Q2 Audio Compex F760X-RS User Manual - page 9
AUDIO & DESIGN (READING) LTD. & Q2 Audio, LLC
Check out Procedure - F760X Series
1: Before switching on unit check that the mechanical zero of the meters is correct – adjust as necessary. Allow the unit
at least 30 minutes to warm up, an hour is better. The FET’s are affected by heat and they should be allowed to attain the
normal operating temperature of the unit before continuing.
2.
Switch on the unit.
Input & Output attenuators fully open (CW)
Expander section switched ‘out’
Stereo-Link ‘out’
Peak Limit ‘OFF’
Compressor section to 1:1 Ratio
Compressor attack to ‘F’ (.25)
System to ‘In’
3.
Connect signal generator to input(s) at a level of -34dBu at 1Khz.
4.
Monitor C6 and C7 on the “A” PCB with a two channel oscilloscope set up to add the channels together. Tempo
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rarily set ratio to 2:1. Adjust “Rec. Bal.” for minimum level on the scope, readjusting scope V/div as necessary to get the
best adjustment of the potentiometer. If the above does not seem to work, check Q3/Q5 for problems. Switch Peak limit
“in” and monitor C14/C15 on the “B” PCB in the same manner as above adjusting the “Rec. Bal.” on the “B” PCB for mini
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mum level on the scope. If problems occur, check Q7/Q8 for problems. Switch “Peak Limit” to “out”. Swtich Switch ratio
back to 1:1, Pk Lim to “”OFF”.
5.
Adjust FET bias pre-set full CW to give maximum output; adjust the inverter pre-set full CW to give maximum
output (about +4dBu output – system gain of 38dB). Adjust the inverter pre-set CCW so level is attenuated by about 1dB
(down to +3dB), then adjust the FET bias to further attenuate the output by 3dB. Output should be 0dBu - system gain of
34dB.
4.
Select compressor ratio of 2:1 and threshold to -20 (this is referenced to the internal peak limit threshold). Using
the channel input attenuator, increase the input until compression is just being indicated (meter will move the width of the
pointer off of “0”), the output will be at approx. -10.2dBu. At the signal generator, increase the input level by 30dB and the
output should rise by only 15dB (+/- 0.5dB). If this compression is greater or less than 15dB, proceed to step 5, otherwise
proceed to step 6.
5.
To adjust the compressor slope (ratio), use the “slope” preset to give correct output. If this pre-set is adjusted it is
necessary to return to step 3 in order to check that the FET bias and overall system gain are correct. If the bias needs re-
setting follow through steps again returning to check the bias if further adjustment is made on step 5.
6.
Increase the input level by 2dB (total of 32dB increase, 16dB approx. indicated on external meter), adjust “meter
range” pot so internal meter reads 16dB gain reduction.
Reduce input level by 2dB for next step (input signal should be at -4dBu).
7. Select 20:1 ratio and -2 on the threshold. Adjust the input level to give 4dB gain reduction indicating on the meter.