Fried 3a woofer

[Guest bjmsam]

I have been using a pair of AR-3a-Improved (European version) speakers as primaries in my HT setup for years but am expecting delivery of my "new" vintage AR9s in a few weeks. While the Adcom GFA-535 (conservatively rated at 80 wpc into 4 ohms) performs well with the AR-3a-Is, I bought a GFA-585 (conservatively rated at 450 wpc into 4 ohms) in anticipation of the AR9's higher power demands. I decided to give it a try with the AR-3a-Is before the AR9s arrive and hooked it up.

Everything seemed fine except for the loud thump I consistently heard through the speakers when powering down the amp. I searched the web and became convinced that relatively violent capacitor discharge is common with large amps and is usually harmless, so I unfortunately decided to continue use. A few days later, my wife and I were settling in to watch a movie when we noticed an acrid smell coming from the left speaker. I followed my nose to the woofer, which would not budge when depressed. I unscrewed the driver and smoke came pouring out of the cabinet! With the woofer disconnected, soft static could be heard from the tweeter and midrange, so the crossover might be shot as well, though none of the caps, resistors or other components were hot to the touch (the volume was almost all the way down during this).

I yanked the GFA-585 and the AR-3a-Is and am now using the GFA-535 with my pair of standard AR-3a (American version) speakers from the living room until this issue is resolved. More web research revealed that Adcom amps of the era suffer from leaky capacitors, and when I removed the top cover for a visual inspection of the internals, I found that mine is no exception. I can't determine whether the capacitors soldered flush with the PCBs are leaking, but the 100uf 100V caps soldered at an angle to the top-rear corner of each input PCB are both oozing a dark gray substance. I see no obvious damage to the PCB itself, so it appears to be a good candidate for repair (to be performed here: http://www.angelfire.com/art2/stereorepair117/adcom.htm), but I'm not happy about the speaker!

[dynaco_dan]

Hi Jim;

Perhaps a speaker relay which opens after powering off the power amp might be in order for additional future speaker protection.

Slow start circuits have been around for decades for slow startups to eliminate the initial startup thump and a guick cutoff to elimate the discharge thump on turn-off.

Fusing of your speaker systems is another good idea in the future.

[Guest bjmsam]

Thanks, Vern. I'm hoping the thump will disappear when the DC offset problem is corrected, but adding protection circuitry sounds like an excellent idea. Which devices and vendors are recommended? If amp modification is required, perhaps enhancements could be made during the repair...

[dynaco_dan]

Hi Jim;

There was several slow start system projects in The Audio Amatuer magazine many years ago, including one by Walt Jung for the Double Dyna 400.

Because of copyright issues they cannot be posted here.

Stereophile Magazine, in J. Gordon Holt day's that is, had one slow start project for the Crown DC-300 amplifier, it included an Amperite relay, I do not have a copy of that, just the brief memory.

I'm non-technical, but there is other much more knowledgeable writers here, please just give them an opportunity to see your situation so that they can respond also.

Also, regarding fusing the speakers, see the "Other forum", "fast blow fuses", for much more information and suggestions.

[johnieo]

>I bought

>a GFA-585 --- in

>anticipation of the AR9's higher power demands.

Jim:

One of the normal problems in consulting at a distance is that often, incomplete information is available to diagnose the problem, so it's easy to go off in the wrong direction.

Let's forget fuses and switches for the moment and consider the amplifier. First- how long has the amplifier been lying idle? days or decades? High voltage electrolytics will suffer oxide thinning when unused for long periods of time, and sometimes it pays to increase the voltage on them slowly the first time; they have been known to explode.

Second- you mentioned a history of leaky capacitors in that model. This would imply something about the OEM cap chosen by ADCOM. Perhaps they realized the problem after some time and changed brands? It sounds like the first issue is to replace the power supply capacitors and see if the amplifier will drive a dummy load. You might want to contact an ADCOM dealer and see what caps they recommend as a replacement. The service person may have seen your problem many times and provide accurate help- no point in re-inventing the wheel.

Your woofer can be repaired, but will cost a bit more than a refoam.

Cheers

[onplane]

Jim,

Sorry about your "unpleasant" experience.

John is right when he says that it's hard to diagnose at a distance. Neverthelesss, it's hard to imagine that those 100uf caps are the problem. I'd start looking where John suggested in the power supply for the amp that failed.

If the power supply is regulating OK, then next to check would be the output devices.

Now, Jim, for the good news, when your AR-9's arrive you are not out of business as long as you can find a mid power amp (25 to 40 watts per channel). Reason I say this is your AR-9's have the terminals that support passive bi-amping.

At normal volumes, your GFA-535 will drive the woofers just fine (providing that you don't attempt ear shattering levels). Then, as I said a decent quality mid power amp will easily handle the mids and tweeters.

Jim, with bi-amping you "split the load" so that you can safely power these monsters ... with smaller amps and with no loss in performance.

Regards,

Jerry

[dynaco_dan]

Hi Jim;

If you amp is decades old, then very likely your electrolytic caps need replacing considering that mostly manufacturers of old used 85' caps and if you are replacing them use 105' caps, suggestion Panasonic.

All electrolytic caps should be replaced in the amplifier not just in the power supply.

Be careful of the capacitors polarity!

This will cost you a little more and maybe be a little more difficult for you to obtain locally.

There is Digikey and Mouser, if mail ordering.

You can usually increase the voltage rating and capacitance value, at least in the power supply, as todays caps are usually smaller than the originals.

By-pass each cap with a 1uf polypropylene cap.

[ar_pro]

The larger Adcom amps will continue to play for some time after they have been physically switched off, finally going quiet when their caps have been drained.

Consider the Adcom ACE-515 power conditioner, which offered delayed switching for the amp & preamp, doing an excellent job of eliminating on/off transients.

[ar_pro]

The GFA-535 will *not* adequately power the woofer section of the AR-9, to anywhere near the capability of the system's design.

It's a mistake to underestimate the importance of adequate amplification to your new 9's Jim - they are one of the most power-hungry designs to come from AR, and will benefit dramatically from a powerful amplifier, even at moderate volume levels.

If you intend to bi-amp (and this speaker works beautifully is this mode), consider a pair of IDENTICAL power amplifiers, working in a vertical orientation (one for the left speaker, the other for the right).

Assuming proper individual amplifier operation, differences in level are then relegated to the balance control of your preamplifier.

Running a stereo amplifier for L&R bass, and a *different*, lower-powered stereo amplifier for L&R upper ranges could create a problem with nonidentical amplifier sensitivities, and the lesser-powered amp will STILL run out of gas first. The top section of an AR-9 is (SURPRISE!) also power-hungry.

You can buy an Adcom 555II for not much more than a 535...a pair of properly-functioning 555's or similar big Adcom amplifiers will be a very cost-effective way of getting wonderful results from the AR-9.

[Guest bjmsam]

Thanks for all the replies!

I contacted Adcom and received the following response: "A typical problem that happens over a decade or so of use with these amplifiers is that some of the capacitors will leak onto the printed circuit board that can create a large DC offset that potentially can damage speakers or the amplifier. The printed circuit boards are made of paper, not fiberglass, which tends to absorb the leaky electrolytic material. The cleaning job requires soaking and washing of the printed circuit board as well as removal and replacement of some components to get in to difficult areas. Our service technician says he uses dish soap and soaks the printed circuit board (due to the paper), others report they use a variety of solvents. Also, suspect capacitors that have caused the leaks or may leak in the future are replaced."

Other guidance from a repair specialist: "Because of the highly specialized front end of these amplifiers, EVERY 555II, 565 and 585 suffers from the same type of problem. And that usually shows up as blown fuses and a burnt speaker on one channel. Completely remove all components from the circuit board, wash both sides of the board with alcohol and acetone, install all new parts including matched low noise metal film resistors, new capacitors, new transistors, custom gain and noise matched transistors for the front end and then set up to specs."

I am confident that my GFA-585 will provide ample power for the AR9s when working properly. The service manual lists capacitor values but not specific part numbers, and DigiKey lists an overwhelming number of choices for the electrolytics that are leaking (100uf 100V and 220uF 25V), which is why I'm considering $hipping the unit rather than pursuing local repair (though I am making inquiries - Adcom indicated that "Any good elecronics servicer should be able to repair the amplifier with this information.").

John, what's involved in repairing the AR-3a-I woofer?

Thanks again.

[johnieo]

>The GFA-535 will *not* adequately power the woofer section of

>the AR-9, to anywhere near ...

Thanks for noting that... It was my understanding as well. Yours is the kind of advice that should be given on this forum. I think it imprudent to advise the use of a small amplifier on these speakers and especially for biamping. Instant listening is not the most important issue here. IMO repair or replacement of the amplifer should be first. If there is a history of leaky capacitors in these old units and yours blew, it would seem reasonable to find the factory fix.

Cheers

[johnieo]

>John, what's involved in repairing the AR-3a-I woofer?

replacement of voice coil and cone. This of course means a new surround. :-(

[dynaco_dan]

>Thanks for all the replies!

>

>I contacted Adcom and received the following response: "A

>typical problem that happens over a decade or so of use with

>

>

>these amplifiers is that some of the capacitors will leak onto

>the printed circuit board

>

>

This would be all electrolytic type caps in circuit and power supply.

They deteriorate whether in circuit on on the shelf, unfortunately.

Acid all over is a mess.

The stock 85'C caps have a shorter life span that the 105'C caps, also called computer grade.

My suggestion of bypass caps was for the power supply caps only.

I put myself in hot water with another member when I also went the extra yard and suggested replacing low noise resistors and possibly upgrading to newer transistors.

For the DIY that has some experience, patience, schematics and tools, all this can be done at home.

After reading what needs to be done with yours, a ballpark estimate would be in order before having it done, it sound very labour intensive plus the parts.

You should be able to get some idea over the internet, site un-seen, there is enough history to have at least a close idea as to cost.

Yours will not be the first or last to have all that is needed done.

Perhaps get back to us with your decisions, please.

I'm of the opinion that a new amp of greater power could be obtained for less than the repair bill you may receive to do that job right.

As a side note, there was a link here to a supplier that offered an integrated amp for $200.00, it appeared to be of great value, only a suggestion.

For your woofer, John is giving you great advice.

Another alternative is ebay for a used woofer, maybe.

If you proceed with a repair, at least you do know what you have inside the woofer.

that can create a large DC offset

>that potentially can damage speakers or the amplifier. The

>printed circuit boards are made of paper, not fiberglass,

>which tends to absorb the leaky electrolytic material. The

>cleaning job requires soaking and washing of the printed

>circuit board as well as removal and replacement of some

>components to get in to difficult areas. Our service

>technician says he uses dish soap and soaks the printed

>circuit board (due to the paper), others report they use a

>variety of solvents. Also, suspect capacitors that have

>caused the leaks or may leak in the future are

>replaced."

>

>Other guidance from a repair specialist: "Because of the

>highly specialized front end of these amplifiers, EVERY 555II,

>565 and 585 suffers from the same type of problem. And that

>usually shows up as blown fuses and a burnt speaker on one

>channel. Completely remove all components from the circuit

>board, wash both sides of the board with alcohol and acetone,

>install all new parts including matched low noise metal film

>resistors, new capacitors, new transistors, custom gain and

>noise matched transistors for the front end and then set up to

>specs."

>

>I am confident that my GFA-585 will provide ample power for

>the AR9s when working properly. The service manual lists

>capacitor values but not specific part numbers, and DigiKey

>lists an overwhelming number of choices for the electrolytics

>that are leaking (100uf 100V and 220uF 25V), which is why I'm

>considering $hipping the unit rather than pursuing local

>repair (though I am making inquiries - Adcom indicated that

>"Any good elecronics servicer should be able to repair

>the amplifier with this information.").

>

>John, what's involved in repairing the AR-3a-I woofer?

>

>Thanks again.

Hi again Jim;

[Pete B]

I think that you'll probably be better off if you can find a used woofer on ebay rather than trying to have that one repaired. There are no exact repair parts for the voice coil, spider, cone etc. and therefore even a pro reconner will just do the best that he can.

That's seems like an early death for the Adcom, can you tell us the brand of cap that they were using. There've been some stories of bad electrolyte formula that's shown up over the years.

I happen to be doing some recapping work on my own equipment and am looking into some of the newer long life electrolytics:

http://www.classicspeakerpages.net/dc/dcbo...ic_page=3#13009