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O2 amp imbalanced on my ODAC/O2 setup for IEMs

post #1 of 8
Thread Starter 

I have the ODAC/O2 amp setup, but I only use IEMs and as some of you may already know, there is channel imbalance at lower volume level.  Since my IEMs are sensitive like customs, I cannot raise it beyond a certain point where there still is noticeable imbalance in the L and R channels, where it gets too loud and would ruin my hearing.  I bought the amp from JDS labs and the potentiometer is Alps.  I've set it to unity gain, and still too loud to get the volume level up to make left and right even.  

 

Any solution?  I must use O2 Amp as the ODAC/O2 setup is the most perfect in terms of performance I've ever ran across.  It's the most transparent, spacial, neutral sound I've ever heard.


Edited by SilverEars - 3/16/14 at 6:00am
post #2 of 8

Lower the digital volume on your PC. Since ODAC is 24/96, you won't lose much resolution at all.

post #3 of 8
Thread Starter 

Are there any mods I can do or is there an O2 amp I can get that would be lower gain?  Maybe change the pot to a better one?

post #4 of 8
Quote:
Originally Posted by SilverEars View Post
 

Are there any mods I can do or is there an O2 amp I can get that would be lower gain?  Maybe change the pot to a better one?

 

Given all pot (beside the really expensive stepped pot that won't fit inside O2's case) has some level of unbalance in the lower range, I'll imagine you will need to go through quite a few pot to find one that has a relatively good match on the lower range. That means it is really unfeasible cost wise. The sensible thing to do is to sent the O2 back to JDS so they can reduce the gain for you. If it is really that loud, you might even want to consider negative gain.

 

Assuming you don't want to modify ODAC (the line-out can be reduced by adding resistor on the ODAC output) and only care about using O2 as a headphone amp, another cheaper and easier (though less ideal) way to do it is to add a resistor adapter on the O2's input, basically lowering the input signal. This will however add noise / worsen the SNR.

post #5 of 8

I'm a big fan of output transformers. They will easily dump 20db of gain without adding any noise. 

 

Here you go for some ideas:

 

http://www.head-fi.org/t/553094/continued-sidetrack-discussion-from-tiniest-portable-amp-i-can-build-nikongod-microtransformer-based-impedance-step-down-box/15

post #6 of 8
Thread Starter 
I'm guessing between DAC and the Amp or the amp output. What about distortions?
post #7 of 8
Quote:
Originally Posted by SilverEars View Post

I'm guessing between DAC and the Amp or the amp output. What about distortions?

 

You can put the transformers in either place. 

 

I am biased towards the output of the amp - a transformer at the output of the amp will reduce the noise of the amp since it reduces everything coming into it equally. A transformer in the middle will not *increase* noise, but since the output signal is relatively lower and noise is a constant, the noise is relatively higher. The problem with this strategy is that good headphone-ish output transformers are kind of hard to find. 

 

There is not much one can do to change the O2 without making it objectively worse.

Transformers do have measurable distortion. And limited bandwidth! But in a good quality transformer, things are kept low enough that you can pass signal through them a few times without degradation. 

Are the largely inaudible flaws from a transformer worse than the blatantly obvious channel imbalance? 

I suppose the same argument could be made for the noise from a resistor network. 

It is a matter of picking which compromise works best for you. 

post #8 of 8
I have the exact same problem as the OP but with full size headphones.
My dac isn't an ODAC,however it's a ES9023 + PCM2706 DAC.

Adding a resistor circuit on the output of the DAC obviously lowers the output but I'm looking for a different solution.

While looking at the ES9023 datasheet I noticed the resistor referred to as R8.
According to the datasheet, it is used to adjust the output level and thus prevent clipping at different supply voltages.

I took a look at the board and it uses a Micrel 5205 3.3V and a 130kOhm R8 value, just like suggested on the datasheet. This apparently limits it to 1.9Vrms.

Now the real question: Could I just lower R8 to significantly reduce the output level? If yes, do I need to replace other components? (I don't think so.) What R8 value should I try? / What is realistic?

Thanks for your help!
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