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!

[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]

Originally Posted by bambadoo

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

Same here.

[johnc124]

Originally Posted by tubesguy

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.