DSL20hr resonance circuit?

[Parkerx02]

This isn't the conventional 1m/.0047 depth pot combo and not in the usual location of being inline with the nfb resistor. I assume it's a gyrator circuit like on the TSL's and others? It seems to work ok, but not great and it's def overly complicated. I've done a ton of mods to my 20hr and its sounding killer, way better than stock. Being I'm never content and need to tinker, and now that it's more classic Marshall sounding and thinner, I want the option to add thump back in. I'm thinking of I'm leaving the presence circuit stock but removing the resonance circuit and installing a conventional depth circuit inline with the nfb resistor. Or I could leave the stock resonance and add a fixed depth circuit to the nfb circuit. I'm leaning towards removing it and doing it the more conventional way. What you all think?

 

[PelliX]

Leave the existing Resonance control and circuit in place and add your depth circuit. There's plenty of room at the back to add a few controls if desired. I don't know how your amp performs, but I tend to adjust the Resonance a fair deal depending on the 'master' volume. Just my .

 

[Parkerx02]

I'm

Leave the existing Resonance control and circuit in place and add your depth circuit. There's plenty of room at the back to add a few controls if desired. I don't know how your amp performs, but I tend to adjust the Resonance a fair deal depending on the 'master' volume. Just my .
[/QUOTE

Leave the existing Resonance control and circuit in place and add your depth circuit. There's plenty of room at the back to add a few controls if desired. I don't know how your amp performs, but I tend to adjust the Resonance a fair deal depending on the 'master' volume. Just my
Thanks for the reply. Why have a depth and a resonance? Ultimately, I'd like to ditch the stock resonance circuit and 5k pot and install a 1m pot with .0047 in it's place. The stock resonance is a gyrator like on the tsl and I think dsl? Wonder why Marshall doesn't just use a conventional depth/resonance circuit?

 

[santiall]

back in the day Peavey had a patent for that resonance circuit. It was completely unenforceable as there was prior art from the 1960s butt still, if you used it, you may have a call from their lawyers and put yourself in a mess. I guess this is why initially the had the gyrator in the JCM2000 with an op amp (that clipped at high levels...), I used a MOS in the JVM and then there were some variations. Diezel used an actual inductor in the same position.
If I had to design a resonance circuit today I would not use the girator anymore as the patent is expired anyway...

 

[Parkerx02]

There was a patent to use the 1m pot with .0047 cap in the nfb circuit? I disabled the gyrator in my TSL100 and installed a fixed depth in the nfb circuit and now it sounds so much better. I'm thinking the 20hr will sound better too. What is a MOS?

 

[santiall]

yes, they did. The cap and pot values don't need to be those that you mention, in fact Peavey used others but the patent is the same:
https://patents.google.com/patent/US5197102A/en

a MOS is a type of transistor. You can make a gyrator with a transistor instead of an op-amp

 

[Parkerx02]

So I replaced the 5k resonance pot with a 1m pot and wired it up to bypass the gyrator and went with the usual 1m/.0047. It sounds great and has less low low bass and its super quiet now. Mine is a 2021 model so the 1m resistors in the gyrator circuit should haven't have been a problem, yet were because I had the wooshing noise people complain about. Now with the gyrator bypassed, no wooshing and super super quiet. Stock the tone stack had .047uf caps for bass and middle. I went to the more common .02/.02 so that along with the 1m/.0047 makes less low low bass and cuts through much better.