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Adcom 555II - Nelson Pass ?
Adcom 555II - Nelson Pass ?
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Old 25th March 2010, 01:28 AM   #51
WithTarragon is offline WithTarragon  United States
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Join Date: Jun 2007
I hate to be a wet blanket, but ....

The Adcom 585 is a big amp with a big power supply, big rail voltages etc. If you don't know what you are doing, this is not the equipment to learn on.

If I have mis-judged your level of expertise, then I apologize. Otherwise, perhaps you should not take on more than an average person can handle.
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Old 25th March 2010, 07:23 AM   #52
anatech is offline anatech  Canada
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Location: Georgetown, On
Adcom 555II - Nelson Pass ?
Hi David,
Well, I was authorized warranty for Adcom for some years. I've seen just about everything that can be done to these as can be done. The current staff at Adcom is totally different than the original staff. The company was sold and moved to a totally different State - so no one there really has a tight grip on the older amps. I would love to see what they sent you, could you email it to bhome at sympatico dot ca?

Adcom used good quality parts in all their equipment. The capacitor problem did not come about due to anything Adcom failed to do properly. This terrible situation affected many companies - like Nakamichi for example. I would be very cautious when considering any "upgrades" to the current parts. Especially avoid any part that is too large for the space alloted on the circuit board. This is extremely important.

Meaningful improvements in performance can be had, but not by swapping parts. To improve any of these amplifiers, there will be some hand matching of parts and possible minor circuit changes. Don't expect a night and day change though.

Capacitor problems occur on 585, 555II and possibly the 555 as well. I never did keep track of the affected models, but it's safe to assume anything produced in the same time periods should be affected. The board cleaning is an arduous process, beyond the normal quality of most audio service shops. What I am saying is that you do have boards with leakage problems, that is unless you've already had the work done to correct this.

Speaking of audio service shops, be aware that you should stay away from those places that perform modifications as part of their business model. These places typically read the internet and copy whatever the current fad is. Since these guys are not real technicians as one would be trained, their workmanship is often below standard. This is true even if they advertise superior workmanship. If they don't know any better, everything they touch is golden - right? Any suggestion to increase the size of the main filter caps (indeed, any capacitors) generally points to a person who doesn't really understand what they are doing.

I understand your desire to learn and work on your own products, however these amplifiers are too big to learn on. Any errors cause huge damage, simply due to the stored energy involved. If you really wish to learn about modifications, I'd highly recommend that you work on smaller, less powerful (and lower valued products). In this way you will really learn what changes have real effects, and the importance of making sure the circuit is working properly to start with.

Another really excellent way to learn first hand is to build an amplifier kit posted on this site. Amplifiers that sound good to begin with are a wise choice, something like a symasym, although there are some others that are just as good. Then you can build it and listen. Then change some parts and listen again.

Personally, I think doing upgrades this way only is risky and just plain silly. What you really need as a minimum is a distortion analyzer and an oscilloscope. A good DVM is something that is a basic requirement just to lift the lid and look inside. Cheap DVMs will not work, you will be measuring voltages in the mV for bias and offset. So the meter not only has to indicate to these levels, but it has to have acceptable accuracy as well. You will need a good audio signal source or oscillator in order to measure the distortion level changes with component changes. You absolutely require some instruments to keep yourself on the right track. I have yet to see modifications that sound better than original if the distortion is increased. It's also completely pointless to attempt changes to any amp that isn't running normally. Fix it first.

"Just because you can, doesn't mean you should" my Wife
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Old 26th April 2010, 06:15 AM   #53
wkbdgeorge is offline wkbdgeorge  United States
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Join Date: Apr 2010
Location: imagination land
So, I have the chance to pick up an Adcom 555 or 555 mark 2. Which would you prefer and why? I would be driving a pair of b&w 801 series 1 speakers. 8 ohm. I dont need the most amazing thing ever, however, I am using this setup for mixing and tracking purposes. Are these units flawed? Im currently using a crown d150. How do they compare? Any help would be most appreciated! -G
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Old 29th October 2010, 07:13 PM   #54
Coyotesx5 is offline Coyotesx5  United States
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Join Date: Oct 2010
I'm new to this site and while I'm not an electronics wiz kid, at 56, I have along history of successfully building kits and soldering/desoldering and modding. I used to have the basic electronics bench instrumentation, can read a schematic, but when I got into med school in 1979, I spent much more time tending to repairing EKG's, EEGs Dynamaps, and pulse oximeters in the OR...I'm a retired anesthesiologist. Anyway, I have been an "audiophile" all of my life...yes, I got sucked into the Krell v. Levinson A/B wars-of-old and bought some serious Class A and other class amps in my day. I've also had ML CLSes, older Polks, and Thorens/Sonus/Grado blah blah blah..equipment. I've built Heathkits...damn old, David Hafler's DH-102, and learned alot from old friends who ran a shop in NJ that repaired primarily analogue equipment..amps, preamps, set up turntables & tonearms, cartridges, speakers and crossovers...Audio Research, Krell, Mark Levinson, Quatre, etc. I steer clear of digital electronics.
I have owned Krell MDA 500's which drove my Thiel CS5i towers (the latter which I still own).
At 56, testosterone has had its way with my inner ear's HF hair cells..so I'm less discriminatory now, but having owned the older GFA-555, I have to say that with beefier filter caps, it was more Krell-like (bass-wise) than the stock 555. That aside...

I sold the Krell KCD/KRC/KSP and both MDA-500s..after only 10 years, many of the caps dried out in the preamp...and a few in the amps...after all, with this equipment, my room A/C had to be on well into October in NJ...hastening the drying process...but I tired quickly of this unneccesary power wastage and the albatross that the high end is to your neck. The wife lost patience with the financial demands of "keeping up" so I just "let it go."

I moved to Scottsdale in '93 and it seems that ADCOM followed me! But a very disappointingly different ADCOM. Heck..they do NO will-call service (like David Hafler and Dalquist used to do years ago back east)...so either learn how to change out caps and beta match your output devices, etc., or pay a bundle on shipping and time and materials.

I want to drive my CS5is with bridged 555IIs (yes, I know...you halve the damping factor and increase the distortion, amongst other things). If I can get two working amps on Ebay or CL for a good price, is their anyone on this forum that just happens to have a schematic for the 555IIs? I have the SM sans schematics.
I think that given the nearly 15-years old that these caps are (Input driver PCB:C104 & 154,and C109 & 159, Left & Right output PCB C202 & 302, & C252 & 352 respectively,and of course the main PS Caps...C802,803,804 & 805... they should probably be changed out as a matter of course. I don't want a dried out or drying cap to result in dead super-expensive hand-matched Thiel drivers (that are no longer made). I don't like mucking around in a piece without the schematics though.

So with the many thousands of years of collective experience on this forum, what would you guys recommend in terms of cap brand and possibly size..(it appears to me that ADCOM took a few shortcuts with component quality), to afford the DIYer guidance in executing an event-less cap change-out? After the change-out, I would have a pro...like one of you guys, for a nominal fee...bench test the pieces to assure that DC offset/bias/other specs were in order..without paying an Ebay-defeating price on the whole job. Criticisms are always welcome....I can hear the critics now!
Sorry for such a long post...part of it was an intro as this is my first post here.

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