Blue 9643X dual pot ??? quality replacment ? - diyAudio
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Old 26th May 2011, 09:12 AM   #1
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Location: nottingham england
Default Blue 9643X dual pot ??? quality replacment ?

I am a volume imbalance on my pre amp which seems to be getting worse, guess the volume pot is the prime candidate ...... does any one recognise this part

blue board mounted dual channel pot with the following numbers written on the side ?

01A2AB28D1515
10K 10K
Mexixo 9643X

If so any suggestions for a quality drop in replacment?


also the boards have a lot of TL072CN op amp, these must be 10+ years old now and better quality alternatives recomended?

Many thanks for nay help or suggestions
( ps I am not technically knowledgable so please keep it simple)

Ian
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Old 26th May 2011, 10:42 AM   #2
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Think I have found the pot

Bourns 91-a2a-b28-d15d15 GBP 9.90 plus 20% vat from RSC - question remains is there a better qualty drop in replacement I could use ?
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Old 26th May 2011, 11:28 AM   #3
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Location: Brazil
Quote:
Originally Posted by ianfromnotts View Post
I am a volume imbalance on my pre amp which seems to be getting worse, guess the volume pot is the prime candidate ...... does any one recognise this part

blue board mounted dual channel pot with the following numbers written on the side ?

01A2AB28D1515
10K 10K
Mexixo 9643X

If so any suggestions for a quality drop in replacment?


also the boards have a lot of TL072CN op amp, these must be 10+ years old now and better quality alternatives recomended?

Many thanks for nay help or suggestions
( ps I am not technically knowledgable so please keep it simple)
Bourns pots, as they seem to be, are good pots.

Abut the TLO72CN, it's difficult to suggest anything without having a look at the schematic. Do you have it?

Those chips are from the '70s, and there are better options now, but it will depend on the specific application. Several discrete parts around them, like capacitors and resistors might have to be upgraded too with better chips.

In fact I'd start an upgrade improving the power supply and eliminating all electrolytic and ceramic capacitors from the signal path. Then go for a chip upgrade.


Carlos
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Old 26th May 2011, 11:47 AM   #4
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Location: nottingham england
Hi Carlos,

many thanks for your reply, as I understand it there were only about 14 of these units ever made in the late 1990s so I guess chances of find a circuit diagram is very small.

The Op Amps appear to be linked to the various input and control switches. Several component groupings are repeated for each switch. I will see if I can find somewhere to post a photo. Its a very neat and tidy board.

I would rather not make to many difficult to reverse mods - as it sounds and looks rather good.
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Old 26th May 2011, 12:03 PM   #5
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http://s665.photobucket.com/albums/v...pAmpssmall.jpg

Last edited by ianfromnotts; 26th May 2011 at 12:16 PM. Reason: smaller file size
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Old 26th May 2011, 01:41 PM   #6
macboy is offline macboy  Canada
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Location: Ottawa, Canada
TL072 is a FET input op-amp. If you were to replace it, I would suggest using another FET input amp, not a bipolar. There are subtle but important differences between circuits designed around a FET vs. a bipolar input op-amp. Most audio op-amps are bipolar. The Burr-Brown (TI) OPA2604, OPA2134, and OPA2132 are all FET input and are considered quite good. The TL072 is not a fast op-amp so don't choose a fast (high GBWP) op-amp as a replacement or you might face oscillation issues. I see that the op-amps are in sockets, which makes it very easy to "try and see".

Even if you don't replace them, pull each from its socket and re-insert it. The pins scraping against the socket connections will remove any corrosion that might have built up over time. I have in the past fixed problems using this simple procedure. This may in fact fix your imbalance problem.
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Old 26th May 2011, 02:24 PM   #7
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opa2134 is ony 1.66 GBP at RS uk.
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