Question about similarity between Bassman-based preamp circuits

[Diego]

Hi everyone,

I’ve read that both the Marshall JTM/Plexi family and the Laney Supergroup are based on the Fender Bassman circuit. I'm unfortunately not very good at reading schematics, so as a Black Sabbath fan I was wondering:
Is it possible to recreate the Laney Supergroup sound using a Bassman- or JTM-style pedal, such as the PedalPCB Tweed Man OD or Covert OD?

If so, which component values would need to be changed to get closer to a Supergroup-style tone?



Thanks a lot for your help!
Diego

 

[ftumch]

Laney made a 30 watt supergroup semi-recently, the LA30BL. They deliberately used an underpowered output transformer to produce subharmonic 'ghost' tones, which is part of the sound

I have one of these amps and can confirm that it weighs far less than a typical 30 watt tube head and that it produces subharmonics

If that's the effect you mean then it might be necessary to saturate a mini transformer and see what happens?

I know Thorpy uses a transformer in his Scarlett Tunic pedal, which is an emulation of a Selmer Treble & Bass front end, so that could be a good place to start in terms of topology

The Iommi sound is a modified rangemaster pushing the supergroup, you can probably get close by pushing a JTM style pedal with a treble booster. There might even be a circuit that combines these two things already

 

[Diego]

Thanks for the reply, really appreciate it!


Checked out the Laney LA30BL – that thing's definitely on my wishlist once the budget allows. Hope your enjoy yours!

I read that with older Laneys and Oranges, the power section – including the transformers – had a noticeable influence on the tone, which helped set them apart from Marshalls. Orange had a different preamp design too, if I’m not mistaken.
For now, I’m focusing on the preamp side, since I’d like to build one anyway. While researching, I read that the Bassman, JTM, and Supergroup circuits are all pretty similar. Since I’d ideally like a Supergroup-style preamp, I thought it might be easiest to take a Bassman- or JTM-based pedal and tweak a few component values to get closer. I’m not even sure how close they really are, or if it’s even necessary to mod a Bassman- or JTM-style pedal to get into Supergroup territory. Maybe they’re already close enough?
I’ve got a Naga Viper clone that I absolutely love, so the Rangemaster part of the Iommi setup is covered.
Also gonna check out the Scarlett Tunic – sounds like a really interesting circuit. Thanks again for the helpful tips!

 

[Blackboarcult]

The Catalinbread Sabbra Caddabra was designed specifically to ape the Supergroup + Rangemaster thing.
Otherwise, you can tweak the EAE Model Fet to Supergroup specs.
IIRC the Iommi setup on the early albums was:
Modified Rangemaster (almost full freq boost as opposed to treble) -> Bass channel of Laney Supergroup fully open -> Mid, Treble fully open and Bass completely off.
It should be fairly easy to remove the Bright channel, remove the source cap on the 2nd jfet stage and implement a fixed tonestack on the EAE Personally, I'd change a few things on the phase inverter emulation and have it clip a bit harder, to match the Supergroup (The Model T has a different kind of power stage), but that's probably splitting hairs...

 

[Einzeln]

T

Thread 'The amazingly versatile Mofeta board'

Mar 22, 2023

After building my first Mofeta board and playing around with it and letting my bass player use it (and ultimately keep it), I decided to make a second one. I made provisions for a few tweaks but ended up using the stock components for that build as well. I have really enjoyed the different sounds that I can get from that pedal that are not the typical "Marshally/Fendery" type sounds. Still, I wanted to see how much further I could take it. I wanted MORE!

So I kept thinking about the schematic of the Mofeta board and realized that a 1987 Plexi has a simliar architecture. So I present to...

• TucsonSean
• Replies: 23
• Forum: Modifications

• 
• 
• 

 

[Feral Feline]

Hi everyone,

I’ve read that both the Marshall JTM/Plexi family and the Laney Supergroup are based on the Fender Bassman circuit. I'm unfortunately not very good at reading schematics, so as a Black Sabbath fan I was wondering:
Is it possible to recreate the Laney Supergroup sound using a Bassman- or JTM-style pedal, such as the PedalPCB Tweed Man OD or Covert OD?

If so, which component values would need to be changed to get closer to a Supergroup-style tone?



Thanks a lot for your help!
Diego

Laney "Toney" Iommi Treblemaster IC-Boost:

Dark Esbat Boost - PedalPCB.com

Compare to Black Country Customs TI-Boost

www.pedalpcb.com

Iommi's signature Black Sabbath tone — Rangemaster-style treble booster with a Laney Supergroup amp — was the goal of Catalinbread when designing the Sabbra Cadabra:

Sabbath Distortion - PedalPCB.com

Compare to Catalinbread Sabbra Cadabra

www.pedalpcb.com

There are a few other vendors for the Sabbra circuit that you may wish to explore, see if they are better suited to your needs: Aion, ELS, GPCB... maybe a few more.



There are similarities, from what I've read, with the Sunn T circuit, with PCBs such as ELS' enabling either circuit to be build (Supergroup or Sunn T). ELS no longer offers the Super Trouper PCB, but the SUPER TROUPER BUILD DOC PDF gives you the schematic to adapt to another PCB or produce a vero/perf/PCB layout of your own.


Since you're interested specifically in copping Tony Iommi tones and the SuperGroup, I would suggest including that in the thread title, you might get better more-targeted hits from people in the know.

 

[ICTRock]

the tweed bassman was based on an example amplifier circuit in RCA's tube manuals. the jtm was copied from that bassman then the superlead plexi added the treble peaker to the "bright" channel and the supergroup and model t are based off of that.

oversimplified history aside, I wasn't aware the super trooper pcb was discontinued but I do happen to have a spare pcb.

 

[Diego]

[EMBED content="threa

The Catalinbread Sabbra Caddabra was designed specifically to ape the Supergroup + Rangemaster thing.
Otherwise, you can tweak the EAE Model Fet to Supergroup specs.
IIRC the Iommi setup on the early albums was:
Modified Rangemaster (almost full freq boost as opposed to treble) -> Bass channel of Laney Supergroup fully open -> Mid, Treble fully open and Bass completely off.
It should be fairly easy to remove the Bright channel, remove the source cap on the 2nd jfet stage and implement a fixed tonestack on the EAE Personally, I'd change a few things on the phase inverter emulation and have it clip a bit harder, to match the Supergroup (The Model T has a different kind of power stage), but that's probably splitting hairs...

Thank you, that’s interesting!
I do know about the Catalinbread Sabbra Cadabra – cool pedal, but I always felt the control layout was a bit limited in terms of flexibility. Also, I thought it wasn’t an actual Supergroup preamp circuit, but more of a soundalike design – kind of like how the Acapulco Gold isn’t a true Sunn Model T preamp either, just inspired by it.
To be honest, thinking about the phase inverter and transformer stuff is a bit too much for me – I’m really just scratching the surface when it comes to building pedals. For now, I’m mostly trying to get close using preamp-style circuits and see where that gets me.

 

[Diego]

T

Thread 'The amazingly versatile Mofeta board'

Mar 22, 2023

After building my first Mofeta board and playing around with it and letting my bass player use it (and ultimately keep it), I decided to make a second one. I made provisions for a few tweaks but ended up using the stock components for that build as well. I have really enjoyed the different sounds that I can get from that pedal that are not the typical "Marshally/Fendery" type sounds. Still, I wanted to see how much further I could take it. I wanted MORE!

So I kept thinking about the schematic of the Mofeta board and realized that a 1987 Plexi has a simliar architecture. So I present to...

• TucsonSean
• Replies: 23
• Forum: Modifications

• 
• 
• 

Alright, that’s kind of what I want to do – identify the component values in a pedal that differ from the Supergroup and change them. Not looking to recreate the whole amp, just get in the ballpark with a preamp-style circuit.
Thanks for the example! I actually saw it before but stopped reading when I saw “Sunn T” mentioned – stupidly, I guess…

 

[Diego]

Laney "Toney" Iommi Treblemaster IC-Boost:

Dark Esbat Boost - PedalPCB.com

Compare to Black Country Customs TI-Boost

www.pedalpcb.com

Iommi's signature Black Sabbath tone — Rangemaster-style treble booster with a Laney Supergroup amp — was the goal of Catalinbread when designing the Sabbra Cadabra:

Sabbath Distortion - PedalPCB.com

Compare to Catalinbread Sabbra Cadabra

www.pedalpcb.com

There are a few other vendors for the Sabbra circuit that you may wish to explore, see if they are better suited to your needs: Aion, ELS, GPCB... maybe a few more.



There are similarities, from what I've read, with the Sunn T circuit, with PCBs such as ELS' enabling either circuit to be build (Supergroup or Sunn T). ELS no longer offers the Super Trouper PCB, but the SUPER TROUPER BUILD DOC PDF gives you the schematic to adapt to another PCB or produce a vero/perf/PCB layout of your own.


Since you're interested specifically in copping Tony Iommi tones and the SuperGroup, I would suggest including that in the thread title, you might get better more-targeted hits from people in the know.

Thanks for that resource!
You are right, that would be catchier, but actually I want to built a preamp in the ballpark of those vintage amps and since I found out the Supergroup is very very close and i am a Sabbath fan I want to build the Laney

 

[Feral Feline]

Thanks for that resource!
You are right, that would be catchier, but actually I want to built a preamp in the ballpark of those vintage amps and since I found out the Supergroup is very very close and i am a Sabbath fan I want to build the Laney

Maybe re-read all of my post, follow the links, ELS in particular.

 

[Diego]

the tweed bassman was based on an example amplifier circuit in RCA's tube manuals. the jtm was copied from that bassman then the superlead plexi added the treble peaker to the "bright" channel and the supergroup and model t are based off of that.

oversimplified history aside, I wasn't aware the super trooper pcb was discontinued but I do happen to have a space pcb.

That is some nice insight!

 

[Diego]

Thanks for the heads-up, and sorry if I missed something, it’s getting late here

 

[Diego]

Hey,

I was away for a bit, so sorry for the late reply.
I had a proper look at the Super Trouper docs and decided change a few component values on the Super Bass side of the Catalinbread DLS since it is very close to the Supergroup anyways.


Also, thanks @ICTRock if that was an offer to send the PCB! Really appreciate it, but I’m in Europe so shipping would probably be a bit much.

Cheers!

 

[Locrian99]

Laney made a 30 watt supergroup semi-recently, the LA30BL. They deliberately used an underpowered output transformer to produce subharmonic 'ghost' tones, which is part of the sound

I have one of these amps and can confirm that it weighs far less than a typical 30 watt tube head and that it produces subharmonics

If that's the effect you mean then it might be necessary to saturate a mini transformer and see what happens?

I know Thorpy uses a transformer in his Scarlett Tunic pedal, which is an emulation of a Selmer Treble & Bass front end, so that could be a good place to start in terms of topology

The Iommi sound is a modified rangemaster pushing the supergroup, you can probably get close by pushing a JTM style pedal with a treble booster. There might even be a circuit that combines these two things already

Isnt this kind of what the sabbra cadabra is?

Edit: need to read whole
Thread not just the first couple posts before commenting….

 

[Diego]

@Locrian99 I am just being specific for no good reason at this point

I'm done with the little mod now.
In the end, I decided to change the Super Lead side to the Sunn T specs because the globally shared values seemed a bit too off for the Super Lead. I also thought about using the trims from the Trouper to get a good bias — do you think this is necessary?

I used the Super Trouper from Effects Layouts and SG schematic from Ico van Diemen / Dr.Tube as a reference to adjust the parts in the PedalPCB Covert. To be honest, I'm not sure at all if this is correct. I got quite confused — especially with the parts I took from the Laney schematic.

*Sorry, as @ICTRock said after this post: all parts numbers reference the Covert schematic

Global Changes
R2 (Trouper R2/R5) - 68k
R8 (Trouper TRIM3) - 100k or Trim e.g. 75k+50k trimmer

Laney Supergroup Side
R3 (Trouper R6) - 1.5k
R5 (Trouper TRIM2) - 100k or Trim
R10 (Laney R8) - 1.5k
C11 (Laney Schematic C8) - 22µF

Sunn Model T Side
R4 (Trouper R6) - 680
C4 (Trouper C3) - 220µ
C19 (Trouper C2) - 470p

 

[ICTRock]

to clarify, all parts numbers reference the covert schematic
re: 33K input resistor (R2) ... this is a common pedal trick in that people don't want to complicate an amp in a box pedal when the amp has high and a low input jacks. both amp input jacks have a 68K resistor, but one jack puts those resistors in parallel, dropping the resistance closer to 33K. fwiw the model t doesn't have high and low inputs and it would be 68K regardless.

there aren't trimmers on the covert for good reason. you don't bias mu-amps like you would single jfet stages. with this in mind, your changes in R3, R4, R5, and R10 are incorrect.

the treble peaker resistor (R8) is 470K in all those amps. the capacitor (C8) varies per amp.
R20 and C19 are a switch change in the covert between the normal and bass channels. your change likely doesn't do what you think it does.

 

[Diego]

Thank you!

1. This makes sense, but I thought the Hi Bass input would be the way to go, so I don't loose signal and have the full frequency range. Did you commonly use the Lo-input with those amps or did I misundersand the schematic and your answer? The High bass input resistance is 68k, isn't it?

2. Ok, I did not know this, I have to look at the differences between mu-amp and cascaded gain stages topology

3. Apparently I did correlate the resistor R8 wrong: is it not the R7 in the Laney schematic (100kΩ)?
4. You dont think it works to have the Laney on one channel and the Sunn (or as close as possible considering some changes effect both sides) on the other side?

 

[ICTRock]

1. you're supposed to decide based on the guitar type ... 68K would be preferred for humbuckers, the parallel 68K (33K) input for single coils.
2. sure but hold that thought.
3. covert R8 is R15 on the super group preamp schematic.
4. this comes down to what you want. do you want the covert to have a singular voicing or an ability to switch between two?

the stock form of the covert switches between super lead and super bass which are drastically different. the super bass is close enough to a model t that you could leave all the super bass parts values in place and not be terribly far off. now you need to solve for changing the super lead settings to laney supergroup settings.

C3 would probably need to be socketed and try something like 2u2, 4u7, 10u, and 22u to see which you like best. I'd socket C8 as well just to see if lowering it to 220p like the supergroup makes the model t side too dark.

now you're left with whether you want different tone stacks. the laney and model t have the same values so you can just accept that C13 will be 270p and R15 will be 56K and that the switch position will not change the tone stack

now here's the rub ... the covert has more gain than the super lead, super bass, model t, or supergroup would have. it's actually much closer to the cascaded gain of the master volume marshall. that's the big difference between mu amps and individual jfet stages.

 

[spi]

Laney "Toney" Iommi Treblemaster IC-Boost:

Dark Esbat Boost - PedalPCB.com

Compare to Black Country Customs TI-Boost

www.pedalpcb.com

This pedal is basically a clone of the TC Elec Spark Boost.

From what I can gather, Iommi was apparently a Spark Boost user (according the TC web site), and somehow Laney got Iommi to endorse their clone of it.

It's definitely not an amp simulator, but it is a nice boost pedal.