And a Boothill 5F1

Discussion in 'Shock Brother's DIY Amps' started by SebC, Feb 2, 2020.

  1. SebC

    SebC Tele-Meister

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    I have an ongoing thread for a 5F2-A which has been incredibly educational, and immediately after that's finished I am starting my 5F1, so here I am with a couple questions in preparation.

    The kit came with a spare filter cap so I can choose to go 22-22-22 or 22-22-10. In my brief research I read that using 10uF on the third node will help in keeping the amp feeling more responsive. Is that so? Dave at Boothill Amps, however, says he recommends 22uF in all three places but suggests asking @robrob to see what he says. Might be worth mentioning also that I'm using a 15w OT.

    One of the things that is most appealing to me about a 5F1 is what I've read that the amp just responds to all your nuances when playing, so that is something I want to preserve. I play in many small venues for which my 5e3 is overkill, so I’m more interested in richness of sound than in power. Here's the layout I made for myself based on robrob's layout and in all I learned in my 5f2a thread:
    4846DE4D-F40E-4D91-AC7E-7ADE4C5242B7.jpeg
    And lastly, I wanted to quickly mention that boothill amps is amazing. Dave honored a $20 credit from more than two years ago. I shared with him the layout I’m following with the additional resistors and diodes and Dave simply added the additional components. Also, since I’m going to change the location of the fuse, he sent two sizes of fuse holders in case one was easier to use than the other. This is my third Boothill kit. Highly recommend
     
    Last edited: Feb 2, 2020
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  2. jsnwhite619

    jsnwhite619 Friend of Leo's

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    There's surprisingly more debate about this than you'd think. I've seen online and personally talked to people who range from "it doesn't matter at that point in the filter section" to "more is always better".

    Personally, I use 30uf - 22uf - 10uf in my 5f1/5f2a builds. I tried it a while back and thought it was the best sounding one I'd built. Extra juice for the power section, less in the preamp to keep the mud out.

    Another example is a Harvard I built last year. I used the same cap lineup as above in it because I liked it so much in the 5f2a that I thought I'd try it elsewhere. It sounded thin, weak, and anemic, and the treble would cut your head off. I tried different voltages, different bypass caps, different bright cap values, no bright cap....went around the world trying to make it sound good. After everything else failed, I replaced the 10uf preamp cap with a 22uf and BOOM -- instantly solved all my problems.

    So, in my experience, it can definitely make a big difference in tone and performance of the amp. A cranked Champ/Princeton with hot pickups will probably benefit from a smaller cap there to keep things brighter & lighter sounding. The Harvard sounded terrible with a small cap there.
     
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  3. elpico

    elpico Tele-Holic

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    The only thing caps should really be affecting in this amp is the amount of hum. I'd go with the 22.
     
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  4. SebC

    SebC Tele-Meister

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    22uF it is then!
     
  5. SebC

    SebC Tele-Meister

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    My biggest concern was loosing sensitivity but from your replies it seems it shouldn’t be an issue
     
  6. Lowerleftcoast

    Lowerleftcoast Tele-Meister

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    On the 5F2-A schematic Pooks wrote.
    "I'm no help on the schematic, but I just wanted to point out that the light is the perfect brightness."


    I noticed the switch in both schematics is in the same position, yet the light is not illuminated on the 5F1.

    The wiring in that part of the circuit looks correct. I think the bulb may be faulty.
     
    Last edited: Feb 3, 2020
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  7. Lowerleftcoast

    Lowerleftcoast Tele-Meister

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    Caps values in parallel add together. So you could test the values in the 5F2A. Clip in another 10uF across the caps in that amp and let us know the results.

    It has been my understanding, the use of lower value caps add to feel/touch sensitivity.
    You are in a position to test that hypothesis.

    I have serious doubts whether a change from 16uF to 22uF would be noticeable. Would a change from 10uF to 22uF be noticeable? Is there a noticeable change in hum?

    Point of info: The cap directly after the 5y3. The max value is 32uF per datasheets.
     
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  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The Champ sounds great with the Fender spec of 16-8-8uF so 22-22-8 would be fine too. As jsnwhite points out the filter values can cause preamp voltage sag or even starvation in the amp he mentioned. To stay close to the original's response/sag/playability I'd stick with 8 or 10uf for that last filter cap.
     
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  9. SebC

    SebC Tele-Meister

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    Well then, 10uF it is! Jaja. Response/sag/playability is what I’m going for. Thanks
     
  10. SebC

    SebC Tele-Meister

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    :lol: I’ll have to draw a new bulb and replace my faulty one!!
     
  11. elpico

    elpico Tele-Holic

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    Sag in a class A amp? Was this measurable?
     
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  12. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Hoping I don't get into a can of worms here, but having read as much as I can find about "class A amps don't sag", I have to believe that phrase only pertains to a certain aspect of the amp.

    A 5y3 at 370v in a Champ sounds a lot different than a GZ34 biased at the same voltage level -- softer & squishier, and more distortion. Rectifier sag?

    Though it only seems to matter at extreme wide-open volumes, a humbucker guitar with a hard 6-string E chord still has the same breathing, blossoming sound & feel that a 5e3 does, to my ears. Like hearing a gunshot from a great distance where you can hear the the muzzle blast then the sonic crack. My Champ/Princeton builds have had the same effect when playing my Les Paul - the sudden response of the amp followed by the "catching up" sound. I don't know if that's rectifier or capacitor sag, but it's noticeable to me.

    From Aiken's site:

    The filter capacitors: The size of the filter capacitors in relation to the amount of current drawn from the power supply also creates sag. The filter caps charge up during the peaks of the AC input cycles, and hold the voltage constant during the "valleys". If the ratio of peak to idle current is high, and the peak current demands are high in relation to the capacitance size, the voltage will sag appreciably during the valleys, creating a lower average voltage. If there is no further filtering, there will also be a 120Hz sawtooth ripple riding on the B+ supply. This normally doesn't induce much hum into the output stage because of the inherent power supply rejection afforded by the push-pull output stage, and the screen supply is usually filtered further with a choke and another capacitor. However, insufficient filtering can induce ripple into the amplifier if the output stage is not well balanced, or if the screen and preamp supplies aren't well filtered.

    Note that sag effectively only occurs in class AB amplifier output stages. A true class A amplifier has no sag because the current draw at full power is the same as the current draw at idle. However, most class A amplifiers aren't biased exactly at the midpoint of the range, and will tend to clip asymmetrically, especially when going into grid clamp on the output tubes, so there will be an offset current component, but it will be much smaller than in a class AB output stage.

    https://www.aikenamps.com/index.php/what-is-sag
     
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  13. robrob

    robrob Poster Extraordinaire Ad Free Member

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    jsnwhite's amp seemed to suffer from preamp sag & starvation due to inadequate preamp filter (reservoir) cap size.

    @jsnwhite619, could you give us a recap about your amp's symptoms and fix?
     
  14. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I just happen to have a thread about it. https://www.tdpri.com/threads/harvard-test-circuit-experiments.938273/

    But, to copy from it, here it is.

    Initially, wanted to go for a humbucker/overdrive setup.
    • 2uf bypass cap on V1
    • raised NFB resistor from 56k to 68k
    • .0033uf cap on the tone knob
    • filter caps - 22uf, 22uf, 10uf (10uf intending to cut extra mud for humbuckers)
    • 6.6k Deluxe Reverb 20 watt OT from Hammond - 1750H
    • 290CAX PT with 275v & 315v taps;
    • Bias pot
    Got it all wired up, and it would cut your head off with the brightness & treble. Even humbuckers were painful with the tone above 5-6. Experimented first with bright caps first - none, higher, lower. Made differences each time, but nothing I liked. I was convinced it was the OT I've never used before. Then, I lowered the NFB resistor to 47k, hoping to tame it. It helped but still not pleasant. I ended up changing the V1 bypass, tone knob cap, NFB, (can't remember what the bright cap is right now) back to stock values except the 10uf preamp cap, and still nothing helped the awful brightness. Again, I figured it must be the bigger OT. I even changed the first resistor in the power section to drop more voltage and lower the preamp voltage - maybe it would darken things? Nope.

    After several days of playing it and changing things around, I finally swapped that 10uf preamp cap for a 22uf cap. Night and day difference! THAT was the biggest change of anything I did and completely transformed the amp. At this point, I have it at stock Harvard voltages - 305v B+, I had it on the higher taps before, but changed that to see if it helped with the bright, hard sound. It stays really clean up to 10 or so with a Tele and doesn't really go crazy with a Les Paul until 8-9, but the LP cranked is a fat, full overdrive that sounds great now. Funny thing is that it has more headroom, but lower output volume, or maybe it's perceived volume since it isn't so painful to experience. Before the filter cap change, I couldn't stand to crank it and be in the room without earplugs, now it's much more subtle.
     
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  15. SebC

    SebC Tele-Meister

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    Here’s some progress with the Champ. As always, anything looks suspicious please let me know! As I said, I am going to go 22-22-10. But I didn’t get to the board today. I drilled a hole for the new location of my fuse holder (Dave at Boothill amps sent a smaller fuse holder knowing I was going to go for an alternate location and that was perfect! I hadn’t thought of it), a hole for the AC cord’s ground, wired that AC chord, fuse and switch, installed some parts and made the ground buses bars
    D6DFB3DC-48AA-4DBF-8D13-4E82AD677706.jpeg

    E0B53BD9-97C3-4DCF-A2E9-0D8785386B3A.jpeg
    ...oh, and printed what will be the tube chart!
    1D0B3E40-6597-4049-B71B-FEB958689D30.jpeg
    I only get to work on this once a week for about 5 hours. But I still feel lucky to get to do it! Much fun
     
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