BYOC Harmonic Tremolo Mod, and help me label my switch

Discussion in 'Burnt Fingers DIY Effects' started by JMac52, Mar 29, 2020.

  1. JMac52

    JMac52 Tele-Meister

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    A month or so ago, I built the BYOC Brown Face Harmonic Tremolo. The kit went together fairly easily and I got it up and running in short order (there are two trimpots to set and then balance the output level through the range of the Depth control).

    I plugged in and hit the obligatory E7 chord, and OK - there’s a tremolo effect going on, and it’s kind of vibe-y/phase-y, but where’d my low end go??? I’ve never heard a real Brown Face tremolo, so maybe it’s supposed to sound like that? I didn’t have time to mess with it before leaving on our spring break vacation, but I did use some idle time to do some research (and try to avoid the news - this was the 2nd week of March).

    In the BYOC design, the low pass filter is formed by a 220K resistor and .01uF capacitor, giving a cutoff frequency of 72 Hz; the high pass is implemented with a 250pF cap and 1M resistor resulting in a cutoff at 637 Hz. Even at only a 6 dB per octave slope, that’s going to scoop a lot of bass and low mids.

    I found a schematic claiming to be from a 1960 Showman - it has the same HPF but the LPF uses a 5nF cap, so the cutoff is 144 Hz. So the scoop wouldn’t be as pronounced.

    Back home, and now with a lot of time on my hands, I started looking at how to mod this thing. I clipped a 250K pot in parallel with the 220K LPF resistor and turned it until it sounded thicker without being muddy. I measured 110K on the pot, giving me 165K total resistance and cutoff around 96 Hz.

    I wanted to keep the stock tone and use a switch to provide the alternative LPF cutoff. The only toggle switch I had was a DPDT mini from an abandoned project, and I had a 100K 1/2W resistor due to an ordering mistake (I have a lot of 1/2W resistors from that same mistake). So I forged ahead with more switch and more resistor than I needed.

    Another challenge was that I would have to unsolder the 9V connector leads in order to completely remove the PCB from the enclosure. Even if I did that, my oversized switch and resistor wasn’t going to fit topside where you expect a switch or knob to be. I could have put it on either side of the footswitch, but opted for the bottom end because, with the PCB still installed, I could see and better control the metal shavings when I drilled the hole. Not really an optimal location for a user, but hey sometimes we gotta make do.

    Pics, audio and FR plots here.

    (I’ve built 8 or 10 pedals from kits - this is the first time I splurged on a painted enclosure. I guess I dig brown)

    If you’ve made it made it this far… I’m taking suggestions for what to label my switch. The idea that’s stuck in my head is a boring “LPF 1-2” (or maybe “1 LPF 2” on the physical label). Gimme some fun suggestions, like a plausible misnomer (out of respect for the heritage of guitar effects) or something boutique-y. And thanks for reading my post!
     
  2. alathIN

    alathIN Tele-Holic

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    I built a Weber ReVibe (just got done debugging) which combinines the basic Fender standalone reverb unit plus the brownface harmonic vibrato your build emulates. The tube version is a notoriously tricky build and from your guts pic it looks like the solid state version isn't exactly a picnic either.

    Caveats - I like brightness and I listened on my phone - but within those limitations your first audio clip sounds closer to how mine sounded with the original recommended component values.
    Yours definitely has the "harmonic" thing going on - it's not just regular tremolo.
    In tweaking mine I did not mess with the high and low pass values but I did a couple of mods/tweaks to get the slow end of the rate to go slower and the high end of the intensity to go higher.
    The thing that is most characteristic of this circuit to me is what TDPRI member Moosie calls "squish." It's a point in the middle of the hi-lo cycle where the tonal range is very limited and it does sound to me like a wah stuck in a partway position, or some of the series out of phase stuff that Brian May used a lot - but it is just in the midpoint between the fading lows and swelling highs and then again on the way back down.
    As it cycles, you do lose some of the bright sparkle on one side and some bass punch on the other. So people whose ears go into withdrawal syndromes when they lose their supply of high end (or low end) are liable to feel the jones with this effect.
    I think you've added a valuable mod to push it more toward the low end for folks who find happiness down there but I'm more of a brightness junkie and prefer the other position.
    I can't tell for sure if you've got the full-on squish at the midpoint - but I'm pretty sure I do hear some of it. Did you record your clips on full slow and full intensity?
    Yours is certainly one of the better solid state versions I've heard - very creditable indeed. Nice work.
     
  3. JMac52

    JMac52 Tele-Meister

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    Thanks for your insights, alathIN. Yes, as with most things audio, it’s very subjective. I wanted to keep the stock circuit and have an option - one or the other may be a better fit in the mix.

    The clips were recorded at slowest speed with Depth at about 1:00. Some of the feedback on the BYOC forum is that the effect doesn’t engage until Depth is around 11:00. I find that it is subtle but potentially usable at low depth. I know there are tonal changes over the range of the controls. I’ll have to spend some more time with it and listen for what you’re describing.
     
  4. alathIN

    alathIN Tele-Holic

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    I definitely like it as a subtle effect.
    For whatever reason I usually seem to want to keep it slow and just take out depth to make it more subtle - or maybe just increase the rate marginally
    I play fingerstyle so a lot of times the effect isnt even obvious until i hold a chord or note

    But for tweaking the circuit or hearing what the effect is doing, my ear is not good enough to hear exactly whats going on unless the depth is maxed and the rate is slowest.

    If you want to hear the "squish" Moosie has a long tweaking thread with sound clips where he is trying to fine tune the sound. Let me see if i can find it.
     
  5. alathIN

    alathIN Tele-Holic

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