Crown DC-300A voltage conversion question - diyAudio
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Old 2nd January 2015, 09:14 PM   #1
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Default Crown DC-300A voltage conversion question

Hello everyone,
my first post here after having read for quite a while. Thanks for all the great info and topics.

I recently got a DC 300A and used it at it's native 120V settings, with a voltage converter. Voltage here in Italy is 220v and most gear here is set either to 220v or 240v but until now I couldn't find the time to convert the DC 300A.

Now, time has come for me to convert it and I opened the bottom cover as written in the manual (I attached the page relative to the voltage conversion).

The reason I posted this thread/question is that, if you look at how the cables are on the terminal strip, it looks like it's already configured for 240v..but the power socket I have is US-standard (3 pins).

Attached are two pictures of the terminal strip and one of the manual, to give you a reference.

I appreciate any kind, literally any kind , of help from anyone willing to contribute.

Thanks again,
Alberto
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Old 3rd January 2015, 01:10 AM   #2
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Location: Coffs Harbour
It certainly follows the manual's transformer wiring guide for 240V as you say. I used the series 2 manual to compare. You probably don't know what type of power socket the previous owner used to power the amplifier. It could have just been improvised with the original US fittings, hence the wrong plug.

The amplifier probably worked acceptably with only 120V mains power as you are now, with a voltage convertor but you should check (measure) the AC secondary voltages according to the schematic as it is now, before attempting to connect direct to 220V mains. For safety, ensure the meter is approved for use at AC mains voltages (CAT. 2 or higher)

The voltage across the secondary windings should be about 87 VAC (red-red) and half that to the centre tap (yellow) wires. The power supply rail voltages should also be about +/- 60VDC . If you only have around half these voltages, there is obviously a simple but dangerous wrong plug fitted.
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Old 3rd January 2015, 10:19 AM   #3
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Thanks for the reply! I contacted the "store" that sold it to me months ago and they said that the configuration seems already compatible with 240v - they also added that this is not a rare case since the previous user could have used a lower voltage setting for this country (hence 120V on a 240V setting) while driving the input signal higher by using a preamp.

This could explain why the amp does sound a bit weak to me compared to what I expected .. Even if I am feeding it with +4dBu and all that.


Would you know or by chance be able to tell me where should I take one of the measurements? I am afraid I'll have to disassemble the whole unit.. IF I could take a measure from just the bottom panel removed it would be great

I am not sure I am able to disassemble the whole thing

Thanks again and very kind of you to be that thorough in the explanation.

Cheers,
Alberto
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Old 3rd January 2015, 06:04 PM   #4
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Read the last paragraph of my post again - The secondary winding of the power transformer (the output) is 2 red wires which are either end of the winding that connect to the rectifier diodes. The yellow wire is the centre tap which is earth. Check the small diagrams of the power supply on pages 35,36 of the linked service manual.

That transformer secondary winding is where the AC is measured. DC is measured across the large smoothing capacitors - the rectified DC outputs. Each capacitor should have either the + or - DC rail voltage of approximately 60V between its terminals. That is, a total of 120VDC across both +/- rail capacitors. Look at the schematic to see how that is arranged. See the simple power supply diagrams shown separately on pages 35,36.
Crown DC-300A Manual - Dual Channel Laboratory Amplifier - HiFi Engine

Also use the manual to locate the several points you could also measure the DC power supplies to the amplifier, such as on the power amplifier module. If that is still confusing , get help from someone who understands conventional DC power supplies and can safely take the measurements for you.

You should still make certain of the voltages - at least the DC supplies to the module - before connecting to a 220V mains supply, since it was sold in an unsafe condition, with no assurances from the seller.
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Old 4th January 2015, 12:49 AM   #5
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Thank you. Makes sense now and you are right: voltages must be checked before replacing the plug.

This is probably the case of someone using it at 240V with a 120V load, and driving the inputs harder with a preamp to gain volume and work around the improper load..but there is no warranty in this so I must proceed with caution.

I will find time to put the unit on the workbench and disassemble it enough to reach for the transformer secondary winding and see at least the AC measure.

Page 35 and 36 look clear but a bit weird to me as I am not an expert..however, finding the two red wires of the secondary winding shouldn't be that hard, with a bit of patience. I can at least start there, better than nothing

Your help is practically invaluable, I am really thankful for what you've provided me with. Thanks for now and I hope to write an update soon!
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Old 14th January 2015, 09:00 PM   #6
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Ok my new tester arrived today I am ready to take some measures. I still haven't found the exact point to measure the DC rails, so I think I'll try and find the two red wires for the transformer, and see if there's approximately 87VAC there.

I suppose I can't measure DC at the two leads of the big capacitors..if this is a stupid question I am asking..it tells me and you how much I'll need to seek professional help.
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Old 16th January 2015, 06:08 PM   #7
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Ok I finally had time to open the Crown and is sitting on the bench.

I think I found where I should measure the AC (see picture attached).

I am allowing myself to ask you, Ian, for a confirmation better safe than sorry!

In the second picture I highlighted where the DC measure should be taken, if I got it right (again, confirmation needed). Those clips seem hard to open..though. I need to be careful as plastics aren't exactly new and might just get ripped apart.

Thanks again for the great help!
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Old 17th January 2015, 05:28 PM   #8
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Confirmed: I am getting around 41-43VAC out of the red-red transformer wires.

I didn't measure the capacitor rails but it seems clear this is already configured for 240V and is only receiving half the power.
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Old 18th January 2015, 12:31 AM   #9
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It worked! The conversion was successful….

But now the red power switch broke (probably of age) and the small metal lever inside the switch became loose, probably shorted the switch for a little while. Now the amp is silent dead, I suspect the switch might be broken.

I am sorry to be in need of your help again..I assume the switch is AC for 120-240V and is before everything, even the transformer..right? Makes sense. I'll see with a tester if I get phase on the terminals of the switch. This is probably just the switch being broken but I need to investigate..hopefully the fuse did not even short.
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