Saturday, January 12, 2008

Quad 405-2 AC voltage considerations

From serial number 83000 and onwards Quad omitted the AC mains voltage selector on the Quad 405-2.
I recently checked such a late model Quad. It did not perform well. The power delivery was not on spec. On the outside of the unit there was a marking: 220V. But in real life the unit was wired for 240V. The Quad 405-1 had a selector with 6 positions, in the service documentation of the 405-2, only for four voltages is explained how to connect the wire links to the primary windings of the transformer. In the Netherlands the AC voltage is 230V, this is one of the missing voltages in the documentation, and the other is 130V. Because of the design, the DC power supply voltage of the amplifier is proportional to the AC mains voltage. So 130 V or 110 V does matter! To complete the documentation I drawn the missing link positions. You can also use these diagrams to rewire any Quad 405 and omit the voltage selector with those tiny wires. If you can hear a difference? I can’t tell you, judge for yourself. Before you rewire the amp, check the AC voltage during some weeks, check what is really coming out of the mains socket. Click on the diagram to get a fully detailed version, I also added some colour.

Joost Plugge

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Anonymous Anonymous said...

Hi Joost,
I just did the ac wiring on a quad 405 circa 1979 s/n:38xxx wired for 240vac as per your diagram but I got no voltage on the secondary. I measured the ac voltage from the wall outlet and it measured 235vac.I triple checked all the wiring before switching on. What could possibly be wrong? Is the early 405 transformer the same as the late 405-2 t/f? Appreciate yr advice.

12:37 PM  
Blogger Stefaan said...

Hello Peter,

In the 240V AC option, all the transformer coils are in series, you should measure about 3.8 ohms in total. Measure the AC input socket on the Quad. Did you place the short links as showed in the diagram to connect the '110V' with the '10V' coils? I checked with a very old 405 and a very late 405-2, the transformers are the same.

Regards Joost

10:39 AM  
Anonymous Anonymous said...

Hello Joost,
Thanks for yr comments. I did not connect the short links. I missed it as I did not enlarge the diagram. My mistake. Anyway, I have already did the wiring differently by tracing the selector connections and wire accordingly. Works perfectly. As for the sound, I hear more weight in the music. Could be my imagination though.

Best regards,

5:12 PM  
Blogger Stefaan said...

Hello Peter,
All ends well, to put things in perspective. I measured a 405-1 in 110V mode. The two transformer coils in parrallel are 0.9 ohms, from the AC input you 'see' 1.2 ohms. So 30% is added by those tiny wires! When you apply the AC, the inductance of the transformer will be large, compared to the DC resistance, but still.....
Regards Joost

6:05 PM  
Blogger Stefaan said...

Robert Buch mentioned the exsistance of a Quad application note to convert a 405-2 to 230VAC operation. In the application note Quad only uses one "10V" winding instead of two in parallel, as they did in the 405's with the voltage selector still in place. From a energy transfer point, it is better to use as many windings as possible, but if you look at the 220V and 110V options, where only the two "110V" windings can be used, the 230VAC option will work with only one "10V" winding.

Regards Joost Plugge

10:42 AM  
Blogger NB said...

-I have 2 quad II power amps ser#41147 and #18589.
I bought them in the UK and now live in the US ...
what do I need to do to switch them to 110V ? I am told I need to buy 2 new 110 V transformers x Quad...$$expensive - is there another way??

12:37 AM  
Blogger Stefaan said...

You could use a 110V to 220V transformer - this is the same as a 220V to 110V transformer used in reverse.

12:41 PM  

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