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Old 13th April 2010, 02:22 PM   #11
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I have a certain experience with soundcards and measurements.

I had a good external soundcard and a good program.
The problems with these "equipment" are:

1) measurements are not often repeatable
2) signal generator has a relative low distortion at 1KHz but then varies a lot with frequency and level.
3)hi frequency output nose at the output will cause some issues when try to scope an amplifier with high gain (like a phono stage)
4) distortion's measurements are not linear with the frequency measured nor the input level
5) you can easily burn the input.
6) if you want t more precise measurements your reading will take something like 10-15 seconds and one more time the measurements is often a little bit different from the previous one due to many factor on the computer like memory occupation, buffers and register situations of the microprocessor at the moment, ram's occupation and so on; this drove me nut a bit

I used it and it was useful but anybody who thinks can build a good measurement's system, should always keep on watch and in mind the points above.

me I finally got a sound technology system 1710A and exeternal generator 1410A just yesterday and looks really good.
When I will have full control on the devices I will be able to make a comparison between the STs and soundcard's system.

Hope this helps.
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Old 13th April 2010, 10:43 PM   #12
rize is offline rize  United States
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Quote:
Originally Posted by Stefanoo View Post
I have a certain experience with soundcards and measurements.

I had a good external soundcard and a good program.
The problems with these "equipment" are:

1) measurements are not often repeatable
2) signal generator has a relative low distortion at 1KHz but then varies a lot with frequency and level.
3)hi frequency output nose at the output will cause some issues when try to scope an amplifier with high gain (like a phono stage)
4) distortion's measurements are not linear with the frequency measured nor the input level
5) you can easily burn the input.
6) if you want t more precise measurements your reading will take something like 10-15 seconds and one more time the measurements is often a little bit different from the previous one due to many factor on the computer like memory occupation, buffers and register situations of the microprocessor at the moment, ram's occupation and so on; this drove me nut a bit

I used it and it was useful but anybody who thinks can build a good measurement's system, should always keep on watch and in mind the points above.

me I finally got a sound technology system 1710A and exeternal generator 1410A just yesterday and looks really good.
When I will have full control on the devices I will be able to make a comparison between the STs and soundcard's system.

Hope this helps.
Stafanoo,

Thank you this is very helpful.

PC based software tools maybe a step in the right direction but I'm doubtful whether they're better for measuring distortion than testing tools designed exclusively for that purpose as opposed to PC's which are multi-purpose machines. If for example my objective is reducing distortion, I prefer to measure the results of my modifications with a more sensitive tool so I can evaluate what has changed with better accuracy. My ears are the final judge but I also like to compare what I hear to what was measured.

There's too much going with the PC motherboard, the processor, the peripherals - plenty of activity that have nothing to do with measuring distortion, frequency & amplitude. If I want to adjust my wrist-watch, the most accurate reference is probably one of those atomic watches at the US Naval Observatory or something similar - not the clock at the local supermarket.

Friend of mine passed along this website from Germany.
http://www.tubelab.com/testing.htm
The applications & graphics look promising and the prices are not too crazy. I worked in the software development industry for 25 years and I'm always weary of spending money on software which IMO depreciates at a faster rate than any well-built testing tool. I still have a DMM from the 80's that serves me well but I wonder how many people still use software that old.

May I ask how much you spent total for ST 1710a and 1410a ? I assume you bought these used ?
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Old 27th April 2010, 12:29 AM   #13
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I needed a quasi-sine wave oscillator to produce a stable signal to balance the signals on the channels of my various stereo equipment- turned out to be mismatched transistors on the ST120 and really old paper capacitors off value in the PAS2 preamp. I built a 2 transistor phase shift oscillator out of the GE transistor manual seventh edition, only I changed the NPN transistors to PNP because I had a junk box full of them. Used a 12 vCT transformer to make 9VDC with capacitors from a dead PC power supply. Need I say I'm unemployed. Nice looking signal on a scope. Besides junk cost me a dual RCA jack output, 1 plug to 2 jack RCA cable, and a couple of 25k pots for level setting. one 20 mv output for phone, one 900 mv output for power amp. I bought an XR2206 but never built it, too many parts, project is done.
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Old 27th April 2010, 12:48 AM   #14
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Hi,

The 2 units were purchased for $470.
They are in a very good shape and perfect working condition.
I recalibrated them and they do both measure very great.

I actually don't understand why the seller which was a professional TV station had both units when the generator which comes in a separate units is the same of the generator of the distortion units (same performance and same features).

So all in all, I am considering to re-sell the sole 1410A Audio Generator, ultra low distortion and low IM distortion too.

If anybody is in case interested, just drop me an email.

I mean I don't have to necessary sell it as I like to have equipment, but all in all is exactly the same generator so...
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Old 27th April 2010, 01:03 AM   #15
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Default distortion analysis

Oh, for distortion measurement on audio, I use my ears. High notes on a piano or violin have a certain sound, with good enough source and speakers you can hear what you want. I'm using Rudolf Serkin "three Beethoven Sonata's" Colombia, LP or CD, also ZZ Top Afterburner Warner (for extreme bass) Also Peter Nero "Warm & Wonderful" LP, RCA, solo work only. Piano on high notes has a lot of impact energy, really stresses the power reserve and transient generation facility. A cheap CD player is fine, but I have been upgrading speakers all my life. the Peavey SP2's I just bought sound an awfully lot like the Steinway console piano located between the speakers. I get a lot more use out of good speaker than you would a waveform generator, too, unless you are selling stuff. I played some Count Basie today, those tracks lifted to CD's off of 78 records really brought back the Intermodulation distorted sound of the bad old days.
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Old 27th April 2010, 01:15 AM   #16
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Unfortunately your speakers are too cheap to evaluate true dynamic of a piano or the timber of the violin or the texture of a voice.

Perhaps I am wrong: are you referring to those speaker?

Buy Peavey SP 2 2-Way 15" Speaker | Unpowered Cabinets | Musician's Friend


No one professional will just build things "only" by listening, altough I do agree with you it ia a big thing.
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Old 27th April 2010, 01:21 AM   #17
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I don't know if I am misinterpretating this too, you said "a cheap CD player is fine".
Did you mean that it doesn't matter the quality of the source?
If so, I guess you are very wrong.

It is like saying that you are drinking water coming from a contaminated area but you are pooring it on a super clean charm glass.

What do you think the water will be like?
it won't only taste bad but it will look dirty as well, doesn't it?

Every element of your audio chaing should carefully be choosen and matched and if there is anything that should be superior, that is definitely the source


Sorry I don't mean to be grumpy or crabby...I just want to make this little point clear.
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Last edited by Stefanoo; 27th April 2010 at 01:23 AM.
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Old 27th April 2010, 03:03 AM   #18
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Default golden eared are funny

You're entitled to your opinion. I've heard a lot of opinions over the years. I listen to different people's ideas of a good speaker, and laugh all the way home, mostly. I played bassoon in HS and piano still, I have some memory of real sound . I liked the Altec-Lansing Voice of the Theater at Long Point Cinema Houston the best, until now. My band director pointed them out as being wonderful (in 1965). Lord Jim the movie was amazing with the Java orchestra, although the LP of the soundtrack I bought was dissapointingly flat. I've had KLH 23, LW Erath-3 ,Peavey T300 speakers before now. The T300's had good highs on axis, but fell off fast with a slight movement of 2' to the side. The bass was weak. The Peavey SP2xt's are built like a VOT, which is why I went and auditioned them, but they have a 1" dia horn driver instead of 4". The newer models at the store with the smooth horn are even better than the jointed horn XP's. Wonderful high piano reproduction, and you can walk around the room without losing all the highs. With the 15" woofer, the bass is entirely adequate, much better than anything before. You can hear the difference in clarity between the Peavey CS800 amp that came with the speakers, just okay, and the DJoffe modification ST120 amp I'm using now. I had to tweak some things on the ST120 to get here, as I said. I'm not saying every cheap CD player is okay, but this $25 RCA one is fine, as good as the turntable on the same LP's Serkin and Afterburner . As I say, the calibrator is the Steinway piano- if you don't know what to listen for, go to the piano store or concert hall and listen, especially to the top octave. I was just listening to some grand pianos tonight on HDTV- weak, no impact, either poorly miked, or the HDTV reproduction is poor, or both. Properly miked violin and cymbal are also good sources, although cymbal construction varies a lot. Pop, jazz, you can't tell what it is supposed to sound like, unless there is solo piano. Lots of speakers do mid-frequencies well.
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Old 27th April 2010, 03:20 AM   #19
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Well I don't know how to say it...or better where to start saying what I want to say.

I think a lot of people do listen to live music (at least I do) and I do personally play classical guitar too.
From a player standpoint, it's not much of a help because you do hear the instrument from another position where instead you are listening through as if you were on the audience or listening to a home stereo system plus when you play you are definitely concentrated on other things.

The more you listen and the more you can get a better handle of the "field".

Said that, I have never heard any $25 CD player being able to cope with any of the live music parameters I know.
If we talk then about a cheap commercial amplifier being able to reproduce the dynamic of a piano or a choral or WHATEVER, then there are tons of technical reasons of why this is not possible.
Just to give you one: usually cheap amp don't have a very powerful outptut stage/PSU combo and this is affects sound big time.
It costs a lot to make a robust power amp.
Then not to talk about measurable distortion and low quality parts and so on.

I do have a cable running from the RCA of my tonearm to the phonostage that just that costs more than twice as much all your system put together
I mean, there is a reason of why a cheap car won't go as fast and won't be as beautiful as a Ferrari otherwise Ferrari will stop making car and rich people won't have any luxury car to buy
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Old 27th April 2010, 06:49 PM   #20
shuang is offline shuang  Canada
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Originally Posted by rize View Post
Thanks for everyone's input.

Book by Morgan Jones - Building Valve Amplifiers, recommends audio oscillators instead of function generator or typical bench oscillator for audio testing with the following specs;

- low distortion < .05% sine valve oscillator 20 Hz - 20KHz.
- wide band meter calibrated to read sine waves
- simple form of THD measurement
- peak programme meter (PPM) for measuring noise

I live in the US and I'm looking at HP and Tek since their vintage gear is known for their reliability. So far I have noted 651A from the mid-60's. The specs for HP 239A from 79' seem impressive for a product 30 years old.

HP 239A specs (bottom)
Audio & Test

Audio oscillators must have seen lot of improvements since 1979 but my budget is below $300. Is HP 239A the best option short of building testing circuits from scratch, assuming I can find one under $300?
The unequalled characteristic of the HP 239A is its distortion specification. For a 3 volts output, up to 20 kHz, the signal distortion is below -95 dB, which is equivalent to a 0.0018 %THD ! In the upper part of its frequency coverage, up to 110 kHz the distortion stay specified below -70 dB (0.032% THD) These unsurpassed characteristics make the HP 239A, a still today highly appreciated reference for distortion measurement on the audiophile test bench.
From the link you provided on the HP239A, I am now a believer, .

Unfortunately I can't find an affordable HP239A.

Any opinions on the HP204C or Krohn-Hite 4200B as a poor man's substitute?

HP 204C Oscillator
Output of the HP Model 204C is a sine wave from 5 Hz to 1 .2 MHz in six overlapping bands. The amplitude is 5 V rms open circuit with a 600 ohm output impedance. The instrument can be line or battery operated. It can be powered from either mercury cells, or from rechargeable nickel-cadmium batteries. One of the main advantages of the Model 204C is high signal purity. Total harmonic distortion approaches 70 dB below fundamental across most of the frequency range.

Krohn-Hite 4200B
The model 4200 is an all solid state, general purpose Test Oscillator that provides a main sine wave and an auxiliary sine wave from 10 Hz to 10 MHz. It operates from AC of 115 or 230 V, 50-400 Hz

The main sine wave output is variable from 0 to 10 volts rms open-circuit or 5 volts rms across 50 ohms. Max power output is 1/2 watt with less than 0.1% harmonic distortion. The auxiliary output is a sine wave fixed at 1 volt rms open circuit, and coincident with the main output.
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