Help: two small problems.

[beepbeep]

Hey all,

It has been a while since I completed my crack and have been enjoying it A LOT, it seems like the "gotta do some upgrades" bug bit me so I ordered the speedball upgrade.
Before installing the speedball kit, I would like to get two small issues out of the way:
  1) There is a "bzzzz" in the background, this is volume level independent, no matter how loud or low I put the volume, the "bzzz" stays exactly the same. It's very hard to hear while listening to music.
  2) At very low volumes, the left channel is louder than the right channel.

The "bzzz" problem probably has a lot to do with my horrible soldering, after finishing the kit, I always said that I'd re-do the wiring because my soldering was bad / ugly.
What kind of wire should I use? I read something about "Kimber TCSS wiring", should I use different wire for connection between my pot and channels?
I might replace the resistors while I'm at it, any tips?

Thanks in advance

beepbeep.

 

[Laudanum]

You can just reflow the solder connections that you feel are poor. Heat the joint adding just a little more solder.  But that may not be the reason for the buzz.  Im not sure what is most likely to cause the sound you describe although it could be ground related I think.  I would try the most simple first like trying different tubes, cables and a different source.  It could also come from some other device or an appliance in the home. You could try plugging into a different circuit just to see.   But other members will have more thorough and experienced advice.

The difference in volume between channels at low volumes is an easy one.  The volume pot doesnt track particularly well between channels at low volume.  It's common with a lot of pots, especially less expensive ones.  You could try another sample of the same pot.  Some are better than others.  Or go with a higher quality pot.  I think that the carbon pots like the one included in the kit actually sound fine but because I already knew of the potential problem with the channel tracking at low volumes, I built my Crack using an Alps "Blue Velvet" pot which is a conductive plastic pot rather than carbon. I think they sound fine and I cant really hear any signifigant differences between different pots that I have tried ... none of them the expensive variety however or the stepped attenuator type.  My ears probably just arent that great or differences are just too subtle for me to notice.  Anyway, the Alps pots are available in the $20 plus range from audio parts sellers.  Or, Mouser electronics has them for about 1/2 that price.  It would take drilling the mounting tab hole in the chassis plate a little bit inside the tab hole for the stock pot to install the Alps pot with the tab intact.  Not a big deal at all.  The Alps pot has PC mount tabs so soldering the wire to the tabs is a little tricky but not difficult. I think that the kit has 20 AWG wire, I used 22 AWG wire that I had on hand just to make it easier to solder to those PC pins.  There is also the PEC Carbon pots that are supposed to be nice for the price although they are in the $30 plus range.  Then there are the TKD pots which are closer to $100.  They are also a Conductive plastic type pot.  Then there are all kinds and qualities of Stepped attenuators ranging in price from the 20 dollar point for DIY from China sellers to hundreds of dollars already built.  Brands like DACT and Goldpoint are expensive and popular.  Most are 23 step or close to that so you dont have the fine control that you have with a rotary pot which is probably more important with headphones compared to speaker.  Those stepped attenuators that are 40 plus step are harder to find and expensive.  The stepped attenuators are supposed to sound better than regualar potentiometers, especially the ladder types I think, where the signal only goes through one resistor per channel. If you do go witha a different pot, make sure it's a log taper, not a linear and a 100k like the stock pot.

So there is my basic primer on pots from my general knowledge perspective, not an experts view in any form.

 

[intojazz]

Laudanum,
Not bad though!
John

You know Laudanum used to settle the nerves better than music way back in the day.
no offense meant Desmond

 

[Billyk]

I used the PEC pot, I thought it was a decent upgrade, moderately priced. I want to think there was a nice improvement of the sound, but that is as always a subjective opinion.
Regarding the buzz; have you tried different tubes? I know I have one or two 6SN7s that exhibit a very low level hum/buzz at all volumes, pretty close to what you describe. 
I have some caps for the power supply and output, but have not had the time. I am hoping to get these in during the cold season when I don't have yard work to attend to.

 

[beepbeep]

Argh, I really hoped that my new tung sol 5998 tubes would solve the problem but they didn't.
Will try some of the other things that were suggested.

 

[Grainger49]

1) Your post indicates that the problem is after the volume control, there is not much before it.  You don't say if the bzzzz is in one or both channels.  If one channel a tube can be the problem.  You sound like you changed one tube but not both.  If both channels have the noise then it might be something in the power supply.

2) Has been well answered. 

There is nothing wrong with your wire, but you can replace it in the audio path if you want to experiment.  There might be something wrong with your soldering.  It might be the cause of the noise.

  .  .  .  Before installing the speedball kit, I would like to get two small issues out of the way:

  1) There is a "bzzzz" in the background, this is volume level independent, no matter how loud or low I put the volume, the "bzzz" stays exactly the same. It's very hard to hear while listening to music.

  2) At very low volumes, the left channel is louder than the right channel.

The "bzzz" problem probably has a lot to do with my horrible soldering, after finishing the kit, I always said that I'd re-do the wiring because my soldering was bad / ugly.  .  .  .   

 

[hopeful]

A couple of additional sources of potential "buzzing" you might investigate:
(1) Have you tried a different 12au7?
(2) Do you have a cordless phone anywhere near your amp?  I have an amperex 6922 in one of my other amps that buzzes like the devil if its anywhere near my phone or base.
(3) Is your headphone cable running near any other electrical devices?  I've noticed that the stock cable on my HD800's actually picks up soft but audible interference if I let it rest in the vicinity of my dac or powerstrip.

 

[beepbeep]

1) Your post indicates that the problem is after the volume control, there is not much before it.  You don't say if the bzzzz is in one or both channels.  If one channel a tube can be the problem.  You sound like you changed one tube but not both.  If both channels have the noise then it might be something in the power supply.

- Both channels have the noise. I changed one tube (the big one, output tube?), is it still worth trying changing little one (power tube?)?
- I think I can eliminate source, RCA cables because the buzzing doesn't change when I unplug the RCA cables.
- I tried changing location of amp and experimented with different powercable, it doesn't seem influenced by some other electrical device.

It's starting to get really annoying, not sure if it is because I'm focussing on it but I'm starting to hear it through some songs.

What's next ?

 

[Grainger49]

If the tube swap of output tubes did not change the noise then try swapping out the driver (small) tube. 

Both channels kind of points to the power supply.  How about posting a picture of the power supply terminal strips.  I'm curious how much solder is on the solder joints and how you made the connections before soldering.  Solder is not really electrical glue.  But is sometimes used as such (RCA jack center conductor, it can't make a mechanical connection first).

Like I said before, it is down stream from the volume control, the source and interconnects are upstream from the volume control.  Still, within the Crack, there is very little in the crack before the volume control.  So your problem seems to be in the Crack.

It could be the tube socket or tube pins.  Try inserting and removing the driver tube several times.  That cleans both the tube pins and the socket.  Can't hurt, might help. 

 

[beepbeep]

Sorry for my late reply, I have been very busy the last couple of days/weeks(?)

- I will mail bottlehead for a replacement small tube (driver?).
- My powersupply connections seem messy, I will re-do them and take a picture.

I have experimented a lot with replacing the amplifier and making sure no other cables or whatever or a cause for the noise, I heard some difference from time to time that made me think the problem was solved, other times it made me believe that the noise was only in the right channel, bottomline: I think there was some placebo stuff going on.

Finally had some time today and REALLY wanted to do the speedball because I don't know how much time I'll have in near future to build it. I'm happy I did:

- The noise is clearly in the right channel only.

One more extra problem:
- All my voltage checks seem fine, except for the final headphone jack test, I measured tip voltage and it peaks up to 22V and goes straight down to 0V afterwards, I have no idea where to start troubleshooting this.. In the meanwhile, I wait a minute after powering up the amp before plugging in my headphones.

Thanks in advance, you guys are a great help

 

[stereo_eyes]

One other comment on your question about the kimber tcss wire. I wired my crack with TCSS because:

1) when I ordered it, it wasn't clear from the site that it was stranded wire, not solid.
2) I hadn't yet read the advice from Doc that any wire was fine as long as it wasn't stranded.

I can't tell you if it sounds different from the stock wire since I built it in the first place with the TCSS wire. But what I can say is that it is a real pain in the rear to use stranded wire. It's harder to strip, and you have to tin the ends if you don't want little stray wires everywhere.  If I had it to over again I would have just used the stock wire.

 

[beepbeep]

Tube replacement did it, thanks for all the replies, guys!

 

[Paul Birkeland]

With the PEC pot, the balance at the lowest volume levels is not always so stellar.  In order to solve this issue, I recommend disconnecting the red and white wires (running from the jacks to the 100k pot) at the potentiometer, then soldering in a 100k resistor between each wire and the pot lug it was connected to.

This will result in the bottom bit of pot travel relatively useless, and channel balance will be more solid in the typical listening range.

-PB