Good deal alert: OPA1688 $1.59 at Mouser!
I just had a surprise while putting a Mouser order together. When I first ordered a bunch of OPA1688s a few weeks ago they were $2.07 each at Mouser (#595-OPA1688IDR). Now the mysteries of Mouser pricing have them at $1.59 each, or $1.43 each in quantity of 10! That is the deal of the century for a chip with these specifications. Buy a handful now before the price goes up again.
I just had a surprise while putting a Mouser order together. When I first ordered a bunch of OPA1688s a few weeks ago they were $2.07 each at Mouser (#595-OPA1688IDR). Now the mysteries of Mouser pricing have them at $1.59 each, or $1.43 each in quantity of 10! That is the deal of the century for a chip with these specifications. Buy a handful now before the price goes up again.
Ah, so that is what happened!
Can you list the other audio-related chips with a price adjustment? I might want to stock up on a few... Back on post #32, any more details about the OPA1689 or is that one still under wraps? I have a board laid out for it, just waiting to pop one in.
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OPA1602 should be priced better than it previously was.
We still haven't released the OPA1689, it's high on my to-do list I promise, just juggling quite a few developments at the moment. It's going to be a fun couple of years for new audio chips! Two duals might actually make PCB layout easier though.
OPA1688s in parallel will make a beast of a CMOY!
We still haven't released the OPA1689, it's high on my to-do list I promise, just juggling quite a few developments at the moment. It's going to be a fun couple of years for new audio chips! Two duals might actually make PCB layout easier though.
OPA1688s in parallel will make a beast of a CMOY!
OPA1688 is a great opamp!
1. for the wson8 package, is the thermal pad connected to V- internally? or it can be connected to gnd or v+? I cannot find this information in the datasheet.
2. is it good to use 1688 in DAC iv output stage? according to datasheet page 23, if the dac current output is >15mA and playback square wave test signal, will the opamp input diodes damage?
3. is it unity gain stable? can it be used as a buffer
4. Is the opamp output already includes resistor internally? Is resistor needed on each opamp output when parallel opamp? what is the the best value
Thanks!
1. for the wson8 package, is the thermal pad connected to V- internally? or it can be connected to gnd or v+? I cannot find this information in the datasheet.
2. is it good to use 1688 in DAC iv output stage? according to datasheet page 23, if the dac current output is >15mA and playback square wave test signal, will the opamp input diodes damage?
3. is it unity gain stable? can it be used as a buffer
4. Is the opamp output already includes resistor internally? Is resistor needed on each opamp output when parallel opamp? what is the the best value
Thanks!
OPA1688 is a great opamp!
1. for the wson8 package, is the thermal pad connected to V- internally? or it can be connected to gnd or v+? I cannot find this information in the datasheet.
2. is it good to use 1688 in DAC iv output stage? according to datasheet page 23, if the dac current output is >15mA and playback square wave test signal, will the opamp input diodes damage?
3. is it unity gain stable? can it be used as a buffer
4. Is the opamp output already includes resistor internally? Is resistor needed on each opamp output when parallel opamp? what is the the best value
Thanks!
1. The thermal pad must be connected to V-
2. You can absolutely use it in the DAC I/V stage. It's actually very difficult to get 10mA to flow into the inputs of the OPA1688 due to the 250 ohm series resistor included as part of the ESD protection (Figure 48, page 22).
3. Yes it is unity gain stable. For modern op amps, you can pretty much assume its unity gain stable unless the datasheet clearly says something like "stable in gains greater than: X" .
4. I'm not sure which resistor your referring to, but there is no internal resistor in series with the output. If you are paralleling op amps then yes, you will need to add external resistors. There is no "best" value. The appropriate value depends on the specific circuit. Low resistor values allow for greater output voltage swing, but cause greater DC current to flow between the two outputs. The worst case DC current flowing between the outputs is 2 x Vos(max) / (2 * R) where Vos(max) is the maximum input offset voltage of the op amp.
Sounds about right.
Just a quick estimation: power in the op amp is the voltage drop across the output transistors times the current through them. For 50mW, that's about 1.265 Vrms at the load. This means that there is 9 - 1.265 = 7.735 Vrms across the output transistors. The current through the transistors is 39.5mArms to deliver 50mW to a 32 ohm load. So the power dissipated is P = I*V = 7.735Vrms * 39.5mArms = 305.7mW
And now you know why high supply voltages are not really a good idea with low impedance headphones. They cause excess power dissipation in the op amp.
Feel free to swap out the OPA1688 for the OPA2172 if you like. Since the 2172 is a bit more expensive you'll be helping us out
I admit that I was the applications engineer at the time that had been playing with the 2172 and figured out it made a nice little headphone amplifier. I proposed that we put it in the 3mm x 3mm DFN package to support portable audio applications and the project was off and running. It was initially a resymbolization but we did change some of the test limits in production (input offset voltage limits are a bit wider) and added some more audio specific characterization to the datasheet. I wouldn't have liked this to be printed on the bag, but these things happen!
I am thinking about building battery powered OPA1688 CMoy amp.
If I make it in standard way with TLE2426, virtual ground chip become weakest point and there is no benefit from 1688 extra power.
So, I am thinking to make 0.1% 47k/47k virtual ground, boosted by an other OPA1688 buffer, both half in parallel, to double current.
Can I connect both buffer's outputs together, or output resistors are necessary ?
If output resistors are necessary, what lowest resistance can I use?
Do output resistors increase ground impedance? If so, which one scenario is preferable - parallel buffers with output resistors or just single buffer without output resistor?
If I make it in standard way with TLE2426, virtual ground chip become weakest point and there is no benefit from 1688 extra power.
So, I am thinking to make 0.1% 47k/47k virtual ground, boosted by an other OPA1688 buffer, both half in parallel, to double current.
Can I connect both buffer's outputs together, or output resistors are necessary ?
If output resistors are necessary, what lowest resistance can I use?
Do output resistors increase ground impedance? If so, which one scenario is preferable - parallel buffers with output resistors or just single buffer without output resistor?
Consider it a cheap ti propaganda - http://www.diyaudio.com/forums/headphone-systems/270294-crocodile-3.html#post4998189
It is hard to argue about what sounds better. I did not try PPA v2, or M3. I only tried "The Wire SE-SE" (another ICs based headphone amplifier popular on diyaudio). Comparing to my implementations of OPA1622 I cannot tell the difference in sound quality between the two. Both headphone amps sound very good and transparent to my ears despite different topologies and max output power capabilities.
Regards,
Oleg
Regards,
Oleg
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