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 PA Systems A forum for discussion of all parts of a sound reinforcement or DJ system: loudspeakers, mixers (desks) etc.

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 19th October 2012, 03:30 PM #1 diyAudio Member   Join Date: Jul 2010 help understanding PA amplifie hi I have this pair of audio Telex PA 500SB amplifier. Its rated 500W on 100V line with minimum permissible impeance of 20 Ohm It also has a 4 ohm tap (which is on emitters of out put resistors) and it has minimum 2ohm permissible impedance load. Question. Each amp has a pull push mechanism through output transformer. so 2 ohm load is actually a bridge load between two output devices out of phase. The rail voltage is 34V supply. In bridged mode the amplifier will see the impedance dropping to 1 ohm. With this load the peak to peak voltage swing available is around 32V , so peak is 16V and rms =0.707x16=11.32V RMS So RMS current =11.32V/1 ohm=11.32A Power available RMS=VxI=11.32*11.32=128Watss??? Should i take peak voltage swing as 32V instead of 16v ? in that case Rms Voltage 32x 0.707=22.62V and Power RMS=22.62V x 22.62A = 511 WATTS. I am asking is because i intent to run 2 , 4 ohm car speakers on each amplifier and want to be sure of its rated power ???? would it devlier 500W or 128 W RMS . Regards
 19th October 2012, 03:40 PM #2 diyAudio Member   Join Date: May 2007 If it is bridged then peak voltage swing is a bit less than supply rail, not half supply rail.
 19th October 2012, 03:55 PM #3 diyAudio Member   Join Date: Jul 2010 thanks so peak is around 32V and Vrms=22.62V , then would i take current draw on nominal 2 ohm load as 2 ohm or 1 ohm as the bridged amp would see it. because in case it sees it as 1 Ohm the power available would be 520W and if it sees it as 2 ohm then it would be 250W ??
 19th October 2012, 04:17 PM #4 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders This seems to be a very similar enquiry raised by you in another Thread. What are you upto? __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 19th October 2012, 05:53 PM #5 diyAudio Member   Join Date: Jul 2010 yes. The query was earlier under solid state diy so it seemed appropriate to post under PA systems instead. The intention is to make single ended class A fully balalnced. i have removed the output transformer and connected each emitter with 4 Ohm resistors, with 4 A continous the output and resistors heat up pretty much and bias point ri.ses steeply. Quiscent current of 2A seems to be ok but keeps the voltage swing to 8V limit and availabe current is also limited. The sound is very very very good. switching between krell FPB and this makes me wondet which is better, although the power and bass slam is limited but the mid range is very soft and warm and highs are very pleasent. So i am trying to figure out is how to get maximum power from this amp. for this i need to understand how much quiscent current can i optimaly flow through them (i will also be incresing the heat sink size substantially) , i have already added 2x90000 uF 40V capacitor bank in parallel with the existing 40000uF and has significantly reduced hum and i intend to add 0.22Ohm resistor in series before adding another pair of 90000 uF making CRC which will significantly reduce ac ripple, the ac ripple i measured at 2A with 40000uf Was 1.9V which reduced to 0.16V . The third improvedment i intend is to make a current sink with say 3-4 A current sink limit base diversion bjt so Iq may be kept at check , improve linearity in ouput and improve ripple rejection further. for this i need to know that under this scheme to make Ve=16V what should be the Iq for this sytem. regards
diyAudio Member

Join Date: Dec 2010
Location: fatehpur
Quote:
 Originally Posted by muddasirwaheedmalik hi I have this pair of audio Telex PA 500SB amplifier. Its rated 500W on 100V line with minimum permissible impeance of 20 Ohm It also has a 4 ohm tap (which is on emitters of out put resistors) and it has minimum 2ohm permissible impedance load. Question. Each amp has a pull push mechanism through output transformer. so 2 ohm load is actually a bridge load between two output devices out of phase. The rail voltage is 34V supply. In bridged mode the amplifier will see the impedance dropping to 1 ohm. With this load the peak to peak voltage swing available is around 32V , so peak is 16V and rms =0.707x16=11.32V RMS So RMS current =11.32V/1 ohm=11.32A Power available RMS=VxI=11.32*11.32=128Watss??? Should i take peak voltage swing as 32V instead of 16v ? in that case Rms Voltage 32x 0.707=22.62V and Power RMS=22.62V x 22.62A = 511 WATTS. I am asking is because i intent to run, 2 , 4 ohm car speakers on each amplifier and want to be sure of its rated power ???? would it devlier 500W or 128 W RMS . Regards
dear sir
from where you got this amplifier and what was the price?
thanking you

 2nd November 2012, 05:41 AM #7 diyAudio Member   Join Date: Jul 2003 Location: Dona paula, Goa What is single ended... You seem to use these terms out of your thinking. Gajanan Phadte

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