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Chipamp IC amp kits & PC boards from ChipAmp

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Old 21st October 2017, 03:52 PM   #21
Hogwild is offline Hogwild  Canada
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jan:

Assuming I'm plugging in the correct numbers, the Overture Design Guide XL spreadsheet, calculates gain at 26.44 dB using the values I've mentioned.

I'm aiming for two separate 2 channel amps. So no, I'm not using many amp boards on the same power supplies. But from what I've read, it's not unusual to put a resistor like that at the output on amps that are not multichannel.
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Old 23rd October 2017, 12:28 AM   #22
Hogwild is offline Hogwild  Canada
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Nigel:

That is very different than what Chipamp originall recommended (3300pF) or what Linkwitz recommends (1500 pF). How will this change things?

You recommend polyester. Anything else I should know? Do people usually use radial or axial or does it matter? Remember, newbie here.
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Old 23rd October 2017, 01:18 AM   #23
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by Hogwild View Post
Nigel:

That is very different than what Chipamp originall recommended (3300pF) or what Linkwitz recommends (1500 pF). How will this change things?

You recommend polyester. Anything else I should know? Do people usually use radial or axial or does it matter? Remember, newbie here.
It depends on what frequency band you want to use.
It should be large enough to kill RF and noise but not so large it starts to reduce the audio spectrum and affect the sound quality.

The formula for working it out is:
1/(2 pi R C)=breakpoint frequency.
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Old 23rd October 2017, 02:35 AM   #24
Hogwild is offline Hogwild  Canada
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Nigel:

Yes, I get that. Thanks. Since both of these values would put sound above audible freq. range (and maybe a harmonic or two after that), what difference does it make which value one chooses? e.g. if it results in 40KHz vs. 45KHz frequency limit

I think I'll with 2.2uF for the Low pass filter, as apparently that's what the now defunct Chipamp.com used to sell on their website for this purpose.

Last edited by Hogwild; 23rd October 2017 at 02:45 AM.
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Old 23rd October 2017, 05:12 AM   #25
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by Hogwild View Post
My question is: In his notes, my friend suggests substituting the current Rm (10k) with a 38.3k resistor. This is also what Linkwitz uses.

If I make the above changes, is it necesary to change Rm, or should I just leave it as is?
You need to make sure 500 uA flows in the MUTE pin in order for the chip to un-mute. Plus some margin. I usually aim between 0.5 and 1.0 mA. You'll have roughly -3 V on the MUTE pin with 1 mA flowing. So Rm will need to satisfy the following inequality:

Rm < (|VEE| - 3)/0.0005

So for ±28 V rails, you'll need: Rm < (28 - 3)/0.0005 or Rm < 50000 Ω.

1 mA gives you: Rm < (28 - 3)/0.001 or Rm < 25000 Ω.

So somewhere in the 25-50 kΩ range is about right. I usually go with 33 kΩ for ±28 V supply rails.

If the current starts getting a bit light, you'll get higher THD. On the other hand if you pull too much current, you probably start affecting the reliability of the MUTE circuit and could destroy the chip that way.

You can change R3 to 1 kΩ if you wish. That'll give you a gain of (1+22/1) = 23 V/V or 27 dB. It'll also lower the LF cutoff, but I see no harm in that.

Tom
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Last edited by tomchr; 23rd October 2017 at 05:14 AM.
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Old 23rd October 2017, 06:36 AM   #26
JMFahey is offline JMFahey  Argentina
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Quote:
JMFahey:
Why would I attract gremlins?
Because minimum recommended gain is 26X (26 times) and you are using 21X , significantly less than the recommended number for stability.
So ... will it uncontrollably oscillate then?
Dunno ... it might do so or, quite probably, work well (sort of) with some speakers, burst into oscillations with others, "sound weird" at times, in an unpredictable way.
Did I use the word "gremlins"?
Now you know why.

Quote:
jan:
Assuming I'm plugging in the correct numbers, the Overture Design Guide XL spreadsheet, calculates gain at 26.44 dB using the values I've mentioned.
Operator error.
The simulator got the "numbers" but operator has no clue about units.

The datasheet refers to a ratio, such as 26X or 26 times the input, your calculator uses decibels.
You don´t seem to know the difference.
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Last edited by JMFahey; 23rd October 2017 at 06:38 AM.
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Old 23rd October 2017, 08:15 PM   #27
Hogwild is offline Hogwild  Canada
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tom:

I have no plans on using any mute switch/function. Does that affect the value of R10 ?

JMFahey:

Where is your reference that the minimum gain for this chip/circuit is 26?
Need your opinion, how small gain can I use with LM3886 (how close to &quot;flat amp&quot?
"It says right in the datasheet the IC needs at least a gain of 10 to be stable."

My gain, acc. to the TI Overture Design Guide spreadsheet, is showing as 21V or 26.44dB. I don't see from where you're getting your numbers.

Gain (V) = 1 + Rf/R3
1 + (20/1) = 21
Equiv. gain in dB = 26.44
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Old 15th November 2017, 02:58 AM   #28
Hogwild is offline Hogwild  Canada
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Oops! I forgot to ask, for the input HP and LP filters, what voltage rating should the capacitors be? I'd like a margin of safety, just in case.

Thanks

Last edited by Hogwild; 15th November 2017 at 03:21 AM.
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