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Low Pass [message #91156]

Thu, 14 November 2019 07:39

Barryso
Messages: 209
Registered: May 2009

Master

Discovered some very weird component matching issues when adding subs to the system.

My plate amp is mono and if you cross it over at 100 hz it sounds odd as mono doesn't work quite right at that frequency. Borrowed a Crown amp and some 100hz 2nd order low pass fmods to use the subs in stereo.

The fmods evidently do something weird with impedance. Simply putting the fmods on the rca plugs (the rca's that will be plugged into the sub amp) dramatically lowers the volume of the main speakers. There's also a frequency shift and the highs and lows seem to just vanish.

This happens before the cable and fmods get plugged into the sub amp. Just putting the fmods on the end of the RCA cable is enough to do it.

The tube preamp has a 200 ohm output impedance going into a solid state amp with a 10k input impedance. The same ugly trick happens when using a solid state preamp with an output impedance of less than 1 ohm. Perhaps it isn't quite so dramatic with the solid state preamp but it's still enough of a change to make the fmods useless.

The borrowed amp is a Crown XLS that has a built in 4th order crossover. The internal crossover is FAR better sounding than the fmods but it doesn't have the preferred 2nd order low pass.

So it's time for plan b. Parts Express has a speaker level crossover that's 100 hz lowpass and is 2nd order. How about a pair of these with a volume pot connected to the speaker outs of a nice Texas Instruments class d amp? Would it make a good sub amp? By putting the crossovers and volume control on the output side of the amp it should bypass the preamp/amp impedance issues.

https://www.parts-express.com/parts-express-100-hz-low-pass-8-ohm-crossover--266-446#lblProductDetails

Has anyone used these or have any idea of their sound quality? Is this a plan or is there a gotcha that I'm not considering?

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[Message index]

		Low Pass By: Barryso on Thu, 14 November 2019 07:39
		Re: Low Pass By: Wayne Parham on Thu, 14 November 2019 10:56
		Re: Low Pass By: Rusty on Thu, 14 November 2019 16:44
		Re: Low Pass By: Wayne Parham on Thu, 14 November 2019 17:39
		Re: Low Pass By: Rusty on Sat, 16 November 2019 08:32
		Re: Low Pass By: Wayne Parham on Sat, 16 November 2019 11:13
		Re: Low Pass By: Rusty on Sun, 17 November 2019 09:09
		Re: Low Pass By: Wayne Parham on Sun, 17 November 2019 14:51
		Re: Low Pass By: OutOfSpace on Sun, 17 November 2019 17:58
		Re: Low Pass By: Wayne Parham on Sun, 17 November 2019 18:39
		Re: Low Pass By: Rusty on Mon, 18 November 2019 10:45
		Re: Low Pass By: Barryso on Mon, 18 November 2019 14:11
		Re: Low Pass By: Wayne Parham on Mon, 18 November 2019 15:07
		Re: Low Pass By: Rusty on Tue, 19 November 2019 11:26
		Re: Low Pass By: Barryso on Mon, 18 November 2019 16:15
		Re: Low Pass By: Barryso on Wed, 20 November 2019 08:19
		Re: Low Pass By: Rusty on Wed, 20 November 2019 09:23
		Re: Low Pass By: Barryso on Sun, 02 February 2020 07:22
		Re: Low Pass By: Barryso on Sun, 02 February 2020 07:27
		Re: Low Pass By: Rusty on Sun, 02 February 2020 10:44
		Re: Low Pass By: Barryso on Mon, 03 February 2020 18:23
		Re: Low Pass By: Rusty on Tue, 04 February 2020 11:21
		Re: Low Pass By: Barryso on Sat, 15 February 2020 07:04
		Re: Low Pass By: Rusty on Sat, 15 February 2020 10:53
		Re: Low Pass By: Barryso on Thu, 26 March 2020 16:05

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