[RLCrisp]

Hi All,

Finished my first amp (PIMETA) a few weeks ago and have been enjoying it a lot. I switched over to the line out of an ipod for my current source and the original gain (I think I came up with something like 10.5 - the multiloop complicates it a bit) is a bit too much for when I use my A900ltd (40 Ohm). My preferred listening level is barely after the wiper actually starts making contact and I would like a bit more range in adjustment. It is better when I use my ER4S but I still don't go much past 1/4 of the pot range.

Since I was going to order connectors and cables to make some interconnects I was thinking about making an "output resistance" interconnect for low impedance phones on high gain amps that is nothing more than a series resistor in each channel. Any suggestions for good parts/boutique resistors to fit this role? (I was thinking somewhere around 25-50 Ohms).

Edit: This should be in DIY, my mistake. Feel free to move it.

Thanks,
Ryan

 

[synaesthetic]

Change out your R3 and R4 for a different gain. Adding resistance to the outputs will change the sound.

Your headphones are very similar to mine. Use the gain calculator on Tangent's site to find out what R3 and R4 values you need to get a gain of 3. That should fix your volume control woes.

 

[RLCrisp]

I realize that would work, I'm trying this more as a versatility thing so that I don't have to change gain with different sources/headphones. I didn't have any sockets when I built the pimeta and was too impatient to wait.

I don't really see why adding output resistance would change the sound though. Usually, if anything, increasing load resistance will help an opamp's harmonic distortion performance. I know that BUF634 in the PIMETA can supply enough current to drive low load impedances (I also have a 2x stack), so this shouldn't really help much since it shouldn't have been a problem in the first place. The result would be the BUF634 supplying less current for a given voltage swing into the load, resulting in a lower current (just like a lower gain would). You can also think of it like a voltage divider. The only reason I could see it changing the sound would be due to thermal noise or some other characteristic of the resistor. It's a very small resistance so noise shouldn't be a concern and I'm not really concinved that the resistor itself would change the sound. Feel free to prove me wrong though, thats why I asked about it =)

On the other hand, I know the ER4P/S converter is nothing more than a small cable. Since the main difference I can see between the ER4P and ER4S is their impedance (27 vs 100 Ohm) I could see the cable having some type of impedance that helps change the sound characteristic. However, the cable cannot increase the headphone impedance, only the total load seen by the output. That was always sort of a mystery to me so maybe that is why I don't see why this would be a bad idea. If anybody knows I have always wondered (to the point of asking etymotic - don't know if they would say under guilt for charging like $70 for it).