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Tone control PCB without capacitors in Cambridge Audio A1 mk3
Tone control PCB without capacitors in Cambridge Audio A1 mk3
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Old 5th April 2021, 04:54 PM   #1
kesrmk is offline kesrmk  United Kingdom
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Default Tone control PCB without capacitors in Cambridge Audio A1 mk3

Hi,
just curious if someone seen the tone control (Bass, Treble) circuit without capacitors? When opened for fixing Cambridge Audio A1 mk3 I could not believe what I saw...
Did CA invented new tone control circuit which does not require 2 pairs of capacitors and resistors for bass and the same for treble?

Kes
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Old 5th April 2021, 05:46 PM   #2
PRR is offline PRR  United States
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Tone control PCB without capacitors in Cambridge Audio A1 mk3
Do the knobs do anything?

Parts-numbering does not match the docs on HiFiEngine.
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Old 5th April 2021, 06:19 PM   #3
kesrmk is offline kesrmk  United Kingdom
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Knobs making some difference but not as expected.
Bass knob makes difference on lower freq. But treble - just a little, not sure if any difference.
So wonder how that even works for Bass...

Definitely need to see the other side of the board...
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Old 5th April 2021, 09:10 PM   #4
tomchr is offline tomchr  Canada
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Well, that's wonky. You can request the schematic for the amp from Cambridge. When I was repairing an A23 they happily shared the schematic.

Tom
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Old 7th April 2021, 09:29 PM   #5
volume knob is offline volume knob  New Zealand
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It looks like the board has been modified, capacitors seem to have been removed and replaced with resistors. I'm guessing somebody wanted to defeat the tone control
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Old 10th April 2021, 09:23 PM   #6
Charles Wallis is offline Charles Wallis
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I am working on what looks like the same model. As you say there are no caps, despite them being marked on the PCB as shown in your pic. I found a schematic online but it does not match this version as it shows caps on the tone board along with +and - 15v voltage regulators. These have been replaced with simple 15 v zener diodes/resistor combinations for the IC power supply. My suspicion is that CA were cuttings costs at this point.
My one had a dud channel and plagued with motorboating and mains hum. I have replaced the two op amps, its a bit better but still distorted. The power amps are OK. There is not much else to replace. Any ideas?
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Old 13th April 2021, 09:35 AM   #7
romeoleung is offline romeoleung  Hong Kong
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Cambridge Audio A1 Schematic
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