Rogue Audio M-120 vs M-150

Brad,
thank you for the excellent follow-up.

I'm expecting (hey, do I look radiant or what?) the amps back soon. They've been gone for three weeks.

It'd be interesting to see how the KT88's match against the JAN GE 6550A's.

I'd also like to try some el34's in there eventually.

I tried running the amps in triode, but I found them too mushy and lacking impact so I've been running them in ultralinear. I will try he new and improved 150's in triode and see how that works out. Can youth change the mode while the amps are on?

Funny thing with the 120's, I first got them they would run hot has h-e-double-hockey-sticks, then I switched from the EH to Svetlana tubes, and the heat dropped by at least 75%. It was so bad at first, I had to keep the AC on and the door open! Heck, standing with bare feet on the floor close to the amps would feel hot, and you would not want to put your hand anywhere too close to the tubes.

I have since tried the EH tubes, and they ran fine without too much heat. Not sure what changed to cause that difference. Maybe they had to "break in" first dot dot dot question mark.

KP

KP;

The wait is not much fun, is it? But is sure makes you appreciate them more when you finally get them back...

The 6550’s I’ve been using are the original tubes supplied with the M-120’s. They are Electro-Harmonix 6550EH. They have seen about 18 months of almost daily use and still test very good so I feel like they are holding up very well. The KT88’s will be the same brand.

I had planned to try some EL34’s but I found so many positive reviews about the new JJ E34L’s that I decided to try them instead.

Interesting comment you make about running your amps in triode mode, I always thought mine sounded their best in triode mode, maybe due to the speakers I use. My speakers are a little different than the norm, they consist of a pair of upright powered subs sitting under a separate pair of “mid/high” array’s. The mid/high array’s are internally high pass filtered at 80hz and the subs are driven with the speaker level inputs via jumpers from the mid/high array’s, so the tube amps don’t have to deliver any current from about 80hz on down. I love this setup, the bass is so effortless and natural sounding, nothing flabby about it. The -3db frequency on the subs is 26hz and they don’t drop all the way off until 18hz. When called upon to do so this setup will shake the room with bass so deep it’s barely audible, something I don’t normally expect from tubed amps. It seems to give me the best of both worlds (of course the sub amps are SS but driven by the tube amps).

I have no idea why you M-120’s started running cooler, mine never did. I live in Phoenix and in the triple digit temps I simply couldn’t keep my living room cooled off while running the amps. Once the temp got up past 85° or so in my living room I just couldn’t take it anymore and would shut the stereo down. In the winter I never needed the heater while the stereo was on and in fact had to take steps to keep the room cool enough, even when the outside temp dropped into the 40’s or lower (which isn’t often here).

I hope you will post your impressions when you get the amps back, I look forward to reading it.

Brad

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