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Chip Amps Amplifiers based on integrated circuits

Help! Can't get a NE5532 stage to work.
Help! Can't get a NE5532 stage to work.
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Old 10th May 2020, 05:48 PM   #11
nigelwright7557 is online now nigelwright7557  United Kingdom
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Quote:
Originally Posted by andyjevans View Post
Thanks Mooly.
- Can you talk more about the "massively unbalanced input resistances" and how to correct them?

- Are you saying that in the image you have posted up in the last post, the D2 diode as shown in that image is incorrect? i.e. it should be the reverse of D1?
D2 is wrong in diagram.
Try pulling 5532 and see if power supply goes back up.
If it does the 5532 is fried.
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Old 10th May 2020, 07:07 PM   #12
Mooly is offline Mooly  United Kingdom
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Help! Can't get a NE5532 stage to work.
Quote:
Originally Posted by andyjevans View Post
Thanks Mooly.
- Can you talk more about the "massively unbalanced input resistances" and how to correct them?

- Are you saying that in the image you have posted up in the last post, the D2 diode as shown in that image is incorrect? i.e. it should be the reverse of D1?
Yes, D2 needs turning 180 degrees. It is drawn the wrong way around.

The 5532 has relatively high input bias currents. These are the tiny currents that flow out of the opamp input pins. Both inputs will be very well matched but the current could be as high as 800 nano amps (from the data sheet).

That doesn't sound much but that current flows out of the input pin and into the 39k and so that develops a voltage of 31 millivolts across that resistor.

You have the opamp configured as DC coupled and so that offset gets multiplied by the gain of the circuit... and you get a high offset at the output.

So to eliminate it (and you could just use AC coupling at the input and output) you should make the feedback resistor equal 39k (which keeps the two input offset voltages the same (31mv for each but zero between the two) and AC couple the 1k to keep the gain at DC equal to unity.

Now 39k may not suit in terms of noise and so on and so the alternatives are to use an opamp with lower input bias currents such as the LM4562 or even a FET opamp which has essentially zero input bias current.
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Old 10th May 2020, 08:19 PM   #13
andyjevans is offline andyjevans  United Kingdom
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Thanks for that, Mooly. I have LM4562 and OPA2134. Will they just drop into a NE5532 circuit with no changes?
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Old 10th May 2020, 08:52 PM   #14
Mark Tillotson is offline Mark Tillotson
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Quote:
Originally Posted by andyjevans View Post
Thanks Mooly.
- Can you talk more about the "massively unbalanced input resistances" and how to correct them?
It not a problem, one input is 39k to ground, and with 0.2ľA of bias current that's a few millivolts of offset, worst case bias current is 0.8ľA (30mV offset).
Quote:

- Are you saying that in the image you have posted up in the last post, the D2 diode as shown in that image is incorrect? i.e. it should be the reverse of D1?
Yes, since the current flows the other way in the negative regulator.
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Old 11th May 2020, 06:33 AM   #15
Mooly is offline Mooly  United Kingdom
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Help! Can't get a NE5532 stage to work.
Quote:
Originally Posted by andyjevans View Post
Thanks for that, Mooly. I have LM4562 and OPA2134. Will they just drop into a NE5532 circuit with no changes?
Yes.
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Old 11th May 2020, 02:30 PM   #16
andyjevans is offline andyjevans  United Kingdom
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Good news - it's all working. Did some fault finding, installed protection diodes, earthed the centre point of the 20-0-20 toroid. No hum, music coming out now. Now I can start optimising the setup.

I have a few different op-amps to play with -
NE5532
LM4562
OPA2134
LM6172
OPA2228
also NE5534, interesting and will be a future project.

I also have two setups - the new dual supply stage and my existing single supply chi-fi board which sounds pretty good in fact. All SMD except the socketed op-amp. Right now listening to a LM4562 in the single supply board. Better than the NE5532, particularly in the treble, and more detail. It's pretty nice. The idea of an initial op-amp stage is clearly realistic in my tube setup.

Thanks guys for all your help up to this point - meant a lot!! I'll post any more news about tweaking it.
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Old 11th May 2020, 05:22 PM   #17
Mooly is offline Mooly  United Kingdom
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Help! Can't get a NE5532 stage to work.
pleased to hear you got it all going.
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