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CTs 3000 clip channel 2

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#1 helloworld

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Posted 13 June 2014 - 09:56 PM

I have 2 CTs 3000. One (amp A) works fine, one(amp B ) has some problem:
- My main line is 240v, so I use a step down transfomer to 110v. Amp A works fine. Amp B red cip flick on channel 2. So I get a new step down transfomer to 120v. Amp B works.
- When Amp B works, seem the channel 2 always gets a smaller signal than the channel 1. I "Y" input for Amp B, and it's still. Channel 2 is smaller 3-6 db than channel 1 on the LED signal of the Amp.
- When I push it, channel 2 go red clip and limit quickly (no sound on speaker) , I just push at >= -10db (may -6db, led channel 1 flash at -10db, led channel 2 is -20, Of course). Channel 2 work for 1-2 seconds and clip, limit. I push harder, channel 1 works ok, sometimes channel 1 limits.
- Onetime, I set channel 1 for main fullrange, channel 2 for monitor. Channel 2 clips quickly although I feed to it a small signal. And after a hard push, channel 1 go clip and limit quickly, this time I do not feed signal to channel 2, but on channel 2 the -10db led lights (light, not flash) and Signal light does not light.
- Onetime, I set channel 1 for monitor, channel 2 for subwoofer(4ohm load). I feed a small signal to channel 1, and a ton to channel 2. Channel 1 signal led flash, sometimes -10 db led flash. Monitor sounds very good. Channel 2 led flash at -10db, only onetime it clips, but does not limit! And the bass is really tight, deep and punch!
- When I test Amp B at no output load, the signal at both channel is equal (will test again)
About the amp A, when it clips, it's hard to limit. I never push my system really hard, I have the dbx DR260 and I set limit on this.
So please give me an advice to shoot this problem.
Many thanks!

#2 joust


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Posted 16 June 2014 - 08:54 AM

Hello to you!

CTS Clip events are difficult to diagnose. You have Clip events when the output signal contadicts (is different from) the input signal :
  • over extension of output signal (normal Clip event),
  • over extension of the i/p signal (more difficult to judge, event may even be taken as an output over extension)
  • and thermal overload.
Also, if you are using low impedance speakers the speaker mode switch has to be set appropriately. The mode switch can be accessed through small openings in the i/p EMI cage : Remove the i/p BBY card and you should see the two small rectangular openings in the cage; The setting towards the rear of the unit is for normal low Z speakers; If using distributed speakers set the switch towards the front. Always verify that the speaker mode switch is set correctly for the loads driven.

Clip and Thermal events may be advertising that the output section is not evacuating heat as efficiently as before; The thermal compound may have dried up, output devices are not sufficiently clamped down and most probably, the temperature sensor foam has dried up. In all eventuality, the output section may need a good refurbishment : removal of the BCA module -> removal and cleaning of the heatsinks, cleaning of the output devices, reapplication of thermal compound on output devices and heatsink, reform the forked clamps, replacement of the t-sens foam and clamping down the output devices. When amplifier is reassembled and ready to test, power up the unit, and verify and adjust the ULOL.

To validate if the refurbishment is successful : Set amp for Low Z speakers; Load amp with 8 ohms speakers; Adjust input signal for 1.4V, 1Khz, sine; Drive amp to barely clipping and leave it driven : the amp should not Clip or go Thermal within these parameters. If testing amp with 4 ohms, the front -10db led should be [barely] lit, Even then, the amp may go into Clipping and eventually, into Thermal overload. I would also verify that both sides have the Clip and Thermal events at the same level and time. If the amp thermals, while using sinea and with 4 ohms load, try changing the input signal using program material (music!) instead. Sine signal is very demanding on output devices in a BCA environment!

Note : if the amplifier has had Clip and Thermal events, it is recommended to cool down the amp before reapplying full power. If the amp is not cooled down, more Clipping and Thermal events will occur.

I hope this helps!


#3 helloworld

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Posted 16 June 2014 - 09:25 AM

Ok, I will test soon. Thank you!