amp that allows for remotely located line level controls? - diyAudio
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Old 27th December 2010, 05:08 AM   #1
thasp is offline thasp  United States
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Join Date: Dec 2010
Default amp that allows for remotely located line level controls?

Hi,

This is a long winded question concerning a multiple room system. Let's say 10 different 2 way coaxial in wall/in ceiling speakers, playing the same signal, which amounts to singing with a keyboard or organ in the background. Or another instrument like a clarinet, or a violin. It comes off the aux of a mixer.

At first I looked at series parallel. It seemed like it would be difficult to have attenuators in this system, near each speaker, and like it would be less flexible in the long term to add to the system opposed to something that is parallel throughout, especially when considering the 10 speakers may be on different levels of the building.

Then I looked into the idea of a 70v system. This seemed great. I have a quality amp that puts out almost 1100 into 4 ohms, which gets me in the mid 60s for output voltage, close enough that I may only need a 70v transformer for each speaker and not an output transformer on the amplifier.

The issue with this idea would be the transformers. Transformer loss, transformer cost. Also, the idea of attenuating the signal once it's come out of the amplifier. This seems like it would add unnecessary cost, but primarily the signal degredation is what I was concerned with. Why have a 70v transformer on a speaker level signal when it doesn't have to be there?

It made me wonder about the idea of using a 5.1 amplifier. Even a multichannel amp that had an attenuator pot for each channel. This way I don't have to worry about transformers, or the load since each speaker or 2 speakers could share a channel. If I have 5 channels and 10 8 ohm speakers, I have 5 channels each driving a 5 ohm load. With the content played, desired playback volume, and size of the rooms these are going into, each channel will barely be used enough to make the amp warm, and each channel is only powering 4 ohms. Lovely, I think.

The problem with this approach becomes splitting the signal to each input channel of the amplifier, since it is the same signal that would be amplified by 5 channels. The main problem is also adjusting it from the listening position, which can be 200-400 ft away from the amplifier.

I couldn't help but wonder if something more electronically "elegant" were possible, in the new world of digitally controlled analog tapering of audio signals. There is a knob on the front of most PA amps that allows you to adjust the level of that channel. It is not attenuating the speaker level signal, it's attenuating X, X being X --} pre driver --} driver --} output transistors --} speakers. The gain stage behind all the others in the amplifier. Having the level adjusting going on there in a product with 5*-10 output channels seems far more elegant for my desired application.

Is there an amplifier that exists that allows me the ability to move this function from the amp's front panel to the speaker'ss location? way to adjust this REMOTELY? To move that pot's function
I give it 1 input signal, that it splits to 5 or 10 speaker level outputs. I can control the speaker level output for each speaker, inside the amp so I have a system where the attenuator I put next to the speaker goes back to the amplifier and tells the amplifier to turn the signal up or down in the early gain stages before it hits the pre driver/driver/output transistors.
In simpler terms, instead of attenuating the actual speaker level signal, the little dimmer I put next to the speaker tells the amp to turn down the line level op amp driving the predriver/driver/output transistors that create the speaker level signal for that speaker.

My follow up questions

a) Is it that such a system exists but my total ignorance on this subject has blinded me to its presence? My theory is that it is and that I am just too ignorant on this particular faction of the craft to know where to get what I want. I really hope this is the case, I love learning new things and if this exists it'd make my life so much simpler.
b) Is it that such a system exists but is typically not used in favor of a 70v because it is more complex/more expensive in situations where fidelity & flexibility isn't really valued over simplicity and cost? (say, in-store audio)
c) Is it that such a system exists but has poor reliability/fidelity/puts too many functions into one box to be desireable to people seeking what I am seeking?
d) Is it that 70v systems don't derail the signal too badly if I use quality transformers and that it is foolish to go crazy with this kind of system when a 70v is just fine for higher fidelity multiroom systems?



----
Here's some background on what I want to do, which is unnecessary to help me with my question. A friend's church asked if I could help diagnose the issues with their sound system. It came out to being bad wiring(HOSA), bad jack soldering on the XLRs, some speakers in need of new tweeter diaphragms, some speakers in need of new woofer cones, and a repaired mixer. It also had some poor fidelity due to a large space with untreated drywall side walls.

Through replacing diaphragms instead of the entire horn assembly, reconing instead of buying new woofers, and getting some good gepco wiring and doing the soldering myself, I was able to get something decent going. For the price some other places want to get them a working mixer and 1 speaker running I got 4 of them running, a new mixer, no more buzz & radio from new wiring and some nice acoustic treatment. I demoed for them what it could sound like if they had some owens corning 703 insulation in a proper enclosure along key points on the walls of a smaller room, and asked about applying this to the bigger room. It made such an awesome difference, at such a low price compared to what pro sound companies were quoting that they decided they wanted to use me to do the entire new system. This came as a total surprise. They bought a new building that's much larger next door and are knocking it down to make one big church. I told them, I am not a live sound man! I am not a venue install professional, or even someone who dabbles in this. This isn't what I do. They insist. And, given other companies offered them less than I did for over 6k, I insisted too. Every step of the way I'd like to ask why something is done a certain way and figure out how to do it better. I started with the question of "why don't churches have any acoustic treatment" and figured out through some research "because most of the installers know better or care." I tried it and it was amazing. So before I impletement a status quo like system for the rest of the ideas I have planned, I'd like to figure out if better is attainable.

My background is that I work in a little room in the back of your recording or rehearsal studio and figure out why an NS-10 crossover sounds bad or why a GML mic pre is oscillating or why a marshall head is dead. Even power amplifier repair is something I am just now getting to the level where I would say I am 1 step above a first-month apprentice. This is totally out of the realm of what I do, but I'd like to give it a shot, because a lot of companies will put in something that "works" without putting something in that is the best. Of all the places they went to not 1 even brought up, much less gave the option of, acoustically treating certain portions of the wall so you could better understand the preacher! I have a theory that what bores people in certain houses of worship is not reverberation but unwanted reflections that muddy the sermon the pastor is trying to get across, and I think getting rid of it is key to a good experience.
I was at the first mass after everything was repaired, and the pastor said "do you hear me this morning?" the people responded "YES!" he asked again, "could you hear me last week" and they all looked around until someone said "NOT REALLY!" It was awesome to see people enjoying something more that they wouldn't have been able to otherwise because the 4k-10k every other company wanted was outside the budget designated by the higher ups for sound. Which is odd, since if you can't hear the priest, you're missing out on a lot of what it means to go to church.
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