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Old 22nd February 2005, 08:36 PM   #31
diyAudio Member
Join Date: Nov 2004
Location: The Sticks, NS
Default Re: Too many op-amps?

Originally posted by hermanv
Your design is probably being driven from a pre-amp or other low impedance source. The input buffers on the HP seem redundant. In my book fewer op-amps is a good thing. 2nd The summing resistors at 100K seem higher than needed lower values typically sound better.

Most pre-amps have output impedances in the 100 Ohm range many solid state pre-amps could be as low as 5 Ohms often lower than most op-amps.
The summing resistors were reduced if you look at the updates of the schematic I have made as the thread progressed.

The problem is my signal could be coming from my soundcard, PS2, VCR ,etc... So I would be assuming they all have a low output impedance. Is this safe to assume?

Without the first buffers my circuit would look like this:

Will this work?

edit: i notice R8 will have to be changed to from 3k3 to 10k now, not that it makes much difference
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Old 23rd February 2005, 12:04 AM   #32
diyAudio Member
Join Date: Nov 2004
Location: The Sticks, NS
I'm gonna need a preamp for a volume control if I want to hook up anything but the computer directly. My apologies,I was getting ahead of myself.

So I can build the circuit without the input buffers to hook up to my computer and if that doesn't work I will use a preamp with a volume control as a buffer because I'm gonna have to build this simple preamp for other inputs anyway.

I really wish I had a receiver with preouts...
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Old 23rd February 2005, 12:06 AM   #33
jleaman is offline jleaman  Belgium
Join Date: Apr 2002
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Originally posted by merlinx76

I really wish I had a receiver with preouts...

Make one : O ) it's simple message me ill show you. : O )
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Old 23rd February 2005, 12:25 AM   #34
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Join Date: Nov 2004
Location: The Sticks, NS
My intention was for this to be a temporary fix until I get a good reciever with a better built-in crossover. (Then I'll have the problem of a 4th order acoustical HP with only a 2nd order LP but I still wont be able to use this circuit because I'll need the front channels to be powered by the receiver and the DAC too.)

Originally posted by jleaman

Make one : O ) it's simple message me ill show you. : O )
I am going to put a preamp circuit in with the crossover.

If you mean make a DIY HT amp, I would like to but it's just cheaper to buy and guaranteed to work as a bonus! (I don't think I am up to the task.)

I haven't even looked at how to build a DAC as the whole idea sounds scary to me.
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Old 23rd February 2005, 05:12 PM   #35
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Join Date: Nov 2004
Location: The Sticks, NS
I couldn't wait so I built a Linkwitz transform on a breadboard. And it actually worked right away! I get a small 60hz buzz but not much.

It seems like the subs are gonna reach Xmax before the mains... I may not even need a HP for the mains.

I am glad I didn't get a 250W plate amp like I had considered because I got the clip indicator to flash on my 370W amp and the subs could still take more. I may have to change the wiring for 2 ohm rather than 8 ohm.

Its just damned hard to get under 25hz with any amount of SPL.

edit: I gonna have to try better positioning for the subs....Walking around the room reveals how much I can achieve. Every little knicknack throughout the house vibrates even way at the other end of the house.
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