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Filament buss question

Discussion in 'Shock Brother's DIY Amps' started by moosie, Nov 23, 2017.

  1. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
  2. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    OK, here's the first round of data. Reverb on zero. Signal input: none, 100 hz, and 5000 hz.

    Depth pot added resistance: 1.77M (two 1M resistors in series, untouched from last time).

    Cathode resistor: 4.72k
    No signal:
    V4 grids A & B, vpp: 1.9, 2.6
    V4 plate A, vpp / max: 72/328 (V4b measured the same)
    V4 cathode min/max: 3.0 / 3.88v

    100 hz signal:
    V4 grids A & B, vpp: 1.9, 2.9
    V4 plate B, vpp / max: 80/328 (V4a same as with no signal)
    V4 cathode min/max: 2.96 / 3.92v

    5000 hz signal:
    V4 grids A & B, vpp: 2.1, 2.7
    V4 plate A, vpp / max: 76/328 (V4b same as with no signal)
    V4 cathode min/max: 2.96 / 3.84v


    Cathode resistor: 6.75k
    No signal:
    V4 grids A & B, vpp: 1.9, 2.5
    V4 plate A, vpp / max: 56/328 (V4b measured the same)
    V4 cathode min/max: 3.12 / 4.16v

    100 hz signal:
    V4 grids A & B, vpp: 1.9, 2.9
    V4 plate B, vpp / max: 64/328 (V4a same as with no signal)
    V4 cathode min/max: 3.1 / 4.24v

    5000 hz signal:
    V4 grids A & B, vpp: 2.1, 2.7
    V4 plate A, vpp / max: 60/324 (V4b same as with no signal)
    V4 cathode min/max: 3.2 / 4.24v


    I did a quick playing test, just real time, not recorded, and couldn't tell any difference with the resistor maxed, or at various mid-way settings.


    Let me know if this is good data, or if I should measure something else. Then, next step? Increase the depth resistor? Continue increasing the cathode resistor?


    I was thinking, I should be able to see the waveform similar to Leo's patent drawing, with the audio at higher amplitude at the top of the cycle. Well, I don't. At either resistance. If I'm scoping it correctly, audio amplitude (relative to the larger waveform) appears to be the same throughout the cycle.


    Speaking of scoping, I noticed a weird thing. If I have probes (1x) on the V4 grids, measuring, and then I move one over to measure the cathode (still 1x), the reading on the untouched probe (on on of the grids) measures higher (from 1.9vpp to 2.6, I think it was). Doesn't matter if I hit Auto to reset in the new positions, or not. Seems to be easily repeatable. Is this Schroedinger's cat? I assume I'm doing something wrong, and am afraid it's messing up my other measurements, too.
     
  3. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    The scope presents a slight leak path to ground that can upset the subtleties of a high impedance tube circuit. It's a trade off in the interest of being able to see what's going on in real time. I do see the effect of the higher cathode resistance in your readings, though.

    So on your playing test, you're hearing very little difference? Just an FYI, what you should be concentrating on is this:

    When does the tremolo effect become noticeable? i.e. at what point do you start to tell something is happening on the Depth knob?

    How profound a harmonic effect are you getting vs what you want, and is in a useful part of the Depth range for you?

    The cathode resistance change should affect the onset point and strength of the tremolo over the sweep range, and how sensitive it is. I would aim to start getting the first hint of tremolo at a low setting, progressing to all out wild harmonic warble at high settings, but that's my taste. It's the nature of the circuit that depth will affect the harmonic strength a good bit.
     
  4. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    OK, I didn't test the depth sweep. I just left it on max, and I didn't hear the signature harmonic warble. Just fairly good normal trem, as we've been hearing.

    I feel same as you, I think. I want more sweep, so earlier onset, and I want max to be wild harmonic.

    So it doesn't appear we've gained on the overall depth / harmonic front, but perhaps to be certain I should record a basic clip at 6k75, and one at 4k75. Tomorrow early as I can I'll test the depth sweep. Hopefully earlier in the day.
     
  5. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    Here are some samples. 4.75k cathode resistor is stock. 6.75k is with the 2k trimmer installed and turned all the way to max resistance.

    Today, I hear a difference. I'm sure it was there yesterday, but I didn't hear it properly. I blame my brain. I scrolled back through the thread, and I may have failed to mention that my CIDP affects my brain, and audio comparison is one of the hardest things for me to get right. Should have led with that, right? :) I can enjoy it when it's right, but I can't objectively compare it, so the recordings help a LOT.

    So, to my ear, listening back to back like this, 6k75 has earlier onset - it's faint but noticeable at 25% of the depth pot sweep, where 4k75 is not noticeable at all, and only just a hair more at 50%. With 6k75, 50% seems pretty useable.

    And at 100%, the 6,75 depth is 'deeper'. Getting there.

    Comments?









     
    Last edited: Jan 11, 2018
  6. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    Here are the 4.75k samples:









     
  7. keithb7

    keithb7 Friend of Leo's

    Age:
    47
    Jan 9, 2010
    Western Canada
    Of the two recent samples, I am liking the 6.75K. Sounds deeper to my tinnitus'd ears.
     
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  8. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    I like the 6.7k samples, too. Sounds like we need a bit more tremolo drive available to both lower the onset point and boost the max available.

    Ok, let's open another front on this.

    R37. What resistors do you have available in the 1M to 10M range? Depending on what you have, we can either parallel values or trade in new ones to tune that.
     
    moosie likes this.
  9. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    I'm prepared. Bought a box of 800+ 1 watt, 1% metal film. All sizes up to 10M.

    Here are 1M and up:

    20180111_211844.jpg


    20180111_211630.jpg
     
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  10. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    Kinda forces my hand whether I do another build... :D
     
    Snfoilhat likes this.
  11. keithb7

    keithb7 Friend of Leo's

    Age:
    47
    Jan 9, 2010
    Western Canada
    Holy crap! I think you’re good for what? 50-60 more Univibe builds?:lol:
     
    moosie likes this.
  12. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    Amazon Prime, what can I say... not expensive, and now I have stuff on hand. :)
     
  13. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    Sweet Baby Ray. That's a lot of resistors.

    Do you have 3.3M, or anything between 3.3M and 4.7M? Swap R37 for the next smallest value down from stock, and check the Depth sweep while playing.
     
  14. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    Will do. Yeah, 3.9M, then 3.3M.

    I'll try now, though I might not be able to do clips tonight. Part of the reason I think I didn't hear it correctly yesterday was the need to play quieter after my wife goes to bed.

    Tomorrow I'm stuck in the infusion chair all day, but should have a chance in the evening.
     
  15. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
  16. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
  17. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    I'm going to listen to these tomorrow. My ears are fried for tonight.

    Would like to hear your thoughts.
     
  18. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    Is that as slow as that will go? I'm having some trouble judging the quality of the effect through ear buds tonight vs my desktop JBL monitors.

    As far as depth, that sounds at least as strong with the 3.9M as what I would expect judging from other demos available. The 3.3M is getting a bit choppy as 100% for my taste, but if you like it roll with it.

    What's your feeling as far as onset point vs the max available? I think we can dial the upstream resistor and depth pot resistor in tandem to change how the sweep happens at this point.
     
  19. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    No, it will go a little slower. I think speed has been 15-20% for all today's clips. I might have bumped it at one point, but around there somewhere. Do you want me to record various speeds?

    Sweep and onset sound about perfect. I think I hear a tiny bit of tremolo on the 0% settings with both of these latest clips.

    The max sounds good, too. I need to listen again, tomorrow, but probably the 3.9M is the charm.

    I'm heading to bed. The nurse comes early tomorrow.
     
  20. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    No, I was just wanting it slower if possible so I could listen more closely to the guitar sound.

    Get some rest, and I hope tomorrow goes well for you. I'm content to pick at it at whatever rate you're happy with.
     
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