SCM50ASLT anniversary and amp pack heat variation.

ATC & other manufacturers design parameters, technical queries etc
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Re: SCM50ASLT anniversary and amp pack heat variation.

Postby Brad Lunde » Thu Dec 22, 2016 8:14 am

It may not be a big deal. Sometimes, the way the amps are built can lead to the differences in heat, or the way the part(s) are made. Sometimes there are heat variations when you are dealing with mirror images as the parts are sometimes arranged differently. It is good advice though that if it's a large difference, it should go to the shop.

Brad
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Re: SCM50ASLT anniversary and amp pack heat variation.

Postby Tomo » Thu Apr 13, 2017 4:51 pm

I had the same issue a few years ago with my 50 annies. I spoke to Bob Polley about it and he said the bias setting was different on each amp - I forget the exact description but it was something like the two amps are adjusted so they match each other in output - they could end up with a different bias settings in the process. I measured the temp of each one and they were within tolerance.

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Re: SCM50ASLT anniversary and amp pack heat variation.

Postby Lemen » Thu Apr 20, 2017 3:43 pm

samsie wrote:Any update on the heat issue?

I own a pair of 50A Anniversary in pro black. I have the same problem. The left one about 5 °C hotter though both of them perform normally.


Hello samsie

5° C would be a reasonable variance I would have thought. I haven't taken any actual temperature measurements myself as yet, but perhaps I should. When I say that the one amp pack is too hot to touch . . . it really is . . . no exaggeration! It's only possible to touch the backplate for a fraction of a second before one's reaction of self protection takes effect to prevent a burn injury! There's definitely a "hot" odour aswell, so I haven't operated the speakers for long periods.

It's taken me a lot longer than expected to get around to arranging to have the speakers returned to ATC for the tweeter upgrade and it's no surprise that ATC are VERY busy. However, the speakers should now be on the "jobs list" and the upgrade should hopefully happen at the end of April or early into May. Of course, this heat issue will be investigated at the same time as the tweeter upgrade, so I will let you know the outcome.
ATC SCM50 ASLT Anniversary (gloss white)

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Re: SCM50ASLT anniversary and amp pack heat variation.

Postby Lemen » Thu Apr 20, 2017 3:48 pm

Tomo wrote:I measured the temp of each one and they were within tolerance.


Hello Tomo

May I ask how you took your temperature measurements and what the values were for each unit please?
What is the temperature tolerance range for this amp-pack?
ATC SCM50 ASLT Anniversary (gloss white)

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Re: SCM50ASLT anniversary and amp pack heat variation.

Postby Lemen » Thu Jul 20, 2017 11:13 pm

By way of a quick update:
The tweeter upgrade is due to be done during the next couple of weeks (I hope).
I'll update this thread again once the work is complete.

Lemen.
ATC SCM50 ASLT Anniversary (gloss white)

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Re: SCM50ASLT anniversary and amp pack heat variation.

Postby studioman » Mon Jul 24, 2017 6:19 am

samsie wrote:Any update on the heat issue?

I own a pair of 50A Anniversary in pro black. I have the same problem. The left one about 5 °C hotter though both of them perform normally.



In theory, a pair of amps, especially if matched, should have the same losses....

For that reason, I wonder if the power FETs are not contacting the heatsink properly.

A competent engineer should check: 1) the bolts that hold the heatsink to the main frame, 2) the bolts which hold the power transistors to the heatsink, and 3) the bolts which hold the circuit board to the amp plate.
If the bolts that hold the power transistors to the heatsink are not tight enough, there will be an inefficient transfer of waste heat to the heatsink.

After all, any heat given off is wasted energy, ie losses, and that suggests that the amp is having to 'work' harder than it should for a given output. It's not a good thing, especially for capacitors and solder joints, to have an amp getting hot because waste heat is not being dissipated by the heatsink as it should.

Many engineers, when working on an amp, are modest in their use of heat transfer compound, which is a metallised paste applied on the back of the power transistors to transfer the waste heat to the heatsink properly. (it's quite expensive stuff in tiny tubes)

It's a little bit tricky on any amp, dismantling the power trannies and slipping more paste behind them, but this might be what's needed.
They say if you can remember the 60's, you weren't really there. Now somehow I have reached 62...oh shit, it's 63 now....How and when did THAT happen?....there's a lesson there somewhere if only I could figure it out...

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Re: SCM50ASLT anniversary and amp pack heat variation.

Postby MevDinc » Mon Jul 24, 2017 7:40 am

I have a pair of the very early ATC SCM20A PRO speakers which I bought back in ca. 1998.
One of them always runs a little warmer (you can tell by just touching the heat fins).
I don't think it's anything to worry about, most likely caused by the different settings of the amps to match the output. I was also told this by ATC.

BTW, after almost 20 years my little ATCs still sound wonderful, they look very different too with heavy metal bodywork (30kgs each!).

Best.
Mev
Last edited by MevDinc on Sun Aug 20, 2017 12:32 pm, edited 1 time in total.
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Re: SCM50ASLT anniversary and amp pack heat variation.

Postby Nopiano » Sun Aug 20, 2017 10:39 am

Lemen wrote:By way of a quick update:
The tweeter upgrade is due to be done during the next couple of weeks (I hope).
I'll update this thread again once the work is complete.

Lemen.

Have you got them back yet?

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Re: SCM50ASLT anniversary and amp pack heat variation.

Postby Lemen » Sun Aug 20, 2017 11:34 am

Nopiano wrote:Have you got them back yet?


They're at the ATC factory as I type, so it shouldn't be too long now I hope.
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