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Old 22nd February 2011, 08:14 AM   #1
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Join Date: Dec 2010
Default Marshall Valvestate 8100 mods, upgrades.

Hey guys. I've had some mods done to this head so far, most of which are found on this forum. I do think that it has great potential, and I'm even considering selling my modded JSX head because of how good this thing is starting to sound. There are a few things I'm considering doing, and I'd like to hear some input and recommendations.

http://www.diyaudio.com/forums/music...onal-mods.html

and also

http://indyguitarist.com/forum/index.php?topic=1531.0

This link above is one of my next moves. I did his other mod and it turned out great, much more bass and thickness going on now.

My next moves are:

1. Upgrade all the crap plastic jacks with something better quality.

2. Increase the wattage of the amp, upgrade PSU. Is this possible? As you all know, one of the weaknesses of solid state amps is that the louder you turn them up, the worse they sound (eventually), from the lack of solid state headroom. I think it would be cool to bump the wattage up to about 200-300W to get some more headroom.

3. Replace all IC's with IC sockets, so I can test which ones sound the best or stack them. Any suggestions on which JFET/IC's to use? The ones in there are TL071CP by Motorola, and a few others. I've seen the OPA2604AP used in the Openhaus and other distortion pedals, and then another one the guy in that link mentions is good. Would it be worth it to upgrade these? Will there be impedance issues or certain values I need to choose?

4. Install a choke. Because why not? lol. They're relatively inexpensive and if they can make it sound better, awesome.

5. Upgrade reverb tank to accutronics. This I've already tested and confirmed works.

6. Upgrade capacitors. I have an orange drop capacitor in there or two, and I know it's a huge myth about just changing caps to make it sound amazing. Obviously once I'm done most things, I would be tweaking the values anyway, so what would be the most reliable and best sounding option for capacitors?

7. Install F.R.E.D.'s in the rectifier section. I know this is also another hyped up thing, but one thing that is lacking from this amp is response. Obviously since it's a solid state amp, it's not going to be that great, but the response could be somewhat quicker.

8. The 12AX7 tube. I've heard that this barely does anything, although there is a significant tone change when different tubes are used. Any suggestions on how to modify this circuit? How much voltage is going to it right now? From what I've gathered, you need a full load of like 200V to make it actually do something.

BTW, I'm getting help from my tech friend with this, which is why I'm a bit clueless, haha. I just want to generate some more ideas than what we've come up with. I know a lot of it might sound costly/a lot of work for a solid state amp, but it sounds great right now and it just needs some more tweaks to sound amazing!
Attached Files
File Type: pdf Marshall valvestate80_80w_.pdf (176.8 KB, 164 views)

Last edited by Xingjitsu; 22nd February 2011 at 08:41 AM.
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Old 22nd February 2011, 11:49 AM   #2
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Join Date: Jan 2011
The tubes seems to be just in the signal path for flavor just to add tube character, maybe you can try removing diodes and see how much distortion actually you are getting from the tubes. also one of the triodes is been used as a buffer maybe the configuration can be changed to achive much more gain.

good luck
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Old 22nd February 2011, 04:12 PM   #3
teemuk is offline teemuk  Finland
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Join Date: Nov 2004
Location: Suomi, Finland
Quote:
Originally Posted by Xingjitsu View Post
1. Upgrade all the crap plastic jacks with something better quality.
The jacks may be plastic but they surely ain't crap. Marshall actually uses very high quality jacks.

Quote:
2. Increase the wattage of the amp, upgrade PSU. Is this possible?
Everything's possible but it will be a tremendous amount of work involving extensive modifications to the existing board designs. You basically need to completely rebuild the power amp and the power supply.

Quote:
3. Replace all IC's with IC sockets, so I can test which ones sound the best or stack them.
I wouldn't bother with that since there are diminishing returns. Unless the current ICs are extremely noisy you won't really gain much by changing them. Sockets may develop intermittency and can actually make the ICs work worse. They are not omitted from typical commercial designs for cost cutting reasons only. Mostly they are only good for prototyping or for ICs that actually benefit from subbing (e.g. EPROM sub to update to a newer software). A solder is way more solid connection.

Quote:
4. Install a choke. Because why not?
Because solid-state designs hardly benefit from one, whereas one can actually make them perform worse.

Quote:
lol. They're relatively inexpensive and if they can make it sound better, awesome.
Yeah, lol. For SS amps drawing much higher currents at much lower voltages you need a big one, at which point they are not relatively inexpensive. Nope, it's not a part that you can just throw in an expect it makes everything sound better.
Quote:
5. Upgrade reverb tank to accutronics. This I've already tested and confirmed works.
This may be a good idea if the replacement tank matches the specs of the current one.
Quote:
6. Upgrade capacitors. I have an orange drop capacitor in there or two, and I know it's a huge myth about just changing caps to make it sound amazing.
I wouldn't really bother so much with type and brand than with actual capacitance values.

Quote:
7. Install F.R.E.D.'s in the rectifier section. I know this is also another hyped up thing, but one thing that is lacking from this amp is response. Obviously since it's a solid state amp, it's not going to be that great, but the response could be somewhat quicker.
Nope. A slight chance is that it could make the PS less noisy but all bets are off even in that. For sure they won't affect "response".

Quote:
8. The 12AX7 tube. I've heard that this barely does anything...
Yet another stupid myth you commonly hear about hybrid amps. In reality the tube has a vital function at the distortion channel.

Personally, I think the 8100 is one of the greatest solid-state amps ever made by Marshall and pretty much has a legendary status as an amp being capable of creating the modern extreme death/black metal tone (e.g. It was Chuck Schuldinger's choice of amp). Honestly, I don't know why to mod such design. If it doesn't work for you then you more likely need another amp than bunch of mods that provide only diminshing returns, if not worse.

Last edited by teemuk; 22nd February 2011 at 04:16 PM.
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Old 23rd March 2011, 10:43 PM   #4
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Join Date: Feb 2008
Location: Jackson,michigan
I was never aware that there were any mods that could possibly make it sound any better than it already does.
I had mine for ten years before some jerk stole it. jer
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Old 30th April 2011, 04:40 AM   #5
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Join Date: Nov 2007
Location: Dallas
I was just troubleshooting a Valvestate. And had a scope on the tube because that
channel was giving very low volume. Well, the tube wasn't the issue, lots of signal
coming out the cathode follower, just nothing after the tonestack...

I could see clearly the grid of V1a forward conducting when overdriven by the opamp
that preceded it. And was of "single ended" even (octave based) harmonic distortion,
distinct from odd (fifths based) harmonics when a push-pull stage is overdriven...

V1b is just a cathode follower and adds little distortion, but does load V1a's plate
slightly, and set a well defined impedance into the tonestack. It also safely drops
the plate DC voltage of V1a down to something reasonable for the next stage.

Oh, what plate voltages did I measure??? I can't recall. Maybe was 145V?
I don't remember if that value was actual B+, or merely seen at V1a's plate.
Was GrooveTube (Sovtek) 12AX7 I found inside, don't recall the fine print...

Last edited by kenpeter; 30th April 2011 at 04:48 AM.
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Old 8th March 2012, 12:35 PM   #6
Nelec is offline Nelec  Australia
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Join Date: Feb 2012
Hi, Firstly I apologise for posting in such an old post .... but I have been looking all over the place for some details on the 8080 gain mod. Does anyone have a working link or the relevant info that used to be contained at:
http://indyguitarist.com/forum/index.php?topic=1531.0

thanks, and again, sorry for the timecapsule like bump .....
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