Pavel Dudek's (Upupa Epops) LM4780 amp

[wim]

As promised, a little fan on the heatsink of the amp, just for in case that.

It's a 12VDC fan, but i runs it on 6VDC so you do not hear any noise.

 

[wim]

Another one....

 

[Upupa Epops]

Fan bring little bit dustiness, I don't use him... Did you have problems with cooling ?

 

[Upupa Epops]

To P-A : " Don't touch my WAGO's....", says Archimedes...

 

[wim]

Yes pavel, it brings dust, but it is only for in case that.

I have no problems with cooling. Reasons to mount the fan: I had the little fan in stock and i had some time to mount it.

So i do not think the fan will work ever.

 

[BNK]

Ok. Third Amp finished with same results: relays close but no sound->input problem.

What do I do wrong?

1. Is a regular cd player output is ok as input?
2. + is connected in the first pin second row. - is connected to the first pin first row (groud).
3. A jumper is inserted to shortcut the - and ground.
4. Output is connected to the wago connectors related to the same input (jp5 pins 1,2).

Any help?

 

[BNK]

I took out the omron relay and put jp4 jumper.
I connected a balanced input (active xover) and now I could hear a loud noise, which is caused of the amp groud not connected to the house ground, but still no sound.

 

[peranders]

If you have the inputs shorted, the amp silent then? Do you get a hum of you touch the input?

 

[Upupa Epops]

How is DC voltage at outputs of both opamps ( pin 6 ) ?

 

[Upupa Epops]

And which opamps do you have at this position ?

 

[BNK]

If you have the inputs shorted, the amp silent then? Do you get a hum of you touch the input?

Both, yes.

How is DC voltage at outputs of both opamps ( pin 6 ) ?

correction: -11.5V.

I use 18Vac toroid.
The tp1,tp2 voltage is 23.9V.
Op amps are opa134pa (TI).

 

[Upupa Epops]

At TP1,2 you must have +/- 12 V DC ! If not, something is wrong ! Are you sure, that voltage regulators are at correct position ? Read again setup instructions !

 

[BNK]

Another thing: The other channel's opamp is getting very hot and there is a white noise on the outside, but if I thouch its input it doesn't affect anything (not like the right/lower) input.

-> I replaced its opamp and it's like the other input now.

 

[BNK]

At TP1,2 you must have +/- 12 V DC ! If not, something is wrong ! Are you sure, that voltage regulators are at correct position ? Read again setup instructions !

It's 24V between them.
tp1, tp2 and ground is 12V voltage.

 

[Upupa Epops]

At outputs of opamps, you must have DC voltage near zero ( +/- a few milivolts ). Which is this value ?

 

[BNK]

At outputs of opamps, you must have DC voltage near zero ( +/- a few milivolts ). Which is this value ?

-9.5mv

 

[Upupa Epops]

So all is OK, problem is probably only in input connection... Which DC voltage are at TP 3 and 4 ?

 

[BNK]

So all is OK, problem is probably only in input connection... Which DC voltage are at TP 3 and 4 ?

0v (as stated in the manual).

 

[Upupa Epops]

If DC voltage are as you stated, problem will be really only in connection of input...

 

[Upupa Epops]

Look at photo in the middle at P-A page and make jumpers the same. If touch + pin beside left or right jumper by finger, you must hear hum from speakers...