Need Help with Audio Note Headphone Amp

[audiosceptic]

I bought this Audio Note Kits HE-6 headphone amp and had it built by a well known Audio Note kit builder, digitalpete. The amp sounds great with planar headphones but I have a problem I need help with.

 

The volume control has a terrible scratch noise when adjusting the volume while music is playing. It will also produce the scratchy noise when the volume control is even touched while music is playing. When nothing is playing the sound is there but barely audible. I emailed digitalpete and he wants me to ship the amp back to put in a new volume pot. In looking at the khozmo volume pot it looks like there are only 11 connections to solder and all are easily accessible so I'm wondering if this is an easy repair? I asked digitalpete what model volume pot this amp had and he wrote back "The Khozmo unit I used is the standard model. It was bought as a 100K stereo. For your application and on khozmo's recommendation I changed the input resistors to 12K ohm which gave the control the proper range of motion. At 100K resistance it was 3:00 before you had any volume level."

 

I'm thinking about either having digitalpete send me the volume pot and replacing it myself (with the help of an engineering friend), or putting in a different, perhaps better volume pot up to the Alps RK50 which is in my BHSE.

 

The questions I have for this group are:

 

1. Is it necessary to have the resistors in place or would a different model attenuator negate the need? Is it common to use input resistors to change resistance for a volume pot?

 

2. Any recommendations on a great volume pot that would work in my application, be easy to install and provide better performance? A non-stepped volume control is preferred.

 

Thanks for any and all input. I attached pictures of the volume pot and the circuit.

 

Edited November 9, 2013 by audiosceptic

[spritzer]

There are known issues with Khozmo pots so I'd advice against installing another one.  No way to fix the pot too as it's just a fucked design/build.

 

I'd replace it with something else, Alps or TKD spring to mind. 

 

http://www.partsconnexion.com/controls_pot_tkd.html

 

I think there is a 20% off deal going on now... 

Edited November 9, 2013 by spritzer

[RudeWolf]

Thanks for the link, Spritz! Might pick up one for the QRV-08. Have you got any experience with the TKD stepped pots? I have a bad feeling that there won't be enough steps.

 

And yeah, too bad the khozmos turn up rotten all the time. They sure look good on the paper... erm monitor?

[kevin gilmore]

the khozmo's can be fixed but you have to take them completely apart

and realign all the wipers for position and pressure. plus fix any bad

solder joints which there are usually a few of.

[audiosceptic]

Thanks spritzer for the reply. I've read bad things about the Khozmo as well so I think I'll go with your TKD recommendation.

 

One question though and pardon my ignorance but would going with the 50K pot avoid the need to put resistors in the circuit for proper volume control? The Khozmo was a 100K pot. They also offer a  TKD10K pot.

[kevin gilmore]

those resistors on the khozmo are supposed to be there.

they are also supposed to be caddok resistors, not what

is shown. they are the shunt resistors to ground and control

the output impedance of the pot.

 

a lower impedance pot is always better for noise. As long

as your source can drive it.

[eggil]

Yeah, my Khozmo has done duty as a door stop. It never worked and had to open a PP dispute to get my money back because he never bothered answering my emails. I guess he didn't want his doorstop back  .

Kevin, fixing them sounds  like a lot of work.

Edited November 10, 2013 by eggil

[spritzer]

Yup, the TKD is just installed as it comes.  Shouldn't need any extra resistors.  Those on the Khozmos should be Caddocks but those look like Takman's which is an option they offer. 

 

Thanks for the link, Spritz! Might pick up one for the QRV-08. Have you got any experience with the TKD stepped pots? I have a bad feeling that there won't be enough steps.

 

And yeah, too bad the khozmos turn up rotten all the time. They sure look good on the paper... erm monitor?

 

Are you referring to the 400$+ monster metal stepped attenuators?  If so then I've never tried them as they are stereo only and who needs that... 

 

The other simply have steps but are 100% pots based on a resistive track so you don't loose any resolution.  Why people use those I truly don't get though...

[kevin gilmore]

Yeah, my Khozmo has done duty as a door stop. It never worked and had to open a PP dispute to get my money back because he never bothered answering my emails. I guess he didn't want his doorstop back  .

Kevin, fixing them sounds  like a lot of work.

 

yep mine is a paperweight too, sits on my desk.  But as it was completely fucked over by hennyo dripping solder

into the insides of the thing, i took it apart to fix it. I did fix it.  But i will never use it because it will not stay fixed.

Great idea, poor execution.