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Old 4th October 2003, 10:44 PM   #1
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Default Help Please - Modded RA931

Hey guys,
I'm having a problem with my Rotel RA-931 that I modified and a Rotel RA820AX that I turned into a power amp. It used to be an Integrated. I installed a Pre-out on the the RA931 right off the Volume Control output. The Main In signal on the 820 goes to the output side of the volume control on the 820. Basically, I'm using one volume control to send signal to two pre-amps sections. I normally use the 931 to run my DM601, sounds fantastic. When I add the 820 to just run the bottom end, the treble goes all goofy ( kinda distorted sounding), sound stage gets narrower, and the timing seems to be off on the notes. I also seem to have to turn the volume up more get get the same level out of both amps. I haven't a clue what's wrong. Am I doing something wrong? Any help would be greatly appreciated!
Drew
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Old 5th October 2003, 07:21 PM   #2
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It's a touchy thing to break the signal path in an amp in the correct place and get away with it. It sounds like your choice left a little to be desired.

If you don't have the schematics, get them. Examine the layout and determine the best spot to break the path. I've added pre-out/main-in jacks on quite a few integrated amps that did not have them originally, and although each was quite different, I've never broken the path anywhere near the volume control (no drive capability there...)

You need to reevaluate your work...
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Old 5th October 2003, 08:41 PM   #3
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Hey EchoWars,
Interesting thought. I'm not sure what you mean by drive capability though, could you explain that? Logically, I just thought of taking the voltage off the volume control to feed two pre-amps basically. Thought it would work. I have the schematic for the RA931 but not for the RA820. The RA820 seems to be very rare. My buddy came up with an idea, he thought maybe it's just out of phase - I'm going to try switching the Interconnects (left right) from the integrated. Right might be left and vice versa. Give it a try before I attempt anymore wiring.
Thanks for the response though. Would the best place the get the signal be after the pre-amp of the RA931 - right before the power amp section? then feed that into the power amp section of the RA820 - bypassing the other pre-amp all together? I didn't think that the pre-amp would have enough juice to power both. Anyways, thanks. Anymore suggestions would be great!
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Old 6th October 2003, 02:52 AM   #4
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By 'drive', I mean any piece of equipment that you connect the output to requires current. If you have no 'drive', then I mean you are not able to supply a proper voltage or current to drive the gear on down the line.

Difficult to make suggestions like this. Certainly the usual place to break is after the preamp section and before the amplifier. On some amps, the preamp has good 'drive', and is also either cap coupled, or at least at 0VDC. On others, there is DC potential that must be accounted for, either by adding a cap, or by choosing to break the path somewhere else. Of course, I have no idea how yours is set up.

Find someone knowledgeable locally and ask for suggestions. Of scan and zip the schematic and post it here. I'd take a peek at it...
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Old 8th October 2003, 11:48 PM   #5
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I received this reply from Rotel:

"Service Manuals are available for Rotel Products, they are available for $20 US, and you can order this by contacting our parts department at (800) 370-3740 to place an order."

They should provide the needed reference material.
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Old 9th October 2003, 12:01 AM   #6
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Hey - Yeah I phoned Rotel Parts and he gladly sent a service manual for a RA820BX4. They didn't have one for a RA820AX. Seems like this is a rare integrated amplifier, probably a European model because it has a Voltage selector in it. But yeah...thanks for the advice!
Drew
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Old 11th November 2003, 07:17 PM   #7
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Hey guys, good news - I got both amps running really well. Instead of taking the signal off the volume control of the RA931, I took it off the output side of the pre-amp section and fed that signal directly into the power amp section of the RA820. It just took some time. The service manual I got for the RA820AX isn't the same as the actually unit I have so it took longer than expected. But man it sounds incredible. Very emotionally engaging!!! One small problem though, maybe someone can help - there is a low level buzz coming thru the speakers when both amps are turned on. The RA931 runs the woofers on my B&W 601s1 and the RA820 runs the tweeters. The buzz goes away if I turn the RA820 off. Any ideas?

Here is my system setup: Rotel RCD930AX CD Player modded. Connected to the Rotel RA931 Integrated via MIT HT5i1m interconnects - runs the woofers on the B&W 601's, pre-out from the RA931 is connected to the RA820 modded via a custom built cable using sliver stranded twisted pair wires. The speakers cables for the low freg are MIT HT3s10ft and the cables for the high freq are Audioquest Type4. I've tried different interconnects between the two amps but that didn't help. Possible ground loop maybe? or a bad cap in the 820 causing feedback?

I can't hear it when I'm listening to music but I just know its there and it bugs me lol. You can barely hear it with no music playing.
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