Parasound HCA-1500A Adusting Bias

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??

Comments

  • joebass3
    joebass3 Posts: 240
    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?

    nia0uzowdedt.jpg
  • pitdogg2
    pitdogg2 Posts: 24,323
    Contact Parasound Customer Service. They have in the past been very helpful.
  • I believe they are referring to R127 for left channel and R130 for right channel adjustments.
  • stevep
    stevep Posts: 326
    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
    joebass3 Posts: 240
    edited November 2021
    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.

    z9khgv6xn5df.jpg


  • joebass3
    joebass3 Posts: 240
    edited November 2021
    Before and after from the right channel.

    2haoj5r6wnks.jpg

    iunzmpnhgte3.jpg

  • joebass3
    joebass3 Posts: 240
    edited November 2021
    Left channel was in the danger zone.

    8vt2ujsyn8q4.jpg

    ok00w5l5njzx.jpg

  • joebass3
    joebass3 Posts: 240
    edited November 2021
    Temps right side before and after
    pmdqdzh4vu8x.jpg

    w07zwaxhbmch.jpg

  • joebass3
    joebass3 Posts: 240
    edited November 2021
    Temps left side.
    9osc5oimgpe7.jpg

    eohbu6hju20k.jpg



  • Thanks for posting the great pictures. I may take a stab at this next weekend armed with these pictures.
    SDA SRS 2.3tl, SDA 1C, SDA 2B (TL mod), Reserve 200
  • joebass3
    joebass3 Posts: 240
    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
    skrol Posts: 3,330
    I believe that I got this from Parasound when I inquired about biasing my HCA-1000A. 1jikpzh36mrv.png

    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.
    Stan

    Main 2ch:
    Polk LSi15 (DB840 upgrade), Parasound: P/LD-1100, HCA-1000A; Denon: DVD-2910, DRM-800A; Benchmark DAC1, Monster HTS3600-MKII, Grado SR-225i; Technics SL-J2, Parasound PPH-100.

    HT:
    Marantz SR7010, Polk: RTA11TL (RDO198-1, XO and Damping Upgrades), S4, CS250, PSW110 , Marantz UD5005, Pioneer PL-530, Panasonic TC-P42S60

    Other stuff:
    Denon: DRA-835R, AVR-888, DCD-660, DRM-700A, DRR-780; Polk: S8, Monitor 5A, 5B, TSi100, RM7, PSW10 (DXi104 upgrade); Pioneer: CT-6R; Onkyo CP-1046F; Ortofon OM5E, Marantz: PM5004, CD5004, CDR-615; Parasound C/PT-600, HCA-800ii, Sony CDP-650ESD, Technics SA 5070, B&W DM601
  • joebass3
    joebass3 Posts: 240
    edited November 2021
    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!
    Post edited by joebass3 on
  • audioluvr
    audioluvr Posts: 5,391
    Bias adjustment is like strippers with huge fake TXT's and long a$$ fake fingernails... Okay I'm going to stop there.
    Gustard X26 Pro DAC
    Belles 21A Pre modded with Mundorf Supreme caps
    B&K M200 Sonata monoblocks refreshed and upgraded
    Polk SDA 1C's modded / 1000Va Dreadnaught
    Wireworld Silver Eclipse IC's and speaker cables
    Harman Kardon T65C w/Grado Gold. (Don't laugh. It sounds great!)


    There is about a 5% genetic difference between apes and men …but that difference is the difference between throwing your own poo when you are annoyed …and Einstein, Shakespeare and Miss January. by Dr. Sardonicus
  • skrol
    skrol Posts: 3,330
    The imagery is astounding. Not sure what its getting at but its astounding.
    Stan

    Main 2ch:
    Polk LSi15 (DB840 upgrade), Parasound: P/LD-1100, HCA-1000A; Denon: DVD-2910, DRM-800A; Benchmark DAC1, Monster HTS3600-MKII, Grado SR-225i; Technics SL-J2, Parasound PPH-100.

    HT:
    Marantz SR7010, Polk: RTA11TL (RDO198-1, XO and Damping Upgrades), S4, CS250, PSW110 , Marantz UD5005, Pioneer PL-530, Panasonic TC-P42S60

    Other stuff:
    Denon: DRA-835R, AVR-888, DCD-660, DRM-700A, DRR-780; Polk: S8, Monitor 5A, 5B, TSi100, RM7, PSW10 (DXi104 upgrade); Pioneer: CT-6R; Onkyo CP-1046F; Ortofon OM5E, Marantz: PM5004, CD5004, CDR-615; Parasound C/PT-600, HCA-800ii, Sony CDP-650ESD, Technics SA 5070, B&W DM601
  • Mr. Sharpe
    Mr. Sharpe Posts: 1,354
    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😊
    Home theater:
    43” Westinghouse Displayer
    Marantz UD-7007 Player
    Emotiva MC-700 Processor
    Adcom GFA-5006 Amplifier
    Parasound Zamp Amplifier
    Ethereal ESO-1 Power Conditioner
    Klipsch RC-10 Center
    Klipsch R34c Fronts
    Klipsch RB-41 Surrounds
    Polk audio PSW-505

    Stereo:
    Polk audio RTA-12c’s fully upgraded crossovers
    DIY 12tc braided speaker cables
    Denon DVD-5910ci Spinner
    Parasound P6 Preamplifer
    Parasound HCA -1500a Amplifier