Power Transformer-series/parallel 110v/220v question

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juniorhifikit

Well-known member
Joined
Jun 14, 2004
Messages
139
Location
California
Question about series/parallel power transformer circuit. I've seen this on a lot of my gear, and did this on my SSL clones, but it's been a while since I wrapped my head around it. This is the circuit from a Hafler amp power supply:
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PowerSupply.jpg


My question is, do I need to keep R124 and R125 (which are there for the 110v mode) and ADD R126 to get 220v; or do I remove them and use ONLY R126; or do I jumper across (short) R124 & R125 for the 220? It seems like with NOTHING at the R124 & R125 position, there's no circuit. Any insite would be greatly appreciated!
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[quote author="juniorhifikit"]My question is, do I need to keep R124 and R125 (which are there for the 110v mode) and ADD R126 to get 220v; or do I remove them and use ONLY R126; or do I jumper across (short) R124 & R125 for the 220? It seems like with NOTHING at the R124 & R125 position, there's no circuit. Any insite would be greatly appreciated!
[/quote]

For 220v mode leave out R124 and R125 and add R126. Those (R)esistors for usual are zero ohms (jumpers). The 'circuit behind' is the power transformer with dual primaries (J9-1/J9-2 for 1st.winding and J9-3/J9-4 for 2nd winding). R126 put these transformer windings in series (joining J9-2 + J9-3) for 220v.
For 110v mode leave out R126 and add R124+R125 to set the 2 primary windings in parallel.

Hope I could help
 

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