We released a new audio op amp this week specifically targeting ultra high fidelity headphone amplifier applications: http://www.ti.com/product/OPA1622
Some of the highlights:
I know the package really isn't hobbyist friendly (3mm x 3mm SON-10) but I thought it would still be an interesting product to many on here.
Some of the highlights:
- 80mArms linear output current (+145/-130 mA short circuit)
- Extremely low distortion into low impedance headphones: FFT on the front page of datasheet shows -133.6dB 2nd Harmonic at 50mW into 32 ohms
- Ground-referenced enable pin compatible with 1.8V logic and click/pop suppression. 5uA of supply current in shutdown mode.
- 2.8nV/rtHz input voltage noise
- 0.8pA/rtHz input current noise
- 2.6mA supply current when enabled
- 136dB open loop gain with 600 ohm loads
- Stability with >1nF cap loads in a G = -1 configuration, no isolation resistor
- Very good PSRR: 97/123 dB at 20kHz.
I know the package really isn't hobbyist friendly (3mm x 3mm SON-10) but I thought it would still be an interesting product to many on here.
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Very impressive, especially HF distortion with significant loading, this is
where things normally fall apart.
Note there is a slight error in data sheet, fig 52, both DAC OP's are same phase.
Also, WRT Fig 52, probably a good idea to buffer the DAC. That is starting to
load the V OP DAC which they are not really suited for.
T.
Thank you for your feedback. As you might imagine, output stage linearity was a major focus of this design. Specifically to keep things from "falling apart" under significant loading.
As for the polarity of the voltage sources in Fig 52, I think it depends on how you look at it. The way I see it, the two voltage sources have opposite terminals connected to the midpoint (where the DC source is connected) so the outputs will be opposite polarity. But I'm no graphic designer...
As for the polarity of the voltage sources in Fig 52, I think it depends on how you look at it. The way I see it, the two voltage sources have opposite terminals connected to the midpoint (where the DC source is connected) so the outputs will be opposite polarity. But I'm no graphic designer...
Do you have a microscope? Actually, the OPA1612 and OPA1688 are available in SO-8, not bad.
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A fair question! And although I was the product definer and systems lead for this part, I don't get 100% control over the marketing folks
But, I can honestly say that when we started working on this part about a year ago, I was very adamant that I didn't want to create a part with excellent specs but terrible sound quality in the real world. I did not want to create just another op amp with mediocre linearity hidden under 140dB of loop gain. Or one with 100V/us slew rate achieved with a crude slew-boost circuit (not all slew boosting circuits are crude though). These sins tend to be exposed in demanding applications.
That being said, there is no IC-level sound quality simulation, so how do you design a good sounding part? Basically we had a K.I.S.S. methodology (Keep It Simple, Stupid) which focused on using the strengths of our semiconductor process in simple but elegant circuits.
Second, we tried to address distortion at the source first. For example because we were targeting headphone applications, we focused heavily on distortion sources in the output stage which included examining crossover distortion under heavy load conditions. We could have just added a whole bunch of open-loop gain to cover up the bad behavior of the output stage, but instead we chose to develop a completely new output stage topology.
Third, we put a lot of work into the actual implementation of the circuitry. For example, the standard op amp pin-out is a pretty huge limitation on performance. It's sub-par for internal routing, and it also makes it darn near impossible to achieve low distortion at low frequency and high output current because of thermal feedback effects. So we threw it out the window and went with something new that let us put both amplifiers on the same thermal line of symmetry. This prevents the output transistors of one amplifier from asymmetrically heating the input stage of the other amplifier (or its own input stage) and causing distortion. Funny story: one of our IC designers actually posted a graph of his daily steps while this project was in the layout phase because he was walking to and from the layout engineer's office so often. It was extremely important to re-simulate the circuit at every stage of layout to include the contributions of parasitics.
These are just some of the approaches we took to achieving a product that sounds good. I've been listening to this amplifier from the first day the silicon came back on MANY different headphones and I'm proud of what we achieved. The ultimate judge however is the market, and I think we (the engineers that worked a lot of long hours on it) are pretty excited to see how the OPA1622 is accepted.
A fair question! And although I was the product definer and systems lead for this part, I don't get 100% control over the marketing folks
But, I can honestly say that when we started working on this part about a year ago, I was very adamant that I didn't want to create a part with excellent specs but terrible sound quality in the real world. I did not want to create just another op amp with mediocre linearity hidden under 140dB of loop gain. Or one with 100V/us slew rate achieved with a crude slew-boost circuit (not all slew boosting circuits are crude though). These sins tend to be exposed in demanding applications.
That being said, there is no IC-level sound quality simulation, so how do you design a good sounding part? Basically we had a K.I.S.S. methodology (Keep It Simple, Stupid) which focused on using the strengths of our semiconductor process in simple but elegant circuits.
Second, we tried to address distortion at the source first. For example because we were targeting headphone applications, we focused heavily on distortion sources in the output stage which included examining crossover distortion under heavy load conditions. We could have just added a whole bunch of open-loop gain to cover up the bad behavior of the output stage, but instead we chose to develop a completely new output stage topology.
Third, we put a lot of work into the actual implementation of the circuitry. For example, the standard op amp pin-out is a pretty huge limitation on performance. It's sub-par for internal routing, and it also makes it darn near impossible to achieve low distortion at low frequency and high output current because of thermal feedback effects. So we threw it out the window and went with something new that let us put both amplifiers on the same thermal line of symmetry. This prevents the output transistors of one amplifier from asymmetrically heating the input stage of the other amplifier (or its own input stage) and causing distortion. Funny story: one of our IC designers actually posted a graph of his daily steps while this project was in the layout phase because he was walking to and from the layout engineer's office so often. It was extremely important to re-simulate the circuit at every stage of layout to include the contributions of parasitics.
These are just some of the approaches we took to achieving a product that sounds good. I've been listening to this amplifier from the first day the silicon came back on MANY different headphones and I'm proud of what we achieved. The ultimate judge however is the market, and I think we (the engineers that worked a lot of long hours on it) are pretty excited to see how the OPA1622 is accepted.
Hi John,
I have pretty good facilities to bring up a part like this. I'm planning on interfacing it with the PCM5102 DAC. Any advice on how to interface these two parts for optimal performance? The datasheet only shows a reference circuit for a differential output dac.
I would probably like to first try it out in a simple CMOY configuration that is DC coupled to the output of the dac. (just a non inverting op amp essentially). If I remember correctly the dac suggests a lowpass filter with something like series 470 ohms with 2.2nF caps. I was planning to tie those outputs (after the lowpass filter) directly to the (+) terminals and then implement a non inverting feedback gain of around 6.
Any tips here would be greatly appreciated.
Thanks
I recall another opamp that departed from the traditional pinout, and even published an article or ap note explaining the shortcomings of the standard pinout.
I don't recall the model number and can't locate the published information - can anybody refresh my memory?
Dale
as I recall AD did some rotated pinouts, very high frequency (for leaded packages at least) can be improved by placing output between +/- VS pins giving smaller loop area for output current
I've also seen soic types with common connected feedback pins on both rows of the package, again allowing reduced loop area, parasitic inductance of the feedback divider
ah, here: Analog Devices : Analog Dialogue : PCB Layout
I've also seen soic types with common connected feedback pins on both rows of the package, again allowing reduced loop area, parasitic inductance of the feedback divider
ah, here: Analog Devices : Analog Dialogue : PCB Layout
And soon we will see an upgrade path for your "End of Live" LME49710 (series) or whats the beef about ... ??
Cheers
Hp
John, not trying to be pedant, but
Did you do any controlled listening test to find out what the actual result of your efforts were, sound-quality wise?
Just wondering - I do agree that good engineering will pretty much assure good sound quality, but still like to proof the pudding.
jan
Did you do any controlled listening test to find out what the actual result of your efforts were, sound-quality wise?
Just wondering - I do agree that good engineering will pretty much assure good sound quality, but still like to proof the pudding.
jan
Jan, listening tests were performed by several of the main customers the product was developed for. These customers were provided samples of the device early-on in the development process and requested to give feedback on the sound quality. If their feedback was not positive, we would not have moved forward with the project.