Hiwatt Super Hi 50 Marshall mod

  • Thread starter Thread starter RedPlated
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FourT6and2 said:
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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Oh wow, didn’t realize all that. I used it for the 4th stage addition and verified everything with the Super Hi I have here. All was correct on the schematic.

I didn’t get into that areas you described. Good to know.

I do seriously wonder though if there have been several revisions of this amp circuit-wise.
 
glpg80 said:
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?
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He always has a super distortion in front and his JCM800 has 6550s in it.

There's a good rig rundown with him on YouTube.
 
RedPlated said:
Oh wow, didn’t realize all that. I used it for the 4th stage addition and verified everything with the Super Hi I have here. All was correct on the schematic.

I didn’t get into that areas you described. Good to know.

I do seriously wonder though if there have been several revisions of this amp circuit-wise.
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The Chinese schematic is still a mystery to me lol. Some random person posted it on SLO Clone but when I asked where he got it, no response. I know Hiwatt was planning on releasing a cheaper PCB version, so maybe made in China? But yeah... that schematic shows some odd discrepancies.

So your Hiwatt has an actual fizz cap in the PI?
 
FourT6and2 said:
The Chinese schematic is still a mystery to me lol. Some random person posted it on SLO Clone but when I asked where he got it, no response. I know Hiwatt was planning on releasing a cheaper PCB version, so maybe made in China? But yeah... that schematic shows some odd discrepancies.

So your Hiwatt has an actual fizz cap in the PI?
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I haven’t even looked for one haha. I never got that far. When I was making the preamp in the Marshall I opened up the Super High to use as verification of the schematic. Everything was spot on up to the 4th stage. I didn’t go past there in the Marshall.

I’m guessing my Super Hi doesn’t have a fizz cap. I just assumed it did because the schematic shows 47pf.

I bet you’re right. They were planning a PCB version.

I’ll check the Super High later. If it doesn’t have a fizz cap I’ll definitely try one in it. I am confident it will make an improvement. But I also don’t want to stray too far from the Hiwatt base tone.
 
I forgot about this… and this is why I’m glad I had the actual amp opened while I did this mod.

The schematic was incorrect in this spot, at least on my amp. The .01uF coupler was in series with the .047, not separated like the schematic shows.

Mine was like this, connected where the black line is. Makes the coupler like .008uF or something weird once it’s in series. But, it sounds great so I guess it’s good.

I think your layout diagram shows it the correct way.

You_Doodle_2023-10-06T00_44_23Z.jpeg
 
Do you know anything about the Leo's Music modded Hiwatts Frank Hannon is playing in this video at 03:17 ?

 
Never heard on that Leo’s mod but it sounds killer. Super bright and tight. Doesn’t sound like it’s got much low end.
 
RedPlated said:
I forgot about this… and this is why I’m glad I had the actual amp opened while I did this mod.

The schematic was incorrect in this spot, at least on my amp. The .01uF coupler was in series with the .047, not separated like the schematic shows.

Mine was like this, connected where the black line is. Makes the coupler like .008uF or something weird once it’s in series. But, it sounds great so I guess it’s good.

I think your layout diagram shows it the correct way.

View attachment 254480
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That's a good catch! You should mention that in the thread on the other forum so the new schematic gets updated
 
Any updates or progress? Hoping to hear it against the moab.
 
Exo-metal said:
Any updates or progress? Hoping to hear it against the moab.
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Yeah, I increased the mains filtering to 220uF and did a couple other tweaks. It sounds even better. The filtering helped tighten it a bit more.

I’ve been super busy but I’ll try to make a clip at some point.
 
Hmmm you know I've got 1959HW on the way that I may try this on if I get ambitious... I think I actually have 220uF 500v cans here somewhere too...

So you're just running the master straight into the Marshall PI?
 
technomancer said:
Hmmm you know I've got 1959HW on the way that I may try this on if I get ambitious... I think I actually have 220uF 500v cans here somewhere too...

So you're just running the master straight into the Marshall PI?
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Yep, master > loop > PI. I’m using one of my own active loops. Not the Hiwatt passive setup.

Some like to go treble > loop > master > PI but I prefer the former.

Stock Marshall power section other than .047 output caps and 220uF mains filters.
 
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RedPlated said:
Yep, master > loop > PI.

Some like to go treble > loop > master > PI but I prefer the former.

Stock Marshall power section other than .047 output caps and 220uF mains filters.
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Thanks! Have to sit down tonight and figure out if I want to do this, a Langner, or some kind of Jose on this one... should be fun
 
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