Questions about Deluxe Reverb-topology

Discussion in 'Shock Brother's DIY Amps' started by Jorma Rysky, Oct 27, 2021.

  1. Jorma Rysky

    Jorma Rysky NEW MEMBER!

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    Created username for asking about DR topology. I have basic understanding of things and signal flow, but lack still deeper understanding. I have this kit built AB763 DR, that I'm free to do what I want, but I'd rather circuit bend it ways that does not burn transformers. Or house. Just kidding, I think I'm able to evade that, but I'm interested why and how too, not just if it works.

    From @robrob 's page:

    [​IMG]

    Why is V4B needed? As far as I know, reverb channel is actually less liked of DR's channels, because added gain. There is already reverb recovery, it gets amplified to unity gain with dry signal. Why dry mixed with reverb needs to pass through another gain stage? If I bypass this, I assume I still get sound out of this thing, but how is it altered? Channels would be in phase, which is good thing, as far as I'm concerned.

    Another question.

    From : https://guitar.com/guides/diy-workshop/build-tube-spring-reverb-unit-amplifier/
    [​IMG]
    Is it possible to modify fender style reverb circuit with transformer to input from before volume and tonestack, and output to grid of V2B? In Swart/Ampeg style, though those are transformerless designs. Phase is not issue, as both designs get sent and return between gain stages, and not around them.

    Not really about DR, but that Swart style reverb for 5F2A. It is said that preamp volume can be turned off, and reverb still works. But doesn't turning volume to zero let whole signal pass to ground, how reverb gets anyt input?

    Thank you, Rysky
     
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  2. sds1

    sds1 Tele-Afflicted

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    There wouldn't be enough signal to drive the output stage otherwise. See the 3.3M resistor prior to reverb mix? This is limiting the dry signal a ton so that the final wet/dry ratio can be higher. The more dry signal the less dramatic the reverb effect. So, an additional gain stage is required to amplify the wet/dry mix back to nominal level to drive the PI.

    I don't see why not.

    Even so, with reverb being a modulation effect I don't believe phase would be an issue either way.

    The volume pot will shunt any signal passing thru it, but in the drawing you provide there are now parallel signal paths, one of which goes around the volume control, and therefore will be unaffected by it.
     
  3. Lynxtrap

    Lynxtrap Tele-Afflicted

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    What are you trying to accomplish? What is the purpose of the mods that you are asking about?
    Would help people here give you advice.
     
  4. Jorma Rysky

    Jorma Rysky NEW MEMBER!

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    Ah yeah, you are right. Never noticed it is so big, thought it is just some kind of mixing resistor without attenuating purpose.


    Okay. Is there something different here, because it is active circuit, cause for my eye it still looks like it would go all to ground? Like if there was two volume potentiometers on a guitar, wired paraller, zeroing one will eat all the volume, even though there is paraller signal path. Or is my logic flawed, what I'm failing to understand here?

    Just hypotethical hacking right now, though I will probably try "Swartifying" reverb. Not removing V4B though, if I want to try Swart reverb without extra gain stage, I could just connect it around normal channels tone stack instead of vibrato's.

    Reverb mod is mainly because I want to try different flavour of reverb, without tone stack affecting it. I could just bypass stack, but then dry signal would also be flat.
     
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  5. NTC

    NTC Tele-Holic

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    Actually, you are correct. The signal from the first triode connects to the pot wiper, which will ground out the input signal. Like the bright channel on a 5E3. Later style amps have the wiper connected to the following stage and it does not affect the first triode's signal.
     
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  6. sds1

    sds1 Tele-Afflicted

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    It's my bad. I've become overconfident and lazy.
     
  7. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The 3.3M reverb mix resistor forms a voltage divider with the V4B 220k grid leak resistor which dumps most of the signal to ground so an extra gain stage is needed to make up for that.

    If you tap the reverb signal from before the volume pot you will vary the dry signal but the wet will stay at its volume level unless you adjust the reverb dwell or intensity. Every time you change the volume you'll need to change the reverb.

    If you tap the reverb signal from before the tone stack your wet signal's tone will not change when the tone control is used so if you turn up or turn down the reverb your output signal's tone will change.
     
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