Help with peavey rockmaster mods?

Can anyone here help me out a bit with my rockmaster mod?
I tried a whole bunch of mods to see what differences they'd make, including:


C4 from .047uF to .47uF
C5 from 820pf to 2200pf
C17 from .47uF to 1uF
These are supposed to allow more lowend through.


R33 from 22kohm to 10kohm
R34 from 10kohm to 5kohm
These raised the preamp's voltage from 290v to 320v

R3, R13, R32 from 100k to 200k
These are supposed to cause harder clipping

After this the bass got too muddy so I restored the caps back to stock with the exception of C5.
Also played around with lowering R20 and R24, which seem to be V2's plate resistors, it made the distortion smoother but was too loose.

I did turn it on to hear how it sounds after each part swap, but somewhere in the process I noticed the bass was getting out of hand.
I remember before the mods with the boost pushed in the bass is kinda big and loose, and when pulled it's tight but a bit hollow. Now I seem to have made the pulled bass as big and loose as the "pushed-in" bass, and the current pushed-in bass is just overwhelming, flubby and not very playable.

Also there seems to be barely any distortion now withthe knob pushed in, and about 3-4 times the distortion with it pulled, I don't remember the difference being this big.

I've since restored each part to stock to see if it helps, but strangely enough I couldn't get the stock sound.

Right now I just have the R3,13,33,34 and C5 mods in place, the rest are all back to stock, and I've ran out of ideas.

Any help appreciated, the schematic is here.
http://www.schematicheaven.com/newamps/ ... preamp.pdf

anyone?

Other than putting each of the mods back to stock one by one until it's completely stock if need be, I'm not sure. Since I have never had enough $ to send any amp anywhere to have it modded (though I'd like to have JerryP do something to one of my amps someday) and have never successfully modded any amp, myself, my 'mods' for the Rockmaster include leaving the boost pushed in and boosting with a tubescreamer instead while adding a bit more meat to the sound with an eq between the pre and power amp -- except when downtuning a fair bit, then I still use the eq but use the Rockmaster's pull boost instead of a tubescreamer. I also hate the crunch channel and just use the guitar's volume to get a range of gain.

Anyway, sorry to hear about the problem, and hopefully you'll get it resolved.

I had a rockmaster and never was sure about what I would change in its tone to actually draw a mod for that
maybe some extra brightness?
what exactly are you looking for?

the rockmaster schematic is a pain in the ass to read
it's easier to draw a mod with the XXX schematic and then find the specific parts in the rockmaster scheme

Thanks for the input guys, guess I'll restore EVERYTHING to stock and see if that fixes it. I'm just worried there might be a bad connection somewhere that's causin the excess lowend and I'll never find it.

I heard from heath on HC that changing the coupling caps to something bigger will move the low end cutoff down a bit so that there's more bass and less of a cocked-wah sound, but after fiddlin around it indeed made the bass bigger but did nothin for the wah sound,
In fact I think it made it worse as now it sounds a bit like an autowah with the pick attack having this filtered sound.
The "wah" sound is really prominent when playing higher notes, it sounds to be somewhere in the upper mids, I'm guessing around 700-900hz area, does anyone know how what I could play around with to affect this frequency range?

I wish I had technical knowledge on that to help, but I can at least bump the thread.

Also, the way I have mine set up with the tubescreamer as a boost instead of using the onboard boost (while tuning to E or Eb) as well as adding some lower mids and just a bit of highs for clarity with a Boss GE-7 between the pre and power amp in that somewhat thick but still cutting range, and it doesn't seem to have much a funky midrange. Admittedly, I hadn't been able to play the Rockmaster in a mix in a long time, only being able to crank it up by itself, and I'm using an old Carvin V412 with Celestion g12m70's and would like to try it at gigging volumes in a mix as well as switching out to a cab with V30's. Anyway, sorry again I'm no technical help, but good luck.

I'll take a look at the schematics later and think of something
the wah character of the rockmaster is related to its whole tone shaping structure
the gain stages are very bass heavy, like a fender, so they cut a lot of bass between stages, keeping mostly mids
also, there's no cathode follower stage, that usually sucks some midrange and gives more tube warmth without adding actual distortion
hi gain amps without CF are usually more dry sounding, very dense on the midrange andmore articulated, but less open sounding
I think the active eq tends to sound middy too
it's a pain in the ass to fight against an amps nature

@Rushtallica
Yeah dude, I tried boosting with my modded TS7, but I think it's totally the wrong boost for this preamp. Like Ericsabbath said, the preamp sounds really dense in the mid range, that ratty sound sounds like a spike in the upper mids, and the TS7 seems to boost the midrange, so it doesn't help at all. Besides I currently have a bug for tinkering, so I'll try until I run out of patience, then I might just get a nice transparent boost pedal and be done with it,

ericsabbath":2ih2ww4d said:

I'll take a look at the schematics later and think of something
the wah character of the rockmaster is related to its whole tone shaping structure
the gain stages are very bass heavy, like a fender, so they cut a lot of bass between stages, keeping mostly mids
also, there's no cathode follower stage, that usually sucks some midrange and gives more tube warmth without adding actual distortion
hi gain amps without CF are usually more dry sounding, very dense on the midrange andmore articulated, but less open sounding
I think the active eq tends to sound middy too
it's a pain in the ass to fight against an amps nature

Click to expand...

Thanks eric, please take a look at the schematics if you've got some time to kill.
I'm thinking about looking at the JSX or XXX preamp section as suggested before to see if I can see some changes peavey deemed fit to implement.
As it stands right all I know about is from the valve wizard guide, so just the plate load voltage, the cathode bypass, and the coupling caps.

I learned from poking around that plate voltage really affects the amount of gain and the coupling cabs affect how much bass, and that's about it.

If you (or anyone else) think of something I really need to know when it comes to tinkering with this preamp please throw it my way.

silentrage":31op6vmk said:

@Rushtallica
Yeah dude, I tried boosting with my modded TS7, but I think it's totally the wrong boost for this preamp. Like Ericsabbath said, the preamp sounds really dense in the mid range, that ratty sound sounds like a spike in the upper mids, and the TS7 seems to boost the midrange, so it doesn't help at all. Besides I currently have a bug for tinkering, so I'll try until I run out of patience, then I might just get a nice transparent boost pedal and be done with it,

Click to expand...

I hear you and wouldn't do it without the outboard eq pedal set the way I have it. I wish I had your patience for tinkering, though. It's cool to hear what things you've tried and the results you've had so far.

Sure dude, the coupling caps, namely C4,5,17 seem to be cutting off the low end, I found out that if I replace one of these with a much bigger value, the bass gets ALLL whooly, but it also becomes really huge sounding and with more character in your chugs, especially on the low B.
I think a good value cap here can give you bigger, fuller bass that's still usable.

Stock I think with the gain knob pushed in the bass is just right, it's nice and full, and tight enough for good rhythm tones, but pulled it gets kinda hollow but really really tight and percussive.
I might try to get it so that the bass is nice, full and still defined when pulled, and I"ll just stick to this mode for its added percussiveness.

V1 obviously has the most influence on all the channels.
I replaced the plate load resistor here with 75k at one point, the stock bein 150k, and it took away most of the gain, the ultra channel is now a crunch channel, it also sounds a lot looser and softer, but it sounded fuller. I think this would be pretty ideal for classic rock stuff or just clean playing, but it wasn't my thing.

V2 doesn't have nearly as much influence it seems, but I could swear at one point I did something to it to make a big difference in tone, so I"ll have to experiment a lot more here.

And like I said, that ratty wah sound is the only real problem I have with the preamp right now, the rest are added bonus if I can get them, but really don't matter if I can't.

Edit: just wanna throw out a disclaimer that I'm a total noob who don't really know anything about tube amps so take what I say with a spork-ful of salt.

Anyone? ^^

I've restored most stuff to stock and it's sounding pretty much OK now, but that ratty noise is my main goal now, it's really annoying me.

Any idea where in the signal chain I can tweak to get rid of it?

try 2200p again on C5 (just like the triple xxx and jsx), but don't mess with C4
C11 seems to be leaking high end before the gain pot, so you can use a lower value
it's 470p, but only 100p would be fine to cut fizz without turning it nasal
C14 is 1n, but you can try higher values to cut less bass after the 2nd stage (I'd try 4.7n)
I'd reduce the first stage cathode cap too
C17 is boosting a lot of upper mids, so a higher value (1u is fine) would make it a bit less middy
a much bigger value like 10u or 22u would start putting it into ENGL ballpark
the 530/Fire/Powerball amps are very close to the rockmaster/ultra/xxx circuit (and pretty much like the bogner triple giant sharp channel), except for that 2nd gain stage, more gain from the next stage and a regular and very scooped passive EQ
so the difference is all in the midrange shaping

ericsabbath":1og8wqxm said:

try 2200p again on C5 (just like the triple xxx and jsx), but don't mess with C4
C11 seems to be leaking high end before the gain pot, so you can use a lower value
it's 470p, but only 100p would be fine to cut fizz without turning it nasal
C14 is 1n, but you can try higher values to cut less bass after the 2nd stage (I'd try 4.7n)
I'd reduce the first stage cathode cap too
C17 is boosting a lot of upper mids, so a higher value (1u is fine) would make it a bit less middy
a much bigger value like 10u or 22u would start putting it into ENGL ballpark
the 530/Fire/Powerball amps are very close to the rockmaster/ultra/xxx circuit (and pretty much like the bogner triple giant sharp channel), except for that 2nd gain stage, more gain from the next stage and a regular and very scooped passive EQ
so the difference is all in the midrange shaping

Click to expand...

THANKS!!!
I'm off to experiment!!!

Wow, awesome info!


I hate to ask anything extra, but although I think adding a chorus in the clean's fx loop is probably a help, are there any other ideas?

hmmm,
I'm tryin to find some filtering components that operate on around the mids and treble range to try and find the culprit to the harsh highs and ratty mids.



If I understand this correctly, this acts like a High Pass, effectly as a RC circuit of 820pf Cap and 110k Resistor. This should be cutting off the low end at 1447.6hz. If I want a more open sound, should I be using a smaller cap to raise this cutoff or a much bigger cap to drop this out of the way of the midrange?
I calculated the cutoff freq with a 2200pf here and it would move it to 658hz, that seems like it would potentially cause some weird midranginess.

Of course my amp design knowledge is shoddy at best so someone please take a look and tell me if I'm on the right track.

silentrage":1gzaut7m said:

hmmm,
I'm tryin to find some filtering components that operate on around the mids and treble range to try and find the culprit to the harsh highs and ratty mids.

If I understand this correctly, this acts like a High Pass, effectly as a RC circuit of 820pf Cap and 110k Resistor. This should be cutting off the low end at 1447.6hz. If I want a more open sound, should I be using a smaller cap to raise this cutoff or a much bigger cap to drop this out of the way of the midrange?
I calculated the cutoff freq with a 2200pf here and it would move it to 658hz, that seems like it would potentially cause some weird midranginess.

Of course my amp design knowledge is shoddy at best so someone please take a look and tell me if I'm on the right track.

Click to expand...

those resistors are in parallel leaking signal to the ground, just like the gain pot
not really working as a "bright cap" (well, not in my limited understanding)
some amps have even lower values, like a 470p in series, and that's partially responsible for the wah mids

Hmm, I'm thinking those 2 parallel 200k resistors are equivalent to 1 100k resistor, so the above diagram should be equivalent to the high pass filter presented here, http://www.muzique.com/schem/filter.htm
but I'm not sure, that's why I ask.

^ Man you're spot on about the design of the amp.
Today I was playing around with the amp and I tried turning off the bass and treble knobs completely, the sound really didn't change that much, a tad less fizzy on the top, and a tad less full on the bottom, but the character didn't change at ALL. It seems the amp is mostly just mids, and I've further narrowed down my problems.

1. The pick attack range is REALLY weird, it seems the sound gets squished right at the pickattack range.

2. There's a layer of obnoxious hair on the pick range, actually on everythin but most noticably on the picking, and it's only noticable with the pull gain engaged. I have trouble understandin the schematic, I'm not sure what the inductors and rectifiers are doing to the pull gain circuit, and I'm not sure how to read the relays, IE. where in the signal chain does the switch take the signal too, and where does it feed it back.

If anyone can help me with that area, I would be super ecstatic, in fact I would probably paypal you some "consultation fees" if you could nail this for me.

Edit: I seem to have noticed a problem with my RM.
Ever since I got it, I would get this crackling noise if I turn any of the active EQs past maybe 2-3 oclock, it sounds like solidstate clipping of some kind. I thought it was just a design flaw, but I asked a forumite on ss.org if his was behavin this way and he said it wasn't.
Any guesses as to what could be the cause of it?

Mine doesn't seem to do that. I wonder if it could have to do with any of the fx loop jacks, though in my experience when they're messed up it effects the sound regardless of where the eq's set, making it thin and low volume, possibly crackly sometimes, and other times even totally cut out.

S... auto wah sound, how do I get rid of it.