parasound hca-3500 bias adjustment

thejck

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.

SeleniumFalcon

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.

carlo_10

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

carlo_10

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

SeleniumFalcon

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.

skrol

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.