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Acoustic Research AR1 sunfire distortion

 

New member
Username: Will_tert

Post Number: 1
Registered: Sep-16
Hi guys. Was using Acoustic Research AR1 loudspeakers for a couple of years.

Some time ago noticed heavy distortion like gargling on one of the subwoofers (this units are driven by built in 500w sunfire)

Open up and found 2 capacitors (470 micro farad 35v) that leaked. Cleaned the board and changed capacitors, but distortion still there.

Tested subwoofer and power supply on the other tower and they works fine.

So, it's definitely the sunfire amp pcb.

Distortion occurs at every audio volume. It just get higher as you raise the volume.

Any ideas what else to try? Other caps seems fine. Maybe I'll replace a couple more, but not sure if distortion is caused by transistors or capacitors.

Here is a picture of the pcb http://s21.postimg.org/x941aqwuf/sunfire_pcb.jpg

Another one from the other half of the pcb http://s22.postimg.org/8kd8lokzl/sunfire_pcb2.jpg

Caps marked in red were leaking and were exchanged. Dont notice any other damage.

Anyone experienced something similar?

Thanks!
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18282
Registered: May-04
.

Are you certain the problem is in the amplifier? Have you checked the driver by itself? If you have repeatedly overdriven the voice coil with a 500 watt amplifier, then you may be looking at the wrong component.


"Tested subwoofer and power supply on the other tower and they works fine."

Maybe that says you have but I'm not sure.




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New member
Username: Will_tert

Post Number: 2
Registered: Sep-16
Hi, yes. Cause I have a pair of this. And put the driver on the other tower and works fine. Even didnt switch back, so Im using the driver from the non working tower on the working one, permanent and it's good.

Sometimes when I turn on the non working one, I get a loud buzzing sound from the driver, other times turns on fine, but distortion and gargling is still there.

Maybe the buzzing on turn on is related to the distortion/gargling problem? What cause loud buzzing sound on this amps?
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18283
Registered: May-04
.

Hum is a ground issue. Buzz is often an issue with leakage across circuits, possibly some DC leaking in.

Do you have a schematic for this amp?

Can you read a schematic and trace a circuit from a schematic?

What tools do you have available for testing?

Are there any large scale integrated circuits in this amp? Do you have the ability to de-solder, replace and solder a 128 pin chip?


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New member
Username: Will_tert

Post Number: 3
Registered: Sep-16
Thanks for your reply.

I dont have schematic. Would be nice to find them.

I can read schematics, not a pro, but I understand basics. Sadly dont have many tools for audio testing (Oscilloscope is a no)

There arent any big integrated chips. Just a 16 or 24 pin. What you see in the pictures, is the entire pcb. There is an additional pcb but dont seem to have much components.

Will try to replace the bigger caps and see how it goes. I think you are right, some DC is going where it doesnt should go. But not sure if that can related to caps or anything else.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18284
Registered: May-04
.

Capacitors and coils block DC. Start with the power supply filter caps. It's fairly difficult to screw up a coil.



Hunting and pecking isn't a plan for repairing an amplifier. You need a schematic with a detailed description of proper Voltage you can expect at each component level. Then preferably you need to be able to check those Voltages and the operation of each component, plus whether it is within allowable tolerances, without having to remove each piece from the circuit board and without electrocuting yourself. You have to trouble shoot with Voltage running through the amp, enough to cause you some very serious hurt.

This isn't the forum for assistance with such materials and procedures. I don't have the schematic and I'm not too interested in such a project being done over a forum. If I started, that's about all I would be doing on this forum since everyone wants to repair their own gear if only someone would hold their hand and tell them what to replace and how to replace it. There are a few other forums out there which might give you assistance. Try "diy amplifier repair forums" in a search engine.

Sunfire is not a cooperative company when it comes to giving away information to private owners who want to have a hand at their own repairs. Very few companies give away their secrets nowdays. You have to be an authorized manufacturer's repair center to order stuff they don't want to sell to the general public.



Personally, if this were my amp, I'd scrap it and buy a BASH plate amp; http://www.parts-express.com/bash-300s-digital-subwoofer-plate-amplifier-300w-rm s--300-750?utm_source=google&utm_medium=cpc&utm_campaign=pla

Really, you need to be able to bring the Sunfire amp up to operational Voltage slowly while monitoring its current draw as you feed it a sinewave signal input. That mean a Variac, a scope and a signal generator plus a good meter to read the Voltages. By the time you assemble all that, you would have paid for another amplifier.

If you don't do this, you risk more damage every time you power up the amp. If you don't locate a problematic component/circuit, then you are searching for a needle in a hay stack.

Scopes tell you when the Voltage spikes, when there is something funky going on in the circuit, etc. It's rather difficult to fix an amplifier by simply replacing stuff till it either works or you get tired of putting money into something that is beyond hope.

Most causes of component failure or distortion/lack of power are caused by component level failure you cannot detect without the proper tools which can mean you replace a cap or resistor or transistor that has failed only to blow up the new part because you didn't fix the real problem, only the result of the actual problem.

This is how a lot of newbie techs work and their bench is filled with blown up parts when they finally get fired.

If there are any proprietary parts in this amp, IMO you should check for availability before you invest much time and cash trying to fix something that can't be purchased. Sunfire isn't a company that is into assisting the owner do repairs in most cases.



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New member
Username: Will_tert

Post Number: 4
Registered: Sep-16
Hi, I think you are right. I found this forum looking for sunfire problems.

And I thought that maybe this amps suffer from a common fault. But looks like it isnt right.

Since Im outside US, cant take to a local repair shop, cause here, they barely know what sunfire is.

I found some nice web for sunfire amps, if you are in US (ebc electronics). Looks like the guy can fix what sunfire doesnt care to fix. But, well, since the cost of sending to US to get repaired is way too high, Im on my own.

I ll search for diy web ou say and see how it goes.

Also will consider another amp in case it cannot be fixed.

Thanks for all your advices.

 

New member
Username: Qatan

Sacramento, California USA

Post Number: 1
Registered: Nov-16
dont even know...
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18298
Registered: May-04
.

Well said!
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