How silent should the Smack be?

[M^Cubed]

I just recently finished up building the Smack kit and I have a very light, but noticeable hum. Should any hum be acceptable or should I go through and check resistances again?

The tubes are NOS matched 7119 Amperex with O halo getter. The hum does not change with volume or with/without source connected and with all impedance balanced / unbalanced selection.

Cheers!
 

[fullheadofnothing]

What headphones are you using? How many hours of use do the tubes have?

[M^Cubed]

The tubes are new from what I understand, so very little (probably about 20 hours at this point)

With the HD800 (128 ohm / Balanced) there is very very close to a black background.

With the HD650 (128 ohm / Balanced) there is a noticeable hum with no music playing.

With the T50rp / Mad Dog ( 32 ohm / SE ) there is a noticeable hum with very low music playing.

This is after letting the amp warm up for about a hour while playing music.

Maybe I should switch to a lower gain 5687 also?

[Paul Birkeland]

Did all your voltages look good after you built the amp?

Does the hum vary with your level control?

Will the hum change if you move the Smack around?

[M^Cubed]

Level control does not change the hum, and movement does not change it.  I will need to re-check voltages, but everything was good after the build.

Maybe the tubes just need some hours on them.

[Paul Birkeland]

It also wouldn't hurt to toss in the 5687's that came with the kit, just to continue the process of elimination.

Also, if the black wire from T18 to power transformer terminal 10 isn't well connected with low resistance to the chassis plate, you would end up with some obnoxious noise. 

[M^Cubed]

I unfortunately do not have the 5687. I received the kit second hand and damaged. I had replace a few things along the way.

I just tried with a Grado style headphone (Symphones Magnum) with 16ohm / SE - during the start up, there is the buzz rush that settles down when everything comes up and it goes dead silent for a brief second and then a very very light hum slightly comes back up. If my room wasn't dead silent I would not hear it.

I'll try to find a pair of 5687's to try and see if that solves it.

Cheers and thanks for the tips.

[Doc B.]

I unfortunately do not have the 5687. I received the kit second hand and damaged. I had replace a few things along the way.

When we are attempting to help from a distance like this it is always helpful to give us as much info as possible. One of the things that often seems to go unmentioned in these support threads is when a kit has been purchased used and either damaged or altered from stock. From your description it sound like it may well be a tube issue, but it would also be helpful to know what about the kit is different from stock besides the 7119s.

[M^Cubed]

Hello Doc,

The kit was originally purchased and built by someone local to me. He had sold it to someone across the country. (who I believe also posts on here)  During the shipping it was pretty much broken to pieces and sent back to the original builder.

I took it off the original builders hands in hopes of salvaging it. It was pretty beat up (broken wires, broken switches, the plastic on the power transformer had cracked and the tabs were loose, but still connected to the internal wiring)

So took it back down to a bare build and started from scratch with new wire and switches. Left the original transformer since it seemed still salvageable.

The 5687 tubes were the only actual part that was not included in some way.

I'm going to try to go through and do all the measurements again.  I had originally reused some of the original wire, but through some head scratching and frustration found shorts in the middle of a couple wires.

I will hopefully be able to provide more info with measurement numbers soon, but I was just hoping to get a good general direction before snooping around under it again.

Thanks!

[M^Cubed]

It might have been the tubes?

 It has lost the hum that I was hearing.