Hello DIY enthusiasts,
I have an integated Rotel RA840BX4 amp that I used to enjoy a lot but had to put aside because it lacks pre-out and main-in connections. In my preferred setup I have a MiniDSP connected between the pre amp and the power amp to fix issues with the room acoustics and to serve as a crossover for my subwoofer.
However, I assume that it might be fairly easy to add those. Looking it the schematic, I guess that I could simply add those by making a cut at the position I marked with an arrow (image below). That seems to give the desired low output impedance (delivered by the NE5532 OPAMP + 100 Ohm resistor R715) and high input impedance (15K Ohm resistor R601 + capacitors).
Would that work as desired?
Thanks! René
I have an integated Rotel RA840BX4 amp that I used to enjoy a lot but had to put aside because it lacks pre-out and main-in connections. In my preferred setup I have a MiniDSP connected between the pre amp and the power amp to fix issues with the room acoustics and to serve as a crossover for my subwoofer.
However, I assume that it might be fairly easy to add those. Looking it the schematic, I guess that I could simply add those by making a cut at the position I marked with an arrow (image below). That seems to give the desired low output impedance (delivered by the NE5532 OPAMP + 100 Ohm resistor R715) and high input impedance (15K Ohm resistor R601 + capacitors).
Would that work as desired?
Thanks! René
Rene, suggest you come directly of the output pins of IC702 (7 and 1 which I assume is L and R) through a 100 Ohm resistor to your output sockets. Take the signal ground from as close to IC702 as you can get.
I added pre-out's on my Marantz PM7000 like this years ago - worked well.
I added pre-out's on my Marantz PM7000 like this years ago - worked well.
The NE5532 might have a DC offset. Shouldn't an extra coupling capacitor be added to the pre-out (after the 100 Ohm R715, which is just next to the IC), one comparable to C601?
Yes - I’d there’s a DC offset then you must include a capacitor (assuming the receiving equipment is direct coupled). A 22 uF Bipolar capacitor should be adequate.
Thank you!
The original circuit has a 10uF cap (C601) parallel to a 1nF cap (C609). You didn't copy that, and I don't see the use of it. Does that small cap make sense of should I just leave it out?
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.. and getting to think about the coupling capacitor at the input of the power amp section: shouldn't that be replaced by a bipolar capacitor?