[Andrea]

These video op-amps with 100 mA current output seemingly have very "audio friendly" specs too.

I've a few 4051 on order. For driving headphones directly, these might well better the LM6171.

The only concern I have is about the 2.5 uA typical input bias current (but the input offset current is 35 nA).

Any thoughts about them? Do you think they are more likely to cause DC offset problems than the LM6171 and 6172 are?

Thanks

 

[Andrea]

bump

 

[Andrea]

Speculation is perfectly fine

 

[Andrea]

I'm feeling like a pioneer. No one knew about these chips before & I brought them to the light

 

[DaKi][er]

I’ve tried them out and they are a nice sounding chip, just they can get a little cranky if you don’t treat them right, good psu bypassing applies
But in the same family is the ths4631, which is even faster, all the more cranky, with a crazy slew rate, and if you get it working sounds all the lot better, I’ve never heard such great cymbals when paired with an M3 amp

 

[Andrea]

Yes but the THS4051/2 have 100 mA linear output current. And I don't like to deal with super cranky chips, they give me anxiety

I want to try them in an unbuffered headphone amp. Power supply decoupling includes tantalum caps on the power rails. The input impedances are supposed to be balanced, to take care of the DC offset.

 

[Andrea]

I just saw that also the THS4631 has a 95 mA current output.

But a 210 MHz GBW chip doesn't sound realistic for audio. Not even the 180 MHz THS4601, which has lower current output anyway.


The THS4501 instead seems very inviting for this application, if only the DC offset thing doesn't prove a big issue. I guess I must try myself.

 

[Filburt]

What exactly makes you think the THS4051 is "very" audio friendly?

 

[Andrea]

Of course, among the chips with high output current that can drive headphones efficiently...

The fact that it has low distortion, with the 3rd harmonic always below the 2nd at least at high frequency, good noise performance, high power supply rejection, and the "right" combination of slew rate & bandwidth for being fast without being unusefully cranky. Perhaps I had to say "very headphone amp friendly"

 

[Filburt]

Having the third harmonic lower than the second is typical of most op-amps I've looked at. Its harmonic distortion isn't *that* low, though. The TI/BB chip I'm looking to try at some point, the OPA2822, has much lower. If it didn't have such high Ib, I'd use it for I/V as it has very fast settling time.

 

[Andrea]

Yes, some other video chips have it even lower at 1 MHz & above but does that matter? I mean, this chip has 70 MHz bandwidth and the ones I know of with lower distortion all have twice to three times the bandwidth. And approaching audio frequency distortion is supposed to sink down...

Giving the datasheet a glance, the OPA2822 is one of those chips. And I reckon its input bias current is too high for it to work well in my particular amp. Finally the supply voltage can't be more than 12V in total & it's not rail-to-rail.

 

[Filburt]

Quote:

Originally Posted by Andrea Yes, some other video chips have it even lower at 1 MHz & above but does that matter? I mean, this chip has 70 MHz bandwidth and the ones I know of with lower distortion all have twice to three times the bandwidth. And at audio frequencies distortion is supposed to sink down. Giving the datasheet a glance, the OPA2822 is one of those chips. And I reckon its input bias current is too high for it to work well in my particular amp. Finally the supply voltage can't be more than 12V in total & it's not rail-to-rail.

You think 9 microamps is gonna break you? ;D. I wasn't recommending the chip to you, personally; I was simply noting that *I* was going to make use of it. Not all chips perform better in the audio band, unfortunately. Anyhow, the 4051 looks OK to me, but I don't really share your exuberance. It may still sound pretty good though.

 

[Andrea]

Sure, different things.


Anyhow, I can't think of many other video op-amps that suit my particular needs. The LM6172 and the LT1364 are the only ones that I've found so far that seem likely to go well. Thus the 'exhuberance' (part of it is just my style of writing I guess

) about the THS4051. Not much more to say - I'll try it when I'll have the Browndogs and the good will.

 

[00940]

Quote:

Originally Posted by Filburt Having the third harmonic lower than the second is typical of most op-amps I've looked at. Its harmonic distortion isn't *that* low, though. The TI/BB chip I'm looking to try at some point, the OPA2822, has much lower. If it didn't have such high Ib, I'd use it for I/V as it has very fast settling time.

The opa2822 looked nice but I'd go for the THS4631 for I/V. The settling time is marginally worse but the Ib is no problem and the gain bandwith seems practically as good.

 

[Filburt]

Quote:

Originally Posted by 00940 The opa2822 looked nice but I'd go for the THS4631 for I/V. The settling time is marginally worse but the Ib is no problem and the gain bandwith seems practically as good.

Well, the 4631 has much worse distortion and noise (not sure of how it'll play out in the audio band, but probably still not as well), though, but yes the 2822's Ib makes it unsuitable. I currently use OPA627 in my DAC for I/V and it works very well. The 2822 I was planning to use as a headphone driver instead.

Andrea - The op-amp characteristics you're looking at (high speed, high output current) are typical of ADSL/HDSL line drivers, so maybe you should be looking at that category. The LM6171/72 and THS4631 are generally used for that, and the 4051 probably is as well.