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Old 31st January 2005, 01:26 PM   #1
wuffer is offline wuffer  Denmark
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Default 1 transformer to lcaudio psu design

i have looked a lot of places and couldent find anything.. all designs was with 2 transformers...
what is the best way to do a 2channel zap with one transformer

i have this and nothing is going to change

one 2*42v 800va transformer from www.elfa.se
8 schotky diodes.. 4 pr channel right???
2 220000 caps 100v.. 1 pr channel..

some uses resistors and smal caps in the design..
i can understand how the ground is made with 2 transformers but not with only one...

hope someone can help me
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Old 31st January 2005, 05:32 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
connect the two secondary windings in series to give 80Vac out.
Connect a 4 diode bride across the 80V and connect a second 4 diode bridge across the same 80V connections. i.e. both bridges in parallel. The spare two wire connection is the power ground.
Now treat each bridge as a completely separate feed to the ZAP. What is a zap?
Connect all the first caps commons with one power ground wire to the star earth and then connect the second caps commons with separate power ground wire to the star earth. Do not make a direct connection from safety earth to power gound nor to star earth. If your transformer has a screen then connect this with a small gauge wire to star earth. If you have an EI or similar transformer connect the frame to chassis or to safety earth. Connect star earth via a low resistor (10R) to safety earth. You can parallel this with a small ceramic cap (RF to earth) and with a hi current bridge rectifier to safety earth. These prevent a hum loop being set up.
does this make sense?
And finally remember to connect your input connectors to the clean ground on your PCB not to any other ground or earth connection.
regards Andrew T.
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Old 31st January 2005, 05:37 PM   #3
wuffer is offline wuffer  Denmark
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thanks.. is it possible you could make a drawing???

zap=zappulse

im not sure what a star ground is.. explain please
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Old 1st February 2005, 07:29 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi wuffer,
I have not yet learned how to attach drawings and other bits to my posts.
I will try to find a thread with a suitable sketch.
Safety ground is where the chassis and the mains input wiring connect.
Power ground is where your main smoothing caps connect to a commom and then to centre tap of transformer secondary.
Star ground (earth) is where all the clean returns (grounds, earths) and dirty grounds connect together. DO NOT commom any decoupling and clean grounds before reaching the star ground.
Many others do it differently, see Leach for an alternative but similar or D. Self or JLHood.
regards Andrew T.
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Old 1st February 2005, 01:13 PM   #5
wuffer is offline wuffer  Denmark
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thanks again.. now i have learned again
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Old 2nd February 2005, 03:47 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi Wuffer,
found part of what you need at ESP site.
http://sound.westhost.com/earthing.htm
Fig 1 is misleading because the shielded interconnect should not be directly connected to the safety earth at any end if you follow his Fig 3.
regards Andrew T.
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Old 2nd February 2005, 03:49 PM   #7
wuffer is offline wuffer  Denmark
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thanks..
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Old 2nd February 2005, 10:24 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi Wuffer,
here is the next diagram.
http://sound.westhost.com/project04.htm
His Fig1 shows a ground running off to the right, this is the single wire going to the star ground. This way current pulses charging the caps do not contaminate the clean grounds.
regards andrew T.
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Old 8th February 2005, 12:00 PM   #9
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Quote:
Originally posted by AndrewT
Hi,
connect the two secondary windings in series to give 80Vac out.
Connect a 4 diode bride across the 80V and connect a second 4 diode bridge across the same 80V connections. i.e. both bridges in parallel. The spare two wire connection is the power ground.
Now treat each bridge as a completely separate feed to the ZAP. What is a zap?
Connect all the first caps commons with one power ground wire to the star earth and then connect the second caps commons with separate power ground wire to the star earth. Do not make a direct connection from safety earth to power gound nor to star earth. If your transformer has a screen then connect this with a small gauge wire to star earth. If you have an EI or similar transformer connect the frame to chassis or to safety earth. Connect star earth via a low resistor (10R) to safety earth. You can parallel this with a small ceramic cap (RF to earth) and with a hi current bridge rectifier to safety earth. These prevent a hum loop being set up.
does this make sense?
And finally remember to connect your input connectors to the clean ground on your PCB not to any other ground or earth connection.
regards Andrew T.
SOunds kind of complicated to me.

2 * 42V AC is perfect for Zappulse, it will give you about +/- 57VDC on the supply rails. 80VAc will kill your Zap modules.

read this for the rest: http://www.zero-distortion.com/start.htm if you don't want to read it all...just build the design on the last page.
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Old 8th February 2005, 12:16 PM   #10
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I think you misread Andrew said to connect the two secondaries in series to realise and 80 volt (centre tapped) transformer. That means it will be 40-0-40 AC (approx 54-0-54 DC), which is ideal for just over 300W into 4 ohms.
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