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Finally Silenced My Stromberg-Carlson ASR-444

U

UnGrounded

Well-Known Member
A bit of a public service announcement...

My S-C ASR-444 has been awfully noisy since the day I bought it... from 100% stock to 100% rebuilt (following a mental breakdown of sheer frustration).

I finally made a desperate attempt to clean up the cluttered preamp wiring. I removed ALL of the ground connections that are soldered to the center "lugs" on the preamp tube sockets, ran wires to a spacious section toward the center of the chassis, and re-grounded them far away from the source...

...and beautifully quiet operation resulted.

At last, my ASR-444 is truly a pleasure to listen to.

Sweet relief.
 
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Good deal, that grounding everything to the closest spot no matter what it is, was always a recipe for hum.
 
With those grounding socket lugs in such close proximity to the source, just makes me wonder how quiet these things were when they left the factory.
 
So let me get this strait,
Ungrounded, Ungrounded them, then Ungrounded, Regrounded the Ungrounded wires. Got it!:D

If you would have scoped the ends before you moved them, Like doing a voltage drop, You would saw something going on between the two ends.
Good call. They should have shielded the wire from the factory.
 
S-C was usually fairly decent about the idea of not using the chassis as a ground, but they were not so amazing about neat wire routing. My ASR-433 and the Signet/33 PA amps are both on the messy side. Sometimes that messy wiring will really cause you trouble.
 
Did SC have heater currents and or filter cap returns going thru the chassis? These currents will produce noise voltages, messing up reference grounds for preamps. Filter cap grounds should be directly connected to the transformer centertap, so no filter cap ripple current ever goes thru the chassis.

I've used the center posts of tube sockets (if they don't have a strap to a mounting rivet or screw to chassis) as local grounds, then connecting them to a star ground. But no heater currents. Heaters get their own twisted pair wiring independent of everything else except a connection to the star. Or to a source of 40 or so volts DC positive.
 
My 433 does not do this. I don't know about the 444. The 433 at least does the two AC heater lines with a hum balance pot off the output tube cathode for about +12vdc above ground. The supply is a doubler rig with the transformer ground connected straight to the can cap originally. It runs in a star outward from there. Split heater supplies too, one per channel.
 
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