Cordell THD analyzer
I got this from from Mr.Cordell:
Thanks for your interest in my THD analyzer article, and thanks for asking before republishing on the web. It turns out that another gentleman and I have been in conversation regarding a possible updating of the design and publication in a magazine, so I would not want it to be republished on the web. However, I'm interested in knowing more about what you have in mind.
Best regards,
Bob Cordell
I got this from from Mr.Cordell:
Thanks for your interest in my THD analyzer article, and thanks for asking before republishing on the web. It turns out that another gentleman and I have been in conversation regarding a possible updating of the design and publication in a magazine, so I would not want it to be republished on the web. However, I'm interested in knowing more about what you have in mind.
Best regards,
Bob Cordell
Harry:
Was Mr. Cordell's response recent (e.g. within the last month or so)? To answer his question, he could take a look at the beginning of this thread. I was planning on building the original, since I was lucky enough to find a set of PCBs from the original article. If he's seriously thinking of redoing the design, I'd be willing to wait and see. It seems the only magazine left with a decent worldwide distribution is "Audio Engineering".
By the way, would you also ask if he's also considering updating the power amp design he published some years ago in JAES (and various MOSFET manuals) with the super high performance JFET front-end?
Thanks!
mlloyd1
Was Mr. Cordell's response recent (e.g. within the last month or so)? To answer his question, he could take a look at the beginning of this thread. I was planning on building the original, since I was lucky enough to find a set of PCBs from the original article. If he's seriously thinking of redoing the design, I'd be willing to wait and see. It seems the only magazine left with a decent worldwide distribution is "Audio Engineering".
By the way, would you also ask if he's also considering updating the power amp design he published some years ago in JAES (and various MOSFET manuals) with the super high performance JFET front-end?
Thanks!
mlloyd1
THD Analyzer
The response was today and I am afraid that I spoke prematurely on the new article since it is tenative and I don't have a date or what magazine it is in. I would press on with the existing project. I am working on getting together a list of articles and web resources on distotion measurement A.S.A.P and will post soon. I don't believe that extremly low distortion measurements are an indication of sound quality but think that measurements down to 0.05 % are not too hard to measure and cound be useful.
Thanks,
H.H.
The response was today and I am afraid that I spoke prematurely on the new article since it is tenative and I don't have a date or what magazine it is in. I would press on with the existing project. I am working on getting together a list of articles and web resources on distotion measurement A.S.A.P and will post soon. I don't believe that extremly low distortion measurements are an indication of sound quality but think that measurements down to 0.05 % are not too hard to measure and cound be useful.
Thanks,
H.H.
PCB source info for Cordell Analyzer from Audio magazine
Folks:
I was able to track down the following info about the source for the PCBs I mentioned earlier:
Circuit Works
85 W. Sylvania Avenue
Neptune City, NJ 07753
(908) 774-1811
Set of 3 boards for Cordell THD Analyzer project was about $45
However, the invoice was dated 16Dec1992 (!!!) so the possibilities are slim. However, if you're feeling lucky, you never know what could happen......
Michael
Folks:
I was able to track down the following info about the source for the PCBs I mentioned earlier:
Circuit Works
85 W. Sylvania Avenue
Neptune City, NJ 07753
(908) 774-1811
Set of 3 boards for Cordell THD Analyzer project was about $45
However, the invoice was dated 16Dec1992 (!!!) so the possibilities are slim. However, if you're feeling lucky, you never know what could happen......
Michael
Here is a program I tried which works very nicely. I get a good 90dB range out of a standard soundcard.
http://www.visualizationsoftware.com/gram.html
http://www.visualizationsoftware.com/gram.html
Re: Cordell THD analyzer
I agree we should respect Mr. Cordell's interests. But for goodness sakes, the article in question was published 20 years ago! Is Mr. Cordell actively working on this article or is he just trying to keep his options open. I hope he can provide some indication on when and were we can expect the new article to be published. If the answer is "I don't know, whenever I get around to writing is and can get someone interested", then this is just being an obstructionist.
I imagine anyone interested in a copy of this article would also be interested in purchasing Mr. Cordell's new article when it is published, even if in the meantime they managed to get their hands on a copy of the '82 issue.
Anyone got a lead on where to buy back issues of Audio?
Phil
I agree we should respect Mr. Cordell's interests. But for goodness sakes, the article in question was published 20 years ago! Is Mr. Cordell actively working on this article or is he just trying to keep his options open. I hope he can provide some indication on when and were we can expect the new article to be published. If the answer is "I don't know, whenever I get around to writing is and can get someone interested", then this is just being an obstructionist.
I imagine anyone interested in a copy of this article would also be interested in purchasing Mr. Cordell's new article when it is published, even if in the meantime they managed to get their hands on a copy of the '82 issue.
Anyone got a lead on where to buy back issues of Audio?
Phil
HarryHaller said:
They laughed when I praised my HD-1
I resurrected a Heath HD-1, new caps, better wiring (star grounding etc.) , faster meter diodes, and replaced the 50 ohm trimming potentiometer with a multi-turn variety. The darn thing is pretty acurate (probably +/-0.02%, down to about 0.03%), certainly not up to my HP339a, certainly susceptible to ground loop problems, but for $10 not bad at all. I guess if I were to gild the lily I would put in a true RMS detector!
I've toyed around with notch filters/elliptical filters/all sorts of configurations. If you are going to make a highly selective notch filter with discrete components you will spend a lot of time matching components.
Here's an important note -- if you decide to use the Linear Tech LTC1063 active low pass filters in a high quality oscillator note that they do not like to be switched mechanically and are susceptible to overload if the + and - rails do not come on at exactly the same time. I owe thanks to Linear's technical service rep who helped me through some problems implementing these filters. You must also filter the "filtered" output as there is some residual tnoise from the clocking source. (This is pointed out in their applications notes) Note further -- the filter design using the LTC1063 in Audio Amateur had the power supply connections incorrectly marked. As they say in carpentry, measure twice, cut once. Linear has some nice filter design "free-ware" on their site.
Jack
I resurrected a Heath HD-1, new caps, better wiring (star grounding etc.) , faster meter diodes, and replaced the 50 ohm trimming potentiometer with a multi-turn variety. The darn thing is pretty acurate (probably +/-0.02%, down to about 0.03%), certainly not up to my HP339a, certainly susceptible to ground loop problems, but for $10 not bad at all. I guess if I were to gild the lily I would put in a true RMS detector!
I've toyed around with notch filters/elliptical filters/all sorts of configurations. If you are going to make a highly selective notch filter with discrete components you will spend a lot of time matching components.
Here's an important note -- if you decide to use the Linear Tech LTC1063 active low pass filters in a high quality oscillator note that they do not like to be switched mechanically and are susceptible to overload if the + and - rails do not come on at exactly the same time. I owe thanks to Linear's technical service rep who helped me through some problems implementing these filters. You must also filter the "filtered" output as there is some residual tnoise from the clocking source. (This is pointed out in their applications notes) Note further -- the filter design using the LTC1063 in Audio Amateur had the power supply connections incorrectly marked. As they say in carpentry, measure twice, cut once. Linear has some nice filter design "free-ware" on their site.
Jack
HP 331A
If you want a quick and dirty solution for measuring audio distortion, just get an HP 334A from eBay. They typically go for about $100. I got my (near mint) 333A for $50. These are good down to about 0.01% on the meter. There are always plenty for sale.
Unless, of course, you want to DIY.
jh
If you want a quick and dirty solution for measuring audio distortion, just get an HP 334A from eBay. They typically go for about $100. I got my (near mint) 333A for $50. These are good down to about 0.01% on the meter. There are always plenty for sale.
Unless, of course, you want to DIY.
jh
HP 33X
These HP distortion meters also respond well to basic tweaking. I replaced all the aging electrolytic caps in mine, did a little bypassing here and there, and the RMS voltmeter's range was extended from 3 to 7 MHz+, and the residual voltmeter noise is now below 14 microvolts.
They are also very stable (except perhaps at the ultimate bottom of their distortion range).
At the same time, they're pretty well useless if you are interested in fine tuning in the really low distortion domain (sub 0.02 %).
Norman
These HP distortion meters also respond well to basic tweaking. I replaced all the aging electrolytic caps in mine, did a little bypassing here and there, and the RMS voltmeter's range was extended from 3 to 7 MHz+, and the residual voltmeter noise is now below 14 microvolts.
They are also very stable (except perhaps at the ultimate bottom of their distortion range).
At the same time, they're pretty well useless if you are interested in fine tuning in the really low distortion domain (sub 0.02 %).
Norman
current soundcards with S/PDIF input?
I am a little wary of anything that sits inside a computer and is powered by it. What are current soundcards that have a S/PDIF input that will accept >20 bits, preferably at 96 or 192 kHz?
TI has a nice 24 bit ADC. With a decent oscillator and S/PDIF transmitter (or even I2S directly), it would make a very good analyzer.
Eric
I am a little wary of anything that sits inside a computer and is powered by it. What are current soundcards that have a S/PDIF input that will accept >20 bits, preferably at 96 or 192 kHz?
TI has a nice 24 bit ADC. With a decent oscillator and S/PDIF transmitter (or even I2S directly), it would make a very good analyzer.
Eric
Jim Williams oscillator
Wow, I had forgotten all about the Williams version of the HP200 (wien using a lamp). So I quickly built one myself just to see. Yup - 0.01% distortion (as far down as my HP 333A goes) right off the bat. No extra filtering, just a one opamp oscillator.
I used a common 5W nightlight bulb we had on hand. They're quite easy to solder to. See schematic below for a 1kHz frequency. Adapt as you need, but this is one quick and easy project.
Now 0.01% may not be low enough for some of you high-feedback fans, but for my zero-feedback tube amplifiers, it's adequate. I measured my new "Cornet" phono preamp with this oscillator (padded down to 5mV) and got a total 1kHz distortion level of 0.02%. Not bad!
Wow, I had forgotten all about the Williams version of the HP200 (wien using a lamp). So I quickly built one myself just to see. Yup - 0.01% distortion (as far down as my HP 333A goes) right off the bat. No extra filtering, just a one opamp oscillator.
I used a common 5W nightlight bulb we had on hand. They're quite easy to solder to. See schematic below for a 1kHz frequency. Adapt as you need, but this is one quick and easy project.
Now 0.01% may not be low enough for some of you high-feedback fans, but for my zero-feedback tube amplifiers, it's adequate. I measured my new "Cornet" phono preamp with this oscillator (padded down to 5mV) and got a total 1kHz distortion level of 0.02%. Not bad!
Attachments
PC polling rate?
One could actually read I2S or any other serial audio format into a PC provided the PC is fast enough to detect changes on the serial clock and the read the data line.
The last time I tried I/O port programming, I could get about 300 kHz on the parallel port and it seemed to be pretty independent of the speed of the computer used, but that was in the times of 75 MHz pentiums and 133 MHz 486s. Anybody know the polling rate of a modern GHz PC running Windoze98 or better and using Delphi?
Eric
One could actually read I2S or any other serial audio format into a PC provided the PC is fast enough to detect changes on the serial clock and the read the data line.
The last time I tried I/O port programming, I could get about 300 kHz on the parallel port and it seemed to be pretty independent of the speed of the computer used, but that was in the times of 75 MHz pentiums and 133 MHz 486s. Anybody know the polling rate of a modern GHz PC running Windoze98 or better and using Delphi?
Eric
Enhanced S Blaster
I have in project to build a bridged tee filter, and to insert it at the input of a standard S Blaster PC card. Correctly designed and constructed, bridged tee can attenuate the fundamental by 60 dB.(Some amplification will be necessary between the filter and the SB card, depending of the level of the signal.)
S Blaster 128 can give correct analysis on a 60 dB range (or more) So, I expect possibilty of measuring distortion in the range -60 to -120 dB (or more), which is exactly that I need to measure audio amplifiers or components... cheap and effective !
Thank you for your comments/advices...
Regards, Pierre Lacombe.
I have in project to build a bridged tee filter, and to insert it at the input of a standard S Blaster PC card. Correctly designed and constructed, bridged tee can attenuate the fundamental by 60 dB.(Some amplification will be necessary between the filter and the SB card, depending of the level of the signal.)
S Blaster 128 can give correct analysis on a 60 dB range (or more) So, I expect possibilty of measuring distortion in the range -60 to -120 dB (or more), which is exactly that I need to measure audio amplifiers or components... cheap and effective !
Thank you for your comments/advices...
Regards, Pierre Lacombe.
Anyone try Praxis? http://www.libinst.com/
I use LAUD (no longer available) to get distortion <.01% which is not great but it is easy to use.
I use LAUD (no longer available) to get distortion <.01% which is not great but it is easy to use.
FFT and Dist.Analyzer
Hi,
One idea I saw when browsing the internet run the signal to a ordinary THD analyzer wich attenuates the fundamental to -60dB feed the output to a cheap 16 bit soundcard with a freeware fft program do the math and calculate the residual I think one can get really low thd figure out of this I don't remember how but it should work.
Hi,
One idea I saw when browsing the internet run the signal to a ordinary THD analyzer wich attenuates the fundamental to -60dB feed the output to a cheap 16 bit soundcard with a freeware fft program do the math and calculate the residual I think one can get really low thd figure out of this I don't remember how but it should work.
Miscellaneous Thoughts
On the Cordell Analyzer: I have the 3 part article and the PC boards, but this is a vary complex project and the selector switches are made out of unobtainium (at least at resonable prices ).
On the Jim Williams Oscillator: The best version uses a CdS photocell, the Vactec VTL5C10 or Clarex CLM410 both made out of unobtainium.
On the Charles Hansen Oscillator: The 5/1998 issue of Audio Electronics magazine has his article on a buildable version of the Williams oscillator.
On SpectraLab software: You can downlord a 30 day trial of the complete package. When the time expires get a new computer and to it again.
On the Cordell Analyzer: I have the 3 part article and the PC boards, but this is a vary complex project and the selector switches are made out of unobtainium (at least at resonable prices ).
On the Jim Williams Oscillator: The best version uses a CdS photocell, the Vactec VTL5C10 or Clarex CLM410 both made out of unobtainium.
On the Charles Hansen Oscillator: The 5/1998 issue of Audio Electronics magazine has his article on a buildable version of the Williams oscillator.
On SpectraLab software: You can downlord a 30 day trial of the complete package. When the time expires get a new computer and to it again.
Miscellaneous Thoughts
Right on brother Can I get a witness?
"On the Jim Williams Oscillator: The best version uses a CdS photocell, the Vactec VTL5C10 or Clarex CLM410 both made out of unobtainium."
You can make this device from an LED and CdS photocell from Radio Shack I think but will have to adjust the circuit for the different transfer function. It looks very doable and has loads of cooliosty potential.
I use the light bulb feedback Wein bridge for my clean AC power and it is very clean. More on the subject of oscillators later and
freeware FFt at:
Fred
Right on brother Can I get a witness?
"On the Jim Williams Oscillator: The best version uses a CdS photocell, the Vactec VTL5C10 or Clarex CLM410 both made out of unobtainium."
You can make this device from an LED and CdS photocell from Radio Shack I think but will have to adjust the circuit for the different transfer function. It looks very doable and has loads of cooliosty potential.
I use the light bulb feedback Wein bridge for my clean AC power and it is very clean. More on the subject of oscillators later and
freeware FFt at:
Fred