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What's the circuitery after the I/V converter?
What's the circuitery after the I/V converter?
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Old 2nd January 2018, 07:41 AM   #1
CHiroshi is offline CHiroshi  Sweden
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Default What's the circuitery after the I/V converter?

Hi!

I recently purchased a Philips CD150 for no money at all, and it had a few problems, the tray wouldn't open properly, and it would randomly refuse to play cds.

The tray problem was easily solved as it was purely mechanical, just a lack of lubrication.
For the rest, I changed all the caps, in both the dac board and the drive board. I was inspired by this blog: Inside Classic Audio: Philips CD150
Everything now works and it sounds great!

Looking at the service manual, I was wondering about a certain part of the output circuit. Please see in the attached schematic, I understand it is a classic I/V amplifier and a low-pass filter after the DAC, but I wonder what the circuitery I've marked (with all the transistors) is, and what it does.

Thanx in advance!
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Last edited by CHiroshi; 2nd January 2018 at 06:19 PM.
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Old 2nd January 2018, 08:19 AM   #2
RogerGustavsson is offline RogerGustavsson  Sweden
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Not an expert in electronics but I think they are muting circuits. You can try to bypass (in parallel with) the 100 F electrolytic capacitors (2384/5) with small value film capacitors. You can also replace them with OS-CON polymer capactiors.
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Old 2nd January 2018, 09:36 AM   #3
jan.didden is offline jan.didden  Europe
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Yes the top are the muting circuits, the other stuff is the power detector, which ensures that the mute is activated anyway until Power Good.

Jan
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Old 2nd January 2018, 01:25 PM   #4
CHiroshi is offline CHiroshi  Sweden
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Quote:
Originally Posted by jan.didden View Post
Yes the top are the muting circuits, the other stuff is the power detector, which ensures that the mute is activated anyway until Power Good.

Jan
Thanx!
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Old 2nd January 2018, 01:30 PM   #5
CHiroshi is offline CHiroshi  Sweden
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Quote:
Originally Posted by RogerGustavsson View Post
Not an expert in electronics but I think they are muting circuits. You can try to bypass (in parallel with) the 100 F electrolytic capacitors (2384/5) with small value film capacitors. You can also replace them with OS-CON polymer capactiors.
For the re-caping I did stick to the original values and sorts, except for the couplings ones you mention. Although I didn't want to go too low on the value, so I used polypropylens, 10uf, which seems ok since my amp's input has an impedance of 50Kohms.
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