List of good Opamps for designing Clean Boost / Distortion Pedals

[Vivek]

Please guide me on the some of the good Opamps for designing Clean Boost / Distortion Pedals for DIY construction, based on

Noise
How close can they get their output to rails
Graceful recovery from rail saturation
Cost and availability

[Fancy Lime]

Construction matters in this case. You can build a great clean boost with a TL071. You can build a great clean boost with a NE5532. But swap the opamps between the two circuits and you will get a significantly worse result. So, we need more input to give you proper recommendations.

The simplest solution is a TL071 with a 24V power supply.

Andy

[LightSoundGeometry]

https://www.mouser.com/ProductDetail/Analog-Devices/AD712JNZ?qs=NmRFExCfTkHkv4a3jawdPw%3D%3D

[amz-fx]

Samuel Groner has a very good paper on op amps that will tell you plenty:

http://www.nanovolt.ch/resources/ic_opamps/index.html

Best regards, Jack

[Mark Hammer]

If you want clean, then supply voltage can often matter as much as chip choice.

[Fancy Lime]

If you want clean, then supply voltage can often matter as much as chip choice.

+1

Unfortunately, rail-to-rail opamps tend to be relatively noisy or made out of unobtainium. I would therefore suggest choosing high supply voltage and making sure that the opamp can never get too close to the rails by placing a couple of Zener diodes with appropriate voltage drops across the negative feedback path. That renders your requirements 2 and 3 moot and allows you to choose a cheap opamp that is not too noisy. Something from the TL07x series will do nicely, as will many other cheap low noise Bi-FET opamps, such as the LF353 (dual opamp, essentially the same part as TL072) or LF356 (single opamp, slightly lower noise than the rest). These can all handle supply voltages of 30V or more. If you run them at 30V and put a couple of 9.1V Zeners in the feedback loop, you have yourself a booster with ±9.7V of headroom, that stays well clear of the rails.

You can also use BJT opamps. There can be lower noise under ideal conditions and might behave better close to the rails. The NE5532 (dual) or NE5534 (single) are popular and easy to get. I like the NJM2068, which is even lower noise and has a bit more headroom. However, with those you need an extra JFET buffer in front, else their input impedance is too low. The extra JFET means extra parts and extra noise. This arrangement can be designed to be lower noise than with a Bi-FET opamp but you need a hard to get low-noise JFET (2SK170, 2SK117, or similar), the differences are small and in either case, you are in territory where any noise produced by the resistance of the guitar pickups (even without any hum) drowns out the noise produced by the booster. So not much point obsessing over noise here in too much detail, although I tend to do that as well.

If you want to use a 9V supply, have a look at Merlin's Glass Blower:
http://www.valvewizard.co.uk/glassblower.html
I doubt it is possible to design a better booster that suits all your requirements and works well with 9V. Merlin has a bunch of great designs but the Glass Blower, though one of the simpler ones, is his masterpiece in my opinion. There are other bootstrapping techniques that allow the opamp to get closer to the rails than it normally could but they are more complicated and less effective.

There are even more tricks to get the output voltage swing close to twice the supply voltage (e.g. 60V for a 30V supply) but then the design gets a little more complex and I am not entirely convinced of the utility of such a device for guitar use...

Cheers,
Andy

[Vivek]

If you want clean, then supply voltage can often matter as much as chip choice.

If you want to use a 9V supply, have a look at Merlin's Glass Blower:
http://www.valvewizard.co.uk/glassblower.html



Cheers,
Andy

Thanks for pointing out the Glassblower.

That's really an innovative circuit idea !!!