[breez]

Does anyone know how the AD823 (or a similar op-amp) performs with a low impedance load with the minimum supply voltage (+3V)? The internal amp in iRiver H120 doesn't seem to like 16 ohm E2Cs and starts distorting even at sane listening levels (THD ~0.4%, but with a not-so-nice spectrum).

I want practically no bulk added to my portable "rig", so my idea is to build a very minimal amp with no volume control, supply from the DAP (+3V available) etc. and packed very tight. The focus wouldn't really be sound quality, but size and trying to overcome the deficiencies of the iRiver amp (it and the line-out are just fine at driving line level impedances). Is there any point in this?

Another (simpler) idea is to add some resistance in line with the iRiver output and make the amp see a lighter load. But what does it really help? To get the same SPL to the Shures I need to increase the volume and the same amount of current will flow than before.

 

[tangent]

Quote:

Does anyone know how the AD823 (or a similar op-amp) performs with a low impedance load with the minimum supply voltage (+3V)?

In my testing, an AD823 began clipping with an 0.5V signal into a 33 ohm load at 4.3V supply. Unless your phones need a lot less than 0.5V to reach maximum loudness, I don't think it's going to work. The AD823 really is a poor cable driver.

If the problem were that easy to solve, we wouldn't need to build amplifiers. Hint.

Quote:

add some resistance in line with the iRiver output and make the amp see a lighter load. But what does it really help?

No dice. That will just increase the voltage required to drive those phones.

 

[looser101]

I use a XENOS 0HA headamp with my iRiver iHP120 (line out) and either Grado SR80 or Sennheiser MX400. It is rather compact and sounds very good. Unfortunately I have no experience with the E2C, but I think it would work nicely as it's designed for low impedance headphones.

Best of Luck,

R

 

[tyre]

Quote:

Does anyone know how the AD823 (or a similar op-amp) performs with a low impedance load with the minimum supply voltage (+3V)? The internal amp in iRiver H120 doesn't seem to like 16 ohm E2Cs and starts distorting even at sane listening levels (THD ~0.4%, but with a not-so-nice spectrum).

If you haven't already seen it, the AD823 datasheet has a schematic specifically for a 3V portable headphone amp. I don't know if E2C's require a lot of current or not but the AD823 puts out around 15mA of which is sort of mediocre. Although I have read about people using them in Cmoys and saying that it works fine. Also, the 823 uses 5mA quiescent current per channel which might affect battery life on the iRiver.

You could try the AD8506 which outputs more than 30mA and is specified to work down to 2.7 volts at 1.15mA quiescent current.