[AstralStorm]

About digital potentiometers: if you want to go expensive ($3.5/piece), you can get 2 channel 25kOhm 1024-step AD5235 with bandwidth of 125 kHz, THD of 0.009%, noise of 20 nV/sqrt(Hz) and crosstalk of -110 dB. That's just one example pot, there are others just as good.
These numbers mean that it's better than many opamps. This is worse than O2 performance, but still extremely good if this is the part that limits the amplifier.
 
The tricky part is that you'll need a microcontroller to run the I2C from buttons. Might as well toss in a DAC.

 

[adityan27]

Doesn't anyone use the UHA-4 as a USB DAC?

 

[lee730]

When I had it I did use it as such for a while before aquring my DACport LX. Then I used the UHA4 as the amp and the DACport LXl as the DAC.

 

[zeitfliesst]

How is this amp for use with sensitive IEM's like the ES5? I'm selling the c421 because there was channel imbalance at low but reasonable volumes. I'm guessing the digital volume control on the UHA-4 will allow me greater flexibility in this regard?

 

[lee730]

Quote:

How is this amp for use with sensitive IEM's like the ES5? I'm selling the c421 because there was channel imbalance at low but reasonable volumes. I'm guessing the digital volume control on the UHA-4 will allow me greater flexibility in this regard?

Yes that is the main reason to get such an amp is due to the digital volume pot. I never had any issues at all with low volume listening and channel imbalance.

 

[Origin89]

Anyone know if the UHA-4 can power the Beyerdynamic DT770 250ohms well? I'd like to buy a pair of these phones, but if I have to buy another amp then I'll toss that idea out the window...

 

[brrgrr]

Quote:

You guys think the UHA4 (OPA209AID) would pair well with my Senn HD25-1 ii? I'm not looking for any added coloration. Increased soundstage and transparency would be great. If it could pull out some more detail that'd be desirable.
 
P.S. - I'd be running it through my Macbook and iPhone 4. 

 
I currently enjoy that very set up.

 

[radiohlite]

i use it as DAC
 
sounds tons better than my crappy laptop soundcard

 

[Origin89]

Quote:

 
I currently enjoy that very set up.

 
Sweet. Any specific improvements you want to comment on? Mine will be coming in a few days. I'm really diggin' the crossfeed option on it. I'm thinking that should open the HD25 up nicely.

 

[zeitfliesst]

I just looked at the manual for the UHA-4, but what does it mean by having a low gain setting at -6db? Shouldn't this be a positive number?

 

[estreeter]

Quote:

how about the Fostex HP-P1?

 
Is that a fair comparison ?? Lets stick to slimline USB DAC/amps. shall we ?

 

[ClieOS]

I just looked at the manual for the UHA-4, but what does it mean by having a low gain setting at -6db? Shouldn't this be a positive number?

Those number are right. They are indeed -6dB and +10dB on low/high gain. Having negative gain is good when you have line-out source + high sensitive IEM, since you are not looking for increase in voltage but rather improvement in control. Also gives you a bit more control over the volume pot.

 

[zeitfliesst]

Quote:

Those number are right. They are indeed -6dB and +10dB on low/high gain. Having negative gain is good when you have line-out source + high sensitive IEM, since you are not looking for increase in voltage but rather improvement in control. Also gives you a bit more control over the volume pot.

 
That's great to hear. By the way, what do you think of the 2db volume increments? 2db for each step sounds like a lot, just don't know how it actually is when using super sensitive IEM's.

 

[AstralStorm]

Thanks for the heads up, I didn't notice this issue - so no UHA-4 on my purchase list.
This is a bit low, since e.g. I tend to use 1/3 of gain 2.4x range (thus about gain 0.66) with my IEMs due to the extra equalization in the chain and that attenuates some notable dB. Without that, the required gain would be half as much and definitely within range of UHA-4.
Gain 1 would actually be much more adaptable in my opinion and probably easier to implement - it's a weird design decision.
 
2 dB is a small noticeable level change. In my case, 0.5 dB is the threshold of detection and many aren't as sensitive - but supposedly even 0.1 dB mismatch can throw direct quality comparisons for a loop.
 
Edit: This means you should have about 20-30 usable volume steps, which should be plenty.

 

[lee730]

Quote:

 
That's great to hear. By the way, what do you think of the 2db volume increments? 2db for each step sounds like a lot, just don't know how it actually is when using super sensitive IEM's.

Generally its gives you a lot of headroom. It would be nice to have even more increments but generally it really wasn't an issue with this amp.