Cambridge Audio Topaz AM1 circuit needed.

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I am having a problem with a Cambridge Audio Topaz AM1 amp. Its Rev 3.0 2009/11/16. The one with no tone controls, only a vol and balance. No output on rh channel, the signal is not getting past the preamp but the output stage does work. I need to know the circuit between the two ICs of the pre amp.
Has anyone any circuits for this.
Thanks
thyristor44
 
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Hello rayma
I dont know where your post went or if I thanked you for your reply. So thanks anyway, unfortunately the hfe a1 circuit is not at all similar to my cut down and probably cheap a1. It has no tone controls at all and lots of links on the pcb where things have been missed out.
The circuit is not at all similar. Not sure how to go forewards
 
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It has no tone controls at all and lots of links on the pcb where things have been missed out.

I think the pcb is the same, and the two op amps are now in direct cascade.
The second op amp should just have two resistors in the nfb instead of the tone circuit.
The second stage could still be inverting, or they could have reworked it to be noninverting.

Can you trace from the first op amp output pin to the second op amp input pin? There may be
a direct connection, or perhaps through a nfb resistor. Otherwise post some close, clear photos
here of both sides of the pcb.
 
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'Seems a version of this very simple dual chipamp model is still current (£89) and as I read on a couple of sites, it does have problems with the volume control itself. Worth checking this out? YouTube
Your youtube video plays pop music and nothing for me about the vol control.
I had heard about the vol control problems but it checks out perfectly and works from the input to it so the main amp is fine.
 
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I am having a problem with a Cambridge Audio Topaz AM1 amp.

Hard to find a schematic, but it appears there are two inverting op amps in series
between the input and the balance and volume controls.

First check for signal getting to the board at the connector. If there is signal,
then maybe one op amp is bad, so check each op amp output pin 1 or pin 7 for signal.
If two of the op amp outputs have no signal, then it's the input op amp U1, since
that one is first.

Also check the input and output coupling capacitors, CC7/8 and CC29/30.
They could go open circuit.
 
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Dont remember where I got this, but this is a reverse engineered schematic of the A1mk3 as I indicated above. It's probably identical to the AM1.

While this schematic includes tone controls, I wouldnt mind betting they have simply left out the controls and configured the two dual opamps to form a (rather pointless) buffer
 

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Yep, from studying the board it's identical. The only thing they have done is added R35 and R36, which are 0 ohm jumpers that connect U1B/U2B's output to U1A/U2A's inverting input.

Check the opamp supply voltages. If they're OK, then suspect the 4.7uF input capacitors CC7/CC8 - the capacitors they use in these units are utter shite.

edit: Ah, yes.. so is the volume pot itself. If memory serves it's a dual 100K linear potentiometer. You should be able to find a suitable replacement easily - just fit it with wires
 
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