Classe Audio Cav180

Publicado por aniello68, 12 Enero de 2022, 18:53

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aniello68

Good evening I have a problem with a Cav180 Amplifier, the input channel 1 seems to have ground problems, even if I leave the inputs disconnected, I have a slight noise, almost as if a ground is missing, and a known defect? Checked the ground and c 'and, check resistors and relays, but it's all good

What have info?
attachment service manual for archive
thanks

Quimtronix

Hello aniello68,
First of all, this CAV-180 power stage is being used with the RCA inputs unbalanced, or balanced Cannon?

If the non-balanced RCA input is used, the bridge must be placed external on the Cannon Connector (already supplied with the equipment) shortocitting from the PIN 1 to PIN 3 as it already came from the manufacturer.

Only if it is used with the Cannon input this bridge must be removed and saved.

Once clear this we can continue
All the best
Quim

Quimtronix

One thing, in the service manual the shematic of the output stage is not drawed, maybe it is very private from the company.

aniello68

Hello covid cause I replied late,
I use both balanced cannon and rca, the problem remains the same, suddenly and as if the mass is missing on ch1 and only on ch1, I have all tightened the screws of the case, but to no avail

Quimtronix

Hello, sorry about the Covid. I too now since Friday I am in close contact with positive.

It would be necessary to separate the fault,
1 if it is in the connectors and input cables or
2 if it is in the input electronic circuit.

Check with the tester in ohms continuity mode, the lowest scale.

Are the connectors ok? Does the ground of RCA channel 1 make electrical contact with the ground of the other RCA channels 2, 3, 4? It should measure almost 0 Ohms.

Does the ground of the cannon connector pin 1 of channel 1 make electrical contact with pin 1 of the other cannon connectors?





aniello68

hello covid aside, let's hope steps as soon as possible, I did all the tests, I also joined the gnds, in addition to measuring them, I moved the ic and relay 'passage on the entrance, it became a mystery

Quimtronix

Hello. Yes, with the Covid it is another different battle.

Maybe then the fault is not on the input part.

Have you tried to bridge the RCA signal to mass, and in the Canon Pins 2 and 3 bridged?   
This indicates it  in the service manual to prove that there are no noise.


ginn

I wanted to indicate that it is not correct to bridge pin 2 and 3, because in this way a short circuit is made in the signal input, what must be bridged is pin 1 and 3, since pin 1 is a shield, pin 2 is positive input and the pin 3 is negative input, so pin 1 and 3 are jumpered to join shield and negative input when using the RCA connectors. If you look next to the XLR connector pins you have the numbering in each hole.

Quimtronix

Hello.
Thanks for the clarification, but
In differential entries to block the signal from outside, the positive and negative signal, pin 2 and pin 3 of the cannon must be short. It is what they do (for example) microphone switches with balanced signal. Pin 3 is only the mesh that goes to the chassis.

Quimtronix

Hello aniello68,
Have you proved something more ?   for attempt to indentify the section where the noise is genered
Regards

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