| Author |
Message |
John Smith
Guest
|
 Posted:
Wed Feb 16, 2005 5:21 am Post subject:
Back to back aluminum electrolytics |
|
|
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the increase
in distortion is due to the caps rather than my naivety with these instruments?
If these measurements are accurate, is the distortion introduced by the caps
equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load measures
..295% distortion.
I appreciate the education you guys are giving me. Thanks.
John
|
|
| Back to top |
|
 |
John Smith
Guest
|
| Posted:
Wed Feb 16, 2005 6:11 am Post subject:
Re: Back to back aluminum electrolytics |
|
|
Guy Macon wrote:
| Quote: | John Smith wrote:
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the increase
in distortion is due to the caps rather than my naivety with these instruments?
If these measurements are accurate, is the distortion introduced by the caps
equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load measures
.295% distortion.
I appreciate the education you guys are giving me. Thanks.
Could you try it at 1V and 0.1V and tell us what results you get?
|
With this setup, the 331A does not have enough sensitivity at these lower
voltages to calibrate the reference level for a reading. That's the main
reason I used 3V. However, I also tried to use enough voltage to exceed a
possible 1V threshold reverse voltage for the caps (if that's important).
But, yes, I can repeat the measurements using some suggestions from Roger
and Robert and try to design the setup to for all the requirements as I now
see them. If I can't get to it tomorrow, it will have to wait until I get
back into town (the 28th).
Thanks for asking.
John |
|
| Back to top |
|
|
Guy Macon
Guest
|
| Posted:
Wed Feb 16, 2005 6:11 am Post subject:
Re: Back to back aluminum electrolytics |
|
|
John Smith wrote:
| Quote: |
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the increase
in distortion is due to the caps rather than my naivety with these instruments?
If these measurements are accurate, is the distortion introduced by the caps
equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load measures
.295% distortion.
I appreciate the education you guys are giving me. Thanks.
|
Could you try it at 1V and 0.1V and tell us what results you get?
|
|
| Back to top |
|
|
Roger Lascelles
Guest
|
| Posted:
Wed Feb 16, 2005 6:11 am Post subject:
Re: Back to back aluminum electrolytics |
|
|
"John Smith" <kd5yikes@mindspring.com> wrote in message
news:ztvQd.1076$kU3.811@newsread1.news.pas.earthlink.net...
| Quote: | The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the increase
in distortion is due to the caps rather than my naivety with these
instruments?
If these measurements are accurate, is the distortion introduced by the
caps
equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load measures
.295% distortion.
I appreciate the education you guys are giving me. Thanks.
John
|
Unfortunately, combined percent distortions do not add arithmetically. For
example, the capacitor might have a nonlinearity which is equal and opposite
to the generator nonlinearity - giving a low distortion reading, and leading
you to believe that the capacitor has *negative* distortion! Since the
distortion readings you quote are all in the same ballpark, I would'nt draw
any conclusions about the capacitor distortion.
Also, the capacitor is dropping most of the voltage, so it it is phase
shifting the oscillator distortion (harmonics) and that can change the way
the oscillator distortion reads on the analyser.
Also, the capacitor - resistor acts as a high pass filter which accentuates
the oscillator harmonics and thus increases the distortion appearing across
the resistor.
My guess is that your capacitor distortion is small compared to the
distortion of your test setup.
I don't know what the lower limit of the 331A analyser is, but it is
probably 0.1% or better. With a better oscillator, you can get your test
setup residual down.
I would pick my resistor to get the same voltage across the resistor as
across the capacitor - at this point, the capacitor is dropping plenty of
voltage, but there is still plenty of output across the resistor. This
seems to be a standard setup used for capacitors - that way you can compare
results with others.
Roger |
|
| Back to top |
|
|
John Smith
Guest
|
| Posted:
Wed Feb 16, 2005 6:11 am Post subject:
Re: Back to back aluminum electrolytics |
|
|
Roger Lascelles wrote:
| Quote: | "John Smith" <kd5yikes@mindspring.com> wrote in message
news:ztvQd.1076$kU3.811@newsread1.news.pas.earthlink.net...
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the increase
in distortion is due to the caps rather than my naivety with these
instruments?
If these measurements are accurate, is the distortion introduced by the
caps
equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load measures
.295% distortion.
I appreciate the education you guys are giving me. Thanks.
John
Unfortunately, combined percent distortions do not add arithmetically. For
example, the capacitor might have a nonlinearity which is equal and opposite
to the generator nonlinearity - giving a low distortion reading, and leading
you to believe that the capacitor has *negative* distortion! Since the
distortion readings you quote are all in the same ballpark, I would'nt draw
any conclusions about the capacitor distortion.
Also, the capacitor is dropping most of the voltage, so it it is phase
shifting the oscillator distortion (harmonics) and that can change the way
the oscillator distortion reads on the analyser.
Also, the capacitor - resistor acts as a high pass filter which accentuates
the oscillator harmonics and thus increases the distortion appearing across
the resistor.
My guess is that your capacitor distortion is small compared to the
distortion of your test setup.
I don't know what the lower limit of the 331A analyser is, but it is
probably 0.1% or better. With a better oscillator, you can get your test
setup residual down.
I would pick my resistor to get the same voltage across the resistor as
across the capacitor - at this point, the capacitor is dropping plenty of
voltage, but there is still plenty of output across the resistor. This
seems to be a standard setup used for capacitors - that way you can compare
results with others.
Roger
|
Thanks, Roger. That's the kind of information I was looking for. I have an
HP 651 Test Oscillator which, if I recall correctly, has lower distortion.
It also has a 600 Ohm output and a 50 Ohm output.
The 331A's lowest switch setting is .1%, so the meter will read .1% at full
scale on that range.
I will repeat the test with the better oscillator and an integrating RC with
a resistor of about 36 Ohms. At 402 Hz, the capacitor should then look like
36 Ohms and the combination would then have an impedance magnitude of 50 ohms.
Does this sound like a better try at it?
Thanks immensely.
John |
|
| Back to top |
|
|
Robert Baer
Guest
|
| Posted:
Wed Feb 16, 2005 6:11 am Post subject:
Re: Back to back aluminum electrolytics |
|
|
John Smith wrote:
| Quote: |
Roger Lascelles wrote:
"John Smith" <kd5yikes@mindspring.com> wrote in message
news:ztvQd.1076$kU3.811@newsread1.news.pas.earthlink.net...
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the increase
in distortion is due to the caps rather than my naivety with these
instruments?
If these measurements are accurate, is the distortion introduced by the
caps
equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load measures
.295% distortion.
I appreciate the education you guys are giving me. Thanks.
John
Unfortunately, combined percent distortions do not add arithmetically. For
example, the capacitor might have a nonlinearity which is equal and opposite
to the generator nonlinearity - giving a low distortion reading, and leading
you to believe that the capacitor has *negative* distortion! Since the
distortion readings you quote are all in the same ballpark, I would'nt draw
any conclusions about the capacitor distortion.
Also, the capacitor is dropping most of the voltage, so it it is phase
shifting the oscillator distortion (harmonics) and that can change the way
the oscillator distortion reads on the analyser.
Also, the capacitor - resistor acts as a high pass filter which accentuates
the oscillator harmonics and thus increases the distortion appearing across
the resistor.
My guess is that your capacitor distortion is small compared to the
distortion of your test setup.
I don't know what the lower limit of the 331A analyser is, but it is
probably 0.1% or better. With a better oscillator, you can get your test
setup residual down.
I would pick my resistor to get the same voltage across the resistor as
across the capacitor - at this point, the capacitor is dropping plenty of
voltage, but there is still plenty of output across the resistor. This
seems to be a standard setup used for capacitors - that way you can compare
results with others.
Roger
Thanks, Roger. That's the kind of information I was looking for. I have an
HP 651 Test Oscillator which, if I recall correctly, has lower distortion.
It also has a 600 Ohm output and a 50 Ohm output.
The 331A's lowest switch setting is .1%, so the meter will read .1% at full
scale on that range.
I will repeat the test with the better oscillator and an integrating RC with
a resistor of about 36 Ohms. At 402 Hz, the capacitor should then look like
36 Ohms and the combination would then have an impedance magnitude of 50 ohms.
Does this sound like a better try at it?
Thanks immensely.
John
|
Might be better to measure magnitudes of frequency components
(fundamental, 2nd, 3rd, etc harmonics) at the output of the oscillator
and at the resistor.
If the RC is far away from the fundamental, one could get: a) low
frequency would give apparent high "distortion" at the resistor due to
RC rolloff; b) high frequency would give same "distortion" due to low
drop across the caps.
Hence the suggestion. One should be able to *calculate* the level of
each frequency component at the resistor, from the RC value and the
oscillator level of each frequency component. |
|
| Back to top |
|
|
John Smith
Guest
|
| Posted:
Wed Feb 16, 2005 6:11 am Post subject:
Re: Back to back aluminum electrolytics |
|
|
Robert Baer wrote:
| Quote: | John Smith wrote:
Roger Lascelles wrote:
"John Smith" <kd5yikes@mindspring.com> wrote in message
news:ztvQd.1076$kU3.811@newsread1.news.pas.earthlink.net...
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the increase
in distortion is due to the caps rather than my naivety with these
instruments?
If these measurements are accurate, is the distortion introduced by the
caps
equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load measures
.295% distortion.
I appreciate the education you guys are giving me. Thanks.
John
Unfortunately, combined percent distortions do not add arithmetically. For
example, the capacitor might have a nonlinearity which is equal and opposite
to the generator nonlinearity - giving a low distortion reading, and leading
you to believe that the capacitor has *negative* distortion! Since the
distortion readings you quote are all in the same ballpark, I would'nt draw
any conclusions about the capacitor distortion.
Also, the capacitor is dropping most of the voltage, so it it is phase
shifting the oscillator distortion (harmonics) and that can change the way
the oscillator distortion reads on the analyser.
Also, the capacitor - resistor acts as a high pass filter which accentuates
the oscillator harmonics and thus increases the distortion appearing across
the resistor.
My guess is that your capacitor distortion is small compared to the
distortion of your test setup.
I don't know what the lower limit of the 331A analyser is, but it is
probably 0.1% or better. With a better oscillator, you can get your test
setup residual down.
I would pick my resistor to get the same voltage across the resistor as
across the capacitor - at this point, the capacitor is dropping plenty of
voltage, but there is still plenty of output across the resistor. This
seems to be a standard setup used for capacitors - that way you can compare
results with others.
Roger
Thanks, Roger. That's the kind of information I was looking for. I have an
HP 651 Test Oscillator which, if I recall correctly, has lower distortion.
It also has a 600 Ohm output and a 50 Ohm output.
The 331A's lowest switch setting is .1%, so the meter will read .1% at full
scale on that range.
I will repeat the test with the better oscillator and an integrating RC with
a resistor of about 36 Ohms. At 402 Hz, the capacitor should then look like
36 Ohms and the combination would then have an impedance magnitude of 50 ohms.
Does this sound like a better try at it?
Thanks immensely.
John
Might be better to measure magnitudes of frequency components
(fundamental, 2nd, 3rd, etc harmonics) at the output of the oscillator
and at the resistor.
|
I do not have and instrument capable of these measurements.
| Quote: | If the RC is far away from the fundamental, one could get: a) low
frequency would give apparent high "distortion" at the resistor due to
RC rolloff; b) high frequency would give same "distortion" due to low
drop across the caps.
|
The RC will be such that Xc = R = 36 Ohms at the test frequency of 402 Hz.
| Quote: | Hence the suggestion. One should be able to *calculate* the level of
each frequency component at the resistor, from the RC value and the
oscillator level of each frequency component.
|
Is this what a frequency-selective voltmeter is for (or, better, a spectrum
analyzer)?
Thanks, Robert.
John |
|
| Back to top |
|
|
Robert Baer
Guest
|
| Posted:
Wed Feb 16, 2005 3:19 pm Post subject:
Re: Back to back aluminum electrolytics |
|
|
John Smith wrote:
| Quote: |
Robert Baer wrote:
John Smith wrote:
Roger Lascelles wrote:
"John Smith" <kd5yikes@mindspring.com> wrote in message
news:ztvQd.1076$kU3.811@newsread1.news.pas.earthlink.net...
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the increase
in distortion is due to the caps rather than my naivety with these
instruments?
If these measurements are accurate, is the distortion introduced by the
caps
equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load measures
.295% distortion.
I appreciate the education you guys are giving me. Thanks.
John
Unfortunately, combined percent distortions do not add arithmetically. For
example, the capacitor might have a nonlinearity which is equal and opposite
to the generator nonlinearity - giving a low distortion reading, and leading
you to believe that the capacitor has *negative* distortion! Since the
distortion readings you quote are all in the same ballpark, I would'nt draw
any conclusions about the capacitor distortion.
Also, the capacitor is dropping most of the voltage, so it it is phase
shifting the oscillator distortion (harmonics) and that can change the way
the oscillator distortion reads on the analyser.
Also, the capacitor - resistor acts as a high pass filter which accentuates
the oscillator harmonics and thus increases the distortion appearing across
the resistor.
My guess is that your capacitor distortion is small compared to the
distortion of your test setup.
I don't know what the lower limit of the 331A analyser is, but it is
probably 0.1% or better. With a better oscillator, you can get your test
setup residual down.
I would pick my resistor to get the same voltage across the resistor as
across the capacitor - at this point, the capacitor is dropping plenty of
voltage, but there is still plenty of output across the resistor. This
seems to be a standard setup used for capacitors - that way you can compare
results with others.
Roger
Thanks, Roger. That's the kind of information I was looking for. I have an
HP 651 Test Oscillator which, if I recall correctly, has lower distortion.
It also has a 600 Ohm output and a 50 Ohm output.
The 331A's lowest switch setting is .1%, so the meter will read .1% at full
scale on that range.
I will repeat the test with the better oscillator and an integrating RC with
a resistor of about 36 Ohms. At 402 Hz, the capacitor should then look like
36 Ohms and the combination would then have an impedance magnitude of 50 ohms.
Does this sound like a better try at it?
Thanks immensely.
John
Might be better to measure magnitudes of frequency components
(fundamental, 2nd, 3rd, etc harmonics) at the output of the oscillator
and at the resistor.
I do not have and instrument capable of these measurements.
If the RC is far away from the fundamental, one could get: a) low
frequency would give apparent high "distortion" at the resistor due to
RC rolloff; b) high frequency would give same "distortion" due to low
drop across the caps.
The RC will be such that Xc = R = 36 Ohms at the test frequency of 402 Hz.
Hence the suggestion. One should be able to *calculate* the level of
each frequency component at the resistor, from the RC value and the
oscillator level of each frequency component.
Is this what a frequency-selective voltmeter is for (or, better, a spectrum
analyzer)?
Thanks, Robert.
John
|
Yes, one use. |
|
| Back to top |
|
|
Roger Lascelles
Guest
|
| Posted:
Wed Feb 16, 2005 3:30 pm Post subject:
Re: Back to back aluminum electrolytics |
|
|
"John Smith" <kd5yikes@mindspring.com> wrote in message
news:30yQd.1416$IU.1402@newsread3.news.pas.earthlink.net...
| Quote: |
Thanks, Roger. That's the kind of information I was looking for. I have an
HP 651 Test Oscillator which, if I recall correctly, has lower distortion.
It also has a 600 Ohm output and a 50 Ohm output.
The 331A's lowest switch setting is .1%, so the meter will read .1% at
full
scale on that range.
I will repeat the test with the better oscillator and an integrating RC
with
a resistor of about 36 Ohms. At 402 Hz, the capacitor should then look
like
36 Ohms and the combination would then have an impedance magnitude of 50
ohms.
Does this sound like a better try at it?
Thanks immensely.
John
|
I get the 36R and 402Hz numbers too, so looks good.
Maxim have an interesting app note :
"Do Passive Components Degrade Audio Quality in Your Portable Device?"
http://www.maxim-ic.com/appnotes.cfm/appnote_number/3171
In this app note tantalums, aluminium electros and polyester caps are
measured. In the app note, the graphs show distortion rising as you go
lower in frequ, which increases the signal voltage across the cap. There is
plenty of distortion at the frequency where the R and C have equal voltages
(99.5 Hz on figure 8), so this should be a good measurement point.
According to fig 8, below the -3db frequency, the distortion rises, but the
output signal decreases, so the audible effect won't be worse at lower
frequency.
Roger |
|
| Back to top |
|
|
John Smith
Guest
|
| Posted:
Wed Feb 16, 2005 8:25 pm Post subject:
Re: Back to back aluminum electrolytics |
|
|
Roger Lascelles wrote:
| Quote: | "John Smith" <kd5yikes@mindspring.com> wrote in message
news:ztvQd.1076$kU3.811@newsread1.news.pas.earthlink.net...
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the increase
in distortion is due to the caps rather than my naivety with these
instruments?
If these measurements are accurate, is the distortion introduced by the
caps
equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load measures
.295% distortion.
I appreciate the education you guys are giving me. Thanks.
John
Unfortunately, combined percent distortions do not add arithmetically. For
example, the capacitor might have a nonlinearity which is equal and opposite
to the generator nonlinearity - giving a low distortion reading, and leading
you to believe that the capacitor has *negative* distortion! Since the
distortion readings you quote are all in the same ballpark, I would'nt draw
any conclusions about the capacitor distortion.
Also, the capacitor is dropping most of the voltage, so it it is phase
shifting the oscillator distortion (harmonics) and that can change the way
the oscillator distortion reads on the analyser.
Also, the capacitor - resistor acts as a high pass filter which accentuates
the oscillator harmonics and thus increases the distortion appearing across
the resistor.
My guess is that your capacitor distortion is small compared to the
distortion of your test setup.
I don't know what the lower limit of the 331A analyser is, but it is
probably 0.1% or better. With a better oscillator, you can get your test
setup residual down.
I would pick my resistor to get the same voltage across the resistor as
across the capacitor - at this point, the capacitor is dropping plenty of
voltage, but there is still plenty of output across the resistor. This
seems to be a standard setup used for capacitors - that way you can compare
results with others.
Roger
|
Okay, here's what I did...
o-------C+--+C----|
|
402 Hz 50 Ohms
|
o-----------------|
At 3V and at 1V input, .32% distortion at input and .38% across the resistor.
Swapped the C and R positions (made it an integrator), changed the R to
33.33 Ohms, and changed the frequency to 440 Hz:
o-------33.33 Ohms----|
|
C
440 Hz +
+
C
|
o---------------------|
3V applied, .31% input distortion, 2.01 V @ .182% across C
1V applied, .31% input distortion, .67 V @ .176% across C
..422 V applied, .32% input distortion, .3V @ .185% across C
The last measurement was the lowest input the 331A could handle and I'm
thinking there may be more error in it than in the first two.
I don't know where I got the idea that the 651A had less distortion than the
204D. A bit disappointing.
I'll go read that Maxim page to which you referred and try to learn
something. Thanks.
John |
|
| Back to top |
|
|
Phil Hobbs
Guest
|
| Posted:
Wed Feb 16, 2005 11:04 pm Post subject:
Re: Back to back aluminum electrolytics |
|
|
John Smith wrote:
| Quote: | Guy Macon wrote:
John Smith wrote:
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the
increase in distortion is due to the caps rather than my naivety
with these instruments?
If these measurements are accurate, is the distortion introduced by
the caps equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load
measures .295% distortion.
I appreciate the education you guys are giving me. Thanks.
Could you try it at 1V and 0.1V and tell us what results you get?
With this setup, the 331A does not have enough sensitivity at these
lower voltages to calibrate the reference level for a reading. That's
the main reason I used 3V. However, I also tried to use enough voltage
to exceed a possible 1V threshold reverse voltage for the caps (if
that's important).
But, yes, I can repeat the measurements using some suggestions from
Roger and Robert and try to design the setup to for all the
requirements as I now see them. If I can't get to it tomorrow, it will
have to wait until I get back into town (the 28th).
Thanks for asking.
John
|
One interesting thing to try would be to apply a variable dc bias to the
point between the two capacitors, varying it from a moderate positive
voltage to a very small negative one, and see what that does to your
distortion measurements. A second interesting thing would be to make
one capacitor twice as large in value as the other (or use a different
technology, e.g. ceramic or tantalum). Your circuit will tend to make
odd-order harmonics cancel, while even-order ones will add. Making the
capacitors asymmetrical intentionally will eliminate this cancellation.
Cheers,
Phil |
|
| Back to top |
|
|
Guy Macon
Guest
|
| Posted:
Wed Feb 16, 2005 11:51 pm Post subject:
Re: Back to back aluminum electrolytics |
|
|
Phil Hobbs wrote:
| Quote: | One interesting thing to try would be to apply a variable dc bias to the
point between the two capacitors, varying it from a moderate positive
voltage to a very small negative one, and see what that does to your
distortion measurements.
|
Excellent idea! If the distortion changes, it pretty much has to
be distortion introduced by the capacitors. |
|
| Back to top |
|
|
John Smith
Guest
|
| Posted:
Thu Feb 17, 2005 3:23 am Post subject:
Re: Back to back aluminum electrolytics |
|
|
Phil Hobbs wrote:
| Quote: | John Smith wrote:
Guy Macon wrote:
John Smith wrote:
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the
increase in distortion is due to the caps rather than my naivety
with these instruments?
If these measurements are accurate, is the distortion introduced by
the caps equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load
measures .295% distortion.
I appreciate the education you guys are giving me. Thanks.
Could you try it at 1V and 0.1V and tell us what results you get?
With this setup, the 331A does not have enough sensitivity at these
lower voltages to calibrate the reference level for a reading. That's
the main reason I used 3V. However, I also tried to use enough voltage
to exceed a possible 1V threshold reverse voltage for the caps (if
that's important).
But, yes, I can repeat the measurements using some suggestions from
Roger and Robert and try to design the setup to for all the
requirements as I now see them. If I can't get to it tomorrow, it will
have to wait until I get back into town (the 28th).
Thanks for asking.
John
One interesting thing to try would be to apply a variable dc bias to the
point between the two capacitors, varying it from a moderate positive
voltage to a very small negative one, and see what that does to your
distortion measurements. A second interesting thing would be to make
one capacitor twice as large in value as the other (or use a different
technology, e.g. ceramic or tantalum). Your circuit will tend to make
odd-order harmonics cancel, while even-order ones will add. Making the
capacitors asymmetrical intentionally will eliminate this cancellation.
Cheers,
Phil
|
Yes, I agree. I just haven't had time. I've got to go pack now. I'll try to
get back on this when I get back in town about March 1.
Thanks for all your help.
John |
|
| Back to top |
|
|
John Popelish
Guest
|
| Posted:
Thu Feb 17, 2005 5:37 am Post subject:
Re: Back to back aluminum electrolytics |
|
|
Phil Hobbs wrote:
| Quote: |
John Smith wrote:
Guy Macon wrote:
John Smith wrote:
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the
increase in distortion is due to the caps rather than my naivety
with these instruments?
If these measurements are accurate, is the distortion introduced by
the caps equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load
measures .295% distortion.
I appreciate the education you guys are giving me. Thanks.
Could you try it at 1V and 0.1V and tell us what results you get?
With this setup, the 331A does not have enough sensitivity at these
lower voltages to calibrate the reference level for a reading. That's
the main reason I used 3V. However, I also tried to use enough voltage
to exceed a possible 1V threshold reverse voltage for the caps (if
that's important).
But, yes, I can repeat the measurements using some suggestions from
Roger and Robert and try to design the setup to for all the
requirements as I now see them. If I can't get to it tomorrow, it will
have to wait until I get back into town (the 28th).
Thanks for asking.
John
One interesting thing to try would be to apply a variable dc bias to the
point between the two capacitors, varying it from a moderate positive
voltage to a very small negative one, and see what that does to your
distortion measurements. A second interesting thing would be to make
one capacitor twice as large in value as the other (or use a different
technology, e.g. ceramic or tantalum). Your circuit will tend to make
odd-order harmonics cancel, while even-order ones will add. Making the
capacitors asymmetrical intentionally will eliminate this cancellation.
Cheers,
Phil
|
I think another interesting experiment would be to make a bridge with
a resistor and back to back electrolytics in one side, and a (possibly
higher value) resistor and film capacitor in the other side, and
amplify the difference voltage between the two sides, after adjusting
the resistors for best phase balance. This should emphasize the
distortion difference between the two kinds of caps and low pass
filter and cancel most of the distortion from the source. You would
need an instrumentation amplifier.
--
John Popelish |
|
| Back to top |
|
|
dd
Guest
|
| Posted:
Fri Feb 18, 2005 1:27 am Post subject:
Re: Back to back aluminum electrolytics |
|
|
In message <4213D942.42185E3E@rica.net>, John Popelish
<jpopelish@rica.net> writes
| Quote: | Phil Hobbs wrote:
John Smith wrote:
Guy Macon wrote:
John Smith wrote:
The thread on back to back tantalums aroused my curiosity. I had no
tantalums, so I used a couple of aluminum electrolytics. They are 22
microfarads at 16V each, Mouser PN 555-16V22 (Elna RVS16V220M-R).
o-----------> -C+ -- +C--|
|
HP 204D Osc 100 Ohms
|
o------------------------|
Using an HP 331A Distortion Analyzer:
Set 3V at 20 +- 0.5 Hz on 204D output.
Read .395 V across the resistor.
Read .193% distortion out of 204D.
Read .365% distortion across the resistor.
So, what can I learn from this? Is there a way to verify that the
increase in distortion is due to the caps rather than my naivety
with these instruments?
If these measurements are accurate, is the distortion introduced by
the caps equal to the difference in measurements (.365 - .193)?
And here's a fly in the ointment-- the oscillator with no load
measures .295% distortion.
I appreciate the education you guys are giving me. Thanks.
Could you try it at 1V and 0.1V and tell us what results you get?
With this setup, the 331A does not have enough sensitivity at these
lower voltages to calibrate the reference level for a reading. That's
the main reason I used 3V. However, I also tried to use enough voltage
to exceed a possible 1V threshold reverse voltage for the caps (if
that's important).
But, yes, I can repeat the measurements using some suggestions from
Roger and Robert and try to design the setup to for all the
requirements as I now see them. If I can't get to it tomorrow, it will
have to wait until I get back into town (the 28th).
Thanks for asking.
John
One interesting thing to try would be to apply a variable dc bias to the
point between the two capacitors, varying it from a moderate positive
voltage to a very small negative one, and see what that does to your
distortion measurements. A second interesting thing would be to make
one capacitor twice as large in value as the other (or use a different
technology, e.g. ceramic or tantalum). Your circuit will tend to make
odd-order harmonics cancel, while even-order ones will add. Making the
capacitors asymmetrical intentionally will eliminate this cancellation.
Cheers,
Phil
I think another interesting experiment would be to make a bridge with
a resistor and back to back electrolytics in one side, and a (possibly
higher value) resistor and film capacitor in the other side, and
amplify the difference voltage between the two sides, after adjusting
the resistors for best phase balance. This should emphasize the
distortion difference between the two kinds of caps and low pass
filter and cancel most of the distortion from the source. You would
need an instrumentation amplifier.
There is a series of articles in UK Electronics World written by a |
capacitor manufacturing specialist on distortion due to capacitors and a
dedicated measurement system / circuit (pcb layout included) articles
published 1/2 years ago most easily available by buying CDs of the last
few years of Eletronics World
--
dd |
|
| Back to top |
|
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|
|
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