punch 55.2 dc on outputs, no sound

[Perry Babin]

With nothing connected to the RCAs, what's the resistance between the RCA shields and the primary ground terminal?

 

[manninen]

18mohm. Meter goes nuts if amp is on

 

[Perry Babin]

Find R32 and R33 and confirm that they're within tolerance.

 

[manninen]

980ohm and 10ohm

 

[Perry Babin]

Is the RCA shield ground broken? See attached file for point where it breaks.

 

[manninen]

Schematic says r33 should be 47ohm, its 10.
R38 and R39 are 47's on schematic and there written 470.
R33 is written 001 or 100.

What to believe

 

[manninen]

Rca ground seems stiff, no loose stuff

 

[Perry Babin]

I was wrong about the shields being directly connected. They are not the expected vertical jacks.

That said, how can you read 18M ohms between the RCAs and the primary ground if those resistors are not open?

The difference of voltage (20v+) between the shields and the primary ground should have burned those resistors.

 

[manninen]

Gonna take it out from heatsink and trace those resistors, straight from resistors seems fine.
After switching amp drawed 44w, turned bias down there was 14w left. After 3mv bias 20w idle. Power supply toroid or what it is heats a little bit.
I dont know if they touched bias potis in the shop

 

[manninen]

now there is board burned between R39 and R114, that should be simple fix.

anything else comes mind before powering it up after fixing?

 

[manninen]

after fixing the trace turned amp on, measured dc outputs was 1,5mv.
there is sound!

now just i have to think has this been all the time one and only cause?
i dont know if shop has taken board out of heatsink.
i cant say if i saw this yesterday when changing regulator.
but now i saw it immediatly

 

[manninen]

Hey Perry,

Have you ever bypass those tone controls from these rf amps? is it easy to do?
id like to see is there any difference bypassing it

 

[Perry Babin]

Soldering a bridge between pins 6 and 7 on U101/201 should do it. I've never tried it.

 

[manninen]

Just thinking if it may decrease some ground noise.
I have only 2V receiver so cant run gain all the way down

 

[Perry Babin]

Even at max gain, there should be VERY little noise. Is it engine (RPM related) noise or hiss?

 

[manninen]

Ground hiss when amp is on.
Whats the deal with these amps?
Fosgate amps hiss rises when you turn gain.
I got harman kardon amp which does not do that

Got two dls amps which doesnt either, but other dls has more ground hiss than rf amp when both are min gain

 

[manninen]

Hifonics vulcan VIII hiss gains most when you need gain.
But its dead silent when on minimum which is 9V

 

[Perry Babin]

The noise generated by an amp should be very minimal. When a normal distance from the speakers (not with ear touching tweeter), the noise should essentially be inaudible unless you're using speakers that are far more efficient than normal speakers.

 

[manninen]

Well, those amps which are noisy on max gain is there something wrong with them?
That hifonics is way too loud when max, should i open thread for it, place for an video again if its normal or maybe some measurements?

 

[manninen]

Perry, What you have to say about caps C122, C124, C222 and C224

As you cee on the picture, this amp is missing C222

What does it do? Should i add missing cap?

If i remember right i got it still factory seals on