Marshall SV20 Hand Wired Heads With Some Mods

[Gtrshred]

The master works just a like a type 2 post phase inverter master volume, except the ground lugs actually go to ground instead of a bias splitter junction since this is a cathode biased amp design. The sound and operation of it works the same though. In the video we have the master volume on a lower volume living room setting.

Thanks.
Short clip but it does sound good.

 

[MikeViking]

If you guys dig the Marshall SV20 amp, here are a couple that were gutted and hand wired with a custom fx loop, an added post phase inverter J-taper master volume and some other mods like a dual negative feedback loop circuit switch and push pull high gain mod with a bright cap selector push pull as well. A 3H choke was added into the design to sweeten things up in the power amp.



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First time poster! I was checking out your work and I am really impressed. The standard SV20 has a 47k negative feedback resistor. I can see the resistor on the board, but then you have another resistor on the Presence control. Are these the feedback mods you noted, and if they are, what is the mod?

 

[xenrelic]

First time poster! I was checking out your work and I am really impressed. The standard SV20 has a 47k negative feedback resistor. I can see the resistor on the board, but then you have another resistor on the Presence control. Are these the feedback mods you noted, and if they are, what is the mod?

Hi Mike, The 47k is the NFB resistor and the presence I'm using is the 25k linear pot setup with a 4.7k resistor to ground and a 100nF cap, like on the JCM800. A standard JMP Super Lead 5k pot setup without the 4.7k resistor will do as well. The feedback mod adds some fixed resonance on one setting and a higher value resistor with fixed resonance on the other setting. You can play around with another 47k in series with the 47k NFB and all the way up to 280k in series if you want a really aggressive rock tone. I usually have the NFB switch feeding either the 8ohm or 16ohm tap, depending on how much clarity I need.

 

[MikeViking]

Thanks for the share. Great info

 

[JC1966]

Hey xenrelic what would just the 2 FX loop board cost? if you would sell them separate and if I got those could you send a diagram ( not good with schematics) and a parts list of what brand type parts you used. on the PTP board, I would like to build a PTP for one of these . I built a 50Watt Plexi clone and would like to have a PTP SV20H ? seeing as I can't find a way on this board to send a PM

 

[xenrelic]

There's only one fx loop board, the other is the emulated di output. If you're not good with schematics, I would recommend getting good with them before starting a project like that, as it will be necessary to determine the correct connections for the transformers and wiring. Paying someone to draw them out for you in layout form would be nearly the same amount of work as if they built the amp for you vs. just learning how to read a schematic properly and having that skill for life.

 

[JC1966]

There's only one fx loop board, the other is the emulated di output. If you're not good with schematics, I would recommend getting good with them before starting a project like that, as it will be necessary to determine the correct connections for the transformers and wiring. Paying someone to draw them out for you in layout form would be nearly the same amount of work as if they built the amp for you vs. just learning how to read a schematic properly and having that skill for life.

ok, I have already built a 50Watt Marshall Plexi clone and a 1960 slant cabinet running 4 Celestion G12T-75 speakers in Series Parallel mode, all in Purple Tolex, with just a diagram, andI have a 18watt TMB combo clone build like a old bluesbreak style started already too. I am also replacing bad 50/50 filter, bias caps, and screen grid caps, in my '72 1959 SL 100Watt head and going thru the whole board to tidy it up. and replace any bad caps and remove the DEATH CAP also. But like I said I am not good at schematics, I can use a diagram and I know electronics and go from there. I took electronics in HS and know about pedal mods, amp building, and electronics, but never learned schematics I can somewhat figure them out, but a diagram is best for me...if you already have a diagram of the way the board and the SV20 are good , if not then I guess there is no reason to make one.
But if you have a diagram let me know, if not, no worries, I will continue with my !8watt build, Thanks for responding