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Any tips on the AD797 Op Amp in a Mixing Desk (Tape Returns)?
Old 2nd February 2009
  #1
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TobyToby's Avatar
 
🎧 10 years
Any tips on the AD797 Op Amp in a Mixing Desk (Tape Returns)?

AD797 for the Tape Returns

I would like to exchange the TLO72 from the Tape Return Input Stage with AD797AN (Just because I have some of them. / Installation as a pair in a 2x 8DIP > 1x 8DIP socket adaptor). - Generally I like the TLOxx (My DDA is full of them. It sounds sweet . .but it’s also a bit slow IMO). I am looking for a bit ‘snappier’ and cleaner solution. The specs of the 797 seem good but I’ve read that it is not an easy chip (trend to oscillate). I assume that I’ve to adjust the resistor network to the given specs of the AD797.

http://www.analog.com/static/importe...eets/AD797.pdf

I’ll also keep in mind to ad on some power rail filter caps and swapping the LQ decoupling cap for a HQ Nichicon or Panasonic (with a MKP 0.1 uf in parallel for the transients / / Thanks to Jim Williams & Svart for sharing their knowledge here at GS). -This is just a start. The next step would be the op amp in the pan section.


- Would you have some adjustment tips for the AD797 in regard to the values shown in the schematic? The source for the tape input is my DA converter with an output impedance of 47Ohm (load Input 600Ohm minimum)

- Any suggestions for other sections where the AD797 would be useful (panorama, master)

- Or, if so, a founded suggestion for another quality op amp type in the Tape Returns

Big thanks in advance
Toby





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Old 3rd February 2009
  #2
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TobyToby's Avatar
 
🎧 10 years
Any 'AD797 in a mixing desk' user here?
Old 3rd February 2009 | Show parent
  #3
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BradM's Avatar
 
🎧 15 years
A drop-in and affordable replacement you may want to try is the TLE2071A. It's basically the next generation of the TL072 and is made by Texas Instruments. I used a bunch of them to upgrade the NE5534's in my tape deck and it was an obvious and musically pleasing improvement. The best part was that they were only $1.50 each.

Give those a try if you are a looking for a more modern op amp, but generally like the tone of the TL072.

Brad
Old 3rd February 2009 | Show parent
  #4
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nosebleedaudio's Avatar
 
🎧 15 years
May know this but, the AD797's max voltage is +-18V. Some consoles run the chips at +-18V, not taking into account the voltage drop across the diodes, if there are any.
Old 3rd February 2009 | Show parent
  #5
This will not be easy. The 797 has a dual pole response, it's generally unstable in a follower config and will not be stable as an integrator. Anytime you close the feedback loop with a cap, you are in trouble. Place a 100 ohm resistor in series with C16 and C18. You also have rather large resistor values in the front end, that will wash out most of the low noise capabilities of the 797.

A better choice is the new ADA4898-1. It also has less than 1 nv noise but has better stability and a large phase margin. It's also much faster.

Jim Williams
Audio Upgrades
Old 3rd February 2009 | Show parent
  #6
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🎧 10 years
you surely can´t blame the TL072 to be slow. Most other OAs for audio purpose are slower. Older Studer desks use chips which have only a fifth of TL072´s slewrate. And Studer desks can definitely not be blamed to sound slow. What is more important than a particular chip is the circuit around the chip. This makes simple chip-swapping with disregarding the circuit into a trial and error thing.
What I never would do is to replace BJT-input chips with FET or the other way around. This changes too much of the important parameters of a circuit design.
Of course you can argue if it sounds right then it´s right. But then you could also replace the chip with a tube....
Old 3rd February 2009 | Show parent
  #7
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BradM's Avatar
 
🎧 15 years
I'm guilty of swapping BJT chips for FET chips. heh I guess I just live by the old adage "if it sounds okay and doesn't go up in smoke within the first week, then it must be good."

Brad
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