8PAKAMP & 12PAKAMP KIT BUILD THREAD

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Joe Malone
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Re: 8PAKAMP & 12PAKAMP KIT BUILD THREAD

Postby Joe Malone » Tue Apr 09, 2019 2:52 pm

nm4711 wrote:Hey there,

I am really happy with my 12PAKAMP, powering a pair of LXmini+. The woofers and subs are powered by a pair of bridged amp channels each and the tweeters by a single channel each. It is powered by an 18 V transformer.
The amp is running quite a while now, but I finally put it into a nice case, so I can share some pictures. ;)

Niklas


Wow Niklas. That is a great looking neat build :-) Thanks for taking the time to load up the photos.

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Joe :-)
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rrp
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Re: 8PAKAMP & 12PAKAMP KIT BUILD THREAD

Postby rrp » Sat Feb 01, 2020 2:28 am

Hi Joe!

I purchased a couple 8pak kits about a year ago, and I’m just now getting around to putting them together. I’m building one kit as 4 bridged amps, and the other as 8 individual amps.

I’d like there to be external volume pots that attenuate from 0 to -infinity at the input of the amp. In the LM3886 datasheet, the example schematic shows an unbalanced 10k pot to ground at the input. Since the 8paks are balanced at the input with a resistor network (I think), I’m wondering how to implement this.

Is the input impedance of the amps high enough that I could hang a balanced attenuator in front of the input? Something like the attached image. Or, would I need to do some kind buffer? If a buffer would be required, maybe I would just get a balanced line receiver like INA134, then use the 10kpot, 1k input resistor combination used in the datasheet. I feel like that might be overkill though.

Any recommendations? Also, would it be possible to get a schematic for the 8pak circuit?

Apologies if this is answered earlier in the thread. I read through it and didn’t quite find what I was looking for.

Thanks!
Raphael


Pad idea:

InputPad.png


Schematic from the LM3886 datasheet that I’m referring to:

LM3886DatasheetSchem.png
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Re: 8PAKAMP & 12PAKAMP KIT BUILD THREAD

Postby Joe Malone » Mon Feb 03, 2020 4:02 pm

rrp wrote:Hi Joe!

I purchased a couple 8pak kits about a year ago, and I’m just now getting around to putting them together. I’m building one kit as 4 bridged amps, and the other as 8 individual amps.

I’d like there to be external volume pots that attenuate from 0 to -infinity at the input of the amp. In the LM3886 datasheet, the example schematic shows an unbalanced 10k pot to ground at the input. Since the 8paks are balanced at the input with a resistor network (I think), I’m wondering how to implement this.

Is the input impedance of the amps high enough that I could hang a balanced attenuator in front of the input? Something like the attached image. Or, would I need to do some kind buffer? If a buffer would be required, maybe I would just get a balanced line receiver like INA134, then use the 10kpot, 1k input resistor combination used in the datasheet. I feel like that might be overkill though.

Any recommendations? Also, would it be possible to get a schematic for the 8pak circuit?

Apologies if this is answered earlier in the thread. I read through it and didn’t quite find what I was looking for.

Thanks!
Raphael


Pad idea:

InputPad.png

Schematic from the LM3886 datasheet that I’m referring to:

LM3886DatasheetSchem.png


Our schematic is very different to the standard which is why the LM3886 takes a balanced signal in. But the Inputpad idea works fine and it exactly how the input trimpot circuit works on the 8PAKAMP pcb. You can connect to the outside trimpot legs and parallel in and out of phase channels at this point and replace the trimpot with a volume pot.
Joe :-)

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rrp
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Re: 8PAKAMP & 12PAKAMP KIT BUILD THREAD

Postby rrp » Tue Feb 04, 2020 4:49 am

Got it. Thank you!

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