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

ampage archive

Vintage threads from the first ten years

Re: Super Tube Screamer - Chip choices

:

8/19/1999 11:14 PM
Daniel R. Haney	Re: Super Tube Screamer - Chip choices Saw the schematic. I agree that the unity gain buffer on the input is superfluous. Might work better on the output in place of the CE buffer IF the opamp had enough drive. -drh --

8/20/1999 9:55 PM

Personally, I think the only place the 'magic' chip makes any difference is in the clipping stage. The JRC4558 isn't the lowest noise device and you would probably be better off using some other low-noise opamp for the rest in the circuit.

I base this on tests I've done with a SD-9 that had a JRC4558 inside which I changed to a low-noise opamp and it didn't sound any different. A little quieter, maybe. The 4558 then went immediately into a TS-9.

All your observations are correct as far as I can tell.

--johng

BTW, the SD-9 really only needs one opamp. They use the second in the package as a buffer in much the same way as the STS.

8/23/1999 1:48 PM

Thanks for the corroboration. The question still lingers in my mind, however, if you were going to select the ideal single op-amp to use for the clipping stage (assuming JRC's, etc. were not available, or that one wanted to use lower noise chips for any other stages) what commercially available single op-amp would be an appropriate sub? Since we have devoted so much time and space to discourse about appropriately selected duals, we may have gotten distracted and ignored a desirable single that is right under our noses, cheaper, more easily available, and in more reliable supply. I could easily be wrong, and it obviously is no help to folks who want to improve an existing unit from the TS-x series (which clearly DEMANDS a dual package), but hey, its worth a try.

8/30/1999 11:13 AM

Based on the suggestions for some of the more modern dual opamps for use in the TS-series, it should not be too difficult to find a single that produces good sound, is in current production and readily available at modest cost. The OP-77, OP-27, NE531 and LM308 (compensation cap required on the last two) are some chips to start with. The LM308 has been used in the Rat and is supposed to be part of its special sound.

Alternately, the damper resistor method described in the article at http://www.muzique.com/amz/latch.htm could be applied to widen the number of available choices. I've found that it prevents latch-up which can be the cause of the glitches that occur with some opamp inputs as they try to switch off.

regards, Jack

8/28/1999 8:53 PM
Hammy	The SD-9 is diodes to ground circuit, and if you read RG's explanation of why the magic chip sounds best, its mainly to do with diodes in the feedback loop. The SD-9 should do with other op-amps. (The one I built sounds great.) Ham

Page 3 of 3