Crack Speedball Hum. Need Help, Pls

[nate craig]

Hi everyone,

I just upgraded to Speedball, I have found a hum on the left and I haven't been able to sort it cause.
I checked the solder joint, visually and with meter, and they all seem fine.
I tried different tubes, rca cables and source, all with the same result.

Does anyone have any other ideas as to where I can search or do?
I am new to building electronics, so any help will be appreciated.



 

[Paul Birkeland]

I would start by providing us with voltage measurements, especially those that differ from the manual.

-PB

[nate craig]

Hi PB:
None of the readings were to far off from the manual, all within 4-5 volts from the manual. The only odd one was that terminals 6 and 10 did not have static readings. The value fluctuated between -2 and +4.

I checked the continuity of all of the joints they are all fine as well.

Any other places or items that I can check that would help guide you to the cause? It also seems that the hum is on both sides, not as I had originally thought.

Thanks, Craig

[Paul Birkeland]

I would then double check that all your 220uF 250V capacitors are well connected.  If one comes loose, the amplifier will hum.

-PB

[nate craig]

Paul,

The solder seems really solid on all three.
Do you think re-soldering them will improve?

[Paul Birkeland]

Twist and pull on them with your fingers (with the amp off).  If one is loose, it will move more than it should.

-PB

[nate craig]

Hi Paul,

Yes, that's what I did, and they are all tight. Is there any other possible source of the hum?

Craig

[Paul Birkeland]

Hum with no cables plugged into the Crack and the volume control all the way down is almost always a loose connection.  When you upgraded the amp, you may have disturbed what was a loose connection, but one that was operating regardless until it was moved.

I would suggest triple checking all your work, and reheating all of the solder joints in the amplifier, just to be sure.

-PB

[nate craig]

Paul,

I notice that the noise goes away and comes back if I touch the top of the input tube (RCA12AU7 Clear)
I know it's not the tube it self because I tested input that came with the kit and got the same hum.
I re-soldered as many of the joints on the socket as I could reach without removing the SpeedBall kit.
Do you think is there anything else to do with that socket before I remove the SpeedBall kit?

Thanks
Craig

[Paul Birkeland]

I notice that the noise goes away and comes back if I touch the top of the input tube (RCA12AU7 Clear)

That generally indicates a loose connection around the 9 pin socket or accompanying terminal strip, or perhaps a bad ground connection between the chassis plate and the IEC socket.

This is very unlikely to be an issue with the actual Speedball itself.  You may find that the hum stays if you remove it.

-PB