Speaker to line level adapter circuit question.

[Flatlander]

I know it can be done with a transformer type adapter or direct box, guitar players call it.

What I would like to do, instead, is not introduce anything into the signal path from my amp to my main speakers. Keeping that path completely pure, I want to supplement the lows with a separate XO, EQ, amp and sub, very similar to a plate amp install, but I already own a good electronic crossover and a nice amp.

Then using maybe a separate cable in parallel with the amps out, add a resistor circuit that will take the 5 Watts/8 ohms from the amp and allow me to plug it directly into a line level input on an active crossover from the power amp out. The crossover has an input impedance of 15K.

In other words I need to drop 6 or 7 volts down to 0.75V

What do I need to do?

I don't want to use a plate amp with a built-in crossover, because I want the main speakers to run full range without being handicapped by a crossover circuit. I already have a number of high quality electronic crossovers to add bass to the natural roll off of the fullrange driver.

Any suggestions will be very helpful. Thanks.

[rpapps]

Hi Flatlander
A 120K resistor in series with the feed to the crossover should do the trick. With the 15K input impedance, this should give you about a 10:1 reduction in voltage.
Cheers
Rob

[Nigel Goodwin]

While a single resistor can work fine, it's entirely dependent on the input imedance that it's feeding, so it's not normally done that way. By adding a second resistor you create a standard 'L' attenuator, and this provides a far more useful lower impedance output.

[Flatlander]

Thanks, guys,

That gets my mind working in the direction I need to go.

I may not have been very clear in my original question. I'm going to try again and maybe it will make more sense with a little more info.

I have a 5 watt tube amp for the main fullrange speaker that I want to corrupt as little as possible. I want to add an electronic crossover to the speaker out, through the XO's line level input at 0.75V.

An L-pad sounds like the way to go, but 120K seems too high for the resistance in an 8 ohm speaker circuit, but I don't really know.

Can it be done this way or not?

[richie00boy]

I use a series 1.8k resistor with 200 ohms to ground to get a 10:1 reduction, which feeds line level inputs. This is a simple conventional attenuator, the crossover taps off the 200 ohm resistor.

The only issue as I see it is that the bass from tube amps with their output transformer is poor - both in lack of depth and tightness of sound, so the resultant sound from the sub will be poor also.

Also, having an output transformer will likely mean that the speaker side is not grounded anywhere.

I made a little pre-out box for my mate to go between the source and tube amp.

[Flatlander]

Thanks for your help.