tweaking JM/SSS style amps for more mojo

[imo1]

Hey all,

I've built a few Dumble style amps now. Ive been touring for the last few months with 2 JM100 type amps. They are great amps. I describe them to other players as the most amazing Twin reverb ever. Very clean, lots of headroom , especially clarity in the bass. Ive really gotten to know the amp, playing it in a lot of different live situations, from outdoor venues, to theaters, to clubs. I've also spent a lot of time messing around in my studio with the designs, tweaking a few different components to see what they design was capable of. I feel like i understand it pretty well.

Recently I did a series of shows in Texas, and then flew up to the northwest to do some additional shows. I brought along my vibrolux reverb head and my 2x12 cab(with Warehouse 65's). I used the Vibrolux a couple of times in clubs that just couldn't deal with a 100 w head(even with a plexi shield). I missed some components of the 100W, but there was a chewiness, both to the "clean" single notes, but also to the rhythm/lead playing that is a big part of my style. This got me to thinking about how to get more of this sound with the Dumble designs. I think at some point I'm gonna build a Fender build(super or vibrolux) and start messing around with the different components to see where I can get some of that sponginess I am missing a little in the 100W build. The two things that jump out to me are the rectifier tube and possibly a slightly smaller OT.

The trick is maintaining the clarity of low end that is so strong with these designs. I'm curious to hear what others have found experimenting in these realms. I love building amps, but my main thing is playing and touring, and really trying to find the right thing for that. Also trying to consider that 100 W is really loud for most venues these days.

Ian

[ijedouglas]

Hey Ian,

This got me to thinking about how to get more of this sound with the Dumble designs. I think at some point I'm gonna build a Fender build(super or vibrolux) and start messing around with the different components to see where I can get some of that sponginess I am missing a little in the 100W build. The two things that jump out to me are the rectifier tube and possibly a slightly smaller OT.

What OT do you have in the amp? I experimented around a bunch with different OTs (Mercury/Classictone/Pacific/Thordarson/Merren/Schumacher) and they made a big difference to the feel of the amp. I think this may be what you are referring to. I really like the vintage schumachers for my ODS 6L6 builds.. Merren for el34s. I currently have a Classictone in my Wonderland build and it sounds good. I tried a Mercury in it a while back and was was a lot stiffer... can be good if you are going for the SRV thing but I preferred a little more give in the amp. Lowering the preamp voltages may also change the feel of the amp, not sure if you have played around there.

Cheers

Ian

[imo1]

Another Ian! As my old friend Mac used to say “us Ian’s gotta stick together!”

Thanks! I have 2 different OTs. One is the MM. the other is the heyboar. I like them, but to me, they sound more like Jimmie Vaughan, which is amazing, but different.
Stevie’s sound was the super/vibroverb combo. When he started playing the SSS live later as part of that rig, he still had those other amps going too, and his sound(which was really more of an Austin thing at the time than a specific thing to him) started evolving to a tighter sound. Again, very cool, but different. I think of that sound on songs like tightrope and the like.

As much as I would love to have a multi amp set up, I’m already straining the acceptable bounds of sound and realizing that I probably need to find a way yo make the touring rig a little more reasonable!

Have you tried tube rectifiers or possibly smaller OT with just 2 tubes? Thinking along the lines of a super or something with some of the dumble implementation and 2x12 instead of 4 10

[ijedouglas]

Have you tried tube rectifiers or possibly smaller OT with just 2 tubes?

Not in any of the ODS/SSS type amps. Tweedle Dee yes but that's a total different beast.

[mojotom]

Well I did build a 50W JM with a tube rectifier and an AC30 OT (smaller OT) and tweaked it a lot since I build it. I like it, especially the reverb, but still not 100% satisfied by it.

Not so long ago I was rebuilding a Vibrolux for a friend, really like that amp (I'm a huge SuperReverb fan tbh) and also got a Vibroverb style amp build by an european brand and I do prefer either amps over the JM, especially with a Strat.
I found the JM has too much attack when I dig in and it feels nice and 3D, etc but I kind of prefer the smoothest attack of an old Fender and how they react when I dig in.
For sure the bass is tight and define on the JM but I wasn't able to tweak it to sound like those two Fender like amps (tonestack, power supply, tubes, etc).

I did try to convert my JM to a traditionnal clean and I thought it was better for me, not quite there as it does lost some volume over the JM but the attack was smoother yet it stays clean even when pushed, you could try that on one of your JM, very easy to do (moving a few wires here and there).

After all those tweaks I start building a Vibrolux and kept the JM as a traditionnal clean for now. You could find a good Silverface SR and rebuild it, both amps have something I can't find on a Dumble design.

[WhopperPlate]

Some of my observations for consideration:

A) tube rectifiers are always good for sponge

B) carbon films instead of metal film are good for sponge . Carbon comp more so. Maybe fill the phase inverter with cf and cc appropriately. If it has MF on the bias grid resistors like most clones that’s one place to certainly consider

C) fender uses lots of carbon comp in the power supply . second order harmonics . Sponge. Chewy.

D) I love LNFB, but it has a tendency to smooth out the frequencies that would get chewy and spongy .

E) lower voltages contribute toward the sponge

F) different transformers from different manufacturers, or even the same manufacturer, can be like apples to oranges

G) I find the stock JM 24k 820R PI can lean out the sound. Marshall PI 10k 470R, or even twin PI 22k 470r, imo has more punch and chewiness.

[neskor]

On my JM50 I did these mods:
1. Vintage Fender power transformer from vintage Super Reverb
2. Tube rectifier and the first power capacitor is 2x50uF in series
3. Removed capacitor on Reverb pot
4. 120K instead of 220K on reverb output
5. Added gain structure 3 way switch
6. Old Fender output transformer
7. LFNB on a switch (mostly running without LNFB)
8. 3 way bright cap on Master pot
9. Running amp on variac, 10% lower than normal voltage
These mods gave me sound that I love more than my '66 Deluxe Reverb and very close to my vintage Super Reverb.

[dorrisant]

Add the cathode driver stage... Opens up bandwidth. Also, experiment with the mixer stage entrance values.

[imo1]

Add the cathode driver stage... Opens up bandwidth. Also, experiment with the mixer stage entrance values.

Curious to hear more thoughts on these changes!

[imo1]

On my JM50 I did these mods:
1. Vintage Fender power transformer from vintage Super Reverb
2. Tube rectifier and the first power capacitor is 2x50uF in series
3. Removed capacitor on Reverb pot
4. 120K instead of 220K on reverb output
5. Added gain structure 3 way switch
6. Old Fender output transformer
7. LFNB on a switch (mostly running without LNFB)
8. 3 way bright cap on Master pot
9. Running amp on variac, 10% lower than normal voltage
These mods gave me sound that I love more than my '66 Deluxe Reverb and very close to my vintage Super Reverb.

Would love to hear what this sounds like. So hard to talk about sound in words. I think some of your comments mirror mine.

[imo1]

Some of my observations for consideration:

A) tube rectifiers are always good for sponge

B) carbon films instead of metal film are good for sponge . Carbon comp more so. Maybe fill the phase inverter with cf and cc appropriately. If it has MF on the bias grid resistors like most clones that’s one place to certainly consider

C) fender uses lots of carbon comp in the power supply . second order harmonics . Sponge. Chewy.

D) I love LNFB, but it has a tendency to smooth out the frequencies that would get chewy and spongy .

E) lower voltages contribute toward the sponge

F) different transformers from different manufacturers, or even the same manufacturer, can be like apples to oranges

G) I find the stock JM 24k 820R PI can lean out the sound. Marshall PI 10k 470R, or even twin PI 22k 470r, imo has more punch and chewiness.

Thanks for these thoughts