A question for the Ashdown RPM-1 owners.

2-Sticks · #1 11-02-2010, 11:13 AM

I have wanted one of these preamps for quite a few years now, and a couple of weeks ago I finally aquired one....YAY! I have spent the last two weeks playing around with it at home, with several different cabs, and I am really impressed. I really like just about everything this has to offer, especially the EQ.

Yesterday I decided to open it up just to see what kind of 12ax7 was in there and found a Chelmer Valve branded tube, which I would assume to be the original. My Question, has anyone experimented with different 12ax7's in the RPM? How often do these need to get changed?

The reason I ask is that I don't really like the drive past 11 oclock, it seems to get a little too compressed and a little 'mushy'. I am not actually planning in using the RPM-1 for heavy gain....so it doesn't really matter, but I am curious.

Anyone out there on TB with some insight for me?

2-Sticks · #2 11-02-2010, 11:16 AM

I forgot to mention that I did do the obligatory search and couldn't find what I was looking for.

2-Sticks · #3 11-03-2010, 09:05 AM

Really?......I find it hard to believe that no one has any input for me.

NecroticImbecil · #4 11-03-2010, 09:46 AM

It could be that these are not as popular on Talkbass as some other brands of preamps, and in a day the few that have owned them have not seen the thread. Someone may chime in with something helpful eventually.

Could also be that, like myself, those who have owned them have not changed the stock tube. I thought both of my RPM-1 units sounded fine as-is. Preamp tubes can last a long, long, longlonglong time. A blues/rock guitarist buddy loved it for guitar with the tube gain cranked, so I can see where that might be too much gain for some bassists. All I can suggest is don't turn the gain up so high that you hate the sound. I know, not helpful, but at least I've bumped your thread.

2-Sticks · #5 11-03-2010, 09:55 AM

NecroticImbecil thanks for the insight and the bump.

markorbit · #6 11-03-2010, 06:48 PM

I used to own a RPM and did open it up for a few tube changes. I don't recall the original 12AX7 being Chelmer, I think mine was either a Sovtek or Electro Harmonix.

It was one of my least favourite preamps at the time. Wish I still had it though to run through a Berg IP to see what it can really offer.

I used to keep the tube drive below 10 o clock or else things got a bit too fizzy. I didn't really like the tube drive on it.

I think in the end I preferred a Tung Sol in there but there wasn't a great deal in it. And you rarely need to worry about changing preamp tubes, it should last years.

2-Sticks · #7 11-04-2010, 09:36 AM

Thanks MarkOrbit, I appreciate your information. I am aware that most 12ax7s should last quite awhile, however I heard rumours from a local tech that these things are known to eat them up.

I was curious if the 'fizzy' drive was a symtom of this. It obviousy isn't, so thank you for that. I think I have a Tung Sol laying around here somewhere, I may just have to try it.

Thanks again.

koobie · #8 11-04-2010, 10:17 AM

I had two of them, and with each preferred the solid-state section of the RPM1 better, was tighter, more focused. What I really liked on the RPM1 was the sub-octave generator, worked pretty well with good tracking, a lot of fun to play with for funky stuff.

Preamp tubes can last from as little as a couple months to many years, it goes all over the map. If your signal has relatively low noise floor and a full response from top to bottom, the preamp tube is probably fine. As you've probably read, different brands & types of 12AX7 tubes can sometimes bring out different characteristics in a given circuit. In any case, it takes about five minutes to swap out a tube. After unplugging the unit from the wall voltage, and being very careful not to touch any of the circuitry, try subbing in a different 12AX7 tube and see how the sound changes.

no4mk1 · #9 11-18-2010, 08:47 PM

I don't have an RPM, but I do have an ABM 300 head which is basically the same pre-amp. I had a few different NOS tubes and tried them all out. I settled on an old Telefunken that sounded really good. Most of the others had that "mushy" sound you described. I think the tube really does make a difference.

Cheers,
Chris

Templar · #10 11-18-2010, 09:57 PM

I had a RPM for a few days, returned it 'cos the VU meter was DOA. However, while it was here, I did swap several vintage tubes just for kicks (Telefunken, Mullard, Bugleboy, etc.)

To be honest, in my RPM, the different tubes didn't seem to sound much different at all (unlike my 201, which brought out the subtleties of the various tubes).