Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: JustMike on January 14, 2019, 08:19:54 am
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I've used some relay switching to bring in a solo boost 2nd master volume and some diode clipping. My intention is to make the 2nd master AND the diode clipping enabled simultaneously. Can I do this with a single relay closure?...Just have the diodes in line with the solo master? The relay closure would shunt the feed from the primary master around the solo vol to ground?
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Maybe. Show us a schematic and we can be more specific.
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It's a 2204 based circuit and I've installed what's shown in the attachment. If I put the diodes between the 250k & ground, the switch shown would enable both, Yes? My reason for this is to have the solo boost volume control to compensate for the volume drop when the diodes are introduced.
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diodes something like this?
it's 4am n I didn't wake up to think :laugh:, I believe you'll find un-intended stuff, but easy to try n un-try
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The way you have it drawn has a few issues:
- It's always bypassed when the footswitch is not plugged in
- When not bypassed, your Solo control actually becomes a reverse "gain" for the diodes, at best it can add the equivalent of the diode's voltage to your signal
- The clipping will be very subtle... potentially undetectable.
- The footswitch cable will act as a capacitor that bleeds a lot of highs to ground (this can be a good thing with clipping, but it's a bit of an unpredictable way to achieve it).
Personally I would separate the clipping circuit from the volume boost. I'd move it before the master, with an inline trim so you control how much clipping you get no matter how the volume is set. I'd use LEDs to not remove too much signal, as much as 3 in a row per side if that's what it takes. Then for the Solo control you have it right, the challenge is that it takes at mininum a SPDT switch (alternate between grounding the clipping circuit or the Solo control).
At the end of the day though, a relay, a diode, an LM7805, a bridge rectifier and two caps isn't a lot of $$$ and you got yourself a relay circuit, no need to send audio down the footswitch cable. And you can do something like I described.
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The schematic I attached is what I used as a guideline. My circuit uses a normally open relay so there's no issues with long cable length or the default position of the switching jack. It's a DP relay so I can also switch the diodes. I just need to know where to put the diodes in relation to the 2 masters so it only works on the Solo volume.
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As simple as it is, it should be pretty quick and easy to just twist two diodes together and start clipping them in until you find that it works or not. Probably take less than 5 minutes.
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The schematic I attached is what I used as a guideline. My circuit uses a normally open relay so there's no issues with long cable length or the default position of the switching jack. It's a DP relay so I can also switch the diodes. I just need to know where to put the diodes in relation to the 2 masters so it only works on the Solo volume.
Ok, then that would work but the "Solo" control wouldn't affect the volume much, it would just affect how much clipping is applied. And in my experience, the overall amount of clipping will be fairly low. It's worth a try though.
IME, the effect will be more pronunced if you strap those diodes to the top of the Master Volume though, with an inline resistor so you can fine tune the amount of clipping. This would make the Solo control totally independant from the amount of clipping (would only increase the volume by your chosen am ount). The downside is that the switching is more involved: bypassed would mean lifting the ground from the diodes while shorting the Solo control, and vice versa. If you have a DPST or DPDT relay, that can be done.
But a few alligator clips will let you experiment with various schemes.
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What if I just put the 2 relay switches in parallel, one NO and one NC with the diodes in series with one (both around the 250k SOLO pot)?