garyvp
Active Member
We use an inexpensive Radio Shack 40 amp PA amplifier to monitor the performance space. We have five circuits and 6 speakers (control booth, dressing room, etc) branching off the output, each with a good quality volume control on the speaker. Most speakers are small, cheap, and from 6-8 ohms impedance. The system has worked fine for years.
However, we have fried several amps in the past two years and I cannot figure out why. Some facts:
• If I meter (I use a Fluke) each speaker I get the name plate impedance at the speaker and on the input site to the volume control.
• The home runs to the amp are anywhere from 50 to 150 feet. Wire varies from 16 to 20 AWG.
• All lines have been tested for continuity, shorts or loose connections
• If I measure resistance at each circuit at the amp, there is a drop. A speaker with a reading of 8 ohms reads 4 ohms right before the amp (when disconnected from the amp). This pattern I consistent with single and double speaker set ups (I expected this for two 8 ohm speakers, but not for singles).
• The resistance of all of the speakers wire together is 3.8 ohms.
• The amp has out puts for 4,8,16 ohms.
• We are using the 4 ohm connection
I was considering placing an impedance matching volume control between the amp and the junction for all the speakers coming in and getting it up to 8 ohms and then use the 8 ohm output.
Any suggestions?
However, we have fried several amps in the past two years and I cannot figure out why. Some facts:
• If I meter (I use a Fluke) each speaker I get the name plate impedance at the speaker and on the input site to the volume control.
• The home runs to the amp are anywhere from 50 to 150 feet. Wire varies from 16 to 20 AWG.
• All lines have been tested for continuity, shorts or loose connections
• If I measure resistance at each circuit at the amp, there is a drop. A speaker with a reading of 8 ohms reads 4 ohms right before the amp (when disconnected from the amp). This pattern I consistent with single and double speaker set ups (I expected this for two 8 ohm speakers, but not for singles).
• The resistance of all of the speakers wire together is 3.8 ohms.
• The amp has out puts for 4,8,16 ohms.
• We are using the 4 ohm connection
I was considering placing an impedance matching volume control between the amp and the junction for all the speakers coming in and getting it up to 8 ohms and then use the 8 ohm output.
Any suggestions?