Marshall SV20 Hand Wired Heads With Some Mods

  • Thread starter Thread starter xenrelic
  • Start date Start date
xenrelic said:


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.
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Thanks.
Short clip but it does sound good.
 
xenrelic said:
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?
 
MikeViking said:
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?
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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.
 
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