C'mon guys, get those bids in! only 10 hours left!
Seriously, this is a hoot. Looks like its well-made.
Cheers,
Bob
Ebay listing ...
$179 USD with 3 hrs and 45 minutes to go approx. 8 bids so far.
I'm going to bet that there are some excited people waiting in the wings to bid that way up in the last few minutes. It's an excellent analyzer.
Bob, wouldn't it be interesting to see a modernized version of your design that utilizes something like a PIC micro-controller? Other people could design an Ethernet or USB interface for it. A 24 bit analog DAC and you have an Audio Precision type instrument. An IEEE-488 bus for the old die hards around here (I'd use that, or Ethernet).
Things that could be.
On another note, Agilent has come out with an audio test set that runs around $15 K USD. Looks nice, but OUCH!
-Chris
$179 USD with 3 hrs and 45 minutes to go approx. 8 bids so far.
I'm going to bet that there are some excited people waiting in the wings to bid that way up in the last few minutes. It's an excellent analyzer.
Bob, wouldn't it be interesting to see a modernized version of your design that utilizes something like a PIC micro-controller? Other people could design an Ethernet or USB interface for it. A 24 bit analog DAC and you have an Audio Precision type instrument. An IEEE-488 bus for the old die hards around here (I'd use that, or Ethernet).
Things that could be.
On another note, Agilent has come out with an audio test set that runs around $15 K USD. Looks nice, but OUCH!
-Chris
Hi Chris,
Yes, that would make a great project. Others have suggested basically the same thing, especially with respect to the PIC. There is so much great technology available to the DIYer today. I've had some limited experience with the PIC at work, and they are just great.
I think the key thing that new technology could add would be in making the implementation easier. Those switching arrangements were very expensive and labor intensive. A PIC and maybe an interface to a PC would really make the unit more versatile and easy to use as well.
Newer op amps, like the LM4562 would also improve the residual performance.
It is scary how much commercial THD analyzers cost these days. Even the good ole HP339A seems to go for about $300-$500 on Ebay, and it does not do much better than 0.002%.
Best,
Bob
Bob,
I estimate that your design cost me around 500USD to make, using good components like new generation opamps at critical places, WIMA film caps, Panasonic FC Electrolytics, 1% Beyschlag resistors, etc. My experience is that electro-mechanical parts (housing, knobs, switches, ......) will easily cost more than 50%. OK, I did have balanced in & out with Lemo connectors, which added to the cost.
And it was really a lot of work with the wiring. So $300 for a HP339A is an easy option for people who do not want to DIY for the sake of it. My motivation then, in addition to taking up the challenge, was the ability to maintain the unit in the future without worrying about obsolete parts. If you buy a HP339, some of its parts are likely to need replacement before long, with unknown costs.
In the end, I am very happy that I built it, and have the satisfaction that my implementation still looks neat compared to others published.
But if one were to use uP or PC based solutions, then the distortion magnifier, together with a 24-bit sound card configured as functions generator and spectrum analyser, is IMHO the simplest solution for most distortion measurements in the audio band. As you know, I am building a version of the distortion magnifier which is very close to being finished. And I shall publish in due course. With 3 opamps (all National LME series), the distortion magnifier costs less than 40USD in electronics, but again decent mechanics parts pushed the total cost to almost 140 USD. Just the Fischer KOH housing with lettering and machining was 50 USD.
Patrick
I estimate that your design cost me around 500USD to make, using good components like new generation opamps at critical places, WIMA film caps, Panasonic FC Electrolytics, 1% Beyschlag resistors, etc. My experience is that electro-mechanical parts (housing, knobs, switches, ......) will easily cost more than 50%. OK, I did have balanced in & out with Lemo connectors, which added to the cost.
And it was really a lot of work with the wiring. So $300 for a HP339A is an easy option for people who do not want to DIY for the sake of it. My motivation then, in addition to taking up the challenge, was the ability to maintain the unit in the future without worrying about obsolete parts. If you buy a HP339, some of its parts are likely to need replacement before long, with unknown costs.
In the end, I am very happy that I built it, and have the satisfaction that my implementation still looks neat compared to others published.
But if one were to use uP or PC based solutions, then the distortion magnifier, together with a 24-bit sound card configured as functions generator and spectrum analyser, is IMHO the simplest solution for most distortion measurements in the audio band. As you know, I am building a version of the distortion magnifier which is very close to being finished. And I shall publish in due course. With 3 opamps (all National LME series), the distortion magnifier costs less than 40USD in electronics, but again decent mechanics parts pushed the total cost to almost 140 USD. Just the Fischer KOH housing with lettering and machining was 50 USD.
Patrick
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Bob,
I estimate that your design cost me around 500USD to make, using good components like new generation opamps at critical places, WIMA film caps, Panasonic FC Electrolytics, 1% Beyschlag resistors, etc. My experience is that electro-mechanical parts (housing, knobs, switches, ......) will easily cost more than 50%. OK, I did have balanced in & out with Lemo connectors, which added to the cost.
And it was really a lot of work with the wiring. So $300 for a HP339A is an easy option for people who do not want to DIY for the sake of it. My motivation then, in addition to taking up the challenge, was the ability to maintain the unit in the future without worrying about obsolete parts. If you buy a HP339, some of its parts are likely to need replacement before long, with unknown costs.
In the end, I am very happy that I built it, and have the satisfaction that my implementation still looks neat compared to others published.
But if one were to use uP or PC based solutions, then the distortion magnifier, together with a 24-bit sound card configured as functions generator and spectrum analyser, is IMHO the simplest solution for most distortion measurements in the audio band. As you know, I am building a version of the distortion magnifier which is very close to being finished. And I shall publish in due course. With 3 opamps (all National LME series), the distortion magnifier costs less than 40USD in electronics, but again decent mechanics parts pushed the total cost to almost 140 USD. Just the Fischer KOH housing with lettering and machining was 50 USD.
Patrick
Hi Patrick,
These are all very good points. The availability of high-quality soundcards and PCs with good software has changed the measurement landscape for the DIYer. The capabilities of these largely digital-based instruments are enhanced by the use of the analog-based DM.
Doing really good THD-20 is challenging, however, even for a 192 kHz soundcard. The 200 kHz bandwidth of an analog THD analyzer is nice to have. Being able to see the actual residual in real time is also nice.
Cheers,
Bob
Bob,
I have a Handyscope 3 which will do 16 bit 2MHz easily, both as functions generator and scope simultaneously. That is why I built the DM, even though I already have your Analyser. Of course this is a more expensive solution than a sound card for 150USD. But for most DIYers who most likely will already have a 24/192 soundcard on their computer, a DM makes a lot of sense.
I need another month and I shall publish everything on the DM then.
Patrick
I have a Handyscope 3 which will do 16 bit 2MHz easily, both as functions generator and scope simultaneously. That is why I built the DM, even though I already have your Analyser. Of course this is a more expensive solution than a sound card for 150USD. But for most DIYers who most likely will already have a 24/192 soundcard on their computer, a DM makes a lot of sense.
I need another month and I shall publish everything on the DM then.
Patrick
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Yes, I'm sorry - you're quite right. I took your 'level control' to refer to the oscillator level.
Hi Patrick,
That Handyscope sounds nice. I don't think I realized that the PC scope cards went up to 16 bits out to 2 MHz analog bandwidth. That would seem to mean that the scope A2D sample rate is at least 4 MHz at 16 bits. Putting the DM in front of that will definitely mitigate the limitations of 16 bits anyway. Does your Handyscope come with FFT and THD software? Being able to do spectrum analysis from 10 Hz to 2 MHz is really nice.
Best,
Bob
> Does your Handyscope come with FFT and THD software?
Yes.
> Being able to do spectrum analysis from 10 Hz to 2 MHz is really nice.
I should correct myself. 3MHz sampling at 14 bit. Still not bad :
http://www.tiepie.com/downloads/documents/HS3_spec.pdf
Not cheap though !
Patrick
Yes.
> Being able to do spectrum analysis from 10 Hz to 2 MHz is really nice.
I should correct myself. 3MHz sampling at 14 bit. Still not bad :
http://www.tiepie.com/downloads/documents/HS3_spec.pdf
Not cheap though !
Patrick
Well, got a HS3 for test, but in spectrum mode the harmonics are way too high, even at 16bit. Got about -70dB THD, see attachment.
At 16bit, we should see about 90dB dynamic. Source was Krohn-Hite 4400A and E-MU 1616m, these are down -120dB normally.
Patrick, if you have some spare time, would you mind to check your HS3 results against Bob's analyzer and, maybe, some FFT's via ARTA/Spectralab etc.
BR
Gary from Vienna
At 16bit, we should see about 90dB dynamic. Source was Krohn-Hite 4400A and E-MU 1616m, these are down -120dB normally.
Patrick, if you have some spare time, would you mind to check your HS3 results against Bob's analyzer and, maybe, some FFT's via ARTA/Spectralab etc.
BR
Gary from Vienna
Attachments
Patrick corrected himself to 14 bits, but that should yield between 78 and 84 dB. It is also possible that the -70 dB just comes from the analog electronics in front of the ADC, since scope vertical amplifiers that go to 2 MHz or more are not often designed to do on the order of 0.01% THD.
Anyway, this points out the value in using the DM. if the DM is set to a magnification of 40 dB, then with the HSO at -70 you might get down to -110 dB, or 0.003%.
Cheers,
Bob
Such devices are handy to do spectral analysis of the notch filter residual but surely entirely unsuitable for direct distortion measurements. Better converters exist (e.g. LTC2215-LTC2217) but -90 dB is still somewhat short of excellence.
With recent audio DA/AD converters and sufficient care/experience it should be possible to get somewhere near -110 dB THD+N at 1 kHz and for a 20 kHz bandwidth. Good enough for most purposes but still inferior to an all analogue analyser. Bandwidth becomes less a problem as more and more converters support 384 kHz and up. Which of course doesn't mean that the noise and distortion performance keeps up at frequencies above the audio range.
Samuel
PS: Bob, are the schematics of your DA still available?
With recent audio DA/AD converters and sufficient care/experience it should be possible to get somewhere near -110 dB THD+N at 1 kHz and for a 20 kHz bandwidth. Good enough for most purposes but still inferior to an all analogue analyser. Bandwidth becomes less a problem as more and more converters support 384 kHz and up. Which of course doesn't mean that the noise and distortion performance keeps up at frequencies above the audio range.
Samuel
PS: Bob, are the schematics of your DA still available?
Hi Patrick,
You did an amazing job on your build! Fantastic!
Your PC scope sounds really promising. Most DSOs are 8 bit, with more expensive models allowing a 12 bit mode. Yours at 16 bit, 2 MHz is very attractive. I did buy one with far lower specs - and it died. I'm having trouble getting it repaired. They won't release schematics and getting it there (far east) is becoming a real issue. It might be garbage.
Hi Bob,
I think that a computer connection is optional and for extended features. Things like setup recall, computer control and data storage and sampling. With a normalized DC, your ADC choices are far more relaxed. Too bad DDS technology wasn't lower distortion, because that would give you an analog sweep ability - or spot checks. Still, the basic instrument could easily be uP run with a keypad on the panel. An analog meter is something I would keep, even if you had a high resolution digital reading. Ever adjust an FM tuner discriminator with only a digital meter? Keep the analog meter!
Updating your basic idea with newer parts should give you a lower noise floor on an already excellent instrument. We do have a number of members that could do the micro-controller side. This would make the killer instrument while also providing a rare kit building experience. I have to admit to missing Heathkit a lot.
You know what Bob? You are to be heart-fully <spell checker> thanked for the creation and publishing of your first project. I'm sure it was a labor of love, and an impressive feat of engineering. The idea of a type II is extremely attractive, especially if you have some help. I don't think a PC scope can replace a low noise purpose built THD meter. Besides, with your meter, you can control the ground currents and noise. Something I found was difficult with a USB based thing.
And yes, the lucky winning bidder has an excellent deal. I wonder how much he knows just how good an instrument he now has?
-Chris
You did an amazing job on your build! Fantastic!
Your PC scope sounds really promising. Most DSOs are 8 bit, with more expensive models allowing a 12 bit mode. Yours at 16 bit, 2 MHz is very attractive. I did buy one with far lower specs - and it died. I'm having trouble getting it repaired. They won't release schematics and getting it there (far east) is becoming a real issue. It might be garbage.
Hi Bob,
I think that a computer connection is optional and for extended features. Things like setup recall, computer control and data storage and sampling. With a normalized DC, your ADC choices are far more relaxed. Too bad DDS technology wasn't lower distortion, because that would give you an analog sweep ability - or spot checks. Still, the basic instrument could easily be uP run with a keypad on the panel. An analog meter is something I would keep, even if you had a high resolution digital reading. Ever adjust an FM tuner discriminator with only a digital meter? Keep the analog meter!
Updating your basic idea with newer parts should give you a lower noise floor on an already excellent instrument. We do have a number of members that could do the micro-controller side. This would make the killer instrument while also providing a rare kit building experience. I have to admit to missing Heathkit a lot.
You know what Bob? You are to be heart-fully <spell checker> thanked for the creation and publishing of your first project. I'm sure it was a labor of love, and an impressive feat of engineering. The idea of a type II is extremely attractive, especially if you have some help. I don't think a PC scope can replace a low noise purpose built THD meter. Besides, with your meter, you can control the ground currents and noise. Something I found was difficult with a USB based thing.
And yes, the lucky winning bidder has an excellent deal. I wonder how much he knows just how good an instrument he now has?
-Chris
Gary's measurements are correct, or similar to mine. I am not sure though whether it comes from the scope or the built-in func gen. But as Bob said, a DM will enhance that by another 40dB or so. I am not looking for a perfect THD analyser, or a substitute for an Audio Precision or the like. I already have the HS3 for quite a few years now, which I find excellent for what I need (scope, func gen, better than 8 bit resoultion). No other USB scope has all these functionalities.
With the DM and a HS3, I can see distortion residuals down to 0.005mV from a 5V signal, which is better than 100dB. The absolute value does not interest me, and I never try to build amplifiers with -200dB THD. The frequency spectrum of the distortion is more interesting, as it allows me to trade between 2nd and 3rd, etc.
Of course you can invest in a proper spectrum analyser, and use that in combination with a good func gen (e.g. Bob's) and a DM to better results. I am sure there are also other good combinations. I merely want to point out what simple, low-cost solution one can have to allow some not-so-absolutely-serious DIYers to do simple THD measurements (namely Soundcard and DM).
I actually asked Bob whether he was willing to let me publish his DM design. He said he would rather tidy it up to his usual high standard first before posting at his website. I of course respect that. So you will just have to wait a while till I am ready to publish my own version, inspired by Bob's but different in many details.
Patrick
With the DM and a HS3, I can see distortion residuals down to 0.005mV from a 5V signal, which is better than 100dB. The absolute value does not interest me, and I never try to build amplifiers with -200dB THD. The frequency spectrum of the distortion is more interesting, as it allows me to trade between 2nd and 3rd, etc.
Of course you can invest in a proper spectrum analyser, and use that in combination with a good func gen (e.g. Bob's) and a DM to better results. I am sure there are also other good combinations. I merely want to point out what simple, low-cost solution one can have to allow some not-so-absolutely-serious DIYers to do simple THD measurements (namely Soundcard and DM).
I actually asked Bob whether he was willing to let me publish his DM design. He said he would rather tidy it up to his usual high standard first before posting at his website. I of course respect that. So you will just have to wait a while till I am ready to publish my own version, inspired by Bob's but different in many details.
Patrick
Were you looking for the DA as in Distortion Analyzer, or were you actually looking for the DM as in Distortion Magnifier?
Best,
Bob
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