Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: schweigc on February 21, 2012, 06:09:47 PM
-
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
-
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.
-
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.
-
... 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.
-
I am out of town on business; I
-
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.
-
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 (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
-
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 (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.
-
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.
-
What about the PEC potentiometer? I have never heard one, but have read that people like them.
-
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.
-
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
-
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
-
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.
-
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
-
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.
I'm a big fan of the TKD 2CP-2511, which is the more expensive TKD model. However I bought my TKDs when the base price was $72, and PCX had a 20% off sale - at $100 full price it is a big ask.
Not a fan of steppers like the Goldpoint in very brief listens. My perfect listening level is always between steps.
-
Hello,
I just got back from out of town. While I am waiting for another pot, I thought I would look at voltages again. I bought a better DMM, and got some strange readings (expected value):
1: 5 (90)
2: .5 (170)
4: 0 (170)
5: 0 (90)
6: 86 (0)
7: 85 (100)
9: 85 (100)
10: 88 (0)
A6: 136 (90)
B1: 135 (90)
B3: 140 (100)
I also got -2 readings on 12, 14, 16 (not sure if negative voltage means anything).
Thanks,
Chris
Sorry, I was measuring some of the wrong terminals (1-10 I *was* measuring the transformer terminals). The out of tolerance readings for 1-10 are as follows:
T1: 135 (90)
T7: 138 (100)
Terminals 6 and 10 jump around from .5 to -50
-
Just double checking here ... what do you measure at T2, T4 and T5?
-
Laudanum,
T2: 165 (170)
T4: 165 (170)
T5: 90 (85)
Thanks,
Chris
-
Would you happen to have another 12AU7 tube to swap in and re-check voltages? Im not one of the gurus here, but a tube swap and then re-checking voltages would be a quick way to rule a bad tube out. I think the voltage will be high if the tube isnt drawing enough current and that can be an issue with one side of the tube itself.
-
I have a couple on the way along with another pot. Thanks for all your help!
-
New tube fixed it. Sounds absolutely amazing!
-
New tube fixed it. Sounds absolutely amazing!
Great that I got one right :-) ... Better that you got it sorted out. Enjoy.
-
Hey guys, I finished building my Crack and have the same issue with the right channel having lower volume output. All measurements checked out. Should I order both tubes or just the front one?
thanks
-
Hey guys, I finished building my Crack and have the same issue with the right channel having lower volume output. All measurements checked out. Should I order both tubes or just the front one?
thanks
Channel imbalance with any rotation of the volume pot or just at the lower end, say below 9 or 10 O'Clock?
-
.sup,
It's the front tube that will efffect channel balance the most (unless the large one is really, really bad), but why not get replacements for both? Some folks have also had some issues with the large, output tube, and why not play it safe, plus it gives you another flavor to try -- say try something like a 6as7 in place of the 6080 -- the presentation is bound to be slightly different and may sound better to you.
Just a suggestion.
Welcome to the BH club!
-- Jim
-
Thank you for the replies and welcome Laudanum and Jim! It doesn't matter how loud I turn the volume the channel imbalance is always there.
The back tube seems to be in really poor condition - oxidized and very old. I will get both it they are not too expensive. Any recommendations as where is the best place to purchase them? Is ebay alright?
Thanks!
-
.sup,
Try here for crack tube info http://www.bottlehead.com/smf/index.php/topic,663.0.html .
Welcome to BH. This Forem is what separates this company from anything else I have encountered. There is no way that I could be involved in DIY Audio without the help of these guys.
Pat
-
Thank you for the welcome and you reply Pat and at the same time apologies for late reply, I have been very busy for the past two weeks.
I have purchased 2x 12au7A/ecc82 RCA Tube CL Top *Test NOS* from ebay. I will first test the front tube and if that doesn't provide an answer I will order 1 power tube. Will report back. Thanks again everybody!
-
Hello guys, I just got the tubes and guess what - channels are now balanced! I am so proud of myself right now as this was my first DIY project and I was really thorough when building and refused to admit to myself I could have done something wrong. I am ecstatic right now as I got the tubes a day before I go on vacation till the end of the month and now I will be able to enjoy myself there even more. I am writing slightly under influence because after last night's live Buena Vista Social club concert I am still sobering up but could not wait to thank everybody who offered help here and the Bottlehead family. I just hope tubes are properly tested before shipped in the future as I was unable to listen to the amp for weeks because of the faulty tube. Thank you again!
Will be working on Speedball next month.
-
Happy to hear that the replacement tube cleared the problem. Enjoy!
-
.sup (do you have a name?),
Great news! Although I've been doing this kind of thing for 40+ years, it's always great to hear when somebody with no experience at all can come in and build one of these kits and end up with a first-rate piece of gear. A lot of work and thought goes into making that possible, and that is what always never fails to impress me about what Bottlehead does.
Enjoy your vacation,
Jim
-
Thank you guys, I really appreciate the kind words and am grateful for the opportunity to be able to build something that actually works, and how it works! Just got back from vacation and the first thing I did was fire up the amp and enjoy myself. ;)
kindest regards, Peter