Crack with Speedball Hum [resolved]

BotEleven · 2261

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Offline BotEleven

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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!
« Last Edit: July 28, 2016, 05:56:02 PM by Caucasian Blackplate »


Offline Doc B.

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Reply #1 on: July 12, 2016, 04:16:31 AM
Have you tried different tubes?

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline BotEleven

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Reply #2 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?


Offline Doc B.

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Reply #3 on: July 12, 2016, 09:07:11 AM
No, you need to use the correct tube.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline MOAR_CORES

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Reply #4 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.


Offline Paul Birkeland

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Reply #5 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

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline BotEleven

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Reply #6 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.


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