Reduction Hum and No Playback [resolved]

OverAnalyst · 3251

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Offline OverAnalyst

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Reply #15 on: August 12, 2020, 10:55:34 AM
ahhhh, yes. After removing the tubes, I get * or 4Mohm range which match the spec.  Good to go there. So I'll go ahead and perform voltage checks, unless there's anything else I should do?



Offline Paul Birkeland

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Reply #16 on: August 12, 2020, 11:13:48 AM
I think you can move on to voltage checks.

Paul "PB" Birkeland

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Offline OverAnalyst

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Reply #17 on: August 12, 2020, 01:30:43 PM
so finally got back to the voltage checks. And I'm also working to the 10.3.19 manual. I have two terminals out of spec (same as first time around)

44 - 78V (should be 0V)
45 - 77V (should be 0V)

I have a couple pics if that helps....



Offline Paul Birkeland

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Reply #18 on: August 12, 2020, 01:42:12 PM
Those are just errors in a manual that our automated download system doesn't want to let go of.  If you have good voltages up front, everything in the back is going to be working OK.

Paul "PB" Birkeland

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Offline OverAnalyst

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Reply #19 on: August 12, 2020, 02:03:59 PM
Still get the hum on both speakers and no playback. I can slightly hear a little noise coming from the record, but it is pretty much nothing.

Back to your reply #12, I did check the RCA inlet plugs. I think I see a problem. The stack in the instructions (page 13) shows the chassis, red flat washer, washer tab, and then the two nuts. On my build, I have chassis, washer tab, red washer, and the two nuts. Looks like my red washer and washer tab are flipped on both RCA plugs. Could this be the culprit???



Offline Paul Birkeland

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Reply #20 on: August 12, 2020, 02:05:16 PM
What AC voltage ranges does your meter have?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline OverAnalyst

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Reply #21 on: August 12, 2020, 02:06:26 PM
600V



Offline Paul Birkeland

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Reply #22 on: August 12, 2020, 02:06:51 PM
That's as low as it will go?

Paul "PB" Birkeland

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Offline OverAnalyst

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Reply #23 on: August 12, 2020, 02:08:51 PM
ahhh, it does measure mV, but will need to dig that up. Fluke 107



Offline Paul Birkeland

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Reply #24 on: August 12, 2020, 02:12:00 PM
You need to set the meter to MV with the ~, then use an 1/8 to RCA cable to connect your phone to the Reduction.  On your phone, download one of the many free signal generator apps and use it to make a sine wave at 60Hz.  With the volume all the way up, you should see 300mV to 500mV at the ends of the RCA plugs with the 1/8" end plugged into your phone. 

Let me know when you're there and we can proceed with tracing some signal in your amp.

Paul "PB" Birkeland

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Offline OverAnalyst

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Reply #25 on: August 12, 2020, 02:22:32 PM
confirmed. I get get 400mV



Offline Paul Birkeland

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Reply #26 on: August 12, 2020, 02:23:56 PM
Groovy!

Plug those RCA cables into the Reduction, leave the Reduction off, then measure the AC voltage across the RCA jacks.

Paul "PB" Birkeland

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Offline OverAnalyst

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Reply #27 on: August 12, 2020, 02:33:31 PM
so I took measurements from the nut and the center of the plug. On the both A and B sides, I read 400mV.



Offline Paul Birkeland

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Reply #28 on: August 12, 2020, 02:44:24 PM
OK, now you'll want to turn your phone down till you see about 10mV coming into the RCA jacks, turn the amp on, then read mV between ground and terminal 6 as well as ground and terminal 27. 

Paul "PB" Birkeland

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Offline OverAnalyst

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Reply #29 on: August 12, 2020, 03:04:31 PM
6 - Around 130mV and fluctuating
27 - Around 140mV and fluctuating