Disabling cross overs and bass boost on ppi pc450 - diyAudio
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Old 15th July 2007, 02:47 AM   #1
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Join Date: Sep 2002
Location: Virginia Beach
Default Disabling cross overs and bass boost on ppi pc450

Hello,
I'm now using a PPI PC450 for my mids and highs on an active system.
I opened the amp up and saw that there are a lot of opamps in the cross over and bass boost circuits.
I tried to follow the signal paths but got lost pretty quick, does anyone know where to jump the boards to disable the bass boost and cross overs?
I believe it should be possible...
Thank you.
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Old 15th July 2007, 06:42 AM   #2
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Join Date: Dec 2005
Location: Northern California
Look for the big blue Mylar capacitors. ( 4.7 ufd 100 volt ) There should be one for each channel. These are the input caps for each power amp channel after all that front end control circuitry your trying to get around. You will not have any input gain controls, or crossovers and bass boost and it will be as straight a input as you gonna get on these without going to a fair amount of trouble.

Good luck
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Old 15th July 2007, 07:28 AM   #3
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Join Date: Sep 2002
Location: Virginia Beach
Thank you! that's just what I needed.
I should have no problems building my own gain stage!

Do you know what max input voltage the power amp can take? That would help a lot.
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Old 15th July 2007, 09:34 AM   #4
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Join Date: Dec 2005
Location: Northern California
Quote:
Originally posted by geom_tol
Thank you! that's just what I needed.
I should have no problems building my own gain stage!

Do you know what max input voltage the power amp can take? That would help a lot.

I would imagine that it was setup to accept the full swing of the op-amp stage in front of the Mylar cap.

One sure way to tell is to setup a sig gen and a dummy load and a very stout power supply, and drive a channel into soft clip while viewing on a scope. But thats more equipment then most folks have handy. For me at my bench no problem, Ten minutes and done. But I have never had a call to test this on a PPI as of yet.


You could try a sine wave in and a true RMS meter on the output to determine the clip level as opposed to the drive level, Simplier but effective I am sure.
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Old 23rd July 2007, 11:48 PM   #5
meepers is offline meepers  United States
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Join Date: Oct 2005
or you could trade me your pc450 for my art series 404. then we both get what we want! cept I have a hard time giving up that amp since I have had it for 10 years.

If your getting rid of the xo, what are you going to be using to get your low cutoff? external xo? or just going with passive units for the speaker? I am running a circa 1993 setup in my car as of now... factory HU fed into a Par-245 *I know, but it was a Par-225 untill the volume pot broke, thats fed into an FRX 223, into the a404 for the fronts, and an a300 for the sub * that is, after I get around to fixing the a300*. I had the noise gate for a while, but i could not tell an audible difference with my alpine cda 7949. but I think now with all my compressed media *mp3* it would make a noticable change on the noise floor.
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Old 26th July 2007, 01:05 AM   #6
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Join Date: Sep 2002
Location: Virginia Beach
My HU is an eclipse cd7000. It has active 3 way XO built in.
PM me if you want to trade I am VERY interested.
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