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robertbartsch
02-24-2009, 06:41 AM
Ok, well this is another reason I'm not found of old electronics.

My Adcom blew and is dumping Dc into the speaker circuits and the fix is $240.

On E-bay a typical version of this amp is worth about $275-300.

What should I do here - toss it inthe trash or take to another repair shop?

BMWCCA
02-24-2009, 08:13 AM
This is how most people (not us!) would list it in an Ebay auction:


Adcom 555-II amp. Mint condition. Lights up. No way to test it. Sold as is. Arc-welded output wiring but doesn't affect the sound. ;)

withTarragon
02-24-2009, 12:43 PM
Ok, well this is another reason I'm not found of old electronics.

My Adcom blew and is dumping Dc into the speaker circuits and the fix is $240.

On E-bay a typical version of this amp is worth about $275-300.

What should I do here - toss it in the trash or take to another repair shop?
It is painful to hear that you might toss it in the trash. They were a great amp in their day.

The safe bet is that the output devices would need to be replaced at the very least. Then you would need to find out why they went bad. So it is understandable why the repair shop wanted to charge you that kind of money.

If you are seriously thinking of getting rid of it, I could use the chassis and transformer. I am a DIYer and have some projects in mind. I live in CT and could pick it up. PM me if you like and suggest a fair price.

On a positive note, you were lucky the DC did not take out any of your drivers.

Thanks,
-Tom

robertbartsch
02-24-2009, 02:10 PM
I did not discuss the details of the mortality with the shop but I assume you assume the output transformers are toast.

...I've only had the amp for about 4 months or so. At first I did not like it much because the LF material seemed to be over emphasized.

Since I am now playing the basement system with a different amp, I kinda miss this, however.

Oh well, I'm done buying 20+ year old electronics - been burned to often.

Russellc
02-24-2009, 02:21 PM
I did not discuss the details of the mortality with the shop but I assume you assume the output transformers are toast.

...I've only had the amp for about 4 months or so. At first I did not like it much because the LF material seemed to be over emphasized.

Since I am now playing the basement system with a different amp, I kinda miss this, however.

Oh well, I'm done buying 20+ year old electronics - been burned to often.
while I know Mcintosh has output transformers on many of their Solid State units, I wasnt aware that Adcom had output transformers? Perhaps you mean output transistors?

Russellc

robertbartsch
02-25-2009, 04:45 AM
....right - output transistors - 16 in all I think!

hjames
02-25-2009, 05:08 AM
....right - output transistors - 16 in all I think!

yeah, so post it to ebay as having blown output transistors and see what happens ... Can't hurt and beats just tossing in a dumpster ...
If you're honest about it when you post the ad, that's a reasonable thing to do.

caveat - before you joined I bought a "tested and working" JBL/UREI poweramp that arrived in a box with just a smidge of popcorn - this is a HEAVY pro amp .., it smelled and when I opened it I found evidence it had cooked pretty thoroughly. After 10 weeks and a lot of yelling and fighting with ebay and Paypal, I did get a refund - only because I disputed the charge on my VISA card!! But THAT seller was just SCUM.

See - http://audioheritage.org/vbulletin/showthread.php?t=17362&page=3 (http://audioheritage.org/vbulletin/showthread.php?t=17362)

clmrt
02-25-2009, 06:04 AM
Robert - didn't you recently put a Crown amp into protection mode? What are you doing that causes so much stress to your amplification?

BMWCCA
02-25-2009, 08:22 AM
Robert - didn't you recently put a Crown amp into protection mode? What are you doing that causes so much stress to your amplification?He was trying to see if the new amps could run in a home environment with their fans disconnected. It seemed to work for the first one, not so well for the second. His other thread should be still around if you're interested. ;)

robertbartsch
02-25-2009, 01:05 PM
BMWCCA:
Well that is a good question.

I am not forcing these amps to high levels of power. The Adcom is a 20 year old piece of electronics that I purchased from Fleebay. After a few months it just crapped out and now pushes DC into the speakers.

The repair shop now claims the power supply needs to be replaced.

The two identicle Crown amps is somewhat misterious. Both amps are refurbished units sold by the factory with full 3 year warranties. One amp runs ice cold. The other is very sensative to heat and needs a cooling fan to keep it from shutting down from thermal heat.

Ducatista47
02-25-2009, 08:43 PM
I wonder if it is not old electronics but solid state electronics generally that are the problem.

I think that bipolar transistors in power amps anywhere but in the power supply have always been a loser. Some progress has been made since the days when their biggest accomplishment was avoiding thermal runaway, but not that much and I have personally given up on the approach.

Me, I don't like the way they sound, I don't need the expensive repairs and the threat of DC, and with the alternatives available today I was very happy to say good riddance.

I have newer gear, all tube right now but I am about to start dancing with MOSFET's too. None of this is costing an arm and a leg and I get great results without expensive NOS tubes or super duper grade new ones.

It seems to me that the promised "reliability" and "superior sound and convenience" of bipolar silicon has played out like sending all the manufacturing to China. Cheaper now but more expensive in the long run. Nothing is really better but there are a whole lot of problems that were not mentioned when we signed on to the deal. Being awash with solid state gear past and present does not bestow legitimacy on it. It just makes it common, familiar and seemingly cheap. But not better or even good.

If one really feels he needs gobs of power to drive high efficiency speakers (???), feel free. Go solid state. Been there, done that, thank you.

Clark

duaneage
02-26-2009, 10:13 AM
I labored over an amp for three weeks, ordered all kinds of parts, went through and replaced anything that looked even questionable. I turned it on and it ran for 10 minutes before popping. Really disheartening. I feel once a SS amp takes a dive the cost and trouble of repair is not worth it. There is a lot of energy in there and when things get weak they die in a spectacular manner

As to eventually death, MOS-FET and other thick film outputs are sensitive to static, and can also develop "holes" in the substrate over time. Add to that dirty heat sinks and dry silicone compound on the transistors and it's possible they can just go out. Although we all romance over how things were made better back then, I think quality has greatly improved today when it comes to transistors. Objective sound quality aside, it's a reasonable argument that a modern amp for 300-400 dollars would do just fine and come with a warranty to boot.

Somewhere out there is a guy with a working Adcom in a crappy case that needs a new chassis, or someone that wants a spare for parts like power supply caps and fans. I would say you should be able to get 100 bucks for the wreck, even with shipping someone will buy it.

robertbartsch
02-27-2009, 10:25 AM
Well I 've owned many tube amps over the years and I would not give two cents for one now.

The new SS amps built today are quite good and reasonably prices; old electronics are just that - old.

sourceoneaudio
02-27-2009, 10:46 AM
Ok, well this is another reason I'm not found of old electronics.

My Adcom blew and is dumping Dc into the speaker circuits and the fix is $240.

On E-bay a typical version of this amp is worth about $275-300.

What should I do here - toss it inthe trash or take to another repair shop?


FYI:
Adcom does take trade ins of old broken Adcom gear towards a new amp/purchase. The GFA-5500 would be a great replacement, ($1500.00) last retail. If you are not looking to trade in the GFA-5802 is a highly sought after high end power amp, last retail was $2200.00. The average used mint condition price with box $800.00 to $1200.00. (Nelson Pass Engineered)

http://www.avrev.com/home-theater-power-amplifiers/stereo-amplifiers/adcom-gfa-5802-stereo-power-amplifier.html
Adcom also is now owned by Emerson. :( Good or bad I don't know, but old Emerson? :barf:

opimax
02-27-2009, 04:54 PM
that last piece of news is damn scary

Somehow Emerson and Pass in the same breath does not seem natural

Mark

BMWCCA
02-27-2009, 05:40 PM
that last piece of news is damn scary

Somehow Emerson and Pass in the same breath does not seem naturalHey! Emerson Electric used to make a damn good ceiling fan! I think my brother had a summer job with them in St. Louis about fifty-years ago. Do they still make anything here in the USA?

grumpy
02-27-2009, 06:01 PM
Emerson Electric
Emerson Radio Corp.

quite different animals as far as I can tell.

So what's going to happen with the blown Adcom?

BMWCCA
02-27-2009, 06:11 PM
Emerson Electric
Emerson Radio Corp.

quite different animals as far as I can tell.You are correct, sir. A look at their product offerings and maybe it is the electric motor company that should be making amps! :o:

Ducatista47
02-28-2009, 08:10 AM
I labored over an amp for three weeks, ordered all kinds of parts, went through and replaced anything that looked even questionable. I turned it on and it ran for 10 minutes before popping. Really disheartening. I feel once a SS amp takes a dive the cost and trouble of repair is not worth it. There is a lot of energy in there and when things get weak they die in a spectacular manner

As to eventually death, MOS-FET and other thick film outputs are sensitive to static, and can also develop "holes" in the substrate over time. Add to that dirty heat sinks and dry silicone compound on the transistors and it's possible they can just go out. Although we all romance over how things were made better back then, I think quality has greatly improved today when it comes to transistors. Objective sound quality aside, it's a reasonable argument that a modern amp for 300-400 dollars would do just fine and come with a warranty to boot.


I agree, and it is a shame but true that repair prices, complexity and difficulty render most transistor amps Kleenex products - throw away.

MOSFETS can be very reliable when designed and put together with skill. Note the startling failure record of Nelson Pass amps. Startling because some of the designs have never had a failure in the field.


Well I 've owned many tube amps over the years and I would not give two cents for one now.

The new SS amps built today are quite good and reasonably prices; old electronics are just that - old.

And the new SS amps will later become throwaway pieces too. Compare that to replacing a tube. Way down the road, eventually perhaps a few caps, on a tube amp easily accessible with simple tools; usually just removing a cover.

Class A tube amps tend to be very simple circuits. My favorite amp is wired point to point. I have never seen more open and easy access.

The hifi shop I use has a tube tester. I look for 5000 hours for my power tubes and at least 20000 for my preamp tubes.

Notice that where heat is the enemy of transistors, tubes and MOSFETS need to be hot to work best, and their amps are designed to run hot and not be bothered by it. No fans, either. Heat rises so the hot parts or their heat sinks are outside or on top. Heat rises, what a concept! In a Nelson Pass authored amp, the heat sinks are designed to regulate the temperature of the output devices to a range, not to keep them cool.

Clark

opimax
02-28-2009, 11:19 AM
I am not an expert or trying to cause trouble, just adding observed info, really :)

My Perreaux 6000b, (300/c mid 80's vintage, are mosfet and do have fans and run very cool. The smaller 3000b 180/c does not have a fan, not noticeably hot, you can tell it is on, but not hot at all.

I originally ran them with fan disconnected but they got hot when pushed so I reconnected them and in the basement away form the listening room. Heck maybe they should be hot, I thought they are well respected amps. :blink:

Mark

Ducatista47
02-28-2009, 12:01 PM
maybe they should be hot, I thought they are well respected amps. :blink:

Mark
I will go with the flow. Everyone says they sound great and I won't argue.

I am sure they were designed to run at whatever temperature they reach when used as intended. I could have added that hot is relative and applies to the part, not the heat sink.

Nelson feels his First Watt F1 and F2 are most of the way there after a five minute warm up, but better after an hour. Cold, they never make it to where they should be. I notice that when people build them from scratch they sometimes use too much heat sink and they never get hot enough.

Like so many things, while it sounds un-American, more is not better here.

Clark

opimax
02-28-2009, 03:34 PM
I leave mine on. Currently I would rather pay higher electricity then repair is my theory. so they always warmed up then too. :applaud:

the adcom 555 I and II, they are mosfets too?

Mark

Ducatista47
02-28-2009, 08:31 PM
According to this review, transistors, not MOSFET.

http://www.stereophile.com/solidpoweramps/678/

But they ended up leaving them on all the time anyway (next review). The review goes on about how it does not suffer the ills of previous transistor amps, but we have all heard that before. As have the tube haters about tube amps. (If you want to hear a tube amp solid state lovers would actually like, try Rogue.)

Clark

Ducatista47
03-01-2009, 11:43 AM
My Perreaux 6000b, (300/c mid 80's vintage, are mosfet and do have fans and run very cool. The smaller 3000b 180/c does not have a fan, not noticeably hot, you can tell it is on, but not hot at all.

I originally ran them with fan disconnected but they got hot when pushed so I reconnected them and in the basement away form the listening room. Heck maybe they should be hot, I thought they are well respected amps. :blink:

Mark

Looking at your post again, I realize the magic phrase is "300/c." That would be too much power for any home use solid state device to dissipate without forced air or advanced (seen a CPU cooler with copper pipes and a radiator?) conductive cooling. What follows gets a Rant Warning and is not about you, Mark.

High power has always come at a high price in all departments. In the high efficiency speaker era when small tube amps ruled (and were all there was), things were quite different. When transistor amps appeared, low efficiency speakers like the AR3 were possible. Transistor amps, when pushed, produce speaker killing clipped waveforms and odd order harmonics. Tube amps do not clip like that and are pretty much second order harmonic distorters. MOSFETS can be designed either way.

That is when the famous JBL white paper (Danger - Low Power) came out. It was all about transistor amps. Push a 20 watt tube amp and it will not kill a speaker with distortion and is generally incapable of sending DC (I suppose nothing is impossible, but I don't see how). Plus, 20 tube watts through a large blue face monitor will set off car alarms out on the street. Like I said, a very high price was exacted for this "progress" in amplification and speaker technology.

Stick with high efficiency speakers (most of us here do), use tube or MOSFET amps, and bury that old "high power needed" idea in the nearest landfill where it belongs. Or save it for Home Theater. I swear if I read one more guy announcing a new project to tri- or quadamp a high efficiency speaker and drive it with 3 x 200wpc I am going to stop reading that forum. I have only been here 3 1/2 years, not a long time, but I am burned out on this particular brand of fiction. A guy needs to know the difference between A) trying to justify complicating a system beyond reason, making it sound inferior and cost too much, and B) admitting that it makes no sonic sense but is really a mine-is-bigger-than-yours quest. Or an "I have this stuff lying around, I have time on my hands, I am bored and don't know when to leave well enough alone and look for real improvements elsewhere" thing. And don't even start to talk about needing more power because 19KZ sounding a little fuzzy. We can't hear it and it takes .01 watt up there anyway. Stick to how the music sounds. By all means biamp if you can get a good enough active, but dividing amplification more ways is killed by exponentially diminishing returns and increasing complexity.

Buy the best first watt you can afford. It is 99% of what you hear with the speakers we like. Sorry to kill another popular plan of action, but Japanese receivers generally have a terrible first watt. They are designed to put watts into low efficiency mediocre speakers typically found in households that buy receivers. The great big models from the Seventies and Eighties were sold to power bookshelf speakers, not floor standing big woofer units. Also know that it is nearly impossible to design a high watt amp with as good a first watt as a smaller amp.

And leave the sound reinforcement systems outside. They have their place and it is not in living rooms. You can't afford the room treatment needed to even attempt to make it work in a home. Besides, Bo knows SR and you do not.

Room treatment - if your system is not bad, dollars much better spent than buying power and/or triamping.

Clark

sourceoneaudio
03-01-2009, 04:54 PM
New Power Amp Info:
http://www.adcom.com/prod/shopdisplayproducts.asp?prodid=1322


Trade in Info:
You can call to find out what they will give for old Adcom gear. They do take it in on trade even though it is not listed.
http://www.adcom.com/tradeins.aspx

GFA-5802 MOSFET:
http://www.adcom.com/prod/shopdisplayproducts.asp?hid=0&cid=0&sid=0&prodid=1151

;)

Ducatista47
03-01-2009, 05:07 PM
Nice. I see the GFA-5400 and GFA-5500 are MOSFET output designs.

"ASI participates in the Rethink Initiative (http://rethink.ebay.com/) and will recycle your trade-in in an ecologically sound manner." I wonder what that is... Scrap to China?

Clark

sourceoneaudio
03-01-2009, 05:21 PM
that last piece of news is damn scary

Somehow Emerson and Pass in the same breath does not seem natural

Mark


http://www.adcom.com/news.aspx

hjames
03-01-2009, 06:49 PM
Emerson Electric
Emerson Radio Corp.

quite different animals as far as I can tell.

So what's going to happen with the blown Adcom?

Dunno - seems the tales here are going to be legendary ...
Doesn't seem that hard to put it on ebay, mention that it cooked and the seller is not an engineer and doesn't know exactly what that means, but it won't power on now ... and just sell the darned thing!

robertbartsch
03-02-2009, 03:33 PM
Do they make tube amps with >200 WPC?

Ducatista47
03-02-2009, 09:43 PM
Do they make tube amps with >200 WPC?
First of all, Robert, I am sorry to have ranted away on your thread. I was considering posting on a new thread and should have gone with the instinct.

The short answer is, yes they do, and they are beasts, and I don't recommend them! They do not sound as good as lower powered units and cost way too much to buy, to retube and to run. And they are huge!

If you really don't like tube amps, from experience, perhaps you would still not find them to your liking. But the fact is that no one using high efficiency speakers needs 200 tube watts. The JBL paper recommended, if I remember right, a ten to one safety margin for headroom over the continuous draw during music playback. Say a speaker is a 92dB/watt/meter, not really very efficient for a large speaker but way better than the average bookshelf. Put six watts through such a unit and it would be damn loud, uncomfortably loud. Times ten, sixty watts. So who needs a 200wpc tube amp? No one who plays JBL's or Altecs, that is for sure. I can guarantee that if you put six continuous watts through a large JBL you would not be able to get to the volume control fast enough to turn it down.

If a speaker needs only six watts to blast you out of the room, the only reason so much power is recommended is not headroom for clean music but headroom so a transistor amp does not enter a mode of operation where it will destroy the drivers. Even so, why recommend so much power? Most people would never turn it up that high. I think JBL was counting on some of their monitors and home speakers being turned up insanely loud by, frankly, fools. Fools still qualified for the free replacement guarantee for drivers, so I'm sure the recommendation was based on financial as well as engineering reasons. Given a clean signal, it says right in the literature, a JBL monitor will hurt you before it will hurt itself. But never underestimate the stupidity of some humans who nonetheless have money. (I remember a post on this very site where a fellow complained that when he turned up his system, he loved the bass but it caused him pain and made him sick.) In other words, it is a rare circumstance where a high efficiency speaker would need a high powered tube amp.

Perhaps if I knew what you were driving I might be able to figure out how much power you would need in a tube amp. You would be astounded what a ten or twenty watt tube amp will drive. Good tube amps, classic or new, are known for having outrageously great iron. The reserve power available is beyond the experience of the uninitated.

I found a sixty watt push-pull tube amp to be enough by plenty to power the woofers of my 4345's. Overkill, really. If I had not biamped them, a couple of watts more than the modest signal I was actually feeding the woofers would have been required to power the whole box. I am sure twenty watts would have been plenty.

Another great opportunity here is to go Class A for the top drivers when biamping. Ask Widget if you don't believe me. A little Class A amp has the best sound in the world. Whereas a six watt Class A tube amp is perhaps a grand for the best there is (not the most expensive, but the best), a 200 watt Class A tube amp would cost a fortune, literally. And not sound as good.

Class A MOSFETS are, if well designed and built, as good as anything. You might investigate the build it yourself designs of Nelson Pass. Ian has built a few and is way ahead of the curve. He sure is great about helping me out, and the resources and help available on the web are almost unlimited. The Aleph J, for instance, is supposed to be astonishing.

Tube or MOSFET (or JFET - Nelson strikes again), any chance to get away from bipolar transistor output will eliminate the need for high power and yield much better sound. Remember, quality for quality smaller amps sound better than bigger amps, and the exception rate to that is close to zero. And no wonder, if you use efficient speakers the first watt is everything, nearly. "What good are the next 199 watts if the first watt sucks?"

Clark

Krunchy
03-03-2009, 06:25 AM
I've been following this thread for a bit as it caught my eye right from the start. When I had the 4345's set up last in June (they are still not set up at this point, home renovations continue here :() I was using two adcoms 5802's to drive them and it sounded fine, really clean. I have no problems with them and although they have more juice than I will ever need (not my main reason for purchasing them, I rarely got them past the half way point) I would have to agree wholeheartedly that the quality of the juice is more important than the quantity.

As a point of interest, I also have another amp that I really like set up with my 4313B's, and that is a Vincent SV-236. This is an Integrated Tube Amp/& solid state, the firts 10w are class A and the remaining 90 are ss.
I do not know what people think of them and frankly do not care as I am very fond of the quality of sound that comes out of my little speakers, the system sounds incredible.....nice and warm, crisp & clean :) an interesting concept altogether.

That said, maybe it would be interesting if we had another thread where people listed some of their favorite ams/systems :blink: :dont-know. For a while now I've been intruigued by the Mark Levinson stuff as well as the Aleph Pass units. I for one would be quite interested to hear what peoples personal experiences are with some of these components.

Lots of candy out there! that in itself could be a problem.;)

robertbartsch
03-03-2009, 01:56 PM
Krunche:

...good idea to have a thread on different amps, I suppose.


Anyway, I've owned dozens of amps both tube and SS over the years. When I was looking for a large amp for a current system speaker build, I stated here that, in the past, I have placed a fair amount of reliance on the published THD stats and that I considered these to be indicative of how conservative a manufacturor rates their amps.

Surprisingly, I learned that most here consider the THD rating of limited use since, according to many here, humans cannot distinguish between amps that have .1% or less THD.

Anyway, based on that advice, in part, I bought a couple of new big Crown SS amps that l enjoy much.

Krunchy
03-03-2009, 03:52 PM
I bought a couple of new big Crown SS amps that l enjoy much.
Hello Robert!
To a large extent thats really what it comes down to is'nt it? As long as you are happy with your set up you are on the right track.
Everything seems to be evolving all the time anyway, have fun now listening to your Crowns my friend & enjoy! :applaud:

jcrobso
03-04-2009, 10:10 AM
Krunche:

...good idea to have a thread on different amps, I suppose.


Anyway, I've owned dozens of amps both tube and SS over the years. When I was looking for a large amp for a current system speaker build, I stated here that, in the past, I have placed a fair amount of reliance on the published THD stats and that I considered these to be indicative of how conservative a manufacturor rates their amps.

Surprisingly, I learned that most here consider the THD rating of limited use since, according to many here, humans cannot distinguish between amps that have .1% or less THD.

Anyway, based on that advice, in part, I bought a couple of new big Crown SS amps that l enjoy much.

Bob also found out that once the amp distortion gets below .1% that it gets increasingly harder to hear.

About a year ago people started complaining about the sound in one of the production studios here at the radio station. The studio has JBL 4412A speakers. I listened to the sound in the studio and something had changed!
There was a fuzziness to the sound, a low level distortion. The people said the speakers were bad, I doubted that it was the speakers. After checking out some things I figured out it was the old Crown DC300, I swapped it out with a different amp, sound was clean again.
I took the DC300 to the shop and hooked it up, put 8 ohm resistors on and put a 1khz sine wave in, hooked up a scope. What I saw on the scope just blew my mind! On the left channel the positive half of the sine wave was clipped about half way up, but the negative part of the sine wave was OK.
On the right channel the negative part of the sine was was clipped and the positive part was OK. This is very high amplitude distortion, but it didn't sound terrible, just kinda fuzzy. From what I saw on the scope I though it should have sounded much worse than it did! :biting:
For years I have know that speaker distortion is usually much higher than amp distortion. The reason that we love JBL is because of their low distortion. This experience has reinforced my conclusion that the quality of the speakers is far more important than the amp. I don't get hung up on amps. I use good amps but I don't go crazy over them, JBL speakers,YES!:D
I not putting down any one for their like or dislike of any brand of amp. John

robertbartsch
03-13-2009, 09:34 AM
well that is good to know that speakers are more important than amps.

Anyway, for many years, I wanted a Macintosh amp but the high price always scared me away.

I am pleasantly surprised that a few high power low cost DJ amps I have acquired perform well in a home setting. Consequently, I will likely never own a Mac.

Ian Mackenzie
03-13-2009, 12:12 PM
BMWCCA:
Well that is a good question.

I am not forcing these amps to high levels of power. The Adcom is a 20 year old piece of electronics that I purchased from Fleebay. After a few months it just crapped out and now pushes DC into the speakers.

The repair shop now claims the power supply needs to be replaced.

The two identicle Crown amps is somewhat misterious. Both amps are refurbished units sold by the factory with full 3 year warranties. One amp runs ice cold. The other is very sensative to heat and needs a cooling fan to keep it from shutting down from thermal heat.

http://www.adcom.com/data/manuals/gfa555IImanual.pdf

Hi Robert,

The manual has alot of coverage on fault conditions but it does hint that the amp is sensitive to load conditions as it is an ultra wide bandwidth design. I would take that as not always stable into capacitive loads. (have a look at the wiring).

Also I am not sure why the power supply would need replacing if the protection circuits (thermal) where working or if the fuses blew (per the manual). My suggestion would be to call up Adcom if you have not already and go from there.

robertbartsch
03-13-2009, 01:39 PM
OK thanks.

Apparently, it is not the power supply but the output boards.

I assume this means some or all of the output transistors are fried. The shop originally quoated me $240 and I said that was more than the value of the amp. They reduced the repair to $170 and we agreed to proceed.

I have not had good luck with old electronics so I'm reluctant to spend good money after bad. In the future, I plan to avoid old electronics since I can't repair stuff like this myself.

The amp did work OK when I got it from Fleebay so I can't blame the seller, I suppose.

TonyM
03-15-2009, 09:58 PM
I'm curious if you ever asked Adcom for a quote. The outputs are usually matched devices and I know for the MOSFET amps some of them are no longer manufactured. I had to order a set through Adcom years ago. The 555 outputs might still be around though but I suspect they need to be matched.

robertbartsch
03-17-2009, 01:47 PM
Tony:

Na.... I did not ask Adcom for the price of the output boards.


I don't beleive I will be using this repair shop in the future, however. It is diffucult to find an honest shop anymore - everyone is a rip-off artist.

LE15-Thumper
03-20-2009, 01:03 PM
I'm curious if you ever asked Adcom for a quote. The outputs are usually matched devices and I know for the MOSFET amps some of them are no longer manufactured. I had to order a set through Adcom years ago. The 555 outputs might still be around though but I suspect they need to be matched.

The outputs in the 555 do not need to be matched as they use emitter compensation resistors to help load share. As I said in my earlier post, I would be very surprised if the OP stage is bad. 90% of problems on those was on the input boards, usually drivers and resistors that would open but show no sign of failing.

I did Adcom warranty from 1988 to 2003

robertbartsch
03-20-2009, 02:21 PM
Thx ....unfortunately, I really can't trust the repair shop. I took a new Crown to them and asked them if they could install a variable control to slow the fans. They called back and told me the fan bearings neaded replacing at $170.

zhid
03-24-2009, 08:47 PM
the man who designed the adcom amps has desiged others as well.



you may find something easy to build, from his designs,

in this forum, utilizing parts from the amp you now have

http://www.diyaudio.com/forums/forumdisplay.php?forumid=8

robertbartsch
03-30-2009, 08:58 AM
..the repair shop told me it was the power supply board that went bad.

The original quote was $240 but they reduced this to $170 after I told them the market value of a Adcom 550 was around $300 or so.

Anyway, they did not replace the power supply board with a factory fresh board but mearly replaced the bad electronic components.

All-in-all, I think it was a bad idea for me to buy old electronics - it just never works out for me.

Uncle Paul
03-31-2009, 01:34 PM
the man who designed the adcom amps has desiged others as well.



you may find something easy to build, from his designs,

in this forum, utilizing parts from the amp you now have

http://www.diyaudio.com/forums/forumdisplay.php?forumid=8

Thanks for that bit if info. I had no idea that Nelson Pass designed the Adcom amps.

hjames
03-31-2009, 05:14 PM
Thanks for that bit if info. I had no idea that Nelson Pass designed the Adcom amps.

Not all of them, no ...
According to Nelson Pass at his DIY Audio site

http://www.diyaudio.com/forums/showthread.php?postid=51801



I designed the 555. I believe the Mk II added a couple
of what were considered improvements, and it seemed
to me that it included triple darlington outputs instead
of 2 follower. I might have the schematic around, but
all told it was a simple bipolar design with a current
sourced input diff pair followed by a common-emitter
gain device that was also current sourced. This drove
the followers.

It was typical of all the 5XXX amps that I did the first one
and then they improved it until it had too many parts,
and then I would design the next in the series

Americo Borza sent me an old 555 in the hopes that I
would update it, and it still sits here, a perfect candidate
since so many of them were built.

Personally, I would score a few of these and run them till
they die and then update them. If you wait long enough,
an update will be issued.

pierce
05-03-2009, 01:21 PM
my experience with 80s/90s vintage electronics is mostly around failing small electrolytic caps. diagnosing and finding all the failed caps is very time consuming, hence the high repair bills. the parts themselves are cheap enough. also, some equipment is a lot easier to access the circuits for service (adcom, hafler) vs others (marantz, onkyo).

gads, back in the late 80s, I had a Marantz 510 (non-meter) fry and take out my old speakers. The amp was putting out like 120Khz at clipping levels, and smoke came out of the Ohm model H woofer and tweeters. Never let the magic smoke out of a good speaker before!

So I go to diagnose the amp, open it up, and holy crap, there's this heatsink tunnel thing with all the transistors on the inside, about 60 solder points on each PCBA to get them off the heatsink and swap any one of the transistors, and it was evident several were fried in addition to the driver board problem that caused the oscillation.

http://www.classic-audio.com/marantz/pics/t_0510m.jpg
pic cribbed from http://www.classic-audio.com/marantz/0510m.html

I gave up and bought a Hafler XL280 and never looked back. Ohm Acoustics graciously traded my fried drivers in for new ones for a very nice price, the replacement woofers were better than the originals (carbon cones, longer travel), yet Ohm said they were optimized specifically to work with the same crossover and cabinet, just allow higher power levels which the smaller drivers were already capable of.

now, if you want a power amp thats -easy- to work on, open up a Hafler XL280 or similar....
http://www.avahifi.com/images/amp/hafler/omegastar_250.jpg

robertbartsch
05-04-2009, 10:25 AM
...frankly, it is all Greak to me.

pierce
05-04-2009, 10:47 AM
simplified version: Capacitors are an important component on most electronics. They come in many varieties, the type known as 'electrolytic capacitors' sometimes go bad with age. This problem was particularly bad with computer boards made in the early part of the 2000s, there were massive failures of boards using certain 'caps' (for short) that were made with defective chemicals, but it also impacts older stuff even made with 'good' caps.

here's a closeup of a computer board that has some caps that have failed. note the tops are swollen, they should be flat.
http://www.badcaps.net/images/caps/kt7/image004.png

Another sign I've seen on older electronics is oozing goo on the bottom.
http://www.badcaps.net/images/caps/kt7/image001.png

Note, btw, those pictures show a bunch of dust all over everything, this has nothing to do with the problem at hand.