Author Topic: TL072 Buffer Question  (Read 534 times)

TL072 Buffer Question
« on: September 27, 2019, 08:13:50 AM »
I did try Tillman preamp on my build and wanted to try out the Op-Amp version. Unfortunately I only have TL072 and didn't get the single op-amp (TL071).
The schematic I am trying is from http://www.generalguitargadgets.com/pdf/ggg_ic2buf_sc_1i.pdf

I have a couple of questions

  • What would be the effect of changing the input resistor values from 2.2M to 3.3M - again due to part availability
  • What would be the effect of combining outputs of both the individual op-amps? Or is that even advisable?

FlyingWild

Re: TL072 Buffer Question
« Reply #1 on: September 27, 2019, 09:25:12 AM »
The OpAmp in the schematic is a TL072, so your okay as you need two amps and the Tl072 is a dual amp OpAmp, the TL071 has only one.

I can't advise on the rest of your questions, sorry.

antonis

Re: TL072 Buffer Question
« Reply #2 on: September 27, 2019, 09:50:44 AM »
What would be the effect of changing the input resistor values from 2.2M to 3.3M - again due to part availability

None
(raising input impedance & noise and lowering input HPF cut-off frequency should be negleted..)

What would be the effect of combining outputs of both the individual op-amps? Or is that even advisable?

No other than doubling output current..
(if this is your case, better do it via a single output and an external transistor Emitter/Source follower..)
« Last Edit: September 27, 2019, 09:54:41 AM by antonis »
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"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

Ben N

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Re: TL072 Buffer Question
« Reply #3 on: September 27, 2019, 09:59:49 AM »
It doesn't really matter, but as a point of interest, the opamp buffer-splitter you are interested in has nothing to do with the Tillman, which is a single JFET buffer. Also, note that it CALLS for a TL072. Yes, you can run the two buffers in parallel.  For this taken to the Nth degree, have a look at http://www.muzique.com/lab/superbuff.htm. As for the resistors, I doubt it will make much of a difference--it may increase noise very slightly, or cause more of a pop if you have a true bypass switch. . You could try it with the 3.3M and see if it works--if not, you can solder in another 3.3M or a 4.7M in parallel with the first 3.3 to get you closer to the original value.  Alternatively, two 4.7Ms in parallel or two 1Ms in series would also be pretty close, but you could also probably go as low as 1M.
Edit: Antonis, great minds, etc.  I would just add that paralleling the two opamp stages might be of value if you are using the buffer as a line driver, but in other applications it offers no particular benefit.
« Last Edit: September 27, 2019, 10:06:21 AM by Ben N »

antonis

Re: TL072 Buffer Question
« Reply #4 on: September 27, 2019, 10:05:30 AM »
If you run both outputs in parallel, take into account the "balast" resistors (R1 - R4 in Jack's superbuffer..) for equall current sharing..
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..