General question about power amps ...

[rigger67]

So I'm running two Meridian monoblocks and often before I know I'm gonna be using the system I'll turn them on in advance so they can "warm up".
Sometimes this can be for an hour or two, like today when I had to pop out for a bit but knew I'd be listening when I came back.

I played a couple of records and they sounded alright but a bit thin.
Now, some three hours later, I've had to turn it down for fear of upsetting the neighbours as it's so loud.
The bass is absolutely belting out and if anything the whole thing sounds positively fat, but in a good way :)

My question is do power amps actually need to be running, ie music playing through them, to reach their full, rich sound ?
I'm guessing it's a resounding yes, but it struck me as odd. If something's "on" - even if it's "idling" it's still warmed up, isn't it ?

Anyone else reached the same conclusion in that it's better to be playing something to get there quicker ??

[struth]

Did you have sources up to working temp.? Shouldnt really need to do that with power amps for hrs. Maybe needs a service?

[Arkless Electronics]

No.

[The Black Adder]

If you have lovely bass at low volume and it loses it at high volume then it could be a speaker problem or some kind of incompatibility between amp and speakers maybe?

[sq225917]

It depends on the amp, a few minutes should suffice. Hours suggests either they're a funky design, which they aren't, or something is on the way out.

Or it could have been noisy mains settling down. My money is on the lady option unless you run a big mains conditioner

[rigger67]

They sound "lovely" at both high and low volumes, but much better after music's been playing for a bit, say one album's worth generally.

I don't know what it is - maybe psychological - but whatever I play second always sounds brilliant compared to whatever went before ..

I don't know .. there's probably nothing in it. Just me going nuts :mental:

[guy]

I have similar experience - although not as pronounced as you seem to be finding.

Whole system seems more capable/informative after a bit of a play. I'm not convinced that it necessarily indicates that something is up with the amp/s, it has happened to me with a wide range of systems (in the old days I just thought that it was my Quad valves warming up) - perhaps it is "expectation bias" on my part, or just my "getting in to the groove".

[walpurgis]

It's common. Both my solid state Class A power amps 'come on song' after about half an hour, as do my valve monos. It's not the pre-amp, that's a TVC. My DACs do it too.

[The Black Adder]

Just me going nuts :mental:

Yup!... I'd go with that, your mechanisms gone. :lol:

[rigger67]

Yup!... I'd go with that, your mechanisms gone. :lol:

Thanks, Josie :D

Trouble is, I can't find my warranty slip :eek:

[Macca]

It depends on the amp, a few minutes should suffice. Hours suggests either they're a funky design, which they aren't, or something is on the way out.

Or it could have been noisy mains settling down. My money is on the lady option unless you run a big mains conditioner

Cherche la femme?

[rigger67]

Cherche la femme?

Mais, Il n'y a pas des femmes ici ce soir :scratch:

[Pieoftheday]

Mais, Il n'y a pas des femmes ici ce soir :scratch:

It's your lekkie or your brain/lugs

[RothwellAudio]

The bias setting of an amplifier depends on temperature. It's normal to use a transistor mounted to the main heatsink to track the temperature of the output transistors and adjust the bias as the output transistors and heatsink warm up. The success of this method depends on how well the sensing transistor tracks the temperature of the output transistors - some amps are more successful in this respect than others. The problem is the time lag between the innards of the output transistors getting hot and the heat travelling through the heatsink and getting into the sensing transistor.
Anyway, the upshot is that some amps' bias setting will go up after playing loud music for a while, and some amps' bias setting will go down. This could well be audible.

[Arkless Electronics]

The bias setting of an amplifier depends on temperature. It's normal to use a transistor mounted to the main heatsink to track the temperature of the output transistors and adjust the bias as the output transistors and heatsink warm up. The success of this method depends on how well the sensing transistor tracks the temperature of the output transistors - some amps are more successful in this respect than others. The problem is the time lag between the innards of the output transistors getting hot and the heat travelling through the heatsink and getting into the sensing transistor.
Anyway, the upshot is that some amps' bias setting will go up after playing loud music for a while, and some amps' bias setting will go down. This could well be audible.

I considered an answer explaining all that and much more besides but have learnt that technical explanations are usually a waste of time.... It goes over most peoples heads so they tend to just ignore it in my experience...

[anthonyTD]

Good post, and explanation Andrew, :) Jez I agree, sometimes its a bit pointless in going into a long winded explanation, when your pretty sure most of the folk reading it are realy looking for a simplified layman term answer! However; In this case I think it was well worth the effort. :)
The bias setting of an amplifier depends on temperature. It's normal to use a transistor mounted to the main heatsink to track the temperature of the output transistors and adjust the bias as the output transistors and heatsink warm up. The success of this method depends on how well the sensing transistor tracks the temperature of the output transistors - some amps are more successful in this respect than others. The problem is the time lag between the innards of the output transistors getting hot and the heat travelling through the heatsink and getting into the sensing transistor.
Anyway, the upshot is that some amps' bias setting will go up after playing loud music for a while, and some amps' bias setting will go down. This could well be audible.

[RothwellAudio]

Of course, my attempt at an explanation was just a brief summary of the topic. I think Douglas Self's analysis of it in his book about power amps goes on for about 30 pages :stalks:

[Oldpinkman]

No.

+1

[walpurgis]

I considered an answer explaining all that and much more besides but have learnt that technical explanations are usually a waste of time.... It goes over most peoples heads so they tend to just ignore it in my experience...

But I like technical explanations. I'm no amp builder, but do have a bit of a clue :).

[Arkless Electronics]

Well I'm just thinking of times when I've spent half an hour providing a detailed technical explanation of things only to find it kills the thread stone dead or it's completely ignored and any posts after it only reply to things before my explanation...:confused:

[rigger67]

Thanks both Rothwell and Arkless for their either informative or potentially informative posts above.

I understood what you were getting at, Andrew.
It's a bit like an output level monitor :)

Thanks again.
Neither of you were ignored.

[Arkless Electronics]

Good post, and explanation Andrew, :) Jez I agree, sometimes its a bit pointless in going into a long winded explanation, when your pretty sure most of the folk reading it are realy looking for a simplified layman term answer! However; In this case I think it was well worth the effort. :)

Yeah the new EE on the block explained it very well:)

There are other factors to take into account in this of course though... I explained a week or so ago that I'd found unexpectedly large variation in electrolytic cap ESR with temp changes of only 20C, which is something I can't recall seeing in any book before. Then there is the same change in Vbe that causes the issue Andrew explained but happening in every SS device to a small extent. This is taken into account in any even half competent design but probably adds to the warm up changes.

I have developed circuitry to completely remove the issue of OPS bias temperature dependence (which is a big issue in most SS amps! One of those things that has me thinking "FFS they're Brasso-ing the mains plugs and fuses but don't even know this is happening":eek:). It's rather complicated but not too expensive and I'll probably use it in a future class A/B amp one day;)

I have seen examples where an amp could, after being turned down, or after a very loud passage which then becomes very quiet, actually show pretty gross crossover distortion for a while whilst the circuitry thermally stabilises, as in Andrew's explanation but taken to the extreme of a really bad example of this happening.

[anthonyTD]

Jez,
Unfortunetly, it may seem like your wasting your breath sometimes :doh: [I can sympathise, and I am sure many of us have felt like that from time to time] but remember, just because you dont get a direct response, doesent mean no one is taking notice! Sometimes I fear folk just dont know, or dont feel confident enough to respond directly to the person who has the technical ability to enlighten them!:D
Well I'm just thinking of times when I've spent half an hour providing a detailed technical explanation of things only to find it kills the thread stone dead or it's completely ignored and any posts after it only reply to things before my explanation...:confused:

[JohnJo]

We're listening.

We're just not saying anything.

That way we don't look as stupid as we are :)

[DSJR]

I have many tales on amps that sound fine from power-on and others that take ages to 'warm up.' When new, a Quad 33/303 reportedly took 15 minutes to measurably sort itself out from cold and I remember the first 606's needing an hour or two, the sound rather grainy until the case became gently warm to the touch. My 405-2's also had some 'tinsel' for some hours of normal listening, or half an hour thrashing into passive ATC's, but sounded lovely after.. The main difference in the Quad 606mk2 was a transformer change and more importantly, an upping in value of the supply caps (10,000 to 15,000uF I recall), but whether this was responsible for an immediately better sound from cold switch-on I really don't know. Some badly capped Chinese 909's aside, I have found the 606 based amp model not to have any undue temperament. The Nakamichi power amps based on Stasis circuits often needed two hours to sort - and this was repeatable too over many examples, so not just one sample needing a tweak...

[Arkless Electronics]

Jez,
Unfortunetly, it may seem like your wasting your breath sometimes :doh: [I can sympathise, and I am sure many of us have felt like that from time to time] but remember, just because you dont get a direct response, doesent mean no one is taking notice! Sometimes I fear folk just dont know, or dont feel confident enough to respond directly to the person who has the technical ability to enlighten them!:D

Maybe...:)

[Arkless Electronics]

I have many tales on amps that sound fine from power-on and others that take ages to 'warm up.' When new, a Quad 33/303 reportedly took 15 minutes to measurably sort itself out from cold and I remember the first 606's needing an hour or two, the sound rather grainy until the case became gently warm to the touch. My 405-2's also had some 'tinsel' for some hours of normal listening, or half an hour thrashing into passive ATC's, but sounded lovely after.. The main difference in the Quad 606mk2 was a transformer change and more importantly, an upping in value of the supply caps (10,000 to 15,000uF I recall), but whether this was responsible for an immediately better sound from cold switch-on I really don't know. Some badly capped Chinese 909's aside, I have found the 606 based amp model not to have any undue temperament. The Nakamichi power amps based on Stasis circuits often needed two hours to sort - and this was repeatable too over many examples, so not just one sample needing a tweak...

The main raison d'etre of current dumping is that it's completely immune to the effects Andrew described earlier.... and as a result of this needs no setting up of the bias in manufacture. The further effects I mentioned still come into play though so it is probably these you are hearing....

Now if only we had PNP valves!:D

[Starterman]

My question is do power amps actually need to be running, ie music playing through them, to reach their full, rich sound ?
I'm guessing it's a resounding yes, but it struck me as odd. If something's "on" - even if it's "idling" it's still warmed up, isn't it ?



The most variable part of the replay chain with respect to temperature is the speakers. So just warming your amp up at idle will not help that (unless the power amps are in or attached to the speakers).

Play it loud, ingest some alcohol and enjoy!

[DSJR]

405's as a breed can run very hot - too hot imo, so I'm sure you're spot on as regards the other changes you mention. I can only report what I heard at the time to back up the amp-warming-up scenario.

[Arkless Electronics]

The most variable part of the replay chain with respect to temperature is the speakers. So just warming your amp up at idle will not help that (unless the power amps are in or attached to the speakers).

Play it loud, ingest some alcohol and enjoy!

If there is no music playing it won't make any difference to the speakers... Actual room temp will matter most here... unless you are thrashing them senseless!

Years ago when I had no neighbour issues I sometimes got the centre plastic dust caps on the bass units of my Mission 770's warm after a good head banging session from the MF A370 driving them!

Another thing is the rubber suspension in a cartridge.... I remember a trend for attaching a small lamp to the side of TT's to shine on the cart and keep it warm... I wonder if there were any warped records when the lamp was left on and the TT not rotating :eek:

Edit: Ah! re read your post and see that you mean as in active speakers heating up speakers from their idling heat:)

[Arkless Electronics]

405's as a breed can run very hot - too hot imo, so I'm sure you're spot on as regards the other changes you mention. I can only report what I heard at the time to back up the amp-warming-up scenario.

Heatsink's a bit small.... Yeah if you thrash em they get hot!

[DSJR]

Oh this one did, believe me :lol:

I replaced it after only a very few months with the baby stereo AVI power amp of the early 90's. Power ever so slightly less but didn't clip hard fortunately (and unlike the often harsh-when-pushed little S2000 integrated they made back then). Thing ran barely warm into the ATC 20's I used at the time.

[anthonyTD]

Of course there are many reasons why systems tend to need time to settle, be it as some have explained amp bias, or speaker suspension cold, etc, etc, the point is; threads like this can be very enlightning when you get the right people to contribute!:)
And I agree Jez, as to PNP Valves.;)