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Old 13th August 2012, 03:37 PM   #1
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Default Amplifier Distortion (Northern Electric)

So I've run into quite a conundrum here. I've just bought two Northern Electric 4045-C Amplifiers. Powering either one on by itself the amplifier sounds great, little bit of hum but other than that great. However, if I turn them both on at the same time (they are monoblocks so I do need to have them both on for stereo) they start to distort horribly. They'll play fine for five minutes and then start distorting all over the place for thirty seconds, play fine, then distort again. I'm not sure what is causing this distortion. Figured it was a power issue since the amplifiers work fine when only one is on. Any ideas?

Found a schematic here

Last edited by cthcamaro67; 13th August 2012 at 03:48 PM. Reason: schematic added
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Old 13th August 2012, 03:58 PM   #2
cancon is offline cancon  Canada
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Haha, I posted that schematic. Crazy amp, HUGE 25hz power transformers. I could never get rid of the background hum in mine. Is yours still running a 5X4 or has it been modified to 5U4?
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Old 13th August 2012, 04:00 PM   #3
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Uses 5U4, that hum isn't too bad on one but the other has hum and a "hizz" that is fairly pronounced that I'm still working on getting rid of. Thanks for the schematic lol I've been using it quite a bit. Replaced/resoldered all the connections to try and alleviate the hum and distortion issue I've been having but to no avail so far.
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Old 13th August 2012, 04:05 PM   #4
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Here's a pic of them, they ain't perfect but they certainly work!
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File Type: jpg 4045-C.JPG (241.9 KB, 134 views)
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Old 13th August 2012, 04:05 PM   #5
cancon is offline cancon  Canada
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Does the hum go away if you short the balanced inputs together?
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Old 13th August 2012, 04:13 PM   #6
cancon is offline cancon  Canada
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Also, are you driving electro-magnetic speakers? if not, have you installed a dummy load to cap the B+ for them?
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Old 13th August 2012, 04:55 PM   #7
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Haven't tried shorting the inputs together, can give that a go tonight. Nope, vintage speakers as well so I've capped the B+. Had these running perfectly in another location, before I took them home, soon as I hooked them up at home this distortion issue arose. I know they work as I can use either independently and they sound just fine, both powered up at the same time sounds like they keep dropping signal intermittently
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Old 13th August 2012, 05:08 PM   #8
kevinkr is offline kevinkr  United States
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Surprisingly and perhaps a first, but I think this actually belongs in the Tubes / Valves forum since these are apparently being used in a home stereo system. (Usually I'm moving guitar amps from Tubes / Valves to Instruments And Amps)

I think you will have a lot more visibility for this particular issue in Tubes / Valves..

Very odd behavior, I'm wondering if this is some sort of extreme ground loop issue. I'd very carefully check the leakage current from chassis to a good earth ground on each of those amplifiers.. Do they behave this way when they are not connected to the pre-amplifier? How are the various components in your system grounded? (not grounded)
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Old 13th August 2012, 05:13 PM   #9
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haha, I had moved it from that thread originally after reading the rules again. If you'd like to move it back that's fine by me. I'm floating the ground at the moment but will check the leakage current from the chassis, maybe throw in a real good ground. Still baffled why the problem only exists in my house. Hooked these back up in my friends shop and they play without a problem. Seems like the amp isn't the culprit here.
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Old 13th August 2012, 05:19 PM   #10
kevinkr is offline kevinkr  United States
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My understanding is these are used as part of your stereo system and are not a guitar or instrument amplifier so it may be legitimately be posted to Tubes / Valves. Instruments and Amplifiers is intended for devices that make music not reproduce it.

Grab an AM/FM radio and turn it on, tune across both bands while the amps are misbehaving and see if you hear anything.. Be quick of course so as not to damage anything - hopefully all will be silent - no squeals or odd noises due to amplifier oscillations.

Make sure the AC connections to both amplifiers are wired the same way in the event that leakage current is the cause of this issue. I'd recommend in any event grounding the chassis of both amps for safety..
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