[Kibble Fat]

Greetings head-fiers!

I've recently assembled a Mini3 amp (gain 2) to use with the LOD of my 6G ipod. I've built one canare interconnect so far and will probably make a silver one this weekend. The issue I'm running into is that at low listening volumes the right channel is slightly louder than the left. I've got a pair of Nuforce NE-7Ms that have 13.6 & 13.7 ohm impedance (right & left). I'm certain its not the LOD that's causing the imbalance as I've checked with other mini-to-mini cords from the ipod's headphone jack with the same result. The headphones and my car's stereo work fine as well. And yes, I know the Mini3 shouldn't be expected to run well at low levels.

My question is where to start replacing resistors (or capacitors??) on the board to balance out the sound. I'm not suggesting other rated values, just using others I didn't use after the matching process. I matched all resistors leaving at least 4 extras and usually to within about 0.2% of eachother.

When I slowly turn up the volume from nothing, the right channel becomes about as loud as a conversation in another room while the left is nearly silent. At normal levels, the focal point of the soundstage seems to be about 25-30 degrees to the right of the direction I'm facing (making up my own terminology here

). I hope this is an easy fix, but I will understand if using these iems is unreasonable...

Thanks for any help you can give!

Eric

PS: Thank you Ti for such a wonderful DIY project. Expect more business from me soon

 

[CodeToad]

When you turn the volume all the way up do you still have an imbalance? Or is it only at the lower levels?

 

[Postal_Blue]

It sounds like poor tracking from your pot. Only way to really fix it is to get a better pot that is more precisely matched at low levels.

 

[Kibble Fat]

Quote:

Originally Posted by CodeToad /img/forum/go_quote.gif When you turn the volume all the way up do you still have an imbalance? Or is it only at the lower levels?

well yes. The volume difference is a fixed amount and becomes unnoticeable at high levels, but these levels are unbearable to listen to for more than a minute.

Quote:

Originally Posted by Postal_Blue /img/forum/go_quote.gif It sounds like poor tracking from your pot. Only way to really fix it is to get a better pot that is more precisely matched at low levels.

Interesting... I assume I can check this with my DMM? I'll have a look tomorrow.

Other thoughts?

 

[Postal_Blue]

Here is a nice writeup on pots and tracking.

 

[amb]

You have some ultra-low impedance and highly sensitive headphones, and even with gain 2 it's probably too much, and it forces you to use the lowest portion of the volume control adjustment range. It is questionable that such headphones need amplification, but unfortunately gain of 2 is the minimum recommended for the Mini³. You could try buying or making an impedance adapter cable for your headphones. It will increase your headphone's effective impedance and reduce its sensitivity, and allow you to use more of the amp's volume control.

 

[Kibble Fat]

That's what I was thinking, but then more than one person on here said that such an adapter causes distortion. If I go ahead and build one, what impedance should I aim for? 32? Also, would a 1/8 W resistor be enough?

I really appreciate the advice guys!

 

[nikongod]

Quote:

Originally Posted by Kibble Fat /img/forum/go_quote.gif That's what I was thinking, but then more than one person on here said that such an adapter causes distortion.

I dont know if distortion is exactly the right word, but mucking about with the output impedance of the amp is known to really screw up some IEM's, particularly those with multiple drivers.
Quote:

If I go ahead and build one, what impedance should I aim for? 32? Also, would a 1/8 W resistor be enough? I really appreciate the advice guys!

i would experiment to find the right value.

32 ohms is probably a good starting point. Get a pack of resistors from radio shack and go to town putting them in series and parallel in various combos until you get a good value. Then buy a pair of nicer resistors (if that appeals to you) in the appropriate value.

1/8W is plenty.

 

[Kibble Fat]

So I had a look at the ALPS potentiometer just now and took some measurements. Do these look normal? According to the graphs, Anything after 70 degrees of rotation is pretty good. The green and yellow highlighted data represent the levels I was listening to with yellow being my limit for extended listening.

BTW, these position numbers are only visual estimates

 

[amb]

I'd say that your measurement shows that it's reasonably good after 50-60 deg. rotation. So whatever you could do to get your "normal" listening volume above this range (i.e., 8 o'clock position), you'll be all good.

 

[Kibble Fat]

I played around with the numbers a bit and determined that a resistance of 9 ohms added to the right channel would tighten up the channel agreement.

Here's some graphs, just for fun:

So before I add resistance to both channels, I'll try to add just the 9 ohms to the right and see (hear) how that works. Thanks for the help guys. I'll post back here with results.

AMB: Is there any way I can contain this correction within the amp's case? That would be amazingly convenient

 

[amb]

Quote:

Originally Posted by Kibble Fat /img/forum/go_quote.gif AMB: Is there any way I can contain this correction within the amp's case? That would be amazingly convenient

Not without some seriously ugly hackage...

 

[gilency]

does that mean the mini3 is not ideal for sensitive IEMs such as the ES3X?

 

[Kibble Fat]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Not without some seriously ugly hackage...

You wouldn't make the gain for the left channel slightly higher (or right slightly lower)?

 

[amb]

Quote:

Originally Posted by Kibble Fat /img/forum/go_quote.gif You wouldn't make the gain for the left channel slightly higher (or right slightly lower)?

Since the pot's tracking error is only in the lowest part of its adjustment range, if you "correct" for it by changing the amp's gain, then it will be off-balance again when the volume is turned up.