Amplifier Maintenance?

[John Chi-town]

I am looking to the forum "Think Tank" to help guide me on whether or not I should replace the caps, etc. on my amplifier. The amp is approaching somewhere around 14 years in age. I have the same question regarding my pre-amp tuner which is now approaching 20 years of age.

I know the full history on the pre-amp as I purchased new. I bought the amp about 2 years ago. The seller stated it had very low hours and was stored more than used. I have no reason to doubt since it was a 10/10 specimen when I received. I would estimate 6 years of average use on the amp, and about 20 on the pre-amp tuner.

Since gradual sound degregation is hard to detect, I am wondering what others have or have not done with vintage SS gear?

My amplifier is an ADCOM 5802, and my pre-amp tuner is an ADCOM GTP 500 II

Thanks in advance!

John

[Guest " "]

The last amp I recapped was 28 years old when I recapped it. Although I do have a cap tester, it doesn't do in circuit testing....but I did test alot of the caps as I pulled them out. They all passed. I had ordered all the parts to do a complete recap so I just replaced everything anyway. The amp sounded the same with the new caps as it did with the old caps.

[T.H.E. Droid]

Adcom uses high quality components, which should hold up well. Unless you are having problems with noise and hum, I doubt you need to replace anything. If you're considering recapping, buy an LCR meter and good soldering iron that is temperature controlled. If your pulled caps are testing within tolerance, STOP, there's no reason to continue. And make sure those big supply caps are shorted and discharged before testing.

[John Chi-town]

Speakerfritz & T.H.E. Droid;

Thanks for your input. Now that I am done updating my speakers, I guess I was looking for another project to get me through the winter. You know, what can I improve/tinker with next. I guess I will just leave well enough alone.

Thanks again!

John

[Groomlakearea51]

SF has a good point. Several years ago I burned my long distance phone calls budget and spoke with Warren Bendler (the Sansui "guru" -see sansui.us), and Tim Schwartz, Bristol Electronics (another "guru" on the vintage ss stuff). The short version was that unless something is wrong, or the amp is noted for crappy components, the cost vs benefit for changing stuff is usually not worth the time or cost. It's like buying esoteric cables, wiring, etc. It normally will never make a reasonable if noticeable difference in terms of the cost involved.

Conversely.... the consensus was that as a matter of routine maintenance, at least when one has purchased a used ss vintage amp, that to have it tested by a competent technician is well worth the cost. My "sources" told me that 90% of what they "fix" are supposedly "perfect condition" amps sold on eBay and sometimes Audiogon. Usually, problems that are found that can be traced back to previous owner abuse, etc. That, and the worst thing that you can do with a vintage amp (or any other amp for that matter) is not use it and let it sit. Things dry out, and many caps, etc., will degrade if they are not brought to operating temperatures every once in awhile.

Keeping the amp clean is, however, another matter. Many failures, according to the gurus (other than spilling stuff on them....) can be traced to dust bunnies accumulating in the chassis. If the dust "bridges" there will be a short, and and the short can cause catastrophic failure. They recommended a complete cleaning, pot and switch cleaning and lube, adjustment when a used amp is purchased. After that, about once a year, remove the chassis covers and blow out all dust with "clean air", or a compressor with dry air. They also recommended that all pots and switches be cleaned, de-oxidized, and lubed at least once every few years. More if you live in a high humidity area.

Hope that is of some assistance.

[John Chi-town]

Groomlake:

Thanks for the insight. Yes, I forgot to mention that I did have the amp bench tested prior to purchase. Everything tested OK at the time. I will definitely take action on the ongoing care of the unit as suggested.

It sounds as if it may be time for me to stop looking for perceived and or non-existent issues......

Thanks again!

John

[AnalogWave]

I'm no expert but aren't Adcom amps "direct-coupled"? As such, when they fail, it's my understanding they dump DC to the speakers and execute them.

[John Chi-town]

Yes they are "direct coupled". At least an older version that I owned at one time the GFA 555 II . Not sure if the Nelson Pass designed MOSFET amps are or not. The 5800 series of amps were different in several ways from other ADCOM amps of the same time period.

As far as "direct coupled" executing speakers, that is news to me.

Thanks.

John

[AnalogWave]

Here is a relevant thread. There are some important links to other threads near the top of the first page. Typical situation really - all are happy up until there is a failure. Matter of time? Who's to say, as you note there were a number of differences between models over the years and I'm not smart enough to know their flaws if any. But it would seem to me if a cap failed in a non DC coupled amp, no biggie... that's when you box it and lick a bunch of stamps. Certain Adcom amps though would seem to me to benefit from some preventative, qualified maintenance to keep them running happy for the long haul. I personally am the original owner of a 535 I'm quite fond of but it mostly sits. Those times I've used it in recent years I push the power button with just the hint of a wince.

[djk]

"in the service manual, it says that the 25V, 220uF electrolytic capacitors on the input PCB assembly (the one
everyone has problems with) have been replaced."

"The driver boards will need to be cleaned VERY thoroughly in an
ultrasonic cleaner and then have new capacitors installed."

If I bought an older Adcom I would replace all the small electrolytics on the circuit boards before they could start leaking, a common problem.

[John Chi-town]

"in the service manual, it says that the 25V, 220uF electrolytic capacitors on the input PCB assembly (the one
everyone has problems with) have been replaced."

"The driver boards will need to be cleaned VERY thoroughly in an
ultrasonic cleaner and then have new capacitors installed."

If I bought an older Adcom I would replace all the small electrolytics on the circuit boards before they could start leaking, a common problem.

DJK;

Your above quote relates to an ADCOM 5802?

Thanks...

John

[djk]

It refers to any brand of any electronic produt made with the defective capacitors that plagued every manufacturer during a certain period of time.

http://en.wikipedia.org/wiki/Capacitor_plague

The above comments about having to ultrasonic clean the boards apply to caps from and even earlier time period.

Small electrolytics can have a very hard, short life.

Any amplifer coming up on 10 years old is a candidate for capacitor replacement (on my bench).

[AnalogWave]

With Adcom amps, there are basically two questions: 1) is it direct-coupled 2) does it have protection circuitry inline to the speakers. I did a quick search and didn't come up with anything but someone somewhere surely knows. I did read that the 5802 has some new (for its time) protection circuit but it was unclear to me if it was designed more to save the amp from itself or the speakers. Or both.

If replacing the caps costs $xxx, it must be more expensive to replace the caps and the damage done after they fail - in an Adcom amp at least. Stripping components and bathing boards in cleaning solutions sounds labor intensive, and if not done right you'll pop it again. I called Adcom years ago when the 555SE came out but I'm not sure of the state of the company now and who there might be there to talk to about the older amps. There must be a shop somewhere with a lot of under-the-hood experience with Adcom amps.

[John Chi-town]

Analog Wave;

Thanks for your insight and recomendations.

Below is a quote from an ADCOM white sheet. It appears that the 5802 is not direct coupled but that the GFP 750 Preamp is which I do not have.

By utilizing HexFet and MosFet designs throughout the GFA-5802, Adcom's
engineers were able to design short, simple signal paths. A quick glance at the
GFA-5802's elegant glass epoxy circuit boards will affirm this "less is
more" philosophy. Reducing the number of components and stages the signal
travels through by definition reduces the potential for distortion and fidelity
loss. Taking this approach even further, Adcom's engineers designed the GFA-5802
with only three active gain stages, as opposed to the 5 or more found in typical
amplifier designs. Once again, the result is improved sound, clarity, and
imaging, not to mention enhanced reliability.

The GFP-750's low voltage
gain stages are single ended Class A designs, the most neutral and accurate of
amplifier circuits. Countless hours of critical listening have confirmed the
sonic superiority of these circuits. And they're direct coupled, which
eliminates capacitor connection between stages. Since capacitors are filters by
nature, direct coupling improves signal transfer and purity.

The following statement relates to the protection circuit which appears to relate to the amp rather than the speakers from what I can gather.

A little extra insurance

A new, advanced protection circuit has been incorporated into the GFA-5802.
It monitors the safe operating perimeters of the amplifier, and if they're
exceeded, it protects the amplifier. This in itself is not unique, however
Adcom's protection system operates entirely outside the signal path. So
even though it offers excellent protection and peace of mind, it does so without
the slightest sonic impact!

I had the amp bench tested, & cleaned less than 2 years ago. At the time everything checked A OK with no sign of cap issues, etc. I will just keep a watchful eye over and continue annual cleaning of boards, and chasis.

Thanks!

John