TL074 as distribution amp - easy question

On p15, fig 25 of this datasheet, it shows how to use the TL074 as a small distribution amp.

http://www.ti.com/lit/ds/symlink/tl074.pdf

I am certain the answer to this question is yes, but erring on the side of caution I thought I'd check...

Q - The four opamps in that diagram represent the four blocks on the TL074 don't they?  So figure 25 is a just single TL074 (plus a handful of other components of course) isn't it?  And you're effectively amplifying the signal in the first opamp, then splitting it three ways and sending it to the other three opamps in the TL074 for three x distribution?

Yes...

Not to quibble with their design, but I would suggest

#1 adding build out resistors in series with each output (say 50-500 ohms)
#2 Do you need a fixed gain of 11x
#3 consider using lower resistance feedback network parts for less noise and less affect from stray capacitance.
#4 consider split supply and if single supply not connecting gain resistor to same V/2 node.

Other than that it's perfect..  ;D ;D

JR

JohnRoberts said:

Yes...

Not to quibble with their design, but I would suggest

#1 adding build out resistors in series with each output (say 50-500 ohms)
#2 Do you need a fixed gain of 11x
#3 consider using lower resistance feedback network parts for less noise and less affect from stray capacitance.
#4 consider split supply and if single supply not connecting gain resistor to same V/2 node.

Other than that it's perfect..  ;D ;D

JR

Click to expand...

Thanks, and great that you've expanded on 'yes'.  But now you're in for more questions!

#1 - why?

#2 - this is a three way DA for the Gyraf headphone amp (or in fact 3 x Gyraf headphone amps).  Gain control will happen with a pot in the headphone amp circuit

#3 I presume that is the 1Mohm resistor as it is feeding back from the output of the opamp to the - input?

#4 - By split supply you mean separate PSU + and - rails?  That's fine, it's going into a 51x frame and will be powereed by +16V and -16V

rob_gould said:

JohnRoberts said:

Yes...

Not to quibble with their design, but I would suggest

#1 adding build out resistors in series with each output (say 50-500 ohms)
#2 Do you need a fixed gain of 11x
#3 consider using lower resistance feedback network parts for less noise and less affect from stray capacitance.
#4 consider split supply and if single supply not connecting gain resistor to same V/2 node.

Other than that it's perfect..  ;D ;D

JR

Click to expand...

Thanks, and great that you've expanded on 'yes'.  But now you're in for more questions!

#1 - why?

Click to expand...

Would you believe "trust me?"....  TL074 are not very low output impedance opamps. Stray capacitance  will create a LPF pole with the opamp's output impedance. Not the best situation for stability.

#2 - this is a three way DA for the Gyraf headphone amp (or in fact 3 x Gyraf headphone amps).  Gain control will happen with a pot in the headphone amp circuit

Click to expand...

Thus my questioning the need for over 20dB of  fixed voltage gain.

#3 I presume that is the 1Mohm resistor as it is feeding back from the output of the opamp to the - input?

Click to expand...

The noise is actually the 1M in parallel with 100K, while the RC is the 1M and any stray C.

#4 - By split supply you mean separate PSU + and - rails?  That's fine, it's going into a 51x frame and will be powereed by +16V and -16V

Click to expand...

Whatever...  You'll figure it out after you build it.

JR

JohnRoberts said:

rob_gould said:

JohnRoberts said:

Yes...

Not to quibble with their design, but I would suggest

#1 adding build out resistors in series with each output (say 50-500 ohms)
#2 Do you need a fixed gain of 11x
#3 consider using lower resistance feedback network parts for less noise and less affect from stray capacitance.
#4 consider split supply and if single supply not connecting gain resistor to same V/2 node.

Other than that it's perfect..  ;D ;D

JR

Click to expand...

Thanks, and great that you've expanded on 'yes'.  But now you're in for more questions!

#1 - why?

Click to expand...

Would you believe "trust me?"....  TL074 are not very low output impedance opamps. Stray capacitance  will create a LPF pole with the opamp's output impedance. Not the best situation for stability.

#2 - this is a three way DA for the Gyraf headphone amp (or in fact 3 x Gyraf headphone amps).  Gain control will happen with a pot in the headphone amp circuit

Click to expand...

Thus my questioning the need for over 20dB of  fixed voltage gain.

#3 I presume that is the 1Mohm resistor as it is feeding back from the output of the opamp to the - input?

Click to expand...

The noise is actually the 1M in parallel with 100K, while the RC is the 1M and any stray C.

#4 - By split supply you mean separate PSU + and - rails?  That's fine, it's going into a 51x frame and will be powereed by +16V and -16V

Click to expand...

Whatever...  You'll figure it out after you build it.

JR

Click to expand...

Haha, slightly ominous sounding answers!  Seems like I'm in for a learning experience!

Thanks for the assistance John.

I'll second the build-out resistors. -The first TL07x thing I ever built that had to drive a long line taught me why!  ;D

wub...wub...wub...  8)