I'm currently putting together a contact mic system to record various instrument and environmental sounds using 20mm piezo discs. Now I've come to the preamp part and need a little help. I'm very new to this.
This design has been chosen: megalithia.com/sounds/tech/piezo/opamp.html, simply because it seems to be the only one with decent documentation.
I know how to follow a simple circuit, what I need help with is how to turn it into a stereo amplifier. I suspect this is stupidly simple, but as I said, I'm very new to this.
Sincerely sorry for all the fuss.
This design has been chosen: megalithia.com/sounds/tech/piezo/opamp.html, simply because it seems to be the only one with decent documentation.
I know how to follow a simple circuit, what I need help with is how to turn it into a stereo amplifier. I suspect this is stupidly simple, but as I said, I'm very new to this.
Sincerely sorry for all the fuss.
An externally hosted image should be here but it was not working when we last tested it.
To make it stereo , just duplicate the circuit , ground must be common to both circuits , you can use a dual op-amp ...
What i doubt is linearity , piezo are not that linear IMHO so i would use a circuit with a frequency response inverse to the piezo response , this would compensate the lack of piezo giving a quasi-flat curve.
I bet better conditioning circuit for piezo exists...
What i doubt is linearity , piezo are not that linear IMHO so i would use a circuit with a frequency response inverse to the piezo response , this would compensate the lack of piezo giving a quasi-flat curve.
I bet better conditioning circuit for piezo exists...
Thanks for the replies.
I have two discs per channel, connected in series, attached to various resonant surfaces. A guitar, a tin flute and a steel plate.
Currently they're just attached with some mild adhesive directly on surface, but I have some disc neodymium magnets in the mail.
This circuit seemed like a good compromise between simplicity and performance. I intend to keep this at a modest hobby level.
Given the noise performance documented I believe moderate frequency non-linearities can be ironed out post ADC.
Any recommendations for a suitable dual op-amp?
I have two discs per channel, connected in series, attached to various resonant surfaces. A guitar, a tin flute and a steel plate.
Currently they're just attached with some mild adhesive directly on surface, but I have some disc neodymium magnets in the mail.
This circuit seemed like a good compromise between simplicity and performance. I intend to keep this at a modest hobby level.
Given the noise performance documented I believe moderate frequency non-linearities can be ironed out post ADC.
Any recommendations for a suitable dual op-amp?
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I am out-of-date on the latest [audio] op-amps but I am sure you can find on other threads. I would think low noise would be critical. Do you want single-ended or dual? Will they be battery powered?
Dual, battery powered.
Problem is that all the piezo preamp designs I've found have been mono, and I don't really know enough about circuit design to discern desirable op-amp properties.
I could of course just double up as proposed by Tesla. It would be the simplest solution, I suppose. If I change the op-amp I'd have to adjust the rest of the circuit too.
What about power, do I need two batteries?
Problem is that all the piezo preamp designs I've found have been mono, and I don't really know enough about circuit design to discern desirable op-amp properties.
I could of course just double up as proposed by Tesla. It would be the simplest solution, I suppose. If I change the op-amp I'd have to adjust the rest of the circuit too.
What about power, do I need two batteries?
Alright, reading has been good. I feel like I'm about ready to start ordering parts, but first.
What adjustments do I need to do to make the above circuit more adapted for the TL072.
I'm in particular uncertain about R1, 2 and 3 at the input (determining input Z as I understand it), and the feedback topology.
And what's the role of C2 in this scheme?
What adjustments do I need to do to make the above circuit more adapted for the TL072.
I'm in particular uncertain about R1, 2 and 3 at the input (determining input Z as I understand it), and the feedback topology.
And what's the role of C2 in this scheme?
None.
By definition "all Op Amps are the same" , which holds true 90% of the time.
In *some* borderline applications (very high or low supply voltage/much lower than usual noise/ultra low power consumption/etc.) you may need to use a special one, but the concept besides Op Amps is "Universal gain blocks".
In this case, requirements are easily met by most.
Only adaptation you'll need is pinout: shown is for a single Op Amp, while TL072 has 2 inside, with different pin numbers.
Just build it as is.
Input Z is 1M (fine) and gain is 10X, which is probably right.
Piezos glued straight to the vibrating surfaces produce strong and clean signals.
You are using an Op Amp meant for dual supplies (say, +/-9V if you run from batteries) with a single one.
Then you need to "split" those 9V into something equivalent to 2 4.5V supplies in series, which is achieved using R2/R3.
You need to couple that center point to ground, using C2.
I suggest you read something about Op Amps or you'll find a problem every 5 minutes
Maybe somebody can suggest a tutorial .
As I understand it, you'll build 2 preamps, and feed those outputs into some kind of stereo mixer, is that so?
In this case, increasing is good, because it lowers source impedance .
What was problematic was wiring them in series, because it lowers capacitance, makes source impedance higher, and complicates a lot proper shielding of the "floating" one.
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).
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).
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].
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.
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.
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
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
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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.
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.
I haven't looked hard for a while http://www.diyaudio.com/forums/solid-state/68793-new-interesting-cmos-op-amps-2.html#post843381 is getting dated, wasn't comprehensive anyway
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
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
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