White noise or "shushiness"

[overnight]

I just got the RM100C used for recording mostly. I bought it sight unseen. After testing an RM50, a friend mentioned I'd like the RM100 even more but I didn't have the bread. So then one comes my way for a reasonable price, I jump and here it is.

I like the amp, some of the tones are truly sweet. I feel like a minority in that I'm NOT playing metal or even hard rock most of the time with this amp. I'm recoding with it and I wanted the vintage tones, sometimes with high gain, sometimes not.

My big complaint is this...

There seems to be a kind of white noise or general "shshshsh"-iness in the high frequencies when playing with higher gain, particularly with humbuckers, though I do get it with the Strat as well. It just seems to kill the focus and clarity of the tone and really becomes pronounced when recording with a good mic and preamp. I have the Plexi, JTM, Top Boost, Tweed and Clean and all do it but the Clean. The Plexi, Tweed and Clean were all modified by the previous owner to have slower gain ramping over-all but they still have the noisiness.

Is this anything anyone here knows about? I don't see too many people talking about it. Is it the output tubes? Biasing? Are there additional mods I can perform on the modules?

Also, the bottom-end is pretty loose in general. Is there a way to tighten it up?

Any help much appreciated.

 

[trendkill1168]

I can tell you this man, make sure you bias your power tubes properly. I had my RM100 for a couple of months and was not happy with the tones I was getting. Get yourself a digital multimeter from Radio Shack, they cost about $19.00 and check your bias settings on the 2 DC setting. Mine were all out of whack and at different settings. I am running my E34L's at 38 millivolts and the amp sounds completely different now. Something that is really cheap to do and takes about 5 minutes but can make all the difference in the world.

 

[skyscraper]

I am also getting the same thing here, but only when I use delay in the effects loop. I have it currently in the paraell loop and tried it in the serial, still cant get the delay to react like it should, dont know why. When I plug the guitar direct through the sl module with out delay, I achieve a pure dry distored sound. When I add the delay through the loop, the paraelle seems to handle it the best but I get this annoying shissssssssss sound when playing leads. I was thinking it was my cab I have a Marshall 1960lead but its like the delay is repeting the shhhhhsssss sound insted of the guitar signal. Any help here please let me know immediatley. Currently the only module im using is the SL+ and Im building it slowly. Im using the rm100s. Thanks folks.......

 

[overnight]

It's been a while but I thought I'd revisit this thread. I checked the Bias and they seem normal. They're Ruby EL34(BSTR)'s biased at 33mV's... which is right in the middle. What I find strange is that I hear some peoples' clips and I don't hear it so much. I actually tried to record and a high gain arpegiation this weekend and it was SO ill-defined and and white-noisy I had to scrap the track and record with a different amp with a pedal. Very very disappointing.

I'm starting to think maybe it's the modules, that I must have all early modules. Thing is, the guy that sold me the amp had modded three of them for lower gain. I have very little confidence in my own abilities to mod a curcuit board as my soldering skills are retarded to begin with. I would consider shipping them off tp be modded if you have a suggestion of where.

If anyone has ideas, some common element I must be missing, I'd really appreciate the post! Thanks

 

[overnight]

I wanted to revisit this thread again to make it known that I've found a solution, for the most part, to the problem I was having with the amp so many months ago. I swapped out the preamp tubes, the 12AX7's, with 5751's and it has gone a long way to alleviating the white noise. 5751's run at about 60% of the power that 12AX7's and I'm guessing that some of the RM units' preamp circuit just overloads more easily than on others.

The fan is another issue. I still can do no real open back recording because of it but if I keep the amp's volume high, put a pad on the mic I'm recording with it isn't such an issue for front face recording.

Anyway, there you have it. Thanks.