Yes, the second circuit fails on all counts, it's an incredibly poor 'design' - although when it's that poor I'm loath to even use the word 'design'.
The first TL071 is going to work MUCH better.
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<< ...the second circuit fails on all counts, it's an incredibly poor 'design'... >>>
"Incredibly poor" seems a bit harsh, since actually the circuit works perfectly as is. It would also work perfectly as the required "Hi-Quality" preamp (that the original poster requires) with the modifications that have been thoroughly hashed out in this thread.
Or if you don't believe that the circuit could work as said, perhaps you could explain your objections? After all, just to say "it's an incredibly poor design" and then leave it at that is a lot like saying, "Your wash will be whiter and brighter." It's a claim made without any apparent basis in fact.
I probably should add that input impedance is not at issue. It's been discussed to death.
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<< ...the second circuit fails on all counts, it's an incredibly poor 'design'... >>>
"Incredibly poor" seems a bit harsh, since actually the circuit works perfectly as is. It would also work perfectly as the required "Hi-Quality" preamp (that the original poster requires) with the modifications that have been thoroughly hashed out in this thread.
Or if you don't believe that the circuit could work as said, perhaps you could explain your objections? After all, just to say "it's an incredibly poor design" and then leave it at that is a lot like saying, "Your wash will be whiter and brighter." It's a claim made without any apparent basis in fact.
I probably should add that input impedance is not at issue. It's been discussed to death.
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<< U1a needs a DC voltage reference I think... >>
I'm not sure what you mean by a DC voltage reference. I think maybe you're thinking of single-suppy circuits, that have the non-inverting input connected to 1/2 supply voltage? But this is a dual-supply circuit.
Or you're talking about bias current? That's served by R3. Bias current tends not to be a problem in buffers because of their unity gain. Even so it's nice to avoid large resistors because of their built-in noise, but two things stand out.
1. If you want megohm impedance, you gotta have megohm resistors.
2. Other posts (sorry, I have none at hand) have reported silent speakers using megohm inputs. I don't know if this would hold true with headphones, which are more demanding.
<< I deleted the post, thanks for re-posting it >>
I noticed you deleted your post, but by then it was too late to delete mine, sorry.
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<< U1a needs a DC voltage reference I think... >>
I'm not sure what you mean by a DC voltage reference. I think maybe you're thinking of single-suppy circuits, that have the non-inverting input connected to 1/2 supply voltage? But this is a dual-supply circuit.
Or you're talking about bias current? That's served by R3. Bias current tends not to be a problem in buffers because of their unity gain. Even so it's nice to avoid large resistors because of their built-in noise, but two things stand out.
1. If you want megohm impedance, you gotta have megohm resistors.
2. Other posts (sorry, I have none at hand) have reported silent speakers using megohm inputs. I don't know if this would hold true with headphones, which are more demanding.
<< I deleted the post, thanks for re-posting it >>
I noticed you deleted your post, but by then it was too late to delete mine, sorry.
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There are at least 3 people critizing your circuit - these summing up to at least one century of audio experience. How do we come to call this a poor design?
Or otherwise- what makes a good design?
A good design is simple, cheap and effective.
Specially if it is intended to help a newbie.
Noise performance should be close to the limits given by physics.
I do not see any of these requirements were met.
Did you ever plug in a guitar?
Or otherwise- what makes a good design?
A good design is simple, cheap and effective.
Specially if it is intended to help a newbie.
Noise performance should be close to the limits given by physics.
I do not see any of these requirements were met.
How did you check that?
Did you ever plug in a guitar?
some details concerning the objections
An input buffer, followed by a gain stage, shows poorer noise performance than a single, non-inverting gain stage. So this secondstage is not only redundant, but counter-productive.
Input noise current of NE5534 creates across pick-up impedance (>100k) an equivalent input voltage even worse than the notorious poor TL062.
Input impedance has been mentioned before....
An input buffer, followed by a gain stage, shows poorer noise performance than a single, non-inverting gain stage. So this secondstage is not only redundant, but counter-productive.
Input noise current of NE5534 creates across pick-up impedance (>100k) an equivalent input voltage even worse than the notorious poor TL062.
Input impedance has been mentioned before....
Obviously inout impedance IS an issue, because it's absolutely crap as is
But utterly pointless first buffer stage (as already pointed out as well), load's of pointless crap before the pointless buffer stage as well.
No coupling cap on the output, no coupling caps on the volume control - you don't DC couple controls.
No HT decoupling capacitors.
There's not a single thing there that makes any sense, where did you dream it all from?.
Edit: Missed one, giving the second stage DC gain, which you don't want, yet another missing capacitor.
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Yup, that's my goof up, and why I deleted the post, thanks for re-posting it.
No, he's using a spilt-supply, so the reference is ground (zero volts).
An externally hosted image should be here but it was not working when we last tested it.
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Hi there!
I have used the TL07x opamp's in everything form HI-FI to my very First Guitar Preamp's and Fuzzbox's since 35 years ago and I still even use them today!!!
I have never had any issues about their quality of sound performance in any situation.
I agree with the rest, the First schematic posted is best suited for use with the high impedance of guitar pickups.
The very First circuit I ever made to be used on my guitar was a very similar circuit called the MXR Distortion +.
I have tried all of the different types input configuration in the past and I always end going back to the same non-inverting high input impedance configuration when it comes to driving it with a guitar for sound quality.
Even if it is to be a clean and non-distorted signal.
The original MXR unit used a LM741 and it was one noisy beast until I swapped it out with a TL07x and I have never turned back since then.
Then I added even more gain stages using a TL074 and it was still quieter than the original unit with a single LM741!!!!
Not sure how much gain you need but I get about .8v to 1.1v peak out of my Strat when I hit the strings a lot harder than I normally would when I am just playing it.
When talking about getting as much as you can out of an opamp you can only get so much voltage swing out of them unless they are a Rail to Rail type.
The TL07x's are not this kind of opamp.
The data sheet will tell you how much of a voltage swing you can get vs your supply voltage (see picture).
Here is the data sheet,
http://www.ti.com/lit/ds/symlink/tl071a.pdf
IMHO opamp vs buffer, they are the same !!!
Typically you can have a buffer (opamp) that has 0 voltage gain (or a little bit of as in this case) and if it has a high impedance input and is it driving a low impedance output (as in this case) then it has current gain and is considered a buffer even the it is not increasing any voltage levels.
The term opamp is a type of amplifier called a operational amplifier and all amplifiers are considered a buffer of some sort or another!!
Also keep in mind that whatever output voltage swing you are trying to get, that the device you are trying to drive will only take so much before it starts to distort too.
Being a fellow guitar player I understand this completely and I have no issues about this.
But most amps won't tolerate much more that about 4v peak before this happens depending on the amp of course.
For most mixers this is another story as they are designed for such voltages swings.
I stated in another thread what my Mackie 32-8 is capable of but I don't remember exactly what my as measured voltages were at this time so I can't quote them.
But it does use NJM4560 opamps with +/- 18v rails and it is much more than enough and in most case to much for anything that I have ever hooked to it so far.
In fact my Gina24 sound card can produce higher peaks than my mixer can!!!
But not by much.
Typically the most you will get out of a TL07x is about 4V to 5V peak on a 12v single ended supply.
FWIW
jer
I have used the TL07x opamp's in everything form HI-FI to my very First Guitar Preamp's and Fuzzbox's since 35 years ago and I still even use them today!!!
I have never had any issues about their quality of sound performance in any situation.
I agree with the rest, the First schematic posted is best suited for use with the high impedance of guitar pickups.
The very First circuit I ever made to be used on my guitar was a very similar circuit called the MXR Distortion +.
I have tried all of the different types input configuration in the past and I always end going back to the same non-inverting high input impedance configuration when it comes to driving it with a guitar for sound quality.
Even if it is to be a clean and non-distorted signal.
The original MXR unit used a LM741 and it was one noisy beast until I swapped it out with a TL07x and I have never turned back since then.
Then I added even more gain stages using a TL074 and it was still quieter than the original unit with a single LM741!!!!
Not sure how much gain you need but I get about .8v to 1.1v peak out of my Strat when I hit the strings a lot harder than I normally would when I am just playing it.
When talking about getting as much as you can out of an opamp you can only get so much voltage swing out of them unless they are a Rail to Rail type.
The TL07x's are not this kind of opamp.
The data sheet will tell you how much of a voltage swing you can get vs your supply voltage (see picture).
Here is the data sheet,
http://www.ti.com/lit/ds/symlink/tl071a.pdf
IMHO opamp vs buffer, they are the same !!!
Typically you can have a buffer (opamp) that has 0 voltage gain (or a little bit of as in this case) and if it has a high impedance input and is it driving a low impedance output (as in this case) then it has current gain and is considered a buffer even the it is not increasing any voltage levels.
The term opamp is a type of amplifier called a operational amplifier and all amplifiers are considered a buffer of some sort or another!!
Also keep in mind that whatever output voltage swing you are trying to get, that the device you are trying to drive will only take so much before it starts to distort too.
Being a fellow guitar player I understand this completely and I have no issues about this.
But most amps won't tolerate much more that about 4v peak before this happens depending on the amp of course.
For most mixers this is another story as they are designed for such voltages swings.
I stated in another thread what my Mackie 32-8 is capable of but I don't remember exactly what my as measured voltages were at this time so I can't quote them.
But it does use NJM4560 opamps with +/- 18v rails and it is much more than enough and in most case to much for anything that I have ever hooked to it so far.
In fact my Gina24 sound card can produce higher peaks than my mixer can!!!
But not by much.
Typically the most you will get out of a TL07x is about 4V to 5V peak on a 12v single ended supply.
FWIW
jer
Attachments
I have read every post of this thread, and with great amusement !!!
"The TL072 is not used for hi-fi"......Ahhhh,ha,ha,ha,ha,ha!!!!!
I re-did a Fostex 454 mixer with all TL072's and it nearly put my big Mackie 32-8 board to shame!!!
There is plenty of evidence that has been offered, Nigel has pointed out many of the things that should be corrected in the circuit.
Having been doing this for so long myself, I have made such mistakes a long long time ago and he is correct!!
Also the OP has already pointed out that he wishes to use a single ended supply thus the need of a different approach is needed in order to make the circuit work correctly and reliably.
That is all I have, Carry on!!
jer
"The TL072 is not used for hi-fi"......Ahhhh,ha,ha,ha,ha,ha!!!!!
I re-did a Fostex 454 mixer with all TL072's and it nearly put my big Mackie 32-8 board to shame!!!
There is plenty of evidence that has been offered, Nigel has pointed out many of the things that should be corrected in the circuit.
Having been doing this for so long myself, I have made such mistakes a long long time ago and he is correct!!
Also the OP has already pointed out that he wishes to use a single ended supply thus the need of a different approach is needed in order to make the circuit work correctly and reliably.
That is all I have, Carry on!!
jer
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