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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

BPPBP - Bruno Putzey's Purist Balanced Preamp (well a balanced volume control really)
BPPBP - Bruno Putzey's Purist Balanced Preamp (well a balanced volume control really)
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Old 8th September 2015, 12:45 AM   #11
Pan is offline Pan  Sweden
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Also, unbalanced in = ground one of the input buffer amps.
Unbalanced out, bypass R15/42 and use as GND.
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Old 8th September 2015, 05:33 AM   #12
Bertel is offline Bertel  Germany
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Default BPPBP - Bruno Putzey's Purist Balanced Preamp (well a balanced volume control...

Quote:
Originally Posted by Joachim Gerhard View Post
I asume that there is also a posibility for unbal ( RCA ) In and unbal ( RCA ) Out.

Joachim, instead of using RCA connectors at the amp, would using cabling as sketched in Figure 6 in the article be possible in your application, with RCA at the source and XLR at the input, and vice versa? (Also described in 12.3.1 here: http://www.hypex.nl/component/weblin...datasheet.html )

Last edited by Bertel; 8th September 2015 at 05:39 AM.
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Old 8th September 2015, 11:01 AM   #13
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by Pan View Post
I wonder if J4/5 is simply there for letting your PCB layout software accepting a GND connection. Zero ohm resistor could be used as well.

It's mentioned in the text.
Correct. I think he calls it 'net-tie' points. CAD software often insists on connection anything with the same name together wherever IT thinks convenient. If you have two ground 'things' that you want to force to connect at a specific point, then depending on your CAD idiosyncrasies, you might be forced to do a workaround like Bruno did. Clearly explained in the (free) article - no excuse NOT to read it!

BTW I had 1000 free boards which are all given out but the Gerbers are available free on the website (under Downloads) so you can have made some yourself, or set up a group buy. It's a small board so not expensive, BUT it does challenge your SMD solder proficiency though. I managed to get two boards together with no mistakes.

Jan
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Old 8th September 2015, 11:39 AM   #14
billshurv is online now billshurv  United Kingdom
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BPPBP - Bruno Putzey's Purist Balanced Preamp (well a balanced volume control really)
I'm short of round tuits at the moment, but if anyone is getting boards made I'd be in for a few to help get the costs down.
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Old 8th September 2015, 11:50 AM   #15
Turbon is offline Turbon  Sweden
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+1
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Old 8th September 2015, 01:30 PM   #16
Bertel is offline Bertel  Germany
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Quote:
Originally Posted by jan.didden View Post
BTW I had 1000 free boards which are all given out but the Gerbers are available free on the website (under Downloads) so you can have made some yourself, or set up a group buy. It's a small board so not expensive, BUT it does challenge your SMD solder proficiency though. I managed to get two boards together with no mistakes.
Many thanks Jan! I have a visual impairment and can't build myself, so I will have the PCB printed and built professionally.

I will try to figure out how to create an Excel Online sheet, so if anyone wants to join me with either a bare PCB or a completely built unit, please let me know. Will get quotes now and publish cost shortly.

Thanks,
Robert
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Old 8th September 2015, 01:50 PM   #17
Turbon is offline Turbon  Sweden
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Hi there Robert.

I want to make my own misstakes so a bare board or two with an recommended BOM would be fantastic !

Regards
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Old 8th September 2015, 02:39 PM   #18
jcx is offline jcx  United States
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Putzeys' comment on the THAT Corp patent is dated - actually Whitlock's patent on diff amp input common mode bootstrapping is public domain now

http://www.google.com/patents/US5568561 coverage expired last winter with the most generous interpretation of term == filing date + 20yr

any new design could consider it without IP concerns
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Old 8th September 2015, 02:44 PM   #19
Bertel is offline Bertel  Germany
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Interesting point jcx, thanks!

Yet Bruno also writes (page 10):

Quote:
I would’ve used the Whitlock’s input chips and implemented the capacitive bootstrap technique as well, except that the distortion performance is not good enough in my view.
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Old 8th September 2015, 02:52 PM   #20
Bertel is offline Bertel  Germany
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Quote:
Originally Posted by Turbon View Post
I want to make my own misstakes so a bare board or two with an recommended BOM would be fantastic !
Fair enough Turbon

Bruno has a parts list in his article already, plus there's a more specific one with manufacturing codes in the Downloads section of Linear Audio website here: Downloads | Linear Audio (this is the direct URL to the BoM).
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