Originally Posted by Stereodude
You don't really know why the components are there. Your statements are completely speculative and baseless. They're probably for ESD protection or maybe they're needed for output stability and the resistor is to limit current draw if you were to short the output. You presume the designers had no idea what they were doing when they designed the circuit. That's probably not true.
True, I really do not know why they are there.
But I surely know what effect those would have on the volume control amp circuitry. It is very well-known among amplifier builders and designers. The undesirable effect is called "capacitive loading".
An expert's opinion as to the undesirability of the effect was attached in my original post.
Your point about ESD is valid
. It is true that the 470pF can help protect the volume control circuitry IF THEY WERE CONNECTED WHERE THEY SHOULD BE. That is, after the 220Ohms resistors.
In that place, the 220Ohm resistors would have had also
insulated the volume control amps from the negative effects of severe capacitive loading due to the 470pF capacitors.
Again with regards to ESD
I tried to get a datasheet for the component used for the electronic volume control used in 4520s but failed. It is well-known, again among electronics builders and designers, that only those components using fet
technology are prone to ESD failure - not those using bipolar technology. If they were made of fet
s, I will think that the 470pF are placed there for this purpose.
As to " limiting current draw "
Notice that the capacitors are connected to the signal and ground traces. The capacitors will short the outputs to ground
at higher frequencies without the benefit of any current limiting resistors. That is another negative side effect of them being placed in the wrong part of the circuit.
I am a bit tired now, so please allow me to stop with my explanations here. I have been teaching for a while and wish to rest from that activity today if I may.
I really do not know why they are there, but I speculate.
Based on the collective experiences of people in the industry that I have had the opportunity to observe and/or share with, these faults typically result not from the design
but from the execution/manufacture. The board where the faults are is called the "input board
". The board layout team/staff may have had simply cut and pasted an input circuitry because they looked very similar
then laid them all out nicely like peas in a pod for the external connectors taking no notice that some are for output, not all are for input
. There they remained unnoticed until now.
But that is just speculation.
Please assist by finding out from Denon why they put those there.