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I did a search and was a bit surprised I didn't find anything on amp burn-in on the forum, so I apologize if I'm duplicating a thread. Just thought I'd share my experience though the burn-in process.
I received my brand-spankin' new MA1s Saturday afternoon (woohoo!). I loaded up the tubes and plugged in the amps to cook about 16 hours overnight in standby. Ralph suggested 24 - 72 hours in stand by, so I cut it short, but I was impatient and the tubes looked good and stable.
Early Sunday morning I installed the amps in my system. No drama. Good. The music came softly to life (wife was still sleeping) and sounded, well, ok. (More about that in a bit) After 30-60 min I muted the preamp and flipped the middle meter switches into the "down" position (1 watt full scale) to adjust the DC offset. The meters on both amps jumped up to about half scale. I twisted the pot to minimize the needle's reading. If I went too far the needle started to climb back up, so I left the pot where the needle was at its lowest point.
I took the pre off mute and the music (and meters) sprung to life. I flipped the middle switch into the up position so as not to peg it when I applied more than a watt of power.
The sound...well, it didn't sound bad, but it didn't sound like my beloved M60s either. The increased dynamics were immediately apparent. Everything sounded much louder. There was also an edge. The music sounded like music--certainly no nasty distortion or coloration--but nothing like the effortless midrange I'd come to expect with the M60s.
A day later they sound ok, but are still missing the special sound (air, spaciousness, depth and width) I was getting from the M60s. The dynamics and power are definitely there--almost too much so as I do most of my listening while working at the computer and it's hard to find just the right low volume with the extra gain stage of the MA1. Not sure if the lack of air and emotion is the burn in, tubes, or amp/speaker combo.
Two days in and things are starting to sound more familiar and musical. There is more air, more spaciousness. Instruments are sounding more natural.
Ralph tells me it takes a couple hundred hours for the amps to hit their stride. I believe it. I'll update this as the sound evolves. Of course once it stabilizes I'll be itching to install NOS 6SN7s instead of the Chinese driver tubes.
Follow Ups:
We think break-in has mostly to do with the filter capacitors used in the amp or preamp. As they form up, they become more effective over a wider range of frequencies and they seem to be more efficient. I say this because over about 6 months or so its possible to measure a slight increase in power supply voltage. I don't think power supply voltage is the whole story but it is an indication that the caps have improved their operation.
This break-in is very consistent and its been independently reported to us many times and with nearly the same descriptions of the changes they hear. I might be convinced that its expectation bias or something similar were it not for the fact that we hear it too and also measure changes.
Ralph,
Thanks for weighing in. I used to be skeptical, but I've heard sonics change over time too much to not be a believer now. I suspect the dielectric changes as you mention. I am still amazed how much things change, though.
Evan
After 72 hours of 24 hr/day operation the amps are definitely starting to come alive with the bloom and body I loved in the M60s. Looking forward to them getting even better over the next week!
Another big step forward (well, actually back as in less forward presentation and deeper and wider soundstage) overnight. This process definitely makes me appreciate audio reviewers' ability to describe changes. While I've heard pretty amazing changes (improvements) over the past 96 hours I find it really hard to describe. The best analogy I can come up with is going from a really good 70s mid-fi stereo, to a good 80s hi-end system over the first 72 hours. The system always sounded good, just not great like I know AtmaSphere (and the rest of my system) can.
At 96 hours the soundstage depth, width, and height is starting to appear. The instruments are rounding out. Maybe this is microdynamics and detail, I'm not sure, but the system is clearly more emotionally moving today than it was yesterday. The music is fuller, and the musicians have moved back further into the soundstage.
It makes me excited to think what further improvements to expect, because at this point the system with stock tubes and 100 hours to go on burn in exceeds what I was getting with the M60s and NOS driver tubes.
I had a little "pop" yesterday out of the right channel--maybe a gassy tube, maybe a slight arc-over based on my experience with the M60s. I checked bias of both amps and the left channel needle was still below zero and at the minima, the right channel had crept up a little bit and took a slight adjustment of the pot to bring back below zero. Both meters are rock solid below zero this morning so things have stabilized again.
The MA-1s after 120 hours have significantly exceeded the M60s across the board: tone, dynamics, space, air, soundstage size, slam, drive, PRAT, bla bla bla. Now I'm grinning! This is what I was hoping for with the upgrade to MA-1s. And I'm still running stock tubes.
Good to hear Evan! I would think that having the 60's as a reference, provides an even better relative comparison of the burn-in process - - with a like, but sonically static baseline.
Hopefully the new speakers - - when they arrive - - will provide for even greater smiles and superlatives.
-Mike
Thanks Mike! I'm sure the new speakers will further add to it!
We were out of town for the weekend, so only ~14 hours overnight. Amps continue to improve. Adjectives like "luscious" "juicy" "gripping" come to mind. I find myself paying more attention to the music playing softly while I'm working at the computer.
After 150 hours of burn in I decided to call it good enough and plugged in my collection of NOS 6SN7s. I put KenRad VT231 pair in the most critical spots closest to the meter (left V1a?), Sylvania VT231s in the 2nd most critical spots (right V1b?), and Sylvania Chrome Dome GTA/B in the remaining 3 spots. Wow the music definitely livened up without brashness, grit, or glare. I'm definitely looking forward to trying full sets of KenRad VT-231s and 5692s. The Sylvania GTAs/Bs will do well in other spots.
Swapped in 5692s for VT-231s and I like them a bit better I think. I've only listened a couple hours at this point, but the music just seems more gripping with the 5692s.
I just realized I left out a couple steps if anyone cares.
I started with a single pair of KenRad VT-231s in V1a--sound better than the Chinese 6AS7GTA in V1a.
I installed 3 Sylvania VT-231s into V1b, V1c, and V2 and a Sylvania 6SN7GTB in V4. Better sound yet. Listened for a couple weeks. Life was good.
Heard short ~1 second static burst in one channel. Tapped on the VT-231s and the pair in V2 were microphonic although they were dead silent and sounded good (when there was no static burst). Used that as an excuse to try out the 5692s, so one pair at a time I swapped 5692s for VT-231s.
None of these changes were earth-shattering. The burn in process was the biggest change, followed by swapping in NOS 6SN7s for the Chinese stock tubes. The difference between VT-231s and 5692 and 6SN7GTs is much subtler--I can be happy with either.
The RCA 5692 was once the "cat's pajamas" among 6SN7 substitutes, but it lost favor over time. I used them in my MFA Luminescence back in the 90s, and then in my MP1. I think I also used them as driver tubes in my MA240 amplifiers, once upon a time. I grew to prefer either the KenRad 6SN7GT/VT231 (black glass) or the RCA 6SN7GT gray glass type, over the 5692. But the 5692 may be less prone to microphonics than most 6SN7s, due to its special sturdier internal construction, as you experienced. In the circlotron output stage of my MP1, I use Brimars.
Lew,
Thanks. I just Googled Brimar--$300@ for used tubes!!! They make the Russian 1548s seem downright reasonable. Pretty daunting especially when 6 are needed at a min.
Evan
I bought a gaggle of Brimar 6SN7GTY, I think, for reasonable bucks but that was probably 20 years ago. I have no idea what the "Y" indicates. Mine have a brown base and clear glass.
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