Signal Pass-Through And Oscillation Check; Bias Re-Trim After Warm-Up; Heatsink Burn-In And Bias Re-Adjustment; Bias Confirmation After Burn-In - Classe Audio Delta Series Service Manual

Signal pass-through and oscillation check

Connect a modified 10-pin plug to the connector next to R119 on the heatsink board. On this10-pin plug
short pins 7 and 8 to pin 9 (on the heatsink side) to activate the O/P and Mute relays. Also add a wire on pin
4 to switch from Balanced (default) to Single-ended input later. On the top end of the plug cut off all pins
except 1 and 9) and plug in the 10-pin cable from CH1 on the AUX power supply on your test jig. Once the
MUTE and O/P relays have been activated, send a balanced test signal (sine-wave) to the balanced input of
the heatsink and observe the output of the heatsink board on an oscilloscope. Verify that there is no
oscillation on any portion of the output waveform and that the gain is 29dB. Repeat with the single-ended
input (you will have to switch the input-select relay from balanced to single-ended by shorting pin 4 on the 10-
pin connector to pin 9).

Bias re-trim after warm-up

About 15 minutes after initial adjustment the bias voltages should be settled. Probe pin3 of each bipolar
transistor on the heatsink board to verify that the bias voltages are all within 1mVdc (between lowest bias and
highest bias). If they are not, some output transistors will need to be replaced. Mark the transistors that need
to be changed and the direction they need to go (up or down), and return the heatsink to production. If all the
bias voltages are with 1mVdc, then put the heatsink on the burn-in bench.

Heatsink burn-in and bias re-adjustment

As the heatsink warms up on the burn-in bench, the bias voltages will rise and the differences in bias between
individual transistors will increase. The bias will need to be re-trimmed after the initial warm-up and then
monitored for 48 hours. The target is to get a TOTAL bias of 50mV on each side of the heatsink. The
"nominal" bias value of 10mV (ignoring any variations between devices) will add up to these target values.
Re-adjust the variac until you have exactly +/-66.0Vdc on the DC-rails. Measure all the bias values (ignoring
polarity) on each side of the heatsink. Enter the measured values in the provided spreadsheet on your
computer. Use the resulting calculated "next trim value" to re-trim the bias until the sum of the values is within
2mV of the target 50mV and let the heatsink burn-in some more. This readjustment will have to be repeated
at least four times over the 48-hour burn-in period.

Bias confirmation after burn-in

Re-adjust the variac until you have exactly +/-66.0Vdc on the DC-rails and re-measure the bias on all the
bipolar transistors (pin3 relative to heatsink output). Confirm that the bias voltages are within 1.5mVdc of one
another. Enter the measured values in the provided spreadsheet on your computer. If the sum of the values is
within +/-2mV of the target 50mV then the adjustment is complete. Measure and note down the temperature
of the heatsink (on the head of the screw that holds the LM35D temperature sensor), and the dc rails (in case
the drifted a touch during your measurement).
Note down (on a sticker) the bias voltage on the resistor that will be accessible to the tester after the amp is
assembled. This resistor is R2 (on a "normal" 5-device heatsink), and R109 (on an "inverted" 5-device
heatsink).
CA(P)2100 AMP Service Manual v1.4 inc voltage change info .doc Page 21 of 50