psu damage input connection

hello, i have vssa amp by shaan- peeceebee. when i connect rca when amp is on, the v+ fuse from the amp burns off! pull out rca, no problem. how i fix this? i'm very nervous problem may occur.

thank you.

STOP , sounds like your RCA is coupling voltages and currents it
is not designed to handle, and passing these to your vssa amp.
A failed source component is likely.:eek:

With power OFF, and power socket out, observe if you
have any loose wires, images would help us to help you.

Does your vssa amp run OK with other source equipment ?

You need to carefully measure with a good multimeter, what
voltage is across the RCA. Observe the insulating ability of the multimeter
probes, and taking care not to touch the RCA.

Normally RCA's are signal connections and should not carry any
harmful voltage or current, but in this case it sounds like another
piece of equipment you use has failed, and is passing that harm on
via the RCA cable.

You ideally need schematics, but failing that post some images
so forum members can assist you.

Cheers / Chris
 

donovas

Member
2014-06-22 6:45 am
sorry, i need to clarify. the amp does it with every rca. and every pcb iteration that i've made of the circuit does that. the rca, whatever it may be, all work ok when it's connected BEFORE the amp is powered on. it's only when the rca is connected WHILE the amp is powered on the problem occurs. hope this clarifies it.
 
amplifiers do not like a disconnected input.
Even worse is a part disconnected input where the barrel of an RCA/Phono has disconnected but the signal pin is still connected.
Many amplifiers will oscillate with the RCA barrel disconnected.
The RF on the signal pin can be enormous and the disconnected barrel means that the shield/screen is not working.

It is probably a massive current pulse through the output devices that is blowing the fuse.
I have this with two commercial amplifiers that I own. The Sugden (I have 4 monoblocks) blows the fuse if I disconnect while ON.
The german bugger blows up the output stage if I disconnect. I have one broken channel and one still OK channel.
All five sit on the shelf unused, until I find a way to solve the problem.
 

donovas

Member
2014-06-22 6:45 am
yes, that's what i figure. when the rca cable goes in, the input pin is connected first.

what if i was to leave 100k resistor from input to ground on the rca socket of the amp?
or a series resistor on the input of the amp? (it already has that on the pcb, after the input cap, but would another one before make any difference?)

here's the circuit for reference.

334892d1362831597-peeceebee-vssaschem.png
 
Your 100pF on the input is not the way I do it.

You can have differential RF filtering. That goes from Signal Hot to Signal Cold.
You can have common mode RF filtering. That goes from Signal Hot to enclosure AND from Signal Cold to enclosure.
You have fitted one half of the common mode filtering.

I would move the 100pF to become parallel to the 10K. That's your differential filtering and it is attenuating RF on the cable from the source right up to the PCB.
Then at the input socket ADD on two common mode filters using 47pF to 1nF connecting Hot and Cold direct to enclosure using the shortest possible cap leads. I use 47pF

You can repeat the common mode RF filtering on the Hot and Cold speaker outputs. I use 1nF
If you have fitted a mains interference filter using the "canned" type electrically connected to the hole through the enclosure, then you have both differential filtering (Live to Neutral) and common mode filtering (Live to can and Neutral to can). If you don't have a canned filter you can create your own filter, but it is better if it is inside a can, electrically connected to your enclosure.

From the above you can see that I consider ALL the cables entering through the wall/s of the enclosure as sources of interference. Once it is inside the RF sprays around looking for any LOOP AREAS to impinge on and generate interference currents.

BTW,
my last few amplifiers & DCB1 use XLR for line level inputs/outputs, even though I am still on unbalanced interconnects. Pin1 connects before pin2 & pin3
The screened star quad (microphone XLR) attenuates RF even for very long cables.
 
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