Rogue Audio M-120 vs M-150

Brad,

I got them yesterday.
I wish I could make a true comparison of before and after, but I made a major change while the amps where gone by adding a wonderful Audio Note DAC.

Like yours, mine came with EH6550's, instead of the KT88's I expected. I have a set of those tubes already,and I can't say I cared for them. Rather dry sound. So I will be sending them back.

Well, I guess I can say it's better since the 6550's didn't sound as bad as I remember them from before. They do run slightly cooler than the 120's (keeping in mind my odd experienced with the 120's as I mentioned above). The biasing is not difficult, even with the do-hickeys placed in the back of the amp they can still be biased through the front.

I found that after all the tubes were biased it was wise to check them all and do another round of adjustments.

Did yours have a lose screw in the front-middle of the case? It seems the face plates don't have the threading for a screw there, but they just dropped the screw in anyway.

I am using GE 6550's now, and I love the sound. But like I said, I can't really do "before/after" with any degree of credibility.

One thing that I really like, is the ultralinear-triode switching on the fly. It was pain before, having to turn off the amps and take out the tubes. That's something else that's different.

Before, UL was clearly better for me, but now it's not so obvious. I'll have to play around with that for a few days before I can decide. Early impression is that the bass seems a touch fuller in UL, but in triode the mids and overall textures appear to be slightly more detailed.

KP

I gave up on the E34L’s, the high end just wasn’t coming around at all and remained extremely rolled off. On songs that previously had very subtle sounds in the high end they completely disappeared. One Dire Straits song, “One of my Friends” where the percussionist is using the brushes very lightly, even that was barely noticeable whereas with the 6550’s it is very distinct and natural sounding. It’s the most drastic change I’ve ever heard from changing tube types. It was as if I had added a tone control and turned the treble all the way down. Maybe if my system had been overly bright before these tubes would have been OK, but my system is not overly bright sounding. I had the E34L’s biased to 39ma as per Mark Walkers instructions. I tried biasing them to 35ma but there was no change. I tried biasing them to 40ma and still no change in the sound but the plates were just starting to glow a dull red so I think that was pushing them a little too hard. I may have to try a set of GE6550’s, although I’m quite pleased with the sound of the EH6550’s, so I may just keep using them. I’m sure there is room for improvement but quite honestly I’m not sure what kind of changes would sound better to me.

I got the KT88’s a couple of days ago but unfortunately one of them didn’t survive the trip so I’m waiting for a replacement. It will be interesting to see if there is any noticeable difference in the sound.

The center front screw on the top cover is not loose on mine, but then I opted to keep the M-120 face plates. I didn’t like the huge “ROGUE AUDIO” engraved on the M-150 face plates plus it saved me a little money. They gave me a great deal on a set of RCA clear top 12AU7’s in exchange for keeping the old face plates.

I guess I had later model M-120’s than you did, the triode/ultra linear switch was on the back of mine just like the M-150’s. I’ve always switched them on the fly without any problems, much easier to compare the sound that way.

Enjoy your new amps, I know I am!

Brad

One correction to my previous post: I had the E34L's biased to 30ma, not 39ma...

Brad