Do i really need high slew rate opamp at the output of my CD-player?

[dotneck335]

Are ANY of the opamps (noted as 'from China') for sale on eBay REAL?

 

[Ken Newton]

...You could try looking at using the Analog Devices ADA4627-1BRZ (make sure you get the BRZ). This is, essentially, the AD version of the OPA627 and it has very respectable specifications. People that have tried it have been very impressed. Many have said it beats the 627. The BRZ are only $10 each, but they are only available in SOIC...

That is interesting. Can you point me to a source for this information - aside from the similar device part numbers? Thanks.

 

[Willi Studer]

Are ANY of the opamps (noted as 'from China') for sale on eBay REAL?

As much as the capacitors from Aliexpress.

 

[ainami]

That is interesting. Can you point me to a source for this information - aside from the similar device part numbers? Thanks.

The ADA4627 is a high speed op amp with FET inputs just like OPA627. It also has very similar specifications (offset, bias, slew rate, settling, etc.) as the OPA627, so I would imagine it reacts very much like the OPA627 in a circuit. You can google around, but here are a couple threads of discussion:

http://www.diyaudio.com/forums/soli...-1-outperform-burr-browns-opa-627-opa627.html

The Opamp thread - Page 194

Take anything said in the "Opamp thread" with a grain of salt, as much of these people are just swapping out op amps in different circuits without understanding what the op amp is really doing.

 

[jcx]

ADI's AD8610/20 directly compares specs to OPA627 in its datasheet

TI also makes later generation op amps with similar "627 replacement" specs

OPA827

OPA164x has even lower input noise, if not the speed


there is no reason I can see from Psychoacoustics to believe sub microsecond op amp settling time has any impact on what can be heard in controlled listening tests

 

[ainami]

jcx - that may be absolutely true. I'm am attempting to corralate the problems I hear with opa2134 and opa2107 with what is shown in the specs. Since both of these op amp have a slow settling time, that's the only factor I can really see.

I looked at the AD8610/20 series. It may be a fast op amp, but it's limited to +/-13V power supply. The ADA4627 allows up to +/-18V, which correlates better to the OPA627. The OPA827 may be a similar FET op amp to the OPA627, but remember it's only half as fast for slew rate, so it's going to react different in some circuits (such as I/V). I've found that slower slew rates translate bass better (in the 20V/uS range). However, high speed 55V/uS slew rates will lose a lot of bass/midbass when used as I/V, but the faster slew rate will track actual analog waveforms better and be more transparent (not impart as much of a signature as warmer op amps).

I could not use the AD8610 because of my +/-15V power supplies, but I would imagine the AD8610/20 does very well in something like a low voltage headphone amp. It even has specs for +/-5V, which tends to illustrate it's designed for lower voltage power supplies.

 

[Extreme_Boky]

If the CD output voltage is 2V RMS maximum and if the band is limited by the IV filter at 22 khz, why I should need a slew rate > 2 V/us in my output opamps (after the DAC)?

I'm asking because I'm using an op-amp with only 3V/us and i like the sound...

Attention is needed, throughout the whole sound reproduction system, to capitalize on a fast OP potential.

Local decoupling would be the starting point. A good rule of thumb, with no measurements needed in the initial stage, would be to use around 10uF electrolytic, approximately 1.5 cm away from the Vcc and Vee, and 0.1uF NPO / COG SMD capacitor as close to the Vcc /; Vee pins as possible. This will "sound" very nice... even with the original OP.

To answer your original question, the band - limiting happens after a fast OP I/V stage. Fast OP, by definition, can be very beneficial. I have attached a pdf document that explains why. It talks about current feedback amplifiers with very low input impedance needed for the current-out DAC's, but it does explain the benefits of fast settling / fast rise-time OP's.

A "lazy" approach where people simply replace a 5534 or such, with a very fast OP, usually results in a glare and harshness, but it doesn't have to be that way. Clean power rails and correct local decoupling should be done first, and then one should try to play with OP's. Otherwise, a disappointment is almost certain.

 

[Baka]

Now a capacitor in the negative feedback loop can help remove some of this settling noise, but I can still hear problems with the opa2134 (even with a very good power supply). I hear the same character with the opa2107 (which has a worse settling time). They both have what is known as that classic "burr brown" warm signature. It's definitely not the "crystal clear" sound.

Absolutely agree.

That warm signature, lack of transparency and dynamics is simply unbearable IMO.

On the other side, LM4562 as a typical non jfet opamp example hasn't gone that far either.

High slew rate, fast settling opamps were my long term favourites.

But of course, YMMV.

 

[Baka]

and 0.1uF NPO / COG SMD capacitor as close to the Vcc /; Vee pins as possible.

Where do you source 0.1uF NPO/COG in SMD and what is the smallest size?

A "lazy" approach where people simply replace a 5534 or such, with a very fast OP, usually results in a glare and harshness, but it doesn't have to be that way. Clean power rails and correct local decoupling should be done first, and then one should try to play with OP's. Otherwise, a disappointment is almost certain.

Totally agree.

As an example, AD in their datasheets always stresses the necessity of tight (as close as possible) local decoupling for their fast opamps.

 

[marce]

Use a small X7R, smaller the better.

 

[Baka]

Thanks.