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Switching Out Opamps
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Drzayuss
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#1
6th May 2005
Old 6th May 2005
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Switching Out Opamps

Hey everyone . . . I really am a novice with regards to electrical engineering . . . Though I do have a question: Is it possible to swith out cheap opamps with expensive ones. For example, what would be involved with replacing the cheap opamps in Amek TAC with some made by API or Millenia? (and can this even be done?)

Thanks,

Justin
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6th May 2005
Old 6th May 2005
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Amek used IC (chip) opamps, while things like an API 2520 are an actual descrete module. They both operate somewhat the same, but the packaging is totally different.

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6th May 2005
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Simply swapping out op-amps is generally a bad idea. They all have different charateristics and the circuit topologies are designed with this in mind.

So, unless you know what you are doing and have schematics to work from, you are probably better off leaving well enough alone and buying another unit.



-tINY

Drzayuss
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6th May 2005
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I have all the schematics . . . I am interested in learning about this stuff . . . Are there better ICs that would work? Can I modify the surrounding circuitry to support a discrete opamp? I am not planning on buying another console . . . I would like to improve the sonics of the one I have. If it can't be done, that's cool . . . but if it can, I would like to learn how.
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6th May 2005
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There were various TAC models made, so the first question is what chips are already in it? Probably TL072's, with maybe some NE5532/NE5534 chips as well.

You'll have a near impossible time retrofitting a discrete opamp module due to the much larger size.

Bri
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7th May 2005
Old 7th May 2005
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The front end is a ssm 2015. The EQ opamps are TL072's. If you replace those the input impedance is high there so a fet input or super beta opamp will work well. A BurrBrown OPA2134 or a Linear Tech LT1352 will work well. The fader amp can be replaced with 2134, or just about any decent opamp. If you use LT1358's you can eliminate the coupling caps.

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8th May 2005
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One potential "gotcha" can be the higher current draw of substituted opamps vs the originals. If swapping out only a few, no biggie...but if dozens/hundreds of chips are swapped out, the OEM power supply may not have enough moxie.

One other thing to ponder. Many desks, etc did NOT use sockets for the chips, so you will need to invest in a quality vacuum desoldering station (and learn how to use it! <g>) to avoid damage to the circuit boards.

Bri
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8th May 2005
Old 8th May 2005
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Good point Brian. The Analog Devices OP275 is a good substitute for the TL072 in most cases and draws a very similar amount of idle current. And despite the opinion of some, it sounds pretty darn good IMO when you have to pass audio through lots of stages, like in a console. It is also quieter and faster, I reckon you will instantly hear an improvement in the high band EQ section of the TAC. If you are going to suck out the existing chips, put in IC sockets, then you can easily give some different opamps a try.

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9th May 2005
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Remember, just because a newer, more expensive op amp can be installed where a garden-variety NE5532 or TL082 used to be doesn't automatically mean that it'll work better (or work at all) and there's certainly no guarantee it'll sound better. The ridiculously acclaimed Benchmark DAC-1 is an example of a device that achieves phenomenal performance out of garden-variety op amps through superb design implementation rather than throwing expensive parts into a box. There may very well be places in your console where a better op amp won't have any audible effect at all, and then there will be places where a newer, faster amp can cause stability problems. The trick here is to do your homework, which means downloading and comparing data sheets, reading books like Walt Jung's op amp treatises and of course asking questions here. You've already gotten responses from some very knowledgeable people. Their opinions will vary wildly, but they know how to achieve the results they're after.
You need to move slowly and confirm your upgrades really are upgrades before you repeat them across multiple channels. The first step before you begin any chip replacements is to make sure the console is in good stock operating condition. Give the power supply a tune-up or an overhaul as necessary, make sure all the logic functions are working, get your switches cleaned up and so forth before you start messing with chips. There's no point in spending a couple grand on ICs to reduce your distortion from 0.01% to 0.003% if your switches are noisy and you have leaky, dried-out caps all over the place, squirting DC current where it isn't wanted and degrading performance by a greater margin. Get your hands on an oscilloscope and see what's going on at various places around the console in the non-audio range. An op amp can't do a great job of buffering an audio signal if it's busy pumping out full-scale oscillation at 250kHz or 3MHz.
Once you're ready to start working, work in the following order. First take care of the power supply and any motherboard regulation or filtering. Then move on to the modules. Do the MONITOR SECTION FIRST. The module that routes signal to your speakers. It does no good to improve the channels and busses if you can't hear the improvements. Besides that, the monitor section is relatively small and a good place to get started. Replace one thing at a time, and listen/measure for changes before you move on to the next part. If a chip upgrade causes RF oscillation, you'll want to know about that before you mess with anything else. It's much easier to find when you know you've only changed one part. As you start replacing opamps with more precise chips you may decide to short out some coupling caps, but that can be trickier than it sounds. There's more to getting rid of DC offset than just buying precision amplifiers. If you do decide to DC-couple some stages, you need to measure the DC voltage on both ends before and after the upgrade and the cap elimination. Learn what all the input offset, input bias current, and drift terms mean in the data sheets and how to predict what a chip will do in a given circuit. It's really not that hard, just some basic algebra.
After you've finished the monitor section, then tackle the master section. Do the main stereo buss first, then the subgroups. Do them two at a time, so you have a stock stereo pair with which to compare an upgraded pair. If you move backward through the signal path like this, you'll always be able to kill all "non-upgraded" inputs to a section and see if it behaves by itself. After the master section is done, and you're already burned out and broke from chip upgrades, then you start thinking about the channel modules. Again, tackle two at a time and take it slow. Spread the work out over a period of time. Most people can use their console and get work done with a couple of channel modules missing, so set a goal of maybe finishing one pair of modules each week (or day or month or whatever your workload permits) until you finish. When you finish this slow methodical approach, you should have a very good idea of which upgrades produced the most significant sonic improvements and which were a waste of time. Then you can share your knowledge here with the next poor guy who decides to spend his student loan on a big Digikey order. Such is the circle of life.
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Drzayuss
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10th May 2005
Old 10th May 2005
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Wow . . . thanks for all the responses . . . certainly a lot to think about. I have another question for those of you who seem extremely familiar with my console (TAC Scropion II new in 93). There is a stereo buss insert. Could I feed this signal to, say a Neve 1272 and use that as my master bus amp?

Justin
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10th May 2005
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Quote:
Originally Posted by Drzayuss
Wow . . . thanks for all the responses . . . certainly a lot to think about. I have another question for those of you who seem extremely familiar with my console (TAC Scropion II new in 93). There is a stereo buss insert. Could I feed this signal to, say a Neve 1272 and use that as my master bus amp?

Justin
Hi

That depends on the level coming out of the insert but it's odds on it will overdrive the 1272 that has around 39dB gain with the preset at max.

You'd be better off with a unity gain 1271 though I'm not sure whether it's worth the effort... it won't make the TAC an 8014!

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10th May 2005
Old 10th May 2005
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Quote:
Originally Posted by Drzayuss
Wow . . . thanks for all the responses . . . certainly a lot to think about. I have another question for those of you who seem extremely familiar with my console (TAC Scropion II new in 93). There is a stereo buss insert. Could I feed this signal to, say a Neve 1272 and use that as my master bus amp?

Justin
The insert is of course after the TAC mix buss amplifier, so the 1272 will not be replacing the circuit doing the actual mixing.
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10th May 2005
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Quote:
Originally Posted by brianroth
One potential "gotcha" can be the higher current draw of substituted opamps vs the originals. If swapping out only a few, no biggie...but if dozens/hundreds of chips are swapped out, the OEM power supply may not have enough moxie.

One other thing to ponder. Many desks, etc did NOT use sockets for the chips, so you will need to invest in a quality vacuum desoldering station (and learn how to use it! <g>) to avoid damage to the circuit boards.

Bri
No worries on this one. Sockets are included. Replacing them with machine sockets is still a good idea. That LT1352 draws 260 microamps vs 1.8 ma for a TLO72. The LT1358 pulls 2.3 ma. With the savings in current draw for the 1352's there's plenty left over for the 1358's.

Try a BB OPA2134 or the LT1358 in the stereo master mix sum amps. You may favor these over the 'ol 5532.

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11th May 2005
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Jim, are you saying these are drop-in replacements. I have a TAC Magnum and although I find the headroom acceptable I would like to experiment with the Master section (I was thinking Hardy 990 but I would need 24v ).

Jim
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11th May 2005
Old 11th May 2005
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Quote:
(I was thinking Hardy 990 but I would need 24v )
The 990C can operate with supply voltages anywhere from +/-12VDC to +/-24VDC.

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11th May 2005
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Quote:
Originally Posted by Bluzzi
Jim, are you saying these are drop-in replacements. I have a TAC Magnum and although I find the headroom acceptable I would like to experiment with the Master section (I was thinking Hardy 990 but I would need 24v ).

Jim
They are in the Scorpion. The Matchless and Magnum are similar. Trying to fit a 990 sized socket and associated coupling and large psu bypass caps in there would be a very tight fit. Try some of the alternative 8 pin dip opamps first, you just might like that.

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12th May 2005
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John - Wouldn't the 990 have more headroom at 24v than at 12v?

Jim - I just figure if you are going to do a mod why not go all the way. However I was thinking more on the stereo output section not every input strip.

Jim
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2nd November 2005
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