Lowering output of a signal generator

[chromesphere]

Hey everyone,

In my never ending quest to learn more about electronics, im currently looking at getting an oscilloscope and a signal generator.  I've worked out the oscilloscope part, but a $200 signal generator is out of the question (the budget is gone), but i saw these cheap (probably rubbish) dds signal generators on ebay.  If it can output a 1khz sine wave ill be happy.

Anyway, my question is, its amplitude is 0.5v which sounds high for your typical guitar signal (need more like 100-200mv?).   Is there a way to lower the amplitude externally without messing too much with the signal?  A resistor on the outpout? 

Heres the link to the signal generator:
http://www.ebay.com.au/itm/DDS-Function-Signal-Generator-Module-Sine-Square-Sawtooth-Triangle-Wave-DC-9V-/181072329261?pt=LH_DefaultDomain_3&hash=item2a28c07a2d

Thanks for your help!
Paul

[amptramp]

There appears to be an amplitude control on the module itself in the enlarged picture and it has a knob on it, so it is intended to be used as the output level control.  Do you need some other control?

[armdnrdy]

There appears to be an amplitude control on the module itself in the enlarged picture and it has a knob on it, so it is intended to be used as the output level control.  Do you need some other control?

In the auction the amplitude specs are listed as:

-- Amplitude amount: 0.5Vpp-14Vpp

So it appears as if the bottom range is 500ma.

[amptramp]

If this is the case, there is probably a resistor in series with the ground lead on the amplitude pot.  If you can find it and short it out, you should be able to get the output down to zero.

[PRR]

> 0.5Vpp-14Vpp

"pp" is Peak-to-Peak". Assuming sine, that's 0.18V to 5V. 0.2V is not wrong for guitar level. An adjacent thread suggests a level closer to 0.4V.

But you do want less.

Generator is fairly strong, guitar-inputs are usually sensitive (low loading). Resistor divider.

You also want some resistance because the strong generator can force the amp input in ways a guitar can't.

0.18V-5V output, 1Meg resistor, geetar jack, 100K resistor, ground. You get 1/10th (actually 1/11th) of the generator, say 16mV-450mV.

The "right way" is a Gain Set, or Attenuator Box. Selectable 1 2 3 6 10 20 40 dB loss. Get any level from 5V to 14uV. But really a 5V-0.18V and a 450mV-16mV range will cover most audio bases.

> a resistor in series with the ground lead on the amplitude pot

Yes; but with that shunted he's still gonna be way down below "1" on the knob to get guitar-ish levels (if the knob had numbers.) At some point, you just gotta clobber the signal.

> cheap (probably rubbish) dds signal generators

Quality control may be only 99.999%; you could get a dud. But IF it works it probably slays all the sine things we used to use. H-P 200AB, big as a toaster oven and near as hot, and wobbles for seconds to days after the least frequency change. Heath IG-18(?) cool but wobbly and then the switches tarnish. A later generation used the something-2000 (decades before 1999) which was solid but the "sine" had points.

[TheWinterSnow]

Can't really chime in on the device itself but I will say that guitar signal (if we are talking about pickups here) best to my knowledge with a proper load averages 1.5Vrms to 3.2Vrms.  The EMG 81 and 85 for example have an output of 3.1Vrms or almost 9Vpp, this is why a lot of guitar's will slightly clip some pedals that run on 9v supplies.  I have hooked up my guitars to an O-scope before with the guitar connected to an amp and the readings when jamming on the guitar registered in that general area on the scope, I have also ran a generator into the front end of an amp and it takes around 2-3Vrms to get the sine wave to distort similarly to a typical guitar signal as well.  That 0.5Vpp would be 177mVrms, which is almost microphone level with typical live instruments like drums or full volume 100+ Watt guitar amps.  You have more than plenty of range with that generator.  If you ever need less signal, a small breakaway board with an active buffered volume control would do the trick.

[chromesphere]

Awesome!  Thanks for the replies guys, it's only 25 bucks, worth a go, sounds like it is usable stock, if not ill try an external mod as you all have suggested.  I would have liked to build a sinewave generator, but im a bit stuck for time and want to focus on other projects....anyway thanks again for all your help!

Paul

[Gurner]

Frankly it chills me to the bone that they can manufacture those things to that price (check out the price of DDS chips alone ...then throw in the time to design a circuit, convert to a PCB, source the parts cheaply, make the boards, distribute,promote,ebay fees etc ...wow)....now I may be wrong, but I doubt they're gonna be selling these in the volume of say Iphones, so heaven knows what amount they hope to 'bag' profit wise from the overall design/project.

For a consumer...it's a festival of win (but as someone who has an eye on the manufacturing side of things....it just takes my breath away)

[armdnrdy]

Cheap labor, cheap wholesale components, automated machinery production line, mass production, stolen technology!

The Chinese (Taiwanese) even stole the "juice" that fills low ESR electrolytic capacitors! It was "lifted" from Japanese manufactuerers. They didn't get the mixture "quite" right, which caused an epidemic of cap failures in electronic goods!

Scroll down to the "Industrial espionage implicated" part.

http://en.wikipedia.org/wiki/Capacitor_plague

[PRR]

> check out the price of DDS chips alone

A 3.5GHz DDS chip is $137..... but a 16MHz chip is $1.65 in the US, and probably cheaper closer to where they make them.

> For a consumer...it's a festival of win (but as someone who has an eye on the manufacturing

Indeed. I wanted to know the power in my house. I found current transformers on close-out, $7 each. Nifty precision rectifier, a buck plus some hours to solder, trim, and box. 200mV panel meters, 5V wart.... all a lot of fiddly-bits I no longer have the inclination for.

Then I found a one-piece V+A meter, 100A current loop, $15 from some broken-english vendor on eBay.