| audiorob |
Hi all,
I'm wondering if anyone has recommendations for distortion analyzing equipment.
I have an O-scope, signal generator, variac, bench power supplies, and voltmeters.
I have and use spice. I am a total novice, but I have built an amp or two. I would like
to test the amps I have built and see if they perform anywhere near what spice reports.
As an Audio Precision instrument (like what Nelson uses) is beyond my budget
(I think they start around $10,000 US), one of the solutions I was considering is
YMEC's DSSF3 software with (hopefully) a 192KHz/24 bit sound card. I'm thinking
this will cost around $500 US, or so. Has anyone used this software and have an
opinion?
I think I am mainly trying to measure THD and bandwidth. I'm open to suggestions
if anyone would care make recommendations.
thanks,
Robert |
|
|
| Nelson Pass |
AP is still the best, IMHO. We recently bought 3 more S1's used
at $1600 each.
You can easily build your own IM analyzer, and with somewhat
greater effort you can make a THD analyzer with a bootstrapped
twin T network and some trim pots. An op amp and a little
light bulb can make a quite low distortion oscillator.
:cool: |
|
|
| audiorob |
| quote: | Originally posted by Nelson Pass
AP is still the best, IMHO. We recently bought 3 more S1's used
at $1600 each.
You can easily build your own IM analyzer, and with somewhat
greater effort you can make a THD analyzer with a bootstrapped
twin T network and some trim pots. An op amp and a little
light bulb can make a quite low distortion oscillator.
:cool: |
Thank you for the input Nelson! I would LOVE to build some of this
stuff, but so far, I don't know what a "bootstrapped twin T network" is.
Again, I'm a CS guy, and a network has a completely different meaning
for me! :) Also, my plan is to use this equipment to check my work.
So we get into a kind of recursive problem here.
On the good side, I _think_ I could build some of the op amp based
oscillators mentioned in the Howowitz and Hill book. I have no idea
how to throw a light bulb into the mix, but the idea makes me smile.
Thank you again,
Robert |
|
|
| Damon Hill |
Ebay can be your very good friend. Use "distortion meter" or "distortion analyzer" in your search.
I've been using the Heathkit IM-5248 intermodulation analyzer and IM-5258 THD analyzer for years; they're really about the minimum level of performance needed to do any serious work. Found a Crown IMA, but both meters were shot. A used Hewlett Packard 333 or 334 is a good starting point for a professional analyzer, and I wouldn't turn down Sound Technology equipment (I think ST still supports their old models).
Sound cards with appropriate software is another approach, but I really want a 'front end' with calibrated attenuator before I risk blowing a good card with too much voltage swing. A used HP 400 series AC voltmeter might be a good start in that direction.
Needless to say, Audio Precision is about the ultimate, but even used System Ones get bid out of my budget range every time. I'd also like some serious spectrum analzyer capability; not just audio range but RF as well. |
|
|
| audiorob |
| quote: | Originally posted by Damon Hill
Ebay can be your very good friend. Use "distortion meter" or "distortion analyzer" in your search.
<snip>
|
Thanks for the reply Damon.
Do you (or anyone) happen to know if this type of equipment is easily damaged? Do people try to sell inoperative/damaged equipment on ebay? If so, is that a common problem? Who repairs this type of equipment?
thanks,
Robert |
|
|
| Damon Hill |
Buying used equipment, especially from people or businesses you don't know, can be risky. I've taken chances on retired HP test gear from Boeing and have gotten some great deals; that IM analyzer I found at a music shop in Florida is probably a lost cause since replacing the meters will run over $200.
Most test equipment is not that hard to break, unless you peg the meters constantly or vastly exceed the recommended input voltages. Age is your enemy; parts can fail and some parts may require creative substitution, if it can be done at all.
Search Ebay a while and make notes of all the distortion analyzers that show up for sale; this will at least give you an idea of what's out there. Most of them are obsolete and the original manufacturer may no longer support them; there are companies that will give you quotes on repairs and calibration, usually at a considerable price (and may be worth it, too).
Pay close attention to the descriptions of any units that interest you; some people are honest enough to tell you that they have no idea if it's working properly or not, and are selling 'as is.'
I've taken a few chances and generally won, but I'm also prepared to troubleshoot and repair--or junk--the equipment I've got. And I do some modifications, too; researching improvements on my spare Heathkit IG-18 audio generator, hoping to lower THD down to the .001% level--current modifications have only gotten it to about .01%. I might tackle some improvements on my working Heath distortion analyzers, too. The Heath IM analyzer doesn't meet specs, so it needs work. |
|
|
| Babowana |
| quote: | Originally posted by Nelson Pass
AP is still the best, IMHO. We recently bought 3 more S1's used
at $1600 each.
:cool: |
What could be the second best at similar price?
I'm eager to buy one
Thanks |
|
|
| jackinnj |
If you can't afford an AP here are a few to consider --
Tektronix DA4084 and AA501, Krohn-Hite 6900, Boonton 1120 and 1130, HP334, 339 -- you can also get very nice results with the heath IM and THD analyzers.
Of the above, you can hook up the Boonton to a computer via a data acquisition card and download the performance data to Excel.
For a high quality oscillator look to Linear Tech's PDF of the LT1115, or you can build the super-oscillator which was in one of their application notes (but you have to work with current feedback opamps which can be a bit tricky).
http://www.diyaudio.com/forums/show...1115&highlight= |
|
|
| Henry Pootel |
What about using this to put one together?
http://focus.ti.com/docs/toolsw/fol...271evm-pdk.html
It comes with some software to measure THD and costs $149.
I am not sure if there is an API that you can use for your applications (what I would prefer).
I hope this helps. |
|
|
| jackinnj |
| quote: | Originally posted by Henry Pootel
What about using this to put one together?
http://focus.ti.com/docs/toolsw/fol...271evm-pdk.html
It comes with some software to measure THD and costs $149.
I am not sure if there is an API that you can use for your applications (what I would prefer).
I hope this helps. |
Just make sure to protect the opamp inputs -- the Boonton uses something akin to this setup (it is more complicated)-- with a relay for belt and suspenders. If you use diode clamps on the input the Vcc and Vee should be as quiet as possible:
 |
|
|
| Roar Malmin |
| I am not able to resist. I freely admit that vanity got the best of me. I have been using a Panasonic VP7722 for the last 15 years, which is an excellent instrument. BUT, R&S just brought to market a contraption called UPV. Fully balanced, dual channel, analog and digital domain. Runs under Windows XP Embedded. Programmability guys. FFT noise floor -140dB. Dynamic range 170dB. The best there is in Norway right now. |
|
|
| Babowana |
| quote: | Originally posted by jackinnj
Tektronix DA4084 and AA501, Krohn-Hite 6900, Boonton 1120 and 1130, HP334, 339
|
Thanks for the info.
I however could find none here . . . |
|
|
| jackinnj |
| quote: | Originally posted by Henry Pootel
What about using this to put one together?
http://focus.ti.com/docs/toolsw/fol...271evm-pdk.html
It comes with some software to measure THD and costs $149.
I am not sure if there is an API that you can use for your applications (what I would prefer).
I hope this helps. |
The evaluation kit, fwiw, does not come with an interface -- this you have to purchase separately. the 5-6K Interface Board. |
|
|
| Stefanoo |
i just opened on another section of this forum a similar post...and then.... i found this thread :)
Anyways, i downloaded the brochure of the analyzer mentiond on the post above.
http://www.rohde-schwarz.com/www/Do...UPV_bro_en.pdf/$file/UPV_bro_en.pdf
it looks very interesting....is it the same of what you are talking about on your post?
If so, how much it costs? do you have an evaluate version dr you bought the complete interface? |
|
|
| Roar Malmin |
Including local tax, and the options that I bought, the price is a little over $40K.
Roar |
|
|
| Stefanoo |
...wait....i don't want misunderstand the price.....
40k equal 40 thousands equal 40.000 $ ???
well....if so....preatty expencive and prohibitive for the majority of us!!!!! |
|
|
| Roar Malmin |
| Correct Stefano. I belive it is the best today, anywhere. |
|
|
| ghg |
Interesting new toy, did you consider the AP range, too ?
Can you do some tests, like this ( taken from the AP2700 manual, copyright Audio Precision ) ?
BR
Gary G. |
|
|
| janneman |
Audio Precision system 1 goes on eBay for 2k-3k depending on options. VERY good deal!
Jan Didden |
|
|
| Nelson Pass |
OK....
As fun as they are, big budget analyzers are off-topic in a
DIY forum.
Centrally, besides non-electrical hand tools, the most essential
elements are (in essential order of starting out):
Multimeter - RADIO SHACK FOR $39 (think about a couple of these)
Soldering Iron - RADIO SHACK FOR $19
Variac - MARLIN P JONES FOR $39
Scope - ANYTHING DECENT you can get used.
1 MHz, 5 mV, dual channel, a trigger that works.
Everything else can be built with these.
:cool: |
|
|
| Babowana |
| quote: | Originally posted by Nelson Pass
OK....
Everything else can be built with these.
:cool: |
Praying for it
Found the bootstraped twin-T in THE ART OF ELECTRONICS
Hmmmm . . .
The schematic looks simple tho . . . |
|
|
| janneman |
| quote: | Originally posted by Nelson Pass
[snip]Multimeter - RADIO SHACK FOR $39 (think about a couple of these)
Soldering Iron - RADIO SHACK FOR $19
Variac - MARLIN P JONES FOR $39
Scope - ANYTHING DECENT you can get used.
1 MHz, 5 mV, dual channel, a trigger that works.
Everything else can be built with these.
:cool: |
... says the man with an AP in very room. ;)
But yes, you can built pretty good amps with these tools, (plus a signal generator, perhaps) if you know how to use them best.
Jan Didden |
|
|
| Nelson Pass |
You build the signal generator and the distortion analyzer
at the same time, and use them to test each other.
:cool: |
|
|
| Curmudgeon |
As a personal preference, I like a faster scope; one fast enough to see any HF oscillation.
My favorite was the original Tek 475; last I checked, a new CRT was prohibitive though. And whilst I'm sharing biases and prejudices, I'd avoid the early digital scopes like the plague. Inadequate sampling rates and poor firmware made aliasing a real problem. |
|
|
| Babowana |
| quote: | Originally posted by Nelson Pass
You build the signal generator and the distortion analyzer
at the same time, and use them to test each other.
:cool:
|
Then, this good enuf (20-20K Hz)?
Thanks |
|
|
| anatech |
Hi Babowana,| quote: | | Then, this good enuf (20-20K Hz)? |
Yes, I'm currently using an LDM-171. Bought it brand new years ago.
-Chris |
|
|
| Babowana |
Thank you very much, Chris.
I will buy 171 or 170 whichever is available in the shop :) |
|
|
| anatech |
Hi Babowana,
I had to redo the capacitors in the power supply, so that might be your first project. Don't increase the size.
-Chris |
|
|
| Babowana |
| quote: | Originally posted by anatech
I had to redo the capacitors in the power supply, so that might be your first project. Don't increase the size.
-Chris
|
Understood.
Any good reason for that redoing?
By the way, the shop informed that only LDM-170 is available.
But, I found the price is too high to be a second hand tool.
If she does not lower the price, I should find another shop.
Tks, again :) |
|
|
| Damon Hill |
God help me, but I just broke my budget and bought one of these:
http://tinyurl.com/ybjpvt
What sort of hi-fi nut spends more money on test equipment than he does on actual audio gear? A DIY-er, of course! I couldn't hope to win the bid on a Heathkit AA-1800 power amplifier, not when I wanted this analyzer, too. The IMD capabilities are what grabbed my interest.
I guess I'll have to sell my two Heathkit distortion analyzer to help pay for this excess, but that's what Ebay is for, yes?
There are three of these Tektronix test sets left. |
|
|
| sam9 |
check
http://audio.rightmark.org
You will need buffers and a voltage divider if you want to protect the inputs of your sound card. The soundcard sampling ratye limits you if you want to do a THD plot all the way to 20k Hz.
However it's FREE. Not an unimportant consideration. |
|
|
| Damon Hill |
| An approach to this could be one of the HP 400 series of AC voltmeters, that has an amplified output. A lot depends on how low the meter's noise and distortion is, of course. Heathkit's IM-5238 is a similar instrument, and I have won the bid on a unit on Ebay, so I will see how well suited it may be as a sound card "front end". |
|
|
| Nelson Pass |
| quote: | Originally posted by sam9
check http://audio.rightmark.org
You will need buffers and a voltage divider if you want to protect the inputs of your sound card. The soundcard sampling ratye limits you if you want to do a THD plot all the way to 20k Hz.
|
That looks really cool. When I get time I'll fire it up!
:cool: |
|
|
| sam9 |
There is also http://www.audiotester.de
No free but fairly cheap. Documentation is in imperfect English. When reading it it's easy to hear it in a Schwarzenegger voice. |
|
|
| jackinnj |
| quote: | Originally posted by sam9
There is also http://www.audiotester.de
No free but fairly cheap. Documentation is in imperfect English. When reading it it's easy to hear it in a Schwarzenegger voice. |
Schwarzenegger is a Austrian, and he has abandoned their economics. |
|
|
| steenoe |
The webadress works if you paste it to the browsers adress line.
How does that smiley end up in the link:confused:
Steen:) |
|
|
| SY |
| The BB software sees a colon followed by D as a smiley. That's an unusual combo in a URL and whoever coded the software didn't think of that. |
|
|
| tschrama |
I'll try again...
ebay link
YES ...:cool: made it... |
|
|
| steenoe |
Does anyone have experience with that software? Sounds almost as being too cheap, easy and convenient to be true?
Steen:) |
|
|
| jackinnj |
You will need to find an SG505 or SG502 signal generator, but there is a Tektronix DA4084 on EBay at the moment, and the initial price is dirt cheap. Note-- it comes with its own TM503 power supply and you CAN NOT put the sig gen in the left most compartment. The DA4084 is very much like the AA501, except it has SINAD instead of intermodulation.
here's a link -- someone should snatch this up:
http://cgi.ebay.com/Tektronix-DA408...1QQcmdZViewItem |
|
|
| df |
@steenoe
I use audiotester now for 2 years and I have burned the line inputs of 2 soundcards:xeye:
The results depend on the quality of the soundcard. You can easily find good ones for little $ at ebay and put it in an old PC.
Daniel |
|
|
| anatech |
Hi Daniel,| quote: | | I use audiotester now for 2 years and I have burned the line inputs of 2 soundcards |
I can not understand why you simply don't buy a THD meter and run the residuals into your sound card. This will precondition the signal for you.
-Chris |
|
|
| gaetan8888 |
| quote: | Originally posted by anatech
Hi Daniel,
I can not understand why you simply don't buy a THD meter and run the residuals into your sound card. This will precondition the signal for you.
-Chris |
Hello anatech
Since the THD meter acted only as a notch filter wen you run the residuals into a sound card, do my old HP333 can do as good as a more modern and costly THD meter if I use it this way ?
Thank
Gaetan |
|
|
| jackinnj |
| quote: | Originally posted by anatech
Hi Daniel,
I can not understand why you simply don't buy a THD meter and run the residuals into your sound card. This will precondition the signal for you.
-Chris |
I think that the problem with this is that folks like to look at that pretty image of the fundamental...but the residuals are where the story is at.
DA's have pretty much crashed in price...what the country needs instead is a good, stable signal generator like a Tektronix SG505 or AP-1 but at a cost of thirty or forty bucks. something like this would advance the progress of civilisation. |
|
|
| anatech |
Hi Gaetan,
You have an excellent unit. The weak point will still be your sound card, however you will have more dynamic range by using the HP 333. Many people miss how good the older HP stuff is. I can only imagine how good the new stuff is!
Old stuff I would love to have : All HP, 3585A, 3562A, 8901B, 8903, a new 6000 series scope and some RF generators. An arbitrary waveform generator would be playing, but lovely to have. ;) I'll bet a simpler load of new gear would more than do the trick.
-Chris |
|
|
| error401 |
From the software analysis side of things, check out BaudLine. It runs only in Linux, but has some extremely powerful signal analysis tools. One of its greatest features is that it can do very long term averaging of the frequency domain, allowing you to get extremely precise frequency measurements, average out noise and transient conditions etc. Of course, basic THD, SNR and other distortion measurements are built-in. While not automatic, it is easily capable of measuring other parameters as well, such as IMD and frequency response.
Very powerful tool. |
|
|
| anatech |
Hi error401,
For now, I am stuck with wind blows. Linux doesn't support enough new cards - but I am liking that OS.
At the end of the day, the sound card is still the weak spot in the system. A THD meter makes a great "front end" and signal conditioner.
-Chris |
|
|
| nonoise |
| quote: | Originally posted by jackinnj
Just make sure to protect the opamp inputs -- the Boonton uses something akin to this setup (it is more complicated)-- with a relay for belt and suspenders. If you use diode clamps on the input the Vcc and Vee should be as quiet as possible:
|
Just a small note on using the diodes as indicated:
there exists one problem with this topology in that the diodes will forward conduct at +/- 0.7 volt if the power supply powering this device were to be switched off.
Instead of the intended Vcc/Vee +/- 0.7 V
This will result in excessive current into the diodes if the source device could produce the required current.
So to clarify don't switch the device with the diodes off while still connected to the source.
A small relay right at the input which drop out when the supply voltage are interrupted will cure this problem |
|
|
| anatech |
The other issue that may come up is the variable capacitance from the reverse biased diodes. Double them in series and drive the new junctions with a buffered version of the signal to eliminate that issue.
Hi nonoise,
A relay was mentioned by jackinnj and it was also mentioned that the diagram was simplified. I imagine this was for exactly the reason you brought up.
-Chris ;) |
|
|
| nonoise |
| quote: | Originally posted by anatech
The other issue that may come up is the variable capacitance from the reverse biased diodes. Double them in series and drive the new junctions with a buffered version of the signal to eliminate that issue.
Hi nonoise,
A relay was mentioned by jackinnj and it was also mentioned that the diagram was simplified. I imagine this was for exactly the reason you brought up.
-Chris ;) |
Hi Anatech, yes the relay were mentioned and were probably used as
recommended but I have seen this type of protection often being recommended in application notes (diodes only) and felt that the potential for miss understanding / inadequate protection should be clarified.
From experience I certainly agree on the potential coupling of noise into the input from the supply lines via the diodes, they could also rectify HF noise and perhaps create DC offset problems.
The addition of a small Common Mode choke might help |
|
|
| jackinnj |
| quote: | Originally posted by anatech
The other issue that may come up is the variable capacitance from the reverse biased diodes. |
I think that the junction capacitance of a 1N4148 is about 2e-12.
Jung, I believe it's in "Op Amp Applications" recommended Schottkey diodes for even lower noise.
 |
|
|
| anatech |
Hi jackinnj,
I imagine it depends on what the impedances are. Certainly this type of issue can often be ignored, and sometimes it may be a surprise.
Your posted diagram should show people how much worth there is in having signal conditioning done for them. What to roll your own one of these people? :devilr:
-Chris |
|
|
| jackinnj |
| I have a HP 339A, in addition to a TEK AA501 and the Boonton 1120 -- the HP339 had gone a little wonky on range switching -- with the oscillator kicking out or taking a long time to stabilize -- here's a word of advise -- just a little DeOxit on the range switching wafers did the trick -- it now consistently gets down into the very low THD% of my SG505 sig gen. |
|
|
| anatech |
Hi jackinnj,
That is the first thing I've had to do with mine. Some of the set screws snapped so I can't get all the knobs off to clean it. :mad: Oh well.
The built in osc. in the HP 339A is pretty good.
-Chris |
|
|
| 1audio |
Having just acquired a new distortion analyzer I started poking around to see what are the current thoughts on them. I have an extensive collection including the Boonton in the schematic.
Re the Boonton input circuit- you will notice that the diodes are isolated from the input by the resistors so its not possible to zap them with any input signal. However that fuse in the chain to the ground relay gets zapped all the time- when you reset the instrument that relay closes so the balanced amp you attached is now driving through the relay and fuse to ground. Otherwise the input circuit can reliably deliver .0007% THD performance.
The HP voltmeter's analog output has a big distortion bump in it since its got the meter rectifiers in the feedback loop.
I just got a Shibasoku oscillator and analyzer to see if they are as good as claimed. They seem to be- a residual system distortion at 10V 1 KHz of around .00006% and a built in harmonic analyzer. I will play with it some more to see if the numbers are real. However for daily use the Boonton is still the easiest and fastest.
My collection includes ST1700B, ST1710, KH6810 (& matching programmable oscillator and a KH 4400 oscillator), Boonton 1120, 1121 & 1130, Radiometer Automatic analyzer (all analog sweeping tracking analyzer) and an HP 8903. The ST's are nice but fragile and showing their age. The KH is good but not as good as the Boonton's. The Radiometer is really neat but more of a collectors item than a daily user. I have access to some AP's but they are so computer centric they are slower to use for circuit optimization. The R&S is a neat idea using passive notch filters in front of an FFT, but expensive.
I liked the cancellation solution, but its far from original. RCA made an instrument with passive networks to do the same thing in the '50s, which I'd love to get for my collection. Peter Walker used the same technique to prove to himself that most amplifiers have inaudibly low distortion and its the speaker that matters.
I think distortion products less than 100 dB below program are just not important but chasing them is still an interesting intellectual pursuit. Getting the other stuff right is easily as important |
|
|
| Pan |
As far as I understand most amplifiers distort audibly even before clipping. Put thru a solid test this shows that only a few amplifiers are audibly transparent. This could indicate that those who have tested and claim transparency among most amplifiers have choosen a less than optimum method.
Also most CD players distort audibly.
My referencs on this matter is LTS, the Swedish "sound technologicall society". As far as I remember of hundreds of amps tested only one have passed the test as audibly transparent on all lewels, a big bridged Bryston amp.
For what it's worth.
/Peter |
|
|
| jackinnj |
Demian --
Since we last saw you on the board I acquired the innards of another Boonton 1120 and one with the usual power supply issues. I also bought a ProLogix USB based GPIB controller, recommended by Conrad.
On the AP2 the Boonton 1120 measures 0.0007% THD with 14V balanced output. The SG505 oscillator measures a tad better than this -- 0.00022%
The most useful test (to my way of thinking) is to look at the distortion residuals with a good spectrum analyzer. The spectrum analyzer will also tell you if your distortion analyzer is actually telling the truth.
The 1/16th amp fuses do blow all the time --
Jack |
|
|
| anatech |
Hi 1audio,| quote: | | The HP voltmeter's analog output has a big distortion bump in it since its got the meter rectifiers in the feedback loop. |
Which one?
The monitor output does not normally come from the rectified meter circuit. Your meter may be suffering form old cap syndrome.
-Chris |
|
|
| 1audio |
Jack:
The Boonton's seem to be too easy to acquire. I think I have 4 of them all told. The KH's residual distortion is around .0002% it seems, similar to the Tek. The Tek stuff was designed by the guys that started AP. The Boonton's servo loop for the frequency may be part of the limitation. On the spectrum analyzer you can see the skirts of the frequency shifting poking up on each side of the notch. The KH doesn't show this. There are some tricks in the KH that may be applicable to reducing the residual of the Boonton.
I have a Wavetek 7530 fft connected to the output of the Boonton. its a good combination. The analyzer removes the fundamental and the fft allows a close look at whatever I want to see. I have 3 7L5's which have some strengths as spectrum analyzers but are too slow for this application usually.
I would love to get the firmware for the Boonton revised to fix that problem but its more than I want to reverse engineer. On one of my Boontons the relay welded shut from the abuse. I had to contrive a replacement.
What software do you have to run the Boonton? I have the NI PCMCIA GPIB stuff for it (and my new laptop ditched the PCMCIA slot for an expresscard slot, drat) that I got to interface with my scope. |
|
|
| 1audio |
| quote: | Which one?
The monitor output does not normally come from the rectified meter circuit. Your meter may be suffering form old cap syndrome. |
The HP 400 a-l tube/SS meters all have the output off the meter circuit. I have been through most of them. Its a cleaver circuit with a lot of gain wide bandwidth (4 MHz) and stable with not too many parts. Thats why the meter is in the feedback circuit. |
|
|
| jackinnj |
| quote: | Originally posted by 1audio
I would love to get the firmware for the Boonton revised to fix that problem but its more than I want to reverse engineer. On one of my Boontons the relay welded shut from the abuse. I had to contrive a replacement.
What software do you have to run the Boonton? I have the NI PCMCIA GPIB stuff for it (and my new laptop ditched the PCMCIA slot for an expresscard slot, drat) that I got to interface with my scope. |
By the servo loop I take it to mean the error detection circuit? I don't think that they had the voltage controlled amplifiers like the SSM2018 "in the day". Some of the chips on that "source" board are truely unobtanium.
I just acquired the ProLogix USB-GBIP Controller so haven't set it to work yet. Conrad uses PowerBasic. I have VB6, VB.NET and QB. Softwire works in Visual Basic dot Net but has been obsoleted by National Instruments. One of the Softwire guys wrote a GPIB routine and I have the code around here somewhere.
I have a National Instruments GPIB Controller, but haven't used it in years.
I was playing around with my HP339A over the weekend --- nice but slow to use. The THD is around 0.0017% There is a wee bit of 60Hz feed through on the HP339A and I can't locate the source -- but you can see it as a spur on the fundamental.
|
|
|
| 1audio |
| The Boonton has a servo loop for the frequency that passes through the microprocessor. It has really good frequency accuracy long term but some jitter from the PLL circuits. |
|
|
| 1audio |
Jack:
Someone had created a small app for controlling the Boonton and posted it. I was going to have a programmer student working for me revise it but he got too swampped with school to make progress. I will try to find the link and post it or the program and source code if I can't find the link but it will be a few days. |
|
|
| anatech |
Hi Demian,| quote: | | The HP 400 a-l tube/SS meters all have the output off the meter circuit. |
You do know how old and out of date that series is, don't you? The 33X series and 8903x types have evolved a fair amount from the earlier types.
-Chris |
|
|
| anatech |
Hi Jack,| quote: | | I was playing around with my HP339A over the weekend --- nice but slow to use. The THD is around 0.0017% |
I use that model as well. The residual THD and noise is spec'd at 0.0018%. I see mostly noise.
| quote: | | There is a wee bit of 60Hz feed through on the HP339A and I can't locate the source -- but you can see it as a spur on the fundamental. |
At those levels the source may be difficult to find. Anything from a shield screw to some power transformer leakage could be your source.
If I can get some FFT happening here, I'll check mine for the same 60 Hz spurs. Did you play with the ground lift switch? Might be some stuff in there creating leakage too.
-Chris |
|
|
| 1audio |
| quote: | | You do know how old and out of date that series is, don't you? |
Yes I do, and how expensive the new stuff is. But the point was a meter to use as an input conditioner for a DIY distortion analyzer. Not to get an old analyzer. (Earlier discussion than you were responding to)
The HP 331-334 are OK but the manually tuned ones will be a challenge to get optimally notched. And I'm not sure the S/N will be good enough to not be the limit in any measurements today. Plus calibration of the chain is a pain since the attenuation and sensitivity of each stage needs to be worked out. This is the problem I have with the Boonton- its distortion output autoranges and doesn't say what that range is, so my FFT is only relative. If its important to someone I have an HP333 somewhere around here that I can test, if I can find it.
I didn't like my HP 8903 much. Its power meter on the front was nice but the rest was clunkier to use than the Boonton. |
|
|
| anatech |
Hi Demian,
The 333A and 334A are auto nulling once you get it close. The 339A (love it!) is not fast, but it is accurate (and auto nulling). The ranges are manually switched so you shouldn't have much trouble with figuring out what range you are on. The voltmeter on mine is deadly accurate. I am shocked to see how close it is actually. Don't sell these things short.
Since the 333 / 334 are 70's units, an overhaul of the power supply would be in order. I can not understand how these instruments stay in as good condition as they seem to. To much to ask for if you want to work with them without going over them. I would not touch the cal if I were you. They hold calibration very well.
I'd have to say that those were worth every single penny. On Ebay, you can sometimes get one at less than $100 USD. 339A's tend to run $400 + and will need switch cleaning at the very least. You do not spray anything into these things, beware or you will create issues. Considering that this includes a very good oscillator and high bandwidth AC voltmeter - not too shabby. The earlier models (33x) had even wider bandwidth I think. I have a 654A (oscillator) and 334A that I am going to fix up for exactly that reason.
-Chris |
|
|
| 1audio |
The 331-334 will null to 500 KHz I think- matches the 200 CD oscillator. FWIW the 200CD special version for low distortion has its output turned down to 7V, otherwise its the same as the standard model. The 331-334 have a meter response to something like 2-4 MHz.
The 654 is a well made instrument, but its distortion floor is pretty high. It has a very flat response. Is that the one with the fancy attenuator? |
|
|
| anatech |
Hi Demian,
Those figures sound roughly correct. They are amazing instruments, especially when you stop and think about when they were designed and put into production.
| quote: | | The 654 is a well made instrument, but its distortion floor is pretty high. It has a very flat response. Is that the one with the fancy attenuator? |
Yes, yes, yes and yes. I plan to investigate the distortion aspect a little. There must be a cure for that. Modern parts may make all the difference. It does look pretty cool. I like these better than the 200 series. Having an output meter is very handy.
-Chris |
|
|
| 1audio |
| The 650 series also have a lot of space in the boxes. The distortion relates to the AGC and the available gain in the loop. Years ago I started to look into replacing the circuit with a new one. Its harder than it may seem. And transistors are not substantially different. I got distracted by the Krohn Hite oscillators which are higher performance. |
|
|
| jackinnj |
The error correction term is discussed in Bruce Hofer's paper for the AES in 1979. Bob Cordell referenced this in in his THD% analyzer from Audio Magazine decades ago. Bob's article is on his website. Hofer designed the SG505.
There is a Boonton 1110 "oscillator only" unit for sale on EBay at the moment -- you'll have to search under boonton as the URL isn't inserting correctly -- the starting bid is $14 which is ridiculously low for an instrument of this quality. If I bid for it my wife would shoot me. I think that the seller actually has 2 of these.
Demian -- my spectrum analyzer is really an HP3577 network analyzer -- I didn't notice the "uncertainty" -- you mentioned. |
|
|
| KSTR |
While it's not a professional solution, I am quite pleased with what a soundcard + FFT-analyser can do. I'm using a semiprofessional 8ch-I/O 24bit/96kHz card, not the newest design (AKM AK4524 codecs, MC33078 buffers, electrolytic coupling caps and all). Still I can have distortion, noise and alias components more than 110dB down in a loopback measurement, at 1kHz and 48k sampling rate. This worsens of course when test freq. increases and also varies with sapmling rate (40k...60k work best for this card). With a modern card, featuring 192kHz rates to get a decent 80++kHz audio bandwidth I guess the results would be really comparable to a typical hardware solutions (not AP, R&S etc precision levels), especially when using a notch filter. A collegue of mine has compared the results of a soundcard based system with good hardware, R&S UPL66, Sprectral Dynamics, HP (don't know the models, though) and found them very similar. Care has to be taken not to kill the inputs with overvoltages, though.
The qood thing with a software solution ist one can easily sync the generator to the analyser and if one uses an exact bin center frequency one can avoid using FFT windows and can get really sharp and skirtless needles, only a single bin in width. With averaging this gives quite a good resolution, especially when a prime multpiple of the bin bandwidth is used and the test frequency aliases and/or IM products with fs give close sidebands. For example, I use 1001.220703125Hz as a 1kHz test frequency at 48kHz fs for a 64k FFT, this is a prime multiple (1367) and the IM sidebands are only +-58Hz. The problem is to find a generator software which handles this input value correctly -- i.e. Samplitude does.
- Klaus |
|
|
| KSTR |
This seems to be essentially the same technique given by Walt Jung and Scott Wurcer in ADI AppNote 245. It differs mainly in the way the signals are subtracted -- they used an instr. amp, Renardson uses current summing. Clever approach, without doubt. I used the Jung/Wurcer method, with additional INAs ahead of the main subtractor, to be able to measure differential amp I/O.
- Klaus |
|
|
| 1audio |
Using a sound card w/ good FFT software is very appealing, however there are a few challenges. First is input conditioning. You need to protect the input from getting fried, you need to provide optimum range adjustment to get the full performance of the card and some type of passive analog output adjustment so the output signal is at its best performance. above the idea of using either an HP ACVTVM or and HP distortion analyzer for this were proposed and they both have merit. The ACVTVM however has too much internal distortion. It could be modified but it would be a big chore. The distortion analyzer has more potential but it needs careful review.
Alternatively an external passive attenuator, balanced, could be fabbed pretty easily and compensated for flat response. Adding a passive notch filter at a few key frequencies will extend the systems performance way down into the mud, limited only by the noise of the soundcard.
I have the Juli@ sound card which does 192/24 and seems to be close to the state of the art and only around $120.
Second challenge is software. I use Praxis and RMAA and get a lot of utility from them. However Praxis is pretty expensive and RMAA is not easy to use for anything other than soundcards. But its possible and RMAA is free. |
|
|
| anatech |
Hi Demian,
I intend to use RMAA and a sound card in the short term running off the monitor output from an HP 339A. Lowering the fundamental has a lot of potential to increase your range, and you still get an idea where your fundamental is. I would much rather tie a spectrum or signal analyzer to the project. Sound cards are too limited in their bandwidth in my estimation. Active circuitry can misbehave up in the MHz as well. You should be able to see this.
I did play with some DSOs with FFT as a feature. This was useful, but the resolution was not good enough to see 60 Hz skirts. Otherwise they did provide useful information.
-Chris |
|
|
| 1audio |
RMAA (the free version, I don't know anything about the pay version) doesn't like to work in a one channel mode or much out of its basic loopback mode. I have made it work, with difficulty.
I have a Picoscope that does a fair job on the output of an analyzer and is good to 50 MHz. My Wavetek FFT goes to 100KHz and that close to the limits of the analyzers. When I hook the 7L5 up I get the same results. On analog audio stuff thats working OK there isn't much to see way up there. Add digital and who knows? Digital by definition should have nothing. However bad execution can leave a lot of nothing up there.
Most of my analog stuff has a power bandwidth of 500KHz+ so I'm familiar with the problems. I was looking at a DC to 100MHz 40 dB gain amp recently. Input Z was 1 MegOhm. It was extreamly unstable and would oscillate if the terminated coaxes got too close to each other. And the oscillation was near the top of the 300 MHz range of my scope. Invisible when the BW was switched to 20 MHz. |
|
|
| anatech |
Hi Demian,
One of my dreams would be to have an HP 3562, or like product along with a 3585. I do some RF work.
Until then, a sound card will have to do.| quote: | | RMAA (the free version, I don't know anything about the pay version) doesn't like to work in a one channel mode or much out of its basic loopback mode. |
The answer is another 339A then. Either that or different software. I'll figure something out some time.
-Chris |
|
|
| gaetan8888 |
Hello
Once a wild, I have seen, for sale , some HP-851B spectrum analyser, did it can do audio spectrum analysis ?
The little I found about it on the web are not clear, it seem to do RF frequency but I don't know if it's go down to audio spectrum and how low distortion it can analyse.
Thank
Gaetan |
|
|
| KSTR |
| Doesn't look any good for audio, I'd say... |
|
|
| redrabbit |
You know you are addicted to DIY electronics when you purchase calibration/test equipment.... to calibrate/test your other calibration/test equipment.
=RR=
(me: Leader 178, Potomac Instruments AA-51/AG-51,....so far... :cannotbe: ) |
|
|
| anatech |
Hi redrabbit,| quote: | | You know you are addicted to DIY electronics when you purchase calibration/test equipment.... to calibrate/test your other calibration/test equipment. |
Guilty as charged. :D
All you need is test equipment that you classify as "major assets". Keep them in good order and try your best to calibrate them. That is expensive.
-Chris |
|
|
| 1audio |
I let myself get locked into this drill. Fluke 732a secondary voltage reference. and then a JRL Kelvin Varley divider plus a Fluke cable compensator to calibrate a Valhalla DC Calibrator then Fluke thermal converters and a 6 1/2 digit dvm to calibrate an Optimation AC Calibrator and a Fluke 8506A enhanced precision AC/DC meter to check the calibration etc. so I could trust the meters so I can know that the level and frequency response of the amp is what its intended to be.
However the reality is that I learned a lot more about the meaning of "uncertainty" and sources of error. Even though most of this stuff is old enough to vote, the state of the art in a standards lab hasn't moved much. Its just a lot easier to use. I played with a galvonometer so that I could say I had but after reading that NIST uses DVM's I retired the galvos to the collection. Chasing parts per million in electronics teaches a lot about noise, grounding, stability and resolution. I also learned a lot from working on and with those instruments. At those levels of accuracy technique and design skill are central to meeting the performance requirements. |
|
|
| Stefanoo |
hello guys....
i saw that the 3d is moving toward the scound card/sw distortion analyzer but....i'm still....could be my preconcept....more inclined to have real instruments.....but a different solution could be as good or even better than that...i know....just by using a very good sound card....but it is challenging.....and the risk to fried your $150 sound card is not appealing to me at all.....therefore i prefer something more solid!!
By speaking of this analyzer here....i would need your suggestion....
On ebay it is possible to find apperantly good deal on HP 334A HP331A and so on....
Once i have read on the forum that a good tool would be the sound technology ad ever since i have searched for it....but it is not easy at all to find one in good working condition and for a relativetly low price.
But it is appealing since it has a low noise signal generator built in..and since i need a sig gen as well...here's the dial.
Right now i ask for some advice....
what used analyzer should i look for at around $150-200 ?
I neeed some soggestion on these...since i have never used a dist analyzer and i would like to buy something that could be a good mate for a long time....not something that once you have learned to use it you throw it 'cause not very precise......but obviously for the range of price indicated i don't expect unbelievable performances as well....
ok that's all folk....hope i was able to exlain sufficiently my self....
thanks a lot for your patience...hope to receive good suggestion. |
|
|
| anatech |
Hi Stefano,
The HP 33x THD meter is a clear choice. The HP 333 and 334 will auto null. You want that. The HP 334 is the same as the HP 333 except that the HP 334 has an AM detector built in. Most people never use this.
If you can find an HP 339 - go for it! That is if it works okay. They normally go around $400 USD or more. I have seen a couple go for around the $375 area. That's still $400 in my book.
Expect to clean the switches by hand. No spray cleaners!
-Chris |
|
|
| 1audio |
Here are some illustrations why low numbers aren't everything and of the value of the spectrum analyzer.
I just picked up an HP467A amplifier. It was interesting because it claims 10W to 1 MHz and would be helpful for a project I'm working on. I thought I would measure it since its an old design ('70s I think) but pretty ambitious.
At max output into 8 Ohms before clipping its shows .006% THD, extremely good even by todays standards for an amplifier. However the distortion residual looks pretty bad:
And on the spectrum analyzer of the distortion output we see how bad it really is:
 |
|
|
| anatech |
Hi Demian,| quote: | | And on the spectrum analyzer of the distortion output we see how bad it really is: |
Which is why I've wanted a spectrum analyzer in the worst way for years.
I'm one guy that needs zero convincing on this. What unit are you using?
I have been considering buying a new 'scope (Agilent 6000 series) that does have some FFT math functions built in. It doesn't have the resolution, but it does give you most of the answers. It seems to be aimed at higher frequency events though.
-Chris |
|
|
| 1audio |
| The spectrum analyzer is a Wavetek 7530A FFT plugin for a Tek 7000 scope. Its in an old 7403N frame I had (with no readout) and the plugin has its own readout. Its quite neat. Its got a 70 dB range so you must precondition the signal and a mag feature that allows high resolution of any small segment of the range. |
|
|
| anatech |
Hi Demian,
What I need to do is play with a number of these signal analyzers (spectrum analyzers) to see what I like the best. Something new that exports data would be preferable and out of my price range! :(
-Chris |
|
|
| 1audio |
This guy: http://cgi.ebay.com/100MS-s-PC-Base...1QQcmdZViewItem
Looks like a close copy of a Picoscope for $150 or so. It has the FFT functionality. Just hook it to the output of the HP339 or even an HP333 and see what you get. nIt may be enough. But you need a computer to see its output. |
|
|
| Stefanoo |
1audio,
My compliment for your equipment and analysis as well....
Can i ask your support?
Sombody told me that the HP 334 or something similar would be a good choice here.
Unfortunatelly i can't catch right now differencies on analyzers since i don't have the necessary experience to say that still....obviously....
i'm really obsessed for this the Sound Technology 1700B.....
Would it be possible for the experienced guys here kto take a look at the specifications and highlight for me the differences, if there are, within the HP334A or similar and the Sound Technology 1700B?
Just Keep in mind that the Sound Technology has a low noise signal generator built in as well...which i need it and that i would eventually have to set money aside since i still don't have it.
Sorry guys to make you do this for me but i have a guy now that i have to give an answer to about the sound technology ad I wouldn't be able bymyself to take a good decision with regard to this subject. |
|
|
| Stefanoo |
and sorry....just as a note on the previous post......
i have read on the web that there are also modifications for the ST 1700B......in case.....does anybody here have more detiled informations on this topic?
And last......is it possible to find a service manual for calibration procedure?....i got this possibilty to get ST 1700B but i don't know if it is the right choice and most of all...i suppose that since these are old stuff if they weren't recently serviced, i supposed that they would need calibration...and the flat rate for it is too hig (talking about $1k...crazyyy!) |
|
|
| 1audio |
I have a 1700b and used it for years. Its a much better instrument thatn an HP334 and more useful, with a built in oscillator. It has auto-null and can consitantly get down to .oo2% or less in the midband. It can be tweaked to have lower distortion with improved op-amps, but its hard since it uses op-amps in cans. There are adapters available.
They can be a pain mechanically with switch interlocks etc. And the oscillator settling circuit is touchy. You can service them yourself but you will need to get suitable optocouplers and jfets for the AGC circuits and be very patient with the switch array.
Here is an example of the highest level of the 1700 series for a reasonable price: http://cgi.ebay.com/Sound-Technolog...VQQcmdZViewItem
It has the higher balanced output and the precision attenuator and the IM analyzer. He's asking $285. |
|
|
| Stefanoo |
Yeah...i saw it already...but thanks for the highlight.
Unfortunatelly that item doesn't work on European standards with the 220-240V 50Hz.
Your post was very usefull...since now, i'm very appealed toward this sound Analyzer 1700B.
I already saw the service manual on line for $14...dangiet they take advantage of everything...tomorrow we will wake up knowing that we have to pay our daily breathing air dose ..... but through PayPal....so we don't have to worry.......hihihi.... :)
So you tell me that with the right tool and with the service manual and with a lot of patience the item can be finely serviced even from who has never calibrated instruments?
Niceee!!!
I' sorry i have never used the tools you mentioned before....what is an optocouplers and what type of jfets do i need for the AGC circuits?
Thhhankkkkssss a lott!!!!
The guy that is selling the 1700B analyzer doesn't know how to run self-tests to guarantee me the funtionalities of the ST....but it took pictures for me showing me some of the tests he was able to run.
He showed me the meter going up.......but obviously i don't know if that is enough to tell me that it's workinng or not.
What should i ask him to do with the analyzer to make sure, at least , that it works?
For the calibration i don't care i will take the time later to do it on my own.
I appreciate your help very much. |
|
|
| 1audio |
| I believe the ST stuff has a universal power input and can be switched for 100-120-240. I don't have the manual in front of me right now but I will check. |
|
|
| Stefanoo |
yes, i would think so, since the seller confirmed me that the 1700B model has a switch on the back for the 220V.
I set the price for the 1700B at $150 which is an half of what the seller of the 1710 is aking for.
I' m sure that the 1710 is a better and more performant unit but i wouldn't like to spend right away $300 for a distortion analyzer since i have never used one...and i would like to learn first and......and if... i 'll became an "expert"... and feel the need for something better....then buy a better analyzer like yours (boonton).
In the meantime, would it be possible for you give me some good hints on how and what to ask to the seller to make sure that the analyzer is working?
hope i'm not bothering you with all this questions.
Thanks in advance. |
|
|
| anatech |
Hi Stefano,
If you want a better oscillator and THD meter, then the HP 339A is my preferred instrument. I have used the 1700. It is a giant and the HP unit will do what you need in a much smaller package. The noise floor is stated at 0.0018% THD - that's it's internal oscillator looped into the distortion section. I have confirmed this.
The ST 1700 is noted for switch contact problems. That was earlier in time. The fact that it is large enough to block you view out of a window is a consideration. I used to want one until I used the 339A.
With regard to the 333A/334A, they have very high frequency response. That is their value. Higher than the ST or 339A. For that reason I have one. One thing I can say is that all of these outperform the Japanese THD meters by a long shot. Leader LDM-171 for example. I have one of those as well. I may try to rework it (it's smaller and pretty - sort of).
In my view, the HP 339A is a better instrument than the ST 1700. This is reflected in the higher cost on places like Ebay. They normally sell for $400 and they need work. Freshened up, they sell for more.
For what it's worth. Demian and I may possibly disagree on this point.
Demian, I can't remember if you said that you have used an HP 339A before or not. I think it was an 8903 (a or b) that you used. I have never seen one in action.
-Chris |
|
|
| 1audio |
I have played with an HP339A but never really used one. The ST700 often has the IM module which really works well. Its big, and the ST1710 is bigger. For some this may not be an issue. The only switch that ever saw much use on mine was the range switch. I left it set at 2X so 20, 200, 2K and 20K were all one push apart. You can do that with the HP339A as well. John Curl uses an ST1700B still, although his has been tweaked with better opamps.
If you look at the photos above you will see that my primary stack of instruments is very tall. I'll post pictures of the lab soon. I need a function generator, a monitor scope and a main scope as well as the distortion analyzer and a DVM and a counter usually. But most may not need so much stuff.
At $400 I would get a Boonton if I could find one. The microprocessor control just makes it easier and faster. Or the Amber looks good. The HP3904 is just a little klutzy to use (poor UI) and its performance isn't much different from an HP339A. All of these have GPIB allowing automation of the measurements. The HP339A commands a higher price partly from familiarity with the name. I used to have a manual for an HP3900, I think, that was a Japanese built analyzer.
The Shibasoku is possibly the lowest distortion instrument made so don't write off the Japanese instruments too fast. But the cheaper ones for assembly lines are pretty modest in performance. |
|
|
|
