Adding pre-out to an integrated amp

[schubert]

I have a Kenwood integrated amp that I use at work to which I'd like to add a pre-out jack for use with a sub. I'm not exactly sure about where to tap in - for one thing I can't find the volume control on the schematic (attached). My thought at this point is to attach wires to pins 3 & 15 of the preamp board, which would catch the signal between the pramp and amp boards. But...there is (+) and (-) going from the preamp board for each channel as well as a ground. The (-) is connected to ground through a 2M resistor. It looks like a balanced connection, but this amp has not balanced connections anywhere else. Or is it running on a virtual ground? Should I just connect to the (+) terminals and ground?

[Tekko]

I use to just tap the output from the volume control, run through a dual opamp as a buffer and then mix the two channels to mono through two resistors in the 5-10kohm range and then run out the signal to a rca jack on the back.

[schubert]

OK thanks Tekko. I think I can do that - my skills are pretty much limited to kit-building, and jerry-rigging stuff like this is kind of new to me. I suppose I'll have to find a power supply for the opamp somewhere (I have a few extra 2134's). I don't have to sum the channels since my sub has R-L line level inputs.

[schubert]

Is this how you would wire the opamp?

[Tekko]

Yes thats a opamp buffer with unity gain. Just tap the signal after the volume control, like at the wipers on the dual gang pot, run to the opamp buffers and then out to the pre out jacks.

The opamp buffers are there to buffer the signal so the input impedance of the subamp doesent affect the signal in the main amp.

[Frank Berry]

Or you could just mix the speaker outputs using a couple of 10k resistors and feed the combined signal to the input of your sub. If the level is too high, add a 1k resistor to common ground on the output of the 10k summing resistors.

[schubert]

OK thanks gentlemen. I'll give this a try, if I can find the volume control taps - the pot itself is inaccessible behind a board, so I'll have to tap in at a connector behind the board, if I can figure out which connection is which.

[sreten]

Hi,

The simplest is simply to use a couple of resistors for mixing and a much lower
one off the speaker outs of the amplifier. Most sub plate amplifiers have this
fitted as a high level input. There is no advantage to not doing it this way.

rgds, sreten.

[Woody1911a1]

Originally Posted by sreten

Hi,

There is no advantage to not doing it this way.

rgds, sreten.

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[sreten]

Originally Posted by Woody1911a1

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Hi, as it says on the tin, a subout is a subout however you do it, rgds, sreten.