New developing issues

[drano81]

Hello all,

I've been using my C2A for quite a few months with no problems at all. There have been a few issues rising recently and I want to address them before starting the stepped attenuator upgrade.

For a few weeks now, there has been intermittent static anytime the headphone cable moves. I've had plenty of cables wear out at this point before, so I thought nothing of it. However, a few nights back, when I turned the amp off (volume pot all the way down first), there was a large pop through the headphones. I have also recently changed my DAC and noticed that the volume pot is now incredibly sensitive... it was not like this before. Time for the manual again and on to resistance/voltage checks.

All resistance check passed with a few oddities...

Left side:
Terminal 4: 3.358K

Right side:
Terminal 12: 2.137K

Terminal 22: Open (both switch positions)

Voltages are stranger. I did this check again in January after using the amp for a month or so just to check. The values have changed since then...

Low Current:
IA: 148.8
OA: 65 (was 73 at previous check)
kRegA: 5.8
bRegA: 148.8

IB: 149.7
OB: 92 (was 73 at previous check)
kRegB: 4.16 (was 5.3 at previous check)
bRegB: 149.7

High Current (L/R):

IA: 192.5 / 192.3
OA: 148.8 / 149.7
bA: 0 / 0

IB: 0 / 0
OB: 88.92 / 109.6 (was 97.05 / 93.83 at previous check)
bB: 148.8 / 149.7

Headphone:
Tip: .002
Ring: .002


Any help is greatly appreciated!

Thanks,
Kevin

[Paul Birkeland]

Noise when moving the headphone cable means you have a wire that's not well soldered in the amp.

[drano81]

Thanks for the quick reply Paul! Would a poorly soldered wire cause the pop at power off too?

[Paul Birkeland]

That is also somewhat of a possibility.

[drano81]

Would it be in the audio path or could it be anywhere?

[Paul Birkeland]

Definitely the audio path, but that's essentially the entire front 2/3 of the amp.

[drano81]

After a busy week, I finally got around to inspecting the wiring. I re-flowed the solder joints on any connection that looked questionable. Nothing really stood out to me as a bad connection per se, but there were a few where the rosin did not completely burn off, so that's what I focused on. Voltages and resistance remained the same, so I powered up the amp and the static from the headphone jack is much better, but not gone.

Is there a specific thing I should be checking on my DMM to resolve this?

This is my third kit I've built and the first with this problem, so I'm kind of stuck. My solder joints look okay, however not every terminal is completely filled with solder. That proved to be a very difficult task throughout the build. All wires have a solid physical connection prior to soldering. Is the complete encapsulation of the terminal a necessity?

I've always had a hard time inserting/removing tubes from the 9-pin sockets. I try to leave slack on the wires for movement, but it's always a struggle. Is this expected with chassis mounted sockets?

Sorry for the ramble. I've had some questions brewing for a while now...

[Paul Birkeland]

Do you still get noise when moving around the headphone cable?

[drano81]

I do... and the left channel will short out, but not the right. The jack was the first solder joints I re-flowed. Could I have a bad headphone jack?

[Paul Birkeland]

I am still 99% sure you have a bad solder joint.  If you have a bad headphone jack, you should be able to poke just on the headphone jack terminals with a chopstick to get the left channel to drop.

[drano81]

I’m sure there’s a bad one in there’s somewhere. Is it okay to fire up the amp with all tubes and headphones and poke around the whole amp with a chopstick? Is there anything I should avoid?

[2wo]

I'd use a cheap set of headphones...John

[drano81]

I’ve finally had some time to work on the amp. I’m going over every joint with a chopstick, and I can’t get it to relocate the problem. However, every time I tap on the chassis plate around the power switch and headphone jack, I get the pops. This has me thinking something is not grounding properly to the chassis?

[Paul Birkeland]

That's more than likely a loose connection.  It could be that a wire going to or from the headphone jack isn't well connected. 

We only use the chassis plate as a shield/safety ground, so it's unlikely that you're going to get pops from something intermittently connected to the chassis plate.

[drano81]

Thanks for all your replies Paul. I found that my manual strippers were nicking the wire (didn’t have the Ideal for 24 gauge). I’m going to do an extensive check and re-wire anything that looks off.

For these terminal strips, is it just best effort to get a good mechanical connection on the bottom row? There’s not a really good way to get a solid crimp, unless my technique is lacking.