RC4559: Replacement for 4739 dual op amp (audio)

Hi Daniel,

Thank you for your reply.

The RC4739; that's it.

I'm looking for the closest possible replacement in terms of electrical values.

I mean: same Input Offset Voltage, same Input Offset Current, same Bias Current, same Slew Rate, etc...

The pin-out does not matter.

I'm not interested by RC4739. I want a current production op amp.

Regards,

Thierry 

Hi Thierry,

if little supply current is important, I would go for the RC4559.

Kai

Hi Kai,

Thank you for your reply.

I'm looking for a model that comes closest in terms of sound.

I know it would be easy to buy an NOS R4739.

I want to use it in a jazz guitar preamp and keeping the R4739's mojo is really important.

Regards,

Thierry 

Hi Thierry,

can you show a schematic?

Kai

Hi Thierry,

Unfortunately, nothing will have the exact same specs as the original amp.  I would think the THD and noise performance of the amp would be the most important factors in determining audio quality.

However, unless you just want the cleanest THD+N/noise performance, it's going to be virtually impossible to decide which has most nearly got the R4739's "mojo."

Here's what I would do, pick a few different parts and order some samples.  Plug them into your board and see which you think sounds best.  I would try RC4559, RC4580, and potentially the TL071 and TL081 devices after that if needed.

Regards,

Daniel

Hi Daniel,

I fully agree with your recommendation to alternatively use the TL071, because the TL071 has much lower input noise current compared to the bipolar OPAmps. This can be advantageous when being directly connected to the pick-ups. That's why I asked for the schematic :-)

Kai 

Good suggestion Kai.  Let's see what Thierry will share.

Daniel

Hi Daniel and Kai,

Thank you for your help.

I also think the THD and noise performance are the most important factors.

From the RC4739 datasheet:

<0.05% distortion into 2kOhm load

10nV/√Hz noise at 100Hz

I don't see theses parameters in the RC4559 datasheet.

Thierry

Hi Thierry,

the noise can be calculated from this data:

Divide the numbers by SQRT (20kHz - 20Hz) = 141 x SQRT (Hz). This yields 9.9nV / SQRT(Hz) and 0.18pA / SQRT(Hz).

Kai

Hello Thierry,

As for THD performance, I'm afraid you're right in that the RC4559 does not have anything in the datasheet.  Keep in mind, this part is almost 40 years old now.

The older noise parameters were often given as integrated values rather than as a broadband spectral density.  For the sake of this example, Kai's calculation is good for comparison's sake.  You can learn more about this topic in the TI Precision Labs Series on Op Amp noise.  Here's a link to video 2 and video 3, which I think you'll find most helpful.  You can use the information in this slide to calculate the integrated noise for the RC4559.

Regards,

Daniel

Hi Thierry,

I'm happy to help and hope you found this information useful.  I know it can be somewhat frustrating trying to work with older parts.  Please, let us know if you have any further questions.

Regards,

Daniel

Hi Thierry,

I think the distortion of RC4559 should be very similar to the RC4739, maybe even a bit better.

Kai