Sound system for small church

[zxcvbob]

We currently have some kind of mixing board for a preamp, going into an old Realistic (Radio Shack) 45W amplifier for the basement and a Carvin FET900-A rackmount (it's just sitting on a table) amp for the sanctuary.  The sanctuary has good acoustics and I doubt we really need a mike at the pulpit, but sometimes the preacher wants to show a video or something with sound.  Or we have a guest speaker whose voice doesn't project well.

That Realistic amp drives a half dozen or so ceiling speakers using its 70V output.  The Carvin is rated something like 2 x 400W and it's driving a couple of big 8 ohm speakers up front; I think they are Yamahas.  I don't know what they are rated but certainly not 400W; I'd guess 100W or 150W. 

I've noticed that the Carvin amp is turned up pretty high but there's not much sound coming from the sanctuary speakers.  And the volume control is very scratchy and has little dead spots.  I've been toying with the idea of replacing that amp.  Would there be any reason not to use a consumer 2-channel stereo receiver instead of a PA system amp?  For example, I can get a refurbished Yamaha RS202 receiver (2x 100W) with a 1 year warranty from Yamaha for $130.

I need to see what model the speakers are and find out what power they are rated for, and what sound level at 1 watt to get an idea what the right sized amp is.

I have a 1970s Technics receiver that I'm not using, and I think I know where it is.  it's rated 10W per channel.  I might take it up there to see how it underperforms to get a baseline.

I also wonder how much power we are losing to resistance in the upstairs speaker wires.  I'm guestimating they are each 75 feet of 16 gauge zip wire.

[bedlamite]

Would there be any reason not to use a consumer 2-channel stereo receiver instead of a PA system amp?  For example, I can get a refurbished Yamaha RS202 receiver (2x 100W) with a 1 year warranty from Yamaha for $130.

If everything is setup with XLR I'd keep it that way. Proper conversion to low voltage RCA is usually cheap garbage and won't last, straight XLR to rca cables can fry the input stage on the amp.

Crown XLS 1002 can be had for about $400, can handle low impedance loads, is 220Wx2 into 8ohms and is the baseline for a quality PA amp. It's class D, so about 80-85% efficient, and lightweight. We've had one cranked at work all day every day running Peavey PR12D's for about a year now, after smoking the plate amps that were in the PR12D's. It runs way cooler than I expected.

https://www.crownaudio.com/en-US/products/xls-1002

The Carvin volume knob potentiometer is probably shot. you might be able to get a replacement or send it out for repair, but it's probably not worth it.

[zxcvbob]

Thanks, it's mostly* XLR into the mixer/preamp and I don't want to touch that.  Then 1/4" TS phone plug cables from the mixer to the power amps.  The mixer does have 3-pin XLR outputs.  I'll check out that amp, thanks.

*there's a CD player that we haven't used in several years that uses RCA connections into the mixer. 

[Tuco]

Two JCM halfstacks, a 50 x 4 Ampeg, and whatever cabinets you can fit in the drummer's van.
The drummer doesn't have a van?
You need a new drummer.

[Brad Johnson]

Would there be any reason not to use a consumer 2-channel stereo receiver instead of a PA system amp?

I doubt the system ever gets pushed hard enough for wiring to be an issue. I wouldn't worry about it. That said, 12 ga zip cord is relatively cheap, under thirty bucks for a hundred foot spool, so upgrading is simple and inexpensive.

For the main amp you could go with a residential amp as a stop gap, but it's better long-term to get something more robust. Bedlamite mentioned Crown. They're always a solid choice. Check with your local music supply store and see if they have anything on the Used rack. There's always someone trading up.

In terms of your stated prob, I would look at your mixing board first. Make sure someone hasn't dorked with gains or messed around with volumes (both channel and master). Reseat all cables and makes sure it isn't a simple dirty connection.

What model is the Carvin. We might be able to come up with simple in situ tests and nail down where the problem is. Parts Cannon repairs are usually unreliable and expensive. Let's see if we can pinpoint a source first.

When you say "volume control is scratchy and has dead spots", do you mean the mixing board or the amp? If the amp, why are you using it for volume? Once the main amp is set, it should remain undisturbed with volumes controlled at the mixing board.

One trick to try on scratchy pots is electrical cleaner spray and spin the heck out of it. Hose it down, then spin it stop to stop ten or fifteen times. That's solved many a problematic volume control.

Brad

[zxcvbob]

Here's a picture of the back label of the Carvin.  (I can't get a hot link pic to work) It's a model FET900A.  I don't think they make them anymore.
https://photos.google.com/share/AF1QipNwbGOtkBV8IiY7Mh4NY9q3fcK3_SueXRSwrZswPe45YmR-5jnWXPBeFCkGYi1NaQ?key=bTgyT2d3bkdqeTdRQW5CZklVcF9DZnhWcjRacVpn  I'll add pictures of the speakers and mixer eventually.  (I'm going out of town later this week, and everything is working okay-ish for now if nobody touches it.)

I was messing with the volume control knob trying to see why the volume was so low even tho' the main outputs on the mixer were set kind of high.  That's when I noticed the volume control knob was scratchy.  I didn't know if they even make TV tuner spray (etc) cleaner anymore.  Also while I was downstairs checking the volume in the basement and the preacher was saying "test, test, test..." into the mic, it suddenly got louder upstairs without anyone touching anything a the mixer or the amps.

I think there's multiple small problems, including loose cable connections somewhere.  I did reseat all the cables from the mixer to the power amps a week ago but i did not touch any of the inputs to the mixer.

[Brad Johnson]

I didn't know if they even make TV tuner spray (etc) cleaner anymore.

DeOxit

https://www.amazon.com/Hosa-D5S-6-DeoxIT-Contact-Cleaner/dp/B00006LVEU?th=1

Brad

[RocketMan]

Some 99% electronic grade isopropyl alcohol will do a good job cleaning potentiometers.  You can get that from Amazon for a decent price.  Inject it into the pot with a syringe and needle, then give it some good end-to-end spins.
Second the notion on the Crown amps.  Almost bullet proof in a church application.  I've been the tech guy at the last two churches I've attended.  We've always used Crown amps.  I've also got a fondness for the Behringer X32 mixers.  Should yoyu ever need a new mixer, get one of those.  Under $3k last time I checked Sweetwater.  (They've gone up about 30% in price since 2022.  Thanks, Bindenomics.) The darn things will do almost everything for you except preach the sermon.

https://www.sweetwater.com/store/detail/X32--behringer-x32-digital-mixer

[zxcvbob]

This is not our current mixer but it's darn close https://www.bhphotovideo.com/c/product/1026878-REG/yamaha_mg12xu_12_in_4_bus.html  I don't know what brand we have but it's analog with about that many inputs and looks very similar.  I think we paid about $200 for it 10 years ago.  I have no idea where we got the Carvin amp and the big speakers up front, they were probably hand-me-downs from some other church.  We very likely bought the Realistic amp decades ago; long before I joined.

This is a tiny country church with 15 to 20 in attendance most Sundays. It probably seats about 100.   A $3000 anything (except a new roof we've been saving for) is way out of our budget.  I appreciate the advise, just want to give some scale to the situation 

The laptop up front that the preacher uses for PowerPoints and occasionally shows videos is hooked up to a little converter box that takes the headphone output and converts the left and right to two XLRs; the converter box is powered by "phantom power" from the mixer.  I have no idea whether that XLR signal is mic-, instrument-, or line-level.  I just barely know what I'm talking about.

[Brad Johnson]

First, let's do some diagnostics.

Know any guitarists with a gig setup they'd be willing to bring in for testing? Run from their board into the Carvin. If volume is still an issue, it's the amp. If volume is normal, it's your mixer or a connection. Could also run from your board to their amp to check board output.

Carvin FET-900 is solid. I'd stick with it if you can, even as a replacement. If it ends up being the amp, you can get a replacement unit in good condition from Reverb for about what you mentioned spending on the stereo receiver.
https://reverb.com/item/17733216-carvin-fet900-a-mosfet-300-watt-stereo-power-amp-amplifier-kiss-34556

Yamaha MG12 is also solid. Tons of them floating around the used market, too. If it ends up being the board, a little patience should get you a replacement for $200-ish.

Consider calling an electronics repair shop (if you have a decent one in your area). See if they have a flat rate for clean, test, and tune of your board and amps. It's amazing what a little TLC/PM will do. They might even have a reduced rate for small venues and non-profits as part of a "Give Back To The Community" program.

Last, don't underestimate the power of social media. Put out a post saying the church is looking for someone who can give the system a checkup and cleaning. Include equipment photos. Five bucks says at the very least you get a couple of good leads, and I wouldn't put it past a qualified someone stepping up and offering to do it free or a greatly reduced rate.

Brad

[zxcvbob]

I drove out there today to take pictures of everything, and while I was there decided to diagnose it a bit.  It's a Mackie 12-channel mixer with digital effects, and the speakers are Pioneer 150W-ers.  The computer sound is going into a Y cable that mixes them into a single RCA jack that gets converted to XLR at -20dB level (the level is can also be set to 0 or -40, but -20 works well)  There's also a DVD player that we seldom use that goes to a different channel on the converter box using a similar Y cable, but that's not working; I think it's the cable from the stage to the mixer.  But that's a problem for another day, I know which input is dead and just won't use that one.

I watched a video last night from Sweetwater that was basically an introduction to mixers.  It was helpful.  One at a time I checked all the gain levels and trims, etc.  I need to download the manual for this mixer because I thought I could adjust the gains until the light started flickering green but it never did that, it started flickering yellow when it was turned way up probably too high (clipping?)  Also I turned the Carvin volume knobs up about halfway and found a spot on the potentiometers that works and we should never have to touch those.  Got everything adjusted so when the main volume sliders are halfway it's a good volume level.

Most of the original problem seems to have been user error.  Maybe one of the kids played with the little mixer knobs and turned things down to zero that I didn't know to check, but mostly likely it was either me or the preacher that screwed something up.   The dead input cable and the noisy volume knobs just confused the issue.  Hurray for not having to buy anything 😂  There's also a ground loop buzz when the computer is powered off and the preacher has said he unplugged something to get rid of that; it's simpler just to mute that channel at the mixer when it's not being used and I know how to do that now.

BTW, we don't have a "sound guy".  I'm a nerd and so is the preacher (that's probably not good having 2 of us) and when something needs adjusting or breaks they expect me to take care of it because he's busy up front -- which I don't mind except I'm just learning how this works and I don't know what Jim has dorked with recently.

[Brad Johnson]

Great news!

Gain knobs, mute buttons, and monitor channels have dealt many a heartache to the unwary or inexperienced.

For your basic setup there's a straightforward way to balance the board but it seems you've already gotten it work work acceptably well. No need to rock the boat now. However, when you get decently comfortable with the setup it would be a nice exercise. Makes general operation easier, too.

This Audio University vid is likely redundant info, same as you got from Sweetwater. Still, hearing it presented in different ways might help flesh out your understanding.

https://www.youtube.com/watch?v=MJAnfSpFtuY

Brad

[zxcvbob]

Great news!

Gain knobs, mute buttons, and monitor channels have dealt many a heartache to the unwary or inexperienced.

For your basic setup there's a straightforward way to balance the board but it seems you've already gotten it work work acceptably well. No need to rock the boat now. However, when you get decently comfortable with the setup it would be a nice exercise. Makes general operation easier, too.

This Audio University vid is likely redundant info, same as you got from Sweetwater. Still, hearing it presented in different ways might help flesh out your understanding.

https://www.youtube.com/watch?v=MJAnfSpFtuY

Brad

Redundancy is good; thanks for the link, I'll check it out.  I should also figure out how the FX work and see if we want to use a little reverb or something (not much, we're Baptists!  LOL)

[bedlamite]