Right Headphone Distortion

[Jake1]

Hey everyone.  I'm using the bottlehead crack with speedball upgrade, all resistances and voltages are normal. Certain songs with very high pitch/synthetic tones are creating a bit of distortion on just the right ear.  The build is dead quiet otherwise and the distortion itself just sounds like the tone is fluctuating around where it should be (above and below pitch).  The distortion is more prominent at high volumes.

Is there any direction someone can point me in that might help troubleshoot this?

Thanks

[Paul Birkeland]

That could certainly be the sound of a cold solder joint.  I would just go through and reheat each joint until it flows out, then move onto the next one.

[Jake1]

I don't have time to take a look tonight but I'll work on it in the next few days and update, thanks for the help.

[Deluk]

You have swapped the leads about to see if the distortion moves with the changes? If the inputs on the headphones can be swapped I'd start there to eliminate those being the culprit.

[Jake1]

Woah great idea I flipped the inputs and it stayed in the right so I guess it was a problem with the headphones.  I'm surprised since they're fairly new but I don't see how it could be the amp.

I tried driving them just from my computer and the distortion is still there so I don't think it can be a problem with the amp.

[Paul Birkeland]

It could absolutely be an issue with the amp.  A loose solder joint can allow DC to develop at the outputs, and that can fry a headphone driver.

[Jake1]

So would I be able to find this abnormal DC voltage?  Is there a place specifically I should look for it?

Also if the driver was fried why would the distortion be only happening in a specific audio range?  And why would it only fry one side since I've swapped the inputs?

[Paul Birkeland]

I would just reflow all of the solder joints.  The common one that we see a lot is the junction of the black wires on the headphone jack, where one will be well soldered and the other will be completely loose.  I'm not saying 100% that this is what happened in your case, but it's sufficiently possible to rationalize at least going through and reheating all your joints to be sure. 

As to why this happens at specific frequencies, that would depend a bit on what's actually going on with the driver.  If you take a DVM and set it to measure DC resistance, what is the DC resistance between the sleeve and the tip vs. the ring and the tip on the headphone plug?

It's also possible that there's a hair stuck and rattling against the headphone driver.

[Jake1]

The sleeve to the tip is ~1000 ohm and the ring to the tip is above 200M as it just overshoots the voltmeter.  The two black wires on the headphone jack do look loose, so you think that connection might have done it?

I looked over all the joints and resoldered to fix the potential cold joints.  Voltages were all normal before and after but is there any other way to check if that changed something?

[Paul Birkeland]

No, I mean unplug your headphones and measure the impedance of the actual drivers of the headphones themselves, unless you have super duper high impedance headphones?

A loose wire on the headphone jack can cause all sorts of issues, a bad sounding amp at minimum!

[Deluk]

Do this sort of testing with the cheapest headphones you have. Anything will do. Don't worry about ohm matching.

[Jake1]

So I need to check the impedance between the two drivers of any set of headphones?  And what should I be looking for here?

[Paul Birkeland]

No, I'm hoping you will measure the DCR of the headphones you have that are damaged.

[Jake1]

I don't have the screwdriver to open them to get to the driver so I can't do that until I get one sorry. 

[Deke609]

Measure resistance (ohms) between (a) tip and sleeve, and (b) ring and sleeve.  See if they match.

If I were you, I'd also follow PB's advice to reflow all the joints in the amp. If there's weak solder joint in there somewhere, resoldering them all will often be a much faster fix than trying to track down the problem joint.

cheers and good luck, Derek