Is the Crack more susceptible to noise?

[Loquah]

My Crack + SB has been working perfectly for well over a year now after struggling with some noise in the early days, but the bell end got a bit rusty so I decided to remove it and polish it.

The simple act of moving the transformer and terminal strips on either side (small movements created by the unscrewing of the transformer screws) has introduced the old power noise back into the system so I'm wondering if my build is flawed or if the Crack is a bit more susceptible than other amps (S.E.X. & Mainline) to surrounding noise sources?

So far I've rewired the signal path from the RCAs to the pot (this helped a lot, but it's still not silent like it used to be) and reflowed the joints on all transformer connections except the heater joints (which looked good and I assumed would introduce noise). I've also reflowed all the joints on the terminal strips to either side of the transformer as well as the power socket, power switch and earth connection.

The noise is a constant low frequency hum which is raised / lowered with the volume control. Any suggestions?

[Paul Birkeland]

I'd crank down on the transformer hardware a bit, just to be sure the transformer cover is grounded properly.

[Loquah]

Thanks PB - I'll give that a go.

[Loquah]

I tried manually grounding the dome with a separate piece of hookup wire, but there's no change when I earth it separately. Interestingly, if I bridge the RCA ground tabs over to the main chassis earth connection, the buzz changes. Is that a sign of the potential source? Something to do with the main chassis earth screw?

[Grainger49]

Have you traced your ground path?  It is a sticky in the Crack folder.

First touch your meter leads together.  This reads the meter lead resistance, always under an Ohm.  Then the ground readings should be 0.1-0.3 Ohms on top of that reading.

[Paul Birkeland]

One of your 220uF caps may have popped loose as well.

[Loquah]

I decided before bed last night to try tracing the ground again. I'll do that today and will check the caps too. Thanks for the suggestions guys.

[Doc B.]

Is the noise still there with the inputs shorted and the volume turned down all the way?

[Loquah]

I've traced the ground circuit and it's 0.3-0.4 ohms all the way (same as the lead resistance on my meter).

I reflowed the capacitor joints again with no change.

Doc, if I short the inputs there is no noise at all at minimum volume. What does this mean? Is the Crack just amplifying noise from the interconnects? If so, why doesn't the Mainline have the same problem?

[Doc B.]

It means the the noise is coming in from whatever is ahead of the volume control. Could be your interconnects are picking up 50Hz. Soft low hum is usually from the magnetic field radiated by a power transformer. Mainline has a lower gauss transformer so it may just be that the radiated field from the Mainline power transformer is not affecting the interconnects as much as the Crack power transformer. Interconnects from coax cable tend to be the best for magnetic field rejection and that is part of the reason we use coax in the Bottlenects.

[Loquah]

Ahhh... I just unscrewed the plugs on the interconnects I'm using and they're a 2-core, not a coaxial - that'd be why the problem surfaced I guess. I've rearranged things and had to use longer interconnects than my usual (coaxial) ones, but I can't remember if I listened to the Crack in its new location prior to removing and the bell for polishing. Either way, at least I know it's not my wiring work in the amp.

[Doc B.]

Understand that I am just guessing at long distance here. You would need to try different cables to make sure that is what the cause is.

[Loquah]

That's OK. It seems the issue is not in the Crack itself, but in something leading up to the Crack. I'm probably going to sell the Crack because I can't see it getting much air time next to the S.E.X. and Mainline which I plan to keep (both of them that is). I just wanted to make sure the Crack was in peak condition before passing it on.