 1: clean with a tiny bit of crunch when striking the strings heavily, 1.5 to 2: nice slight crunch to light overdrive, 2 to 3 nice overdriven sound. Past 3 or a bit more, it becomes too fuzzy for my taste.
Mind you, I have humbuckers on both my axes, but even with reduced volume on the guitar pot, I kind of regret not being able to use the full range of the volume pot even when the gain one is on 0.
3. I'm affraid it lacks a bit power when playing with my drummer. No external speaker output, and no real preamp output to direct it to my peavey, which as no power amp input or effect loop return for that matter. So chaining both amps would use the Peavey preamp in the signal chain.

I realize my knowledge is limitted, but:
1° Do you think I can make some testing directing the headphone out of the Avenger to the instrument Input of the Peavey without damaging any of these amps? If so any recommandation on the settings of both amps?
2° In case this test is not possible, is there any way to anticipate what part of the Avenger produces this nice tone and dynamics? I would like to know if there is some probability the nice crunch and dynamic response may be lost if I find a way to direct the préamp of the avenger into a poweramp and speaker (probably guitar type ones).
3° do you think there would be some mod possibilities to have the gain knob dropping some highs when rising the gain and some other mods to change the range of the volume knob?

Not a question, but might be the goal after all:
If tests indicate that there is a possibility that this preamp + external power amp and speaker retains the very specialized tone I have, I could be tempted to use its preamp as an alternative to the one built in the Peavey. That would obvioulsy call for some work (a power amp input for the Peavey, a true preamp out for the Avenger, some A/B switch, etc...), but if the result has a chance of being good, why not?

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