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AD827JN op-amp in IC sockets? Is this okay? Help!

207.225.89.26
Posted on March 31, 2000 at 12:41:26
Dan


 
I am trying to determine if it is okay to replace the existing op-amps in the Link DAC with AD827JN op-amps. I understand that this is the op-amp of choice, but the mfrs. data sheet cautions agains using it in IC sockets due to stray capacitance and other concerns.

Can someone please help me put this issue to rest so that I can order parts? Myself and several others are considering the mods to the Link and are trying to determine which op-amp is safe to use. Burr Brown makes a suitable replacement which is more stable and less expensive, but not nearly as fast.

Any input would be appreciated. Thanks in advance,

Dan

 

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Re: AD827JN op-amp in IC sockets? Is this okay? Help!, posted on March 31, 2000 at 14:36:49
Ric Schultz


 
MSB themselves just stick the AD 827 into the IC socket (in the MSB Gold), I have not seen one with the Nelson upgrade, but I imagine they use it with the socket as well. I personally remove all sockets, being a less is more kind of guy.

Ric Schultz
EVS

 

Re: AD827JN op-amp in IC sockets? Is this okay? Help!, posted on March 31, 2000 at 14:42:40
Jon Marsh


 
Let's put this in perspective. This is a video OpAmp. It has a 300V/usec slew rate (very fast). It has 15 nV/root Hz input noise- not all that quiet. It does have low power consumption, and low input offset. To have a power amp which matched it's GBW and SR, scaling for gain, it would have to be about 6000V/usec slew rate. You're going to have trouble finding that.
Is the 827 the best choice for a CD Player output stage? That's a personal call, I could probably argue otherwise, though I certainly wouldn't fault the DC characateristics (0.5 mV offset) or GBW and SR. However, using high GBW video amps requires special techniques just to make sure they don't turn into an oscillator. I've discussed some of that in another MSB DAC upgrade post recently. If you don't have a scope and the experience to measure and trouble shoot the circuit, I would proceed with caution. Since I don't know what the existing opamps in the Link DAC are, I can't tell you if BurrBrown OPAS2134's would be an upgrade, but their DC characteristics, GBW and SR, and very low distortion make them an eminently reasonable choice for experimentation, as long as the existing design uses some good local bypass for the OpAmps; they work fine in sockets. There are a host of other design issues, including power supply bypass, radiated noise, use of coupling caps in the output stage (a no-no in my opinion), and other matters (such as the DAC's themselves) which will probably frankly swamp the sonic differences between those two parts, in a product at the Link DAC's price point. The OPA2134 are moderately low noise, and are JFET inputs, so input bias current related offsets will be non-existent, as well as most other input impedance effects, unless the associated circuitry is very high impedance, (unlikely), in which case the nonlinear JFET input capacitance will cause some rise in HF distortion.
Unfortunately my favorite "cheap" OpAmp is not available in a dual, but try the 2134's and see what you think- it's a no risk proposition, compared with the 827. The 2134's are popular retrofits for recording mixers, and I've yet to hear a PCM playback device that could equal a good live mic feed. But, don't expect the opamps, whatever you use, to turn your DAC into SACD.

Regards,

Jon

 

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