faint hum in left channel (speedball)

[kill_surf_city]

I just installed the small circuit board and the voltages are all correct and all LEDs come on. There is a faint hum/buzz in the left channel. It's not affected by turning the volume pot up or down. It does however disappear for a few moments when i tap the chassis with my finger. I also hear slight micro-phonics in the left channel when I do this as well/ I can hear the tap on the chassis through my left channel but not on the right channel. Where should I look for a problem?

Oh also, the hum is only there when I have the RCA inputs connected. It seems to sort of come and go. Like I just turned the amp back on and put on the headphones and the hum is now completely gone.

Update: I installed the large circuit board and havent had a problem. Even the noise i heard in the left channel when I tapped the chassis is almost non-existant. As far as listening to music goes, my Crack sounds fucking sublime. Speedball is amazing.

 

[Paul Birkeland]

You likely have a loose solder joint that's acting up.  If this issue returns, you'll want to reflow all of the joints in the amp.

 

[kill_surf_city]

You likely have a loose solder joint that's acting up.  If this issue returns, you'll want to reflow all of the joints in the amp.

yeah i just turned it on today and noticed the hum randomly reappeared, but then after a few moments it went away again. I'm wondering if it could just be one of the tubes just warming up. When I play music it's not noticeable at all.

 

[David Joiner]

I just recently built my crack, haven't put in my Speedball yet, but I had a similar issue with a left channel hum/ringing. Very light, and no change with the volume knob. As it was in only one channel I figured it probably was a solder joint somewhere. I could also get it to ring and reverberate when I tapped on the chassis, so I tapped and tapped trying to isolate the location. Seemed loudest near the input tube, so turned it over and re-flowed all the solder joints on the input tube socket and any others that didn't look perfect.

Well, still had the hum/ringing. I figured it was just the circuit noise as it was nearly unnoticeable. A few days later it seemed to get louder, and even a light brush on the cabinet caused the hum to increase, even the headphone cord rubbing on the wood chassis made the left channel to ring! OK. That wasn't right. I started tapping around the chassis again, this time, though, I tapped on the input tube itself (I had avoided that the first time) and distinctly had the ringing sound increase, even with tiny light taps. I even lightly rubbed the tube top tip with my finger and could get it to ring, (kinda like rubbing a crystal glass with a wet finger sound).

Powered everything down, let the tubes cool, then took the input tube out, gave it a look over, gave it a couple light thwacks with my finger nail, a bit of a shake, then reinstalled it. All Quiet! Odd? I know, but it worked.

David

 

[kill_surf_city]

I just recently built my crack, haven't put in my Speedball yet, but I had a similar issue with a left channel hum/ringing. Very light, and no change with the volume knob. As it was in only one channel I figured it probably was a solder joint somewhere. I could also get it to ring and reverberate when I tapped on the chassis, so I tapped and tapped trying to isolate the location. Seemed loudest near the input tube, so turned it over and re-flowed all the solder joints on the input tube socket and any others that didn't look perfect.

Well, still had the hum/ringing. I figured it was just the circuit noise as it was nearly unnoticeable. A few days later it seemed to get louder, and even a light brush on the cabinet caused the hum to increase, even the headphone cord rubbing on the wood chassis made the left channel to ring! OK. That wasn't right. I started tapping around the chassis again, this time, though, I tapped on the input tube itself (I had avoided that the first time) and distinctly had the ringing sound increase, even with tiny light taps. I even lightly rubbed the tube top tip with my finger and could get it to ring, (kinda like rubbing a crystal glass with a wet finger sound).

Powered everything down, let the tubes cool, then took the input tube out, gave it a look over, gave it a couple light thwacks with my finger nail, a bit of a shake, then reinstalled it. All Quiet! Odd? I know, but it worked.

David

Weird! Yeah I've gotten the humming to completely stop. The only thing I'm getting now is a very, very faint high pitched ringing/hum. It almost just sounds like an electrical hum, you know like you hear near power lines, but super faint and only in the left channel. I'm still gonna go over and re-flow all the solder joints. But I think I'm having the same issue where it seems louder when i tap the larger tube. I'll try what you suggested though. It sounds like your issue was specifically with the power/large tube. Maybe a loose filament or something?

 

[Jameson]

Did you try tightening your amp hardware?

 

[kill_surf_city]

Did you try tightening your amp hardware?

Like the screws on the chassis and transformer?

 

[kill_surf_city]

I just recently built my crack, haven't put in my Speedball yet, but I had a similar issue with a left channel hum/ringing. Very light, and no change with the volume knob. As it was in only one channel I figured it probably was a solder joint somewhere. I could also get it to ring and reverberate when I tapped on the chassis, so I tapped and tapped trying to isolate the location. Seemed loudest near the input tube, so turned it over and re-flowed all the solder joints on the input tube socket and any others that didn't look perfect.

Well, still had the hum/ringing. I figured it was just the circuit noise as it was nearly unnoticeable. A few days later it seemed to get louder, and even a light brush on the cabinet caused the hum to increase, even the headphone cord rubbing on the wood chassis made the left channel to ring! OK. That wasn't right. I started tapping around the chassis again, this time, though, I tapped on the input tube itself (I had avoided that the first time) and distinctly had the ringing sound increase, even with tiny light taps. I even lightly rubbed the tube top tip with my finger and could get it to ring, (kinda like rubbing a crystal glass with a wet finger sound).

Powered everything down, let the tubes cool, then took the input tube out, gave it a look over, gave it a couple light thwacks with my finger nail, a bit of a shake, then reinstalled it. All Quiet! Odd? I know, but it worked.

David

I swapped out the RCA 6AS7G tube i bought with the Sylvania 6080 that the Crack came with and all the problems are now completely gone even the sound i would hear in the left channel when tapping the chassis. Just completely gone and when the amp is turned on with no music playing it is absolutely black, no ring or hum at all.

When I shake the RCA tube it sounds like a bad lightbulb. I loved that RCA tube, but I'm wondering if I accidentally damaged it somehow when I was building the Speedball last week.

 

[Paul Birkeland]

The noise you are hearing is usually little bits of broken off glass rattling around internally, which is completely normal for glass vacuum tubes.  It still could be that there's a loose solder joint in the amp that's acting up, so I wouldn't be in a rush to discard that tube.

 

[kill_surf_city]

The noise you are hearing is usually little bits of broken off glass rattling around internally, which is completely normal for glass vacuum tubes.  It still could be that there's a loose solder joint in the amp that's acting up, so I wouldn't be in a rush to discard that tube.

yeah I'm still going to re-flow the solder joints. I do have some that I know may be suspect. If I still have the issue with that tube after re-flowing the joints, is it safe to assume that it's the tube?

 

[Paul Birkeland]

That can be a tough question to answer.  You would want many hours on a different set of tubes to really know for certain.

 

[kill_surf_city]

That can be a tough question to answer.  You would want many hours on a different set of tubes to really know for certain.

I re-flowed all the solder joints, most looked good but there were some from early on in my build that were very suspect, so i fixed those. Hum is completely gone, but I'm still getting that noise when I tap the chassis. It's even worse when I tap the power tube. But as far as listening to music goes, it sounds perfect. Could be the rattling of that possible piece of glass you speculated might be there, but I've rattled the tube around a bunch and whatever it is that's moving around in the tube is stuck in the very top of the tube, so I'm wondering if that's what making the popping sound when i tap the tub/chassis.

Think this is worth looking in to?

 

[Paul Birkeland]

Yeah, that's microphonics and wouldn't be abnormal.  Just don't tap the tube while you're listening to music.

 

[kill_surf_city]

Yeah, that's microphonics and wouldn't be abnormal.  Just don't tap the tube while you're listening to music.

Thanks Paul!