What Audio Research power amps have you owned or admired?

[DaveyF]

Sparky, Thank You. That is exactly the same advice as my tech gave to me. Interestingly, there was a tremendous amount of disagreement on this issue with other members. My tech is well known on the West Coast, he is the only Mac authorized tech here in S.Calif and I tend to think he knows of what he talks.
He commented that he suspects that there are somewhat less scrupulous tech's and manufacturer's who see an opportunity to run up your bill as the reason for so much cap replacement.

 

[karma]

HI Davey,
I suspect that much of the madness I spoke about is caused by the "vintage movement" where folks are buying less than first class equipment that is getting old. Indeed, there may be some capacitors that have failed. But, I think most folks just don't know enough technically about the issue and they are just parroting what they are reading on the internet. It has turned into a feeding frenzy. And it's crazy.

In some cases I can buy into replacing old electrolytics but plastic caps? It makes no sense.

An example: Recently, I repaired an old MAC 1700 receiver that someone gave to me. It was built around 1968. Once repaired (a bad transistor) it worked perfectly. Glad I fixed it. It's nice. It found a home in my garage system where it looks and sounds very nice. It's capacitors are over 40 years old!!

Sparky

 

[microstrip]

Sparky, On another thread, there was a considerable discussion about the need to replace all my Caps in my ARC D70Mk2 due to the age of the amp. Since your amp is appx. the same age, are you considering cap replacement soon? I was told by my tech, that the caps have a very long life and should not need replacement for many more years, however, many of the members here did not agree. So far, I have resisted the idea of cap replacement....I would guess in your case, the cost would be even more astronomical!

Just my opinion - may be others will have different opinion.

Replacing the electrolytic capacitors in old gear is not a straight yes or no question. You have to ask what is the equipment, type and function of the capacitor and cost of replacing it.

The greatest problem that can be caused when an electrolytic capacitor goes wrong is leaking to the PCB and chemically destroying the copper tracks. Also, if it goes in short it can cause great damage to other components and indirectly to the PCB.

The effect of age on the electrolytic is usually a drastic reduction of capacity and increase of the ESR (equivalent series resistance) at high frequencies. As far as I remember the D70 only uses electrolytic capacitors in the power supplies, immediately after the rectification bridges - not a critical place. As the smaller capacity ones are inexpensive, I would replace them. For the expensive big capacitors of the power supply I would measure them as they are screw types, or just check for the ripple value.

All electrolytic capacitors of the D70 are heavily bypassed, I would not mind about the increase of ESR at high frequency - perhaps one reason more to postpone changing the capacitors.

Another aspect to consider is that since tubes have a limited life, users usually are much more cautious about leaving them permanently on than owners of SS amplifiers, and the number of operation hours can be guessed buy the number of times the tubes were replaced.

As there are so many variables to consider, perhaps the best advice is listening to the advice of people who have longer experience with vintage ARC than me!

 

[DonH50]

^^^ +1.

I worked my way through HS and college doing TV repair, among other things, and saw numerous cap failures of all types. including paper, mylar, teflon, poly, etc. All capacitors degrade over time and (primarily) temperature; electrolytics more so due to their physical design. I have not looked recently, but in the past a new electrolytic would have perhaps 20 - 50 % excess capacitance over the nominal specified value, and was expected to degrade to 50% of nominal at end of life (EOL). Lifetime is heavily dependent upon use, primarily load/ripple current and temperature. I seem to recall ~10 years being fairly typical for industrial caps. Note that, as microstrip implies, some may fail much sooner, and some may last much longer. I have measured some very old (20 - 30 years) caps that were still "working" but down to ~10% of their nominal value. If the component still works with only 10% of the capacitance, and lot probably will, then you can argue whether or not it is worthwhile replacing the caps.

When I went through and replaced all the big supply caps in a friend's tube amp (though he didn't think they wre needed, my measurments said otherwise) the most noticable impact was in the bass. Measurably and sonically it was much better.

For myself, I would measure the cap and decide whether or not to replace it. For a component, especially a tube component, that is 10 or more years old I would at least do a careful visual inspection of the electrolytics.

FWIWFM - Don

 

[Jay_S]

The blue power supply caps in the D70 II appear to be standard Mallory caps that simply screw in and out. It looks like they would be very easy to replace.

 

[mep]

The blue power supply caps in the D70 II appear to be standard Mallory caps that simply screw in and out. It looks like they would be very easy to replace.

I love the funky red plastic end caps that sit on top of the blue power supply caps and they never sit quite right because of the wiring they are covering.

 

[karma]

^^^ +1.

I worked my way through HS and college doing TV repair, among other things, and saw numerous cap failures of all types. including paper, mylar, teflon, poly, etc. All capacitors degrade over time and (primarily) temperature; electrolytics more so due to their physical design. I have not looked recently, but in the past a new electrolytic would have perhaps 20 - 50 % excess capacitance over the nominal specified value, and was expected to degrade to 50% of nominal at end of life (EOL). Lifetime is heavily dependent upon use, primarily load/ripple current and temperature. I seem to recall ~10 years being fairly typical for industrial caps. Note that, as microstrip implies, some may fail much sooner, and some may last much longer. I have measured some very old (20 - 30 years) caps that were still "working" but down to ~10% of their nominal value. If the component still works with only 10% of the capacitance, and lot probably will, then you can argue whether or not it is worthwhile replacing the caps.

When I went through and replaced all the big supply caps in a friend's tube amp (though he didn't think they wre needed, my measurments said otherwise) the most noticable impact was in the bass. Measurably and sonically it was much better.

For myself, I would measure the cap and decide whether or not to replace it. For a component, especially a tube component, that is 10 or more years old I would at least do a careful visual inspection of the electrolytics.

FWIWFM - Don

HI Don,
What do you think accounts for the difference between your bunches of bad capacitors and my ONE bad capacitor? Remember, I was doing hi fi repair full time for 13 years. These were my shops. I have worked on thousands of amplifiers And other audio components. Come on, tell me. I think I know the answer but I want to hear your speculations. Clearly, we have had different experiences.

Just to add a bit more emphasis, I have been working full time in electronics for over 50 years. Bad capacitors are not part of my experience. If you think I am butting heads with you, you are right. You have put my credibility on the line. I'm not going to let you get away with that without a good explanation.

Of course, my question infers that neither of us is exagerating.

Sparky

 

[DonH50]

Hi Sparky,

Didn't mean to start an argument nor question your abilities, sorry. Counting those years in HS/college I've only been doing this about 40 years, and most of that was/is not in audio (high-speed data converters and related ICs, GHz stuff). I should note that I tend to read the content of a post, only noticing the poster after. I treat everyone pretty much the same, for better or worse. I think you may have mis-interpreted my stating my experiences as placing yours into question; not my intent by any means.

Most of my early work was on TVs and some test equipment and that is where I saw by far the most cap (and most everything else) failures. As to what caused failures, it was usually pretty obvious, generally age, heat, and high voltage. In some cases decoupling caps would die when the big electrolytics failed and placed exorbitant ripple current on them. Flybacks would arc and put surge current through the ceramic flywheel caps. Tubes would arc and blow coupling caps. Some of those old tube sets were 10+ years old and had seen better days. The smaller caps tended to be mylar and ceramic, with a few teflon/poly types (I saw more of the latter in instruments like 'scopes and spectrum/network analyzers). As the sets went more SS, modular, and down-sized components, design margins were relaxed and failures increased. Of course, catastrophic failure in other things could blow the caps, e.g. an open snubber diode could put 20 - 30 kV across that 5 kV cap on the low leg of the plate circuit. And so forth and so on. To be clear, most of the time the problem was not a small capacitor failure but something else.

In the hi-fi world, by and large the smaller capacitors were under far less stress and I saw far fewer failures, though there were a few. The really nasty trouble-shooting dogs were not the blown components (caps or otherwise), it was the sneaky little things... One of my most painful memories is finding a bad (leaky) coupling cap in a Denon reference preamp. Finding the problem when everything went to heck was easy; when the problem was 0.05% THD instead of 0.005%, things got ugly!

I worked in the gov't world (for contractors, not direct) for most of my career and there were numerous publications on the reliability and lifetime of everything, including caps. Unfortunately I no longer have ready access to those standards. In the RF world, and particularly in amps, cap failure is a given at times. Companies like ATC (American Technical Ceramics) made their reps on better, lower-loss, more reliable RF coupling caps, starting with bigger ceramic models.

All I can say is I am sorry. I was not in any way questioning your credibility, but rather presenting a (my) different background and set of experiences.

Hope that helps - Don

 

[karma]

HI Don,
Apology accepted. Look, when you write things like you wrote, the context and application is vitally important. As I said, I suspected I knew the answer to the apparent contradiction. And I did. You were speaking about TV and high voltage which is a far more stressful environment than hi fi. Perhaps everybody here understands the difference, but I doubt it. Statements like yours is exactly how the capacitor madness in current hi fi is fueled. You need to be much more careful with your writing not only out of concern for the feelings of your forum friends (me) but also for the general speading of good information in the proper context.

BTW, since we are playing the resume game, I'll tell you that my early experience was designing high speed digital data communication systems (PCM telemetry) produced for NASA as a contractor and for the last 25 years working for Los Alamos National Laboratory designing things I can't talk about. This is in addition to my 13 years owning and running two high end hi fi repair shops. Should I mention that I built my first hi fi amp when I was 12 in 1953, a Heathkit? I have been into audio ever since as deeply as my income would allow. BTW, my ears still work well.

So, we have comparable experience. Given this, I would expect you to have the wisdom to understand that your words carry weight. Use them wisely.

Personally, I value your knowledge and experience. I think we could have a lot fun swapping stories over a mug of brew.

Sparky

 

[MylesBAstor]

HI Don,
Apology accepted. Look, when you write things like you wrote, the context and application is vitally important. As I said, I suspected I knew the answer to the apparent contradiction. And I did. You were speaking about TV and high voltage which is a far more stressful environment than hi fi. Perhaps everybody here understands the difference, but I doubt it. Statements like yours is exactly how the capacitor madness in current hi fi is fueled. You need to be much more careful with your writing not only out of concern for the feelings of your forum friends (me) but also for the general speading of good information in the proper context.

BTW, since we are playing the resume game, I'll tell you that my early experience was designing high speed digital data communication systems (PCM telemetry) produced for NASA as a contractor and for the last 25 years working for Los Alamos National Laboratory designing things I can't talk about. This is in addition to my 13 years owning and running two high end hi fi repair shops. Should I mention that I built my first hi fi amp when I was 12 in 1953, a Heathkit? I have been into audio ever since as deeply as my income would allow. BTW, my ears still work well.

So, we have comparable experience. Given this, I would expect you to have the wisdom to understand that your words carry weight. Use them wisely.

Personally, I value your knowledge and experience. I think we could have a lot fun swapping stories over a mug of brew.

Sparky

Gosh we were almost out there at the same time. Spend a week at the biomedical site at Los Alamos studying the effects of negative-pi mesons on cells in culture Painful almost at the dose rates the machine produced!

 

[DonH50]

Sparky, tube circuits such as many of the ARC amps under discussion do involve high voltage, at least in the 300 - 1000 V range, so I am not sure my comments are totally irrelevant, and I have had to replace caps in various tube audio gear over the years... However, I will bow out of this; maybe I'm not cut out for forum writing. Discussions are easier with a blackboard/whiteboard/piece of paper. - Don

 

[karma]

HI Don,
I would say moderate voltages. My D250 (250W/chan) uses 425 volts B+. 1000 Vlolts? I've never seen a hi fi amp with 1000 Volts. And nothing in the signal chain sees this voltage. This is certainly not high voltage but not transistor voltage either. This voltage is the B+ for the output tubes. Of course, the power supply does see this voltage but other than the filter caps, nothing else. The small signal tubes run at around 325 Volts.

I have never had a capacitor failure with any of my amps over what? 40 years? Of course, none of the early stuff is still around.

I can see that you are going to defend your position to the end. I can only tell you that your claims are not matched by my experience.

You don't have a communication problem. Rather, you think most other folks are idiots.

BTW, I note in your profile you have no tube amps. I assume in your past you have.

Sparky

 

[microstrip]

IMHO there are many types of capacitors, design topologies and we can not have straight rules or make generalizations based on single person experience.

Sometimes a bad design choice makes capacitor change mandatory - I am remembering the Graaf OTLs. As tube OTLs do not have output transformers, the peak currents involved in output stage could be very large and the power supply capacitors frequently needed replacement.

A friend of mine recently had all the electrolytic capacitors of his vintage FPB series Krell amplifier replaced - the technician measured the tens of old capacitors and a few of them were less 10% nominal capacity. Similar situation for 40 year old Quad equipment, specially for the old plastic encapsulated red Roderstein electrolytic capacitors.

Although the situation is completely different from audio electronics, I can add that our laboratory has many crates filled with NIM electronic modules, some of them about 30 years old, that stay powered on 24 over 24 hours, almost 365 days per year. I asked our technician for the most frequent faults and his answer was a) input transistors (surely due to bad use during manipulations! ) , b) open electrolytics and c) shorted tantalum capacitors.

 

[DaveyF]

Micro and Don, I think the problem lies with people giving poor advice on the web based on no real evidence.( Not saying this is apropos to your particular posts, but in general) In my case, I was instructed to replace all of the caps in my amp simply due to the age of the amp. My tech saw no reason to do that, since the amp was performing to spec and showed no evidence of cap failure. It is fairly obvious that a cap or for that matter any part can fail due to numerous reasons including age; however, I think what Sparky is saying is that unless the part has actually failed, why replace it....which is exactly what my tech said.
My tech's experience with failed caps in ARC amps is exactly the same as Sparky's. My tech's comment was that in his long professional experience, this wasn't a common problem due to age and if the electronics under question were using a good quality cap to begin with, why replace it if there was no need to. There are enough 'scare tactics' in the industry and IMHO, we do NOT need another.
The tubes, OTOH, are a different story and I did end up replacing all of those.

 

[karma]

HI,
Sure, I agree that capacitors do fail. Just not often. I will give another example. I have a collection of Tektronix scopes, plug-ins, and bench test eqipment set up in my garage electronics shop. This comprises over 40 plug-ins, 15 scopes, and a transistor curve tracer as well as a huge variety of bench gear (about 25 pieces). Most are the 7000 series insruments, meaning mostly solid state (all but the CRT's). The curve tracer is much older and is all vacuum tube. None of this stuff is newer than about 30 years. Most led 24/7 laboratory life styles. They all work perfectly. I have not seen ANY kind of failure other than dirty switch contacts and pots. The point is this. Tektronix products are great. They are designed to last. They DO last. Great hi fi gear, such as ARC, are designed with the same values in mind. Other gear? Well, ...........?

Hell, I even have some General Radio and Fluke gear that was built in the 1950's and they still work fine.

I know that a case can be made in special situations. But, the issue here is hi fi, not 24/7 test equipment or anything more exotic. Or equipment that must operate in rugged environments. HI fi equipment lead soft lives. Do not try to broaden this conversation into areas that we are not concerned with.

But, let's cut to the basics. I want you to state your opinion, clearly. You know mine. Do you think it is rational to routinely change out capacitors from hi fi amps? This includes typical plastic caps as well as electrolytics. The only Tantalums I have seen in audio gear is in my Revox A700 R to R tape deck (1974 vintage) where they are working just fine. I want to find out where you stand on this specific question. Please state your case so clearly that anyone can understand you. I am not interested in theoretical possibilities.

The battle I'm fighting is not the unusual case but the ordinary case.

Sparky

 

[DonH50]

This is ridiculous. My experience does not match yours, so we get into a big fight over it? I'll answer what I think you asked, then let it go so you can finish:

1. "High" is relative. As I said, my professional experience is IC design, so anything over 50 V is "high" to me. Just like 100 MHz is high to an audio designer, and 1 THz to me.

2. Highest B+ I have seen was ~1200 V in a tube amp with cascode stages. Don't recall the brand as it was a long time ago but it was not ARC. My old ARC amp ran ~600 V B+ (D79). My friend's D90 had around 400 V B+, but a grid at -125 V. An arcing output tube took out a coupling cap and the bias pots. Sometimes bad things happen to good amps.

3. Small (coupling) cap failures I saw in hi-fi amps tended to be due to other failures, like arcing tubes or fading electrolytics/power diodes affecting decoupling caps, as I believe I said. That is when they get exposed to HV, in my experience (which does not match yours, I get it).

4. I have owned a number of tube components through the years but none are in my current system. I recently sold my beloved D79, and have an SP3a1 preamp and a couple of other amps in the closet (one an old Eico EL34 kit rig I just can't seem to walk away from). I sold my tube (ARC) crossover many years ago. I have built numerous Heathkits, tube and SS, but remember few of them. I do miss my old Apache...

5. "Rather, you think most other folks are idiots." I do not see where you got that from my posts, but am tired of apologizing for what I see as a difference in experience.

6. "Do not try to broaden this conversation into areas that we are not concerned with." The topic was capacitor failures; I will concede I brought in experience outside the hi-fi arena, but I have some in that area as well.

7. "Do you think it is rational to routinely change out capacitors from hi fi amps?" No, of course not, and I do not believe I ever said that. I would inspect and measure if I could to determine if a component, any component, needed changing. I have reconditioned older electrolytics when I could and gotten years more use from them.

Hope that covers it - Don

 

[microstrip]

This is ridiculous. My experience does not match yours, so we get into a big fight over it? I'll answer what I think you asked, then let it go so you can finish:

1. "High" is relative. As I said, my professional experience is IC design, so anything over 50 V is "high" to me. Just like 100 MHz is high to an audio designer, and 1 THz to me.

2. Highest B+ I have seen was ~1200 V in a tube amp with cascode stages. Don't recall the brand as it was a long time ago but it was not ARC. My old ARC amp ran ~600 V B+ (D79). My friend's D90 had around 400 V B+, but a grid at -125 V. An arcing output tube took out a coupling cap and the bias pots. Sometimes bad things happen to good amps.

3. Small (coupling) cap failures I saw in hi-fi amps tended to be due to other failures, like arcing tubes or fading electrolytics/power diodes affecting decoupling caps, as I believe I said. That is when they get exposed to HV, in my experience (which does not match yours, I get it).

4. I have owned a number of tube components through the years but none are in my current system. I recently sold my beloved D79, and have an SP3a1 preamp and a couple of other amps in the closet (one an old Eico EL34 kit rig I just can't seem to walk away from). I sold my tube (ARC) crossover many years ago. I have built numerous Heathkits, tube and SS, but remember few of them. I do miss my old Apache...

5. "Rather, you think most other folks are idiots." I do not see where you got that from my posts, but am tired of apologizing for what I see as a difference in experience.

6. "Do not try to broaden this conversation into areas that we are not concerned with." The topic was capacitor failures; I will concede I brought in experience outside the hi-fi arena, but I have some in that area as well.

7. "Do you think it is rational to routinely change out capacitors from hi fi amps?" No, of course not, and I do not believe I ever said that. I would inspect and measure if I could to determine if a component, any component, needed changing. I have reconditioned older electrolytics when I could and gotten years more use from them.

Hope that covers it - Don

Don,

The nice think about WBF is that we can exchange experiences and read about different opinions of others in a friendly, sometimes passionate and irreverent way. We should not need to apologize for having different opinions or adding interesting extra-information.

Concerning point 7, it is not an easy decision, but it is also an economics decision. In some types of equipment an electrolytic capacitor failure can trigger an extensive and expensive repair, as they are usually used to decouple DC points. Most technicians will replace all or all except the power supply capacitors for a modest price - the capacitors are inexpensive, and unless access to the boards is tricky it can be done very fast by a skilled person with adequate tools. If someone is intending to keep a vintage piece of equipment he just got from the second hand market for many years, my opinion is that he should consider having the electrolytic capacitors replaced - very few people have your or Sparky experience and can give him correct advice in this complicated situation.

BTW, one other aspect is that many service people do a poor job replacing the capacitors - always look for qualified people!

 

[mep]

I thought it was pretty much an industry accepted standard that after 20 years, high voltage power supply electrolytic capacitors are probably at end of life and should be replaced. What good is it if they are still *working* but only have a fraction of their original capacitance?

 

[jadis]

If there is a downside to the new generation ARC amps, it would be the fact that they chose to make tube biasing not individually done. The VS110 had 8 power tubes and all tubes have individual biasing pots, so one can specifically nail the bias to .65mv as ARC states. The VS115 now has only 4 biasing pots instead of 8. 1 pot of 1 tube should be set to .65mn and its partner tube have a range of .57 to .72mv. The same procedure holds true for the remaining 3 pairs of power tubes. I wonder why the 2nd tube will flutter with that kind of wide range while the first tube is dead set to .65mv. So the first tube is .65 and the 2nd tube can read as high as .72 or as low as .57 which makes both tubes' lifespan pretty unequal at such settings. My good friend with the 610T reports that his 18 tubes per monoblock are controlled by only 2 pots, V1 and V2, with each controlling 8 tubes each based on the earlier method I described on the VS115. V1 is set at .65, and the other 8 can have varied readings anywhere in between .57 and .72mv. And some readings now are below the minimum so he has to change the tubes though the tubes are not that old. Somehow, in the near future, I might be getting this same problem, with unequal biasing figures for a so-called 'matched pair' of tubes. But then again, maybe ARC has their own reasons.

 

[microstrip]

(...) But then again, maybe ARC has their own reasons.

I can not find the reference anymore, but it seems they do it express to avoid the use of tubes with very different parameters in the paralleled sections, that could affect sound performance of the amplifier. You can adjust tube bias current controlling the DC voltage of the tube grid, but some other parameters will still be far from those of the other tubes.

BTW, if you buy closely matched tubes and after they some time they are not matched anymore it can be an indication you have to replace them. Some suppliers of matched tubes are able to supply you with a single tube for the case of a misfortune if you send them the sorting codes of the original tubes.

My VTLs have individual bias, but I avoid using very differently measuring tubes - I always buy and extra 25%, measure them, age them for 50 hours, measure again, and use the "out-of- match" for other applications, such as power supplies of ARC equipment.