Audio Generator or Function Generator? Which to get?

On Mon, 13 Mar 2017 09:27:50 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>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:


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.

On Mon, 13 Mar 2017 13:43:04 -0500, amdx <nojunk@knology.net> wrote:

>On 3/13/2017 3:26 AM, oldschool@tubes.com wrote:
>> I've been looking into buying an Audio Generator (Sine and Square Wave).
>
>   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

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. 

On 3/13/2017 2:33 PM, oldschool@tubes.com wrote:
> On Mon, 13 Mar 2017 13:43:04 -0500, amdx <nojunk@knology.net> wrote:
>
>> On 3/13/2017 3:26 AM, oldschool@tubes.com wrote:
>>> I've been looking into buying an Audio Generator (Sine and Square Wave).
>>
>>   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
>
> 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.
>
>> http://www.ebay.com/itm/171999013818




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In article <74qdcctjlg47haiip530nl5npshooo59q1@4ax.com>, 
oldschool@tubes.com says...
> 
>
> 
> 
> 
> 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.....
> 

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.

<oldschool@tubes.com> wrote in message 
news:vaicccta9pdjea9abbc1074l06705f6677@4ax.com...
> I've been looking into buying an Audio Generator (Sine and Square Wave).
> I mainly want this to run thru an amplifier to listen to the frequency
> repsonse of the amp and speakers. Nothing very scientific, just to see
> what these amps and speakers can do.... And on occasion to inject an
> audio signal into amp sections to dee if the audio is passing that
> stage.
>
> Originally I was looking at some of the old tube gear, such as the Eico
> model 377. I also looked at the Heathkit IG-18 a transistorized version
> from the 70s. Because I like that old test gear, I'd be happy to get
> either of these, or another similar. Both of these are Sine and Suqare
> Wave.

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. 

On Monday, 13 March 2017 16:09:59 UTC, dca...@krl.org  wrote:
> On Monday, March 13, 2017 at 4:28:39 AM UTC-4, olds...@tubes.com wrote:

> > I've been looking into buying an Audio Generator (Sine and Square Wave).
> 
> 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.

It _can_ be more reliable, but making it so is a challenge most equipment fails. 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.


> So you are better off buying something new.  Getting a replacement vacuum tube may be nearly impossible.

it's not. On the rare occasions it is, boost the heater voltage, if it's not physically broken.


NT

On 13/03/2017 09:32, Jasen Betts wrote:
> On 2017-03-13, oldschool@tubes.com <oldschool@tubes.com> wrote:
>> I've been looking into buying an Audio Generator (Sine and Square Wave).
>> I mainly want this to run thru an amplifier to listen to the frequency
>> repsonse of the amp and speakers. Nothing very scientific, just to see
>> what these amps and speakers can do.... And on occasion to inject an
>> audio signal into amp sections to dee if the audio is passing that
>> stage.
>
> Any reason you've not looked at PC software?

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.

>> My search on ebay lead me to something called a "Function Generator".
>> What the heck is that??? And also called a DDS device. (I have no clue
>> what DDS means).
>
> 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

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.

http://www.intersil.com/content/dam/intersil/documents/icl8/icl8038.pdf

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.

-- 
Regards,
Martin Brown

Martin Brown wrote:

> 
> 
> 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.
> 


** 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 

On Monday, March 13, 2017 at 8:43:24 PM UTC-4, tabb...@gmail.com wrote:

> > Solid state equipment is a lot more reliable than vacuum tube equipment.
> 
> It _can_ be more reliable, but making it so is a challenge most equipment fails. 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.
> 
> 
> NT

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 1500 years.  

                                         Dan

On Tuesday, 14 March 2017 09:22:05 UTC, Martin Brown  wrote:

> 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.
> 
> http://www.intersil.com/content/dam/intersil/documents/icl8/icl8038.pdf

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