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Old 16th January 2009, 08:06 PM   #1
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Default Class D & REL Subwoofer

Hi there.

My Class D amplifier (Fenice 20a) is working fine and an adequate substitute when I don't want to warm my valave amp up, however, I have recently bought a REL Strata 5 and can't get it to work with it. I've contacted REL with the following reply

"This is quite common now as digital amp don't have a constant earth so things like distortion are very common so we have made a special lead that gets around this, you can order one from your local rel dealer at a cost of 100.00. hope this helps*all the best"

I don't fancy paying 100 for a lead, any knowledge of this problem or ideas would be appreciated.

Stoat
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Old 16th January 2009, 09:37 PM   #2
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Stoat,

The Fenice outputs are full-bridge, meaning they are not referenced to ground. The positive and negative of each output are both referenced to Vs/2.

You can use any cheap line level converter marketed for car audio (see example link below).

http://cgi.ebay.com/CAR-AUDIO-RADIO-...QQcmdZViewItem
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Old 22nd January 2009, 04:05 PM   #3
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Default Still no good

Bought one of these, yes the outputs of the line out are common but they are isolated from the inputs (obvious now I've thought about it) so they are no good.

The REL subwoofers have a single phono input for Home Theatre LFE and they have a High Level input for high-fi. The High Level input is connected to your amplifier loudspeaker outputs.

So I'm still a bit stuck...........
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Old 22nd January 2009, 08:26 PM   #4
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The outputs of the adapter are isolated (why would you think this is no good?), so just use a Y adapter to go from stereo to mono.
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Old 23rd January 2009, 02:01 PM   #5
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Sorry, I've not been very clear, I'd been hoping to use the loudspeaker output of the Fenice to drive the high level input of the sub-woofer as REL recommend.

I am using the phono input on the sub-woofer connected to my LFE feed from my HT system (completely separate system except the common sub-woofer).

I was hoping to avoid having to have to use the phono input or build a second amplifier to "just" drive the REL and that there was a clever way of getting a common earth from the Fenice. I presumed this "clever way" existed since REL are selling a lead that can do it (I don't know what this "lead" is and if it has some active (powered) components in it).

Please accept my apologies if I sounded short, it wasn't meant.

Stoat.
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Old 23rd January 2009, 09:38 PM   #6
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Well, are you against just using some kind of switch setup on the line level input to switch between the high to low adapter and your HT receiver output?

Do you know anything about else about the device from REL? It might also just be similar converter that uses the line level input on the sub.

There is a way to do what you want, but it does require some DIY know how. I don't know what you comfortable with doing.

Basically, you need to put a capacitor in series with one of the outputs (+ or -) on each channel. The positive lead of the capacitor connects to the amp output and the negative lead goes to the REL high level input. This blocks the DC bias on the output and allows you to use the power ground of the fenice as the common ground which you can connect to the REL.

You will need to know (or measure) the impedance of the high level inputs on the REL so you can choose the appropriate size of the capacitor.

If you don't quite understand what I mean I can try and draw diagram (I'm not to good at it though).
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