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Question: Low-Volume Channel Imbalance

post #1 of 5
Thread Starter 

I recently purchased a Schiit Modi / Magni stack for use with my Audio-Technica ATH-M50 (38 ohm) and Grado SR80 (~32? ohm) headphones. I am very happy with it, except for the channel imbalance at low volumes.

 

Things I already know:

  • Low-volume channel imbalance is a common issue with budget analog volume controllers (link).
  • My headphones are low impedance.
  • My amp has high gain (5).
  • The combination of the previous two points means that my headphones will be loud without turning the amp's volume pot much.
  • I can decrease the volume digitally on the transport, thus allowing me to increase the volume pot on the amp to avoid channel imbalance, but this can lead to data loss (link). Disregard whether I can actually perceive the lost data.

 

I read that the O2 suffers from the same low-volume channel imbalance as the Magni, but I also understand that it has / can have lower gain (the default from JDS Labs being 2.5 / 6.5, but available as low as 1.0).

 

What I want to know:

  • Would a lower gain mean that I could turn up the volume pot further (thus avoiding channel imbalance) without my headphones being so loud?
  • Would sidegrading to the O2(+ODAC) be worth the money and effort?
  • Alternatively, can I mod the Magni to have lower gain?

 

Tangentially related: With nothing playing, if I turn the volume pot to max (and even before max), I can hear quiet static with my M50. Is this normal? (I hear that the Magni is supposed to be dead silent.) Would I experience the same thing with the O2?

post #2 of 5
Quote:
Originally Posted by shadowox8 View Post

What I want to know:

  • Would a lower gain mean that I could turn up the volume pot further (thus avoiding channel imbalance) without my headphones being so loud?

Yes.

Quote:
Originally Posted by shadowox8 View Post

  • Would sidegrading to the O2(+ODAC) be worth the money and effort?

Probably, depends on your goals.  

 

Quote:

Originally Posted by shadowox8 View Post

  • Alternatively, can I mod the Magni to have lower gain?

Theoretically, yes, depends more on how it's built and if it's practical to get in and modify.  Haven't been in one, so I don't know.  If it's physically possible, it's electrically possible too.

 

 

Originally Posted by shadowox8 View Post
Tangentially related: With nothing playing, if I turn the volume pot to max (and even before max), I can hear quiet static with my M50. Is this normal? (I hear that the Magni is supposed to be dead silent.) Would I experience the same thing with the O2?

Try the same test without something connected to its input, you might be hearing noise from the source device.  "dead silent" is relative, could mean a lot of different things.  But with a high-gain amp and 99dB sensitivity headphones, you could be hearing noise that may not otherwise be audible.  If the noise is coming from the source, then any amp with similar gain would have the same result. If you tried playing audio that way, you might find the sound level dangerously high.  

 

All circuits have a noise floor, and it's always measurable, which also means that with enough gain it can be audible.  The task is to have the residual noise be below the noise of the source material, which with the right gain structure, shouldn't be a problem for any amp.

post #3 of 5

Looking at the PCB and parts used, appears to be a bourns ptd90 dual gang series potentiometer (actually the best small footprint pot you can get IMO). As you know - posted, channel imbalance at low volumes is normal with them with both 10 & 20% models, generally only 1 in 3 match well at low volumes. Sometimes 1 in 4, or 1 in 5 depending on the batch. Same with other brands such as alps. I generally just clear the units that test poor on ebay - describe the poor matching in the description. Good for testing or only using 1/2 of the pot.

 

Not sure what value they used, have never researched it but one could test several and find a unit that matches well - cure your problem. Not many take the time to test every pot - labor is way to high and rejects are massive.


Edited by Garage1217 - 6/18/13 at 7:04pm
post #4 of 5
Thread Starter 
Quote:
Originally Posted by jaddie View Post

Probably, depends on your goals.

Could you expand on this? I'm new at this, so I might not be thinking about all the things I should be.

 

Quote:
Originally Posted by jaddie View Post

Try the same test without something connected to its input, you might be hearing noise from the source device.

You were correct; disconnecting the amp from any input removed the noise. It was very quiet to begin with, and I would never be listening with the volume pot nearly that high anyway, so it really doesn't matter.

post #5 of 5
Quote:
Originally Posted by shadowox8 View Post

Could you expand on this? I'm new at this, so I might not be thinking about all the things I should be.

 

You were correct; disconnecting the amp from any input removed the noise. It was very quiet to begin with, and I would never be listening with the volume pot nearly that high anyway, so it really doesn't matter.

If you're playing from a device like a PC that would drive a DAC (in other words, not a portable device), then the 02/DAC combo should improve your noise issue.  Make sure it's ordered set for low gain.  The 02 combination is a very neutral and uncolored system, if that is the goal, you should be very happy.  Some like the amp to offer a bit of flavor, I prefer to inject flavoring with EQ, and just let the amp do what a good amp does....amp.  I don't own the 02/+ODAC, but I do have two 02 amps that I built, and they work fine with players, computers and external DACs. I also use it for a headphone monitor amp when I do any video production.

 

The noise you heard was clearly from the source.  PC sound cards are not always great, and PC power supplies are notorious. 

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