Building a symmetrical PSU B1 buffer

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Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
adamus said:
no offset, my multemeter reads 0v on the millivolt setting. The led strings are 5.7 for the css, and 9.1 for the vref matched very closely each side.

The preamp consists of a r2r remote vol control > DC B1

This then feeds a push pull el84 amp (baby huey). It then feeds some KEF q5's, although i am building some brines ft1600 mkII (fostex 167e).

how did it change the sonics? Deeper soundstage, slightly better seperation. Slightly (ever so slightly) cooler presentation. Clarity is the word.
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Tea-Bag said:
mine sounded better after a few days.
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adamus said:
My sounds great from the word go. how did the soncis change?

I have come from pedja rogic buffers, which were quite dependant on the otuput cap.
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No worries then, I don't see anything you have to touch in the LED strings.

It is true, it will sound looser after some initial play. Its the electrolytics in the shunts mainly needing to flex a bit.

Big relief sans cap, and a money saver too. I know.

Nice system BTW. I especially like Baby Huey as a concept.

Regards
 
M

massimo

Member
Joined 2002
merlin2069er said:
Hi, I've got a quick question.

Looking at bom v4.2 there are 5x 100uf caps needed. I see the spots for them on the board.

I'm wondering where decoupling cap B (which is supposed to be near c517) where does that go? It's 150nf/63v film cap.

Thanks,
JG
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100uF: use best quality (Pana FC/FM or Elna Silmic) for the 4 caps in the shunts and a std quality one for the turn on delay

Decoupling A and B: these two caps can be any MKT or Mylar from 100 nF to 220 nf, whatever you have handy. The "A" cup has been "forgotten" drawing the pcb and must be soldered under the board. Turn the pcb and see the cap "B" (100 nF on silkscreen) pads: one is connected to the center pin of the LM7812, the other to the pin close to the center of the board. The "A" caps goes to the center pin of the regulator and the other pin, close to the pcb edge.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
No. The 150nF is in the BOM, only if the peculiar ''relay chatter'' phenomenon ever occurs again, just for being ready. With BC517 is highly unlike to occur. So if no BC517 is available, but say a BC550 is, and some relay types or makes prove to buzz mechanically, you strap the 150nF cap underneath board between collector and base of the lower BC550 that pulls the relay coil's current. The 100nF has a board position right next to the 7812 and it is for decoupling that reg's input since there is some inductance on the rather long pcb foil that gives it the juice from the main filter's tap off for it.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
If the 150nF proves non needed for chatter, nothing is needed there. Its not an audio circuit so to decouple better the 7812's output for better treble for instance. With the relay drive there are two possibilities. 1. Clicks, releases normally. 2. Buzzes. The second possibility is remote if using BC517. We just had some weird buzz with some relays in the proto builds in two cases. That was with simple npn driver, not Darlington like BC517 is. Just because the other guys with same configs did not mysteriously get it, we included the cure if with simple npn drive. Namely the 150nF cap, so to be there if something arises or BC517 isn't available to someone. Yet if it ends up surplus to a build and no other use for it, you can strap it across 7812's out to ground underneath, no problem.
 
merlin2069er

merlin2069er

Member
Joined 2008
DSC00081.JPG


Here's my board so far:

I'm waiting on some 170's, and got to sort out my leds.

2 things:

2 jumpers are required on the board right? (1 extra if you use 12v relays)

I've got decoupling cap b on board 100n right next to the 7812.

So decoupling cap A is not needed?

Thanks,
JG
 
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