Audio Generator or Function Generator? Which to get?

Col

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Those are proving popular at the bottom end. I gather they're good except near the top of their freq range, when it gets a bit weird. They do audio and much more. But as you say, longevity is another matter. But at $14 it's hard to complain.

NT

Any reason you've not looked at PC software?

look it up on wikipedia. it means that inside there's some sort of computer generating a digital wavform, that gets converted and comes out the output

you can probably buy he same thing from china on ebay, for about the same price, most large scale vendors are present in multiple marketplaces.

it will probably last longer than a few months, especially if you put it in a good case.

it's probably a square wave at 128 times the DDS output frequency. it might be useful for other purposes

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For the price you might as well get a function generator. Most of the audio type signal generators put out sine waves and some square waves. The function generator can put out those and many other waveformes. I have one of the China function generators that lets me hook it to a computer and any kind of waveform I can draw on the computer screen, the generator will put out.

The one I have will go from below audio to about 25 MHz. They make some other models that only o to about 6 MHz for a few dollars less. It is dual chanel so you can put signals into a stereo if you want to. Each chanel can be set sperate. It includes a frequency counter so you can input a frequency and see what it is. I am not sure how accurate it is above the audio range. There is no difference in audio and RF as far as to what you get out, just the range of frequencies, so you can use it as an rf signal generator if you want. They are not shielded being in a plastic case.

The waves other than a sine wave starts to degrade above about 1 MHz. There is a modification that is on youtube that I made to mine to help that out. You probably would not want to try that as it involves changing about 6 or 8 of the SMDs, but the parts were less than $ 20 from one of the larger companies. I did it mainly to see how it would work and am learning how to work with the SMDs.

There are some vidios on youtube about this one and probably others.

In addition to looking at Ebay , look at AliExpress. Sometimes identical items are much less expensive at Ally or Ebay. Try including diy to find kits.

Solid state equipment is a lot more reliable than vacuum tube equipment. So you are better off buying something new. Getting a replacement vacuum tube may be nearly impossible.

Dan

(...)

That DDS generator only goes up to 65KHz, does not have a built in frequency sweep feature, and does not have a sawtooth output or built in detector suitable for displaying a frequency sweep on an oscilloscope. To sweep an audio amplifier with a DDS, you will need a sine wave generator feature, and an up/down counter or frequency modulator to sweep the frequency range.

First look at a real function generator. Next, build a checklist of the features you need. Then, go shopping using the feature list. You're doing this backwards.

Note: You can use a PC sound card as a swept audio source and function generator: etc...

Most of the PC based oscilloscope and spectrum analyzer programs have built in generators. I use Visual Analyzer: and Spectrum Lab: Both have built in generator functions, including two tones for intermodulation measurements.

This scope program has a tolerable white/pink noise generator.

Hint: Buy a higher resolution USB sound card that will do 24 bit 96 KHz, 192 KHz, or if you have money to spend, 384 KHz clock rate. The common 44/48KHz devices don't make very good test instruments. External USB is better because sound chips built into a PC or laptop pickup noise from everywhere.

However, I must admit that $15 test equipment is lots of fun to play with. I have LRC meters, function generators, DDS RF generators, return loss bridges, noise generators, etc most of which cost about $15.

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If you have any interest in building one, look up the XR2206. It is an old but a pretty cool chip. It will do many functions up to 1 Mhz. Lots of info available, I even see one Arduino controlled unit.

Mikek

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Also search "suite", which seems to be a common miss-traslaion of "kitset"

Electrically, tubes are harder to bust...

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Ebay has a XR2206 kit for $9 with a case.

Here's a 4 part video of assembly, part 4, you can find 1,2 and 3.

Mikek

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Thanks to all who replied. I read that WIkipedia article, which explained what these things are, (even though that article was like reading a legal manual).

When I descibed this thing, I actually had looked at several of them from China, which all looked identical. One of them said it goes to

8mhz, using the BNC connector labeled HS. Either way, that dont much matter, since I have my old Eico tube signal generator, for RF use.

I probably am doing this backward, but I really was not looking for something like this. I was looking for an old tube based audio generator, such as the Eico 377. But you know how ebay tends to show a hundred other things that are similar, and these function generators came up. I had to spend a good amount of time reading about them, since I was not familiar with them at all.

I am somewhat aware about using a computer with software to act as a signal generator, oscilloscope, etc. I'll have to read up more on all of that, but in all honesty, I would not even consider connecting my laptop computer to anything other than and audio input connector on a tube amp. I said I also want something for testing interstage circuits, and that means applying a test probe to a spot inside a device that may have 400 or more volts on it. Even with a capacitor and other protection, there is no way in hell that I am gonna risk destroying an expensive and fragile laptop computer. And while I have several spare deshtop machines, I do not keep them in my shop. I dont have the space and I dont want to be distracted by computers when I'm soldering. If I do take any computers in my shop, it's my laptop, and I only do so to view a schematic on the screen.

In all honesty, what I really want to buy is still an old tube type audio generator. That is what was made for the gear that I mostly work on, and that old tube stuff is built to hold up, as well as being easy to repair if it breaks. The problem is that this old tube stuff is selling for way too much money on ebay. Heck, some of those old Eico

377's are asking as much just for shipping as I am willing to pay for the whole thing, and one of them looks like it went thru a war, and is being sold For PARTS.....

Which reminds me, does anyone know of other sources for buying that old tube test gear, besides ebay? There must be other sources.... It's NOT Amazon, I checked, even though I have never cared much for Amazon. They just dont sell old stuff like this.

I might still buy one of these DDS devices, just for the heck of it. For $15, I'm sure I'll have some fun with it..... I actually found some of them (identical( located in the U.S. for $17. (I dont buy from China because it takes too long to get the stuff). I also found another one in the US that comes with the matching wall wart for $23. (Which I'd probably buy, or I will just end up having to spend another $5 or more to order that wart separately.

So, the bottom line is that I may buy one of these DDS devices, but I will still continue to look for the tube type audio generator which is what I really want in my shop for testing my old tube gear.

I suppose I could look this up, but I have other things to do at the moment, so I am just gonna ask.... What is Arduino? I'm Old School, so I dont know much about all this new technology.

Skip it, just look at this if it is of interest go look at the video.

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Back when it was made (probably around 1960 to 1980) that was the best that could be had for a reasonable price. Now the items comming from China are much beter. I used something like that old generator about 25 years ago tunig some coil and capacitors. As I needed them on a exect frequencyto make a filter. I used a freq counter to set the generator. Had to keep one eye on the counter to make sure the generator was not drifting. I would have loved to have the China generator I have now. Digital readout, just set the numbers and it stays put in the audio range.

Spearking of repairing the old gear, have you checked the price of some of the tubes and capacitors that are in the old gear ?

Even using some of the China oscilloscopes is a joy. Press a button on them and off to the side is lots of info about the trace. Voltages in RMS and peak to peak. Even the frequency. That will take the place of a voltmeter in many cases.

After fighting using the old test equipment for years I finally got to the place where I could get the more modern equipment. Sure makes things easier to work on when you can depend on the test equipment and not have to wonder if it is the test equipment or the item to be repaired. Like the old signal generator may have some slight hum on the signal and you may think that hum is comming from the unit under test.

Plenty of cheap function generators out there that do the basic sine, triangle and square-wave.

Its worth checking the spec - if they start with sq-wave and convert to triangle and then sine; the sine could be a bit lumpy.

Starting with sine gets better wave purity, but accuracy is not so good and the sq-w M/S ratio can be off.

There are some good articles out there on testing audio response with other waveforms - a perfect square wave is the sum of an infinite series of sine waves. Taking that the other way round - a half-decent square-wave can tell you as much as a lot of different sinewaves all at once.

At one time it was trendy to test audio with sawtooth, but I haven't seen any new articles recently.

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items are much less expensive at Ally or Ebay. Try including diy to find kits.

It _can_ be more reliable, but making it so is a challenge most equipment f ails. If 50 year old valve kit is working it has proven itself, and any new electronics has a very low chance of lasting that well. So in practice old valve kit is on average more likely to last better.

tube may be nearly impossible.

it's not. On the rare occasions it is, boost the heater voltage, if it's no t physically broken.

NT

Indeed. I favour Daquarta (sp?) for this sort of thing.

The paid for version will even give you a realtime FFT vs time waterfall plot of the input signal and the signal generator part continues to work after the evaluation period. It can do the usual waveforms well enough for all but the most demanding tests.

It is easily good enough for most audio work and allows you to see harmonic content of signals in realtime. The only disadvantage is that it perhaps isn't going to like mains voltages on the inputs/outputs of your PC so you would need to be careful.

There used to be old school analogue function generator chips that made a triangle wave and then applied diode shaping to get a pseudo-sine wave. HP made one design implementation that was surprisingly good. Intersils 8038 was the poor mans alternative for DIY.

These days DDS is probably the way to go since it can do so much more. Testing power amps it is wiser to use frequency shaped noise rather than pure sine waves since you can hit mechanical resonances and damage acoustic drivers with quite modest power levels of pure sine wave.

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Regards, 
Martin Brown

** Giant HUH ???

Testing amplifiers does not involve speakers AT ALL !!!

Sine waves are the primary and still most revealing method.

BTW,

any speaker that cannot survive short term sine wave testing is not worth owning.

You could not be more WRONG.

.... Phil

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fails. If 50 year old valve kit is working it has proven itself, and any n ew electronics has a very low chance of lasting that well. So in practice o ld valve kit is on average more likely to last better.

I do not agree with you. A fifty year old valve kit that is working does not prove that it is a reliable gear. There may have been 50 thousand of those produced and all have failed except for one.

Way back in the 1960's the mean time to failure for some transistors was 15

00 years.

Dan

I built one of those decades ago. What a car crash. The wave forms were hopeless. I don't remember the details to know why, I presume the problem was the 8038 though.

NT