My implementation of the Cordell Distortion Analyser - Page 11 - diyAudio
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Old 31st January 2010, 02:56 PM   #101
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Originally Posted by jackinnj View Post
C'mon guys, get those bids in! only 10 hours left!

Seriously, this is a hoot. Looks like its well-made.

Cheers,
Bob
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Old 31st January 2010, 03:05 PM   #102
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Originally Posted by Bob Cordell View Post
C'mon guys, get those bids in! only 10 hours left!

Seriously, this is a hoot. Looks like its well-made.

Cheers,
Bob
That's how mine looked inside

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Old 31st January 2010, 10:00 PM   #103
anatech is offline anatech  Canada
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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
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Old 31st January 2010, 11:49 PM   #104
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Quote:
Originally Posted by anatech View Post
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
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
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Old 1st February 2010, 01:24 AM   #105
EUVL is offline EUVL  Europe
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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

Last edited by EUVL; 1st February 2010 at 01:30 AM.
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Old 1st February 2010, 03:21 AM   #106
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Originally Posted by EUVL View Post
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
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Old 1st February 2010, 03:32 AM   #107
EUVL is offline EUVL  Europe
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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

Last edited by EUVL; 1st February 2010 at 03:37 AM.
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Old 1st February 2010, 04:39 AM   #108
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Well I sure wouldn't sell mine for $207, so somebody got a great deal.
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Old 1st February 2010, 05:12 AM   #109
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Originally Posted by giulianodes View Post
Hi abraxalito,
I refer to Q7 FET (see image).
Yes, I'm sorry - you're quite right. I took your 'level control' to refer to the oscillator level.
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Old 1st February 2010, 03:11 PM   #110
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Quote:
Originally Posted by EUVL View Post
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
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
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