I'm interested in building this:
http://www.madbeanpedals.com/EP/schematics/424.gif
Which seems to get all it's clipping from overdriving the opamp, sans diodes. What are the relevant clipping characteristics of opamps themselves? Should I be looking for any specs in particular?
You could try some TL072 or 062 there and see how it goes.
You mean replacements for the 4558?
Yeah instead of the 4558. Just wondering if there's any information about clipping different opamps, either from data sheets or anecdotal.
Madbean site seems down at the moment. But LM308 is a good one to overdrive. It's a single, so would need two to replace a 4558.
OTOH, I once breadboarded a Son of Screamer with 2x LM308s, just to see what it would sound like. I didn't make any other circuit changes except the compensation caps. Well, it sounded awful. So something else needed to be changed, but I didn't bother with it any further.
I would look at some datasheets and find op amps that have big differences in various parameters. Try breadboarding them at the same time in identical, simple op amp distortion circuits and A/B switch them.
Slew rates come up often with this question.
You know how to do a "site" search on a search engine? Type in "best op amp clipping site:diystompboxes.com". There will be more info than you want, going years back. To call this a perennial question is an understatement. Have fun!
Yeah, i also gathered that a "slow slew-rate" kinda "rounds" the clipped waveform so it becomes more pleasant for the ear. I'm sure there's some electronic magic to further "sand off" the edges of a hard rectangular wave.
Quote from: KarenColumbo on January 12, 2018, 03:14:07 AM
some electronic magic to further "sand off" the edges of a hard rectangular wave.
Yes, a low-pass filter.
Quote from: FiveseveN on January 12, 2018, 03:56:43 AM
Quote from: KarenColumbo on January 12, 2018, 03:14:07 AM
some electronic magic to further "sand off" the edges of a hard rectangular wave.
Yes, a low-pass filter.
Easily formed with a small cap in conjunction with Op-Amp's output current limiting resistor..
I built one of these recently, put in a TL072 while i was waiting for the 4558s. It sounded pretty good, i was convinced and would have used it on my board, but then the 4558s arrived and it sounded a hell of a lot better in my opinion
Hi,
I'll second the TL072. Most of the distortion of the Marshal Guv'nor comes from its TL072. I breadboarded one and I remember taking off the LEDs for some reason. Still sounded good.
I have the impression that the Klon works like this as well.
I traced a distortion from a local pedal company a few months ago. Just two TL072 gain stages and some filtering. Very good tone, but a little noisy.
IIRC NE5532 sounds horrible.
EDIT: The Sansamp Bass Driver, and I think the GT2, both use TL2264s, which are rail-to-rail versions of the TL064, for clipping.
Quote from: marcelomd on January 12, 2018, 07:14:19 AM
Most of the distortion of the Marshal Guv'nor comes from its TL072. I breadboarded one and I remember taking off the LEDs for some reason. Still sounded good.
Guv'nor actually sounds pretty same with Leds, Si diodes or none ... :icon_wink:
(didn't ever try it with MosFets..)
IMHO, it's mainly due to Op-Amp distortion topology and not to any particular Op-Amp..
+1 agree about lower slew rate being some kind of guide. You want some distortion, but you don't really want absolutely square waves.
Another thing that no-one has mentioned yet is lock-up or phase inversion, which you won't find mentioned in data sheets. Some op-amps don't like having the output driven to the rails, and will hang with the output stuck at one rail or the other, or invert the phase when the signal would go out of range. Neither sounds good at all!
My personal opinion is that older op-amp designs tend to sound better - 741 era rather than the latest greatest OPxxx hi-fi whatever.
Tom
Some Tech 21 Sansamp (amp sim) designs rely on op-amp distortion - there is nothing else in the gain/boost area that can clip or limit. They use CMOS rail to rail Texas TLC series for that area of the circuit. The other op-amps (different types) in those probably never clip.
Behringer clones of those products use Texas TL Bi-FET amps and don't sound very nice at all if clipping IMHO.
I sometimes wonder if CMOS op-amps are the "Elephant in the room" with stompbox designers. They have been around for years, cheap as chips ... and designers ignore them ... ah but they're noisy.... and slow...
Quote from: anotherjim on January 12, 2018, 09:27:21 AM
Some Tech 21 Sansamp (amp sim) designs rely on op-amp distortion - there is nothing else in the gain/boost area that can clip or limit. They use CMOS rail to rail Texas TLC series for that area of the circuit. The other op-amps (different types) in those probably never clip.
Behringer clones of those products use Texas TL Bi-FET amps and don't sound very nice at all if clipping IMHO.
I sometimes wonder if CMOS op-amps are the "Elephant in the room" with stompbox designers. They have been around for years, cheap as chips ... and designers ignore them ... ah but they're noisy.... and slow...
Tech 21 uses TLC2264 in the Sansamp series. TLC2264 + zener diodes in the character series.
Behringers use regular TL064s. Just opened my BDI21 (Bass Driver clone) to check. The BDI21 is good for adding warmth, but not for all out distortion.
I don't know about CMOS opamps, but my current favourite overdrives all are CMOS (4049, 4007) or MOSFET based. Worth checking...
Some of these pedals mentioned (sansamp, guv'nor etc) are trying to replicate at least the idea of the sound of an overdriven valve amp: Even the Rat, with it's hard clippers and overdriven opamp, is aimed at a hard rock, "amp distortion" sound. The Midfi demo tape fuzz is supposed to replicate the sound of a tascam four-track audio cassette recorder input being rudely saturated by a guitar plugged straight in: As such, i don't think the actual opamp matters that much. Doug said at the other place that he put 4558s in the early ones and TL072s in more recent builds. I think I have a 1458 in my clone and it sounds pretty good (being over 40yo, I spent much of the 1990's recording heavily effected, input-violating backwards guitar onto a hissy tascam in my bedroom so i can see the nostalgic appeal).
Quotethe sound of a tascam four-track audio cassette recorder input being rudely saturated by a guitar plugged straight in
i both love and know that sound well, i lived on a 424 for years! pretty sure those are TL072s in the signal chain
If it's was me I'd socket the op amp and audition new ones as they arrive.
I did find this.
https://www.technobotsonline.com/dual-op-amp-similar-to-ua741-rc4558.html
I Really like the FA1 with a 4558.
The circuits are very similar except the FA has a Fet Amp input buffer.
A lot depends on your other gear too. Of course playing style, your ears......
Have fun socket the sucker and play op amp roulette.