Hiwatt Super Hi 50 Marshall mod

  • Thread starter Thread starter RedPlated
  • Start date Start date
RedPlated said:
4th stage is in. And switching relay. Sounds killer on 4 stages. It’s nice having the Marshall power section, especially the presence circuit.

A lot going on around that tube. I haven’t even changed the stock grounding in the amp yet but it’s really quiet, even on 4 stages. It’s cool that you don’t have to add a tube, too.

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lol looks fun :) You work fast

Isn't part of the special sauce in this circuit is the Hiwatt PI? So while it can technically work with three tubes, I think a bit of something is lost with only three. The Hiwatt Presence control is also part of what makes them unique.
 
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FourT6and2 said:
lol looks fun :) You work fast

Isn't part of the special sauce in this circuit is the Hiwatt PI? So while it can technically work with three tubes, I think a bit of something is lost with only three. The Hiwatt Presence control is also part of what makes them unique.
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Definitely sounds different. Hiwatt is fizzier in the top end. Especially with presence at noon or more. Overall, the Marshall is tighter.

I’d say I probably prefer this circuit with the Marshall. It still sounds unique compared to other Marshall mods and has plenty of gain. A lot, actually. But the structure is tighter, more clarity and it doesn’t need as much volume to sound good.

That being said, I don’t think I’ll be selling the Hiwatt. It does have a certain growl at high volumes that’s addictive. And takes boosts like a champ.
 
RedPlated said:
Definitely sounds different. Hiwatt is fizzier in the top end. Especially with presence at noon or more. Overall, the Marshall is tighter.

I’d say I probably prefer this circuit with the Marshall. It still sounds unique compared to other Marshall mods and has plenty of gain. A lot, actually. But the structure is tighter, more clarity and it doesn’t need as much volume to sound good.

That being said, I don’t think I’ll be selling the Hiwatt. It does have a certain growl at high volumes that’s addictive. And takes boosts like a champ.
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Could be interesting to play with the presence cap value in the Hiwatt, add a depth control, and tweak the NFB value slightly. Might help bring the fizz down a bit and tighten 'er up.

Oh, so are you using the Super Hi values in the PI or you're running the regular Marshall PI? The Super Hi has a sort of SLO voicing going on with the 0.047uF PI couplers and lower value grid leak resistors. So it's passing more bass and kinda flubby. But swapping those for the typical Marshall values of 0.022uF and 220K would certainly tighten things up in the Super Hi amp itself. Then you could add a real depth control to bring back in some low end thump. Add a 47pF fizz cap, and play with the NFB resistor value and it might really address some of the issues with the circuit.
 
FourT6and2 said:
Could be interesting to play with the presence cap value in the Hiwatt, add a depth control, and tweak the NFB value slightly. Might help bring the fizz down a bit and tighten 'er up.

Oh, so are you using the Super Hi values in the PI or you're running the regular Marshall PI? The Super Hi has a sort of SLO voicing going on with the 0.047uF PI couplers and lower value grid leak resistors. So it's passing more bass and kinda flubby. But swapping those for the typical Marshall values of 0.022uF and 220K would certainly tighten things up in the Super Hi amp itself. Then you could add a real depth control to bring back in some low end thump. Add a 47pF fizz cap, and play with the NFB resistor value and it might really address some of the issues with the circuit.
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I’ve got all Marshall power section in the Marshall. .022/ 220k, 82k NFB, .1uF/5k presence, 220k/.0047 depth, etc…

In the Super Hi, I still want to do 220k bias splitters. I’ll change the power tube grids to 5.6k. I think it has 47pf fizz cap from factory.

In the Marshall I’m going to try .047 PI couplers to add a tad more low end. Still with 220k bias splitters.

I’ve been playing the Marshall at low bedroom volumes and it sounds so good. Can’t do that with the Hiwatt.
 
RedPlated said:
That would be SICK!

Mojotone has the black face plates for a JMP. And Sourmash will make an all black head shell.

Damn. Now I’m thinking I might have to do this too!
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Well you have a very willing customer number 1 right here hahaha
 
This one sounds amazing, a little darker than your MOAB clips, bit more grunt? Sounds like it would work really well for more modern type metal
 
Sounds great! Are the changes all based on the schematic online or were there some differences from your actual amp?
 
Exo-metal said:
Can u share a clip of the 4th stage yet Jeremy?
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Yeah I’ll make one tomorrow. I took a day off from amps today haha.

I‘ll finish tweaking it and make a clip.

I also have some 220uF ARS radial filter caps coming tomorrow. I’ll try those for the mains supply in the Marshall, similar to the Hiwatt.
 
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FourT6and2 said:
I kinda want to build one now from a DR504 clone. Would be a nice change of pace from Joses.
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I asked Nik if he could do something like this these were hard to come by and expensive. Unfortunately the only information I found was the layout that you started.
 
ClintN667 said:
I asked Nik if he could do something like this these were hard to come by and expensive. Unfortunately the only information I found was the layout that you started.
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The schematic on SLOclone would be all he needs. It’s pretty much spot on.
 
That 3 stage design reminds me of Zakk wyldes 89 live tone. That pinch harmonic squalk I’ve never heard in a typical Marshall modded or not. I’ve always heard his stuff was stock but they’ve always been hotter than a stock JCM2203 in my experience. Maybe he was playing hiwatt influenced modded Marshall’s?
 
RedPlated said:
The schematic on SLOclone would be all he needs. It’s pretty much spot on.
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I still haven't gone through it part by part, but I've found a handful of errors. I don't have the amp anymore so I can't confirm it 100%. But the Chinese one has a wrong B+ dropper value, wrong PI plate values, fizz cap is shown in schematic but there wasn't one in my amp and there usually isn't one in Hiwatts. I think there are a few other discrepancies too. I'll sit down with it and try to find the errors in a few days, unless you want to
 
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