Peavey Rockmaster pre mods

[rockon1]

Been doing some digging on some mods to warm up the Peavey Rockmaster pre. Some guys have been replacing C14 and C17 using a .0022uF in place of C14 and a 1.0uF in C17. My question is the C17 looks like standard cap(at least one Im familiar with) and C14 looks like a square white block? The schematic labels it as .001R630 I just need a bit of guidance as to exactly what type of cap to use. Any help much appreciated! Bob

http://www.schematicheaven.com/newam...ter_preamp.pdf



........

[Enzo]

They are just caps, you would use the same type caps you would for any tube amp. The white rectangles are just film caps. Shaped like that, they could if they wanted stuff a ton of them on a board in a small space. A lot more than they could with orange drops or something.

You don;t have to use square ones, though you could easily find them in the values you want at Mouser or Allied or wherever.

.001R630 - .001uf, radial leads, 630v. Radial leads means they come out all on one side. As opposed to axial leads which come out opposite ends.

PV also will use small ceramic caps. They look like resistors, except they are often a pale green color.

[rockon1]

Thanks Enzo. Cant seem to find .0022 R630 at Mouser. Of coarse I may be looking in the wrong place. I have located some .0022 600v orange drops though. Stupid question-is this cap directional? I see that the other cap I want to replace is.

(The other cap is .47A16 which I take to mean .47uf axial 16 volts.) Thanks again Bob

[Enzo]

Only the electrolytics and tantalums are polarized. We don;t call that directional.

Film caps are non-polar.

www.tubesandmore.com has both orange drops and Mallory 150s in .0022uf 600v.

Mouser had some, but in lots of 3000 or more mostly. I didn't look in Allied or Digikey, but they are prime suspect for having them.

[rockon1]

Thank you for the link. Think I'll order some from AES then. Bob

[Guitarist]

I remember spending hours and days modding mine. The lead channel is amazing thanks to the unique tone circuit. I was able to clone the Lynch Mob tone pretty well. I could never get a clear clean sound out of it though.
Good piece for a burn channel only, maybe 9.5/10.
Those caps you could find at any electronics parts store.

all the best,

[rockon1]

I remember spending hours and days modding mine. The lead channel is amazing thanks to the unique tone circuit. I was able to clone the Lynch Mob tone pretty well. I could never get a clear clean sound out of it though.
Good piece for a burn channel only, maybe 9.5/10.
Those caps you could find at any electronics parts store.

all the best,

Well I replaced the C17 with a value 1.0 uf and couldnt hear a difference-maybe a tad fizzier if thats possible? . Dont have the C14 yet so I went back to stock for now.

I popped in four Mullard long plates since Im fortunate to have about 15 of them. I also discovered plugging into the low gain and using the boost pull function (instead of the reverse). The Mullard LP's add nice low mids,clear upper mids and highs without being harsh. They also add some "bark" to the distortion. They burn channel does sound nice!



Until I understand more about what Im actually doing to the circuit I'll probably leave it alone. To that end in the pic above the C1 is C14 in the RM and C2 is C17 in the RM. From the site I got the pic from it states increasing the C2 (C17) wot result in much audible difference. That makes sense cause I didnt hear any. It also says increasing the C1 (C14 in my case) will increase bass response. Heck Im not sure if I even want to do that. Id prefer more lower mids really.
A few thoughts-
1)Decreasing the R1 will reduce gain supposedly. The pre comes with 150 K there. That might be a good mod. But should I decrease it later in the gain stages or earlier?


2)Its got a lot of high end . Perhaps a snubbing resistor or two across these resistors?

Its kind of important I only work on it as few times as possible since I dont think the ribbon cables will like being bend a lot.

Important questions-

1)If the circuit uses a polarized cap do I need to replace it with one?

2) Why is the C1 in my Rockmaster rated at such a high voltage value of 630 volts? Thanks Bob

[tedmich]

Well I replaced the C17 with a value 1.0 uf and couldnt hear a difference-maybe a tad fizzier if thats possible? . Dont have the C14 yet so I went back to stock for now.

I popped in four Mullard long plates since Im fortunate to have about 15 of them. I also discovered plugging into the low gain and using the boost pull function (instead of the reverse). The Mullard LP's add nice low mids,clear upper mids and highs without being harsh. They also add some "bark" to the distortion. They burn channel does sound nice!



Until I understand more about what Im actually doing to the circuit I'll probably leave it alone. To that end in the pic above the C1 is C14 in the RM and C2 is C17 in the RM. From the site I got the pic from it states increasing the C2 (C17) wot result in much audible difference. That makes sense cause I didnt hear any. It also says increasing the C1 (C14 in my case) will increase bass response. Heck Im not sure if I even want to do that. Id prefer more lower mids really.
A few thoughts-
1)Decreasing the R1 will reduce gain supposedly. The pre comes with 150 K there. That might be a good mod. But should I decrease it later in the gain stages or earlier?


2)Its got a lot of high end . Perhaps a snubbing resistor or two across these resistors?

Its kind of important I only work on it as few times as possible since I dont think the ribbon cables will like being bend a lot.

Important questions-

1)If the circuit uses a polarized cap do I need to replace it with one?

2) Why is the C1 in my Rockmaster rated at such a high voltage value of 630 volts? Thanks Bob

C17 is a cathode bypass cap and it can be used to add a boost at certain frequencies, the RM is very close to the Bravo, with an extra gain stage and some other changes. The C17 equivalent in the Bravo has a series resistor which can be 47k, 38k or zero ohms to ground; this attenuates the boost. A bigger cap will boost to lower frequencies; the 0.47uf will boost at >1k Hz. Valve Wizard has a nice article which helped me with this concept here:
http://www.freewebs.com/valvewizard1...Gain_Stage.pdf

best not to mess with the anode load resistors (R1); they can make things way bad fast; tweaking the cathode bypass caps gives BIG changes to tone: check the PV VTM schematic it has a TON of caps to switch in and out to dial in the tone, even with series pots to vary the boost as Mr. Wizard mentions

[rockon1]

C17 is a cathode bypass cap and it can be used to add a boost at certain frequencies, the RM is very close to the Bravo, with an extra gain stage and some other changes. The C17 equivalent in the Bravo has a series resistor which can be 47k, 38k or zero ohms to ground; this attenuates the boost. A bigger cap will boost to lower frequencies; the 0.47uf will boost at >1k Hz. Valve Wizard has a nice article which helped me with this concept here:
http://www.freewebs.com/valvewizard1...Gain_Stage.pdf

best not to mess with the anode load resistors (R1); they can make things way bad fast; tweaking the cathode bypass caps gives BIG changes to tone: check the PV VTM schematic it has a TON of caps to switch in and out to dial in the tone, even with series pots to vary the boost as Mr. Wizard mentions

Wow lot of good info! Have to go to work now but Im looking foward to reading thru the link you provided.Those ribbon cables worry me a bit so it would be nice to get it right the first (or second ) time.Thanks much! Bob

[silentrage]

I'm looking into modding the rockmaster, done a bit of reading on the valve wizard pdf, and I'm thinking about changing around the values for the cathode bypass cap and resistors, anyone got any values that works well in smoothing things out a bit? or know any similar articles on how tonestacks are designed?

[tedmich]

I'm looking into modding the rockmaster, done a bit of reading on the valve wizard pdf, and I'm thinking about changing around the values for the cathode bypass cap and resistors, anyone got any values that works well in smoothing things out a bit? or know any similar articles on how tonestacks are designed?

many mods for the rockmaster out there; Jerry at FJA Mods makes good $$ doing this and examples abound on youtube but no one says exactly what is done.

Dan S. has posted on HC a few times on his mods, but he seems to want a Fender tone (?) also he states:
"I hate to modify anything, but I feel this is worthwhile:

1. The Mid control on the clean channel EQ doesn't really work so well. As you turn it clockwise it adds more mid-bass, but keeps an overall scooped response. This is caused by a capacitor across the Mid potentiometer. Peavey used a .015uF cap (C9) there. You could simply remove it, but that will result in the mid pot turning into more of a gain control considering its 50k ohm value. Instead, I recommend replacing C9 with a smaller value, between .003uF to .005uF.

2. The effects send & main outputs' coupling caps are too small, and may act as a low cut filter. This is noticeable if the unit is plugged into products with an input impedence below 100K ohms. The result is a thin sound, which is especially noticeable on the clean channel. To prevent this replace C40 & C30 each with a 1uF 400V film cap. You may be able to get by with a 250V cap, it all depends on the cathode voltages at each location."


also Heath at HC has posted two reasonable mods (Peavey Ultra Plus mods - Harmony Central Musician Community Forums) 3/4 way down the page. He recommends coupling cap C14 (0.001uf) -> 0.0022uf, and cathode bypass cap C17(0.47uf)->1uf. Both of these would add mid/bottom to the tone, and the pull boost would not be so radically scooped. You could even add a series ~10k pot to C17 to set the pull boost level, like Valve Wizard mentions in his excellent article on cathode bypass. Look to the evolutionary descendants of the PV Ultra amps; the XXX and JSX for other reasonable changes.

Good tubes help too!

Tonestack design? You should be able to master that black art in a scant couple of decades....""There Be Dragons..." indeed

[silentrage]

Thanks, I found the other two after posting here and the Dan S mods sounds very useful.

Since the one I have is a beater anyway, I'm just gonna take valve wizard's free chapter 1 I got and try to apply it to some experimentation, and see what I find.

Safety-wise, if I keep one hand in my pocket while poking around in there I should be fine, right? If I have to ask I should probably look more into safety, haha.

Maybe I'm not using the term tonestack correctly. What I mean is I'd like to find out, say how to get the highs pot to adjust in a certain frequency range, how to get the bass pot to adjust in another range, and how this part of the circuit filters the signal with its various caps and resistors.
Is this the black art you're referring to or am I misusing the term "tonestack"?

[tedmich]

Thanks, I found the other two after posting here and the Dan S mods sounds very useful.

Since the one I have is a beater anyway, I'm just gonna take valve wizard's free chapter 1 I got and try to apply it to some experimentation, and see what I find.

Safety-wise, if I keep one hand in my pocket while poking around in there I should be fine, right? If I have to ask I should probably look more into safety, haha.

Maybe I'm not using the term tonestack correctly. What I mean is I'd like to find out, say how to get the highs pot to adjust in a certain frequency range, how to get the bass pot to adjust in another range, and how this part of the circuit filters the signal with its various caps and resistors.
Is this the black art you're referring to or am I misusing the term "tonestack"?

No, I am just daunted by tonestack (T/M/B) design, but many others here have a good knowledge of it...its not rocket science! The RM is very close to the Bravo (I have one) but has an additional tube gain stage and different tone controls:
Bravo: active +/- 15dB bass & treble, passive mid -15dB for that scooped sound.
RM: bass, treble as Bravo, Mid active notch/peak with 2 selectable push/pull freq boost points

The JSX has a fat switch in between the first two gain stages, and a variable level for the infamous dual diode "noise gate" after tube stage 3 which is active only on the clean channel.

Safety wise, just common sense helps: no work while plugged in, use caps rated at or higher than PV original voltages (~600V coupling caps, 50-100v on tone, just ~10v on cathode bypass) be careful with polarized components (electrolytic or tantalum caps, diodes) and ideally discharge the big filter caps with a resistor before doing any work, some guidance here: http://studentweb.eku.edu/justin_holton/caps_p.html
http://www.drifteramps.com/safety.html
also some great tube info here: http://www.geofex.com/
follow link to tube FAQ in top left of front page

[silentrage]

Sounds like it might be a good idea for me to check out the JSX preamp schematics to see if I can learn something from there since it's supposed to be one of the smoother peaveys.

[tedmich]

Sounds like it might be a good idea for me to check out the JSX preamp schematics to see if I can learn something from there since it's supposed to be one of the smoother peaveys.

Yes its a good evolution, very close to the XXX, both share a MUCH better FX loop than the RM/Bravo. All (but the Bravo) have schematics at schematicheaven.com

New tubes will of course be the fastest and surest bet to better tone with your RM; swapping components, even with careful planning, are much more likely to degrade (or destroy) your preamp (especially early in your modding career). Use the community here and elsewhere, plan carefully and have fun!