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[Adam Greene]

Greetings all.  For good or bad I've invested heavily (for me) in Alto Professional Black series speakers a couple of years ago. Said goodby to my old Mackie sa1530's.  Bought 4 of the 15's and 4 of the 10's. I kept my old subs.  I do small church events mostly. Indoor and outdoor. I have a Midas M32 for mains and monitor mixing. It features 4 stereo matrix mixes with crossovers, delays etc built in.  The problem is with the Alto amp modules. I had one fixed under warranty and now I've had a 2nd one go out not under warranty.  Not really go out, but they start making a high pitched noise rendering them unusable. I've converted subs from powered to passive before, but I want to convert 2 of the 10's to biamp with NL4 connectors. That would give me one spare amp module. (Believe it or not, the 10 and the 15 amp modules are exactly the same - power rating and all.)  The reason I want to convert them is, no one that I can find will even tackle repair of these modules. They put a nasty yellow glue on all the circuit board connectors.  Alto wants $700 for a new module.  While that might make sense for one, from what I've researched, this amp problem is common with this model. I really need to get a few more years out of these.  My question is - can I wire the HF driver directly to the nl4 connector and cross the amp at the appropriate frequency?  Not sure what that would be but guessing in the 500 to 1k range. I know the LF driver will be fine straight off a crossed over amplifier. Thanks in advance for your advice and help.
Adam Greene.

[Len Zenith Jr]

  My question is - can I wire the HF driver directly to the nl4 connector and cross the amp at the appropriate frequency? 

Wiring the HF driver directly to the amp is usually a bad idea as turn on\off thumps can damage the driver. A ~20uf poly capacitor rated for ~200 volts should be wired in series with the driver to prevent that from happening. If the crossover is around 1k then you might want a bigger cap, say 40 uf.

[Sam Feine]

If you are careful about voltage levels you can likely measure the output of each pass band on one of the good amp modules. This will let you know if there is any DSP going on in the amp module (more than likely on a modern powered speaker). This will also let you see what crossover frequency and slope is being used. With a bit of effort in Smaart, Systune or equivalent you should be able to reverse engineer any processing to load into external DSP. MY recommendation is to run the amp into 8 ohm (or whatever load the drivers are) dummy loads at low level. Measure the output with a standard interface but be very careful not to go over a couple of volts out of the amp module.

[Chris Grimshaw]

This is gonna be difficult to do right.

I recently pulled apart and tested a fairly cheap active speaker to find out what the onboard DSP was doing. The answer was, quite a lot. To make matters worse, it was volume- and time-dependent.

At low levels, it has a particular EQ curve, including a not-inconsiderable LF boost. Increase the level, and the bass boost starts disappearing. Push it far enough, and RMS limiters come in and clamp the output right down to protect the drivers from thermal stress.

I'd be very surprised if there wasn't something similar going on with your speakers.
Get an 8ohm resistor capable of dissipating a few hundred watts (I use four 100w aluminium-clad resistors bolted to a heatsink) and use a pot to drop the signal down. Maybe stick it through a DI box before hitting your interface - you don't know if the amp module is bridged, so go for ground lift so you're not shorting the amp module to ground via your computer.


So yes, it is theoretically possible to do this. The DSP required is non-trivial, and reverse-engineering their DSP won't be easy, either. If you pay yourself a sensible hourly rate, that $700 for a new module isn't looking so bad...


Chris

[Kevin McDonough]

yeah,

seconding what everyone has said, the problem isn't the physical conversion of the cabinet, that's just a bit or wiring and soldering etc. The problem is matching the DSP properly to make it sound good.

A reamping DI box will step the voltage of the amp module down to a manageable level that can be fed into the transfer function of a measurement program (Smart/Systune etc) and you can get an idea of what EQ, crossover, etc is set, and try and match it with a new processor and amp rack.

A growing issue these days is that DSP is becoming increasingly cheap, so even cost effective passive speakers often have loads going on, and it can sometimes take some fairly expensive/complicated rack processors to replicate this.

K

[Steve Garris]

Too bad you didn't see this. You could have had new boxes at $250 each:
http://forums.prosoundweb.com/index.php/topic,166850.0.html

[Adam Greene]

Yea that's getting a little complicated for me.  The sad thing is these are really great sounding for a mid level portable point source cabinet. As far as I can tell Alto has discontinued this line at least in the US. Although, the last I checked they are still promoting them on their site.   I'm not a speaker designer or electrical engineer - just a humble electrician who loves sound systems and recording. Been doing live sound in Churches going on 30 years.  I will probably go to the used market and pick up a used box with a working amp module then experiment with the left over box. I saw a 15 on eBay the other day for 500 or so.  Thanks to all. You guys are serious!

[Adam Greene]

I saw when the bottom fell out of the price. Kinda makes you sick. I cannot find any new ones anywhere now much less at a close out price.

[Stephen Kirby]

The RedBox tap thing is a good idea.  It would let you measure what the DSP is doing under the reactive load of the drivers in the cabinet.  People with degrees in acoustics and software are pretty common these days and even low cost consumer devices have a fair amount of sophisticated code going on.

A mini-DSP plate amp is pretty close to the same cost as the replacement.  Running all the FIR and such outboard will require a fairly costly DSP, plus however many channels of power amp.

If you don't trust the gear you have now, get it working and sell it.  Basically cut bait.  It will be cheaper over the long run.  There are some real cost thresholds for professional level reliability.

[Kevin Bayersdorfer]

Just a thought. Looks almost the same size. All out now though.https://www.parts-express.com/dayton-audio-pma800dsp-2-way-plate-amplifier-800w-2-channel-with-dsp-and-bluetooth-2000---300-793

[Scott Holtzman]

Just a thought. Looks almost the same size. All out now though.https://www.parts-express.com/dayton-audio-pma800dsp-2-way-plate-amplifier-800w-2-channel-with-dsp-and-bluetooth-2000---300-793

That sure looks like the same amp.  Alto doesn't publish the crossover frequency but it sure looks like the 3k listed on the published specs. 

[Adam Greene]

The physical deminsions are different. The Altos are 17" long vs 15". The controls look very similar though  -'except the Alto's have a button to connect via Bluetooth and control with an app. The crossover frequency is what would be concerning to me. That has to be right even to just use them as monitors.

[Kevin McDonough]

The physical deminsions are different. The Altos are 17" long vs 15". The controls look very similar though  -'except the Alto's have a button to connect via Bluetooth and control with an app. The crossover frequency is what would be concerning to me. That has to be right even to just use them as monitors.

Even if the design isn't exactly right, if the controls and stuff look so similar then there's a good chance that this supplier may make the amp module you're looking for too (or they may come at least from the same OEM factory).

May be possible that they may provide a route to sorcing the part, even if Alto aren't using it any more.

[Scott Olewiler]

The physical deminsions are different. The Altos are 17" long vs 15". The controls look very similar though  -'except the Alto's have a button to connect via Bluetooth and control with an app. The crossover frequency is what would be concerning to me. That has to be right even to just use them as monitors.

So does whatever timing/alignment DSP is going on in the OEM amp.  A generic amp has to assume where the drivers are located relative to each other. With all the possible horn/woofer combinations there are in powered speakers it's never going to match the original "hard coded" DSP that the manufacturer has in there. I have to assume that an amp module for any given manufacturer's 12" powered speaker is internally different than the same series 15" powered speaker. And if it's not then I would expect the horn length may vary. etc.

[Mal Brown]

So it would cost you $1400 in Alto replacement amps to get whole again... until the next amp goes south....   in my market I see QSC K10/K12 on CL for 350 to 500 per box.

That would be a way better investment in my opinion.

I tried Mackie thumps as monitors back there ... same experience.  Took my lumps and moved on...

The other thought is pick up a used set of decent passive tops and a good amp.

Pretty sure that many of us here have excess inventory in those.  Still good boxes but we moved on to bigger, better, self powered, etc.  in my case my original ‘A’ rig is gathering dust - 1 last gig the weekend of 7/14 as the client loves it.  After that - $200 a box will take it away.

I would bet that I’m not alone in that scenario...

[Adam Greene]

Thanks to all who contributed to this thread. Your detailed knowledge is amazing. I suspect however, for my needs (stage monitors) I could get by with crossover at the optimum frequency and slope - time align the drivers, and  exterior amplifiers. Maybe a little eq. All of which my Midas board can handle.  I'm really not trying to make these couple of boxes sound amazing, just good for monitors. Now getting the ideal crossover frequency etc may be a different matter.  I have pushed these boxes pretty hard for some outdoor stuff I did last year with no more problems till now, so hopefully I will not be throwing them away anytime soon. At least until I can afford an upgrade.
Thanks again
Adam.

[Adam Greene]

...and a soldered in line capacitor to the HF driver. I already have extra amplifiers. 

[Chris Hindle]

  I'm really not trying to make these couple of boxes sound amazing, just good for monitors.

Adam, in my experience, the Monitors are MORE IMPORTANT than the PA.
If you can't get "the Talent" happy on stage, the performance WILL suck.
I have big beefy bi-amp wedges, with LOTS of power behind them. I get lots of smiles from the stage.......
Go for amazing. You won't regret it.
Chris.

[Adam Greene]

Adam, in my experience, the Monitors are MORE IMPORTANT than the PA.
If you can't get "the Talent" happy on stage, the performance WILL suck.
I have big beefy bi-amp wedges, with LOTS of power behind them. I get lots of smiles from the stage.......
Go for amazing. You won't regret it.
Chris.

Thanks for the advice Chris.  I agree 100%. I do strive for excellence in everything I do. Like I said earlier, I'm going to pick up a used box and experiment with the 1 leftover box to see if this is even doable. I really have nothing to lose at that point since I should be able to pick up a used one for 2 to 300 dollars cheaper than a replacement module. I do not have the know how to strictly match the DSP going on, but in my experience, I might be surprised how good it will sound. I will give an update when I try it. If anyone sees one of the Alto Black 10, 12 or 15 on the used market in or around the GA or AL area, at a descent price - 400 or so. Let me know.
Thanks.

[ProSoundWeb Community]