Will RIGOL DG1022U be appropriate for audio repair and calibration work? - Page 1
Forum section: electronics / beginners

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 05:37:56 am
content: Hi to all,I am trying to obtain a function generator that I mainly going to use to repair audio equipment. It seems like I will be better off with an audio generator but I'd like to get a newer piece of equipment that I will be able to extend to other repair work in the future. The other options I consider are Instek SFG-1003 or Instek SFG-1013. Please advice if these newer function generators will be good companions for audio. Any advice is highly appreciated!

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2016, 08:54:47 am
content: Most function generators (either digital or analogue ones) have rather poor sine-wave distortion performance. If you are specifically interested in distortion measurements then you would probably be better findingor makinga low distortion RC oscilator. For square wave testing they should be fine though.

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 01:12:13 pm
content: Thank you, Gyro! Would you recommend any models?Sent from my iPhone using Tapatalk

author: rstofer
author_rank: Super Contributor
timestamp: May 20, 2016, 01:51:47 pm
content: I'm not in the audio business but the datasheet lays out the THD at < 0.2% for the sine wave in the audio spectrum. I have no idea whether this is high, medium or low. Page 3 here:file:///C:/Users/Richa.DESKTOP-1K83UAF/Downloads/DG1022_datasheet.pdfI would expect all digitally synthesized sine waves to have a higher level of distortion. One solution might be a low pass filter on the output to knock down any harmonics. But harmonics of what? If the tone is 1 kHz, there is room for a lot of harmonics if the filter is set to 20 kHz or so.eBay is loaded with audio signal generators of dubious quality and no warranty. I didn't see any of the old time HPs and that's where I would go if I was interested in quality sign waves.Then again, is the function generator just being used to inject a signal and chase it down the rathole? In that case, a small amount of distortion might not matter. If, OTOH, the generator is being used as a source in the design of low distortion amplifiers, it might not be the right tool.I actually want to use the arbitrary feature to derive signals representing potholes in the roadway that I can feed to my analog computer simulation of an automobile suspension. That would be very cool!

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 04:28:01 pm
content: Thank you again. This is exactly my dilemma. I want to avoid buying an old HPs or similar because they more likely will be out of specs. I thought I should buy the newer FG and with possibility to use it for other tasks too. However, as far as I hear they are not great fit for audio. I am still not sure what I should end up getting.

author: Lightages
author_rank: Unknown
timestamp: May 20, 2016, 05:31:17 pm
content: If your intent is to merely supply audio signals to the input of a device under test, then a sound card output and the appropriate software will be more than good enough. If you want to inject signals into specific circuits then you could use a music player with certain files saved on it in wav or flac format that were generated using free software. If you are interested in this I am happy to provide more details.

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2016, 05:46:58 pm
content: ^^ That sounds like a good method of generating low distortion test signals to me.You might want to consider breaking possible ground loops with a decent quality audio transformer (Edit: not needed if using a portable player obviously).

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 05:52:17 pm
content: Definitely, I would like to hear about these options Lightages is talking about. The only concern about this method is to avoid damaging computer and it is more cumbersome. Thank you.

author: rstofer
author_rank: Super Contributor
timestamp: May 20, 2016, 05:55:36 pm
content: Quote from: vladc77 on May 20, 2016, 04:28:01 pmFor your purposes, why not just build one:http://www.bobsdata.com/audio_sine_wave_generator/index.htmlYes, a Function Generator would be cool to have but somehow I have avoided it all these years. I might buy the 1022A just because I want the 'arbitrary' function but I get that with the Digilent Analog Discovery gadget.Speaking of the Analog Discovery, it has a headphone jack output from the arbitrary waveform generator and somebody has gone to a lot of trouble to create an audio specific application:http://www.thestuffmade.com/audioanalyzersuite/publish.htmhttp://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/I have version 1 and I like it a lot. There's nothing like a 27" screen for a logic analyzer. Actually, I have dual 27" monitors on my development computer so I can get great visualization of the scope on one screen and the other instruments on the other screen. Very nice for old eyes...

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2016, 06:06:20 pm
content: There are many options for self-constructed standalone low distortion (some extremely low) sine-wave oscillators on the web, eg:http://www.janascard.cz/PDF/An%20ultra%20low%20distortion%20oscillator%20with%20THD%20below%20-140%20dB.pdfhttp://www.edn.com/electronics-news/4389675/Low-distortion-oscillator-tests-measurement-circuitshttp://sound.westhost.com/articles/sinewave.htmhttp://moorepage.net/RC.htmlThe actual complexity and component count is quite small, particularly if you only need a fixed frequency, say, 1kHz or a few switched ones.P.S. It's also possible to generate nice sharp square waves with a bit of CMOS logic and an AC coupled attenuator on the output.

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 07:04:58 pm
content: Thank you for the information! The Digilent option is quite interesting. However, I already got Rigol DS 1054Z Digital Oscilloscope. I want to pair it up with a decent low distortion function generator. I may try building my own. Thank you Gyro and rstofer for the links! On the other hand, I am still looking to get the manufactured one if I'll find the good match. As far I understood, the RIGOL DG1022U is out of the option. It is a high distortion and possibly just too much. I thought that the RIGOL DG1022U for the price and versatility could be a good option but not really good for audio. Am I correct?Does anyone familiar with Kenwood FG 273a? Will this FG suitable? The specs I found state it is less than 1% distortion. It looks like still high.It seems like the lowest distortion results can be achieved with the computer/software based approach that Lightages will possibly provide more details. It also can be the most affordable. Am I correct here?Thank you again!

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2016, 07:57:33 pm
content: Unfortunately the Rigol DS 1054Z is only an 8 bit resolution scope, its FFT function isn't going to go low enough for the generator or amplifier distortion to be the limiting factor. It probably won't be able to see the difference between the various generator options.You may be able to get some useable results out of it if you pair the generator with a sharp notch filter to remove the fundamental, but even then the scope probably won't have the dynamic range to compare the magnitudes of the different distortion harmonics.Sorry

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 08:02:47 pm
content: Will Rigol 1104Z work better for this? Can you recommend these sharp notch filters that may help? Thank you!

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2016, 08:11:01 pm
content: I'm not an expert on Rigol stuff, but it looks as if the 1104Z is a 12 bit scope, so yes, 16 times higher resolution.For reference I use an old Picoscope ADC216, it's only 333ksps, but it's a true 16bit scope with 96dB resolution and noise level to match.Edit: You would build the notch filter yourself - Google 'Twin T filter'. The circuit is simple, matching the component to achieve best notch depth less so.

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 08:15:17 pm
content: RIGOL DG1022U can be hacked to become the same as 1104. I am still interested in learning what notch filters I may need to have. I need that scope not only for audio but prefer to use it for audio too.

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2016, 08:18:29 pm
content: Sorry, you probably missed my edit re. the notch filter.

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 08:20:29 pm
content: Thank you! I can see it now. Do you think I can be fine without notch filters with 1104z? I just checked specs here:http://www.tequipment.net/Rigol/DS1054Z/Digital-Oscilloscopes/?search=true#tab-specificationsIt says Rigol DS1054x is 12 bit high resolution.

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2016, 08:32:11 pm
content: Well 12 bits would give a maximum resolution of 244uV relative to 1V, ie. 0.0244% or -72dB (assuming my maths is correct). The other limiting factor is the noise level of the input circuitry of the scope, which tends to be higher with higher bandwidth. I really don't know how close to the theoretical resolution you would get in practice.Put it this way, it might be enough depending on your needs but notch filtering would certainly help.

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 08:34:46 pm
content: Thank you for the info!

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 08:37:26 pm
content: I still want to find out if Kenwood FG 273 will be suitable for audio? Is anyone familiar with this one? Thank you!

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2016, 08:44:15 pm
content: From what I can see on the web it has a maximum sine distortion of about 1%, fairly typical of function generators.

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 08:50:57 pm
content: Yes, that's true. I need to have something closer to 0.05%. It seems my options are limited.

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2016, 08:55:51 pm
content: You ought to be able to achieve that sort of level fairly easily if you build something. You really want to be looking for 'Audio signal generator' or 'Audio oscillator' as a search term rather than function generator.

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 08:59:52 pm
content: Agree, my idea of scalable approach is not going to work. I wanted to get something newer as Rigol 1022 but it is no way to go. Anyway, it is going to be cheaper but more narrowed approach. Thank you for your support!

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2016, 09:08:31 pm
content: I wouldn't give up on using a PC soundcard (maybe a USB one with USB isolator) for both generating and analysing - it's probably your cheapest and most promising direction at this point. You ought to be able to get to the 16bit level in the audio band.

author: vladc77
author_rank: Regular Contributor
timestamp: May 20, 2016, 09:12:29 pm
content: Agree too! I need to learn about it more. I can see bunch of the apps even for iOS. However, it looks not promising at the first glance. Maybe my expectations are too high. The only concern about it is a possibility to damage the computer. I read about it in a few places that it is a possibility. I need to learn about proper connection options.

author: rstofer
author_rank: Super Contributor
timestamp: May 20, 2016, 10:03:49 pm
content: Quote from: vladc77 on May 20, 2016, 08:37:26 pmWell, if the FG273 distortion actually is 1% it has 5 times as much as the DG1022A.BTW, are you sure about the 1022 'U' model? I thought we were looking at the new and improved 'A' model even though TEquipment still lists (but doesn't have) the plain 1022 model.The idea for the notch filter is to have sharp response around a single frequency and attenuate signals outside the passband. So, if you wanted to test at 400 Hz, you would have a filter tuned to this frequency and signals outside the bandwidth would be greatly attenuated. Then you need another filter for 500 Hz and 600 Hz and so on.Here's a tunable notch filter but I would want to see the LTSpice output before discussing it:https://www.bing.com/images/search?q=audio+notch+filter&view=detailv2&&id=CAD8CC1D0F257543D53E19F09F546D606A884614There are filter designs all over the internet.The DG1022A only has 0.2%, somehow I could live with that. If it wasn't clean enough, I would consider building up some notch filters. That way I would have a full featured FG for non-audio projects. But that's just me...

author: vladc77
author_rank: Regular Contributor
timestamp: May 21, 2016, 04:26:41 am
content: rstofer, yes, I was referring to Rigol DG1022U. This is what currently available. For example,http://www.ebay.com/itm/RIGOL-DG1022U-DG1022A-Arbitrary-Waveform-Function-Generator-AWG-25Mhz-2-chs-FG-/161131138600?hash=item25842a0e28:g:hc0AAOSwnLdWrLJtYes, the distortion is not that high. I misread something about the Kenwood 273. It is with even a higher distortion level. This is why I initially was looking for Rigol DG1022U. However, I got impression from here that it is still on a high side for audio. My understanding is that the acceptable distortion level is no more than 0.05%. I will be happy to get this one if that works. I guess I still do not have a definite conclusion on it and highly appreciate if more people will help to clear out on it.

author: vladc77
author_rank: Regular Contributor
timestamp: May 21, 2016, 04:29:00 am
content: I am also leaning toward trying a software based approach. It is still not all clear to me about how I safely can do it. My understanding is that I have to have:Software like - VIRTINS Multi-Instrument, Tone Generator Software or Visual Analyser. Fortuantelly, There are many choices. Not sure which one is the best.A decent sound card - I believe I already should have it on my MacProConnection cables. This is not fully clear to me yet. My understating, I should have 3.5mm Stereo to Composite RCA cable from sound card to the audio hardware. I also should have some intermediate filter to prevent damaging sound card. Do not know which one.I believe this approach is for replacing Audio Tone/Signal Generator with very low distortion level.I believe I also can have this connection via USB where I need to use an usb isolator and an USB device. This approach is even more unclear currently to me.I believe this approach is for replacing much more than only Audio Tone/Signal Generator. It can be suitable for Frequency Counter, Oscilloscope, Signal Analyser and more.Can anyone share with more details? Any advice is greatly appreciated!

author: funkyant
author_rank: Unknown
timestamp: May 21, 2016, 04:57:20 am
content: My audio Sig Gen of choice is the NTI MR-PRO.http://shop.nti-audio.com/pd_minirator_mr-procfm.cfmThe much cheaper MR-2 is also good value:http://shop.nti-audio.com/pd_minirator_mr2cfm.cfmThe on-board sound on your Mac Pro, I'm sorry to say, is crap and I certainly would not use it to generate reference tones.

author: vladc77
author_rank: Regular Contributor
timestamp: May 21, 2016, 05:03:29 am
content: Yes, they are good ones but cost as much as a decent modern Digital Function Generator. My understanding they carry only audio generator functionality. As a result, It may be then more reasons to buy something like Rigol DG1022U. I thought that if I am going to use a software based approach it will be a very cheap one. I may be wrong.

author: funkyant
author_rank: Unknown
timestamp: May 21, 2016, 05:18:26 am
content: Quote from: vladc77 on May 21, 2016, 05:03:29 amYou're not wrongBut I have the DG1021 and as others have suggested, it just not up to spec as an audio generator for anything critical.If you want to do it cheap as possible and get most bang for your buck then for sure a software solution will be best. Just start with the on board sound, and if you find you are hitting the limitations of that, there are plenty of cheap-ish USB soundcards with decent DAC's these days.

author: funkyant
author_rank: Unknown
timestamp: May 21, 2016, 05:20:28 am
content: Check out this software:http://www.nch.com.au/tonegen/

author: Lightages
author_rank: Unknown
timestamp: May 21, 2016, 05:25:52 am
content: You still haven't mentioned how you intend to use the FG. Is it to inject anywhere on the circuit or just at the normal inputs? There are many things to consider. Common grounds, loading, voltages. You also mention that you have a Mac. Do you have a PC? I am only familiar with software for the PC. One of the best and cheapest (free) is:http://www.sillanumsoft.org/How you connect it to what you want to test is wide open depending on what the equipment is.http://makezine.com/projects/sound-card-oscilloscope/http://www.instructables.com/id/Use-Your-Laptop-as-Oscilloscope/?ALLSTEPSThat is for an input, but outputs are a different matter.It is possible that all you need is the correct cabling with no extra components.So, where are you planning to connect?

author: vladc77
author_rank: Regular Contributor
timestamp: May 21, 2016, 05:46:38 am
content: Thank you funkyant. It is good Tone Generator.Thank you Lightages for great links. I may need to have it for both reasons. I am running Windows on my MacPro. I also have a PC computer.Will injection at the normal inputs be OK with only 3.5mm Stereo to Composite RCA cable? Do I need anything else for safety? I believe it will be good for sending tone signal to the tape deck.Regarding injecting the signal to the circuit board, I believe you are saying I need to consider about common grounds, loading, voltages. Is any affordable ready solution I can get?You said that I just may need the correct cabling with no extra components. What are you referring to? Is that a regular 3.5mm Stereo to Composite RCA cable or a special one?Currently, I need to calibrate/analyze few tape deck. I also need to trace the problem on the circuit board at one of the decks. It is not working. One channel is dead. In addition, I just want to learn about the possibilities and be ready when I need it. Thank you again.

author: Lightages
author_rank: Unknown
timestamp: May 21, 2016, 05:53:15 am
content: Quote from: vladc77 on May 21, 2016, 05:46:38 amYesQuote from: vladc77 on May 21, 2016, 05:46:38 amToo many considerations to post. Do some searching on the webs and you will find many circuits to take care of certain needs.Quote from: vladc77 on May 21, 2016, 05:46:38 amAgain, not enough information to know what you need. If it is to inject signals, that is one thing. If it is to look at signals, that is another. Google is your friend in this case.

author: vladc77
author_rank: Regular Contributor
timestamp: May 21, 2016, 06:00:31 am
content: Quote from: vladc77 on May 21, 2016, 05:46:38 amQuote from: Lightages on May 21, 2016, 05:53:15 amIs that Yes for OK with no safety precautions?Quote from: vladc77 on May 21, 2016, 05:46:38 amQuote from: Lightages on May 21, 2016, 05:53:15 amQuote from: vladc77 on May 21, 2016, 05:46:38 amQuote from: Lightages on May 21, 2016, 05:53:15 amI understand. I need to look on google. I just wanted to get some sort of overview in general. I may need to inject and/or look at signals and experiment, not clear agenda at the moment. I wanted to gather information to create a PC based lab with all safety precautions, especially, preventing damaging computer or sound card. Thank you anyway!

author: bson
author_rank: Unknown
timestamp: May 21, 2016, 11:00:02 am
content: Quote from: rstofer on May 20, 2016, 10:03:49 pmMy DG1022A measures 0.0100% across the audible spectrum on the HP 8903B, at slightly above typical line levels (500mV rms). That's about the same as the 8903's internal source. Compare this to the Siglent SDG2122X at 0.0060% (0.0045% using an external reference) and my HP 33120A at 0.0040%.The instrument spec is just a max value and will be very conservative. And even if it's 0.2% it's not that big of a deal since it can be subtracted from the total system THD+N measurement, as long as it can be reliably measured in isolation.For repair purposes all of these are fine for test tone generation since even 0.01% is completely inaudible no matter what its nature. For quantitative design analysis less is a little better so the system is dominated by the DUT.

author: rstofer
author_rank: Super Contributor
timestamp: May 21, 2016, 03:04:57 pm
content: Isolating the ground loops can be done in at least 2 pretty simple ways:1) Use a battery powered signal generator. For troubleshooting, the 1022A is overkill and something with a couple of op amps and a 9V battery would be ideal.2) Use an audio matching transformer (probably 1:1 ratio) to isolate the signal source and its ground from the DUT input and its ground.You can just buy an isolating transformer setup, already built and in a box for about $9:https://www.vminnovations.com/Product_48848/Boss-B25N-Ground-Loop-Isolator-Noise-Filter-.html?rd=gpf_48848&gclid=CMC1q7qy68wCFYZefgodrn0A7QSearch the Internet for 'isolating ground loops in audio systems'.There is no way in **** I would use my PC as a signal source for a circuit that was known to be defective.The more I think about it, the more I like the OP AMP solution. It's small, cheap, battery powered and expendable. I would save my good equipment, and especially my PC, for things that are presumed to work.

author: vladc77
author_rank: Regular Contributor
timestamp: May 21, 2016, 06:21:17 pm
content: Quote from: bson on May 21, 2016, 11:00:02 amThank you bson! It is very informative and changes my view on it.

author: vladc77
author_rank: Regular Contributor
timestamp: May 21, 2016, 06:39:31 pm
content: Quote from: rstofer on May 21, 2016, 03:04:57 pmThank you rstofer! It is very helpful. I already ordered Boss B25N RCA to RCA Ground Loop Isolator. I wanted to clarify here. It seems like that using B25N will be 100% safe to send tones from a signal generator (computer or any), not need to follow options 1 and 2 above. Right?However if I understood correctly, it is not safe for signal source for a circuit testing. Alternative for that is to have OP AMP solution. Is that correct? Please clarify.I was looking for OP AMP solutions. I found mostly DIYs to maker it myself. I may do it but most likely later. Would you recommended something that available for purchase or appropriate kit to make it myself. I was looking for the options and did not find something within 20Hz -20kHz yet. Thank you again.

author: rstofer
author_rank: Super Contributor
timestamp: May 21, 2016, 10:37:36 pm
content: Quote from: vladc77 on May 21, 2016, 06:39:31 pmI didn't find a suitable 'kit' that covered the entire spectrum. I didn't search eBay and I didn't spend a lot of time looking. I kind of like the multi-range unit I linked to above. But it is a DIY project - fun but time consuming. I did find some fixed frequency signal generators but I don't see the utility in those.For running a sound card, how about an old PC that is due for retirement. I have at least 3 Dell OptiPlex systems that are expendable. But you can absolutely bet on the fact I will never use my Surface Book as a signal source.Technically, the isolation transformer should be entirely adequate for eliminating ground loop (hum) but what happens if you cross up 120V with the secondary of the transformer. Well, it's still a transformer so the 120V appears on the sound card and the motherboard. I'm just not going there.No matter what it took, if I were doing debugging mains powered stuff where there was any possibility of getting into voltages above 5V, I want an expendable source.Other people will scoff at my hyper-vigilance but that's the way I feel about troubleshooting stuff that could potentially destroy my equipment. I started with one problem, now I have two!You could take every precaution and check every test point with a multimeter but still slip up and hit something that might not mix well with your source.

author: vladc77
author_rank: Regular Contributor
timestamp: May 22, 2016, 06:47:08 am
content: Thank you rstofer! It looks like I can experiment with many things. I may get an older laptop for $50 and should be fine for a while.

author: vladc77
author_rank: Regular Contributor
timestamp: May 24, 2016, 05:36:49 am
content: Another question, I tried Arta software based signal generator with sending test signal via sound card. For some reason, I cannot have a signal higher than 22Khz. I mean that even I set Sine waves with frequency more than 22kHz, the frequency counter never get measurement higher than 22kHz. I used Fluke 289 for this measurement. Does it mean the sound card has a limitation to output more than 22Khz. The spec on sound card states that it is 24bit, 192kHz capable sound card. Can anyone clarify what is wrong? Thank you!

author: rstofer
author_rank: Super Contributor
timestamp: May 24, 2016, 01:08:03 pm
content: Quote from: vladc77 on May 24, 2016, 05:36:49 amA very brief look on the Internet shows that the upper frequency limit for sound cards is often on the order of 20 kHz. Sure, they are 'sound' cards so why have an upper limit that is inaudible?Are you sure the 192 kHz applies to the output frequency or is it the sample rate. Got a link to the data sheet?You could read the FAQs for your software and find out that this limit is quite common when the sound card has an anti-aliasing filter:http://www.artalabs.hr/faqs.htm

author: vladc77
author_rank: Regular Contributor
timestamp: May 24, 2016, 06:39:57 pm
content: Thank you again rstofer! it all makes sense now. I believe the sound card just do not go over 22kHz. It seems like it is still workable for testing audio via sound card but need to realize about the upper limits. Thank you!

author: The Soulman
author_rank: Super Contributor
timestamp: May 25, 2016, 06:36:59 pm
content: You could play around with this (free) software, I use it frequently and quite happy with it.It's pretty cool actually.http://www.sillanumsoft.org/If the need arises you could always go with a high quality external sound card such as a RME or MOTU,a isolation transformer would also be a good idea to use, depending on what you're doing.

author: vladc77
author_rank: Regular Contributor
timestamp: May 26, 2016, 07:14:53 am
content: Thank you The Soulman! I may need to buy a good external sound card. I hope it wouldn't be as much as a decent audio/function generator.