Quiet Hum?

[Paul Birkeland]

Can you expand on loose hardware? I just went around tightening all the screws, but is there more than just that?

Yup, just that.

Why would the power line hum not be affected by the pot? I looked at 36L and the transformer nut, and they were separated by several millimetres of space.

If there's something nasty riding on your powerline, it may be getting into the power supply, which would be a noise that would be there regardless of volume knob position usually. 

An attenuating headphone adapter may be useful here if the noise persists.

[bmkuter]

An attenuating headphone adapter may be useful here if the noise persists.

Cool! I've never heard of those, I'll give them an order. I've noticed in my amp testing that when I'm using my Sennheisers, the noise isn't audible at all.

Thank you for all your help.

[bmkuter]

Is there a way I can measure my amp's performance if I have an oscilloscope and a signal generator? I was thinking of just connecting the RCA input wires to the signal generator, but where would I probe on the output end?

[Paul Joppa]

Take the output from the speaker terminals, to start with. If your scope is sensitive enough, you can quantify the hum and noise. Short the input (a shorting RCA is best, but usually just turning the volume all the way down is equivalent).

[bmkuter]

Thanks!

I just remembered that on page 40 - 41 of the instructions, when attaching the 270k resistors, the ones supplied with my kit matching the picture were closer to 370k. Typo in the instructions?

[Paul Birkeland]

There is no 370K resistor in our inventory, and only one carbon film 1W resistor in our inventory.  What color codes do you see on yours?  Did you measure the resistance with them before you installed them?

In any event, as long as they are both about the same value, they could be 200K or 500K and it wouldn't make much of a difference.

[bmkuter]

I think it must have been a typo in the number itself. The colours matched the instructions.

Weird question, should I be able to hear the amplifier working? Like with headphones off and ear a few inches from the transformers.

[Paul Birkeland]

If you have a tone or music playing through the amp, then yes, you will hear some very low level noise coming out of the amp.  If nothing is playing and you hear something like the power transformer buzzing, that would tend to suggest that the hardware is loose or there could some DC present on your AC mains that causing a bit of noise in the power transformer.

[bmkuter]

Yea there's definitely a slight hum when muted. Think that could be causing all this humming?

[Paul Birkeland]

It's a possibility.

[bmkuter]

I listened to my Crack last night and could hear the same static, but not on my Yamaha integrated amp (or incredibly faintly).

EDIT: Went back to reread the manual and noticed this part in the FAQ, which accurately describes the hum (Hissing or low hum noise is not there at low levels, can hear it when I turn the volume up to max -That's normal and you will probably find the listening level deafening at that loudest volume setting). I can really only hear it on more sensitive headphones.

EDIT 2: The headphone attenuation adapter arrived and it completely solved the problem! Thanks for the suggestion!