Sunday 1 December 2019

Fuzzhead FX MOuSeFET

Here is a variation on the Rat theme. I wanted to do a MOSFET Rat since I have a few CA3240 dual op amps lying araound and I like the sound of MOSFET transistors of hard clippers. Caps is enlarged a bit for a bit more low end and a switch for a 10uF running in parallel with 2,2uf cap is added for a bit more gain and low end. Stock output FET buffer is replaced with the second half of the op amp.


 

 


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8 comments:

  1. spectreman28 January 2020 at 23:08

    Hey! Thanks for these layouts!!

    Any idea if a TL072 or NJM4558 would replace the CA3240?

    Or any other suggestions on dual op amps?

    Thanks again!!

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    1. fuzzhead29 January 2020 at 18:29

      Yeah, you can use other dual op amps but the sound may change slightly.

      Delete
  2. Anonymous11 September 2020 at 17:39

    Tried putting this one together after liking the Dronestortion but I can't get it working yet. I'll keep trying to debug on my end but I had a couple of issues: (1) I don't see the 39nf at K15-17 on the schematic. Is that a typo was just added later? (2) Using a basic probe my signal is stopping right around the tone pot. Something just seems off at Tone 3 going to Q2. Again, I'm relatively new but it just doesn't look right. Anyways, love the designs.

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    1. fuzzhead11 September 2020 at 17:54

      Cool that you take a stab on this. Yes, that 39nF cap between the tone control and buffer is missing in the schematic. Will update it. But it must be there to isolate the output buffer from the rest of the circuit.

      As for the signal stopping between the MOSFET clipper and tone 3....are you sure you have the link between gate and drain of Q2? And at Q1 as well? These must be tied together to operate as clipping diodes and let the signal pass through.

      Or else you can try another MOSFET since they is quite sensitive, I've got several that failed due to static shock. Als check the cuts in that area.

      i really like mine. More of a modern sounding Rat-like distortion but with the 10uF cap switched in it can get quite heavy and buzzy.

      Delete
    2. Anonymous22 September 2020 at 23:05

      Well I think I need some reading glasses for these old eyes. After picking this up again and looking at it, I realized I put in two electro caps backwards. I think that may have fried the CA3240 :( Anyways, fixed it and experimented with some dual opamps and the JRC4558D is the winner. Unfortunately, I can't compare it to the CA3240. Good overall as it stands. Does not have smooth sustain or decay. I swapped out the 2N7000s for BS170s and it smoothed it out. However, I loved an OD in front of Rats and with the BS170s it didn't hit right. The OD in front of the 2N7000s was nice though. Anyways, good circuit. I'll have to try it out with the CA3240 when I get a hold of one. Though, I really don't NEED another Rat variant.

      Delete
  3. radubor29 March 2021 at 12:32

    Very good sounding Rat-like distortion! I used a TLC2262.
    Thank you a lot, fuzzhead!

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  4. summerwolf26 June 2023 at 02:53

    Thanks for creating/posting this one fuzzhead! I built this one last week, screwed up one of the caps and finally fixed yesterday. haven't done a side-by-side with my RAT (yet) but this one sounds awesome (and I like it more since I built it. lol)! I'm working on building your other designs and will post photos/videos once I have a chance. Great work!!!!!

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    1. summerwolf26 June 2023 at 02:56

      I should also mention - I used a JRC4558D since I had a few leftover from another project but may swap if I get the CA3240 (but it really sounds great 'as is').

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