There is a way to make an amp measure reasonably well but sound poor. Just use insufficient amounts of negative feedback, so that the higher order products are not properly suppressed. It helps if the open-loop amp has high distortion. You can also arrange for signal-related bias shifts, so that full power sine waves and normal music are heard at different bias settings - you can then choose which you want to be correct.
Alternatively, have a really good amp with very low distortion at all orders, because there is enough feedback around a fairly linear circuit. Some people will then claim that it is too 'clinical' or insufficiently 'musical'. This just means that they don't know the difference between an instrument amp and a sound reproducer - they prefer some low order distortion. Nothing wrong with that, provided that you realise that this is what is happening.
I don't take much notice of simulations. They can be a useful design tool, as long as you don't believe them too much.
Alternatively, have a really good amp with very low distortion at all orders, because there is enough feedback around a fairly linear circuit. Some people will then claim that it is too 'clinical' or insufficiently 'musical'. This just means that they don't know the difference between an instrument amp and a sound reproducer - they prefer some low order distortion. Nothing wrong with that, provided that you realise that this is what is happening.
I don't take much notice of simulations. They can be a useful design tool, as long as you don't believe them too much.
I agree,
I would not say that anyone should use these ideas to create "design" an amp. These are just some peoples opinions. To me the difference between an OK and good amplifier is its ability to present detail without distortion at low and high levels equally well! However there lies the problem, the amp would have to be linear at all frequencies! (Off topic)
The interesting thing is that you can hear a difference with capacitors types etc when put in "high level" commercial designs. So I would think that they cannot all be inferior.
I think there is more going on here with ideas of "burn in" than lack of feedback and bad design. If this was the case why not just use cheap polyester caps and overcome any problems with feedback. I know some do! LOL.
Are you saying that if you replace a polypropylene cap with a wax paper you can hear no difference in your amps?
Regards
M. Gregg
I would not say that anyone should use these ideas to create "design" an amp. These are just some peoples opinions. To me the difference between an OK and good amplifier is its ability to present detail without distortion at low and high levels equally well! However there lies the problem, the amp would have to be linear at all frequencies! (Off topic)
The interesting thing is that you can hear a difference with capacitors types etc when put in "high level" commercial designs. So I would think that they cannot all be inferior.
I think there is more going on here with ideas of "burn in" than lack of feedback and bad design. If this was the case why not just use cheap polyester caps and overcome any problems with feedback. I know some do! LOL.
Are you saying that if you replace a polypropylene cap with a wax paper you can hear no difference in your amps?
Regards
M. Gregg
Here is some more interesting info,
http://wduk.worldomain.net/pdf/ClarityCap_Technical_Report.pdf
Just for interest
Regards
M. Gregg
http://wduk.worldomain.net/pdf/ClarityCap_Technical_Report.pdf
Just for interest
Regards
M. Gregg
Thanks for that link.
As I read it...Clarity hired a university researcher to do the 'unbiased research' for them....and then......
Basically, Clarity deliberately designed a 'comparison cap' with poor mechanical resonance properties and then tested that cap against one of their 'good ones'...and listeners preferred 'their good cap' in a 'blind test'.....
It would have been more convincing to me if they had just compared their high-priced cap against an 'ordinary' low priced cap from one of the big manufacturers....I wonder why they didn't do that?
It would have been more convincing to me if they had just compared their high-priced cap against an 'ordinary' low priced cap from one of the big manufacturers....I wonder why they didn't do that?
You're not their target audience.
They seemed surprised that sine wave and impulse tests gave the same answer. Any EE would be surprised if they did not. I don't know why they looked for inductive effects, as they should have realised that this is unlikely to occur below RF freqs.
A mechanical resonance would show up in electrical properties. If it did not then it would have no effect. In addition, it could only have an effect if the cap has signal voltage across it - most caps do not.
How much notice should we take of research part-funded by someone who is trying to sell us something? They seem to attach great importance to the fact that it was carried out at a university, and part-funded by the government. This sounds like a standard KTP job, employing a recent graduate who wanted to stay in the uni environment but could not find a postgrad research studentship. Those who, like me, have done government funded research in a university will know that this is no guarantee of anything.
A mechanical resonance would show up in electrical properties. If it did not then it would have no effect. In addition, it could only have an effect if the cap has signal voltage across it - most caps do not.
How much notice should we take of research part-funded by someone who is trying to sell us something? They seem to attach great importance to the fact that it was carried out at a university, and part-funded by the government. This sounds like a standard KTP job, employing a recent graduate who wanted to stay in the uni environment but could not find a postgrad research studentship. Those who, like me, have done government funded research in a university will know that this is no guarantee of anything.
Gotta love these "technical reports" and "white papers". I liked their detailed description of the various parasitic components of caps and the conclusion that they drew a complete blank when it came to the listening test. They couldn't find a correlation between a "good sounding" cap and its measured data -- as long as the parasitics were negligible. Fair enough.
The mechanical resonance part is mumbo-jumbo at best in my opinion. The measured data is unit-less and it isn't even described what they are measuring. Vibration tests have been done for many decades, yet they have to design their own innovative vibrator. Really?!
It seems logical that a can cap with some goo inside (electrolytic cap) will have some resonance modes where the can squishes the goo, thus, changing the capacitance (and parasitics). If an amplifier is designed to be sensitive to this change in capacitance, some undesired output signal will be created when the cap is excited mechanically. But as VictoriaGuy points out, what's missing completely from their "report" is the comparison between a capacitor from a major cap manufacturer (or preferably several) and their own cap.
~Tom
The mechanical resonance part is mumbo-jumbo at best in my opinion. The measured data is unit-less and it isn't even described what they are measuring. Vibration tests have been done for many decades, yet they have to design their own innovative vibrator. Really?!
It seems logical that a can cap with some goo inside (electrolytic cap) will have some resonance modes where the can squishes the goo, thus, changing the capacitance (and parasitics). If an amplifier is designed to be sensitive to this change in capacitance, some undesired output signal will be created when the cap is excited mechanically. But as VictoriaGuy points out, what's missing completely from their "report" is the comparison between a capacitor from a major cap manufacturer (or preferably several) and their own cap.
~Tom
Bingo! Getting from time domain (impulse response) to frequency domain (sine wave testing, frequency response) and back is just a matter of a Fourier/Laplace transformation. You can't change the time behavior without changing the frequency behavior correspondingly.
~Tom
And absolutely no mention of the types of circuits the caps were used in for the listening tests. Maybe they were listening to them fall on the floor.
I generally find that for the same capacitance, a high-quality polypropylene capacitor has much greater command of the lower frequencies. I mean, a 10000 uF polypro cap makes a much, much deeper thump when it hits the floor than a 10000 uF electrolytic cap.
However, when applying a DC voltage with reverse polarity the polypro caps make no sound at all, whereas, the electrolytic caps often exhibit a solid impulse response - albeit a bit time-delayed. The NOS types are definitely preferred in this application as the pressure relief valves in newer caps adds a white noise component to the sound. This really obscures low-level detail in the sound stage.
~Tom
I hesitated to post in this thread since some of what I am going to say is opinion, and opinion is.........
Fact:
I am an EE. I design "mission critical" equipment where human life may depend on the equipment functioning correctly. I have worked there for 38 years. The equipment typically operates on low voltages, from 6 to 18 volts, in harsh environments. Capacitors are typically ceramic, tantalum, or aluminum electrolytics. Audio frequency response is tailored for intelligability and must meet strict specifications over temperature extremes. X7R or Y5V ceramics are not used in the audio path. No burn in of individual components is performed. The completed equipment is burned in before being tested for spec compliance. The primary purpose is to weed out infant mortility and defective components. All potential component suppliers must meet strict criteria before being put on the qualified supplier list. All potential components must meet strict criteria before being qualified for use. Every flippin component in the device must be qualified.
Fact:
I used to have access to a nice HP component analyzer that could measure ESR, ESL capacitance value, and DF at various frequencies and DC bias levels. Unfortunately they decided to clean up the lab while I was away on christmas vacation several years ago. The analyzer and the old TEK curve tracer were scrapped.
When I was designing the Tubelab SSE I took dozens of electrolytics in to work and tested them for use as the cathode bypass on the output tubes. Many have asked why I specified a certain Panasonic 1500 uF capacitor where a smaller value should suffice. The truth is that I bought a bunch of caps and tested them. That particular cap was selected because the ESR was low and relatively constant over the entire audio band. All caps tested on that occasion were fresh from DigiKey of Mouser with no prior use. Only reasonably priced electrolytics suitable for cathode bypass use in the 330 to 4700 uF 50 or 63 volt range were tested.
I also tested some caps that I had on hand and some that I had previously used. I have a large quantity of 4700 uF 35 volt electrolytics left over from a satellite receiver design I did years ago. They are about 25 years old. I have some that are NOS, and some that have been used in power supplies and as cathode bypass caps. I found definite differences in the ESR between the used caps and the NOS caps. The used caps were pretty consistent regardless what they were used in. The NOS caps were all over the place. Some better than used, some much worse. Leaving a crummy cap biased up overnight on the analyzer made no difference.
Fact:
I have a big box full of 470 uF 50 volt electrolytics from the 1970's. They were originally used in 24 volt power supplies. I have tried them as cathode bypass caps in tube amps. I have used them in guitar amps with good results. Some of those amps are now 30 years old and still kicking. I have tried them in HiFi amps and they always sounded NASTY! I brought some to the analyzer and found out why. These caps turn into inductors in the upper audio range. These are old and do not have vented cans. They make a big bang when plugged into the wall outlet!
Fact:
The characteristics of an electrolytic cap will change with age. The effect is accelerated with increased operating temperature. Some electrolytics are specified for as little as 1000 hours OF USEFUL LIFE at the maximum operating temperature.
Opinion:
I don't buy into many of the burn in theories proposed about components. Speaker drivers - definitely. NOS tubes that haven't been used in a long time - definitely. NOS new production tubes - burn in to weed out junk is required. Electrolytic caps - maybe. NOS carbon comp resistors - maybe. Other components - doubtful. Speaker wire - yeah, I'm not going there.
Opinion:
If I wanted to break in an electrolytic cap (or any other component), I would subject it to the same conditions that it would see in actual use including temperature if possible. For a cathode bypass cap that would mean 15 to 35 volts with some AC current flow. How do you do this?
Fact:
I devised a method for testing electrolytic caps since the component analyzer was scrapped. The same setup could be used for burn in. You need a DC power supply, and audio generator capable of cranking out some power, I use an old tube type HP 200AB, an old OPT or other transformer, and a scope (optional for burn in). Connect the primary of the OPT to the audio generator, and wire the secondary of the OPT in series between the DC power supply and the cap under test. Connect the scope across the cap.
Adjust the DC power supply to apply the desired DC bias across the cap. Turn up the audio generator to force an AC current through the cap. Vary the generator frequency and watch the scope. Ideally you should see only DC across the cap. THe crummy 470 uF caps mentioned above show some AC at all frequencies, and a large peak (several volts) in the 5 KHz range (its been a few years since I have done this). A good cap may show 10's of millivolts with no peaks in the audio range. This should be no problem as a cathode bypass.
Fact:
I am an EE. I design "mission critical" equipment where human life may depend on the equipment functioning correctly. I have worked there for 38 years. The equipment typically operates on low voltages, from 6 to 18 volts, in harsh environments. Capacitors are typically ceramic, tantalum, or aluminum electrolytics. Audio frequency response is tailored for intelligability and must meet strict specifications over temperature extremes. X7R or Y5V ceramics are not used in the audio path. No burn in of individual components is performed. The completed equipment is burned in before being tested for spec compliance. The primary purpose is to weed out infant mortility and defective components. All potential component suppliers must meet strict criteria before being put on the qualified supplier list. All potential components must meet strict criteria before being qualified for use. Every flippin component in the device must be qualified.
Fact:
I used to have access to a nice HP component analyzer that could measure ESR, ESL capacitance value, and DF at various frequencies and DC bias levels. Unfortunately they decided to clean up the lab while I was away on christmas vacation several years ago. The analyzer and the old TEK curve tracer were scrapped.
When I was designing the Tubelab SSE I took dozens of electrolytics in to work and tested them for use as the cathode bypass on the output tubes. Many have asked why I specified a certain Panasonic 1500 uF capacitor where a smaller value should suffice. The truth is that I bought a bunch of caps and tested them. That particular cap was selected because the ESR was low and relatively constant over the entire audio band. All caps tested on that occasion were fresh from DigiKey of Mouser with no prior use. Only reasonably priced electrolytics suitable for cathode bypass use in the 330 to 4700 uF 50 or 63 volt range were tested.
I also tested some caps that I had on hand and some that I had previously used. I have a large quantity of 4700 uF 35 volt electrolytics left over from a satellite receiver design I did years ago. They are about 25 years old. I have some that are NOS, and some that have been used in power supplies and as cathode bypass caps. I found definite differences in the ESR between the used caps and the NOS caps. The used caps were pretty consistent regardless what they were used in. The NOS caps were all over the place. Some better than used, some much worse. Leaving a crummy cap biased up overnight on the analyzer made no difference.
Fact:
I have a big box full of 470 uF 50 volt electrolytics from the 1970's. They were originally used in 24 volt power supplies. I have tried them as cathode bypass caps in tube amps. I have used them in guitar amps with good results. Some of those amps are now 30 years old and still kicking. I have tried them in HiFi amps and they always sounded NASTY! I brought some to the analyzer and found out why. These caps turn into inductors in the upper audio range. These are old and do not have vented cans. They make a big bang when plugged into the wall outlet!
Fact:
The characteristics of an electrolytic cap will change with age. The effect is accelerated with increased operating temperature. Some electrolytics are specified for as little as 1000 hours OF USEFUL LIFE at the maximum operating temperature.
Opinion:
I don't buy into many of the burn in theories proposed about components. Speaker drivers - definitely. NOS tubes that haven't been used in a long time - definitely. NOS new production tubes - burn in to weed out junk is required. Electrolytic caps - maybe. NOS carbon comp resistors - maybe. Other components - doubtful. Speaker wire - yeah, I'm not going there.
Opinion:
If I wanted to break in an electrolytic cap (or any other component), I would subject it to the same conditions that it would see in actual use including temperature if possible. For a cathode bypass cap that would mean 15 to 35 volts with some AC current flow. How do you do this?
Fact:
I devised a method for testing electrolytic caps since the component analyzer was scrapped. The same setup could be used for burn in. You need a DC power supply, and audio generator capable of cranking out some power, I use an old tube type HP 200AB, an old OPT or other transformer, and a scope (optional for burn in). Connect the primary of the OPT to the audio generator, and wire the secondary of the OPT in series between the DC power supply and the cap under test. Connect the scope across the cap.
Adjust the DC power supply to apply the desired DC bias across the cap. Turn up the audio generator to force an AC current through the cap. Vary the generator frequency and watch the scope. Ideally you should see only DC across the cap. THe crummy 470 uF caps mentioned above show some AC at all frequencies, and a large peak (several volts) in the 5 KHz range (its been a few years since I have done this). A good cap may show 10's of millivolts with no peaks in the audio range. This should be no problem as a cathode bypass.
Like I said this was all done several years ago so the exact frequency might have been 3 KHz or 8 Khz but it was in that range. The capacitors in question were made in the early 70's. I think I still have some, but no longer use them in anything due to their age. When I get some time I want to reproduce these experiments in a more controlled manner. Don't know when that will be.
I hear that there may be a piece of equipment floating around the plant made for measuring the effective impedance of battery cells. I am going to check it out to determine usefulness for cap testing. It's much smaller than the old component analyzer, so I might be able to hide it in the lab somewhere......
Hello,
Mechanical resonance was identified as the variable of interest / culprit.
Not fact but speculation. Is there a relationship between cost of the capacitor and minimal resonance? I would suspect the price above some break point (eliminate the low quality control stuff) may not have a lot to do with performance.
Limiting the range say (picked from the sky for conversation) to 0.47 uf metalized polypropylene plastic capacitors some cost a dollar some cost 20 dollars some cost more. Is there a test to sort through the hype? Perhaps a sweep of impulse test to weed out the hype and mechanically resonate capacitors.
To stay on topic I am looking for the most bang for the buck!
DT
All just for fun!
Mechanical resonance was identified as the variable of interest / culprit.
Not fact but speculation. Is there a relationship between cost of the capacitor and minimal resonance? I would suspect the price above some break point (eliminate the low quality control stuff) may not have a lot to do with performance.
Limiting the range say (picked from the sky for conversation) to 0.47 uf metalized polypropylene plastic capacitors some cost a dollar some cost 20 dollars some cost more. Is there a test to sort through the hype? Perhaps a sweep of impulse test to weed out the hype and mechanically resonate capacitors.
To stay on topic I am looking for the most bang for the buck!
DT
All just for fun!
In order for something to resonate, it will have to be able to support a standing wave within the component. In order for this to affect component performance, the expansion/compression of the wave will have to change component parameters. A polypro cap (in its simplest form) is two layers of film with some polypropylene plastic film in between. The whole thing is then dunked in epoxy. I highly doubt you'll be able to get it to resonate mechanically in the audio range.
As far as the question of why some polypro caps cost $1 and others $20 for the same capacitance... Some of it is probably due to higher manufacturing costs. A lot of tricks are pulled to lower the ESR and ESL of film caps. And in other cases, there may be requirements of ability to fail safely (X, Y caps) that could drive up cost. But like so many other things in audio, a lot of the cost riser is, in my opinion, hype.
~Tom
Aw, man... I feel your pain. There should be laws against that!!
Few years ago, I was able to pull my TEK 2465B, some HP power supplies, and a Fluke scope meter off the cart as the recycling guy was loading it up. I just happened to be a tad early that day and was able to catch things as they were free-falling towards the scrap heap.
~Tom
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