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Oberheim Matrix1000 - changed battery, got noise on audio output

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Oberheim Matrix1000 - changed battery, got noise on audio output

Postby hansvonderfuel@gmail.com » Wed Sep 04, 2019 10:59 pm

I just had a professional engineer replace the battery on my Matrix 1000 synth, as patch memory was not working. Patch memory works now, but instead I have gotten a terrible noise on the audio output.

I ordered the replacement battery and battery adapter from:
https://www.ebay.co.uk/itm/163771198138

The engineer took off the existing battery that was soldiered onto the circuitboard, and replaced it with the adapter with new battery inserted.

When the unit is turned off, with power cable and audio and midi cables connected, the noise that I now get on the audio output, is really loud. When I turn the unit on, the noise is reduced to a hum which can be heard if I turn the volume knob on my audio interface up, it’s noticeable when recording sounds from the Matrix1000.

Here’s the thing: If I take the battery adapter, which has wires attached to the + and - pin, and touch the chassis of the Matrix 1000 with the 3rd pin which is not in use, the noise disappears. If I take the battery out of the adapter, and again, touch the chassis with the 3rd pin, the noise does not disappear. The 3rd pin is, according to the engineer, a + pin as swell. If I touch the chassis with the + side of the battery, the noise disappears, and if I touch the chassis with the - side of the battery, the noise disappears. If I leave the battery’s + side attached to the chassis, and screw the metall cover back on, the synth won’t start up. Therefore I conclude that it’s not a good idea to attach the 3rd pin to the chassis. But the fact that doing so, removes the noise, indicates that there must be a solution to get rid of the noise. The engineer is a specialist on equipment for boats and shipping, so he’s not a synth man. Maybe somebody reading this is, and can help me identify a solution.
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Re: Oberheim Matrix1000 - changed battery, got noise on audio output

Postby Hugh Robjohns » Wed Sep 04, 2019 11:08 pm

From your descriptions, I'd hazard a guess that there's a re-assembly error -- an earth connection is missing because of a missing screw securing a PCB to the chassis, perhaps, or a wiring loom or ribbon cable isn't fitted correctly.

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Re: Oberheim Matrix1000 - changed battery, got noise on audio output

Postby Arpangel » Sat Sep 07, 2019 6:43 am

Or.....some of these battery adaptors come with two, or three legs, and it's often that only two are needed. It's best to chop the unused one off, otherwise it can get in the way and short things out. Just a thought. I'd take it apart and make sure all connectors are tight etc.
Besides, the engineer should have done a mechanical and audio check before delivery. IMO it's essential when doing any work like this.
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Re: Oberheim Matrix1000 - changed battery, got noise on audio output

Postby hansvonderfuel@gmail.com » Mon Oct 14, 2019 7:40 pm

The engineer managed to fix it in the end, and remove the noise on the output.

He did this by attaching a wire to the audio ground, and attaching the other end to a screw that attached the circuit-board to the chassis, which I suppose is chassis ground (or earth). The wire looks a bit out of place on the circuit-board, and I'm not sure if this is the 'proper' way to fix it, but at least it works now, and I can use my Matrix1000 with no hum on the output. Apparently, the audio signal is supposed to be connected to the ground connection at some point in the circuit, so there you go..

Many thanks for your suggestions
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Re: Oberheim Matrix1000 - changed battery, got noise on audio output

Postby Martin Walker » Tue Oct 15, 2019 1:21 pm

Glad you're finally sorted, although that fix does sound a little strange, and ought to be implemented as standard by the manufacturer.


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Re: Oberheim Matrix1000 - changed battery, got noise on audio output

Postby James Perrett » Tue Oct 15, 2019 1:29 pm

Just wondering if the engineer left off a locking washer or used the old one in the wrong place so that a pad that was supposed to be connected to the case was left floating.
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Re: Oberheim Matrix1000 - changed battery, got noise on audio output

Postby Hugh Robjohns » Tue Oct 15, 2019 2:03 pm

hansvonderfuel@gmail.com wrote:He did this by attaching a wire to the audio ground, and attaching the other end to a screw that attached the circuit-board to the chassis, which I suppose is chassis ground (or earth). The wire looks a bit out of place on the circuit-board, and I'm not sure if this is the 'proper' way to fix it, but at least it works now, and I can use my Matrix1000 with no hum on the output. Apparently, the audio signal is supposed to be connected to the ground connection at some point in the circuit...

The audio circuitry, and the audio outputs, are all referenced to 0 volts, and the chassis should also be connected to the same 0 Volts to provide effective screening. Normally, the chassis and audio ground reference connect at a 'star point' at the power supply, and in class-1 equipment the mains safety earth often goes to the same point as well. It would appear in your case that one of those connections was missing for some reason.

As I said earlier, there has probably either been an assembly error (such as a grounding screw or shake-proof washer not replaced correctly), or a critical ground connection in a wiring loom or connector has fractured and failed. It seems James is thinking along the same lines. ;-)

Your engineer has essentially bypassed the problem by adding a separate grounding wire... Although it's not clear whether he has extended the audio ground onto a floating chassis, or extended the chassis ground onto a ground-less audio board! But I guess if it's now working it doesn't really matter...

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