What Audio Research power amps have you owned or admired?

[naturephoto1]

It’s all about reaching thermal equilibrium. The more components you have and the more mass you have, the longer it will take to reach it. The D-250 is a monster amp with lots of parts (take a look at that power supply schematic for instance) so it doesn’t surprise me that it would take longer to warm up than the average component.

However, all gear that I have ever owned (tube or SS) sounds better after it has been on for several hours and has been playing music during the warm-up time. This is where a music server comes in handy. I never turn off SS gear and I hit the random button on the music server and let it crank out tunes for two hours before I go down to listen. I do hate doing that with tube gear, specially tube power amps because you are eating up tube life. And for a D-250, that’s no trivial matter. It wasn’t trivial with my Jadis Defy 7 MKII either.

I know that Nelson Pass indicates that my First Watt M2 SS power amp sounds good right after the initial slow start up, but sounds its best after I believe 30 minutes or more once all of the Class A parts have gotten warm/hot.

Rich

 

[microstrip]

(...) And it isn't like the amp sounds bad; it's just that one starts to get more of everything on the recording esp. space, harmonics and body.

Myles,
Excellent and true remark. cj tube amplifier does not sound bad from cold, but spaciousness only comes after the first recording.
Old Audio Research amplifiers took longer to warm up and sometimes sounded edgy immediately after power on. The fantastic Classic 150 sounded thin at power and took more than one hour to warm up. As one friend of mine once said - it starts sounding good when it is time to go to bed! But it drove its Sonus Faber Extrema's better than anything else.

 

[jadis]

As one friend of mine once said - it starts sounding good when it is time to go to bed! But it drove its Sonus Faber Extrema's better than anything else.

That's why I listen mostly early in the morning.

 

[tdh888]

Myles,
Excellent and true remark. cj tube amplifier does not sound bad from cold, but spaciousness only comes after the first recording.
Old Audio Research amplifiers took longer to warm up and sometimes sounded edgy immediately after power on. The fantastic Classic 150 sounded thin at power and took more than one hour to warm up. As one friend of mine once said - it starts sounding good when it is time to go to bed! But it drove its Sonus Faber Extrema's better than anything else.

I agree w/ you microstrip the Classic 150 really takes some time to warm up. By the way I' ve noticed my old ARC equipment if I use it daily around 3 hours per day the warm up time becomes shorter. in about 30 mins or so the sound is around 90 of its full potential%.

 

[DonH50]

Not sure how we got onto warmup times... While as thermionic devices tubes take longer to warm up than SS, it happens to both, and is a very complex process depending upon virtually every aspect of the circuit and the signals going through it.

My memory is that it took my D79 quite a while to "warm up", as did my SP3a1. IIRC, the preamp's output took a good 5 - 10 minutes to stabilize, and I always waited at least half an hour before making any measurements. An hour? Dunno' either way...

 

[jadis]

By the way I' ve noticed my old ARC equipment if I use it daily around 3 hours per day the warm up time becomes shorter. in about 30 mins or so the sound is around 90 of its full potential%.

I have that same observation. In my case, I noticed when I play the system daily like for 3 days straight or more, the sound just is fantastic compared to having a day or 2 break in between. Specially after a 1 week break of not playing the system, the first day after that sounds terrible.

 

[microstrip]

Not sure how we got onto warmup times... While as thermionic devices tubes take longer to warm up than SS, it happens to both, and is a very complex process depending upon virtually every aspect of the circuit and the signals going through it.

My memory is that it took my D79 quite a while to "warm up", as did my SP3a1. IIRC, the preamp's output took a good 5 - 10 minutes to stabilize, and I always waited at least half an hour before making any measurements. An hour? Dunno' either way...

Don,

Do you remember what were the changes in measurements between the 5-10 minutes and the half an hour delay? I have tried to measure differences but with my setup - 24bits 192Khz EMU tracker could not detect any variation in THD and noise.

 

[DonH50]

Gain (transconductance) increased rapidly during that initial few minutes, then slowly reached its final (slightly higher) value sometime after that. If I took more exact measurements I do not recall. The other thing that changed was the bias circuit; the zeners would exhibit less dynamic resistance as they warmed up and the op point would shift slightly. THD dropped slightly, and IIRC noise actually went up a hair but would be higher initially, then drop and rise very slowly to just a little higher value as gain came up. The preamp had a slow d.c. offset that would move around a bit before gradually dying off after the first 5 - 10 minutes. Again IIRC, the amp exhibited much less change than the preamp, but it had much more supply regulation and better bias circuits.

Most SS electronics change very little after the first few seconds, I believe due to a combination of better (albeit more complex) bias circuits and higher feedback that results in higher temperature stability. Both THD/IMD and noise tended to go down for SS circuits, but the warm-up was seconds instead of minutes. However, some of the big SS amps and a few preamps would take a little longer; these tended to run "hot" (higher current and thus temperature) and their device gain would increase and output impedance decrease over the first few minutes. Changes after a few minutes tended to be very small.

HTH - Don

 

[microstrip]

Gain (transconductance) increased rapidly during that initial few minutes, then slowly reached its final (slightly higher) value sometime after that. If I took more exact measurements I do not recall. The other thing that changed was the bias circuit; the zeners would exhibit less dynamic resistance as they warmed up and the op point would shift slightly. THD dropped slightly, and IIRC noise actually went up a hair but would be higher initially, then drop and rise very slowly to just a little higher value as gain came up. The preamp had a slow d.c. offset that would move around a bit before gradually dying off after the first 5 - 10 minutes. Again IIRC, the amp exhibited much less change than the preamp, but it had much more supply regulation and better bias circuits.

Most SS electronics change very little after the first few seconds, I believe due to a combination of better (albeit more complex) bias circuits and higher feedback that results in higher temperature stability. Both THD/IMD and noise tended to go down for SS circuits, but the warm-up was seconds instead of minutes. However, some of the big SS amps and a few preamps would take a little longer; these tended to run "hot" (higher current and thus temperature) and their device gain would increase and output impedance decrease over the first few minutes. Changes after a few minutes tended to be very small.

HTH - Don

Don,
As you say, measured differences are minimal - much less than if for example you change the tubes of the devices, as tolerances in transconductance and plate resistance between tubes of the same type are reasonably large. But the differences in sound after a long warm-up are really big, of much higher magnitude than what we get by swapping tubes. Should we conclude that the differences are due to the heating of the passive elements?

The effect is particularly difficult to understand in very simple circuits, such as the cj top preamplifiers - the active circuit is just a composite triode made with several triodes in parallel, and a very simple regulated solid state supply. All built with military grade components and their special Teflon capacitors.

Even manufacturers known for their reluctance to accept "audiophile" components and magic report warmup - I attach a few lines from a Benchmark high quality microphone preamplifier.

 

[DonH50]

To be clear: measured differences in most SS audio equipment was minimal after the first few minutes; more significant changes in tube equipment was observed, though the audibiity of a spur moving from -70 dBc to -80 dBc can be debated.

My SP3a1 had abut the simplest circuit and longest warm-up period of any equipment I have owned. I attribute that to the simplicity; no active bias control, low feedback etc. As a result, the thing would drift significantly over time (and other things, natch). Simpler is not always better... And yes, everything in the case shifts over temperature, and passive components frequently affect the operating point of the active comonents. Extreme precision applications are very challenging; the characteristics of the wires and printed-circuit boards also change, for example. I designed a 16-bit DAC and had to figure out a way to keep the tempco of the on-chip wiring out of the picture. Precision lab equipment, such as the mW/mmW generators and spectrum/network analyzers used in my previous work, would often include the requirement of 8 to 24 hours of on time before using to allow the oscillators and amplifiers to stabilize.

Noise caused by d.c. biasing of capacitors is a different effect, related to traps and fields, not thermionics, IIRC.

All IMO - Don

 

[karma]

HI All,
Concerning warm up, I have a theory. The greatest thermal mass that must reach temperature stability are the output tranformers. On the D250 these are huge. It's very hard for me to imagine that the smaller components such as resistors, capacitors, diodes, etc., aren't ready to go at full performance after, say, 15 minutes. They should be fully up to temperature.

Tubes have very little thermal mass. On a good tube tester, they settle out in a matter of minutes.

What's left? The output transformers, that's what. Also, in the D250, the transformers are not in the direct air flow of the four fans. So, they would not get the full benefit of the heat produced by the 6550's much less the general heat produced by the power supply. They receive their heart from simple radiation from the output tubes and only on one side at that. Of course, they do have intermally generated heat but that is small potatoes. Ultimately, it's the intermally generated heat that does bring the transformers up to temperature. Maybe that's why the warm up period on all these amplifiers is so long.

I have often wondered what would happen if a person installed small electriic heaters over the tranformers with a thermostat and timer control. This might allow the transformers to come up to temperature much faster but then would switch off after some predetermined time, say 1/2 hour. There is no reasonable way to redirect the fan air flow over the transformers so there is no help there.

I see a whole new tweak market here. You know, transformer heaters complete with tip toes, detachable power cords, fancy finishes, precision thermostats and timers, and cat proof. How could it miss???

If the VPI Brick could make it as a "must have" (yes, I have bricks too!!) audiophile item, why not a "Precision" transformer heater?

Sparky

 

[DonH50]

Hmmm... Anything is possible, but I suspect other things, like components around (and in the chassis beneath) the tubes that heat up due to the heat from the tubes. Convection can be slow, and it can take a while for everything to reach final thermal equilibrium.

However, I am sure the tweak market is there regardless...

 

[karma]

Hmmm... Anything is possible, but I suspect other things, like components around (and in the chassis beneath) the tubes that heat up due to the heat from the tubes. Convection can be slow, and it can take a while for everything to reach final thermal equilibrium.

However, I am sure the tweak market is there regardless...

HI Don,
Yes, I understand your argument. And you may well be right. This is the main reason I have never tried the transformer heater experiment. However, the more I think about it, the more it makes some sense to me primarilly because of the transformers large thermal mass. I wish I had some multichannel thermocouple test equipment so I could monitor various points on the intrerior of the amp to determne the rate of heat flow. This would take some of the guess work out of my speculations. It would be a large step forward to fix the warm up problem.

But as a tweak I think this has some potential. It makes at least as much sense as some of the snake oil out there. You know, I hope, I'm not really serious....unless it works.

Sparky

 

[jadis]

Talking about transformers, and specifically ARC power transformers, I have noticed in my old VS110 and this new VS115 amp that the power transformer runs really hot to the touch specially after 1 and half hours and onwards, while the 2 output transformers are just mildly warm. There is a huge disparity in temperature here even at the 2 hour point. I worry sometimes if this may cause the power transformer too much stress or may cause it to break down someday. I really wanted to call ARC at times but they might think this is a trivial question.

 

[MylesBAstor]

Talking about transformers, and specifically ARC power transformers, I have noticed in my old VS110 and this new VS115 amp that the power transformer runs really hot to the touch specially after 1 and half hours and onwards, while the 2 output transformers are just mildly warm. There is a huge disparity in temperature here even at the 2 hour point. I worry sometimes if this may cause the power transformer too much stress or may cause it to break down someday. I really wanted to call ARC at times but they might think this is a trivial question.

Thing is it's more than just the simple act of warming up or being on. I can leave an amplifier on for hours and it still needs an hour of music to sound it's best. So if it was simply bringing the output transformer up to "operating" temp, then leaving an amplifier on for an hour would be sufficient and it isn't. Unless playing cause a further increase in operating temp????

 

[jadis]

Thing is it's more than just the simple act of warming up or being on. I can leave an amplifier on for hours and it still needs an hour of music to sound it's best. So if it was simply bringing the output transformer up to "operating" temp, then leaving an amplifier on for an hour would be sufficient and it isn't. Unless playing cause a further increase in operating temp????

I usually don't turn on just to warm up idly, Myles. I play with music from the opening minute. So the heat of the power tranny and the output trannies gradually builds up. But, as I noticed, at near the 2 hour mark and up, with music playing from the beginning, it's the power tranny only that really heat up on its sides, like you can't touch it for more than 10 seconds. Really hot. Now I've heard from a friend here who played his Jadis 200 one Sunday for the whole day, like morning to evening, and the result was, the power trannies broke. Which gives me a little worry bout my ARC amp as to how hot the trannies can be without harm getting in its way. I mean at the point where you cannot touch the power amp, can you still run it for 5 more hours of music? This is what I have been wanting to ask the ARC technical guys.

 

[DonH50]

@Sparky: A relatively inexpensive DMM with a thermocouple would do the trick -- you could get several and just plug them in. You could also get one of the little IR handhelds, but they are harder to isolate...

@jadis: Call them! They are nice folk... Hot transformers can cause problems, including a loss of efficiency in the magnetic core, but too hot to touch may not be too hot for the transformer. Recall 85 degC is the upper industrial temp rating for most components, or about 185 degF -- that would probably burn you.

 

[jadis]

@jadis: Call them! They are nice folk... Hot transformers can cause problems, including a loss of efficiency in the magnetic core, but too hot to touch may not be too hot for the transformer. Recall 85 degC is the upper industrial temp rating for most components, or about 185 degF -- that would probably burn you.

Thanks for the info, Don. I will.

 

[karma]

Thing is it's more than just the simple act of warming up or being on. I can leave an amplifier on for hours and it still needs an hour of music to sound it's best. So if it was simply bringing the output transformer up to "operating" temp, then leaving an amplifier on for an hour would be sufficient and it isn't. Unless playing cause a further increase in operating temp????

HI Miles,
Certainly, running a signal (music) through the amp causes a temperature increase. With no signal, the there is just basically the bias current running through the output tubes and through the output transformers, none. And the high voltage portion of the power supply is just idling. This is the lowest power state the amplifier can be in.

As soon as a signal, AC (audio) is present, it causes current to pass through the output tubes, the ouput transformers and the power supply supplies the necessary current to the tubes. Heat definitely increases. As for the remainder of the amp, the small signal tubes and circuits and the low voltage power supplies, a present audio signal makes little difference because they are low power circuits and produce little heat no matter what the signal condition is.

With some amp topographies, the driver tube for the output tubes is also a current hog. This is true for the D250.

So, your observation makes total sense. I too always have music running through my amp as it warms up.

Sparky

 

[karma]

Talking about transformers, and specifically ARC power transformers, I have noticed in my old VS110 and this new VS115 amp that the power transformer runs really hot to the touch specially after 1 and half hours and onwards, while the 2 output transformers are just mildly warm. There is a huge disparity in temperature here even at the 2 hour point. I worry sometimes if this may cause the power transformer too much stress or may cause it to break down someday. I really wanted to call ARC at times but they might think this is a trivial question.

HI jadis,
I would not hesitate calling ARC about your observation. It could be an important one. I know I'm a question asker and sometimes I ask dumb questions. But if you don't know the answer, there really is no such thing as a dumb question. And any smart person would think no less of you.

Call them then report back to us.

Thanks, Sparky