Peavey Rockmaster pre mods

[Enzo]

I missed something. Weighs a ton? The little one-space rack mount preamp???

[silentrage]

I think he means the rockmaster head, which is a 120w(?).
I would hazard a guess it's some form of rockmaster preamp and a classic 120 poweramp slapped together, but that's purely speculating.

[Joey Voltage]

I missed something. Weighs a ton? The little one-space rack mount preamp???

:LOL:, Yeah, I'm Talking about the heads they produced, which share nearly identical circuitry IIRC. They kinda looked like airport Trams, and weighed a ton

[rockon1]

The Ultra's sound just right to me. The Rockmaster pre is hit or miss depending on my mood. Sometimes it just sounds too hard -not warm like the Ultra. Bob

[Enzo]

Oh I own an old Rock Master head, but I don;t see much similarity in the preamps. The Rockmaster pre sure doesn;t have that pump control. The OP said Rockmaster pre.

[Joey Voltage]

oh no not the older rockmaster head, which probably weighs a ton too!, I'm talking about the rockmaster pre, and the older Ultra, which share very similar preamp topologies.

[rockon1]

oh no not the older rockmaster head, which probably weighs a ton too!, I'm talking about the rockmaster pre, and the older Ultra, which share very similar preamp topologies.

Something fairly simple then must be responsible for making them sound night and day. One day I'll get back to it. Bob

[Joey Voltage]

Something fairly simple then must be responsible for making them sound night and day. One day I'll get back to it. Bob

Well for one, one is only a Preamp, and therefore influenced by whatever external PA you would be using, whereas the other is mated to a PA, that may have been voiced to work with it. This alone will account for a lot of difference. the only component difference between them IIRC is that the rockpro pre had a 150K RP for the the second stage, and a 100K RP for the third, whereas the the first series Ultra had these swapped around. Otherwise they are pretty identical.

[garyhb]

Fizz in Rockmaster 120 watt head

Hi
re fizz & weird vibrato

Thanks guys for these posts - helps a lot.

I've owned an RM 120 watt head head for 20 years and it's steadily gotten more fizzy during overdrive. I'm running it with 2 power valves pulled, through the main out into a Celestion Sidewinder (150w @ 8 ohms). It also makes a strange, slow, vibrato effect especially noticeable on lower notes. I recently changed all the valves to JJ Teslas which gave a little more gain but the fizz n vibrato remains.

Would you have any clues to these problems?

Any help is greatly appreciated.

Gary

[Enzo]

Hi Gary, welcome to the forum.

May I suggest you start a new thread for your amp? You will get better response than tacking on the end of a 38 post thread about a different amp.


You might explore power supply caps here.

[garyhb]

Fizz

Hi Enzo

Thanks for the reply. Will do.

regards

Gary

[Jazz P Bass]

Tone Stack

Duncan has a nice tone stack calculator.
TSC

[fuzznut]

The rockmaster lives again! I had one sitting in my attic for 10 years. I recently pulled it out of there, and fired it up (with a Peavey classic 50/50 amp and 4x12 x-pattern V30s & G12H30s). I was then immediately reminded why it's been in the attic: it has this certain midrange peak that is very annoying after a couple of minutes, and no matter what you do, you can't dial it out. I was about to stow it away again, but then I remembered something about my marshall JMP-1 when I was poking around in there and modding it. In the JMP-1, there is a low pass filter after the distortion circuit. I remember removing it, just to see, and it sounded like dookie without it. I went hmmm, I wonder if the rockmaster would sound better with a low pass filter in there. So I found a suitable spot, across R400 with a .0047 cap, and... WOW!!! What a difference!! That annoying peak is gone, and the sound is much more even, and fuller. Between the edge control an the presence control on the power amp, the highs are much nicer now and not fizzy.
So whoever has a rockmaster, I suggest trying this. The .0047 cap is not written in stone, it depends on your gear, but I found that for me the annoying midrange starts leaving at .0022, and above .001 I have to compensate the HF rolloff too much with the edge control. Try it!!

BTW, I only use crunch and ultra with the gain pulled. With the gain not pulled, the circuit uses negative feedback to reduce gain, and to me it sounds less lively, although a bit fatter, than the pulled gain, true cascaded circuit.

[tedmich]

Bravo! Empirical method at its best!

[garyhb]

Hi Fuzznut,

I take it you're talking about the preamp and not the 120w head?

garyb