[ishtob]

i only heard that for the first generation shuffle

 

[villekille]

Yes, the sound quality of 1st gen shuffle is good but the noise is not a good thing..it's high pitched whine and it's there even when the volume is set at minimum.

But the problem can be resolved by using a headphone amp. I guess that even if the switching frequency is high and well beyond the audio band, it can still somehow make this kind of noise. And it's not just my player, I actually bought a new one and it's the same thing, just "bad" design.

 

[balou]

the exact chip in Xins amps is either MAX1795, MAX1796 or MAX1797 (they're pretty much the same, except for max output current). Xin once mentioned it that it was one of these chips, buried deeply in the forums. I first tried to id the chip with pics (to no avail), but then found this info on his forum after quite some searching

edit: I _think_ he mentioned it being one of the best-sounding step-up converters he tried out. but don't quote me on that. what it certainly offers is low parts count, and high efficiency in the power-consumption range of most portable amps

 

[NelsonVandal]

If you can tap 3.7 V from the Pod, you can build a very small amp. It seems that AD8615/8531 is used in Xin Reference, and people are happy with it. Why not use the dual AD8616 for left and right, and AD8532 for virtual ground with two resistors as voltage divider and the other half for output ground. I think power capacitors are very overrated in 3 ch amps, and you don't have to use 15000 uF. Just use small ceramics and one small electrolytic for both of them, eg OS-CON 47 uF. The largest parts will be jack and volume pot. One easy way of doing it is to use a Mini3 board (but then you have to use TLE2426 as VG/voltage divider and use a single AD8531) and cut off the power section

.

 

[ishtob]

hm.. is there any way to make virtual ground without dividing voltage? that way there's less need to boot the voltage too much. or possible jsut run off the 3.7v from the ipod

 

[FallenAngel]

Quote:

Originally Posted by ishtob /img/forum/go_quote.gif hm.. is there any way to make virtual ground without dividing voltage? that way there's less need to boot the voltage too much. or possible jsut run off the 3.7v from the ipod

Like I said, LM2664. And it's 3.3V from the Ipod, not 3.7.

 

[ishtob]

would the LM2664 contribute to noise?

 

[NelsonVandal]

Quote:

Originally Posted by ishtob /img/forum/go_quote.gif hm.. is there any way to make virtual ground without dividing voltage? that way there's less need to boot the voltage too much. or possible jsut run off the 3.7v from the ipod

You have to use some kind of voltage divider. If you tap voltage (3.3 or 3.7 doesn't matter) from the iPod, the easiest way is to use a TLE2426 if you go for a Mini3 board. If you are going to build a stripboard amp, using one half channel from AD8532 with two resistors as dividers will be an alternative (look at the PINT schematic how it's done). Both alternatives are very lean on current. You will not lose any voltage. You are just splitting the rails. If you don't use virtual ground (and use negative rail as ground), you'll need an input and an output cap/channel. The sound will be degraded and it'll take up more space.

This thread has made me decide to build such an amp myself for my iRiver IHP120. I can tap 3.7 V from it and use line out. I'm going to order a Mini3 board and AD8616/AD8531. I'm going to use a smaller 3.5 mm jack and probably use a switch instead of volume control with input attenuation suitable for IEMs and HD650. This is to make it as thin as possible. Maybe I can find a smaller pot instead.

 

[balou]

salvage one from an old cdrom (those who still had a play button and a headphone out) or an old portable radio