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Chip Amps Amplifiers based on integrated circuits

Adding bass boost to Mini3
Adding bass boost to Mini3
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Old 28th February 2011, 04:59 AM   #1
spaceconvoy is offline spaceconvoy
diyAudio Member
Join Date: Feb 2011
Default Adding bass boost to Mini3

I posted this on the DIY subforum at Head-fi, but didn't get any response, so I thought I'd try over here Can anyone help?

I have a Mini3 already built (high performance version), and I'd like to add a bass boost but I'm hopeless with any electrical engineering. This is as far as I've figured out, which is basically just the PPA bass boost grafted onto the Mini3:

Click the image to open in full size.

I'm planning to snip the leg of the existing R4, then run two wires to the extra bass boost circuit. Size isn't an issue for me, and I'm going to buy (or make) a bigger case to fit everything, with the bass boost circuit installed on perf board next to the existing Mini3 board.

I used Tangent's calculator to figure out the value for RX and CX, but I'm not sure if the existing R5 will effect things, since the PPA circuit doesn't have a resistor in that place. Also, I'm not sure if I need to change the value of the pot, since RX is so much higher than in the PPA circuit... see, I told you I was hopeless

Can anyone tell me if there's something wrong with this plan, and how I could fix it? Or is it possible that I've actually figured it out properly???


Also, if I want to add crossfeed, could I wire it in front of R1? Or would placing it after the volume pot cause problems? It would be easier than trying to scrape the trace away and attach new leads to the board in the tight space between the input and the volume... Thanks!
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Old 28th February 2011, 07:01 PM   #2
pacificblue is offline pacificblue  Germany
diyAudio Member
Join Date: May 2008
R5 won't affect things.

The calculator does not give you the value of Rx alone. It gives you the value of the combined resistance of Rx and the Bass Boost potentiometer. That will vary with the setting between 0 Ohm and 45,5 kOhm. You can use the calculator to find out how the bass boost changes its shape with different potentiometer settings.

The input of the crossfeed circuit comes from the output of the amp and the output of the crossfeed circuit goes to the phones.
If you've always done it like that, then it's probably wrong. (Henry Ford)
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Old 1st March 2011, 07:05 AM   #3
spaceconvoy is offline spaceconvoy
diyAudio Member
Join Date: Feb 2011
Thanks for clarifying that for me... but doesn't that mean RX would have to be zero or else you'll always have some boost even when you turn the pot all the way down? In that case, I guess my pot should be 500k and I should take away RX completely.

Also, I was planning on using the low impedance crossfeed before the input, which I've read is a better solution, plus, I'll chain my input caps before the crossfeed circuit so I can put everything in one enclosure. But now that I think about it, it probably needs to go before the amp's volume pot, right? Oh well, I guess I'll have to scrape the board...
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