Tuesday, 7 November 2017

Guyatone PS-021 Guitar Exciter / Compressor

A vintage pedal from the 80s.
I've removed the flip flop switching system and buffers (thanks Zach for the help).
Hopefully it will fit in a 125B box.
You can find original thread and schematic here.
Updated schematic is available in our Forum section. 
Thanks Dino for his explanatory video.
12/11 Layout Updated! Readded the input buffer as Aion's suggested.

... and the LM13700 version


  1. Replies
    1. not see Volume 2, only 3 and 1

    2. First - it is a layout. Not a schematic.

      Second - you have three lugs on your volume pot, yes? Lugs 1 and 3 connect to board as pictured. You take a wire to lug 2 and that wire is your output. Thus, the output comes from the pot, not from the board.

    3. very thanks for your explaining¡¡

  2. Nice! Just fixed the bass version for a friend and this is just a perfect effect. Dyna comp to simplified BBE Stinger to BMP tone stack. Sounds just amazing. Aion might be putting a RTS PCB out in a few months and if that'll fit in 1590B, i might get me one of those. If i find the time i may build this layout anyway.

    Had my eye on the schem, but figured i didn't want to take a go at it - as it is huge. Thanks Alex!

  3. Hello!
    Anyone have built it? I've just finished, but it didn't work as I heard in demos: it has a low level and distorted output. All the pot seems to work.
    In the schematic, the 22K trimpot looks strange to me. In all Dynacomp variants, it is only 2K. Maybe this could be a problem?

    Thank you!

    1. I don't think trimpot is needed at all. It was necessary for old 3080 ICs, because they had some sort of unequal inputs, LM13700 doesn't have that problem.

    2. Just verifying Aion's trace to my unit now. Trimmer is 2K2. NOT 22K.

  4. So, it's verified now? looks fine.

  5. Just built this unit (lm137000 version) but I get major problem.
    I get a distorted sound on the output.
    I also find that when I strum on my guitar the output goes suddenly to zero.
    I have sound only when playing mildly or when I play my splitted humbucker with lowered the volume knob.
    Probing the circuit, I find that this happens on PIN7 of 4558 ( I used TL072 also) which is Out2. Everything seems to work untill then.
    Used 22k trim as well as 5k trim (didnt have a 2,2 at the time as Dino T. suggested).

    Any thoughts? Is this verified by anyone?
    LM13700 version

  6. Not verified. Yet.

    Finished mine (3080 layout) today and there a few issues with the current layout.

    Removal of the electronic switching is wrong. The way it's currently done leaves Q3 emitter to pass DC to LM324 pins 6 and 7. This will stop the signal from flowing correctly through the first opamp stage.
    - Remedy: If you build either of the orginal layouts, pull the 47K (R20 in Aion's Schematic) connected to LM324 pin 6. Replace that with a 10K + 220n + 47K in series. 10K to Q3 emitter, cap in the middle and 47K to where it was. The 10K is needed to lower the signal, 220n is decoupling the two stages and 47K is as it was. This will work.

    The trimmer is definitely 2K2 (most would prefer 2K trimmer), so that's wrong in the Schematic and the layout.

    Level pot is pretty much useless as log taper. Use B50K.

    I also noticed that none of my TI LM324s worked right. Had some vintage ones with "ENGLAND" on them and some contemporary ones. I had an ugly distortion in the background. Wouldn't believe it at first, but once i sticked an ST Micro branded LM324 in, the circuit worked great.

    Great circuit and awesome layout Alex. Basically just two labels should probably be swapped (2K2 and B50K) - and 10K + 220n added. The board could also maybe use a series polarity protection and a 1M pulldown for the input.

    Still. I'm very happy with mine now.