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00dc2 17th September 2010 02:35 AM

Rotel RB-970BX problem
I bought one of these power amps off ebay hoping that i could drive it from the output of my total bithead (DAC and headphone amp)

Headroom Total Bithead - Headphone Amplifier | HeadRoom Audio

I connected it up and slowly ramped the gain on the bithead and i heard a slight noise from the speakers and the rotel powered off and now doesnt power on at all.

I know i am supposed to use a preamp, but I didnt think the input to a power amp would be so sensitive. The manual for the rotel says the overload level is 5V and i assumed the USB powered headphone amp can only got that high at the most.

I've just downloaded the service manual and will take a look at that but i have no experience doing this sort of thing so any help would be really appreciated.

bob91343 17th September 2010 03:04 AM

Start with the power line and main switch and fuse if any. If you get power to the transformer, see if you get power out of the rectifiers.

If you don't get power to the transformer, maybe you blew a fuse. Yeah, a volt or so at the input of a power amplifier will drive it pretty hard.

00dc2 17th September 2010 08:12 AM

The rail fuses blew, i replaced them and she plays fine through the total bithead.. i just had the volume turned up too high in windows.. i turned that right down and started from there...

now i set the volume to 50% in winamp or mpc and then use the vol control on the little headphone amp starting at 0.. gives good volume control

What is the chance that i damaged the rotel by overdriving the input on it?

birdyman 17th September 2010 03:34 PM

Depends on your head phone amp output voltage level.
In reality, Not so high of it??

00dc2 17th September 2010 04:55 PM

not entirely happy with the rotel, it is hissing when there is no music playing.. i'd like to figure out if its the headphone amp that is feeding it or the rotel itself

with the headphone amp plugged into the rotel but with the input level/gain turned down to zero there is a hiss.. when there is nothing connected to the input of the rotel it produces complete silence..

i wonder if the headphone amp has some dc or i dunno some noise or there is a mismatch between its output and the rotel's input.. cos the headphone amp plays very cleanly with my Sennheiser HD600s

i am guessing that the headphone amp isnt really that clean and the headphones are far less sensitive to noise on their inputs than the rotel.. but if only i could find a nice and clean source to drive them with to really test them.

djk 17th September 2010 09:14 PM

A quick fix might be a 1:1 transformer.

EDCOR - S2S10K/10K

Andy5112405 19th September 2010 10:53 AM

Try running with no input or, even better a shorting plug on the input of the Rotel. The Power Amplifier should be virtually silent in this situation.

I would suspect that your "hiss" is coming from the output of the computer.

00dc2 19th September 2010 11:10 AM

when i run it with the input open circuit it is silent.. your suggesting i short the inputs? is that a good idea (gulp)? (i have no idea)

silence with open circuit inputs suggests the amp is in good nick?

Andy5112405 19th September 2010 02:40 PM

If it's silent with NO INPUT there is no need to try it with shorting plugs.

The amplifier sounds good to me.

00dc2 19th September 2010 09:56 PM

great, thanks for your help!

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