Monday, 12 April 2021

Benson Preamp

 Schematic and suggested trimput setup at PedalPCB.




26 comments:

  1. What?!! Now I'm mad...really mad!! Watch what I'm gonna do with you Benson suff!...

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  3. It´s donne now. Completely ravaged, indeed! For him to learn. Perfect layout. Changed a bit some values (27 nF/18 nF on Tone); 2sk117 on transistors; big mustard caps (from he sixties) in all. Man, it roars as hell. Wilder than the original. Uncivilized as he should!
    Tag it, mister Fuzzhead! I'll never be able to thank you enought!...

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    1. Great! Tagged. Yes, those SK117 has alot of punch, one of my favorite J FETs.

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    2. Where do you chaps get your SK117s from, can't seem to find them anywhere

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    3. Hey Ian - I don't know how much this might end up costing you with shipping and such, but pedalhacker here in California has a bunch of NOS 2sk184 jfets right now. The specs are pretty close to 2sk117's from what I can tell.

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    4. Cheers Chris, that shop certainly has an interesting selection. In the end I added the missing 10uf cap and it sounds much better - no horrible noise although its a real pain tuning in the fets

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  4. Just finished mine, used J201's and the required settings for the trimmers but it sounds really farty :S any suggestions?

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    1. Tried different J201 transistors but it still sounds weird :S help is welcome :)

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  5. Hi. You better try to tune the trimmers by ear. Till you find the proper spot. It takes a lot of search. I know, I buil two, one with 2sk117, and the other with J201 (smd with adapter). One thing is for sure: while you're not there, the sound can get very weird and onoxious (or no sound at all). But once you found it is to set and forget. Good luck!

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    1. Thx for your reply! I'll try to tweak it a bit more!

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    2. Okay I tried to tune it by ear and it's much better now! The tweaking is pretty tricky thoughh... thx guys

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  6. By he way, where did you get your J201s?...

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    1. Fingers crossed that your J201s are legit since the ones I got from Banzai a couple of years ago were fakes.

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    2. How can I check if they are fakes?

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    3. The normal J201 I bought were all out of spec, but I got great results with MMBFJ201. Its the smd version of the J201.

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  7. That's the problem with J201: a lot of fakes arround. For the price they are selling it (Banzai), I would'n't put my hands on fire for them. For me, a lot of SKs (117,170...) will do better, cheaper and no danger with fakes.
    Great lost for mankind Fairchild passing. :O/

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  8. built this wee guy used mmbfj201 but man, the squealing is quite intense and sounds very fizzy. after about 11pm on the gain dial just squeals the only way it goes away is when the treble is all the way down

    any ideas?

    Q1
    d - 5.2v
    s - 0.22
    g - 0.04

    Q2
    d - 4v
    s - 0.22
    g - 0.00

    Q3
    d - 4.00v
    s - 0.17
    g - 0.21

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    1. i should mention Q1 was biased with the 12k resistor in mind

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    2. Did you solve it? I have the exact same problem

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  9. I'm also getting some pretty horrendous squealing with this one. I tried 201s I got from Tayda (thru hole and SMD) as well as some SMDs I got from GuitarPCB. 4.5v on all the drains. These same FETs sound fine in my other builds. anything else that might cause the squealing?

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    1. Try to add another 10uF from G13 (+) to K11 (-). It worked with mine. No more squealing.

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    2. I did actually! noticed it on the PedalPCB schematic. it worked when I just touched the leads to either side of the 1k resistor, but for some reason when I soldered it in it killed the signal. i snipped the positive leg and signal came back and so did the squeal. I'm gonna play around with it some more before I give up. I'll report back if I get it working.

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  10. I’ve had that with j201’s. But I love them. It’s worth the struggle to find some that are quieter I feel. The most temperamental stuff always seems to sound the most inspiring. But adapting the smd is rough.

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  11. Interesting new version just released with q1 replaced by a germanium transistor. Sounds pretty simple. Might be worth a play with.

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