Sound Quality Vs. Measurements

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Tvr, I have a Dyna Mk4 tube amp that has a cap problem. It actually MOTORBOATS when I turn it on. I have a Marantz 10, (not 10B) with a cap leakage problem. OF COURSE, caps fail, but WHY change them when they still work OK? So what, a little extra ESR? You have mid-fi anyway, like having a Chevy and getting a valve job every 30,000 mi. Are you racing? If not, wait till the compression drops so much that the engine misses.
 
Anatech, Point well made that vintage equipment is likely far from its original performance. I did replace the electrolytics as they have practical life expectancy of 7 to 10 years. As a side benefit, the newer parts have lower ESR.
7 to 10 years is very pessimistic for good quality electrolytics... try 20 years or more.

My current AV receiver is coming up on 19 years old (I only use it as a stereo amp) and although its had a couple of minor repairs including two small signal driver transistors in one of the main output channels none of the caps have been replaced or needed to be replaced.

For many years I had an early 70's Sony amp as a spare amp (a TA-1150) and again, it had a couple of repairs over the years including new output transistors after being subjected to shorted outputs before it was given to me, but as far as I know or could see none of the caps had ever been replaced, nor needed to be, and apart from a slightly scratchy volume control it was still working perfectly when I gave it away a couple of years ago, by which time it was close to 40 years old...

As far as I can see electrolytics made in the last 30-40 years are a lot more reliable than we give them credit for, they generally either fail from excessive heat, or lack of use. As long as the design doesn't place them in a location that gets hot and the equipment gets occasional regular use so the oxide coating is maintained they can last a long time indeed.

Leave the equipment turned off for 10 years and you might have a problem, yes.
 
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5 to 8 is manufactures spec. Feel free to verify, I did. We had a lot of trouble when I was in industry as we did have that hot warehouse. I was in the failure analysis lab at the time and had to look into this problem. Performance mattered and we measured, as opposed to "sounds OK to me". People are touchier when they pay hundreds of thousands for equipment. Anyway, as I said, I change at about 20. The point originally being made is vintage equipment is not only older design and older component design, but some may not be up to original spec for other reasons. Aluminum electrolitics are one of those. Pots, connectors, switches, relays, and the bad habit or wire wrap posts are others. But then again, there is no such thing as a GOOD pot, connector, relay...... Any adjustment may not be correct, like bias or symmetry.
 
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Tvr, this 120 is a sad sort of amp, and I am sure that even EB thinks so, compared to the others that he produced for Hafler, and his later power amp. It is like a 3 cylinder auto, when 4,6,8,or 12 cylinder autos are available. This is because of the input stage, not the output stage.

Finally seeing the schematic, that unballasted current mirror with the peculiar diode definitely got my attention :) There must have been a reason, although I guess EB has sworn off the forum.
 
For the record, EB and I have known each other for about 37 years. Back in 1975, we used to have lunch in Geneva, Suisse, to have lunch looking at the lake. There we discussed circuit design at a slightly higher level than we are discussing here. This is where 'breakthroughs' are made and exchanged, and the rest is history.
 
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Ah yes, watching "le jet" while eating the local delicacy, small fish from lake Geneva is a great experience. Last week was in Boulder sipping cask conditioned IPA at Whitney's discussing how to age moon rocks via laser excited MS-TOF and how to best implement averaging methods.

But about Hafler amps..

The best one before the transnova stuff was by far the XL-180, IMHO. The front end with dual complimentary cascoded 2sk/2sj Jfets and 6 2sk134/2sj49 mosfet outputs per channel was pretty decent for a $600. amp. It also had separate rectifiers and filter caps per channel, unlike earlier models, for a quasi dual mono supply.
To sound best, the outputs need to be biased hotter than spec'ed in the manual. With a decent efficiency speaker, when used in the class A range, the sound is pretty good.
I think Richard Marsh had something to do with the design, which makes sense based on his AA articles on cascoding JFET fronts ends from about that same time frame. And of course, the EB designs, which I also built and still own, had a very similar front end.
manual w/ schematic
http://www.hafler.com/techsupport/pdf/XL-280_amp_man.pdf
review
Hafler XL-280 power amplifier | Stereophile.com
 
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Actually, capacitors do have mechanisms that do reduce performance over time. Even the manner of installation can have profound effects on serviceable life. One common example are radial capacitors installed without proper lead forming. This creates stress in the lead to rubber seal. It is telling that this issue has been addressed by sealing the bottom of the capacitor with what looks like epoxy. Those capacitors tend to survive the effects of time much better than untreated capacitors. The rubber is clearly the weak link in those capacitors

Look at carbon composition resistors. Aside from being noisy and being sensitive to temperature, moisture applied voltage, stress created by improper lead forming can act as a catalyst to normal aging effects. Just about any part you can think of has possible performance reduction due to time.

I do agree that some parts will check good compared to the normal performance for that part. However, the smaller the capacitor (in this case), the more quickly it loses fluid. ESR and DA almost certainly increase. So for small electrolytic caps, replacement is often a prudent move. The same thing can be said for older resistors where they are found near the beginning of a chain of amplifying stages and in the audio signal path. Of course, that constitutes a modification, or improvement. Most of the filter capacitors I check are performing well. I test them in circuit and under load. If they are pulled, I check them out of circuit.

I think that a very basic principle pretty much explains why older equipment needs work before any assessment begins. It is completely pointless to compare equipment with unknown defects. In fact, comparison can only be valid if the equipment in question is working it's original specifications. Wouldn't you agree (anyone?)

Hi tvrgeek,
Sometimes those older designs are still current. This happens more often than you might think. Older component design may not be a detriment. Take the case of the chassis mounted twist-lock capacitor. Those are a really good design. They dissipate a lot of heat safely into the chassis and also air. Too bad many equipment designers mount dropping resistors directly to the terminals. That heats the capacitor beyond where it would be on it's own. Great package though. Understand that old part design was carried out by real engineers who knew what they were doing. They were not unintelligent people at all. There are enough poorly designed new components around, so maybe throwing stones at glass houses isn't wise.

-Chris
 
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Actually, capacitors do have mechanisms that do reduce performance over time. Even the manner of installation can have profound effects on serviceable life. One common example are radial capacitors installed without proper lead forming. This creates stress in the lead to rubber seal. It is telling that this issue has been addressed by sealing the bottom of the capacitor with what looks like epoxy. Those capacitors tend to survive the effects of time much better than untreated capacitors. The rubber is clearly the weak link in those capacitors

Look at carbon composition resistors. Aside from being noisy and being sensitive to temperature, moisture applied voltage, stress created by improper lead forming can act as a catalyst to normal aging effects. Just about any part you can think of has possible performance reduction due to time.

I do agree that some parts will check good compared to the normal performance for that part. However, the smaller the capacitor (in this case), the more quickly it loses fluid. ESR and DA almost certainly increase. So for small electrolytic caps, replacement is often a prudent move. The same thing can be said for older resistors where they are found near the beginning of a chain of amplifying stages and in the audio signal path. Of course, that constitutes a modification, or improvement. Most of the filter capacitors I check are performing well. I test them in circuit and under load. If they are pulled, I check them out of circuit.

I think that a very basic principle pretty much explains why older equipment needs work before any assessment begins. It is completely pointless to compare equipment with unknown defects. In fact, comparison can only be valid if the equipment in question is working it's original specifications. Wouldn't you agree (anyone?)

Hi tvrgeek,
Sometimes those older designs are still current. This happens more often than you might think. Older component design may not be a detriment. Take the case of the chassis mounted twist-lock capacitor. Those are a really good design. They dissipate a lot of heat safely into the chassis and also air. Too bad many equipment designers mount dropping resistors directly to the terminals. That heats the capacitor beyond where it would be on it's own. Great package though. Understand that old part design was carried out by real engineers who knew what they were doing. They were not unintelligent people at all. There are enough poorly designed new components around, so maybe throwing stones at glass houses isn't wise.

-Chris
 
diyAudio Member RIP
Joined 2005
For the record, EB and I have known each other for about 37 years. Back in 1975, we used to have lunch in Geneva, Suisse, to have lunch looking at the lake. There we discussed circuit design at a slightly higher level than we are discussing here. This is where 'breakthroughs' are made and exchanged, and the rest is history.

Sorry to indulge in off-topic, but if it please the Moderators:

I have great respect for Erno. Unfortunately, once a while back in a fit of general pique (those times that a good friend should advise you to sleep on something for a few days before release) I sent a letter to a magazine and criticized three articles in one issue all at once :eek:

One was a very nice article about JFET circuits from Erno, one a error-ridden piece by the editor, and one by Norm Thagard (who merely got a highpass filter number wrong). I wan't really that negative, but the EDitor printed the letter and didn't himself otherwise respond (and reprinted the same errors later), Norm responded diplomatically and we became thereafter friends, and Erno was a bit p-ohed. But I expressed genuine disappointment, because I had hoped to hear about some new parts or new topologies regarding JFETs. And as we all know, the economic exigencies have at best left us all with fewer and fewer good parts (despite the much-appreciated existence of Interfet and LIS).

So I apologize very belatedly.

One of my prized possessions is a map from about 1640 of Lac Léman.

Brad Wood
 
diyAudio Member RIP
Joined 2005
Actually, capacitors do have mechanisms that do reduce performance over time. Even the manner of installation can have profound effects on serviceable life. One common example are radial capacitors installed without proper lead forming. This creates stress in the lead to rubber seal. It is telling that this issue has been addressed by sealing the bottom of the capacitor with what looks like epoxy. Those capacitors tend to survive the effects of time much better than untreated capacitors. The rubber is clearly the weak link in those capacitors

Look at carbon composition resistors. Aside from being noisy and being sensitive to temperature, moisture applied voltage, stress created by improper lead forming can act as a catalyst to normal aging effects. Just about any part you can think of has possible performance reduction due to time.

I do agree that some parts will check good compared to the normal performance for that part. However, the smaller the capacitor (in this case), the more quickly it loses fluid. ESR and DA almost certainly increase. So for small electrolytic caps, replacement is often a prudent move. The same thing can be said for older resistors where they are found near the beginning of a chain of amplifying stages and in the audio signal path. Of course, that constitutes a modification, or improvement. Most of the filter capacitors I check are performing well. I test them in circuit and under load. If they are pulled, I check them out of circuit.

I think that a very basic principle pretty much explains why older equipment needs work before any assessment begins. It is completely pointless to compare equipment with unknown defects. In fact, comparison can only be valid if the equipment in question is working it's original specifications. Wouldn't you agree (anyone?)

...
-Chris

Someone recently posted in another thread about his NAD3020 developing hum. A few replies blamed the bulk caps, and the initiator said that they had visibly leaked. But from his description it sounded like the epoxy that the factory applied around the bases to affix the parts to the board. As I have one of those amps I had noticed this, and as well had had a recent failure with a similar manifestation, which turned out to be in the auxillary supplies, and was traced to a nearly open-circuited 'lytic for one of the aux rails.

No complaints about the 3020 though --- the best bargain I think I've ever gotten in an audio component. Thanks again to KOJ for the recommendation so many years ago!

Brad
 
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