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TOPIC: Noise Floor?

Noise Floor? 5 years 11 months ago #173

Hooked up a purchased GinSing to an Arduino Uno (GS release 3 / Arduino 1.0 - Uno). Took some standard in-ear monitors, and connected them to the 3.5mm jack. Ran the welcome sketch.

Could hear the sounds, but the unit seems a bit noisy, especially when no sound is playing. Do I need a certain ohm level for my monitors? Is this a known issue?

I would like to use GinSing for audio art projects, and I'd like to be able to use the 3.5mm jack, but I don't want hiss playing through the system when no sound is playing. Do I have to gate this? Also, the gain pot (R5) seems really dirty / noisy when I turn it.
Last Edit: 5 years 7 months ago by administrator.
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Re: Noise Floor? 5 years 11 months ago #174

The noise is most likely coming from the LM386 amplifier IC. Gating it would be a good option if possible. Since you probably don't need the amplifier you could also tap the signal directly by removing the IC and tapping pin3 and pin 4 as your output. This still goes through the volume pot. If you wanted to bypass the pot you could tap from the negative side of C5 instead of pin 3. In the latter case the volume level would still be pretty close to line level. If you still hear noise coming from C5 its probably EMF induced that may be unavoidable.

In the original version ( V1.0 ) the audio output came directly from C5 to the headphone jack and it had a very low noise floor, so I'd guess you'd find this might work well for you. I would recommend you download the V1.2 schematic if you have not already done so to see where the output stage goes as you can move up the circuit experimenting with noise vs. volume output.
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Re: Noise Floor? 5 years 11 months ago #175

Thanks for the quick response. Don't know if I'll have time to work up the signal chain as you suggest any time soon, but when I do, I'll try and remember to post the results here.
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Re: Noise Floor? 5 years 11 months ago #176

"When adjusting volume, take special care when connected to either headphones or stereo input as you may damage your ears and/or the device it might be connected to."

By the way, this warning should really be more prominent and provided to users who do not necessarily do their own assembly. Experience with consumer electronics leads most people to trust that a headphone jack is not going to produce damaging decibels unless (or in some cases even if) the volume is cranked. You should give fair warning to your users before they cause harm to themselves.

Also, is R5 audio (log) or linear taper?
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Re: Noise Floor? 5 years 11 months ago #177

Thanks, I look forward to the results of your experiment. I will update the user guide with a big bright notice about the volume level - its your kind of feedback that helps make the product more user friendly ( and ear friendly! ).

The pot is a linear pot.

One thing that might be an even quicker test is to take a short piece of wire and stick it between pin 3 (input) and pin 5 (output) of the IC socket with the chip removed. If that works for you you should be able to operate that way on a permanent basis without the need to do any soldering or modify the board in any way.
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