Thanks Mooly, I'll keep that in mind- regarding measuring the FET current draw
@jackinnj thanks for the suggestion, still I'm starting to suspect the piezo input is being accurately reproduced even with the circuit I have, but that the problem is the unnatural sound gotten from the sensors being super close to the strings... if this is the case then even a circuit with insanely high headroom wouldn't fix it. Im open to any suggestions or experiments to figure out if this definitely is the case... for example, if there was a well known hardware preamp device that in fact does have insanely high headroom, I could maybe rent the device, and patch my dry piezo signal through that and give it a listen.
@bucks bunny- yeah the piezo sound like that is an unpleasant sound to my ears too... unnatural and harsh. I don't know if you've tried any IRs lately... but it really might be the solution for this. I haven't found the exact match for my guitar (and now I'm looking into recording my own IRs), but I'm very impressed in how certain IRs seemingly totally get rid of the piezo harshness. Of course now I'd like to figure out exactly WHY that works too lol
@jackinnj thanks for the suggestion, still I'm starting to suspect the piezo input is being accurately reproduced even with the circuit I have, but that the problem is the unnatural sound gotten from the sensors being super close to the strings... if this is the case then even a circuit with insanely high headroom wouldn't fix it. Im open to any suggestions or experiments to figure out if this definitely is the case... for example, if there was a well known hardware preamp device that in fact does have insanely high headroom, I could maybe rent the device, and patch my dry piezo signal through that and give it a listen.
@bucks bunny- yeah the piezo sound like that is an unpleasant sound to my ears too... unnatural and harsh. I don't know if you've tried any IRs lately... but it really might be the solution for this. I haven't found the exact match for my guitar (and now I'm looking into recording my own IRs), but I'm very impressed in how certain IRs seemingly totally get rid of the piezo harshness. Of course now I'd like to figure out exactly WHY that works too lol
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You can demonstrate the effect of insufficient headroom easily on some circuits -- and this is such a circuit -- lower the supply voltage. Before you toss one of the batteries when it reaches 7V or so; or pick up a [what we used to call] lantern battery - 6V; or set your variable bench supply(*) to 9V and lower it half a volt at a time.
Or you can line up some 1N400x's in series, forward biased, feeding the anode of the one on the end with 9V. Then each node will be 600 to 700 millivolts (guess-timating the ~10mA value -- the graph only goes down to 0,1A!) down from the one above it.
I think you'll find clipping to be a very different sound than what you're hearing.
* If you don't have a variable bench supply, this might be a good reason to get one. Stuff that runs on batteries should be tested over the full range of declining battery voltage. You might be surprised at some of the other design shortcomings / oversights that become apparent at a different operating voltage.
Cheers
Or you can line up some 1N400x's in series, forward biased, feeding the anode of the one on the end with 9V. Then each node will be 600 to 700 millivolts (guess-timating the ~10mA value -- the graph only goes down to 0,1A!) down from the one above it.
I think you'll find clipping to be a very different sound than what you're hearing.
* If you don't have a variable bench supply, this might be a good reason to get one. Stuff that runs on batteries should be tested over the full range of declining battery voltage. You might be surprised at some of the other design shortcomings / oversights that become apparent at a different operating voltage.
Cheers
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Thanks for the info Rick, I might have to try that diode voltage drop trick, I don't want to buy a variable bench supply just yet... though probably will in the future. Now that you mention it I'm guessing I might know what that clipping sounds like, every time a battery starts to die out. Overall, I recall an increasing "soft" distortion, accompanied with volume swelling down to nothing eventually. But the next time I'll try and pay attention to when the battery just starts to go... and listen critically. You're right... that sound is definitely not anything like the piezo harshness.
So yesterday I tested the TL062 in the circuit, and though almost identical sounding to the OPA2134, I eventually noticed some faint distortion on loud bass notes, so thus far I’ll stay with the OPA2134. I think I’ll start a new thread as recommended by Mooly.
Next up when I get time, is measuring current draw, might just continue that in the new thread though, as this thread was mainly about the 9V versus 18V condition- and 18V not making a difference for this particular circuit.
Next up when I get time, is measuring current draw, might just continue that in the new thread though, as this thread was mainly about the 9V versus 18V condition- and 18V not making a difference for this particular circuit.
Ah, that's interesting. Not sure what to say to the distortion tbh 🙂 it would have to be looked at on a scope really using a test signal to get an idea why it occurs.
using a multimeter I found that
- the OPA2134 is drawing 7.72 mA
- one pair of JFETs is drawing 1.2 mA
- total circuit (without LED and additional JFETs) is 9.02 mA
so I'm guessing I could just add 2.4 mA for the other 2 pairs of JFETs for a total of 11.42 mA?
I measured the TL062 and it only draws 0.64 mA... quite a difference!
Actually realized how easy it was to measure my current circuit and it measures 10.82 mA (incl all three JFET pairs and LED).
So simplifying it, the OPA2134 draws approx 8 mA, and each of the JFET pairs draw on average 1 mA each.
So simplifying it, the OPA2134 draws approx 8 mA, and each of the JFET pairs draw on average 1 mA each.