high quality sine wave ? - Page 1
Forum section: electronics / beginners

author: RGK
author_rank: Contributor
timestamp: March 17, 2017, 04:38:46 pm
content: Primarily for audio applications I'm looking to add high quality sine and maybe square waves.I already have a Digilent Analog Discovery, so want a step up from that.I see categories of function generators and arbitrary waveform generators and even something like the Keithley 2015+THD. I'm sure there are also vintage boxes that could be well suited to this task. Not sure what would serve me best.Other supporting equipment is an HP334A and Rigol DS1054 scope.Any suggestions for new or old equipment to look into?BK

author: alm
author_rank: Super Contributor
timestamp: March 17, 2017, 04:54:16 pm
content: For used you might consider theTektronix SG505(with TM5xx mainframe). Should be THD < 0.0008%/-102 dB 20 Hz - 20 kHz. Together with the AA501 (measures THD) this was the predecessor to the Audio Precision One. Can regularly be found on eBay.I believe the sine wave oscillator in the Keithley 2015+THD was quite mediocre.I do not think you will find an instrument doing both square waves (beyond sync output) and low distortion sine waves. There are some function generators that do a decent job (THD < 70 dB), but they do not come close to the dedicated oscillators like the SG505.

author: Gyro
author_rank: Super Contributor
timestamp: March 17, 2017, 06:33:20 pm
content: Unless you're lucky enough to find a nice analogue sinewave oscillator on ebay (they do come up sometimes), your best bet is probably to build one or more spot frequency oscillators, eg. 1kHz and 10kHz.There are plenty of designs around for Wein bridge oscillators, or possibly Twin-T type. Actual component cost is minimal, a couple of decent opamps and some Rs and Cs (and possibly a torch bulb). Using fixed frequencies makes it easier to tweak component values for absolute minimum distortion and also lets you put them in a small screened boxs with a battery (no ground loops or PSU noise). You also need to include some output attenuation.Square waves aren't a problem, you can easily knock up an oscillator with some CMOS logic (probably 74HC).

author: james_s
author_rank: Super Contributor
timestamp: March 17, 2017, 06:37:28 pm
content: You could try building your own. There are many circuits out there based on the original unit that HP is famous for developing.

author: oldway
author_rank: Super Contributor
timestamp: March 17, 2017, 06:59:25 pm
content: I do not know for what application you need this sine wave generator.I do a lot of repairs of vintage amplifiers and I use a function generator by making this approximation: distortion of the device in test = measured distortion less the distortion of the generator (0.3% in my case)On the other hand, since the distortion of the transistor amplifiers is always very low due to the high feedback rate, I make such measurements only on tube amplifiers to optimize the polarization.

author: danadak
author_rank: Super Contributor
timestamp: March 17, 2017, 10:22:34 pm
content: What are your specs for "high quality" ? How do you want to controlamplitude and frequency ? Describe the application in a more completefashion,g. specs, interfaces, etc.. so forum can help you better.Regards, Dana.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: March 18, 2017, 12:47:07 am
content: Quoteif "audio applications" have anything to do with qualifying audio signal processing electronics or amplifiers to human listening limitsit would mean you really don't have to look for technically "high quality sine" by easily achieved electronics for a long while nowthere are "low distortion sinewave generator nutz" similar to the Vref and Time types - but none are really that important to engineering products for audio reproduction

author: RGK
author_rank: Contributor
timestamp: March 18, 2017, 02:06:36 am
content: Thanks folks for the great input. Lots to follow up on. Obviously I came to the right place.I should point out that I'm not an EE or professional, just an idiot hobbyist who enjoys building audio amplifiers and related equipment and likes good tools and making (potentially unnecessary) measurements. For example on some creations I want to measure and tweak the dominant harmonics and phase. My impression is that the sine output of for example the Digilent or even the Keithley 2015+THD is marginal for this sort of thing, and alm picked up on that right away.This is the "Beginners" area, but perhaps my subject line was misleading. I don't think I'm looking for/need state of the art performance, but if I can get most of the way there for a modest investment that would be great. Definitely want to avoid getting the wrong tool for the job.Appreciate the input!

author: tautech
author_rank: Super Contributor
timestamp: March 18, 2017, 02:50:06 am
content: Have a look at both the SDG2000X and 1000X AWG's.While THD is only 0.075 %, there's some nice stuff you can do with phase adjustments like in this thread:https://www.eevblog.com/forum/chat/a-valentine's-day-activity-for-your-scope-and-function-generator/The SDG1000X series have the ability to do sine and square waves to the full frequency of the model.http://siglentamerica.com/pd.aspx?tid=16&T=1All the documentation is there, just drill down to find it.

author: RGK
author_rank: Contributor
timestamp: March 18, 2017, 02:58:01 am
content: Quote from: evb149 on March 17, 2017, 07:47:29 pmLooks like this thread? Files apparently pulled May 2016 and AWOL.https://www.eevblog.com/forum/buysellwanted/who-would-like-an-ultra-low-distortion-audio-oscillator-pcb/BK

author: JoeN
author_rank: Frequent Contributor
timestamp: March 18, 2017, 05:34:59 pm
content: Quote from: evb149 on March 17, 2017, 07:47:29 pmInteresting, I just did that project a few months ago. It does create a sine wave which looks quite good. I have not had the ability to completely test it out so far for the claimed THD.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: March 18, 2017, 07:21:29 pm
content: better "prosumer" soundcards/usb digital audio interfaces of the past decade do comfortably better than -100 dB for THD, Noise, Spurs, better than -120 dB harmonics possible with somefor audio testing these are the cheapest, most flexible source/measure devices - with free software tools tooif you want to get into "numbers games" - with notch filter and gain you can make spot measurements deep in the noise floor, averaging long recordsway beyond human hearing limits for audio reproduction systems with rational "gain structure"/sensitivity set for natural live music sound levels

author: RGK
author_rank: Contributor
timestamp: March 18, 2017, 08:40:07 pm
content: Thanks for that. Any links to a BOM or builds? Likely more of a project than I'm after right now, but interesting.BK*forgot to quote - remark is WRT evb149 glensstuff .zip file*

author: RGK
author_rank: Contributor
timestamp: March 18, 2017, 08:41:38 pm
content: Very nice. Did you make your own board or get it from Janascard? I've made an inquiry to them.BK*forgot to quote - remark is WRT to JoeN Janascard oscillator project*

author: RGK
author_rank: Contributor
timestamp: March 18, 2017, 09:26:08 pm
content: Quote from: RGK on March 18, 2017, 08:40:07 pmAh, links to useful diyA threads from the buy/sell/trade link. Component BOM is ~$185 but the project is deleted/not supported by the designer, so could be a bridge too far in my case.BK

author: Robaroni
author_rank: Frequent Contributor
timestamp: March 18, 2017, 10:29:50 pm
content: Check out the MAX7400 series.https://datasheets.maximintegrated.com/en/ds/MAX7400-MAX7407.pdfRob

author: JoeN
author_rank: Frequent Contributor
timestamp: March 18, 2017, 11:29:03 pm
content: Quote from: RGK on March 18, 2017, 08:41:38 pmI laid it out in DipTrace and ordered it from OSHPark. I can't say my layout is an expert layout, I simply tried to make sure all the parts were laid out intelligently and as closely as possible to their dependent parts and used a four layer board with three of the layers for the three rails planes, bottom one (-15V) with some signals too. Power input connector was one I already had, SMA output was my choice. Diodes, resistors, zeners, pots, capacitors were parts I chose myself. On the Linear sheet Jim Williams says to use ceramic capacitors nowhere, so I did what he advised, using only electrolytic and PET capacitors, and the 47pF capacitor is mica. Someone else might design with different parts for those, the PDF didn't specify specific exact passive parts and connectors.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: March 19, 2017, 12:22:55 am
content: "no ceramic" is painting with too broad a brushNP0 is a low k ceramic dielectric that gives near perfect distortion performance excepting for some leaded types possibly having bad end metallization/lead attachment issuesMica is a very variable natural material that can be as poor as better Mylarand Mylar/Polyester is the worst common plastic film dielectric - Polypropylene is better, Polystyrene measures best for low audio frequency distortionCyril Bateman's "Capacitor Sound" series did serious measurements, Bruce Hofer of Audio Precision gives simailar recommendations in his seminars/presentationsthehttp://www.diyaudio.com/forums/equipment-tools/205304-low-distortion-audio-range-oscillator.htmlhas many measurements, references, commentary if you really want to get into a analog oscillator buildI would just recommend a decent soundcard like the ESI Juli@from the diyAudio thread, showing 24 bit mode may be necessary to even see the distortion:

author: RGK
author_rank: Contributor
timestamp: March 21, 2017, 02:45:40 am
content: Quote from: JoeN on March 18, 2017, 11:29:03 pmThanks for that and also evb149 for bringing it up. Bought the oscillator PCB and also the notch filter PCB from Janascard. Will update after it arrives to compare layout. So I guess I'll end up with a state-of-the-art sine wave after all....BK

author: rsjsouza
author_rank: Super Contributor
timestamp: March 21, 2017, 02:59:35 am
content: For ultra-pure sinewave generation I drool over theKrohn Hite 4402... Someday I will get one.

author: JoeN
author_rank: Frequent Contributor
timestamp: March 21, 2017, 03:00:10 am
content: Quote from: RGK on March 21, 2017, 02:45:40 amI never saw that they offered it for sale. I checked their site again and I still don't see it.http://www.janascard.cz/aHome.htmlIs it offered somewhere else or did you simply ask them?

author: RGK
author_rank: Contributor
timestamp: March 21, 2017, 03:51:03 am
content: Quote from: JoeN on March 21, 2017, 03:00:10 amYep, inquired by email and heard back promptly. $33 paypal later boards are on the way. I'm not skilled enough to do my own PCB layout!BK

author: RGK
author_rank: Contributor
timestamp: March 21, 2017, 03:56:07 am
content: Quote from: rsjsouza on March 21, 2017, 02:59:35 amNice!BK

author: TimFox
author_rank: Super Contributor
timestamp: March 21, 2017, 07:26:48 pm
content: Almost as good as the K-H 4402 is the -hp- 339A THD analyzer, which includes a low-distortion generator. The residual distortion in mine measures about 0.002% (-94 dB) which should be good enough for any normal applicatioin. Units such as the 339A have the advantage that the analyzer tunes directly to the internal oscillator frequency, and will lock to an external oscillator when the frequency is approximately correct. Also, the indicated fraction of distortion scales automatically to the input signal. You can learn a lot about the DUT by analyzing the distortion output signal, which has the fundamental removed.

author: RGK
author_rank: Contributor
timestamp: March 21, 2017, 11:53:36 pm
content: Will a good oscillator + the HP 334A be just as good as the HP 339A? I picked up two of the former, which set me on a path for a decent 1kHz sinewave reference. Looking at the distortion output with fundamental removed was definitely part of my plan.How does the K-H 4400 compare to the K-H 4402?BK

author: Audioguru
author_rank: Super Contributor
timestamp: March 22, 2017, 01:24:32 am
content: Quote from: Robaroni on March 18, 2017, 10:29:50 pmI made a sinewave that had 10 steps and about 6% distortion with a CD4018 and a few resistors. Then I filtered it with National Semiconductor switched capacitor filter ICs that had 8 Butterworth orders and the output distortion was so low that it could barely be measured.Guys have taken a buzzer sound and filtered it with switched capacitor filters and ended up with pretty good sinewaves.

author: nfmax
author_rank: Super Contributor
timestamp: March 27, 2017, 04:01:17 pm
content: Quote from: TimFox on March 21, 2017, 07:26:48 pmThe oscillator part of the 339A was made as a standalone oscillator model 239A - quite a small dinky little thing, and no fan so they tend to be in immaculate condition internally. I have one and it works nicely, but they areveryrare on the secondhand market. As well as low distortion, it has good level setability right down to sub 1mV, and it the output is isolated from ground - two essential attributes for a low distortion audio source.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 27, 2017, 05:50:15 pm
content: previous thread might have some related discussionhttps://www.eevblog.com/forum/testgear/waveform-generating-displaying-question/

author: TimFox
author_rank: Super Contributor
timestamp: March 29, 2017, 11:06:41 pm
content: Quote from: RGK on March 21, 2017, 11:53:36 pmThe residual distortion in the 334A is not as good as in the 339A. Both the 333A and 334A will auto-tune the frequency and phase when the manual tuning and phase knobs are close to the correct values for the external oscillator. Another advantage of the 339A is that the distortion value indicated scales automatically to the input level, while the 334A/333A require a manual adjustment to 100%.