Median Compressor PCB - Available Now!
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jesuscrisp
Well-known member
PCB number 676 is definitely not coincidence.
eh là bas ma
Well-known member
"Median compressor" ?
I really thought PPCB was releasing a clone of Guyatone PS-21 like Aion's Meridian compressor !
I really thought PPCB was releasing a clone of Guyatone PS-21 like Aion's Meridian compressor !
I wouldn't compare these 2 circuits, first time I have heard of the Guyatone mentioned!
You need 4 of these adapters if you want to use the same IC:
Feral Feline
Well-known member
I like the LED's placement d' horlogerie. Sweet.
airbud
Well-known member
Tl072 or JRC4558? or something less common?
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.
airbud
Well-known member
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!
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...
JTEX
Well-known member
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.
airbud
Well-known member
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.
andrewsrea
Well-known member
I just started into this compressor build. After stydying the design, it appears to me to be a simplified single channel of a Universal Audio 1176 studio compressor, sans the high-end hi to lo impedance transformer, using mostly FET ICs instead of discrete FETs and running on about 8.7V instead of 20V. The compression is typically hard to notice, other than a clean instrument (or music program) sounds lifeless when you turn it off, after finding the sweet-spot settings.
I am guessing this is Brian Wampler answering back to the PRS 'Mary Cries' compressor pedal.
The Guyatone and Alion are based on the Dynacomp / Ross style of compressors, which color your sound to create a more noticeable effect.
ninjagrips
Member
I've just built this, but I haven't put it into an enclosure or attached the switch and jacks, yet.
I'm curious about the 2N5457 Transistors. How do I measure them to make sure they're good for the build?
I have a T7 tester, but it's been acting funny. Most of the 2N5457's I'm trying to measure are just coming up as resistors. It was doing this the other day with a few BC108C's I got from Stomp box parts, too. The BC108C's were coming up as two diodes.
Is the tester the problem, or did I get bad transistors?
Can I check them by hooking up the pedal and using a multimeter?
Also, is the trim pot there to bias the transistors? If so, do I just set them to 4.5V?
Thanks!
I'm curious about the 2N5457 Transistors. How do I measure them to make sure they're good for the build?
I have a T7 tester, but it's been acting funny. Most of the 2N5457's I'm trying to measure are just coming up as resistors. It was doing this the other day with a few BC108C's I got from Stomp box parts, too. The BC108C's were coming up as two diodes.
Is the tester the problem, or did I get bad transistors?
Can I check them by hooking up the pedal and using a multimeter?
Also, is the trim pot there to bias the transistors? If so, do I just set them to 4.5V?
Thanks!
Can't answer your questions but 2N5457 have been obsolete for some time so they may be fake? MMBF5457 is the SMD equivalent, these are still widely available and can be used with adapter boards.
ninjagrips
Member
Yeah, I'm aware that there are a lot of fakes out there, I just don't know how to properly test them without the pricey Peak DCA Meters or whatever.
I'm not sure I trust this T7 that I've got. There have been times that I tested a transistor and got a reading, and checked it again 30 mins later and it came up as a resistor or two diodes. I don't get it.
I suppose I'll just have to hook this pedal up and see what happens.
I'm not sure I trust this T7 that I've got. There have been times that I tested a transistor and got a reading, and checked it again 30 mins later and it came up as a resistor or two diodes. I don't get it.
I suppose I'll just have to hook this pedal up and see what happens.
