I would like to build acoustic guitar preamp based on Fender Acoustasonic circuit.
I got 15V power supply and some TL072, I need one-channel preamp with line-level output of 600-700mV.
Could you help me to understand, following the input and EQ (U1) which part (op-amps) of the circuit to use and how ?
Thanks to All!
I got 15V power supply and some TL072, I need one-channel preamp with line-level output of 600-700mV.
Could you help me to understand, following the input and EQ (U1) which part (op-amps) of the circuit to use and how ?
Thanks to All!
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First off, a TL072 is a poor choice for an opamp, methinks. An OPA1642 is much quieter, cleaner, and faster.
A TL072 works well in this type of amplifier, the noise is low enough not to be noticed and bearing in mind we are talking guitar/instrument amplification, sometimes that tiny bit of noise is good.
If you are running directly from a piezo pickup, you must have a very high impedance or there will be no mid/bass. That is where the TL07* range with FET input stages comes to its own. Very high impedance. If you have a pre amp on the guitar, the Fender design is fine.
Watch out for any copyright on the design!
If you are running directly from a piezo pickup, you must have a very high impedance or there will be no mid/bass. That is where the TL07* range with FET input stages comes to its own. Very high impedance. If you have a pre amp on the guitar, the Fender design is fine.
Watch out for any copyright on the design!
Many thanks!
Yes, this is all for acoustic guitar - active and passive pickup systems.
My goal is to get a line-level 600mV output with only two TL072s..... would this work as on the picture below
I guess that the R10 might be raised little bit, isn't it ???
Thank You!
Your pickup pre amp on the guitar will produce a lot more than 28mV. Suck it and see would be the answer and fit a 50k pot where R10 is.
I disagree---a TL072 WILL produce enough noise to be noticeable. And although some even-order harmonic distortion may actually be pleasant to the ear, noise NEVER is. An OPA1642 is also an FET design with high enough input impedance to not be a load to the pickup, while still being quiet, clean, and also provides rail-to-rail performance to extend headroom. Copyright isn't an issue if building for your own use. Also avoid using ANY electrolytic capacitors in the signal path--use film types instead; the 2.2uF values shown in the schematic should be raised to at least 10uF.
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All this i true by the numbers of the data sheet, but absolutely irrelevant to the application of a acoustic guitar piezo pre-amp.
If you look at the source impedance of a piezo pu you will find that noise is given by hi-Z- source noise, not by any voltage noise of TL074.
btw, did you know that commercial piezo pickup / equalizer units are equipped with TL064?
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Hi and thanks!
So, generally, the schematic doesn't seem fake, isn't it?
Does 'Phase' switch seem to be OK too ?
Just trying to make it all clear before assembling the circuit.
> I got 15V power supply
The plan calls for Plus-And-Minus 15V. "+/-15". Do you understand that bit?
The exact voltage is not critical. +/-12V works, as will +/-18V (but NO higher!!).
If you have TL07x in hand, use them. They have been fine in bazillions of guitar interfaces and effects, quieter than the best 12AX7, and quite tame in "poor" layouts.
Dotneck335 is correct: the TL07x hiss voltage is audibly higher than a OPA1642, and the OPA1642 has a hiss-current spec but the TL07x does not give a number. Nevertheless, the TL07x is the go-to part for both guitar pickups (including piezo) and low-price condenser mikes (so its hiss-current must not be huge or very variable).
The plan calls for Plus-And-Minus 15V. "+/-15". Do you understand that bit?
The exact voltage is not critical. +/-12V works, as will +/-18V (but NO higher!!).
If you have TL07x in hand, use them. They have been fine in bazillions of guitar interfaces and effects, quieter than the best 12AX7, and quite tame in "poor" layouts.
Dotneck335 is correct: the TL07x hiss voltage is audibly higher than a OPA1642, and the OPA1642 has a hiss-current spec but the TL07x does not give a number. Nevertheless, the TL07x is the go-to part for both guitar pickups (including piezo) and low-price condenser mikes (so its hiss-current must not be huge or very variable).
Hi,
Do you mean acoustic guitars' on-board pickup systems? have you really seen them ?
I have opened my B-Band pickup box several times but op-amps and other semi-conductors are not marked as far as I remember.
If so, this circuit would be absolutely fine to use internally in the guitar's body.
When using a high-impedance source, it's not the VOLTAGE noise that dominates, it's the CURRENT noise. And the OPA1642 shines in that regard. Commercial units use the TL064 because of its VERY low current draw, and they're CHEAP.
Yes, I have seen some of these 9V powered PreAmp/Equalizer sets including one from a Yamaha acoustic guitar.
TL064 certainly exhibits one of the highest noise voltages, but obviously this is no issue in that application.
Besides its low price the quite low power consumption makes it attractive.
I do not see what is "obviously no issue" with a TL064. It has an outrageously high noise voltage spec (42 nV√Hz) that is SEVEN times as much as an OPA1642; although the datasheet does not specify current noise, it is likely similar to a TL072--TWELVE times that of the OPA1642. It is also SIX times slower. The TL064 excels at its design goal--"the JFET-input operational amplifiers of the TL06x CC+ series are designed as low-power versions of the TL08x series amplifiers". If the low power consumption is paramount (as in battery-powered devices), then its use is justified; otherwise it is a poor choice.
It's not an issue, because seven times less than inaudible is still inaudible. 🙂
If you could cool your OPA1642 with liquid nitrogen, the way NASA and JPL do with their ultra-sensitive satellite receiver equipment, you could make it much quieter yet (77 Kelvin vs roughly 300 Kelvin for room temperature; roughly a quarter of the temperature means thermal noise voltages and currents should be roughly halved).
And, for this application, the super-cooled OPA1642 wouldn't be any better than an ordinary room-temperature TL072, either. Fourteen times less than inaudible is still inaudible, too!
The facts are that electro-acoustic guitars are instruments with inherently rather low dynamic range. Piezo pickups put out fairly hefty signal voltages. On top of that, the SPL demanded from the acoustic guitar amp will be moderate (because electro-acoustic guitars will feed back like crazy at high SPL levels). Finally, this type of guitar is normally used with a "clean" setting - which means amplifier gain is low, and therefore so are output noise voltages.
All this adds up to no hiss problem when amplifying electro-acoustic guitars. I can't remember having heard annoying amounts of hiss from any commercially available acoustic guitar amp in recent decades (and you can bet your boots those amps weren't using premium-priced speciality opamps).
My experience is that the hiss and rumble from air-conditioning systems and / or any cooling or ventilation fans in the room is what usually sets the noise floor in (amplfied) acoustic guitar performances. Let's not forget audience noises, either.
-Gnobuddy
Doggone it!! Still can't figure out how to get those liquid nitrogen tubes hooked onto my Martin guitar!! Maybe I should use the nitrogen to cool the ROOM instead and rid that pesky A.C. hiss & rumble!!
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