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Warm up time on class A amps?

Discussion in 'Amps and Cabs [BG]' started by Suatie, Mar 12, 2013.


  1. I have recently read somewhere that it can take about half an hour, for a class A amp (not tube) to reach its full power output.

    I typically practice about an hour a day, is it a good idea to turn the amp on 30 minutes before using it, not that I need the full power to practice, just curious...

    My ears are a bit shot, and I don't really hear the difference in volume, how much difference are we really talking about?
     
  2. KJung

    KJung Supporting Member

    Not sure about warm-up, but would be very surprised if you had a class A amp. Class A is, from what I understand, primarily used in preamps, and there is no 'warm-up' needed.

    Simple answer... don't worry about what is under the hood, and just play. Short of turning an amp on immediately after bringing it in from being frozen in your trunk, there really is nothing that you need to do other than turn it on and play.
     
  3. Nah. Any solid state amp can make its full power dead cold. Tubes obviously have a warm up period but it's on the order of 30s.

    Now, there is a school of thought that an amp won't sound its best until everything is nice and warm. That may or may not be the case, depending on the amp. In general, electronics work better cold than hot but when it comes to sound perception, electronically worse could be better sounding.:p
     
  4. This is probably what I read.

    I am using a Warwick WA600, which sounds very good, it is supposed to have the Hellborg designed Class A circuitry, obviously not the same as their million dollar Hellborg series.
     
  5. KJung

    KJung Supporting Member

    That again is the preamp circuitry (they talk about 'class A amps' in the marketing literature, but then list 'class A preamp (again, very common) in the specs. A 600 watt class A amp would weigh about 200 pounds!

    Zero issue. Nice amp!
     
  6. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    And the heat sinks could serve as your homes furnace as well!
     
  7. KJung

    KJung Supporting Member

    talked about above
     
  8. mystic38

    mystic38

    Dec 4, 2012
    Mystic CT
    given that a class A amp dissipates full power all the time then there is not a snowballs chance that a 2U rack unit can be a 600W class A amp.. unless it came with a griddle top :)..hmm bass practice and cook breakfast at the saem time!

    it simply has a class A preamp and since tubes are not mentioned then its a solid state preamp.. so lets say by the time you turn it on and plug your bass in, its ready.

     
  9. Hi.

    A class A POWER amp (something Yours is not) usually needs a bit of time to stabilize. Just like class B does.

    If the biasing circuitry is done correctly, it's usually mounted on the heatsink so the amp would have a "tolerable" distortion behaviour even when it's cold.

    The power stays the same regardless of the temperature, the distortion doesn't.

    Some folks can hear that distortion, I sure as hell can't.

    HOWEVER, this is Hi-Fi talk, not about MI amplification.



    There was small class A SS recording amps around back in the day and probably still is, but none was powerful enough to even rehearse AFAIK.

    IMHO class A power amp offers no advantage in MI use, mainly because our ears are used to class A/B behaviour.

    Class A pre-amps on the other hand, are plentiful as has been said numerous times in this thread.

    Regards
    Sam
     
  10. Slight derail: These are the most powerful truly class A amplifiers I've ever seen (or heard of for that matter). They use an 833 telecom tube. The driver tubes are KT88s! They can do ~150W each and dissipate 800W each at idle. You can feel the heat radiating off them from 6' away. They warm a room quite effectively. 110lbs each, excluding the external power supply. Really good sound.

    $350k for the pair. :D

    SH-833.
     
  11. But HOW good do they sound for $350,000?

    I wonder how many are sold, I am sure more than we expect...
     
  12. They definitely don't sound ~$340k better than a good hifi power amp. :p
     
  13. dincz

    dincz

    Sep 25, 2010
    Czech Republic
    The only class A amp I remember is the Fender Champ - 5 glorious watts!
     
  14. KJung

    KJung Supporting Member

    On a side note, Warwick is more 'loose' with their specs than most companies. They ran into this on a recent thread posted about their entrance into the class D/SMPS world, where they basically said that 'all other class D amps are crap, and we have finally found out how to do it right'.

    It seems here, they are intimating that their 'full weight' amps are 'Class A', which makes them 'better' than other full weight amps. It seems what they are talking about is a class A preamp, which I understand is quite common.

    Seems like they are making nice amps, but I sure don't like this company much. IMO!
     
  15. From memory only, I visited the old Acoustic Control Corp. a couple times with my 360/361 and was told the power amp in the 361 cab was class A. First visit was after a improper repair done at a local (Ventura) shop that used some 10% tolerance resistors, ACC spec'ed 1% only. Can't remember now if it had two banks of 8 or 12 matched transistors on the heatsinks.
     
  16. Gaolee

    Gaolee Official leathers tester and crash dummy Supporting Member

    The 361 power section is class A? I'm not sure I would believe that, although I own one and know it is spectacularly heavy. It runs wide open all the time, so you have to make sure everything is plugged into it and on before you plug it into a power outlet. Nope, it doesn't have an on/off switch. It is an odd beast, but it sure sounds good and I love it.
     
  17. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    You don't need to warm up you amp before using it. What you read about it not being able to reach its full output power till it is warm is not something that you need to be concerned with as far as playing is concerned.

    If your amp has been out in the cold and is not at room temperature, I would wait for it to warm before powering it up. But that's a different thing.

    A tech who is going to perform some adjustments on your amp, such as a bias on your output transistors, would want to warm it and his test equipment up until it reaches a steady state.
     
  18. I do remember the lead tech and unit designer clearly upset at the hack job and explaining to me (they were aware of my electronics back ground) the design and ramifications of using non-spec'd parts. I don't think they were attempting to deceive me, at least I was unable to catch any deception at that time. :)
     
  19. The 361 is definitely class AB. They couldn't put enough cooling in there to manage the heat from the bias current required 200W class-A amp.

    A quick look at the schematic confirms it.
     
  20. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Thought they pulled a pretty dirty trick on Spector, I'll tell you that much. But the amps are still interesting to me...well, only the separate Hellborg power amp...and only because it's one of the very few SS power amps with an output transformer and the only one being made currently as far as I know.
     

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