I have noticed that there is a very noticeable delay in my DA-60 Jadis integrated before it will utter even a muted distorted mumble never mind sound good. The time always seems too long. There is no doubt that the automatic biasing mechanism which I see as being a single voltage delivered to the filaments of each tube and does not employ any noticeable feedback regulation. This type of biasing is not true bias but an automatic voltage level delivery system circuit. The true turn it on and watch the amps bias based on the output for any given input level can be seen in Woolcotts and Audio Valvle for instance. The Slow/soft start my amps go through is merely a protection circuit as best I can tell, to ensure that electrical inrush is muted and it must go through a slow, stepped up, variac like start. My other amps Cyber 800 Consonance monoblocks again declare it a self biasing amps but the tubes this time warm up from that ice cold distorted sound to tolerable in less than a minute the Jadis is about 2 minutes. I am not going to touch the optimal time to good sound. In terms of plain old listenable sonics how fast do your amps get up and smell the coffee. (this is not a comment on slew rate)
Philjolet - it depends what kind of semiconductor is limiting slew rate of an amp. If it's bipolar transistor it will gest faster with temperarture - opposite for MOS.
I read an article (several years ago) that talked about slew rate and amplifier temperatures. Basicly it said that a cold amp has a higher slew rate and the sound takes on an edge but as it warms up the slew rates gets slower and the sound is smoother and closer to what the manufacturer intended.
As to comments about SS gear taking more than a minute after power on to stabliize - whether temperature or otherwise - that should not happen. If you have equipment that does so then, whatever you paid for it you paid too much because it is very poorly designed. Having designed and built more than a few amplifiers, and worked with a wide variety of applications of manufactured electronic equipment - this just does not happen. As to audio gear - I have never had a SS item that exhibited temperature stabilization problems - from Yamaha recievers through Mcintosh amps. Indeed, the last time I saw a piece of properly functioning electronic equipment that required any amount of time to stablize was thirty years ago - a black and white tube tv. Actually, one little 'trick' to see if you have connection problems on a pcb is to spray different areas of the board with freon (or now Gore friendly freon) - there is never a change in the functioning of the equipment or the waveform observed on a scope unless you hit a bad connection - you can spray a transistor all day long and you won't see a difference - this of course is with equipment that was designed and built by someone who knew what they were doing.
Aball - my class D amp (Rowland 102) does not even have heatsink, just small dissipation pads on PCB. Very low heat and very low mass = very short time to equilibrium. Mosfet is not so senistive to temperature but like every Mos structure it gets slower. Class A gets hotter and the mass is much larger (in order od 1000x). Wouldn't time to equilibrium be longer?
Your Phd is exciting - I read a little bit of Karsten Nielsen Doctorate (I'm sure you know about him). He left company and Icepower is no longer separate entity - it's fully B&O. So there is a remote chance (but still) that you'll get fired on compeltion of your doctorate (just kidding).
Nielsen's work (on multiple feedback and oscillator) describes his modulator as tamed hysteritic converter but in reality isn't it pretty much sigma-delta modulator with H-bridge and Zobel.
Kijanki - I am getting a phd in Class D circuits and have witnessed variations with temperature in PWM waveforms first hand. Whether it is audible or not is a good question but the feeback loop really has to work to keep the duty cycle in check (mainly because the voltage feedback loop is very fast and few audio modules use the slower current control loop). Tracking a musical signal is tough work and beat frequencies are all over the place, some of which are thermal.
Also, depending on the level of switching frequency, it can take longer than expected to reach thermal equilibrium. It depends on the modulation scheme and signal as to what the duty cycle is but typically, it is 50%. In this case, I doubt that they will reach equilibrium faster than Class A. Those Gryphon amps would burn your hand in less than 5 minutes despite massive heat sinks, if they weren't playing music, whereas I have had thermocouples attached to switching devices and watched their temperature rise in real time and it took about 15 minutes for the curves to level off with an output current of 100A (multiphase buck). If the devices are attached to heat sinks in addition to the multi-layer PCB, it will take much longer still (lots of mass, little energy). You can look at a Class A amp as having 100% duty ratio and 10x the bias current. It will be hard for a Class D amp to beat that kind of energy level, regardless of the mass involved.
As a result of all this, I would leave a switching amp on all the time. Besides, it hardly uses any power.
MOSFETs are actually not as sensitive to temperature as BJTs. Voltage drive doesn't pay much attention to variations in circuit impedance - unlike current drive. Not to mention having positive temperature coefficients.
Abal - any piece of gear sounds better after few minutes but sometimes it is combined effect of, for instance, speakers sounding better (tweeters' ferrofluid getting warmer etc). In case of the class D it probably achieves full temperature of output transistors faster than class A (smaller mass to heat-up) but it is not even relevant here since time (duty cycle) and not the voltage is important parameter here (before passive low-pass filter). Output Mosfets, if anything are slower (less accurate) with temperature.
My s.s. amp is ready to play in about 10 seconds from cold power up. However, for it to sound good & re-confirm to me why I spent so many $ on it, it takes about 40 minutes. FWIW.
09-10-08: Aball It is only normal for SS to be slower to reach thermal equilibrium since they generally don't consume as much power. However, my experience with Gryphon Class A amplifiers is similar to tube amps: super hot in no time! Class D amps are at the opposite end of the spectrum.
This has definitely been my experience. I got in the habit of keeping my high current SS amps on all the time, and am unsure how much that might have contributed to my electric bill. When I got in to playing guitars into tube amps, I was surprised how little warm-up time was required to hear the difference in tube swaps and the like.
My McIntosh MC240 sounds great within 5 minutes but it sounds even better about 1 hour later. I tested its biasing with a multimeter connected to the internal circuit and it settles down after about 30 minutes but the sound doesn't change much during that time. The output transformer takes about 1.5 hours to reach thermal stability.
It is only normal for SS to be slower to reach thermal equilibrium since they generally don't consume as much power. However, my experience with Gryphon Class A amplifiers is similar to tube amps: super hot in no time! Class D amps are at the opposite end of the spectrum.
In 10 minutes my Audionote Kageki amps sound pretty good. But then again, by that time I am more into the music and so it could be purely psychological and not actual improvement I am hearing.
From my experience solid state stuff takes WAY longer to warm up, some taking a few hours before really being at their best. This was not a problem for me because I kept the equipment on all the time, something I would not do with tube gear.
Interesting....I never really thought about it. I think SS amps get up faster than my tubes....but it's just a guess as I normaly have them going 30 minutes before some serious listening. Hey how about How long to put the brakes on? My SS amps take about 40 seconds before the music quits after I hit the off switch.
Since my new Onkyo A-9555 integrated took about 130 hours to fully (or nearly fully) break in, I am loathe to turn it off. But the cool thing is that when it's idling, being class D it draws only 0.3 watt! So I just leave it on guilt-free and it's always ready to go.
I thought this thread was going to be about transient speed, and the Onkyo is quick and articulate as well.
My Wavelength 45 Customs are up and attem in about 15-20 minutes, while my First Watt f4 sounds pretty grizzly until about 45 minutes and really only starts showing its potential after about 1-1.5 hours. It ain't just a thermionic vs. SS thang.
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