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Old 17th June 2013, 04:53 AM   #2841
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by ghg View Post
Would you mind to post screen shots of the two monitor outputs of the VP7722A ( via your HP spectrum analyzer )
and the readings of 2fo, 3fo etc. ?

BR

Gary

I just took a look. Neither make any sense to me. You know what that means? -- I will have to read the manual, i guess.

-RNM
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Old 17th June 2013, 08:01 AM   #2842
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Hi all,

I hope I can ask you for help with this ...

I've been reading through bits of this thread but there are too many posts and links to other threads etc. for this to be a feasible approach for me. So I hope one of you can guide me to just a few posts and/or threads where I can find a description on how to build this:

- A sinewave low-distortion oscillator typically working in the frequency range of 10-50 Hz (lower) to about 20 kHz (upper - higher than this would also be interesting).

- A low-distortion square wave oscillator - to be used for audio yet possibly with a wider frequency range (upper range up to preferably 100 kHz). If the sine wave oscillator & the square wave oscillator can be identical - i.e. it's possible to switch between the two output wave forms - this is preferred but not needed.

I'm looking for a complete build description incl. PCB layout and with as low distortion as possible considering reasonable availability of parts & not too expensive to build. I am also interested in a tip for a second-hand oscillator as long as they have good distortion specs (preferably around 0.001% or better).

Also, I need to be able to adapt it to the 2.5 VDC midpoint of an ADC - might you have any tips on the most feasible way to do this so that distortion specs are kept?

I'll appreciate your assistance in this appreciated

Jesper
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Old 17th June 2013, 12:53 PM   #2843
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Hi again,

Smiles at the last sentence of my previous post

Quote:
I'll appreciate your assistance in this appreciated

Anyway, I decided to read a bit into this thread and read about Victor's oscillators - it looks quite impressive ... So I've decided to buy one or two of those for references.

However, I wonder if it would also be feasible to build/get a variable frequency oscillator but don't know what the specific use of this would be ... Might one of you be willing to shed a bit of light on this? I'm into DAC & ADC design, as well as electrostatic headphones design. I imagine a variable oscillator - or maybe a sweep oscillator could be useful here ... may one of you have some input here?

And then there's the square wave generator. I've found this from Linear Tech.:

http://cds.linear.com/docs/en/datasheet/1799fc.pdf

... yet wonder if precision in square wave testing also harbors some insights into how a circuit works ...

Again, I'll appreciate your feedback on this.

Jesper
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Old 21st June 2013, 03:22 AM   #2844
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by 1audio View Post
Ill try to get one from TI. Maybe they will let me borrow one. None are audio compatible or easy to use. I think HPworks can be persuaded to work with some of these. Otherwise its demo software or roll your own.
What is the status on your getting it... update pls?

Thx-RNMarsh
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Old 21st June 2013, 04:52 AM   #2845
1audio is offline 1audio  United States
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Jesper,
A .001% THD oscillator won't be useful if you don't have a way to analyze the signal. You will need a suitable analyzer or soundcard (really almost no cards are in this league of performance). and software etc. plus experience looking at the issues. Its a steep learning curve. The best option for a square wave (and possibly the most useful general purpose source) would be a good function generator. If you search for "krohn function" on eBay you will find many good examples to chose among.

For verifying DAC performance you have many parameters to check for, not just distortion. You need to check for response, noise, linearity, jitter and a host of obscure details that are quite important. Usually you need a very good analyzer with sophisticated digital enhancements. However with the sound card and some patience and external analog preconditioning you can check many of the key parameters.

Similar for electrostatic headphones, where you will need everything from an electrostatic voltmeter to check the bias voltages (no other real options for this) to high impedance high voltage probes, to acoustic couplers and measurement systems.

Again not simple but potentially very satisfying.
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Old 21st June 2013, 05:17 AM   #2846
1audio is offline 1audio  United States
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Richard:
TI just changed the sales rep for us again. Every 6 months it seems. When the new rep is introduced I'll ask. Hopefully next week. Good thing is that the new sales rep usually means a fresh slate for demo boards.
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Old 23rd June 2013, 12:27 PM   #2847
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Hi Demian,

& thank you for replying to my questions

Just briefly so that you know where I come from audio-wise: I've been involved particularly with audio amplifier design for some years and with the help of others, probably some luck, and a personal zeal for creating the "best" possible musical sound it is my impression that I/we have made some quite good amplifiers etc. over the years. My sources of inspiration have mainly been the designs from the French magazine "L'Audiophile" and a small Danish, now demised, high-end brand named Holfi. All designs were comparatively quite simple.

However, during this design period I have been sort of "blind" since my only sources of assessing the circuits I made were my ears , an oscilloscope and a not-too-precise sine wave/simple square wave generator. With this I could check bandwidth, oscillation, square wave reproduction and a few other factors.

Now I'd like to expand on this - "see" a little better, if possible. Not in a way that I get the full "armamentarium" available for audio design measurements - but so that I have the equipment that allows me to observe and - with reasonable discernment - get information about what is going on in a circuitry or with a certain component.

To that end I've considered:
  • a best quality ADC soundcard (I've seen your comments on the AKD5394a) like the ADS1675 or the AD7760 EVMs because they also allow me to look at what’s going on at higher frequencies. Reading the last posts it seems to me that you & RNM are leaning towards the ADS1675, however, when looking at specs the AD7760 appears to have lower distortion - or may I be missing something? ... Also, the ADS1675 – as far as I can see - gets its clock from the FPGA which (to my knowledge) could mean that there’s some jitter in the clock and it may not be much improved e.g. by replacing the FPGA clock with a better type. But maybe you would like the extra bandwidth ... ?
  • Getting a suitable selection of signal generators to allow e.g. for IMD measurements of circuits and components. I’ve seen your post about jitter testing frequencies #2080, but can I ask you which frequencies would be suitable for analog measurements? To that end I've been wondering if there are some frequencies that could be related to the Western World's musical tuning, i.e. centered around 440 Hz ... Or maybe Bob Cordell's MIM suggestion: 9.0 kHz, 10.05 kHz and 20 kHz ...

    CordellAudio.com - A Fully In-Band Multitone Test for Transient Intermodulation Distortion

    May you have some ideas or insights on this that you can share?

    Reading parts of the thread here, a suitable selection of Victor’s oscillators would be my choice e.g. combined with an LME49990 + LME49600 opamp/buffer for higher voltage, lower impedance drive capability and low low-frequency noise.
  • And then a function generator of good quality for various measurements. I've come to think that I may actually use my USB DAC for this (Amanero Combo384 + DSD1794 from TI) if this is feasible?

    You mentioned "Krohn function" which I’ve searched for on ebay. However, they only show up in the US or Israel and in both cases shipment and customs would almost double the price (I live in Denmark). In case you don't think I can use my USB DAC do you then know of a European alternative?
  • Eventually I’d also like to be able to measure jitter but have no clue how to do this & no space in my mind to learn about it right now :-) But will be very interested shortly!
  • This also applies to measurement tools for the electrostatic headphone ... I’ll have to come back to that at a later point in time - but thanks for also just briefly replying to that in your previous post.

... Any insights appreciated ... & I hope I haven't asked questions that have already been touched upon earlier in the thread ...

Greetings,

Jesper
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Last edited by gentlevoice; 23rd June 2013 at 12:39 PM.
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Old 23rd June 2013, 05:48 PM   #2848
RNMarsh is offline RNMarsh  United States
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Just some general comments for you:

If you want to avoid importing anything, then sound cards for source and data input would be the cheapest. This thread was about how to upgrade used commercial test equipment... specifically the HP-339A... to see if it can be improved and by how much. There are many other used brands (Krohn-Hite, etc) and right now there are many Panasonic audio analyzer models that are good to use (eBay) but not super cheap and you have that import duty again. The K-H 4402B was lightly reworked and produced THD of .00005% (1KHz) and .0001% (10KHz). The modules from Vicktor (eBay) do as well but not as flexible - so you need several to cover the range of frequencies but may be your lowest cost, highest performance alternative for a source of ultra-low THD.

Thx-RNMarsh

Last edited by RNMarsh; 23rd June 2013 at 05:52 PM.
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Old 25th June 2013, 09:06 AM   #2849
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Hi Richard,

Thanks for your comments and suggestions ... Currently I'm more inclined towards the soundcard solution for data capture (convenience, wide frequency range, reasonably low noise) - "ghg" in this thread apparently has achieved quite good specs with a PCM4222 EVM card:

DIY Analog-to-Digital Converter project.Audio measurements tool

To be able to characterize higher frequencies my main interests are the ADS1675 & AD7760 (as I've written) although I yesterday looked at some 16 bit EVM cards with ~85 dB SNR and 80 MSPS which mean that they could be used in the MHz frequencies - e.g. for some analysis of noise in digital circuitry.

For the oscillator part it's more open as I'd like the flexibility of variable frequencies, as you touch upon, yet also with the IMD option. So maybe a variable oscillator combined with 1-2 of Victor's oscillators ... According to "ghg"'s measurement with the PCM4222 the K-H 4400 - which is currently on sale at ebay - is capable of quite good performance (can't find any K-H 4402s).

Additionally, I assume that a variable HF oscillator reaching into the MHz frequencies could be interesting to characterize digital circuitry, oscillations and such ...

But I'd like to add that I'm really a novice when it comes to having experience with what is sensible to measure & also how to interprete such measurements sound-wise. It was thus very tempting to ask in this thread about this as I had noticed that you & Demian & Bob Cordell & Samuel Groner was active in the thread.

However, I didn't intend my questions to go beyond maybe a few short posts and as I have the impression that I have "twisted" the thread in my direction beyond what seems feasible I'll leave it here for now.

But thanks for the replies you both gave

Jesper
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Last edited by gentlevoice; 25th June 2013 at 09:30 AM.
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Old 30th June 2013, 09:06 PM   #2850
davada is offline davada  Canada
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Hi Guys,

Where in an SVO is the best place to inject an external oscillator for frequency locking and at what attenuation?
Any suggestions on method of coupling? I want to include this in revision 2 of my SVO. There was some mention of "If injected in the right place." some time ago I think by Ed.

Cheers,
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Last edited by davada; 30th June 2013 at 09:08 PM.
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