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Chip Amps Amplifiers based on integrated circuits

Squeezing maximum gain from one dual op-amp?
Squeezing maximum gain from one dual op-amp?
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Old 2nd February 2018, 11:44 PM   #11
nigelwright7557 is offline nigelwright7557  United Kingdom
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Rather than use the max gain you should be looking for actual required gain.
That way you aren't introducing any more distortion than you have to.
Also the bandwidth will probably be better with less gain.
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Old 3rd February 2018, 12:42 AM   #12
Eps is offline Eps  United States
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Quote:
Originally Posted by rayma View Post
Should work.
Do you feel like it matters to have the NAB on the first or second stage in terms of noise? Also will changing my VDC from 12v to 9v affect gain or introduce other issues or even bonuses?

On another subject, what would be the proper way to split the output of this preamp so that it went to both a 1/4" out as well as back into a recording tape head? Would that entail just splitting off to a bias resistor (or trimmer) to lower the level back down to acceptable record level or would you need any additional parts to keep the split in signal more protected? (I hope that makes sense)

I know I'll need to attempt a DC bias recording circuit which I have heard is not an easy feat... I'm having a hard time finding examples online somehow, just a ton of AC bias circuits which I can't use for my project.

Last edited by Eps; 3rd February 2018 at 12:56 AM.
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Old 3rd February 2018, 12:46 AM   #13
Eps is offline Eps  United States
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Quote:
Originally Posted by nigelwright7557 View Post
Rather than use the max gain you should be looking for actual required gain.
That way you aren't introducing any more distortion than you have to.
Also the bandwidth will probably be better with less gain.

Ok cool, I'll keep that in mind. I'm in need of a good deal more than the circuit gives in its current one stage state. I've also been thinking that having the ability to push things into a bit of saturation/distortion (if I need) in the second stage may be a nice option. Will see if there is "nice" involved in the actual tonalities!

Last edited by Eps; 3rd February 2018 at 12:54 AM.
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Old 3rd February 2018, 01:48 AM   #14
rayma is offline rayma  United States
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Quote:
Originally Posted by Eps View Post
Do you feel like it matters to have the NAB on the first or second stage in terms of noise?
Also will changing my VDC from 12v to 9v affect gain or introduce other issues or even bonuses?

On another subject, what would be the proper way to split the output of this preamp so that
it went to both a 1/4" out as well as back into a recording tape head?
If the eq is earlier in the circuit, there's more headroom. If the eq is later in the circuit, there's less noise.
Lower supply voltage gives less headroom.

If the eq is in the first stage, you could connect the recording tape head to that output,
instead of going through the second flat stage, if the first stage's gain is enough.
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Old 3rd February 2018, 04:52 AM   #15
gigigirl is offline gigigirl
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Default Have a look at this one

Hi, I am actually using this as a Pre/Pre while my MC Phono Pre is being upgraded. I put it in as a stop gap, but am very impressed & it is untra quiet & gets scarily close to my $2,000 MC Pre. Maybe it could work in your application.

NE5532 Dynamic Microphone Stereo Preamp Amplifier Board + Signal Shielding C8J9 | eBay
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Old 6th February 2018, 02:15 PM   #16
Eps is offline Eps  United States
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Quote:
Originally Posted by rayma View Post
If the eq is earlier in the circuit, there's more headroom. If the eq is later in the circuit, there's less noise.
Lower supply voltage gives less headroom.
Somehow I'm only managing to send the circuit into oscillation in this format. Can you think of anything that I should look at first to avoid this?

Thank you
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Old 6th February 2018, 06:42 PM   #17
rayma is offline rayma  United States
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Quote:
Originally Posted by Eps View Post
Somehow I'm only managing to send the circuit into oscillation in this format.
Check that the nfb goes to the inverting input in all stages.
Can you post your schematic?

Last edited by rayma; 6th February 2018 at 06:47 PM.
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Old 7th February 2018, 04:50 PM   #18
Eps is offline Eps  United States
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Quote:
Originally Posted by rayma View Post
Check that the nfb goes to the inverting input in all stages.
Can you post your schematic?
I think I'm am following that but I could be wrong. I have attached my schematic. The unlabeled resistor is a 100k.

I have tried this using 750ohm to ground as you had suggested before for R6 but it has similar style behavior.

Do I need to remove C3 and R5 for this scenario? I'm confused as to how to handle both R5 and R6.

Thank you
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Old 7th February 2018, 05:42 PM   #19
Eps is offline Eps  United States
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Quote:
Originally Posted by rayma View Post
Check that the nfb goes to the inverting input in all stages.
Can you post your schematic?
Ok so I got the feedback to stop, just had something in the wrong place

I'm trying to play with the values of R6 and R5 to raise db without distortion.
I've noticed that it seems like R5 isn't necessary, but is that correct?
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Old 7th February 2018, 05:48 PM   #20
Mooly is offline Mooly  United Kingdom
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Squeezing maximum gain from one dual op-amp?
You seem to be missing a resistor between pin 6 and pin 7.

The overall gain is set approximately by the ratio of the resistor between pin 6 and 7 and the resistor from pin 7 to ground (via its cap of course). No resistor gives unity gain (and it may not be stable like that).
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