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Old 20th September 2010, 08:25 PM   #1
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Default bf245b transistor orientation/chip protection

Hi, I am building this sp/dif buffer as suggested on the Lampizator site the schematic is on the page
CD Transport Digi-Lampizator
Click the image to open in full size.
It is a simple question :do I have the flat side of the "D" facing the signal wire ????? I take it the sp/dif signal enters the transistor on the centre pin.....It is not that I am too lazy to experiment , I am just worried wrong orientation would blow the signal generator chip or something nasty and the Quad 99 I am using is made of very very flimsy parts , I think it would be hard to repair..Thanks Alan...
ps if I am worried about blowing chips can you protect them by using a diode in series along the signal wire??
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Old 20th September 2010, 08:33 PM   #2
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Default cannot figure out how to put a picture on here

the link has not worked hopefully the picture of the schematic will appear here
Click the image to open in full size.

you will have to scroll to the bottom of the page for the diagram
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Old 21st September 2010, 08:47 AM   #3
Tfan69 is offline Tfan69  Italy
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hello,
this is the pin configuration of the bf245b, signal enters in G pin, which is at bottom looking at D
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File Type: jpg piedinatura_bf245.jpg (10.6 KB, 20 views)
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Old 21st September 2010, 08:56 AM   #4
Luke is offline Luke  New Zealand
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are these optimised for the sa7220, or can i use this on any chip?
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Old 21st September 2010, 03:37 PM   #5
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Default still confused

Tfan69....does the power come in on the "s" or "d" pin then??????.....sorry for being so thick...

Luke .....I have no idea I was just going to connect it and see what happens....I do not even know what spdif generating chip I have ...all I know is is that a stock quad 99 is a very very poor affair indeed and needs all the help it can get
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Old 21st September 2010, 03:51 PM   #6
Tfan69 is offline Tfan69  Italy
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just look at the scheme and the pin image, power enters from d
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Old 22nd September 2010, 08:30 PM   #7
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Default 0.3v dc

Hi, Tfan...I have built the buffer and am running it off a 9volt battery for a minute...its built as a external unit and plugs into the rear digital output socket on the player....and outputs to an external dac.... SO ....all rca grounds /battery ground and resistor grounds share the same rail........Before I plugged into the player , I put a multimeter on the output hot pin and found it is outputing 0.3volts DC before any sp/dif signal is applied....I was suprised to see the DC as I thought the 10 uf capacitor was supposed to block it....I have double checked everything and cannot see how I have varied from the diagram....so is this an acceptable amount of dc to be going to the dac or have I indeed messed up??? I have not plugged the unit in as I am worried about the dc....is my grounding right?
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Old 22nd September 2010, 09:57 PM   #8
mjf is offline mjf  Austria
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hello.
you can connect a res (typ.100k or so) from output cap to ground.......so that (big) cap can be charged.
are you shure that output cap reads 10uf ? or is it 10 nf (red schematic with the tube)?
greetings
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Old 22nd September 2010, 10:01 PM   #9
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Default 10uf

its definately a 10uf non polar just a cheap brand...i have left the thing powered and now when I read the pin i see....0.02volts dc....could this be evidence of the so called "burn in" of a electrolytic???? is 0.02v safe for the dac? I will raid my parts bin attach a resistor like you said .....see what happens
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Old 22nd September 2010, 10:30 PM   #10
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it worked......o.oovolts...so I tried putting a 75ohm ...and the same result.....listening to it now.....can't say I am hearing any improvement in sound quality or details etc...maybe 9v is not enough...will have to mess around with the resistors as well
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