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Old 28th October 2009, 08:01 PM   #1
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Default PA12 Apex chipamp

I now have 8 of these PA12 power opamps (pulls).
http://www.cirrus.com/en/pubs/proDatasheet/PA12U_S.pdf

I built one "test" channel using a datasheet schem. meant for the similar but lower-powered PA10.
(sounds quite good, for just one channel.)
I am testing it with a +0 to 50v, 5a (adj) bench-supply for now...and a passive input pot.
....I've yet to determine (build) an appropriate PSU.
http://www.diyaudio.com/forums/attac...1&d=1256764153

However I also found this one recently for the PA12....
(here I altered the feedback resistors from 100k/1meg to show 50k/500k....and the volume pot from 100k to show 50k, because I only have Noble 50k audio pots on-hand.)
http://www.diyaudio.com/forums/attac...1&d=1256764153

I am struggling to determine the Rcl resistors. I have tried reading/understanding the related documents, and the formula requirements
including: psu voltage, psu max amps, and the chip's SOA.
I'd rather not guess at this....I have a limited supply of these units, and they are quite expensive to replace.

Anyone care to help me out a bit ?

Also...any zener or transient absorber protection recommended ??
http://www.diyaudio.com/forums/attac...1&d=1256764153
BTW, there is an Excel program for determining the needed values, but it may not be working correctly in my copy of OpenOffice.
Linear Power Design Tool


Thank you ever so much,
=RR=
Attached Images
File Type: gif PA10_amp_schem.GIF (8.2 KB, 581 views)
File Type: gif PA12_datasht_schem.GIF (18.9 KB, 490 views)
File Type: gif zener_protection.GIF (12.2 KB, 510 views)

Last edited by redrabbit; 28th October 2009 at 08:19 PM.
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Old 28th October 2009, 08:40 PM   #2
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Also willing to parallel these, add an input buffer....
and try to turn this Chimp, into a Champ.

I have a big 4-device heatsink, ready-to-go with the TO-3-8 holes already....

=R=
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Old 28th October 2009, 09:15 PM   #3
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Parallel Connection
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Old 29th October 2009, 12:32 AM   #4
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Larger image.....http://i5.photobucket.com/albums/y17...t/DSCN2075.jpg

Click the image to open in full size.
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Old 30th October 2009, 08:09 PM   #5
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Quote:
Originally Posted by redrabbit View Post
I now have 8 of these PA12 power opamps (pulls).
http://www.cirrus.com/en/pubs/proDatasheet/PA12U_S.pdf

I built one "test" channel using a datasheet schem. meant for the similar but lower-powered PA10.
(sounds quite good, for just one channel.)
I am testing it with a +0 to 50v, 5a (adj) bench-supply for now...and a passive input pot.
....I've yet to determine (build) an appropriate PSU.
http://www.diyaudio.com/forums/attac...1&d=1256764153

However I also found this one recently for the PA12....
(here I altered the feedback resistors from 100k/1meg to show 50k/500k....and the volume pot from 100k to show 50k, because I only have Noble 50k audio pots on-hand.)
http://www.diyaudio.com/forums/attac...1&d=1256764153

Quote:
Originally Posted by redrabbit View Post
I am struggling to determine the Rcl resistors.
You could take advantage of the [url=http://www.cirrus.com/en/pubs/appNote/Apex_AN09U_B.pdf]Foldover Current Limiting
.


Quote:
Originally Posted by redrabbit View Post
Also...any zener or transient absorber protection recommended ??
Depends on how you intend to use the amplifier. Following the third schematic in your first post, D1 through D6 should be used, if you expect that amplifier to be used in rough conditions. E. g. if the you are not the only person, who uses it, and the other person(s) do not have the knowledge or do not care about the well-being of the amplifier. You have to find your personal compromise between safety (protection kicks in and degrades the sound) and sound quality (protection never kicks in). E. g. if the input signal surpasses the forward voltage of D5 and D6, the resulting distortions might be worse than the clipping that would ocurr without those diodes. D1's and D2's effect on the sound are quite harmless, so there is little to say against them. D3 and D4 protect the amplifier from the unlikely situation of too high supply voltage. You will have to analyze, whether that can happen with your PSU, why and how and then, whether those diodes can suppress that effect.
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Old 31st October 2009, 08:06 PM   #6
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Well, I built two channels of the "PA-12" schematic I posted...and there was not much power, and a lot of audible distortion. The culprit was the "noise gain" Rc/Cc combo.
I took those off completely, and it sounds much better to my ears.

Perhaps I will try to run some tests, to see what the holy machines tell me.

=RR=

Last edited by redrabbit; 31st October 2009 at 08:08 PM.
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Old 7th November 2009, 04:50 PM   #7
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My mistake on the "noise gain" Rc/Cc combo...I used 0.02 uf, instead of 0.002 uf...hence the distortion. But even with that cap, I can hear what sounds like harshness and emphasis in the treble region. However, I may need to adjust the Rc/Cc values.


Quote:
E. g. if the input signal surpasses the forward voltage of D5 and D6, the resulting distortions might be worse than the clipping that would occur without those diodes.
These input protection diodes.....run two or three in series (1n4148, each direction)??

--->|--->|--->|---
---|<---|<---|<---

This note explains a lot....
AN19 (apex app note)

=RR=

Last edited by redrabbit; 7th November 2009 at 05:03 PM. Reason: case of ADD
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Old 2nd December 2009, 09:34 AM   #8
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Built another two channels with the PA-12.

Also tried many different power supplies.
An HP +15v switching PSU (but the 20k switching freq was too noisy)...two Lambda modular single supplies in parallel (to get +15v)....and a RO switching unit (+15v @ 3 amps) which without any extra filtering, was dead quiet !

And this one, 200VA toroid unregulated +35v (case is ready for PA-12 chip implantation).

http://i5.photobucket.com/albums/y17...t/DSCN2269.jpg

http://i5.photobucket.com/albums/y17...t/DSCN2270.jpg

http://i5.photobucket.com/albums/y17...t/DSCN2271.jpg

=RR=

Last edited by redrabbit; 2nd December 2009 at 09:47 AM.
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Old 21st April 2010, 06:17 PM   #9
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I finished this chipamp.
I put a preamp before the pots, then signal was sent to the amp. The amp boards ware set at about a gain of 7.
This was kinda a mix of Apex datasheet schematics, and Rod Elliot chipamp preamp/volume added pots.....so it's really an integrated amp...minus the switch selector. I use an outboard switch selector.....this way, every time I build a preamp or poweramp, I don't have to build a selector switch every time.

Last edited by redrabbit; 21st April 2010 at 06:23 PM.
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