Parasound HCA-1500A Adusting Bias

joebass3

Just picked up this amp and although it sounds great, I've noticed the left side of the amp is considerably hotter than the right. Has anyone here done the bias procedure? Any pics or videos floating around that could help me out? I've found a spec of 15mv +/- 2mv and also the schematic. Trying to figure out where exactly to take the readings??

joebass3

Found some information online. I am confused on this statement "measurement should be taken across R130 and R127". Is this correct? And other than my voltmeter reading a positive vs negative number, does polarity matter when taking the readings?

pitdogg2

Contact Parasound Customer Service. They have in the past been very helpful.

SeleniumFalcon

I believe they are referring to R127 for left channel and R130 for right channel adjustments.

stevep

If you look at the schematic R127 and R130 are two of the output transistor emitter resistors for the left channel. Like pitdogg2 suggested I'd double check with Parasound to see if they want you to measure the voltage across both resistors or just one. Across both would be my expectation but I've seen both ways.

joebass3

Thanks for the advice. I contacted Parasound tech support and got some good info. It appears the pic I posted above is not the correct way to connect the voltmeter. It should be connected across EITHER R127 or R130. Also R127 and R130 are the resistors for the left channel and R227 and R230 are for the right channel. I did my testing across R130 and R230. Although the amp appeared to be working fine the readings were way off. Who knows how long before this thing may have imploded. Adding a pic to clarify the correct voltmeter connections.

joebass3

Before and after from the right channel.

joebass3

Left channel was in the danger zone.

joebass3

Temps right side before and after

joebass3

Temps left side.

Navy_Goat

Thanks for posting the great pictures. I may take a stab at this next weekend armed with these pictures.

joebass3

Navy_Goat wrote: »

Thanks for posting the great pictures. I may take a stab at this next weekend armed with these pictures.

Two things I found out that may help you out. The pots are EXTREMELY sensitive so be very careful. Also turning them CW reduces the voltage and CCW increases the voltage.

skrol

I believe that I got this from Parasound when I inquired about biasing my HCA-1000A.

On DIYAudio, Mr Curl suggested biasing the HCA-1000A higher based on temperature. Similar is likely true for the HCA-1500A. Might check on DIYAudio to see if there is advise.

I did find that I have to keep my HCA-1000A well ventilated. It is actually remote located in my basement where the hybrid water heater keeps things quite cool (58 degF in the winter). I could probably bias even higher now buy why push it.

joebass3

I had found that pdf also when I was searching the procedure online. Maybe I should bump mine up a little higher but when I mentioned 15mv +/-2mv to the Parasound tech he advised me to stay on the conservative side, so maybe I shouldn't push my luck. I also messaged a guy on DIYAudio who was very helpful and walked me through the process. Thanks for the info!

audioluvr

Bias adjustment is like strippers with huge fake TXT's and long a$$ fake fingernails... Okay I'm going to stop there.

skrol

The imagery is astounding. Not sure what its getting at but its astounding.

Mr. Sharpe

Cool thread, I’ve had this amp for quite a long time and it simply has no issue pushing a pair of RTA12’s.... beautifully at that.

I used to have it plugged into a Furman elite power conditioner and always thought it strange one side was warmer than the other and it was almost like one channel was not as loud but since changing conditioners to ethereal super outlets it evened out. I feel like I should jump in there and maybe check this out though just to be safe..... and sometimes I feel the need to take things apart😊