parasound hca-3500 bias adjustment

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thejck
thejck Posts: 849
in Electronics
Does anyone have experience with doing this? Can you point me to where I can find the output resitors and TVR 1 and 3

Special Bias Adjustment Procedures for the Parasound HCA-3500

The bias tracking circuit of the HCA-3500 requires being set with no signal applied and again with a signal
applied. When the HCA-3500 has an input signal connected, The bias rises to its high level setting.
1. Connect a DV voltmeter (in the millivolt range) across any of the emitter resistors.
2. With no signal applied, adjust TVR 1 until the bias level is 3 mV +/- 1 mV
3. Apply a 1 kHz sine wave to both inputs of the HCA-3500 Do not connect a load to the output.
4. Adjust TVR 3 until the bias level is 20 mV +/- 2 mV.
5. Confirm that the bias has remained at 20 mV +/- 2 mV.

This is picture I found online But I can take closer pictures of a particular side if needed.
g5xdva04wi6d.jpg
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Comments

  • SeleniumFalcon
    SeleniumFalcon Posts: 3,485
    edited December 2021
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    According to the schematic the emitter resistors are 0.22 ohm 5 watt resistors (probably the white colored cermet type resistors R63 for example) connecting any of the output transistor's emitters to the output. TVR1 connects resistor R139 (470 ohm) to the base of Q30, TVR3 should be located close to transistor Q1's base.

    9f338g0349x9.png
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  • carlo_10
    carlo_10 Posts: 3
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    Hi guys, could you answer me?
    I also have a HCA 3500 and I need to adjust the bias
    QUESTION 1)
    The input signal that must be sent to the Parasound HCA 3500 must be a sine wave of 1Khz but how many mV (milliVolt)?

    QUESTION 2)
    Thanks for the reply , should the signal be sent to both inputs ie left and right channel at the same time ?

    QUESTION 3)
    Should the bias be adjusted first for the right channel and then for the left channel?
    Thank you
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  • carlo_10
    carlo_10 Posts: 3
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    Hi guys, could you answer me?
    I also have a HCA 3500 and I need to adjust the bias
    QUESTION 1)
    The input signal that must be sent to the Parasound HCA 3500 must be a sine wave of 1Khz but how many mV (milliVolt)?

    QUESTION 2)
    Thanks for the reply , should the signal be sent to both inputs ie left and right channel at the same time ?

    QUESTION 3)
    Should the bias be adjusted first for the right channel and then for the left channel?
    Thank you
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  • SeleniumFalcon
    SeleniumFalcon Posts: 3,485
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    1). the amplifier's specification is given as: Input Sensitivity:
    1 V for 28.28 V; 2 V for full output. I would use 2.0 volts @ 1kHz for full output bias adjustment.

    2). the instructions indicate the signal should be to both channels.

    3). probably best to do one channel (say right channel) then the other channel, then go back and check the right channel again.
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  • skrol
    skrol Posts: 3,337
    edited May 2023
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    Instructions from Parasound. I believe this agrees with what SeleniumFalcon stated above.

    By the way, there is a bad YouTube video on biasing a Parasound amp that erroneously has referencing the voltage to ground instead of across of the emitter resistor.

    832btqrz6o7u.png
    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
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