Channel imbalance

[schweigc]

I got my crack last week and spent a thoroughly enjoyable eight hours assembling it. I am completely blown away by the sound quality (I have the speedball upgrade but hear no reason to install it yet).

The only problem is a noticeable channel imbalance. The left channel is louder than the right. Furthermore the potentiometer is not consistent, i.e. sometimes the 11:00 position is louder or softer. Is this merely a pot problem or could this be a tube?

If it is a pot problem, would a stepped pot fix the channel imbalance?

I am very excited to hear this amp without the imbalance. Already I am thrilled to finally hear my HD 650s being properly driven.

Thanks,
Chris

[Paul Birkeland]

Hello Chris,

There will be some potentiometer imbalance in the lowest bit of travel.  A stepped potentiometer will solve this.

Do the channels balance out when you crank the volume up a bit?  If not, this would indicate other possible issues.

[schweigc]

Hi Paul,

Thanks for your quick reply!

The imbalance is not consistent, it does start to even out as volume increases. When I first finished the Crack, comfortable listening was at the 12:00 position, the imbalance was not very bad. Now the comfortable listening position is at 9:00 and the imbalance is very distracting. Sometimes the pot can travel 10 to 15 degrees without noticeable attenuation and then jump several dbs.

[Paul Joppa]

... Sometimes the pot can travel 10 to 15 degrees without noticeable attenuation and then jump several dbs.

Of course the first thing is to check that the screw on the knob is tight ...  :^)

Assuming it is, then this sounds like a bad pot, or a dirty one. Being new, it should not be dirty inside unless you've dripped solder or flux or beer into it (haha!) - give Eileen a call or email and ask for a replacement. Be sure to give her your name, your forum moniker is not listed on the order forms - that's why we ask you to use your real name in the signature line.

[schweigc]

I am out of town on business; I

[Laudanum]

The stock pot is inexpensive and actually sounds fine, but tracking, especially at low volume, can be a problem.  I have several of these pots and they measure all over the place.  It wouldnt be a surprise for a bad one to pop up here and there.    That said, for a very affordable replacement that tracks well even at low volume, the Alps "blue velvet" pots are good.  They have pins for thru-hole mount which makes them a little harder to solder wire to them, but very doable.   Of course, there are more expensive pots that are more highly regarded and plenty of debate about the "sound" of pots.  But that aside, for about $12 (Mouser) the Alps pot should solve your tracking / channel inbalance problems.  They are pretty smooth, track well at low volume and all the way through the range and sound fine.   Personally, I dont like the idea of a stepped control on a headphone amp unless it is something with a lot of steps (40+) which is expensive.  I think having fine control over the volume is necessary in a headphone amp.  But just my opinion.

Alps RK27 series pot ("Blue Velvet") , 100K "audio taper"  ...  http://www.mouser.com/ProductDetail/ALPS/RK27112A00AK/?qs=sGAEpiMZZMuarXojuOTscwVDmX9fHUSLvlV84oHMUXs%3d

BTW,  the shaft diameter is 6mm, not 9mm as listed on the Mouser site.  So the control knob does fit just fine.

[lior.amsalem]

Just to add that you can also find the ALPS pot with easy soldering "lug type" connections here:
http://www.ebay.com/itm/Alps-100K-x-2-Volume-Potentiometer-Stereo-Vintage-Amp-/220950827929?pt=Vintage_Electronics_R2&hash=item3371b21399#ht_1650wt_1093
That's what I've ended up using.

Greetings,
LA

[Laudanum]

Just to add that you can also find the ALPS pot with easy soldering "lug type" connections here:
http://www.ebay.com/itm/Alps-100K-x-2-Volume-Potentiometer-Stereo-Vintage-Amp-/220950827929?pt=Vintage_Electronics_R2&hash=item3371b21399#ht_1650wt_1093
That's what I've ended up using.

Greetings,
LA

Thats interesting.  Never seen that before.   Must not be available in the US, unless I just havent seen them yet.  It would be logical for ALPS to produce a lug version and I always wondered why they didnt.  Cool.

[Grainger49]

Lor,

Those are from Hong Kong.  Sometimes they are first class products, sometimes they are counterfeit.  It is a crap shoot.  I'm just saying buyer beware.  I don't know this seller.

[BNAL]

What about the PEC potentiometer? I have never heard one, but have read that people like them.

[Laudanum]

Lor,

Those are from Hong Kong.  Sometimes they are first class products, sometimes they are counterfeit.  It is a crap shoot.  I'm just saying buyer beware.  I don't know this seller.

Yeah, thought about that.  Cant be much profit in it but that hasnt stopped them before :-)
I'd just stick with the known to be ALPS pots, they arent hard to wire with the pins.

[Laudanum]

What about the PEC potentiometer? I have never heard one, but have read that people like them.

Supposed to be good for the money but reports of some of them being noisy (scratchy).  Digikey sells them in the US.  I think about one whenever I place an order there but Ive been happy with the Alps.

http://search.digikey.com/us/en/products/KKA1041S28/KKA1041S28-ND/770961

[Noskipallwd]

I've found this to be an excellent pot for the money,  http://www.partsconnexion.com/tkd_73335.html, if I don't use a stepper I'll use this one.

Cheers,
Shawn

[Laudanum]

I've found this to be an excellent pot for the money,  http://www.partsconnexion.com/tkd_73335.html, if I don't use a stepper I'll use this one.

Cheers,
Shawn

The $100 TKD's also seem to be well regarded if one wants to spend more.  If I were on a budget and just didnt favor the ALPS Blues for whatever reason, I would probably either spring the 39 bucks on the "budget" TKD that Shawn linked to, or the $30 something for the PEC and hope I got a quiet, acceptably balanced/good low volume tracking sample.  In fact, I probably will eventually take a chance one day and try the PEC in Crack.  Now that Im very familiar with the conductive plastic ALPS in the amp, I would really like to see if the carbon PEC sounds different/better.  But I just dont find anything "wrong" with good recordings.  

[Noskipallwd]

Yes, Desmond is right the TKD model that sells for $100 is an improvement over the cheaper one. I've felt that if I am going to spend 100 might as well go an extra 30 or so dollars and get a goldpoint mini-v or other equivilant stepped attenuator. I have found the cheaper TKD to be quiet and smooth from bottom to top. It is trickier to solder than the alps as it is a bit smaller.

Cheers,
Shawn