Spark while voltage testing

[Krishk]

Hi Paul,
After getting the tubes relit again I redid the voltage tests and I found these terminals to be a bit out of the suggested range given in the manual. Should I be alarmed by these rather high voltages? The terminals not listed all came back within the range.
Thanks!

Terminal 2: 208 volts
Terminal 4: 208 volts
Terminal 7: 123.8
Terminal 9: 123.8 volts

 

[Deke609]

Just a shot in the dark here: you might want to (a) double check your mains voltage coming out of your wall outlets, and (b) make sure you wired the transformer for the corresponding voltage. It looks like your measured voltages are about 20% high. I imagine a mains voltage of 120V or more with a transformer wired for less than 115V would result in higher voltages.

cheers, Derek 

 

[Krishk]

I see, I used a different power strip to wire my transformer than the outlet I used to test the amp. Will that explain the difference I am getting? Thanks!

 

[Deke609]

I doubt it, but I can't say for sure. To take the strip out of the equation, try measuring the voltage coming out of the power strip.

[Edit: apologies - I misread your post. If you're not powering the amp through the power strip, and instead directly from a wall outlet, I'd measure the voaltge coming out of the wall outlet - that said, measuring both would tell you whether your power strip is putting out less voltage - in which case I'd say there's something wrong with it).

cheers, Derek

 

[Krishk]

I'm sorry, I didn't correctly identify that I used a surge protector, not a power strip, to figure out the voltage to wire my amp. Would a surge protector change the result?

 

[Deke609]

Dunno    Just measure it!

 

[Krishk]

I see what you mean, the voltages are the same and when I redid the powerline voltage test, the voltage came back as 123 volts. So I must have misread the multimeter. Anyways fixing the wiring should solve my high voltage issue then right? Thanks!

 

[Deke609]

Anyways fixing the wiring should solve my high voltage issue then right? Thanks!

My guess is "yes", but at the very least you'll be a lot closer 

cheers, Derek

 

[Paul Birkeland]

If you have 123V coming out of the wall and you wired for 120V AC, then I'm not worried about those voltages that you have which are a bit on the high side.

 

[Krishk]

Just to update, I reconfigured the transformer setup and now passed all my voltage tests. I tried the amp with a pair of zmf headphones and the amp sounds incredible! I have a very slight buzz when I have nothing playing, this is probably result to a faulty solder join right? Thanks for all the help with my build guys!

 

[Paul Birkeland]

A bit of a buzz could indicate that one of the 220uF caps isn't all the way soldered.  You can wiggle each one and see if the leads move through the terminal strips.

A little bit of buzz with the volume control turned all the way up and nothing plugged into the inputs is also completely normal and not indicative of anything amiss.

 

[Krishk]

What's weird is that I hear the buzz with my zmf headphones but not with other sennheiser ones, could this be a cable issue?

 

[Paul Birkeland]

I would start by looking at those 220uF filter caps and being sure that you hear the noise with the volume pot turned all the way down.