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Old 20th April 2013, 01:07 AM   #1
diyAudio Member
Join Date: Oct 2010
Default 100V line test amp

Hi guys,
working as an AV service tech, I have found the need for a portable amp to test 100V line systems.
I was thinking along the lines of this circuit by silicon chip

I'm guessing the ouput of the LM386 will be too low to run more than a few speakers tapped at 40W.

Would I be able to use a 20W / 40W bridgemode amplifier (ah-la radioshack) instead?
Can i still use a speaker transformer in reverse, as per the sil-chip circuit?
Can i (long shot) make it battery portable?

any help is .... helpful
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Old 29th April 2013, 09:11 PM   #2
PetruV is offline PetruV  Romania
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Join Date: Dec 2012
Location: Bucuresti
You can use a tda 2003 powered by a 12v battery with a reverse speaker transformer at the output
Just a kid who likes building and modding things.No inspirational quote here for you
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Old 30th April 2013, 12:27 AM   #3
diyAudio Member
Join Date: May 2009
Location: New Zealand
Yes, a cheap chip amplifier driving a mains transformer in reverse will do. No need to use a proper audio transformer if it is just for testing. For example, for an amplifier rated at 10W into 8 ohms, that's about 9 volts RMS. Use a 10 watt transformer with a 24V secondary and 230V primary , or 12V secondary and 110V primary.
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Old 30th April 2013, 12:39 AM   #4
DUG is offline DUG  Canada
diyAudio Member
Join Date: Jan 2003
Location: mississauga ontario canada
You don't need to test the 100V system at 100V.

If you do then you will have to provide the total amount of power the speaker taps are set at.

If you have (for example) five set at 10W tap and 3 set at 20W tap then to operate at 100V you will need a 110W amp.

If you operate the same load at 10V you will need only 1.1W.

Start looking at it this way and you might have an easier goal for your portable test set.

If you designed a test set to produce 10Vrms and you monitored the current into the system, then you could calculate the total loading that has been placed on the 100V system.

Just an idea.

It is just math.
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."
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Old 7th May 2013, 11:30 PM   #5
opcom is offline opcom  United States
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Join Date: May 2008
Location: Texas
Use a 400Hz filament transformer from some aircraft junk. Very small size for the power. 6.3VAC ->115VAC. a 0,5A or 1A winding is plenty for most uses.
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