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Old 6th February 2013, 07:41 PM   #11
Limp is offline Limp  Norway
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Output will go straight into a portable PCM recorder.
Very good. Thanks a lot for all the help, it's highly appreciated.
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Old 7th February 2013, 10:56 AM   #12
Tesla88 is offline Tesla88  Italy
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I suggest the use of NE5532 in place of TL072 , it's a dual LO-noise op amp , anyway TL072 is good...
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Old 7th February 2013, 12:59 PM   #13
JMFahey is online now JMFahey  Argentina
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NE5532 is an *excellent* Op Amp and in some characteristics "better" than TL072, but "eats" over twice the current, a no no in a 9V battery powered preamp.
And the only "useful difference" in this case (which is somewhat lower noise) does not justify the halved battery life because anyway the signal it preamplifies is very high (so much so that the danger is overdriving the input) and to boot comes from a capacitive source, which damps hiss *a lot* by definition.
NE55XX are preferred in line powered mixers and preamps, whwre they handle much lower level signals and there is not a PSU problem.

In fact, battery powered effects, preamps, and active guitar electronics use TL062 , somewhat less impressive specs, but incredible 1/5 the current needed (meaning batteries last, say, 1000 hours instead of 200 , a BIG advantage in an instrument).
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Old 7th February 2013, 11:20 PM   #14
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Quote:
Originally Posted by JMFahey View Post
NE5532 is an *excellent* Op Amp and in some characteristics "better" than TL072, but "eats" over twice the current, a no no in a 9V battery powered preamp.
I do not know all the requirements by the OP but small powerful (>2000mAH) Li battery packs are readily available. A rechargeable 2200maH 12V Li cell cluster is about the size of two cigarette packs [no, I do not condone smoking]. I have a few in my workshop.

The higher voltage, and higher current capacity of a 12V cluster might give the OP more options and more assurance [of continuous power].
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Old 12th February 2013, 10:29 AM   #15
Limp is offline Limp  Norway
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Right.
I've spent some time researching these single rail op-amp circuits, and it has resulted in some minor changes to the circuit I posted in the OP. Basically it is now an amalgam of fig. 2 from here and fig. 6-1 from here, and values adjusted according to the recommendations in the text.
I did consider the 5532, but it seemed to be a pretty wide consensus on that the TL072, and other FET input op-amps, will be best suited to handle a high impedance source.
I'll probably do some further adjustments when I get all the parts, but I think this is about as far as can I get with just reading and calculating.
C2, the two jumpers and the rheostat are added in case I'd wish to use it to amplify condenser microphones.

Click the image to open in full size.
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Old 12th February 2013, 10:45 AM   #16
jcx is offline jcx  United States
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decades ago CMOS op amps were avoided in audio because of "popcorn noise"

I think the newer processes are lots better - there are low noise, low Iq CMOS op amps with better specs than the TL062 or 72



the spare op amp should be wired up to be stable - don't want drift, noise causing the output to swing wildly - buffering the supply spliting R divider as an active gnd is a good use

Last edited by jcx; 12th February 2013 at 10:47 AM.
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Old 12th February 2013, 11:25 AM   #17
Limp is offline Limp  Norway
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As the thread title suggest I intend to build it as a stereo amplifier, I just didn't bother to draw it all in.
Any suggestions for a good CMOS candidate? Low power consumption is also a desirable attribute.
I know there better FET alternatives than the 072 too, but they are usually rather expensive or unavailable to me.
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Old 12th February 2013, 11:44 AM   #18
jcx is offline jcx  United States
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I haven't looked hard for a while new interesting CMOS op-amps is getting dated, wasn't comprehensive anyway
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Old 12th February 2013, 01:51 PM   #19
Limp is offline Limp  Norway
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After some rummaging about, I think I found one: MCP6022.
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Old 12th February 2013, 02:47 PM   #20
JMFahey is online now JMFahey  Argentina
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Your schematic on post#15 looks good.
TL072 is the one used by EVERYBODY (Marshall/Fender/Laney/Peavey/Crate /..... /etc.)
Maybe there's a reason for that.

EDIT: why do I suggest an "old boring" Op Amp, instead of a "new exciting" one?
Well, it depends on goals.

If you already built a dozen Mic preamps and are bored stiff with them, ok, start plugging new chips in the old circuits.
Personally I'd try to design new circuits, but hey, that's me

But as you seem to need a working Preamp to actually be used to make Music, well, I'd try to avoid (unnecessary) surprises and build a robust well tried circuit.

Otherwise, you are walking a minefield.
As in: did you notice the MCP6022 is designed for PSUs of 2.5 to 5.5 V (single rail)?
With an absolute max rail of 7V?
Meaning that 9V battery would probably destroy it.
Not nice to find that after you built it

Last edited by JMFahey; 12th February 2013 at 03:04 PM.
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