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Chipamp IC amp kits & PC boards from ChipAmp

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Old 4th September 2017, 06:58 PM   #1
Hogwild is offline Hogwild  Canada
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Default input RC

Hi everyone:

I've had to take a very long extended break, but now am ready to try to finish up some work on my Chipamp LM3886 dual mono project.

Question: What are the components at the beginning of the circuit? IT was marked as a Zobel network, but IIRC, Allan from (the now defunct) Chipamp.com said it was an input RC filter. Is that correct? Is it a LP filter? HP filter? Does anyone know?


Thanks
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Old 4th September 2017, 07:05 PM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by Hogwild View Post
Chipamp.com said it was an input RC filter. Is that correct? Is it a LP filter? HP filter?
At the input, it's a low pass filter, if the capacitor is a small value and is connected to ground.
It's a high pass filter if the cap is a large value and is in series with the signal.
You also can have both, like this. http://www.circuitbasics.com/wp-cont...2-1024x862.png

Last edited by rayma; 4th September 2017 at 07:10 PM.
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Old 4th September 2017, 08:54 PM   #3
Hogwild is offline Hogwild  Canada
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Thanks. The cap, Cz appears to be a Vishay 100nF 63V. I'm guessing (no knowledge at all of electronics) that this is a "small" value?

I have almost no knowledge/experience with electronics, so I'm having a hard time being sure of the resistor (Rz) colours. It looks to me like Orange Violet Gold Gold. When I tested it on two diff. boards with a DMM, it measured 2.8 ohms. As for ground, the two components were never added to the Chipamp.com schematic. And I don't know how to tell just by looking at the PCBs.

Can anyone confirm these values?

Is that a LP or HP filter? (I don't know what high or low values would be, due to my lack of knowledge).

Thanks

Last edited by Hogwild; 4th September 2017 at 08:59 PM.
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Old 4th September 2017, 09:07 PM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by Hogwild View Post
Thanks. The cap, Cz appears to be a Vishay 100nF 63V. It looks to me like Orange Violet Gold Gold.
it measured 2.8 ohms. Is that a LP or HP filter?
The 100nF is a relatively large value, and is a coupling capacitor, forming a high pass (bass cut) filter.
A Orange-Violet-Gold-Gold resistor should be 3.7R with 5% tolerance.
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Old 4th September 2017, 11:05 PM   #5
Hogwild is offline Hogwild  Canada
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Okay, so....have I got the colours wrong or ?? Here's the LiquidAudio page on which he shows building his kit
LM3886 Chip Amp / gainclone amplifier construction project

There is a closeup photo captioned "Here's a reverse view..." showing the input resistor Rz and its colours.
Can you tell from that photo what colours those are? It's hard to see on my board.
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Old 4th September 2017, 11:11 PM   #6
tomchr is offline tomchr  Canada
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Is this the resistor you're talking about? It's a 2.7 Ω. 1 W or 2 W type (should really be at least 2 W).

That's on the output. It's part of the Zobel network.

Tom
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Old 4th September 2017, 11:19 PM   #7
Hogwild is offline Hogwild  Canada
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Yeah, no schematic. I was told by Allan @ Chipamp that in spite of the designation "z" for Zobel, neither of these components constituted a Zobel network, that they were an input RC filter, but my knowledge level is zero. Can anyone else be sure?
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Old 4th September 2017, 11:29 PM   #8
tomchr is offline tomchr  Canada
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You can always follow the traces on the board. Show where it connects. I bet that resistor and the grey 100 nF cap next to it are connected in series. One end of the series connection connects to pin 3 (output) of the LM3886 and the other end connects to ground. That'd be the Zobel network.

Tom
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Old 5th September 2017, 12:15 AM   #9
Hogwild is offline Hogwild  Canada
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Er...are you sure? I am planning to use a MiniDSP for crossover duties. That won't get in the way of the MiniDSP will it? If you're sure that it's a Zobel, and I want an input RC, I will need to add my own, I guess, right?
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Old 5th September 2017, 01:13 AM   #10
nigelwright7557 is offline nigelwright7557  United Kingdom
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There is often a low pass filter on the input.
This is to filter out RF from radio etc

I had an old amp many years ago without one that picked up police radio very well.
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