Hello all,
I have a friend who has a small school and was using a home theater amplifier to run 9 speakers that range between 8 to 16ohms. It was all ok as they were connected to the amplifier's different channels never creating a big load (low impedance) on the amplifier.
Knowing that I am an audio enthusiast, he asked me to help him to add a microphone to his system and to make it be able to play music on all channels. And whenever needed, be able to stop the music on a single classroom and play the microphone.
So what I did is buy a PSPVC6 from Pyle. It is a 6 channel high power stereo speaker selector. It has two pairs of speaker inputs, 6 pair of outputs and buttons to select channel A (music) and B (microphone).
Then I connected the selector inputs to speaker output channels A and B of the existing amplifier (Denon AVR-1909). This is a multi-zone amp so I connected the music player to DVD input (RCA) and the wireless mic at CD input (RCA).
It worked good for about 1.5 years until one day, out of the blue, the amplifier started going into protection mode.
It was then that I started to check impedance everywere.
I found that when all speakers are connected to the same channel on the Pyle selector, the load on the amplifier goes down 2 ohms which explains why the amplifier would go to protection mode. However, it doesn't explain why it worked for 1.5 yr.
I adviced my friend to buy a 2ohm stable amplifier such as BEHRINGER EUROPOWER EP2000. However, before buying anything else, I thought post my question here to see what would my fellow audiophiles advice.
P.S. I thought about a 25 or 70 volt system but these would require buying this kind of amplifier and perhaps impedance matching transformers which might be more expensive than buying a 2ohm stable amp. What do you think?
Thank you and Viva HiFi!
I have a friend who has a small school and was using a home theater amplifier to run 9 speakers that range between 8 to 16ohms. It was all ok as they were connected to the amplifier's different channels never creating a big load (low impedance) on the amplifier.
Knowing that I am an audio enthusiast, he asked me to help him to add a microphone to his system and to make it be able to play music on all channels. And whenever needed, be able to stop the music on a single classroom and play the microphone.
So what I did is buy a PSPVC6 from Pyle. It is a 6 channel high power stereo speaker selector. It has two pairs of speaker inputs, 6 pair of outputs and buttons to select channel A (music) and B (microphone).
Then I connected the selector inputs to speaker output channels A and B of the existing amplifier (Denon AVR-1909). This is a multi-zone amp so I connected the music player to DVD input (RCA) and the wireless mic at CD input (RCA).
It worked good for about 1.5 years until one day, out of the blue, the amplifier started going into protection mode.
It was then that I started to check impedance everywere.
I found that when all speakers are connected to the same channel on the Pyle selector, the load on the amplifier goes down 2 ohms which explains why the amplifier would go to protection mode. However, it doesn't explain why it worked for 1.5 yr.
I adviced my friend to buy a 2ohm stable amplifier such as BEHRINGER EUROPOWER EP2000. However, before buying anything else, I thought post my question here to see what would my fellow audiophiles advice.
P.S. I thought about a 25 or 70 volt system but these would require buying this kind of amplifier and perhaps impedance matching transformers which might be more expensive than buying a 2ohm stable amp. What do you think?
Thank you and Viva HiFi!
An amplifier that is 600 (real, not marketing) watts at 8 ohms will drive a 70 volt line directly. A used RMX850 bridged mono works perfectly (300 per channel at 4 ohms). The EP2000 (RMX1450, or any of the clones out there) will sort of drive two 70 volt lines - it delivers about 50 volts per channel. That will work ok, but put out about half power compared to what the sum of the taps is. Won’t hurt anything, and won’t work the amp real hard, just a little under utilized. Bridged it needs to drive a 100 volt line - but the matching transformers are less common. The EP4000 will directly drive two 70 volt lines, and I doubt you’ll ever run out of power. Can run a lot of 30 and 60 watt 70 volt speakers.
Something like a Behringer EP2500 will run 2ohm, probably with enough power to melt the speakers connected, if you were to crank it up.
NB - the EP2500 (more recently it was rebadged to EP4000) has significantly more current capacity than the EP2000 (which was an EP1500).
You could also try used iNukes or the newer NX range. Please bear in mind that fan-cooled amplifiers need cleaning out occasionally. They'll hoover up any nearby dust and coat the heatsinks.
Chris
NB - the EP2500 (more recently it was rebadged to EP4000) has significantly more current capacity than the EP2000 (which was an EP1500).
You could also try used iNukes or the newer NX range. Please bear in mind that fan-cooled amplifiers need cleaning out occasionally. They'll hoover up any nearby dust and coat the heatsinks.
Chris
Using one of the big budget P.A. amps as a 70 volt driver (with a transformer at each speaker) limits the power to each speaker so you don’t melt them, and allows you to add at will until it is fully loaded (add the watts).
If accumulated dust is a problem (it can be) then use a passive cooled amp. If you don’t need as much power - you can find older hi-fi amps that can do 300 watts per channel at 4 ohms and are bridgeable to run 70 volts. Back in those days they over built them so they could be used in light and medium duty P.A. And if you don’t run at full power, ie, only connect “100 watts” worth of load it will be easy on the amp. If you really don’t need a ton of power you could use a Behringer A500. Bridge it and drive a 70 volt line with 50 volts. You get half power and an easy load - like loading the amp down with 16 ohms. Or drive two 25 volt lines in stereo mode and it’s about perfect. 25 volt transformers can still be had - it is less common these days because you can’t run as long a line at 25 as you can 70 due to voltage drop.
If accumulated dust is a problem (it can be) then use a passive cooled amp. If you don’t need as much power - you can find older hi-fi amps that can do 300 watts per channel at 4 ohms and are bridgeable to run 70 volts. Back in those days they over built them so they could be used in light and medium duty P.A. And if you don’t run at full power, ie, only connect “100 watts” worth of load it will be easy on the amp. If you really don’t need a ton of power you could use a Behringer A500. Bridge it and drive a 70 volt line with 50 volts. You get half power and an easy load - like loading the amp down with 16 ohms. Or drive two 25 volt lines in stereo mode and it’s about perfect. 25 volt transformers can still be had - it is less common these days because you can’t run as long a line at 25 as you can 70 due to voltage drop.
Please draw a simple diagram showing current amplifier, rooms, and speakers in them including each speaker impedance.
My point being I presume you currently run them in parallel, which is not needed or advisable, and alternate connections might solve your problem, buying nothing extra.
I often help Schools and Churches, charging nothing, plus they often have nil or zero budget anyway, and rewiring existing bstuff.
A typical example: one of them was loading amp with less than 1 ohm, and amp survived only because thin long completely inadequate speaker wire added a couple ohms in series ... it survived but overheated and regularly self turned off (that was the original complaint) and on again when cooling.
I simply series wired 2 to 4 speakers present ar each place (gym patio, main children assembly hall, eating room, etc.) or speakers along corridors, so each speaker line was from 16 to 32 ohm , with individual "enable" switches ... works like a charm and is my standard solution in such cases.
You "might" do something similar but please give us a block diagram first.
All this based on it being a *small* School.
Larger ones, of course, will need a properly designed and wired 70V system, but then it´s presumed they can afford it, not only the Audio components (amp/speakers/transformers) but also the installation which requires significant manpower.
Hello again!
Thank you all who have replied!
JM Fahey,
I will post a picture of the diagram I made by hand shortly.
Please know that I found out the following:
1. The impedance at the input of the Pyle Selector (what the amplifier sees at its output) goes down to less than 2ohms when ALL the switches are set to one of the channels (A or B).
2. When only one switch is set to a channel, the impedance at the input of the selector is about 8ohms and decreases as more switches are turned to the same channel.
3. The impedance at the input is infinite when no switches are set to that channel.
3. Points 1, 2 & 3 above happen regardless of whether the speakers are actually connected or not.
4. This leads me to think the selector has a bunch (maybe 6 or 12) of transformers inside with 8ohms at their input winding which get connected in parallel as the switches are turned to a particular input channel; ergo the less than two ohms (8/6) measured at the input.
Therefore, I still think the cheapest solution to my friend's problem would be to buy a reputable 2ohm stable amplifier such as the BEHRINGER EUROPOWER EP2000. Then as one of you advised, have the L & R inputs of each channel of the selector connected in series to bring the final impedance that the amplifier would be "seeing" to more than 2ohms.
Please remember the purpose of the speaker selector is to be able to have music in ALL rooms and, when desired, turn off music in one particular room and address it with the microphone.
Again, thank you all!
Viva la HiFi!
Thank you all who have replied!
JM Fahey,
I will post a picture of the diagram I made by hand shortly.
Please know that I found out the following:
1. The impedance at the input of the Pyle Selector (what the amplifier sees at its output) goes down to less than 2ohms when ALL the switches are set to one of the channels (A or B).
2. When only one switch is set to a channel, the impedance at the input of the selector is about 8ohms and decreases as more switches are turned to the same channel.
3. The impedance at the input is infinite when no switches are set to that channel.
3. Points 1, 2 & 3 above happen regardless of whether the speakers are actually connected or not.
4. This leads me to think the selector has a bunch (maybe 6 or 12) of transformers inside with 8ohms at their input winding which get connected in parallel as the switches are turned to a particular input channel; ergo the less than two ohms (8/6) measured at the input.
Therefore, I still think the cheapest solution to my friend's problem would be to buy a reputable 2ohm stable amplifier such as the BEHRINGER EUROPOWER EP2000. Then as one of you advised, have the L & R inputs of each channel of the selector connected in series to bring the final impedance that the amplifier would be "seeing" to more than 2ohms.
Please remember the purpose of the speaker selector is to be able to have music in ALL rooms and, when desired, turn off music in one particular room and address it with the microphone.
Again, thank you all!
Viva la HiFi!
You will want to high pass filter a 70 volt system, the small transformers on your everyday ceiling speaker don't want to see much below 100hz. Too much low frequency level will saturate the transformer and it will look like dead short to the amp.
The larger the transformer the more low frequency it can handle.
With clean power, good speakers and good transformers and 70 volt system can sound decent.
The larger the transformer the more low frequency it can handle.
With clean power, good speakers and good transformers and 70 volt system can sound decent.
when submitting a post use the GO ADVANCED tab on the right, the new text editor window will display a bunch of new features look for the "paper clip" symbol that will allow you to attach pictures.
Hello all,
Please find a sketch of the current system attached.
Note that none of the speakers have a transformer, as they are regular home theater speakers.
Also, the speaker selector creates a load of 2ohms on the amplifier when all speakers are guided to one channel.
In my mind it is still cheaper to buy a reputable 2ohm stable amplifier at $250 USD and keep the current speakers and current selector than buying a new 70v amplifier, speakers with transformer or transformers to go with current speakers... What do you think?
If you think going to the 70v system is better, please provide examples of a good amplifier and speakers.
Again thank you all afor your input!
Please find a sketch of the current system attached.
Note that none of the speakers have a transformer, as they are regular home theater speakers.
Also, the speaker selector creates a load of 2ohms on the amplifier when all speakers are guided to one channel.
In my mind it is still cheaper to buy a reputable 2ohm stable amplifier at $250 USD and keep the current speakers and current selector than buying a new 70v amplifier, speakers with transformer or transformers to go with current speakers... What do you think?
If you think going to the 70v system is better, please provide examples of a good amplifier and speakers.
Again thank you all afor your input!
Attachments
If you really really want to go cheap all you need is a $50 mixer. You do have four amplifier channels not two. Just feed all four the same signal and you can drive all your speakers at once. Put multiple speakers that are in each room in series to raise their impedance. Then put no more than two rooms in parallel on each amplifier channel.
Thank you for your reply.
Doing what you suggest will not allow me to address one classroom at a time with the mic while leaving music for the others.
If you have 100 speakers then yes use a 70V system, but each transformer looses 1.5dB so between the amp transformer and the speaker transformer, you loose half (3dB) the audio power. And only very expensive 70V transformer are fit for music. Also, any amp with VI protection will puke when connected to a transformer ~zero ohms DC.
So, If you have only a dozen speakers, you should series parallel them. You will get more power even with #18 wire, and better sound than using transformers. This does not allow local volume controls.
It is most likely that some electrician changed the wiring on you, or the amp has developed bad electrolytic caps.
So, If you have only a dozen speakers, you should series parallel them. You will get more power even with #18 wire, and better sound than using transformers. This does not allow local volume controls.
It is most likely that some electrician changed the wiring on you, or the amp has developed bad electrolytic caps.
Actually it's more like 1ohm and that isn't going work. There is an easy solution that won't cost any money, for each room that has more than one speaker simply wire those two speakers in series. That will raise the overall impedance when all speakers are selected but still allow the mic to be addressed to individual rooms.
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