OPA1656: High-Performance CMOS Audio Op Amp

[johnc124]

Last week TI put a preliminary datasheet online for the OPA1656, a low noise, very low distortion op amp targeting audio applications and fabricated in a CMOS process.

http://www.ti.com/product/OPA1656

I just checked and the sample button for the prototype devices is now active:

http://www.ti.com/product/OPA1656/samplebuy

I started this project in 2017 with the designer of the OPA1622, and although I had a change in my role at TI before the device was released to market, I'm still very proud of what was accomplished. The goals of the project were fairly straightforward:

1. Start with the OPA1688 architecture which gives very good distortion performance, even with low-impedance loads. Beef up the output stage even more.

2. Push the input voltage noise down as much as possible. Ideally below the OPA1652 and OPA1678 levels, which are fabricated in the same process.

3. Don't let power supply current limitations get in the way of performance. OPA2134 and NE5532 both have power supply currents of about 4mA per channel, and have been widely adopted in the market (understatement). That seemed like a reasonable target for the supply current of the OPA1656 as well.

A quick snapshot of the OPA1656 performance specs:

• 2.9nV/rtHz broadband voltage noise
• 6 fa/rtHz broadband current noise
• -131 dB THD+N at 1kHz, 600 ohm load, 3.5Vrms signal, 80-kHz measurement bandwidth
• 53 MHz gain bandwidth product, 24V/us slew rate
• >100mA output current
• 4.0mA typical supply current, 4.5mA max

I'm looking forward to seeing what people think of the device, and hopefully it finds its way into a few projects on here!

Christmas comes a bit early this year! The single channel version of the OPA1656, called the OPA1655, released yesterday and the product page is now live on ti.com: https://www.ti.com/product/OPA1655

It doesn't look like units have been stocked yet for ordering, but they should be in-stock soon.

 

[tomchr]

±20 V, 100 mA, THD ~-130 dB @ 2 kΩ load. $1-something @ QTY 1k. What's not to like?

It looks like this one has the phase kink (lead/lag compensation) towards UGBW as well. That's the only drawback I can see. It makes it a little harder to use this opamp in a composite amp. That's not a show stopper, though. I'll just have to work harder to get around it.

Nice work John (et al.)

Tom

 

[bambadoo]

Really nice. Unable to request samples though.. (well for any product)

Your cart contains more items than is allowed. Please limit your cart to 0 items.

 

[davada]

Looks like a very nice candidate for an ULD oscillator.

 

[Boydk]

Just ordered some samples. Will be playing around with a 2 stage riaa and try these as second gain stage.

 

[tubesguy]

Really nice. Unable to request samples though.. (well for any product)

Same here.

 

[johnc124]

Same here.

Much to the frustration of some of us, TI cracked down on free sample requests coming from accounts created with personal email addresses (e.g. gmail.com, yahoo.com, etc.) because the company felt that free samples to those accounts did not result in business. If that is the case here, your best option might be to purchase the devices from the TI store, using the "add to cart" button. Looks like they are $2.49 each to buy 5 of them.

 

[tubesguy]

Thanks, John, I'll do that.

 

[diyiggy]

Hi johnc124,

I'm a little lost in all the new TI references...

It's certainly off topic and I apologize for that but what could be the best oaps candidate (soic8 or dil8) at TI for I/V purpose with dac chip outputting no more than 1mA ?

Are there oaps with non feedback loop for this task in the catalog ? Transconductance ones ?

Many thanks and forget it if the question has no sense here as I have no EE background.

 

[johnc124]

For a DAC chip with a low output current, I would suggest op amps with FET type inputs, either JFETs or CMOS. Low output current would mean the transimpedance gain of the I/V circuit will be high, and the input current noise of the op amp will be a significant contributor. There's no shortage of candidates here, and the new OPA1656 is a great option, but you could also check out: OPA1642, OPA1678, OPA827, and the newer OPA828, or also OPA2810. If you just wanted to use a single 5V supply, the OPA1671 is good.

All op amps employ feedback, but I think the core of what you're asking is do we make any dedicated ICs for converting DAC output current to voltage that don't employ feedback? And I'm not aware of any, but that task could also be performed with a simple resistor. Most current-output DACs don't like to see a varying voltage on their output though, so there will be additional distortion from this approach.

 

[soekris]

Hi johnc124,

I'm a little lost in all the new TI references...

It's certainly off topic and I apologize for that but what could be the best oaps candidate (soic8 or dil8) at TI for I/V purpose with dac chip outputting no more than 1mA ?

Are there oaps with non feedback loop for this task in the catalog ? Transconductance ones ?

Many thanks and forget it if the question has no sense here as I have no EE background.

TI have the opa860/opa861 Transconductance amplifiers....

 

[diyiggy]

Thank you so much for the hints.

I had (indeed) in mind AD844 & OPA861 (not sure the first don't use feedback!) after reading many threads here and there but was asking myself if there were something better with all the launchs from several years now...My very basic undestanding is they were good to be loaded with relativly high impedance outputt of current outputt dac chips while giving at their outputt a good enough low impedance voltage for our hihi purpose... But I'm not able to understand why they were chosed by some because of their non feedback design. I may mistaken as my knowledge is at dust level.

Thanks for that list, I'm to lurking at those oaps.

 

[MikeHartshorne]

Hi everyone - wanted to take the opportunity on this thread to introduce myself, I am the engineer that is assuming John's old role as Audio systems engineer in the precision op. amp. group at Texas Instruments. I also have been an audio enthusiast for quite a while, having tinkered or created several guitar effects/amps. Now that John is ascending the management hierarchy, he may not be able to post as often or may forget some technical details (just kidding, of course!), please let me know any questions about TI's audio amps. I'm also hoping to post the circuits we test here in our lab as they come in, stay tuned.

 

[BrianL]

Oh my!

 

[DPH]

Mike, pleasure to have you join us.

 

[rayma]

I'm looking forward to seeing what people think of the device, and hopefully
it finds its way into a few projects on here!

Thanks a lot, it looks great. Congratulations on your promotion.

 

[johnc124]

Hi everyone - wanted to take the opportunity on this thread to introduce myself, I am the engineer that is assuming John's old role as Audio systems engineer in the precision op. amp. group at Texas Instruments. I also have been an audio enthusiast for quite a while, having tinkered or created several guitar effects/amps. Now that John is ascending the management hierarchy, he may not be able to post as often or may forget some technical details (just kidding, of course!), please let me know any questions about TI's audio amps. I'm also hoping to post the circuits we test here in our lab as they come in, stay tuned.

Welcome to the party Mike.

And don't worry, promotions haven't kept me out of the lab yet...

 

[sottomano]

TI have the opa860/opa861 Transconductance amplifiers....

Yeah....if only....these parts would be capable of higher voltages. But limiting it to ±6 or so Volts is very limiting (pun intended).

But, I wanted to say, it is really nice from you John (and TI) that you show up here!

 

[DPH]

One thing I noticed is that the 1/f knee is a fair bit higher than the OPA165x series, which means for a substantial portion of the "critical" audio bandwidth, the latter is probably a bit quieter. Nonetheless, the higher idle current budget does enable some very nice traits and makes for a very nice general purpose opamp across a wide range of network impedances.

 

[johnc124]

One thing I noticed is that the 1/f knee is a fair bit higher than the OPA165x series, which means for a substantial portion of the "critical" audio bandwidth, the latter is probably a bit quieter. Nonetheless, the higher idle current budget does enable some very nice traits and makes for a very nice general purpose opamp across a wide range of network impedances.

I would caution you against using the "knee" in the noise curve to compare parts, and the OPA1652 and OPA1656 are a great example of why. Both parts actually have identical 1/f noise. If you pick a point on the 1/f portion of the noise spectral density curve you can see that the two parts are essentially identical. For example, at 10Hz both parts are approximately 35nV/rtHz. The knee in the OPA1656 noise curve is higher because the broadband noise of the OPA1656 is lower (2.9nV/rtHz as opposed to 3.8nV/rtHz).