Wampler warm 741 overdrive

[madstayen]

Wow what a crappy ass tone!!!!!!!!!!!! It sucks big time!!! High on bass, low on treble, and extremely dull!!! And I get white noise as well. Must say, I expected a bit more from the 741 opamp than what it delivered! It sounds a little bit better (marginally) through my marshall MG102, but through the Vox there's absolutely nothing appealing to it. A J201 booster is a million times more quiet, and gives a vibrant sound, especially if you run it through the Vox.

Disappointed!!!!! 

[madstayen]

Maybe i should add a marshall type tonestack to it, hmmmm...

[Mark Hammer]

1) Woofiness or bass-heaviness can be repaired by making C4 1uf instead of 10uf.  Indeed, given all the other errors in the original schematic, maybe it was supposed to be that value.

2) The 741 IS a noisy op-amp, which is why we tend not to use it anymore unless the design specifically needs a trait that chip possesses.  Part of why I suggested upping the value of that 25pf cap was to remove audible hiss (although C1 ought to do some of that).

3) On a different forum, we were having a discussion today abut what Vox amps "like", and it would seem that EL84-based amps can sometimes be picky about what they want to drive them.  Not VERY picky, but let us say that a narrower range of pedals seem to appeal to users of EL84-based amps than might appeal to users of 6V6 or 6L6-based amps.

4) The tonestack you are thinking of will eat up a lot of signal, making it difficult to push your amp hard at less than max gain settings.  I suggest checking out the variations of the "stupidly wonderful tone control" ( http://www.muzique.com/lab/swtc.htm  http://www.muzique.com/lab/swtc3.htm ) which tends to provide decent tonal control - if not quite the flexibility of a T/M/B tonestack - with minimal signal loss.  If you want a little more output, at the forfeiture of a bit of clipping, add a germanium or schottky diode in series with D1 so that you have 2 diodes going in that "direction" and 3 going the other way.

5)  The original MXR Distortion+ used a 741, but it also provided the bias voltage (what comes via R3) from a pair of 1M resistors, rather than the pair of 10k that Brian used.  Moreover, the Dist+ used a 1M resistor where R3 is in this drawing.  When you consider how little current is arriving at pin 3 after it has to travel through two 1M resistors, compared to 10k and 470k, as in this circuit, that may be partly responsible for the pleasing tone from the 741 in that case.  Many here have noted how difficult they found it to get any sort of clean tone from the chip in their own Dist+ builds, which leads me to suspect that the chip was distorting in the absence of the diodes, and then the diodes would clip again.  So, just for the hell of it, try subbing a pair of 1M resistors for the pair of 10k resistors in positions R6/R7, and see if that brings you any closer to  a likeable tone.

[madstayen]

Okay, swopped for two 1M0's in series, it's more smooth than before. Then swopped the 1N4148 for an ultrabright LED. Not much difference, but it gives it the feel of the Boss HM-2, but less fuzzy (more gritty). Still extremely hissy though!

[madstayen]

BTW, I like that tone control, will add it tomorrow and see. Might roll over to my J201 boosters aswell! hooah!

[chi_boy]

You're half way to a DOD 250 too.  The grey version is supposed to be highly regarded.  I know I like mine, but haven't compared to the other variants.

There are only a few extra parts and if you have this on the breadboard it should be no big deal.

[madstayen]

thanx, was thinking of doing something extra with it. Might just get a tone that can be appreciated.

[amptramp]

The maximum gain in the schematic is over 200.  Now look at the characteristics of the 741 - you can't get much gain at all at high frequencies and certainly not more than the open loop gain.  The data sheets for the device from here:

http://datasheetcatalog.com/datasheets_pdf/L/M/7/4/LM741.shtml

don't even quote a frequency response, but you can guarantee that if you dial in more than a gain of about ten, the high frequencies will fall off.  This can be interpreted as a "warm" tone or "dull" depending on the circumstances.  Of course, with enough signal input, you will clip and reduce the gain, so this does get used and some people like it. To keep your options open, the best thing you can do is install a socket so you can find whatever op amp suits your purposes best - the 741 is one of a galaxy of op amps which could occupy this position and most have the same pinout, so you can swap in whatever you want.

[Mark Hammer]

I had earlier recommended use of a 1M + 1M reference-voltage source, following the lead of the MXR Distortion+, and that appears to have provided some audible benefit.  I can't say that I have EVER seen another circuit, apart from the Dist+, that used resistor values that high, but then not many op-amp clippers use the 741.

My sense is that those values are useful in the context of the 741, but not likely in the case of other chips.  So if one IS going to try out other single op-amps (and there is no reason not to), it might be advisable to also consider reverting back to a different sort of Vref divider, such as the original 10k + 10k, or maybe somethng as high as 47k + 47k.

Heck, maybe it's time for someone to socket the Vref resistors, try out different vales with different chips, and whip up a series of graphs, and see if it does make a difference.