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-   -   Dangerously wrong diagram at apexjr? (http://www.diyaudio.com/forums/chip-amps/118100-dangerously-wrong-diagram-apexjr.html)

xiphmont 24th February 2008 07:12 PM

Dangerously wrong diagram at apexjr?
 
Is it just me or is this pic at Apexjr showing how to hook a center-tapped transformer up to a BrianGT power supply board dangerously wrong?:

http://www.apexjr.com/images/BrianGTPCB.JPG

(on the page http://www.apexjr.com/miscellaneous.html )

those instructions seem OK until PG+ and PG- are joined together somewhere on the amp board, and then the transformer is being shorted for half the cycle as the output from Yellow to Red is being dropped directly through two of the diodes...

It will seem to 'work', as in the output voltages will seem correct, but the transformer will be buzzing like Hell... until something melts...

richie00boy 24th February 2008 07:28 PM

No it's fine. It is not the transformer that gets shorted, it's the lower two diodes in the top bridge and upper two diodes in the bottom bridge, thereby making them redundant.

xiphmont 24th February 2008 07:32 PM

Quote:

Originally posted by richie00boy
No it's fine. It is not the transformer that gets shorted, it's the lower two diodes in the top bridge and upper two diodes in the bottom bridge, thereby making them redundant.

Uhhh.... no. You *can* use this board with a center tapped transformer, but *not* the way it's illustrated. Ie, the proper way to do it would eliminate four diodes, jumper the connections into a single bridge, and tie the CT, PG+ and PG- together.

The way it's illustrated in the pic will cause either the transformer to catch on fire, a diode to blow up or the fuse/breaker to blow.

[edit: had an extra BrianGT rectifier board and CT transformer around. Wired it as displayed and sure enough, transformer buzzed, lights on workbench dimmed, then fuse blew when I alligator-clipped PG+ and PG- together. But, multimeter read 60v across +/- as 'expected'.]

Monty

Apex Jr 24th February 2008 10:40 PM

Thank You Dave and Roddy for the heads up...

I've been selling toroids for the Brian Gt's boards and
Troystq ( Troy St Geramain) sent over the picture which
he used to hook up the boards...

Looks like I'll have to take it down...
Anyone else a picture of there hookup's

Steve @ Apex Jr.

xiphmont 24th February 2008 11:07 PM

Quote:

Originally posted by Apex Jr

Anyone else a picture of there hookup's

Steve @ Apex Jr. [/B]
I can take some. All mine were originally soldered up for dual secondaries tho, and desoldered/modified later for CT transformers, so they may not be the clearest examples because there's solder all over the place :-)

Monty

xiphmont 25th February 2008 01:08 AM

Here are pics of a CT transformer (one of the apexjr 25-0-25 100VA Avel toroids in fact) connected to a new-style snubberized rectifier board, as comes in the current chipamp 3886 kits.

The unused diode pads have solder on them because this board was sitting around assembled for a dual-secondary transformer and I unsoldered the extra diodes and added jumpers to modify it for the center tapped transformer.

Oh, and warm white LEDs are the new blue :-)

http://web.mit.edu/xiphmont/Public/PSU-CT1.jpg

http://web.mit.edu/xiphmont/Public/PSU-CT2.jpg

http://web.mit.edu/xiphmont/Public/PSU-CT3.jpg

tangmonster 25th February 2008 05:15 AM

There is also another problem i found with a different power supply floating around on the net and used on BrianGT lm3886-manual pdf

http://www.diyaudioprojects.com/Chip...wer-supply.png


Either the CAP or the Diode bridge must change around, because i can just SEE that electrolytic exploding!!

cabbagerat 25th February 2008 05:38 AM

xiphmont's pictures are right. For reference, there is a circuit diagram I drew, and some alternative pictures in this thread:
http://www.diyaudio.com/forums/showt...hreadid=116512

tangmonster 25th February 2008 05:49 AM

Your picture is correct, But in the one in my post the + output of the bridge is connected to the - pin of the 10000uF cap , This is INcorrect.

Or am i overlooking something stupid?

cabbagerat 25th February 2008 06:37 AM

Quote:

Originally posted by tangmonster
Your picture is correct, But in the one in my post the + output of the bridge is connected to the - pin of the 10000uF cap , This is INcorrect.

Or am i overlooking something stupid?

The diagram in your post is incorrect, but it seems as though the one up at chipamp.com now is correct.


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