Compression indicator LED?

PeterOne

I'm an absolute beginner to electronics so forgive me if I'm asking a stupid question. I've done a couple of Fuzzdog kits and now I've challenged myself to make an Orange Squeezer on stripboard. I'm breadboarding at the moment and had the idea of adding an LED that lights up as the sound compresses (like the LED on the Diamond compressors).

My question is: how simple would it be to do this? Would I be able to replace D1 with an LED, or would I have to add something more sophisticated? (schematic link below)

I've looked at a couple of circuit analyses for different effects but can't find one that breaks down a compressor pedal circuit, and being new to all this I don't know exactly what part the diode plays in compressing the signal.

This is the schematic & parts list I've been following: http://pedalparts.co.uk/docs/Squeezer-MkII.pdf

Ravenous

I don't think replacing D1 with an LED will work.  I guess this because it's in series with R10 which is 1.5 K, so the current in that part of the circuit is quite low, probably too low for the LED to light.

(It would not do any damage to temporarily try an LED though.)

I think the "proper" way to do this would be to take the voltage either at the top of that LED, OR at the top of C4, run it into an op-amp  buffer and then to a comparator which would light the LED.  But that would mean a lot of trial and error to find components that work...

Kalimna

Apologies for hijacking this thread a little, but whereabouts did you find the circuit analyses? Ive built a few pedals now, with varying degrees of success, and would like to learn a little theory behind the pedals. Especially when they don't work - for instance I have an EHX Small Clone clone that is causing me grief (dry signal passes fine, but no modulation)...

'fraid I cant help you with your LED question though. Have you tried asking over at Tagboard Effects?

Adam

PeterOne

Ravenous said:

I don't think replacing D1 with an LED will work.  I guess this because it's in series with R10 which is 1.5 K, so the current in that part of the circuit is quite low, probably too low for the LED to light.

(It would not do any damage to temporarily try an LED though.)

I think the "proper" way to do this would be to take the voltage either at the top of that LED, OR at the top of C4, run it into an op-amp  buffer and then to a comparator which would light the LED.  But that would mean a lot of trial and error to find components that work...

Thanks, I had a look into comparators and it all went over my head - I think I'm trying to run before I can walk but thanks for helping!

Kalimna said:

Apologies for hijacking this thread a little, but whereabouts did you find the circuit analyses? Ive built a few pedals now, with varying degrees of success, and would like to learn a little theory behind the pedals. Especially when they don't work - for instance I have an EHX Small Clone clone that is causing me grief (dry signal passes fine, but no modulation)...

'fraid I cant help you with your LED question though. Have you tried asking over at Tagboard Effects?

Adam

Once I'm more up to speed I'll try Tagboard Effects as well, I've printed out their stripboard layout which I'm planning to follow once I've tested it on a breadboard.

The circuit analyses I've been looking at are on these sites:
https://www.electrosmash.com/
http://www.coda-effects.com/p/tips.html

Kalimna

Thanks for that - they are a couple of sites I am familiar with but haven't explored extensively. Time to pay them another visit.

Cheers,

Adam

salty_morsel

Hiya. Here is a quick description of the circuit:

It consists of a non inverting amplifier formed from IC1B, with an ac gain of 22. The Gain =  1 +( R8/R9). The dc gain is 1 due to c5.

Q2 &  R5 make a jfet constant current source biasing the source terminal of Q1. Q1 is configured in a common source arrangement, where the output signal is taken from the drain terminal. The jfet drain , connected to the input signal from the guitar is fed to the input of the amplifier.

The way the circuit appears to work is by returning a portion of the amplified signal through D1 to the jfet gate (Q1). As the gate voltage rises the jfet will act as a shunt, diverting more of the input guitar signal to ground. So as the guitar gets louder, the input signal level to the amplifier is reduced ... This gives effect of compression.

To answer the original question, The voltage on Q1's gate could be fed to the spare opamp (Q1a, configured as a current source), and used as control signal to vary the current through a LED.  I suspect this would take quite a bit of fettling to get the result you want tho! You would also need a npn transistor such as a 2n2222 to make the current source. I will try to sketch this out of you are interested in trying to make it.

HowH that helps a bit. 

Kalimna

Salty_Morsel - thanks for that detailed post, very illuminating. I don't suppose you have a website or suchlike with other circuit analyses? Or could you recommend any books suitable for a beginner that discuss how groups of components work together? (For instance, I know what capacitors, resistors, transistors do, but not neccesarily what they in combination with each other - if that makes sense?)

Cheers,

Adam

PeterOne

@salty_morsel Thanks for that description - I thought very roughly that was what it was doing but your description is a lot more detailed so at least I know I'm on the right track.

I'd appreciate you sketching it out if it's not too much trouble - then again I laid it out on a breadboard and didn't get any sound out of it so no rush, I've got troubleshooting to do already!

salty_morsel

@Kalimna , the best book I can recommend is "The Art of Electronics" by horrowitz and hill. It's very readable, and has (outdated but still useful for audio) advice for practical electronics, as well as easy to follow descriptions of common analog circuits and old school digital design. most academic text books I have used are v mathematical in approach and not that accessible for beginners. Tbh there may well be better hobbyist books available, plus the web. Electronics is a broad and complex subject but don't be put off, and enjoy leaning about your areas of interest. 

Kalimna

Thanks for the info - I will hunt out a secondhand copy of this book I think. The web is all well and good, but in my experience so far (over several areas from guitar (and guitar effects) building to bread making to photography to rose pruning), there is very little in the way of an 'accuracy filter'. So recommendations are extremely worthwhile. 
Cheers,
Adam

salty_morsel

Ahhh yes. This is very true regarding accuracy filter. Mind you there are loads of schematics available on the web, great as a reference source. Be sure to buy the actual textbook , not the lab exercises companion book. I hope you find it useful!

BigMonka

Kalimna said:

Salty_Morsel - thanks for that detailed post, very illuminating. I don't suppose you have a website or suchlike with other circuit analyses? Or could you recommend any books suitable for a beginner that discuss how groups of components work together? (For instance, I know what capacitors, resistors, transistors do, but not neccesarily what they in combination with each other - if that makes sense?)

Cheers,

Adam

@Kalimna try having a good read through the electrosmash website where effects pedal circuits are broken down into their constituent sub-circuits, it’s good stuff. Here’s a link to the breakdown of the Rat https://www.electrosmash.com/proco-rat