Attenuated SV20C

[dwagar]

I've been playing since about '64. I've never owned a non Master Volume Marshall before.

But I abolutely love how this amp sounds.

I see a lot of people compaining about how loud they are, even on the 5 watt setting, once you jumper the channels and crank it to where you want it (I run it at about 8 on hi treble and 4 on normal). I think that's because so many, like me, have never dealt with a non MV amp before.

It was too loud for band practice, too loud for a gig (we mic everything).

I have an old THD Hotplate, but I discovered a thread on the Marshall Forum (Simple Attenuator in the Workbench area), which are supposed to be quite good. I'm a hack, but I can solder and drill shit. So I thought I'd build one. Someone posted somewhere it'd be cool to have an attenuator with a footswitch for a solo boost. I contacted the fellow that designed it (JohnH, he's very helpful and very active over there), he already had a design for one and sent it to me.

So I built one that has -7dB (reactive load, always on), -7dB and -3.5dB switchable, and -3.5dB on a foot switch. It works great. Kick the footswitch in for rhythm, turn it off for solo. And to my old ears, it doesn't change the tone at all. And I can run the amp on the 20W setting, I think there's a bit more tone hiding there.

Now it's a perfect amp for me.

 

[Emiel]

A cheap attenuator with a solo boost? How cool!

I browsed through the topic on the Marshall forum, it's huge and there seem to be multiple versions of the schematic. Can you show us the latest design/schematic you ended up using?

 

[dwagar]

John has it on top of P. 97, this is the one I used

I made a couple of changes. I built the 16 ohm version, I put only one output jack on it (the SV20C has a single 10" speaker). Because the SV20 has a 5 watt setting, and because I was planning on using the amp for practices and gigs (not for home), I left the -14dB Stage out of it. I built the foot switch with -3.5dB resistors (his schematic shows it at -7 : resistors R3 and R4, I used R7 and R8), I felt that jump in volume works for me.

This schematic is, I believe, designed to handle up to 50W.

 

[dwagar]

here's a pic before I put the LED in.

 

[guitarbob123]

I have the same amp but I'm not quite so handy with soldering etc. so I bought one of the Weber MiniMass attenuators instead.

Have to say the amp is an absolute animal and perfect for what I need it to do.
I had (well, still have but it's not in the same country as me) a 100w Marshall half-stack and it was impossible to ever get it above 1.5 on the master before I'd be rattling windows and shaking walls.

I don't jumper, I just plug into the high treble 1 input, keep the high treble vol around 7, still roll the normal channel vol to 10 (it makes a slight difference somehow when it's left fully open) and then everything else is around 7 all across, gets that late 70s live Aerosmith/ACDC/Thin Lizzy/UFO sound that I love.

Love how the amp responds to dynamics and the vol/tone controls on the guitar, no extra channels or pedals required

 

[jb_abides]

Was just checking these out and also came across this recent review, enjoy.

 

[appetite4tone]

John has it on top of P. 97, this is the one I used

I made a couple of changes. I built the 16 ohm version, I put only one output jack on it (the SV20C has a single 10" speaker). Because the SV20 has a 5 watt setting, and because I was planning on using the amp for practices and gigs (not for home), I left the -14dB Stage out of it. I built the foot switch with -3.5dB resistors (his schematic shows it at -7 : resistors R3 and R4, I used R7 and R8), I felt that jump in volume works for me.

This schematic is, I believe, designed to handle up to 50W.

I was thinking of building this. I saved your schematic is there more information instruction diagrams and parts list anywhere to make this as easy as possible. It would be my first project of the sort. I have the same amp and have been wanting to start soldering modding and building so I'm reading about this stuff and purchased a soldering station.

 

[Cliff Gress]

I jumper the low input of the treble to the high normal input and plug into the low normal of my head. Then run the volumes at 3 and 9 respectively. The amp really likes a Greenback.

 

[appetite4tone]

I jumper the low input of the treble to the high normal input and plug into the low normal of my head. Then run the volumes at 3 and 9 respectively. The amp really likes a Greenback.

I have a greenback in mine to and was fiddling with the two volumes like that and felt like I was on to something so now I'll try your settings and see. Do you use the fx loop. I thought delay and univibe sounded awesome ran there. Dave Friedman was saying that the fx loop is pointless in this amp. I disagree. What do you think

 

[appetite4tone]

I have a greenback in mine to and was fiddling with the two volumes like that and felt like I was on to something so now I'll try your settings and see. Do you use the fx loop. I thought delay and univibe sounded awesome ran there. Dave Friedman was saying that the fx loop is pointless in this amp. I disagree. What do you think

I jumper the low input of the treble to the high normal input and plug into the low normal of my head. Then run the volumes at 3 and 9 respectively. The amp really likes a Greenback.

I jumper the low input of the treble to the high normal input and plug into the low normal of my head. Then run the volumes at 3 and 9 respectively. The amp really likes a Greenback.

Like this?

 

[dwagar]

I was thinking of building this. I saved your schematic is there more information instruction diagrams and parts list anywhere to make this as easy as possible. It would be my first project of the sort. I have the same amp and have been wanting to start soldering modding and building so I'm reading about this stuff and purchased a soldering station.

The thread has become a monster, but Gene has posted a layout diagram and wiring diagram. You'll just have to get a coffee and wade through it I guess.

Some of the guys are using import (China) parts from EBay or AliBaba to keep the cost down, I prefer to use what I consider better, I ordered most everything from Mouser.

 

[WillyW]

I can't play mine cranked at 20w, but I can play it cranked and attenuated, my sv20c sounds wonderful to me.

 

[Cliff Gress]

Like this?

Yes to the jumper, but the normal volume is 9 the high treble 3. Never used the fx loop.

 

[kristinaflores]

I selected a 10” Celestion V-type speaker for convenient portability without compromising on tone.
dinosaur game

 

[graybeard65]

I have an SV20C and the Weber Mini-Mass - I agree that the amp is a beast, and can cover a lot of ground -

I run it jumpered - both volumes at 2 for a sweet SRV sound, and go with 8 and 6 for a great classic rock sound with a Les Paul.

Agreed that without the attenuator, it’s stoopid loud for home use, even at 5 watts. The Weber tames the beast nicely, but does shave a little high end off. Nothing that you can’t eq a bit, or add a treble boost and problem solved.

 

[RowanButler]

Non-MV Marshalls can be a beast to tame, but it’s great that you found a solution that keeps the tone intact while making it usable at different volumes. Having a footswitchable attenuator for solo boosts is a genius idea—especially with an amp that thrives on being cranked. How does it compare to using the THD Hotplate in terms of tone transparency?

https://scaryteacheronline.com

 

[dwagar]

IMO the JohnH is a tad more transparent, but I've always been pretty happy with the Hotplate too - it has a low and a high tone switch for shaping tone.

 

[dwagar]

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[dwagar]

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[K Dub]

I have a JohnH Attenuator on top of my Marshall SV20C. A Well-Known Member on the Marshall Forum built it for me.