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Switchable V1 bypass cap for 5G9... would this work?

Discussion in 'Amp Tech Center' started by King Fan, Sep 25, 2020.

  1. King Fan

    King Fan Poster Extraordinaire

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    Pretty basic question, I hope. As you know, the input wiring on a 5G9 is like a 5E3 -- the bright/normal hi/lo four-holer. The stock V1 bypass cap is also the usual suspect -- 25uF.

    I really *like* the standard bright tone on my 5G9 -- other elements of the circuit (47uF reservoir? LTP? fixed bias? etc.) seem to keep the rich thick bass from getting at all 5E3-flubbish... but it is still pretty darn rich and thick. Also, given the tighter sonics, the normal channel is boringly similar to the bright channel, even if you downsize its coupling cap to say .02uF.

    Experts like @tubeswell suggest dropping the V1 bypass to something more like 2.2uF. I have some spare eyelets in the area due to moving the grid stoppers to the input jacks. So say I want the option to do 2.2 *or* 25uF:

    Is this the right way to do a switch? Are my 'anti-pop' resistors right? Is there a better way? Would routing the wires to the base of the chassis near V1 be OK? Other thoughts?

    upload_2020-9-25_10-59-19.jpeg
     
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  2. King Fan

    King Fan Poster Extraordinaire

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    If I'm honest, I'm a bit embarrassed to ask -- seems like I might be one of those folks who tell other builders, "or just put 'em both on a switch." But somehow switches don't always click for me (to coin a phrase) and then I'm not smart enough to get pop prevention, especially as it relates to positive or negative-end switching. So I'm hoping somebody smart'll just throw me a rope... :)
     
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  3. BigDaddy23

    BigDaddy23 Tele-Holic

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    That looks good mate...the anti pop resistors are correct. The only thing I would do is mount the on a DPDT instead of the single you have. Not sure on that bypass cap value. ......perhaps smaller again?
     
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  4. King Fan

    King Fan Poster Extraordinaire

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    Thanks, mate. Did I mention I was switch-stupid? Could you spell out or draw out why/how you'd use a DPDT instead of an on-on SPST? Are you saying it'd be better to hang the resistors on the switch but an SPST would create problems if I did?

    And I agree 2.2uF may not be the ideal 'other' value. Before I build the switch circuit, I figure I'll clip in a smaller value and parallel a few caps to see 'how small is big enough.'
     
  5. Dan_Pomykalski

    Dan_Pomykalski Tele-Meister

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    2.2uf and 25uf will probably be good. I usually go with 1uf and 25uf. Anything bigger than 1uf and there doesn’t seem to be enough of a difference (but I think 2.2uf will be close enough to 1uf).

    You could also have the 25uf on a switch so it parallels the 2.2uf. Why? I don’t know...

    Also, I think I read somewhere once that even if the bypass caps aren’t grounded, they’re still have an effect on the signal (I don’t know how...). I could be completely making that up though, but you could also put the positive ends on the switch just in case.
     
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  6. elpico

    elpico Tele-Afflicted

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    You only need a single pole switch and one resistor, the 2.2u can be left always on. You can switch whichever end of the 25u is more convenient and the pop resistor can go on the switch.
     
  7. King Fan

    King Fan Poster Extraordinaire

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    Excellent, @elpico , thank you very much. That makes a ton of sense. Much simpler. Maybe like this, then?

    upload_2020-9-25_20-24-5.png
     
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  8. King Fan

    King Fan Poster Extraordinaire

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    Tried drawing wire runs to put the switch on the bottom between V1 and V2. This is a stainless chassis and I worry about drilling a hole between the bright and normal inputs.

    But the wire runs to the bottom ended up somewhere between long and just goofy, given I have those extra eyelets toward the top. I also hope maybe I can loosen and displace the entire input jack array to drill the hole and wire the switch -- maybe.

    I'm gonna think about this for a spell while I make sure I have the right switch, cap values, etc -- and then maybe do the parallel cap-clip trials to see if the game is worth the candle. Or worth all the possible screwups that might happen drilling stainless steel in a crowded, delicate corner of an amp. :)

    I suppose one happy outcome of parallel-cap trials would be if I like the smaller cap and don't find I miss the 25uF. Sing we me now: It's a gift to be simple... it's a gift to be simple....
     
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  9. Jon Snell

    Jon Snell Tele-Holic

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    Screenshot 2020-09-26 at 19.35.10.png What I do is very similar and works well. The only difference is I use a 22k anti pop resistor across the contacts.
    The wiring run is not critical as it can be a piece of screened lead if it worries you. Run the ground on the switch as the sheath of the screened cable to the ground point of the fitted capacitor and the inner to the new cathode bypass capacitor from the switch.
     
    Last edited: Sep 26, 2020
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  10. King Fan

    King Fan Poster Extraordinaire

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    Thank you. That sounds great. I'm gonna draw it on a piece of paper to make sure I can visualize it -- heh, I'm getting DIYLC fatigue from all the variations I'm thinking about.
     
  11. Jon Snell

    Jon Snell Tele-Holic

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    Just made a rough drawing but the lead can be as long as you want if screened just not alongside heater wires.
     
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  12. King Fan

    King Fan Poster Extraordinaire

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    Good idea. Thank you very much.
     
    Last edited: Sep 27, 2020
  13. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Yeah, like mentioned above, I think I would have the 2uf always on and the 25uf ON/OFF to parallel with it. The boost cap/switch I added to that 5881 5f2a a few months ago would pop a tiny bit the first time it was switched after turning on the amp, but it wouldn't pop again after that. I had a 1M between it and ground.
     
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  14. tubeswell

    tubeswell Friend of Leo's

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    You could just wire the 2uF permanently in and have the 25uF switching in parallel with it using an SPST

    (Oops - late to the party - I see someone else already said that)
     
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  15. King Fan

    King Fan Poster Extraordinaire

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    OK, I'm gonna be collecting the parts and doing some clipped-in parallel cap tests. For grins, and for folks who want a 3-way option, I did come across this mod from a 2013 post. This is drawn on a 5E3 layout...

    upload_2020-9-27_8-50-10.png

    If it's hard to read, he's using a 0.68uF 'Marshall-size' cap when the switch is in center off position, with the 'on' settings giving him 2 or 10 (or that could be 25) as options.

    FWIW he says he doesn't use resistors and doesn't get any pop, I guess because there's always a cap in circuit.

    Keep it simple, KF, keep it simple!
     
  16. tubedood

    tubedood Tele-Holic

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    On my 5F2-A build I added a switchable voicing switch on the 1st gain stage... 1uf or 25uf. Nice tonal differences between the 2. I didn't use pop resistors, but the pop doesn't bother me.
    I don't find myself switching it too often.
     
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  17. dan40

    dan40 Tele-Afflicted

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    I have also done the mod in the same way as your last pic and it works fine with very minimal popping. Nice option to have when switching between singlecoils and humbuckers.
     
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  18. King Fan

    King Fan Poster Extraordinaire

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    Good info, thanks! Do you run the 0.68 / 2 / 10 values Stingray did? And where did you put the switch and run the wires? Rob's right: why use a two-way switch when you could have three...
     
  19. dan40

    dan40 Tele-Afflicted

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    I like a .68uf in a Marshall style circuit but when it comes to Fenders I prefer a 25uf and something between 1uf and 5uf on the first gain stage. A Fender circuit always sounds a bit thin to me with a .68uf bypass cap.
     
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  20. King Fan

    King Fan Poster Extraordinaire

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    Thanks, great! Fits nicely with my pre-conceived notions. :):):)
     
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