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[Jon McElvain]

We have a 70V amplifier that is on it's last leg due to being in a stack for an unknown many years even though it only has vents top and bottom.  It stops working from time to time so a replacement is needed.  We use it to power the various speakers throughout the church hallways and classrooms.

I'm thinking that something like a Rolls RA170 Mono Power Amplifier - 70V/70W Audio Distribution for under $200 from B&H might do the trick.  There is only one connection on the current amplifier so I think a mono amplifier would be sufficient.

What do I need to know about these amplifiers?

[Tom Bourke]

What is the make and model of the existing amp?  Has the existing system been changed since original install?  70 volt systems tend to be fairly robust unless some one has miss wired something.

[Ivan Beaver]

We have a 70V amplifier that is on it's last leg due to being in a stack for an unknown many years even though it only has vents top and bottom.  It stops working from time to time so a replacement is needed.  We use it to power the various speakers throughout the church hallways and classrooms.

I'm thinking that something like a Rolls RA170 Mono Power Amplifier - 70V/70W Audio Distribution for under $200 from B&H might do the trick.  There is only one connection on the current amplifier so I think a mono amplifier would be sufficient.

What do I need to know about these amplifiers?

First you need to know the wattage of the load on the amp.  This is done by adding up the wattage taps on ALL of the speakers and then adding 10% or so.

Or you can measure the IMPEDANCE (NOT DC RESISTANCE) by doing an impedance sweep.  single tone tests don't always tell the whole story-especially if at the test freq the impedance is higher than normal.

Are you sure it is the amp-and not a break in the line somewhere?

[PAULBORDON]

Try looking for the same amp on "the bay" should be able to find it very reasonable used...

[Jon McElvain]

The only way to get the amp working again that I could find was turning the volume on the amp way up. There is a needle that gives an indication that an input signal exists and it just goes dead from time to time. It seems to start having issues after being on for about half the service.  It doesn't seem to he hot to the touch, but we know it has been without ventilation for a long time, probably 10 years. I have no idea how old it is, but can check the manual the next time it am at the church.

[Jon McElvain]

Ivan - would I be ok to just make sure I match or exceed the wattage of the current amplifier?  It has been working for over ten years, possibly a lot more, and just recently started having issues. Nothing has changed in the system that I am aware of. I will verify the signal source again, but I am fairly sure more than one of us has checked that previously when the issues started.

[Mike Caldwell]

-Double check that you have good signal at the input to the amp.
-What is the make and model of the amp you have now.
-How many speakers are on the 70volt system.
-Are they just plain old ceiling speakers, the kind with a $5 speaker fastened to a metal perf grill or something a little more refined.
-What are they tapped to.

An amp that's rated at 600 watts into 8 ohms will drive a 70 volt system.
If you do need an amp and it only needs to be single channel the budget Crown XLS1000 bridged will do the trick. It has the added benefit of a basic internal DSP that will allow for adjustable high pass filtering, key to good 70 volt operation. That amp maybe a little over kill for you but they can had for about the same cost as decent 70 volt amps while offering most likely a better over all amp and direct drive output.

[Ivan Beaver]

Ivan - would I be ok to just make sure I match or exceed the wattage of the current amplifier?  It has been working for over ten years, possibly a lot more, and just recently started having issues. Nothing has changed in the system that I am aware of. I will verify the signal source again, but I am fairly sure more than one of us has checked that previously when the issues started.

Yes you can run an amp that has a greater wattage capacity.

As long as the actual levle coming out of the speakers is the same-you will be fine.

It is never a bad idea to run a larger amp

[John Roberts {JR}]

It is still worth troubleshooting before investing in a new amp.

Amplifiers generally do not fail gracefully so if it is working intermittently that suggests a possible bad connection in input or output side. Less likely but possible source of intermittence is thermal shut down.

To troubleshoot input side, provide a known good audio source. For output side disconnect speaker wires and connect one speaker. A normal (not 70v) speaker could be connected with amp volume turned down.

If you determine that the amp is sick and not worth repair, then replace.

JR

[Jonathan Johnson]

The only way to get the amp working again that I could find was turning the volume on the amp way up. There is a needle that gives an indication that an input signal exists and it just goes dead from time to time. It seems to start having issues after being on for about half the service.

I'm guessing that there is a component or connection on the input that is failing, and turning up the input signal breaks through some resistance barrier. The problem might be somewhere between the volume control and where the meter taps off. It might be the volume pot itself.

[ProSoundWeb Community]