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Heiwashin
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Help need small signal cleaner

Fri Mar 17, 2017 6:14 pm

So I've had a digital piano in my truck for about 6 months and it's been great. I spend a good amount of my spare time on it but I have one gripe. It's so quiet. Even if I have everything else turned off it's too quiet to hear things as clearly as I'd like. I tried using a 1/4 to 3.5 to connect to truck but I get a powerful buzzing. I've never had to deal with cleaning up a signal in this situation before and i figure I'd poke more seasoned before I go googling around.

Piano powered by 120v inverter running off of truck batteries. 3.5mm aux input on radio faceplate. No audible hum from pianos speakers. Saving space is more important in the solution then keeping cost low. Whatever solution is needed to be durable against vibrations and impact.
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chuckula
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Re: Help need small signal cleaner

Fri Mar 17, 2017 6:19 pm

I'm not the world's greatest expert at all this analog silliness, but my guess is you are encountering ground loop noise.

Numerous ways to fix it, here's an article with some solutions that might be helpful and don't look crazy expensive: http://www.techhive.com/article/3063590 ... stems.html

Another potential option: Look into a higher quality inverter since that might stop the noise before it ever comes out (not sure if your current inverter is already really good or not, there are a whole lot of cheap but not very good inverters out there).
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Heiwashin
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Re: Help need small signal cleaner

Fri Mar 17, 2017 6:24 pm

It's a pretty high end 1500 watt continuous however I'm unable to change it anyway due to company policy.

On a funny note I've seen pictures of guys that hook up a 300 watt inverter to some random lighting wires. It never ends well.

Well I found some 3.5mm isolators on Amazon. I wonder how well it works. How exactly does it seperate the grounds.
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chuckula
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Re: Help need small signal cleaner

Fri Mar 17, 2017 6:33 pm

Other wacky ideas:
1. Check for impedance mismatches between the truck's speakers and the output of the piano (impedance mismatches are almost obligatory).

2. This could be related to the other problems, but I'm assuming there's a stereo built into the truck that's also hooked to those speakers. It might not be practical, but disconnecting the stereo so that there's nothing else connected to the speakers could be a poor-man's solution that might help.
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Heiwashin
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Re: Help need small signal cleaner

Fri Mar 17, 2017 6:39 pm

Cost isn't the problem, the real problem is that I can't fiddle with anything on the truck. I guess it'd be nice if a guaranteed solution that didn't require modifying the truck in any way was under 150$
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Re: Help need small signal cleaner

Fri Mar 17, 2017 7:42 pm

Sounds like it is running through the truck's stereo so impedance of truck speakers is irrelevant. The ground loop theory is where I'd put my money. Could also be the cable picking up radiated EMI from the inverter, in which case a better cable might help.
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Heiwashin
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Re: Help need small signal cleaner

Fri Mar 17, 2017 8:04 pm

just brew it! wrote:
Sounds like it is running through the truck's stereo so impedance of truck speakers is irrelevant. The ground loop theory is where I'd put my money. Could also be the cable picking up radiated EMI from the inverter, in which case a better cable might help.

I was using a junky Walmart cable. Have an isolator and a new cable on order but I'd still like to know exactly what the isolators doing.

Mpow Ground Loop Noise Isolator for Car Audio / Home Stereo System with 3.5mm Audio Cable (Black) https://www.amazon.com/dp/B019393MV2/re ... Zyb09W86XQ
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ludi
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Re: Help need small signal cleaner

Fri Mar 17, 2017 11:53 pm

Heiwashin wrote:
Have an isolator and a new cable on order but I'd still like to know exactly what the isolators doing.

Automotive grounds are incredibly noisy. A passive isolator typically includes a 1:1 isolation transformer for each channel, the idea being to NOT have a direct shield ground connection between the source and destination devices. It also breaks the loop if there is more than one path from the equipment back to ground (as can happen when both the power supply and the audio cable create separate paths back to the same ground point, in this case your truck's frame).
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Re: Help need small signal cleaner

Sat Mar 18, 2017 2:14 pm

ludi wrote:
Heiwashin wrote:
Have an isolator and a new cable on order but I'd still like to know exactly what the isolators doing.

Automotive grounds are incredibly noisy. A passive isolator typically includes a 1:1 isolation transformer for each channel, the idea being to NOT have a direct shield ground connection between the source and destination devices. It also breaks the loop if there is more than one path from the equipment back to ground (as can happen when both the power supply and the audio cable create separate paths back to the same ground point, in this case your truck's frame).


Ludi got the basics. A ground loop is caused when a signal has two different paths to ground and due to distance, poor connection, or numerous other reasons, the two paths have different voltage potentials. Then end result is that a current flows over the ground cable, this allows all sorts of noise to ride along with the good signal you want to amplify. In home audio, it generally presents as a 50/60Hz hum, though you can get other noise, up to crazy stuff like receiving AM broadcasts. A ground loop isolator removes the direct ground connections, by, as ludi noted, using a pair of isolation transformers. The result is that there is no direct electrical connection between input and output. This removes one of the two ground paths.

If you have the option to power the keyboard from batteries, try it. If the noise goes away, that strengthens the ground loop theory. It doesn't prove it though as there are other ways noise can get in the line output but not be audible in the onboard speakers. Still, trying the ground loop isolation will be the easiest and cheapest thing to try first and has a high probability of addressing the problem.

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Heiwashin
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Re: Help need small signal cleaner

Sat Mar 18, 2017 2:18 pm

Well the piano doesn't use batteries but i did order the 3.5mm isolator that i linked. I just hope it does a good job.
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Re: Help need small signal cleaner

Sat Mar 18, 2017 2:23 pm

Heiwashin wrote:
Well the piano doesn't use batteries but i did order the 3.5mm isolator that i linked. I just hope it does a good job.

If it has a DC in jack you could rig something. Is the AC power an external brick or does it take 120VAC directly?
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Heiwashin
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Re: Help need small signal cleaner

Mon Apr 03, 2017 7:39 am

The isolator certainly reduced the noise but it's still far too loud. I think I'm going to try getting a battery powered headphone amp next. Any suggestions on a good one.
Looking for Knowledge wrote:
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