Signal Generators

Subjects that don't have their own home
Post Reply
izzy wizzy
Old Hand
Posts: 1034
Joined: Fri Nov 02, 2007 7:02 pm
Location: Folkestone
Contact:

Signal Generators

Post by izzy wizzy » Wed Jan 29, 2020 7:01 pm

This might have been covered before so maybe all I need is a pointer.

What's the deal with the low cost DDS singal generator arbitary waveform generator or whatever they're called gizmos that litter ebay. They seem cheap for what they do assuming I know what they do, Compared to basic old school function generators made by Thurlby Thandar, Jupiter, GWinstek etc which I think are now called analog function generators.

I'm asking as I need one and wondering have the DDS things popped up in place of the analog ones while I haven't been looking? And if so, are they worth it at £50 or so? I'm not measuring distortion but want something to stick into my amplifiers to see if they're going properly. I don't need a new thing and don't really want to spend more then £100 unless I have to.

Thanks for any help.

Cheers,
Stephen

User avatar
ed
retired
Posts: 4177
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

Re: Signal Generators

Post by ed » Wed Jan 29, 2020 7:21 pm

I made one back in the day when my farnell lfm4 packed in. There is some background here:

http://www.vitalstates.org/diy/amplifie ... siggen.htm

The simple way I looked at it was based entirely on what I wanted it for. I wanted to do distortion measurement and at the time(2010 ish) the affordable dds chips weren't up to it so I ended up with a wien bridge.

About 3 years ago I had another look and the dds chips had improved quite a bit. I was half way through an updated diy version when I got sidetracked....it hasn't resurfaced yet.

The dds versions on ebay all seem to have high distortion but I'm sure that's ok for just checking the waveform and detecting clipping etc. The bottom line is you get what you pay for and if you want low distortion in dds then you gots to pay.
There's nowhere you can be that isn't where you're meant to be

User avatar
Nick
Site Admin
Posts: 12377
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

Re: Signal Generators

Post by Nick » Wed Jan 29, 2020 11:08 pm

I use a sdg1020 that I got several years ago now, it was a bit more than those ebay DDS jobs, but basically the same thing, I suspect its 12bit DDS so only 0.02% or so distortion with the sine, but for day to day use its great. If you want lowish distortion then PC and sound card or a CD player are probably the cheap way of getting that. I do have a analogue 1kHz source that has 0.00001 THD, but that’s for high days and holidays.

Bottom line DDS can be great, but don't know just what the £60 ones on ebay are like.
Resistance isn't futile it's V / I.

User avatar
shane
Shed dweller
Posts: 2933
Joined: Sun Sep 16, 2007 12:09 pm
Location: Kept in a cool dry place.

Re: Signal Generators

Post by shane » Thu Jan 30, 2020 8:21 am

If all you want is something to shove in the input of an amp to see if anything comes out of the output, there are a number of signal generator apps you can download to a smart phone for free. Probably horrendous distortion though.

izzy wizzy
Old Hand
Posts: 1034
Joined: Fri Nov 02, 2007 7:02 pm
Location: Folkestone
Contact:

Re: Signal Generators

Post by izzy wizzy » Thu Jan 30, 2020 8:35 am

ed wrote:
Wed Jan 29, 2020 7:21 pm
I made one back in the day when my farnell lfm4 packed in. There is some background here:

http://www.vitalstates.org/diy/amplifie ... siggen.htm

The simple way I looked at it was based entirely on what I wanted it for. I wanted to do distortion measurement and at the time(2010 ish) the affordable dds chips weren't up to it so I ended up with a wien bridge.

About 3 years ago I had another look and the dds chips had improved quite a bit. I was half way through an updated diy version when I got sidetracked....it hasn't resurfaced yet.

The dds versions on ebay all seem to have high distortion but I'm sure that's ok for just checking the waveform and detecting clipping etc. The bottom line is you get what you pay for and if you want low distortion in dds then you gots to pay.
You got a lot of interesting stuff on those web pages. Now you got me looking at micro controllers and LCD displays :)

izzy wizzy
Old Hand
Posts: 1034
Joined: Fri Nov 02, 2007 7:02 pm
Location: Folkestone
Contact:

Re: Signal Generators

Post by izzy wizzy » Thu Jan 30, 2020 8:45 am

Thanks for the replies as they help focus on what I want. Don't think I'm fussed on low distortion but I have a phone app generator and that doesn't do what I want - not enough drive and fiddly to use.

The thing that concerns me about the cheaper DDS gizmos is the lack of knobs and never seen one going/being used. I like to wiggle the frequency around and wind the level up and down to see how things react. If that's done by inputing a setting rather than turning a knob, then that device isn't for me. When there's panic under fire, I want to grab something and wind it down. I hate menus, layers of menus to reach a setting. Is that how the cheaper DDS gizmos work? I've done quite a bit of reading but I guess I'm after feedback from folk that have used both.

So would those prejudices describe the device I'm after as an analog generator? Or have I misread how the DDS machines work?

Maybe I'm too much of an analog person. He says going back to look at microcontrollers, LCD displays ....

User avatar
Nick
Site Admin
Posts: 12377
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

Re: Signal Generators

Post by Nick » Thu Jan 30, 2020 9:06 am

The one I have has a knob that will adjust the parameter you last picked, or you can type in the value you want. Each output also has a on off button. But again, I don;t know about the £60 version. I agree with all your requirements.
Resistance isn't futile it's V / I.

User avatar
ed
retired
Posts: 4177
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

Re: Signal Generators

Post by ed » Thu Jan 30, 2020 10:49 am

there seem to be a few on ebay at the moment. This one caught my eye:

https://tinyurl.com/v5xn9km

it appears to have the same functionality as my old farnell lfm4 but without the output level monitor. It has the same buttons as the lfm4 and it has knobs to twiddle, and more to the point, has the same distortion levels as the lfm4. I'm suspecting this may be analog rather than dds.
There's nowhere you can be that isn't where you're meant to be

izzy wizzy
Old Hand
Posts: 1034
Joined: Fri Nov 02, 2007 7:02 pm
Location: Folkestone
Contact:

Re: Signal Generators

Post by izzy wizzy » Thu Jan 30, 2020 11:31 am

That one caught my eye Ed after you mentioned the Farnell one you had.

This DDS one https://tinyurl.com/rgfyapg looks OK too.

The cheap DDS ones seem very small and reckon I'd need a magnifying glass to read the display.

Thanks guys. All very helpful.

User avatar
Nick
Site Admin
Posts: 12377
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

Re: Signal Generators

Post by Nick » Thu Jan 30, 2020 11:32 am

Yep, looks very analog
Resistance isn't futile it's V / I.

User avatar
Nick
Site Admin
Posts: 12377
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

Re: Signal Generators

Post by Nick » Thu Jan 30, 2020 11:43 am

This one looks like its got a rotary encoder, so should give the required functionality.

https://www.ebay.co.uk/p/5027043225?iid ... 5603&rt=nc

Here is the manual (I think).

http://gotronik.pl/img/FY6600_Series_Users_Manual.pdf

Sine distortion is not great.
Resistance isn't futile it's V / I.

izzy wizzy
Old Hand
Posts: 1034
Joined: Fri Nov 02, 2007 7:02 pm
Location: Folkestone
Contact:

Re: Signal Generators

Post by izzy wizzy » Thu Jan 30, 2020 11:59 am

I thought one of those would do it until I saw the size of it. And the screen size is 50mm and with all that info on it, I can't imagine me seeing much of it. And it was at that point this thread started.

simon
Eternally single
Posts: 4344
Joined: Thu May 24, 2007 11:22 am
Location: People's Republic of South Yorkshire

Re: Signal Generators

Post by simon » Thu Jan 30, 2020 12:38 pm

This won't help Stephen but what I've done in the past is create some test tones and sweeps in Audacity, saved them into my Squeeze Center library and then I can just play them, in a loop if necessary.

It's been very educational, along with a spectrum analyser ap on my tablet/phone, though I don't know how accurate they are for proper measurement. But they are my favourite price - free!

izzy wizzy
Old Hand
Posts: 1034
Joined: Fri Nov 02, 2007 7:02 pm
Location: Folkestone
Contact:

Re: Signal Generators

Post by izzy wizzy » Thu Jan 30, 2020 12:45 pm

simon wrote:
Thu Jan 30, 2020 12:38 pm
This won't help Stephen but what I've done in the past is create some test tones and sweeps in Audacity, saved them into my Squeeze Center library and then I can just play them, in a loop if necessary.

It's been very educational, along with a spectrum analyser ap on my tablet/phone, though I don't know how accurate they are for proper measurement. But they are my favourite price - free!
That might be very helpful at that price. None of the other stuff is going anywhere and I got all the rest :) Can speriment to see if it's for me.

Post Reply