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Chipamp IC amp kits & PC boards from ChipAmp

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Old 1st February 2018, 12:44 AM   #11
Hogwild is offline Hogwild  Canada
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When you say "no input", do you mean with input wires shorted?

If so, you should be able to make out those numbers from the above screenshots.
It fluctuates between About 2.8 and 3.8 mV peak to peak. For both boards I tested. I think the scope was in DC coupling mode for that measurement. I believe that is the icon being displayed in the above screenshots.

This is confusing. Definitions on the web for "DC offset" displaying on a scope are different than what you're describing.

I tried attaching the jig with the POT on it. This time, I got less a noisy waveform, but I'm guessing still messed up. It seems like the input wires are extremely sensitive to attachment quality and/or being moved. Is this normal? The POT on the jig has the following markings on it:

1 Borton 2 CW 3
3006P 103
N036 (upside down)

Does this mean anything to you?

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Originally Posted by scottjoplin View Post
DC offset is the voltage measured across the speaker terminals with no input. Ideally it will be zero, but is more likely to be around +/- 10mV to +/- 50mV. Use a multimeter if you have one or your scope set to dc coupling, for your noise measurements ac coupling is fine

Last edited by Hogwild; 1st February 2018 at 12:55 AM.
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Old 1st February 2018, 01:22 AM   #12
Hogwild is offline Hogwild  Canada
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Oh, it looks like the POT on that jig I have is a Bourns 3006P 103. It's a 50K 3/4W model. The weird thing about it is that the scope signal doesn't seem to change no matter how much I adjust the POT screw. This is strange, because a while back, when I played music through either amp board, the POT did adjust the volume up and down.
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Old 1st February 2018, 12:14 PM   #13
scottjoplin is offline scottjoplin  Wales
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That's a trimmer pot, not really suitable, you need a normal pot similar to this PDB182-K420K-103A2 Bourns | Mouser United Kingdom
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Old 1st February 2018, 01:11 PM   #14
JMFahey is offline JMFahey  Argentina
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Donīt overthink it, you are not testing that amp the way you will actually use it.

Just connect a speaker at its output, a sound source (PC/MP3 player/Smartphone/CD player) to a volume pot, between 10k and 50k, Audio/Log taper preferred, and from it to the amp, using a coaxial cable.
Also coaxial cable and properly soldered connectors between sound source and potentiometer (a real one, with metallic case soldered to ground)
Also place the amplifier board inside a metallic case or at least on a piece of wood, to which you glue a piece of kitchen type aluminum paper, then ground it to amp ground with a piece of wire, and place an insulator (cardboard or a magazione will do) on aluminum so it does not short PCB bottom.
Play some music and *then* worry or not about Hum and external noise.
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Old 1st February 2018, 02:31 PM   #15
Hogwild is offline Hogwild  Canada
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Quote:
Originally Posted by JMFahey View Post
Donīt overthink it, you are not testing that amp the way you will actually use it.

Just connect a speaker at its output, a sound source (PC/MP3 player/Smartphone/CD player) to a volume pot, between 10k and 50k, Audio/Log taper preferred, and from it to the amp, using a coaxial cable.
Like I said, I used coaxial cable previously, and it just seemed to create more noise. When I removed it, I got less noise.

Quote:
Originally Posted by JMFahey View Post
Also coaxial cable and properly soldered connectors between sound source and potentiometer (a real one, with metallic case soldered to ground)
Also place the amplifier board inside a metallic case or at least on a piece of wood, to which you glue a piece of kitchen type aluminum paper, then ground it to amp ground with a piece of wire, and place an insulator (cardboard or a magazione will do) on aluminum so it does not short PCB bottom.
Play some music and *then* worry or not about Hum and external noise.
I'll try that. I hope finding a volume POT at a bricks and mortar store doesn't take too long.
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Old 1st February 2018, 03:06 PM   #16
Hogwild is offline Hogwild  Canada
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Is there any reason I should not use the one Chipamp.com sold? It was an Alps Blue Velvet RK27. When I look at Mouser, they have about 10 different version of it. Which one should I buy? I'd prefer a through hole model if it has larger (easier to solder/desolder) terminals.

Does anyone still have any of the matching PCBs that Chipamp.com made for those POTs.
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Old 1st February 2018, 03:19 PM   #17
scottjoplin is offline scottjoplin  Wales
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They're good pots, this one in suitable, dual gang (I presume you are making a stereo amp) 10Kohm audio taper. RK27112A0-S20-C0-A103 ALPS | Mouser United Kingdom I've seen PCBs for them on eBay
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Old 1st February 2018, 04:34 PM   #18
Hogwild is offline Hogwild  Canada
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scottjoplin:

Thanks. Unfortunately, they are on backorder at Mouser in Canada and the US. Digikey doesn't sell them either. Where else can I look in North America that might have them?

As for the PCBs, will a cheap Chinese one work, or should I look for something else? I don't suppose anyone knows where I could find one of Chipamp's own boards? Are the ALPS pots they sell on eBay from Asia counterfeit or are they genuine?

Last edited by Hogwild; 1st February 2018 at 04:44 PM.
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Old 1st February 2018, 05:14 PM   #19
Keruskerfuerst is offline Keruskerfuerst  Germany
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Can you give some more information?
PSU, board, values at LM3886,.....
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Old 1st February 2018, 05:14 PM   #20
scottjoplin is offline scottjoplin  Wales
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I wouldn't worry too much any half decent pot will do, put the Alps on order if you particularly want one. As for the PCB, Chinese ones will be fine
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