Crown CTs2000 overheating

[MarinZ]

HI there!


Does anyone have experiance with Crown CTs2000 amplifiers?


I have more than few, they are overheating somehow even when idle, no signal on input, no load on output......driving somethng like 1.8A @230V mains. I check all and it seems to be fine, also sound is ok, no distrorzion or so....
I am suspecting something is wromng with output filter, which is hard to measure because is below main board......so to get there i need to reassembly whole thing. Also i suspect that there is some noise above 20KHz but nothing, also no noise on power supply rails (main +/-160V DC, +/-15VDC, 5V dc etc....).


If something did had similar problems it could share with me. Going to measure more and try to find reason.....also if someone has service manual (not only schematic, i have them) for eother CT's2000 or CTs3000 i would be thankful to got it. Note that CTs600 and 1200 even same look, they are completly different (AB class) so those manual is not usable.

 

[rayma]

i suspect that there is some noise above 20KHz but nothing,

Could be high frequency oscillation causing the overheating.

 

[wg_ski]

Crown’s BCA circuit is a little different from regular class D - the switching losses are there whether there is a load (signal) or not. It stores much more energy in the output inductor, which “idles” at half the peak current capability of the amp. The output transistor heatsink in my CE4000 runs at the same temperature idling as it does in operation. Still a lot cooler than a class AB amp at moderate output, but not as low as say an iNuke at idle. The advantage is that heavy peak loads don’t cause thermal cyclling or dangerous cross conduction. The disadvantages are that the peak current without distortion is strictly limited to 2X what the inductor idles at, and that there is more total idling dissipation because the power transistors conduct that current on half a cycle, and the freewheel diodes conduct that same current returning it to the supply. Less what was lost in Rds(on) and the rise/fall of the switching waveform... which is probably drawing your 1.8 amps.

 

[MarinZ]

hmmm....that makes sense what does produce heating (disipation) but still it not makes sense why is maybe heating too much because temperature alarm goes on! And it's HOT, even fans start and runs at high speed. But since there are no service manual i cannot say for sure which is normal current on idle mode. Output filter seems to be ok.

 

[MarinZ]

A bit update......just hook it up on my R&S anylzer and under 1KHz on output 280W@4ohm only one channel driven, it draws 4A from mains, which is around 900VA........class D should be power efficient? 😀

 

[wg_ski]

Running HOT hot is abnormal - they don’t even do that at war volume. Warmer than you would expect from an idling amplifier is quite normal. Offhand, however I don’t know of anything that would cause the switching waveforms to degrade that wouldn’t cause it to just quit working altogether or get highly distorted. It would take further study - starting with how much DC each channel draws off the supply. Could be the power supply generating excess heat somehow, which would be a risk for failure at war volume.

 

[MarinZ]

Will try to measure that to.....even is bit hard because DC capacitors are on power amp board, not on SMPS board.......but i can try.....
And power supply is not generating heat, it's the amplifiers itself.....also filter coils are warm too.