The right side of my amplifier is a lot hotter than the left side after running it for about an hour or so. I am told this might be a bias issue. Is this something that is fairly user serviceable or should I take it in for a repair to a local amp store?
Anyway familiar with the HCA-3500 and the schematic?
Anyway familiar with the HCA-3500 and the schematic?
I am currently modifying a pair of Polk SDA 1.2 speakers. Including soldering and desoldering things from a new PCB. I know how to use a solder gun I know how to use a multimer I can understand basic circuit layouts but I dont know what they mean or do.
If you gave me a PCB board and inductors resistors and caps and a schema i could put it all together.
If you gave me a PCB board and inductors resistors and caps and a schema i could put it all together.
part of the reason why i am concerned is because the upgrade that I am doing to my speaker (well documented on the polk forum) involves replacing a coil with a much lower DCR. this reduces the overall inductance of the speaker. I checked with Richard @parasound and he said the amp would be able to handle it.
So far I got the left speaker done and set up with the lower DCR inductor and the right one is stock. So when I put my hand on the amp I was surprised that it was the right hand side that was hotter than the left
So far I got the left speaker done and set up with the lower DCR inductor and the right one is stock. So when I put my hand on the amp I was surprised that it was the right hand side that was hotter than the left
Depending on bias circuitry, it is possible for bad contact inside the quiescent current setting pot to result in increased current, sometimes dramatically. These pots need to be cleaned and quiescent current readjusted. Should be routine for a hi-fi workshop, otherwise it generally isn't too hard to do as long as you have service docs, a suitable kind of contact cleaner (a bit of a science in itself), a multimeter and suitable test leads.
Can you, jck, do it without screwing it up? If you can do it, and TRUST your capabilities, then get two medium size clip leads. Attach one end of each to a multimeter that can measure milliVolts. When you open the case, find ONE convenient EMITTER RESISTOR to put the opposite clip lead ends, across the resistor. Now you are in a position to measure .015-.025 Volts.
Attach clip leads BEFORE turning on the amp. Wait at least 1/2 hour before determining the final quiescent current as determined by the voltage drop across the EMITTER RESISTOR.
IF the voltage drop, over time is NOT in the range of .015-.025 Volts, then find the trim pot that adjusts the measurement. You have to look for it. BE VERY CAREFUL NOT TO TURN THE POT TOO MUCH, until you get a feel for its range.
That should do it, but BE CAREFUL!
Attach clip leads BEFORE turning on the amp. Wait at least 1/2 hour before determining the final quiescent current as determined by the voltage drop across the EMITTER RESISTOR.
IF the voltage drop, over time is NOT in the range of .015-.025 Volts, then find the trim pot that adjusts the measurement. You have to look for it. BE VERY CAREFUL NOT TO TURN THE POT TOO MUCH, until you get a feel for its range.
That should do it, but BE CAREFUL!
Like John says, do use an insulated driver and don't press too hard as the pots are somewhat fragile. He is also correct in stating that there are 2 pots in series. Adjust TVR1 which is the idle bias adjust and set it for 4mV(+/-1mV) DC on your voltmeter with the leads across one of the .22 ohm emitter resistors. I would let the amp idle for at least 30 minutes before doing this. The HCA-3500 amplifier also has a dynamic bias adjust and you set TVR3 to 18mV(+/-2mV) DC while applying an audio signal (music will do). After removal of the audio signal, it will take a couple of minutes for the bias to drop back down to idle. I have seen a number of HCA-3500s with the dynamic bias around 40-50mV and the heatsinks are quite hot.
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