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Forum Index : Microcontroller and PC projects : CMM2(retromax) sound issue

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markboston36
Regular Member

Joined: 27/10/2020
Location: United States
Posts: 76
Posted: 03:34am 20 Nov 2020
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I setup my retromax today and upon turning it on i hear a low hum coming from the speakers. also anytime I do anything on the computer such as open the files app i hear a odd noise like the cpu is grounded somewhere on the board.

Has anyone else noticed this? im assuming anything from circuitgizmos is tested before its sent out so im not sure whats causing it. its not the speakers ive tested them with my laptop and no hum.

i did purchase a new usb power supply and usb b cable i haven't tested those yet but ill do that tomorrow.
 
hitsware2

Guru

Joined: 03/08/2019
Location: United States
Posts: 719
Posted: 04:36am 20 Nov 2020
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I had similar and found it was from the monitor .
Watch while listening and look for relation .
If so try moving things around ....
my site
 
TassyJim

Guru

Joined: 07/08/2011
Location: Australia
Posts: 6283
Posted: 04:46am 20 Nov 2020
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Most problems with the audio are caused by overloading the audio lines.
The audio from the CMM2 is designed for line level audio and expects an impedance of around 5k ohms.
If your audio amp is designed to plug into a headphone socket, it will have an impedance of a few hundred ohms.

Try putting 4.7k ohm resistors in series with the audio line.

https://www.thebackshed.com/forum/ViewTopic.php?FID=16&TID=12788

If that doesn't work, you will have to look at a line isolator to remove a ground loop.

But try the 4.7k resistors first.


Jim
VK7JH
MMedit
 
markboston36
Regular Member

Joined: 27/10/2020
Location: United States
Posts: 76
Posted: 01:21pm 20 Nov 2020
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speaker impedance is 4ohms. i have another pair of speakers that are 10k on my main system but im waiting for a new power supply. guess ill be doing a switcheroo. thanks for your responses guys.
Edited 2020-11-20 23:31 by markboston36
 
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