Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: BotEleven on July 11, 2016, 08:32:03 PM

Title: Crack with Speedball Hum [resolved]
Post by: BotEleven on July 11, 2016, 08:32:03 PM

Hi All,

I've had my Crack with Speedball for about 7 months now. Thoroughly enjoying it with my HD600 but it has this nagging hum which had been annoying me. I'm trying to get a pitch black background that folks seem to rave about.

The hum is very slight, more noticeable on the left channel than the right. The level does not change with the volume pot. Tying the RCA inputs together has no effect either. I've also tried different power outlets, and made sure there are no other electronic devices within 5 feet of it.

I've just re-flowed all connections, except A1 through A9 for fear of burning the LEDs. All ground connections seem solid with 0-0.1 ohms. I've also tried the chopstick test to poke at all joints, but I could not hear any changes in the hum either, other than the microphonics when the amp gets tapped.

Any suggestions on what else I may try find the root cause of that hum? I can provide a picture of my build, resistances, and voltages if that would help.

Thanks!

Title: Re: Crack with Speedball Hum
Post by: Doc B. on July 12, 2016, 04:16:31 AM

Have you tried different tubes?

Title: Re: Crack with Speedball Hum
Post by: BotEleven on July 12, 2016, 08:23:07 AM

Not yet since I only have a couple of spare 12AX7 from my guitar amp. Read that those aren't really compatible. Do you think I can try those just to check if the hum goes away?

Title: Re: Crack with Speedball Hum
Post by: Doc B. on July 12, 2016, 09:07:11 AM

No, you need to use the correct tube.

Title: Re: Crack with Speedball Hum
Post by: MOAR_CORES on July 23, 2016, 08:53:13 AM

Quote from: Doc B. on July 12, 2016, 04:16:31 AM

Have you tried different tubes?

I am having the same issue as OP
High pitched but low volume hum predominately in left channel.
I've take similar countermeasures as OP.
However, my hum goes away temporarily (for a minute or two) if I tap or knock on the crack.

Which tubes would cause this? The input driver or the output tube?
I can replace both if necessary.

Title: Re: Crack with Speedball Hum
Post by: Paul Birkeland on July 24, 2016, 05:32:36 AM

Quote from: MOAR_CORES on July 23, 2016, 08:53:13 AM

However, my hum goes away temporarily (for a minute or two) if I tap or knock on the crack.

This is a flaky solder joint in the amplifier that isn't conducting properly.

-PB

Title: Re: Crack with Speedball Hum
Post by: BotEleven on July 26, 2016, 08:48:57 PM

Just a follow-up on my original hum issue.

I've managed to borrow a couple of 12AU7 tubes from a coworker, tried them, and that hum is gone. Guess I'll be shopping for a new one of my own.

Another thing I've noticed is that the microphonics are also gone with my coworkers tube's. Never realized how annoying they could be until it is completely silent. Typing on my keyboard used to bring slight pinging noises from the stock tubes.