This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.

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.


  1. 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.

  2. Just 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.

    1. Anche io l ho appena costruito però nn funziona. Forse perché Q1 e un pnp?

  3. Hi! I cant find de PDF, what is the folder? thanks!

  4. Great compressor, just what I was looking for my bass head loop.
    I built it with 4 npn C838 (hfe = 100) works very well, also add a resistance of 820 ohms in serie to the ratio control.

  5. The perfboard solder side is not reversed! Doing it right now!

  6. Just 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....

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  8. HI 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?

  9. Saya tidak perlu mengganti Q1 dengan NPN transistor,
    Saya 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