Tuesday, December 9, 2014
Simple Transistor Compressor
FSB member Mictester came up with this design a couple years ago. Utilizes 4 transistors, 1 PNP and 3 NPN, though you could probably use an NPN in place of the PNP. Best to socket and try a few different transistors. The schematic says BC213L for Q1 and BC183L for Q2-4, but any medium gain transistors should work okay (2N2222, 2N2907, 2N3904, 2N3906). I added some of the mods suggested in the FSB thread for higher input impedance and noise reduction.
I made this and worked great. I needed to replace the PNP with an NPN transistor. I even replaced the 1n4148 diodes with 1n4001 and still worked.
ReplyDeleteAwesome! Thanks for verifying!
DeleteJust built it. Hope to make another contribution here. I also used an NPN transistor for Q1. I tried an PNP one without success. The ratio pot functions as a rheostat there. However, when it was turned to the lowest resistance. There was some helicopter noise. So I have to add a resistor in series with the ratio pot. 47 or 100 ohm would be fine.
ReplyDeleteAnche io l ho appena costruito però nn funziona. Forse perché Q1 e un pnp?
DeleteHi! I cant find de PDF, what is the folder? thanks!
ReplyDeleteLooks like I never made one... until now. It's in the Misc. folder.
DeleteGREAT! Thanks!
DeleteGreat compressor, just what I was looking for my bass head loop.
ReplyDeleteI built it with 4 npn C838 (hfe = 100) works very well, also add a resistance of 820 ohms in serie to the ratio control.
The perfboard solder side is not reversed! Doing it right now!
ReplyDeleteJust did it and i can report that the pnp input buffer do not work and have to change it to a npn transistor as others mentioned above. The perfboard underside (solder side) is not reversed and have a minor inconsistency. After some debug it works! Great compressor for low part count! Didnt understand why the pnp input buffer do not work....
ReplyDeleteThe original PNP was wrongly drawn in the very earliest drawing (it's corrected on FSB now). I can't imagine why I did that at the time!
DeleteI'm glad that you're getting good results from the corrected version!
Mictester
This comment has been removed by the author.
ReplyDeleteHI Wonder if any one can help me with this compressor? the input signal goes through the 1st PNP transistor but will not go past the second transistor,, Not sure what the problem is,, any suggestions?
ReplyDeleteUse npn for ALL ok.
DeleteWhich transistor to use? 2n2222??
DeleteIm getting helicoptor noise
DeleteAlmost any small signal NPN transistors will work, but you might want to consider using lower noise types such as 2N3904 or BC550 to prevent hiss. The 2N222 is really meant as a switching transistor - it'll work, but might be hissy.
DeleteThe "helicopter noise" is instability and can be caused by a poor quality supply filtering capacitor. Try tacking a 100nF capacitor from +9V to ground - this might help.
Cheers
Mictester
Saya tidak perlu mengganti Q1 dengan NPN transistor,
ReplyDeleteSaya tambahkan disana sebuah resistor 10K tepatnya d pin emitter pnp,
Dan berfungsi dengan baik,
Saya menggunakan transistor 2N3906 dan 2N3904 disana.
Terima kasih untuk sekemanya
There is a mod to increase output signal?
ReplyDeleteHi Fernando
ReplyDeleteThere are three ways you can increase the output, but all have further implications:
You could increase the value of the 2k2 to the +9V rail from the collector of the third transistor. This will give you higher output, but will make the compression more sensitive, since you'd be putting more signal into the base of the fourth transistor, turning it on "earlier". If you're going this way, make it a small change - try 2k7, and see that it doesn't cause problems.
The second approach is to use a higher value output pot. This would mean that the output impedance would also rise (might not be a good thing) and the working point of the last transistor would change, altering the onset of compression again - as above. You could try a 22k or 25k pot and see if it helps...
The last way (and the one I'd favour) is to use another amplifier stage tacked on to the end, like an EH LPB1 - it's such a simple circuit that you could probably find space for it inside your box!
Cheers
Mictester
I changes all transistors to BC550 (more gain) and the problem with output ended. Is possible change some resistor to a potentiometer to change parameter as release or attack?
DeleteUPDATE!! - PLEASE USE ALL NPN TRANSISTORS IN THIS CIRCUIT!
ReplyDeleteMictester
Why don't you upgrade the picture then?
Deletehi folks, I built it and it works perfect, in fact it works better together with overdrive pedals compared to Mictester Guitar Compressor, since the latter cleans up a lot when used together with other overdrive pedals.
ReplyDelete