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Tl072 lower power, low noise replacement
Old 1st February 2020
  #1
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Tl072 lower power, low noise replacement

Hi guys I'm new to the Forum, so thank you for having me.

I'm building a summing amplifier to mix a multi-coil pickup and using a Tl072 at the moment. Since my bass already has another circuit preamp in it I was thinking of using something that performs close to a tl072 but with lower power consumption and, same or less noise.
This will be running from a single 9v battery, so, battery life is also important.

I have considered the Tl062 but the noise might be a problem.

I would appreciate any suggestions.


Thank you
Old 1st February 2020
  #2
Gear Addict
I have used and can recommend the TLC2262 for active bass circuits. Very low power consumption (0.2 mA/ch vs 1.4 for the TL072), slightly lower voltage noise (12 vs 18 nV/sqrt(Hz)), much lower current noise (0.6 vs 10 fA/sqrt(Hz)) and it has a rail-to-rail output and "almost-rail-to-rail" input (Vdd- - 0.3V to Vdd+), always good for this application.
Old 1st February 2020
  #3
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That is great. Do you think I could just drop it in place of the tl072? The circuit has been made already, it would be great if I could just replace it without further adjustments.
Old 1st February 2020
  #4
Gear Addict
Pretty much, just the usual 100n ceramic cap between supply pins close to the opamp (probably already there) and, if it drives the output directly, although the 2262 is already quite good at driving capacitive loads, a 100R series resistor to improve phase and gain margins with long cables, just to be safe.
Old 1st February 2020
  #5
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Quote:
Originally Posted by Cabirio View Post
Pretty much, just the usual 100n ceramic cap between supply pins close to the opamp (probably already there) and, if it drives the output directly, although the 2262 is already quite good at driving capacitive loads, a 100R series resistor to improve phase and gain margins with long cables, just to be safe.
That cap, usually I use a bigger cap from Rail to Ground of the Power supply. like 100uf
On the opamp itself, I use nothing, just the normal summing opamp configuration with a small 100p cap in parallel with the feedback resistor. Is that what you mean?
Old 1st February 2020
  #6
The fet input OPA1642 draws 1.5 ma and is rail to rail. It has very low noise at 5 nv/hz/sq. For bipolar the OPA1662 does 3.3 nv noise at 1.5 ma. The OPA 1692 mosfet draws only .5 mv and does 3.3 nv noise, the best power vs noise performance.

Opamp rules still apply to each device.
Old 2nd February 2020
  #7
Gear Addict
Quote:
Originally Posted by garfo View Post
That cap, usually I use a bigger cap from Rail to Ground of the Power supply. like 100uf
On the opamp itself, I use nothing, just the normal summing opamp configuration with a small 100p cap in parallel with the feedback resistor. Is that what you mean?
No, I mean local supply bypassing, a small ceramic cap between supply pins as close as possible to the opamp, usually 100n unless the data sheet specifies something else. This is in addition to whatever large cap you have elsewhere for global bypassing and to the feedback cap.
Old 2nd February 2020
  #8
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Quote:
Originally Posted by Cabirio View Post
No, I mean local supply bypassing, a small ceramic cap between supply pins as close as possible to the opamp, usually 100n unless the data sheet specifies something else. This is in addition to whatever large cap you have elsewhere for global bypassing and to the feedback cap.
I understand. It will be running from a 9 volt battery, it might not need all that extra filtering, but there's no harm in doing so.
Old 2nd February 2020
  #9
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Quote:
Originally Posted by Jim Williams View Post
The fet input OPA1642 draws 1.5 ma and is rail to rail. It has very low noise at 5 nv/hz/sq. For bipolar the OPA1662 does 3.3 nv noise at 1.5 ma. The OPA 1692 mosfet draws only .5 mv and does 3.3 nv noise, the best power vs noise performance.

Opamp rules still apply to each device.
Will try to find the opa1642 and compare it with the tlc2262 and see which one will work best for my case. But that ine looks good if it was a straight comparison with a TL072.
Old 2nd February 2020
  #10
Gear Addict
Quote:
Originally Posted by garfo View Post
I understand. It will be running from a 9 volt battery, it might not need all that extra filtering, but there's no harm in doing so.
It's not filtering, it's supply bypassing, needed to prevent oscillation due to non-zero impedance supplies (like a 9V battery) and supply lines. Brief explanation here, for more info this app note is a classic.
Old 2nd February 2020
  #11
Gear Addict
Quote:
Originally Posted by garfo View Post
Will try to find the opa1642 and compare it with the tlc2262 and see which one will work best for my case. But that ine looks good if it was a straight comparison with a TL072.
Jim's recommendations are pretty much some of the best opamps currently available, but be aware that all are VSSOP/SOIC only, so you will need browndog adaptors. It's also debatable whether you will benefit much from their stellar performance in this particular application, it's not like you're upgrading the summing opamps in a studio console...
Old 3rd February 2020
  #12
Besides everything else debatable I've not found anyone that likes excessive hiss. TheBurrBrown OPA1652 at 2.9 nv noise is as quiet as it gets for a fet input opamp. Depending on the circuit design and resistor values those can deliver less noise than the lower noised bipolar counterparts because the jfets don't read the resistor thermal noise. If you use resistors above 10k ohms that will matter.
Old 3rd February 2020
  #13
Gear Addict
But this is a summing amp with no gain (I assume), so resistor thermal noise is going to dominate. Simulation of the typical inverting summer with two inputs and 10k resistors all around shows an EIN of -103.1 dB for the TLC2262 and -108.7 dB for the OPA1652 (which, in this particular circuit, is only 1.3 dB noisier than an ideal opamp, so, yeah, it's very good). In fact using 100k resistors worsens things (as expected) but also reduces the difference between opamps, -98.6 dB for the TLC2262 and -99.9 dB for the OPA1652, since thermal noise dominates even more now. In any case those are all more than acceptable figures given that what the opamp is summing is signals coming from bass pickups, not the quietest thing around.

Personally I'm more than happy with the TLC that lives inside one of my active basses, but if you want the very best and don't mind fiddling with browndogs, get the OPA, why not.

Edit: I did it quickly and made a mistake in the simulation. The figures above have been corrected, the comments still apply.
Old 4th February 2020
  #14
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Quote:
Originally Posted by Cabirio View Post
But this is a summing amp with no gain (I assume), so resistor thermal noise is going to dominate. Simulation of the typical inverting summer with two inputs and 10k resistors all around shows an EIN of -103.1 dB for the TLC2262 and -108.7 dB for the OPA1652 (which, in this particular circuit, is only 1.3 dB noisier than an ideal opamp, so, yeah, it's very good). In fact using 100k resistors worsens things (as expected) but also reduces the difference between opamps, -98.6 dB for the TLC2262 and -99.9 dB for the OPA1652, since thermal noise dominates even more now. In any case those are all more than acceptable figures given that what the opamp is summing is signals coming from bass pickups, not the quietest thing around.

Personally I'm more than happy with the TLC that lives inside one of my active basses, but if you want the very best and don't mind fiddling with browndogs, get the OPA, why not.

Edit: I did it quickly and made a mistake in the simulation. The figures above have been corrected, the comments still apply.
Thanks guys. I have chosen the TLC2262 or the TLC2264, have ordered both. The reason is that power consumption needs to be reduced cause I'm already using a big preamp for my bass.
I was going to use 100k resistors for mixing and feedback resistors because that is what I have seen on other projects, but I am actually trying to understand what would the best values be to make sure that there's no cross talk between the pickups and also as little noise as possible?
Also, should I buffer the pickups before Summing them?
These are questions that are making me more confused the more I dwell into the subject...
I have ordered the TLC2264 in case I need to first buffer them and then Sum, but I'm not sure if this is really necessary.
Any suggestion on what type of values i should be looking into? my pickups measure both around 7.7k.
Old 4th February 2020
  #15
Gear Addict
What's the layout: each pickpup -> vol. -> summing opamp -> tone? Something else? What's the value of the pots you're using? The reason I ask is that loading affects very significantly the frequency response of a pickup, so it all depends on how you intend to arrange the circuit. Also, you said there's already a preamp in there, how is it connected? A schematic of the whole thing would help.
Old 5th February 2020
  #16
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Quote:
Originally Posted by Cabirio View Post
What's the layout: each pickpup -> vol. -> summing opamp -> tone? Something else? What's the value of the pots you're using? The reason I ask is that loading affects very significantly the frequency response of a pickup, so it all depends on how you intend to arrange the circuit. Also, you said there's already a preamp in there, how is it connected? A schematic of the whole thing would help.
It's a multi-coil pickup, it's just the pickups, no pots. Do you know Wal basses? It's a multi coil pickup where each string has its own individual humbucker, like on Wal's.
I ended up putting the E string humbucker in series with the D string humbucker, and done the same for the other two. I have two hot signals now that need to be mixed. This is all for the same pickup. It's better to leave the preamp out of it because it's not relevant for what is being worked on here.
Each one measures around 7.7k. I just want to mix them without losing the full power of each one and have no cross talk between them.
At the moment I have them mixed passively like you do it on a Strat and it loses volume and sounds pretty weak compared to only when one of them is ON.
Attached Thumbnails
Tl072 lower power, low noise replacement-img_20200205_085337.jpg  

Last edited by garfo; 5th February 2020 at 09:55 AM.. Reason: adding an attachment
Old 5th February 2020
  #17
Gear Addict
If this schematic is correct, Wal pickups expect to see a load impedance of around 220k, so you could use that resistor value and no buffering. EIN will be -96 dB, probably still well below pickup noise. Note that in that case the cap in parallel with the feedback resistor shouldn't be bigger than 10p or so, otherwise you're building a low pass filter and your highs are gone.

For the lowest possible noise, use buffers and 10k resistors in the summer (going even lower gives you little advantage noise-wise and puts a more difficult load on the opamp). The attached circuit will drop EIN to -102.1 dB and has the advantage of being able to adjust pickup loading to taste, just increase or decrease the biasing resistors of the buffers for more / less highs.

Edit: forgot to mention that there will be no crosstalk at all with either option. What you're getting now is mutual pickup loading, each pickup sees the other one as a low impedance to ground so basically you get a voltage divider. Which is why, counterintuitively, a humbucker wired in parallel is quieter than just split to one coil.
Attached Thumbnails
Tl072 lower power, low noise replacement-garfo-buff.png  
Old 5th February 2020
  #18
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Oh man, thank you so much for creating that circuit for me, I really appreciate it!!!
So do you reckon even with the summing amp I will lose volume from the overall final mix?
I mean, I don't mind that, as long as the pickups aren't interacting with each other, which is the overall point if all this.
Edit: I just properly read what you said and fully understand that this is the way to go. Thank you so much.
Old 5th February 2020
  #19
Gear Addict
Quote:
Originally Posted by garfo View Post
Oh man, thank you so much for creating that circuit for me, I really appreciate it!!!
So do you reckon even with the summing amp I will lose volume from the overall final mix?
I mean, I don't mind that, as long as the pickups aren't interacting with each other, which is the overall point if all this.
My pleasure! No, you won't lose any volume with the summing amp, you only get this mutual pickup loading effect when you just connect them together passively.
Old 5th February 2020
  #20
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I will be using this schematic as it is what I have imagined just with the right resistor values.
Also, I'm assuming you have left the 100n cap from opamp rail to ground out of the equation because it's implied.

Edit: forgot to mention I will need to use one more opamp to flip the phase again as this pickup(bridge) will then be mixed with a neck pickup on the preamp that already exists on the bass. Therefore, noise might increase a bit more, but I'm sure it will be ok.
Old 5th February 2020
  #21
Gear Addict
Quote:
Originally Posted by garfo View Post
I will be using this schematic as it is what I have imagined just with the right resistor values.
Also, I'm assuming you have left the 100n cap from opamp rail to ground out of the equation because it's implied.
Yup. BTW here you want an X7R ceramic but don't be tempted to use that also for the inputs to the buffers, there you want film caps.
Quote:
Edit: forgot to mention I will need to use one more opamp to flip the phase again as this pickup(bridge) will then be mixed with a neck pickup on the preamp that already exists on the bass. Therefore, noise might increase a bit more, but I'm sure it will be ok.
EIN is -100.6 dB with the circuit below, just 1.5 dB noisier and still pretty good. OTOH you could simply flip the wires on either the neck or bridge pickup. If you do that, don't leave the unused opamp section floating, connect it as a buffer, output to in(-), and in(+) to Vb, second circuit below.
Attached Thumbnails
Tl072 lower power, low noise replacement-garfo-buff2.png   Tl072 lower power, low noise replacement-garfo-buff3.png  
Old 5th February 2020
  #22
Summing passive electric guitar pickups is a losing proposition. Too much thermal noise, too much loading, the pickups will be dulled in the high frequencies. You may never reach the pickup's resonant peak that way, just a big high frequency droop.

Here each pickup is buffered by a low noise opamp with a 5 meg input impedance. Then the output is low impedance and 10k sum resistors can be used. That way all the bandwidth and response of the pickup is heard.

220k ohms is too low to load a pickup with.
Old 5th February 2020
  #23
Gear Addict
Quote:
Originally Posted by Jim Williams View Post
Summing passive electric guitar pickups is a losing proposition. Too much thermal noise, too much loading, the pickups will be dulled in the high frequencies. You may never reach the pickup's resonant peak that way, just a big high frequency droop.

Here each pickup is buffered by a low noise opamp with a 5 meg input impedance. Then the output is low impedance and 10k sum resistors can be used. That way all the bandwidth and response of the pickup is heard.

220k ohms is too low to load a pickup with.
220k is the normal load for those pickups with the Wal active circuit linked above. A Jazz Bass pickup is loaded with around 80k (three 250k pots in parallel plus the usual 1M amp input impedance) and it works just fine with cable capacitance to give the required resonant peak. And, as calculated, it doesn't look like noise will be a problem here even without the buffers...
Old 5th February 2020
  #24
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I'm sure upping those resistors a bit would be fine to increase the input impedance, but 5M seems overkil.
Will be experimenting, but overall, it seems good.
Old 6th February 2020
  #25
Five meg ohms is required if you want to hear the full pickup bandwidth. Most never have as it's rather open sounding and intimate. You also have a choice of taming that by using a no-load tone pot. When off = 5 meg ohms, when on, 250k with the tone loading cap. It's very easy to hear the shift through a wideband DI as the resonant peak is gone with the 250k load.

Options are paramount in a wide choice universe.
Old 7th February 2020
  #26
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Quote:
Originally Posted by Jim Williams View Post
Five meg ohms is required if you want to hear the full pickup bandwidth. Most never have as it's rather open sounding and intimate. You also have a choice of taming that by using a no-load tone pot. When off = 5 meg ohms, when on, 250k with the tone loading cap. It's very easy to hear the shift through a wideband DI as the resonant peak is gone with the 250k load.

Options are paramount in a wide choice universe.
I see, but there will be no pots, the pickup will be mixed actively and then move on to the next stage to be mixed with the neck pickup actively.
So the only load it will see will be from those resistors on the buffers.
Old 7th February 2020
  #27
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Quote:
Originally Posted by Cabirio View Post
220k is the normal load for those pickups with the Wal active circuit linked above. A Jazz Bass pickup is loaded with around 80k (three 250k pots in parallel plus the usual 1M amp input impedance) and it works just fine with cable capacitance to give the required resonant peak. And, as calculated, it doesn't look like noise will be a problem here even without the buffers...
Cabirio, in case I want to boost the signal a little bit, should I look at increasing the Feedback resistor?
I ask this because there might be a way of me getting the full potential out of the pickup. that is, taking four individual outputs, one per string, from the pickup. If I can manage that, the output will be a bit lower than at the present moment and I might need to recover some gain so that I can match better with the Neck pickup. I might this on the Phase invertion stage, but just not sure of what to do to amplify the signal above unity.
Old 7th February 2020
  #28
Gear Addict
Quote:
Originally Posted by garfo View Post
Cabirio, in case I want to boost the signal a little bit, should I look at increasing the Feedback resistor?
Yes, just increase the feedback resistor in the summing stage: e.g. 22k will give you a gain of 2.2, 33k -> 3.3 gain, etc. Don't forget to reduce the parallel cap accordingly, e.g. 47p for 22k, 33p for 33k, etc.
Old 7th February 2020
  #29
The feedback resistor should be close to the DC resistance of the guitar pickup. A 6k Strat pickup should have a 6k feedback resistor. That way source and feedback resistance is matched and DC offsets are at their lowest. The shunt resistor from the inverting input to ground is where you take additional gain as that will be the same or lower value than the feedback resistor. That will also lower resistor thermal noise as the guitar pickup sets the true resistive load from the opamp. The 5 meg load resistor sets the AC impedance but the opamp will read the lower 6k DC resistance.

Here I either use a no-load pot on basic preamp/buffers but my other circuits have active EQ. Some are 3 band fixed, some are two band sweep bell curves. Those tune from 40hz to 22k hz.
Old 7th February 2020
  #30
Gear Addict
It's single supply, Jim.
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