poweramp need a preamp?help urgent pa system

prorms · 26th August 2006, 09:36 PM

the only part I got for the preamp is the 3 band tone controll
but they dont speak the same language with the poweramp
I need a preamp that will increase the sound of microphone just a
1/4 phone jack mic Iam trying to build PA system

prorms · 26th August 2006, 09:37 PM

I know its not impressive

AndrewT · 27th August 2006, 10:34 AM

Hi,
you show 7.13v after R28.
That is too low. Did you measure this voltage?

The R10 to R15 ratio is very high. 47k:100 gives a gain of 471times (+53.5db)!!!

MikeB · 27th August 2006, 11:57 AM

seanmacss, your poweramp does not need a preamp to start to work, it needs a cleanup of mystery parts (r5 for example) and finally a real power supply. (using a +/gnd/- voltage) This floating supply does not look reliable. Reduce R10 to 27k (must be the same as r3) and increase r15 to at least 500ohm.
With the single 56v supply you will get at most ~30watts into 8ohm.

How should the input diffamp work with +5.44v at +input and 6.24mv at -input ?

sorry,
Mike

27th August 2006, 10:34 AM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, you show 7.13v after R28. That is too low. Did you measure this voltage? The R10 to R15 ratio is very high. 47k:100 gives a gain of 471times (+53.5db)!!! __________________ regards Andrew T.

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27th August 2006, 11:57 AM	#4
MikeB diyAudio Member Join Date: Apr 2004 Location: Gütersloh	seanmacss, your poweramp does not need a preamp to start to work, it needs a cleanup of mystery parts (r5 for example) and finally a real power supply. (using a +/gnd/- voltage) This floating supply does not look reliable. Reduce R10 to 27k (must be the same as r3) and increase r15 to at least 500ohm. With the single 56v supply you will get at most ~30watts into 8ohm. How should the input diffamp work with +5.44v at +input and 6.24mv at -input ? sorry, Mike

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