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Old 9th October 2007, 09:12 PM   #1
skogs is offline skogs  Norway
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Default input sensitivity too low on PA-amp

hi. when i connect my pa-amp to the subwoofer-preout on my main amp, i have to turn the pre-amp output and the input gain on the pa-amp to the max to get enough volume on the subwoofer. so i need a curcuit which increases the signal strength so it matches the pa-amp! (775mV i think)

whats a such curcuit called? can i find something like that on esp's pages? (going to order some stuff from there soon)

Řyvind
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Old 9th October 2007, 09:49 PM   #2
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Default HI!

What tipe of power amplifier is in the subwoofer encl.

Btw. do you have schematic of sub.amp.

Re3gards zeoN_Rider
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Old 9th October 2007, 10:04 PM   #3
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You just want a gainstage. How you do that depends on your preferences and what you have. A simple opamp cct would do.

If the poweramp for your mains is seperate, just pad the signal level down on that to match. Two resistors per channel and 10 mins work.
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Old 9th October 2007, 10:21 PM   #4
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Default Hi!

Two resistors per channel and 8 mins work,thats how I would do.

I think.

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Old 9th October 2007, 10:29 PM   #5
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Old 9th October 2007, 10:43 PM   #6
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PA-amps often need higher level than line level (preamp output). The old school mix boards do this and act as the preamp. Depends on how much you want to spend or how much time to invest. The easy and expensive way is to buy a preamp. The longer, more fun and may be cheaper way is to build a little opamp circuit to act as your preamp. I guess the fast and cheap way might be to get a used mix board, a simple one from DJ or PA systems. It will do the preamp for you.

-SL
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Old 10th October 2007, 06:50 AM   #7
skogs is offline skogs  Norway
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i will be using a H\K avr245 as main amp. and TA2400 PA-amp for the subwoofer. im going to build a preamp for it, including 8-band eq, individual phase controll, adjustable lowpassfilter, a rumble filter, and now hopefully a gainstage.
Is a such gainstage complex to build? anyone have design for me?

the power amp for my mains are not seperate by btw.
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Old 10th October 2007, 07:17 AM   #8
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Whatever design you choose will likely have an input and/or output buffer which will most likely be an opamp. Change one or two resistors in the feedback network(s) and you'll be able to set it over a range.
Edit: most will probably have a level control anyway.
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Old 10th October 2007, 09:15 AM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
an input buffer with +6db to +12db of gain would do.
It might be much simpler than that.
Can you post a schematic of the amp?
It may be possible to change the gain of the amplifier. It might just be one resistor that needs lowering to effect the +6db gain change.
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Old 10th October 2007, 10:31 AM   #10
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Quote:
PA-amps often need higher level than line level (preamp output
Most PA amps and most commercial amps only require a signal of .775 to achieve full power. The home line of products however require usually 1.00-1.50v to achieve full power.

Like Andrew mentioned in his post an input buffer of +6- +12 db
of gain would probably do the job. It is probably a far smarter thing to do than to raise the gain of the amplifier.
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