(I think) blown capacitor on new crack build [resolved]

[Paul Birkeland]

Can you carefully measure the voltage at A8?

 

[chris@tradeweapon.com]

1.63V

 

[Paul Birkeland]

How about A7?

 

[chris@tradeweapon.com]

Small spark when measuring at A7. A7=0V.
Remeasuring A8, it is now 13.3! I checked it several times, this time, and last time.

 

[Paul Birkeland]

And the LED is not lit?

That LED is toast.  You can temporarily place a wire between A3 and A8 to get around this issue.

 

[chris@tradeweapon.com]

Thank you, Paul. I really, really appreciate your help. 

That LED did go (i.e.; it no longer glows) and a wire from A3-A8 did get the voltage at A8 back to 1.6. The other voltage measurements in the manual are back to matching the ranges. Earlier in this thread 1 and 7 which were (I think) erroneous are now in range.

A7 = 0, is that correct? I have assumed it is.

The amp turns on and the tubes glow. The other LED glows. When I 1st turned it on, it had more low grade background noise, which didn't change with the volume knob. It produces sound. The amp still has pops and clicks, some loud. I assume this is my apparently abysmal soldering! Would you perhaps advise an overhaul level, desolder/remove some solder, re-solder to sure everything up? Humbling!

Tx

 

[Paul Birkeland]

Pops and clicks could certainly be solder joint issues.  One thing we will recommend is to plug an inexpensive pair of headphones into the amp and poke around the circuit with a wooden chopstick to see which joints set off the noises. 

 

[chris@tradeweapon.com]

Hi

I have done the chopstick test, and patched that wire past the dead LED. I can't really get it to crackle by touching anything. Today I turned it on, let it warm up for 30 mins or so, then plugged in a DAC and sacrificial headphones. For maybe 5 minutes, sounded noise free. Then, there was a loud crackle/pop. I took the headphones off my head (it was loud). I don't quite understand why, but the music player stopped. Laptop> USB> DAC> RCA> Crack. When I pressed play again, it played OK.

I have a few times been over the soldering and can't really find an issue. Frustrating. I am guessing it is still likely a soldering issue somewhere?

Thanks again for the hand-holding.

 

[Paul Birkeland]

If the music player stopped, it's possible that what's going on may not be in the Crack itself.

 

[chris@tradeweapon.com]

I do think it is very, very odd.  The same setup has always worked without issue (same laptop>DAC>[amp]>headphones) with at least 2 other amps. I will go and try it with another amp again now.

 

[chris@tradeweapon.com]

There was a poor solder joint at the bottom left-most (closest to the 9-pin socket) point of the headphone jack. There are 2 black wires connected to it and a repeat of the "pencil test" with a bit more vigour revealed consistent crackling when either black wire was touched.

I have plugged in proper headphones finally.

I'll use it for a bit, then swap some tubes, then put in the Speedball in a few weeks.

Thank you again for your help. It has been humbling and rewarding.

Best,
Chris

 

[Deluk]

Don't forget to replace the led.

 

[chris@tradeweapon.com]

Thanks for the reminder. I absolutely would have forgotten to do that. I've just ordered a replacement pack from the Bottlehead shop.  Is it safe to use the amp normally before this is replaced? If not a safety issue, is there a quality issue?

What electrical function does the LED serve? Does it drop the voltage slightly or something along those lines?

Thanks again.

 

[Natural Sound]

Thanks for the reminder. I absolutely would have forgotten to do that. I've just ordered a replacement pack from the Bottlehead shop.  Is it safe to use the amp normally before this is replaced? If not a safety issue, is there a quality issue?

What electrical function does the LED serve? Does it drop the voltage slightly or something along those lines?

Thanks again.

Wait until you get your replacement LED's. Their function is to bias the cathode on the 12AU7.

 

[chris@tradeweapon.com]

Thank you.

 

[Paul Birkeland]

The amp is 100% safe and fine to use with one LED if you have the jumper between A3 and A8.