Best replacements for the TL 071 op amps in my Trident

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Best replacements for the TL 071 op amps in my Trident

Postby Chris H » Thu May 19, 2005 2:12 pm

Any suggestions for replacing the TL 071 op amps in my trident ?
Some options that seem ok are the analogue devices AD 825 and the Burr Brown OPA 627 , the 2nd option being a fair bit more expensive, but being described as having a warmer more valve type sound.That might be sales crap to make people pay an inflated price for a simple op amp too!!!
Someone suggested the new AD fet models. I haven't a clue what ones are suitable. I'm actually thinking of using one type for the first 8 channel strips and another for the next 8.
Any advice welcome ....Otto or Rob....?
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Postby rob » Thu May 19, 2005 2:26 pm

Try OPA134. Note that they draw almost twice as much current from the power supply, so a wholesale swap over could mean an 'upgraded' PSU.
There are also other more subtle issues involved with this sort of IC swap, so start out with minimum commitment and see how it pans out.
I quite like these OPA opamps, give them a whirl!
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Postby Chris H » Thu May 19, 2005 4:08 pm

Thanks Rob . I'll do one ch-strip and hear how it sounds. The power supply is not the best and a re build is the next to do, to get better sound out of the thing. It sounds great recording from the inserts (there are no direct outs) but as soon as i send a signal out of any one of the 8 groups the sound gets cloudy, opaque, mist on the lense sounding. I'm happy using it for the 16 preamps at the moment but in the future want to get the sub groups and master section really happening. I'm thinking of putting Telefunken, Siemens, or Neve line amp modules in for the master on a seperate power supply as the desk runs at 17 volts.
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Postby Henry » Fri May 20, 2005 12:05 am

NE5534 should be straight swap without power supply problem?
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Postby rob » Fri May 20, 2005 9:20 am

5534 also draws 4mA but they have other requirements for stability. If running at a gain of less than 3 they require a 22pF cap to be added between pins 5 and 8. So, unless you have analysed the circuit details a straight swap could be a disaster.
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Postby ottowr » Fri May 20, 2005 2:16 pm

Yeah the OPA134s etc are probably a good choice, they have similar impedances to the 071 family.

Are 071s the only chips in there? I would have expected duals (072/082)and quads (074/084) as well. If there are there are more esoteric chips you can try like the LT 1358 dual and LT1359 quad (600V/us Slew Rate, 2.5mA Maximum Supply Current per Amplifier).

Change one stage at at time and check for instability with a CRO before moving on. High slew rate chips can make the circuitry unstable at high frequencies.

If you're using low offset chips then you could probably bypass some interstage coupling capacitors as well.

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Postby Chris H » Fri May 20, 2005 10:37 pm

There are 3 TL071 CP op amps in each chanel strip, no other ic's.I will give Allan a look at them and he will set me on the right path re the finer details.You see some people approach these issues from a facts and figures perspective, which is esential , then there are those who have the facts and figures knowledge but add to this an understanding of the desirable sound qualities that recording people find musical etc etc...so i'm after some options that will sound better than the 071 in the circuit of the Trident. I will let Allan look at the circuit and give him a few op amp options, that is the aim. From my research so far it seems some of the new Analogue Devices op amps are a popular choice eg the AD 825. My original thought was a discreet op amp like the API 2520 ar the jensen 990 but thoey arn't suitable i have been told.
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