Median Compressor PCB - Available Now!

airbud said:
Tl072 or JRC4558? or something less common?
Click to expand...
For comps, it's a pretty good idea to stick to the lowest noise opamp you can. (The 072 was low noise for it's time but opamps have gotten a lot better)
Reason being, however much gain reduction you are getting, you then have to make up that gain. The self noise of each opamp stage is going to increased by that makeup gain. As comps are usually very early in the chain, that noise is further amplified by any clipping(and more make up gain) further down the signal chain.
@JTEX , being the noise floor chaser he is, can probably chime in with some recommendations. I'd at least spec it with a readily available OPA through hole part though.
 
jwin615 said:
For comps, it's a pretty good idea to stick to the lowest noise opamp you can. (The 072 was low noise for it's time but opamps have gotten a lot better)
Reason being, however much gain reduction you are getting, you then have to make up that gain. The self noise of each opamp stage is going to increased by that makeup gain. As comps are usually very early in the chain, that noise is further amplified by any clipping(and more make up gain) further down the signal chain.
@JTEX , being the noise floor chaser he is, can probably chime in with some recommendations. I'd at least spec it with a readily available OPA through hole part though.
Click to expand...
ah, so maybe the OPA2134? I've used that in a couple pedals but I don't have ton on hand since they're like 6 bucks a pop.

I literally just this morning started thinking about paying better attention to component quality. Upgrading the opamps from the BoM was one idea, so this is very top of mind.

Thanks!
 
airbud said:
ah, so maybe the OPA2134? I've used that in a couple pedals but I don't have ton on hand since they're like 6 bucks a pop.

I literally just this morning started thinking about paying better attention to component quality. Upgrading the opamps from the BoM was one idea, so this is very top of mind.

Thanks!
Click to expand...
It's a double edged sword with pedals. They're inherently low fidelity. But in non-clipping situations, I try to be mindful of the noise. Higher quality(lower noise) opamps, no mlccs in the signal path, quality low ESR electros if they have to be in the signal path.
But that's just me. No right or wrong. It just helps me sleep less badder. But I would advise keeping noise in mind at the front end of your signal chain(compressors, buffers, clean boosts). Here's a good one from JTEX
JTEX said:
As usual, I am of the strong opinion that TL072 has no business being in a top notch guitar buffer in 2023. It's just too noisy at 18nV/sqrt(Hz) (same as the thermal noise of a 20k resistor). I would pick something with less than half that noise. And of course, it would also have to have very low current noise to do well with high impedance sources, so either JFET input or super beta bipolar (my new favorite). My best suggestions as a guitar buffer: OPA205/206/207, OPA145. Or, if you have all the money and want the quietest possible op amp that can handle high source Z, get an OPA827, or even two of them in parallel if you're nuts (I am, and I've done it).
Click to expand...
Note, he's talking about onboard buffers...
 
I will be trying Texas Inst. LM833N which shows almost identical slew & noise specs & JRC4580's!
My enclosure is completed with Footswitch & Pots waiting for the PCB which has arrived but not on my side of Australia yet!
 
Last edited:
When chasing the lowest possible noise you have to take a holistic approach. Parts around the op amps, mostly resistors and/or the source resistance, play an important role in the overall noise. For instance, a single 10kΩ resistor in series with the input makes almost as much noise as an entire TL072, so it doesn't make sense to use a much quieter (and $$) op amp unless the circuit around it is up to par. It pays to teach oneself to do noise analysis in a SPICE circuit simulator, such as SIMetrix or Tina-TI, or even LTspice if you can stomach it (I can't). I learned a LOT this way.
 
jwin615 said:
It's a double edged sword with pedals. They're inherently low fidelity. But in non-clipping situations, I try to be mindful of the noise. Higher quality(lower noise) opamps, no mlccs in the signal path, quality low ESR electros if they have to be in the signal path.
But that's just me. No right or wrong. It just helps me sleep less badder. But I would advise keeping noise in mind at the front end of your signal chain(compressors, buffers, clean boosts). Here's a good one from JTEX

Note, he's talking about onboard buffers...
Click to expand...
this is super helpful! differentiating use cases is really important and makes a lot of sense to me. same regarding caps in the signal path. a couple pedals I've made have been noisier than I'd like, so having some ideas around that is great.
 
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