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Old 28th November 2020, 11:00 AM   #1
yayage is offline yayage
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Hi,

I want to change the OPs in my vintage Kenwood PreAmp .
Some Modifikations were discussed here years ago.

The goal is to place good sounding OPs with less DC-Offset at the outputs.
I guess i have to choose low input bias current types.

In the schematic Output there is a JRC 5532DD which causes 150mV Offset.

Is there OPA2132 / OPA 2134 a good choice ?
Or maybe a LM4562? The input current is higher, but about 20mV Offset would be acceptable.

The input buffers are JRC4580DD with 100mV Offset and a very low slew rate.
Maybe there are the LM4562 a good choice too ?

Jay
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Old 28th November 2020, 11:17 AM   #2
Mooly is offline Mooly  United Kingdom
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The offset is not a problem in that design, and if anything I would say it defines a known and stable small voltage across the coupling caps.

The OPA's would generate near zero offset but as mentioned that isn't an issue anyway.

The LM4562 is possible replacement for the 5532 but I would advise that whatever you fit that you check any residual offset and reposition the coupling caps accordingly to suit any change in polarity of offset.
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Old 28th November 2020, 11:24 AM   #3
analog_sa is offline analog_sa  Europe
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Quote:
Originally Posted by Mooly View Post
I would advise that whatever you fit that you check any residual offset and reposition the coupling caps accordingly to suit any change in polarity of offset.
Do you think that at a 100mV polarity makes a difference? In what way?
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Old 28th November 2020, 11:34 AM   #4
Mooly is offline Mooly  United Kingdom
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100mv offset and its polarity makes a difference to electrolytic coupling caps and I would rather have 100mv with correct polarity across such a cap than have it reversed.

Any DC offset in an AC coupled circuit has no impact on audio quality whatsoever.
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Old 28th November 2020, 11:36 AM   #5
yayage is offline yayage
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I want to get rid of the coupling Cs ��
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Old 28th November 2020, 11:40 AM   #6
Mooly is offline Mooly  United Kingdom
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That could be misguided but its your choice

You will have to study the circuit in detail and see what the effect of such changes will be.
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Old 28th November 2020, 01:14 PM   #7
yayage is offline yayage
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Therefore I posted the schematics to get an opinion from the pro's ;-)
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Old 28th November 2020, 01:22 PM   #8
Michael Bean is offline Michael Bean  United States
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Quote:
Originally Posted by yayage View Post
I want to get rid of the coupling Cs ��
Yeah...Silly manufacturers are always putting extra parts in their products that don't need to be there.../s

Question: Why? Do you have a reason...or just a belief?

Mike
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Old 28th November 2020, 04:24 PM   #9
Fast Eddie D is offline Fast Eddie D  United States
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As long as you don't stack the poles, coupling caps have zero impact on audio reproduction (if sized correctly).
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