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Basic 5e3 question: Which bypass cap do you mod?

Discussion in 'Amp Central Station' started by King Fan, Jul 8, 2018.

  1. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    A popular 5e3 bass / flub tamer is to reduce the capacitance of the cathode bypass cap (from 25uF factory to something like 10, or 4, or even less). Most posts imply (a few state) they're talking about the V1 bypass cap, but I've seen one or two where they explicitly swap the V2 bypass cap. Which is it?

    Besides the obvious differences of V1 vs. V2, it strikes me V1 shares this cap between both cathodes, and also, Rob's well-liked '3-way NFB' mod actually omits the V2 bypass in its 'second' position.

    So, beyond the 'usual' way to do it, if you wanted to do Rob's bypass-cap-lift option, would it make more sense to swap the V1 bypass cap?
     

  2. SacDAve

    SacDAve Poster Extraordinaire Silver Supporter

    Age:
    66
    Dec 23, 2009
    Rocklin Ca.
    I agree it dose make more sense if you have the NFB. Also the way I look at it to change the bypass cap V1 or V2 is a pretty simple job so why not experiment a little.
     

  3. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    IF...big IF...I wanted to change a 5E3’s reaction to lower frequency input, I would start at the other end of the circuit. I would bump up the first stage of filtering to 40 MFDS. I would listen to the amp to Assess that change. I would then look at the coupling caps....maybe go to .047mfds in both the preamp and after the PI. Assess that. If I still wanted more change, I would go to the input preamp bypass and do some tinkering there.
    If I wanted to just deal with cathode bypass caps, I would start at the input stage since that signal is amplified from that point on. I actually like what the 5E3 does. I run them hot and work the controls on the guitar and my pick attack....big cleans to scream at the same volume. IMHO and ime, these small amps are great amps for coming to an understanding of the effect of the input signal on the circuit.....player control. In other words, heavy hands create mud and flub, ime. To remove that aspect from a 5E3 is to create a different amp that will not do what a 5E3 does.
    Ommv....
     
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  4. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Thanks, SacDave, good idea. I like to A:B test with a pair of alligator leads -- much quicker than a solder / desolder cycle to get to B before your ears have forgotten A. I think I will experiment with the bypass cap value on V1, since some people find 10uF to be still too big and others like stock just fine.

    Wally, I always value both your opinion and your experience. :) Thanks.

    And you're just one of several experts I respect who mostly tend to "Let the amp be a 5e3." I experimented with coupling cap values for a long time, but recently came to feel I'd gone too far with a layout of .047. .022, .022, .022 right to left through the PI. The amp seems a bit too polite when you open the cage door. So I was hoping to go back toward stock coupling caps (maybe a .047 or .022 in the bright channel) but with a *small* bypass cap change might cut the ugly part of flub without changing the bass-y richness that makes the Deluxe what it is.

    I can't do R/C math, but I've seen folks show at length how 0.022 coupling caps and 10uF bypass caps don't alter audible frequencies. They suggest that 'flub' is due to sub-threshold frequencies and distortion.

    You can also see folks do the math to show that coupling caps at 0.01 or a bypass cap at 4uF doesn't affect frequencies 'above your low E string'. This seems to be like a less useful threshold, since I assume rich, good bass involves harmonics or overtones lower than that in the audible frequency range. If you read carefully, many folks do find these values alter the sound of the amp -- more Marshall, if you will.
     

  5. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    KingFan, when you get to changing that first stage of filtering, you will find a difference, ime. Of course, the 5Y3 has limits. Iirc, it is spec’d for a max input capacitance of either 20 or 30 mfds. fender used 40 mfds there in BF/SF Champ/VibChamps/Broncos, though. If the amp had SS. Rectification, the one can really push that first cap’s value and things get very interesting.
     
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  6. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Yeah, Wally, folks cite the 5Y3 tube specs that say it shouldn't see a filter over (IIRC) 30uF -- but my VibroChamp and thousands of others, as you point out, have tolerated 40uF for half a century.

    Here's the question, I guess. Do you find a bigger filter cap has other 'tightening' effects on the 5e3 besides just taming flub? I have a kind of contradictory wish to have a 5e3 that *can* sound pretty darn vintage, but has a 'cleaner' or more modern tone available. This is why I started just with swapping coupling caps in only one channel -- and I may end up there, too. Problem is, I can never quite decide if I want my bright channel or my normal channel to be the 'vintage-y' one. Votes are welcome on that too. :)
     

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  7. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    IMHO, ‘flub’ is the opposite of tight low end. A large first stage of filtering will eliminate flub in that part of the amp. It will not inhibit creation of overdrive in the amp. I have heard a boutique amp being demo’d For a prospective buyer...I ‘nosed’ in on the private demo....that had aHuge, tight, punchy low end. I knew that he had built with a lot of capacitance I that first stage just by hearing that aspect of the amp...and after he asked me to repeat my query so as to confirm my beLife he begrudgingly sharedthat he had two 220mfds in series for 110mfd in that first stage. That amp also had some of the creamiest overdrive I have heard...with just a change of pick attack. I don’y Know exactly what his preamp looked like, but I have some firm suspicions. Great amp......I couldn’t afford the purchase price, but it was worth it, imho.
     
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  8. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Well, I may just have a 40uF F&T sitting in my drawer. Or, if I recall my cap math, if I have an extra 16 or 20, capacitors in parallel sum, so this'd be a great place to do my alligator clip testing... :)

    I heard more from my amp expert friend. He said he went to changing the V2a cathode bypass cap on his 5e3 since he found changes to the V1 cap messed with the Fender-y sound, made the amp a bit too polite and = messed with the onset / voicing / quality of the distortion. So in the 5e3 he likes to mess (a little) with the V2 bypass cap -- he goes down to 10uF, says he found 4uF too 'thin.' His theory is there's less voice shaping in the V2a slot in a 5e3, which in my very limited understanding makes sense.

    Reminds me of folks who find it useful to put the tweed V1 (or V1a) bypass cap on a switch to get two different values -- one to sound stock, the other to sound modded.

    So at least I have a theory of *why* you might alter the V2a bypass cap instead of the V1 cap. And, as an experiment, it'd be way easier to clip in different values on V2a then trying to compare V1 changes with V2 changes using clips in *both* places.

    Finally, I can do this A:B before I try Rob's NFB / bypass lift / stock mod.
     

  9. dan40

    dan40 Tele-Holic

    865
    Aug 19, 2015
    Richmond Va
    I have read that some builders prefer to leave the first stage fully bypassed (stay with 25uf) for hum cancelling purposes due to heater/cathode leakage, and lower the second stage bypass caps instead. I like to run both stages with 5-10uf bypass caps personally as I feel it keeps the low end full without allowing it to get too flubby.
     
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  10. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Thanks, Dan. I’ve valued your insights on 5e3s (and other stuff) elsewhere in my research. That’s another issue I hadn’t considered.
     
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  11. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Having reminded myself that caps in parallel are additive, I think I'll tack a 10uF on the V2a cathode and clip another alongside it with alligators. See what happens. But I gotta revert some coupling caps back toward stock first.
     

  12. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Why would you want to increase the capacitance of a cathode bypass cap in the preamp when the perceived problem is flub?

    Fwiw, I think the 5E3 is a great amp just as it is. I like a P12Q in one rather than a P12R....but the low end breakup is still available even then. I like that. How else is one going to get that sound when wanted...and it is a valid sound, imho.
    As for dealing with excessive low end in the preamp, I like a bass cut tone control on the guitar the only time I find it to be needed is if I am pushing a lot of gain, but it is handy in those situati9ns when one wants to ‘clean up’ that low end.....and it is very temporary as compared to changing the basic nature of a classic circuit. Ommv....
    The other way to control an amp is with the overall guitar output.....pick attack and /or volume control at the guitar. I don’t neuter an amp in order to avoid that very personal aspect of the control of the signal. I can put a 5E3 on 8 or higher on the volume and get any sound I want from very clean to completely saturated just by exercising that personal control at the instrument. Again....ommv....
     
    Last edited: Jul 10, 2018

  13. peteb

    peteb Friend of Leo's

    Apr 25, 2003
    Cascadia
    With caps and clips you can’t reduce capacitance in the pre amp, but you can easily up the filter capacitance.



    I was looking forward to the ultimate filter cap test, what effect will 40 mF of capacitance in the first filter cap spot in a 5E3 have?




    I agree with Wally, it is worth a try.
     

  14. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Re clipping in an extra cap, I’d clip in two 10s to approximate a 25, then unclip one to compare. Didn’t mean I’d clip in two 25s. Sorry. Confusing.
     

  15. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    But.....since you are trying to deal with an excess of low end, why increase the value of the cap there at V2 when one would perhaps choose to reduce the amount of low end by decreasing the size of that bypass cap? Perplexed I am.
     

  16. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Sorry. I’m still explaining it backward. My goal is to try a 10uF instead of the stock 25. I definitely want to try a reduced bypass value, as you say.

    The good news is I have a 30 uF filter cap in my parts drawer. Not quite Wally-spec 40, but should do a lot more filtering than the stock 16.
     
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  17. Uncle Daddy

    Uncle Daddy Tele-Meister

    248
    Sep 26, 2015
    Maldon, England
    I've fitted my latest build with 22-22-22 filtercaps, which will hopefully smooth out the lower end a little before it hits the pre-amp without losing much of what makes a 5e3 what it is. I'm more interested in the effects of the small OT I fitted. I noticed that many kits come with an overly large OT, so I went for one as close as I could find to the original. I'm really building this one as a studio amp, so looking for early saturation.
     
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  18. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Yeah. A 'bigger' OT seems to be one of the most popular 'upgrades' in cloning older / smaller Fender amps. But like you I want a vintage sound -- I'm running the CT 40-18022, 8K into 8 ohms, which they claim is a precise replica of the original. I hope the reverse engineering works better here than it does in their 'replica' PT, which (perhaps due to wall voltage) is known to actually yield too-high B+.

    Folks do all sorts of things to 'tighten up' tweed amps. In reading lots of threads, you see tons of speaker swaps, OT upsizing, PT current boosting, rectifier changes, etc.

    But I've noticed a lot of experts point out flub doesn't start in those components (especially, of course, the speaker, which is probably the most common and most expensive 'fix' suggested). And like Wally, a lot of those same super-pros point out you eventually gotta learn to *work* the 5e3, not change everything that makes it what it is.

    I'm guilty of trying to balance in a few changes that won't alter it's stock character but may give me a slightly personalized version. I'm leaving the interactive knobs (finally got them kind of sorted), the 12ay7 (of course), and my Weber 12a125a. Based on my experiments so far, I'm keeping my 470k PI grid stopper, which I really like, but thinking of adding Rob's prePI MV to give it a slightly tunable effect. I'm gonna add 470R 3w screen resistors on the power tubes. I run metal films for the input resistors -- less hiss. I'm going back *up* to 0.1 on both normal coupling caps, and 'up' to a .047 in the bright channel (with the current .022 in reserve). The coupling cap changes are why I wanted to try a 'small' bypass-value drop, maybe in V2 where it might be more subtle.

    If all that works well, I may try Rob's 3-way NFB / V2-bypass lift / stock switch. A nice thing about that and the prePI MV is the ability to go right back to stock values.

    Finally, as a result of this thread, I'm gonna try Wally's bigger first filter cap. :)
     

  19. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Awaiting the results of the first stage of filtering change with interest....
     
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