"Un-integrating" an integrated amp

[Dave Jones]

I posted this in another group, but I think I probably posted to the wrong group. [Mr. Moderator, please feel free to remove either this, or the one in the "electronics" group.]

Hello folks. I've been learning quite a lot over in the loudspeakers group. I think this is probably my first posting here. Naturally, it's because I'm looking for help. :-)

I am using a powered subwoofer and an external crossover (Richter Scale) with a Rotel RA-02 integrated amplifier. The amp has a preamp-out, but no main-in. So currently I'm running the subwoofer through the low-pass of the crossover, and running the mains fullrange.

Can anyone tell me how run the mains through the high- pass of the crossover? I've asked the place I bought the RA-02 from if I could get the schematics for it, but they were not keen on the idea.

I'm thinking there's probably a single place where the pre-amp feeds the main. I could clip those wires and run them to a couple of RCA females added to the back of the cabinet.

Stupid idea?

[HDTVman]

Dave Jones, does the amp have a tape monitor loop? If so:

1. connect the tape out to the crossover input.

2. connect high out to tape in

3. low out to powered subwoofer input

Now by turning on and off the tape loop you can hear the difference between full range and high pass to you main speakers.

Later BZ

[Dave Jones]

Originally posted by HDTVman
Dave Jones, does the amp have a tape monitor loop? If so:

1. connect the tape out to the crossover input.

2. connect high out to tape in

3. low out to powered subwoofer input

Now by turning on and off the tape loop you can hear the difference between full range and high pass to you main speakers.

Later BZ

I thought of doing that, but then the volume control knob on the amp won't turn the sub up and down will it?

[Added a minute later.] I tried it. As expected, the volume control has no effect on the sub. However, it does let me hear what it would sound like if I *could* hook it up properly.

[Added a few minutes later yet.] Hmmmm. I think I see what you are getting at. It's very hard to tell any difference at all. Maybe I don't need to muck with the amp after all.

But I would still like to have pre-out and main-in. I had an NAD integrated amp years ago that had that feature, and I thought it was nifty. It came with some little bridge connectors to run pre-out into main-in when you weren't using an external processor. Why aren't ALL integrated amps made that way, rather than virtually none?

[HDTVman]

Your correct about the volume control. I'd get the schematic for the unit and see if I could find where the point is that the preamp output and the normal amp split up. Most likely just after the volume control. You could open up the circuit going to the power amp there and route the amps input to jacks on the back panel. Be sure to use caps to protect the amp input and be sure to provide a DC / grd. reference for the amp if it's DC coupled.

Of course this is at your own risk you know.

Later BZ

[leadbelly]

Originally posted by Dave Jones
I'm thinking there's probably a single place where the pre-amp feeds the main. I could clip those wires and run them to a couple of RCA females added to the back of the cabinet.

Open it up and have a look. Most likely the preamp PCB and power amp PCB's are distinct and tracing the signal will be easy.

[Dave Jones]

I obtained the technical manual from the US service reps for Rotel (twenty bucks post-paid), and did the mod. I appropriated the "Aux 2" input for the new main-in, so I didn't even have to drill any holes in the box. It was surprisingly easy. I posted on the Solid State bb offering to describe how to do it, but no one appears interested.