JM/SSS tweaks

[norburybrook]

Well after some recent posts by Rootz about the amp he's made it got me thinking about my SSS, also with Erwins project on going the SSS is on my mind.

So knowing that SSS#004 is similar to my JM/SSS I thought I'd try a few things.

I've looked at MHartmans 004 and after a message from mojotom I decided to do the power supply dropping resistors like the 004 replacing the 22k and 2.2k with the 6.8 and 1k ( I ended up with 2x 15k to give actually nearly 6.8k on measuring and 2x 2.2K)

this gives the B+ for the pre amps more juice.

I now have 220-235vDc on v1 and 2.

I also added a 68pF across the P.I. like 004 and similar to what's on a bluesmaster too.


I then thought about the voltage divider which caused so much consternation on my build.

Stock is 68k/1M but I ended up with 120K/1M

I replaced the 68k with a 250k pot and marked those 2 points so i now have a variable gain structure pot which is which is similar to the new classic reverb sig gain switch from 2 rock.

I also fitted a bypass switch for the contour.

So my amps is now more SSS#004 like but without the filters.

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Now is it possible to put a switchable FET circuit in here without needing a relay as I have a spare board and FET? i thought this would be a nice addition and might be possible with some sort of jack switch.

I have done the relay version on 3 recent builds as Martin did a great layout for it, but I can't work out how to change that into a jack switching version...if that's even possible.

M

[rootz]

That is a good idea: get the Fet on a regular switch instead of a relay.

I’m sure you’ll figure out how to do it. I think you’d need a dpdt on-on toggle switch. Miniature would be fine. How to wire depends a bit on the relay you’d normally use. Most are coil - common - normally closed - normally open. With a switch the comm would be the centre legs. The outsides are no and nc. Same wiring, only in a slightly different order.

[norburybrook]

That is a good idea: get the Fet on a regular switch instead of a relay.

I’m sure you’ll figure out how to do it. I think you’d need a dpdt on-on toggle switch. Miniature would be fine. How to wire depends a bit on the relay you’d normally use. Most are coil - common - normally closed - normally open. With a switch the comm would be the centre legs. The outsides are no and nc. Same wiring, only in a slightly different order.

thanks Rootz, I wanted to have it on a footswitch tough, so perhaps a relay is needed for that. I do have a rectifier board wired up ready to go from my last build so I'd just need power. I think I might have a small transformer kicking around as well, so it's just a case of fitting it all in

I'll have a root around in my boxes today and see what I've got.

I've had the amp hooked up with a H&K tube overdrive pedal in front. Probably the most transparent OD pedal I've tested, really nice, but then it's all proper tubes (12 AX7)so it should be. It's just quite large and need a hefty power supply.

M

[sonicmojo]

Thank you Marcus for your tweaking info! I just got started on my next build over a year after getting the A/N chassis and have been reading through all the old threads. My donor Bassman 100 iron is definitely a heavy anchor for this sucker but fits okay and I hope sounds good! I will probably incorporate some sort of switches for the voltage divider and negative feedback as well. I tested out a JMOD 100 at one point a couple of years ago and thought it was way too quiet for 100W so maybe that had the same type thing going on. I am thinking about a "boost" foot switch that would pop in more resistance for the voltage divider and take out the negative feedback at the same time. Not sure if that will work well or not but I have extra holes at the speaker outputs to test it out.

[rootz]

I don’t quite get how the voltage divider makes the amp too quiet. The dry mixer makes up for the loss of gain, that is before the mixing resistors. When comparing voltage divider input with output after the coupling cap, the gain should be almost 1 IIRC.

IMHO the gain structure switch on the TR is a simple way to get some overdrive from an otherwise pretty clean preamp. The preamp of the Wonderland puts out how much signal? 200V p-p?? Easy to overdrive the dry mixer with that, as would it be to push the PI into oblivion. I think even with a 1meg/47k divider you’d be able to fully drive the PI.

[norburybrook]

I don’t quite get how the voltage divider makes the amp too quiet. The dry mixer makes up for the loss of gain, that is before the mixing resistors. When comparing voltage divider input with output after the coupling cap, the gain should be almost 1 IIRC.

IMHO the gain structure switch on the TR is a simple way to get some overdrive from an otherwise pretty clean preamp. The preamp of the Wonderland puts out how much signal? 200V p-p?? Easy to overdrive the dry mixer with that, as would it be to push the PI into oblivion. I think even with a 1meg/47k divider you’d be able to fully drive the PI.

Rootz as I said before that 68k/1M divider gives 0.6v from 10v input for example that's a huge loss. When I first built my amp I thought I'd made a mistake somewhere as it was quiet compared to my other 100w amp I had the bluesmaster. In fact it was quieter than my 30w Rocket. After speaking to others ands posting the schematic on another forum a few pro builders like Jelle Wellagen and Bruce Egnator said it was this divider that was the issue and questioned the validity of the schematic/layout. They said it was like having a master volume on 2 and to try different divider.


with the 68/1M I cannot drive the amp into any kind of gain with the gain on full using a tele/strat , if I turn off ALL the FFB local and master then there's just a bit of 'hair'. Dialing up to 120/150k-1M and you start to get some gain.

I ended up with a 120K and now have the variable knob to take up to 250K. It makes a difference in this circuit. Perhaps this circuit is different enough from yours that you don't have this issue. The reverb is a 3 tube reverb(IIRC) on these amps so there's more going on



M