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Old 10th January 2006, 12:52 PM   #11
anatech is offline anatech  Canada
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Hi MichaelB,
Check lead dress inside in case someone has worked on the unit. The other, most likely problem is the power supply as others have pointed out.

The easiest way to find this out is to hang an oscilloscope on the supplies and have a look.

-Chris
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Old 10th January 2006, 12:53 PM   #12
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Quote:
Originally posted by anatech
Check lead dress..
Good point!
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I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort
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Old 10th January 2006, 05:31 PM   #13
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Hi, When I had a fault with my rb-993, Rotel service provided me with a service manual.

I have since deleted it, but if you call and ask them they are surprisingly helpful.

I phoned last week about a fault on my RC-995, the tech talked me through the basic checks on it. it took a while but he explained in great detail everything i needed to do. mostly just discharging caps as I don't have a oscilliscope but give them a call.
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Old 10th January 2006, 05:44 PM   #14
tubenut is offline tubenut  South Africa
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I am not sure if the 993 is the amp, I will check with a friend of mine.

There was a Rotel multi channel power amp where the first batch produced had a problem. They needed some re routing done with their earth paths (breaking a track or 2 and running a wire or 2 instead to different points.) Here my friend did this beforte the amps got to market, perhaps some slipped through...
The symptom of the design fault / problem was............................................... .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. ..............wait for it................................HUMMMMMMMMMMMM!! !!
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Old 14th April 2014, 11:36 AM   #15
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I know this is an old post but I have a similar problem with my rotel rb-993 power amp. I've had it for 15+ years and I think this hum has always been there i've put up with it and i've moved several houses since.

The hum / buzz occurs in both tweeters of my b&w 703s.

I've tried:
- Disconnecting HK receiver and rca cables
- Just having rotel power amp on and speakers connected
- Just having the rotel power amp connected to power board (filtered)
- Power amp connect straight to wall

Some of you have mentioned MOV, earthing issues, discharging caps with an oscilliscope... can someone help me with some basic diagnosis and if I need to do any of the following please walk me through it as i'm not an electrical engineer and don't want to get fried
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Old 14th April 2014, 11:53 AM   #16
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Is it hum or buzz?

The tweeters will be insensitive to 100Hz hum but will be sensitive to buzzing.

Are the bass drivers humming ?

I'd be looking to replace C906-909 and check D005 and D006

Last edited by KatieandDad; 14th April 2014 at 12:01 PM.
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Old 14th April 2014, 11:58 AM   #17
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The service manuals for most Rotel gear are readily and freely available.

http://bwgroupsupport.com/manuals/rotel-service
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Old 14th April 2014, 12:19 PM   #18
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>I'd be looking to replace C906-909 and check D005 and D006

That's clearly not happening (by me anyway).

I'd say it's more a buzz.
It drops in tone but is consistent.. zzzzzzzzzzzlllllldddddzzzzzzzzzzzzzzlllzzzzzlllllz zzzzzzzz

Only from the tweeters not the mid or bass drivers.
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Old 19th April 2014, 04:25 AM   #19
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I took the p amp into my local hi-fi specialist and we did the following.

'hooked it up to reference speakers using original power cable'
- a hiss could be heard from both tweeters when ear is close to them

'plugged in a shielded power cable, apparently worth $600'
- same result

'plugged into power filter'
- same result

We then looked at another setup using a more expensive and new power amp around $5k and $9k speakers. They too had a hiss, I'd say probably 1/3 the volume of my rotel + speaker hiss. The company apparently prides themselves on creating the purest noise fee equipment, i didn't get the name of the company.

So if anyone stumbles across this thread my general consensus is you will experience a small hiss/ buzz/hum noise coming from your speakers when connected to a power amp and it's perfectly normal. Unless your dealing with more expensive power amps, $5k+ and beyond might be a different universe ....that's something I'll probably never know.
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Old 19th April 2014, 08:48 AM   #20
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Quote:
Originally Posted by Drada View Post
I took the p amp into my local hi-fi specialist and we did the following.

'hooked it up to reference speakers using original power cable'
- a hiss could be heard from both tweeters when ear is close to them

'plugged in a shielded power cable, apparently worth $600'
- same result

'plugged into power filter'
- same result

We then looked at another setup using a more expensive and new power amp around $5k and $9k speakers. They too had a hiss, I'd say probably 1/3 the volume of my rotel + speaker hiss. The company apparently prides themselves on creating the purest noise fee equipment, i didn't get the name of the company.

So if anyone stumbles across this thread my general consensus is you will experience a small hiss/ buzz/hum noise coming from your speakers when connected to a power amp and it's perfectly normal. Unless your dealing with more expensive power amps, $5k+ and beyond might be a different universe ....that's something I'll probably never know.
The trick is to change the nature of that hiss.

Dan.
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