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Rotel rb985 and soft start
Rotel rb985 and soft start
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Old 13th December 2012, 02:44 PM   #1
Flua is offline Flua
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Join Date: May 2012
Default Rotel rb985 and soft start


I have a Rotel rb-985 that very often takes out the fuse on the house main circuit when its turned on. These amps seem to be known for this.

I bought a soft start from ebay, based on NTC 10-D20 thermistors:

Assembled High Power Soft Start Up Board 220V Operation Best for Audio Amplifier | eBay

..and since there was no documentation supplied, I haves some questions.. There are 6 connection points on the curcuit, 4 are for the mains in/out. I understand those..

The last 2 are marked on/off. Will these need a secondary dc supply, or should they just be connected to be "on", and the amp is turned on by its normal on/off switch?

I will just say that I will only fiddle with the mains after the amp has been turned of for a week, and it will also be moved outside before I turn it on again. Wearing my protective outfit..

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Old 13th December 2012, 03:23 PM   #2
jaycee is offline jaycee  United Kingdom
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Location: Norwich, UK
If there is any documentation or a schematic with this kit, it should show it. If it doesn't, I'd request that from the seller.
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Old 13th December 2012, 03:24 PM   #3
KatieandDad is offline KatieandDad  United Kingdom
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It's not exactly clear from the e-bay description but it looks as though the board has a built in reactive power supply which is incredibly dangerous as there is no isolation from the mains voltage.

If I am right, and please check VERY CAREFULLY then all you need is a 240V isolated switch to remotely switch the relays. No need for a second power supply.

You MUST - MUST - MUST obtain a circuit diagram for this before you even think about using it.
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Old 13th December 2012, 05:11 PM   #4
AndrewT is offline AndrewT  Scotland
Join Date: Jul 2004
Location: Scottish Borders
insist on a schematic and wiring diagram.
If they cannot supply these, then claim as "unfit for described use" and get your money back.
regards Andrew T.
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Old 13th December 2012, 05:29 PM   #5
Flua is offline Flua
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Join Date: May 2012
I have asked but still not recieved any.

I will follow your advices. Incredibly dangerous does not sound good.

The guy also sell another soft start that I didnt see when I made the order:

Assembled Soft Starter Start Up for Power Amplifier w Thermal Dectector Protect | eBay

There even I can see the transformer. There also is scematics in the add. Seems like this one is "just" to connect to the mains(?).

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