Audio Generator or Function Generator? Which to get?

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. But what I am finding is the prices combined with high S+H fees,
make these things very costly, and I have not found any of them which
claim to work. Sold as-is, for parts or repair. So, I may end up paying
$60 or more and getting something that dont work, likely needs new caps,
and so on..... If they were $25 or less, I'd take a chance, but not for
that kind of money.

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). But I carefully looked at this NEW device, sold without
a box (case), but only needs a power module and test leads. They sell
for around $14 from China, but since I dont care to order from China,
I'll probably have to hunt one down from the US, and pay around $5 or
$10 more. But that's ok. These have both the Sine and Square wave, as
well as Triangle wave (what does that sound like?).

While I prefer the older stuff, for around $20 a cheap wal-wart, and a
little work putting it into a box, I'd probably buy one of these, *IF*
it will do what I need..... I have read all the info on the ebay pages,
but I am not 100% sure that this is a modern replacement for the old
audio generators. One nice thing, is that they will show the exact
frequency on the digital readout.

IS THIS WHAT I AM LOOKING FOR?
Is something like this made to really be used, or is it just another toy
that does little and fails in a few months?

And can something like this work to test tube amps, without blowing up
from the high voltages in tube gear?

One last thing that has me puzzled. There are two BNC connectors. One is
labeled DDS, tho other is HS.

I found this in the description.
DDS frequency range: 1Hz-65534Hz, high-speed frequency (HS) output up to
8MHz.

I dont understand how or what the high speed feature does. Why would an
audio frequency be or need "high speed"? And what is the point for this
device to go above 20,000 cps, since we cant hear that anyhow? Going up
to 8MHZ seens senseless, unless this also serves as a RF signal
generator.

Here is the ebay URL.

http://tinyurl.com/h5celuc

 

[Colin Horsley]

On 13/03/2017 19:26, oldschool@tubes.com wrote:

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).

https://en.wikipedia.org/wiki/Direct_digital_synthesizer

Col


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[Jasen Betts]

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?

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

But I carefully looked at this NEW device, sold without
a box (case), but only needs a power module and test leads. They sell
for around $14 from China, but since I dont care to order from China,
I'll probably have to hunt one down from the US, and pay around $5 or
$10 more. But that's ok. These have both the Sine and Square wave, as
well as Triangle wave (what does that sound like?).

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.

IS THIS WHAT I AM LOOKING FOR?
Is something like this made to really be used, or is it just another toy
that does little and fails in a few months?

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

And can something like this work to test tube amps, without blowing up
from the high voltages in tube gear?

One last thing that has me puzzled. There are two BNC connectors. One is
labeled DDS, tho other is HS.

I found this in the description.
DDS frequency range: 1Hz-65534Hz, high-speed frequency (HS) output up to
8MHz.

I dont understand how or what the high speed feature does. Why would an
audio frequency be or need "high speed"? And what is the point for this
device to go above 20,000 cps, since we cant hear that anyhow? Going up
to 8MHZ seens senseless, unless this also serves as a RF signal
generator.

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

--
This email has not been checked by half-arsed antivirus software

 

[pfjw@aol.com]

You can get a CD, tape or vinyl record that will do this, and it will also test the reproducer at the same time.

http://www.soundstagedirect.com/analogue-productions-the-ultimate-analogue-test-lp-180-gram-vinyl-records.shtml?gclid=Cj0KEQjwhpnGBRDKpY-My9rdutABEiQAWNcslAdJZ8Oa_AoFf0E003jJYsI8x2OYXqe8Pxxv4cGi8cUaAiwd8P8HAQ

https://www.amazon.com/Stereophile-Test-CD-Compact-Disc/dp/B00008FUKK

http://www.gennlab.com/alignment_cassettes.html

http://usrecordingmedia.com/ancaltap.html

A function generator will be of use combined with a scope so that you can observe "before" and "after", but as a simple source of sound, not so much considering the real-estate it requires (Chinese chip devices excepted). However, if you do intend to get a (good) scope, then by all means a function generator is useful for several reasons.

Note that some very good frequency generators operate both in AF and RF. Look for one of those unless you truly *WANT* a function generator. It won't be cheap for a good one, but it does put it all in one box. Or, you could go for the gold and get one that also has a waveform function - more money, but more utility as well.

Peter Wieck
Melrose Park, PA

 

[Ralph Mowery]

In article <vaicccta9pdjea9abbc1074l06705f6677@4ax.com>,
oldschool@tubes.com says...

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. But what I am finding is the prices combined with high S+H fees,
make these things very costly, and I have not found any of them which
claim to work. Sold as-is, for parts or repair. So, I may end up paying
$60 or more and getting something that dont work, likely needs new caps,
and so on..... If they were $25 or less, I'd take a chance, but not for
that kind of money.

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.

http://www.ebay.com/itm/DDS-Dual-channel-Signal-Source-Generator-
Arbitrary-Waveform-200MSa-s-25MHz-W9U7-/162074779152?
hash=item25bc68de10:g:CwgAAOSw74FXOayX

 

[pfjw@aol.com]

Hamfests.
Radio Shows.
Local radio clubs (there is at least one, often several in every state).
Craig's List.
Put up a want-ad on Craig's List.
Yard and Garage sales - especially in older neighborhoods.
TV Repair shops - Amazing what some of them have sitting in the back room - *IF* one still exists in your area.

And if you are anywhere near/around Kutztown, PA in May, the Kutztown Radio Show will have what you need at reasonable prices.

Peter Wieck
Melrose Park, PA

 

[Jeff Liebermann]

On Mon, 13 Mar 2017 02:26:56 -0600, 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.
Here is the ebay URL.
(...)
http://tinyurl.com/h5celuc

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:
<http://www.daqarta.com/dw_gen.htm>
<http://www.instructables.com/id/PC-Sound-Card-Signal-Generator-Interface/?ALLSTEPS>
etc...

Most of the PC based oscilloscope and spectrum analyzer programs have
built in generators. I use Visual Analyzer:
<http://www.sillanumsoft.org/prod01.htm>
and Spectrum Lab:
<http://www.qsl.net/dl4yhf/spectra1.html>
Both have built in generator functions, including two tones for
intermodulation measurements.

This scope program has a tolerable white/pink noise generator.
<https://www.zeitnitz.eu/scope_en>

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.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[amdx]

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


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[amdx]

On 3/13/2017 1:43 PM, amdx 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

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

> http://www.ebay.com/itm/171999013818

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

> https://www.youtube.com/watch?annotation_id=annotation_1309899397&feature=iv&src_vid=n9sbUxz92uM&v=sKRbb0rJzOE

Mikek




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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.

 

[amdx]

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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On Mon, 13 Mar 2017 12:33:27 -0700 (PDT), "pfjw@aol.com" <pfjw@aol.com>
wrote:

Hamfests.
Radio Shows.
Local radio clubs (there is at least one, often several in every state).
Craig's List.
Put up a want-ad on Craig's List.
Yard and Garage sales - especially in older neighborhoods.
TV Repair shops - Amazing what some of them have sitting in the back room -
*IF* one still exists in your area.

And if you are anywhere near/around Kutztown, PA in May, the Kutztown Radio
Show will have what you need at reasonable prices.

Peter Wieck
Melrose Park, PA

Where I live, in a very rural area, there is really no such thing as
Hamfests unless I drive hundreds of miles. There is one in August, which
is 60 miles from here. I plan to go to that, but that's months away.

The last TV shop closed up about 10 years ago, around here. Even Radio
Shack (25 miles away), is now a small corner in an appliance store.

I am an avid yard/garage sale addict. If I see one, I MUST stop and see
what they have.... <LOL> But electronic test gear is not something I
have ever found. Around here, I'm more likely to find farm machinery and
all the usual household junk.

No, I am NOT near PA.

I will look at Craigslist though. I have bought from CL quite a few
times, but I never put a want-ad on it. That is a good thought.

Dont they have any "Ham Fests" (Or similar) online?

Because of where I live, I have to buy all my electronics parts and
stuff online. There just is no other source nearby. (except for that
very minimal Radio Shack store).

Now, if any of you guys are looking for farm tractors, and machinery,
cattle, horses, or anything like that, I can help. (Just dont ask me to
ship them)

 

[Ralph Mowery]

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.

 

[Benderthe.evilrobot]

<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.

 

[Phil Allison]

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.

** Fuck I hate pig ignorant, bloody crossposters !!!!!!


" ** 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

 

[pfjw@aol.com]

Off his meds, again.

 

[Martin Brown]

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

 

[rickman]

On 3/13/2017 4:26 AM, 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.

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. But what I am finding is the prices combined with high S+H fees,
make these things very costly, and I have not found any of them which
claim to work. Sold as-is, for parts or repair. So, I may end up paying
$60 or more and getting something that dont work, likely needs new caps,
and so on..... If they were $25 or less, I'd take a chance, but not for
that kind of money.

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). But I carefully looked at this NEW device, sold without
a box (case), but only needs a power module and test leads. They sell
for around $14 from China, but since I dont care to order from China,
I'll probably have to hunt one down from the US, and pay around $5 or
$10 more. But that's ok. These have both the Sine and Square wave, as
well as Triangle wave (what does that sound like?).

While I prefer the older stuff, for around $20 a cheap wal-wart, and a
little work putting it into a box, I'd probably buy one of these, *IF*
it will do what I need..... I have read all the info on the ebay pages,
but I am not 100% sure that this is a modern replacement for the old
audio generators. One nice thing, is that they will show the exact
frequency on the digital readout.

IS THIS WHAT I AM LOOKING FOR?
Is something like this made to really be used, or is it just another toy
that does little and fails in a few months?

And can something like this work to test tube amps, without blowing up
from the high voltages in tube gear?

One last thing that has me puzzled. There are two BNC connectors. One is
labeled DDS, tho other is HS.

I found this in the description.
DDS frequency range: 1Hz-65534Hz, high-speed frequency (HS) output up to
8MHz.

I dont understand how or what the high speed feature does. Why would an
audio frequency be or need "high speed"? And what is the point for this
device to go above 20,000 cps, since we cant hear that anyhow? Going up
to 8MHZ seens senseless, unless this also serves as a RF signal
generator.

Here is the ebay URL.

http://tinyurl.com/h5celuc

I haven't read all of the posts in this thread, but I see a lot of
confusion of the terms "function generator" and "audio generator".
Audio simply refers to the frequency range of the signal generated
without saying anything about the manner in which it is generated. But
most signal generators output a sine wave and perhaps a square and
triangle wave. As others have said, they were often analog circuits
that shaped one waveform into another. This is different from an
"arbitrary waveform" generator which some seem to be calling a function
generator.

An arbitrary waveform generator has a pattern in memory which is played
through a DAC to produce any function you wish which must repeat only
when the memory capacity is reached.

A DDS is another type of repeating waveform signal generator that also
uses digital logic and a DAC. It uses an incrementer to model the phase
of a signal cycle which then is translated into a waveform and played
through a DAC. If you want a sawtooth wave, you just play the phase
value through the DAC. A sine wave may be generated using a lookup
table or some simple sine generation functions. Other waveforms can be
generated using the lookup table or other mathematical functions. But
all these signals must repeat at some period as defined by the amount
the phase register is incremented at each clock. In fact, that is the
strength of the DDS over an analog signal generator, the frequency of
the output signal is very accurately defined.

I'm not sure why you think these devices would not be reliable or are
inherently inferior. The Ham community have been using DDS for some
time now. Even if they aren't used to directly generate the frequency
needed, they can be used as a tunable reference frequency with a PLL to
generate a very accurate frequency of nearly any rational value.

--

Rick C

 

[rickman]

On 3/13/2017 3:23 PM, oldschool@tubes.com wrote:

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).

Wikipedia often is written by those with a certain level of elitism
rather than an interest in explaining topics to all who wish to learn.
It is not uncommon for a technical article to be written at such a high
level that a reader needs much more than just a casual understanding of
the topic.

In my opinion, this is one of the ways Wikipedia has failed.

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.

How exactly would a computer distract you while you are soldering???
That is very unclear.

If you want to deal with tube circuits you need a buffer between any low
voltage equipment and the tube equipment.

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.....

Maybe there's a reason why tube equipment isn't made much anymore?

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.

Try connecting with a Ham club. They often use old equipment.

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.

The problem with buying wall warts is getting one that does what it says
it does. If you type in 5v, 1A for a wall wart on ebay, the first
hundred or so units have the same picture, are priced within a nickle of
each other and contain a single transistor for the entire active circuit!

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.

You could just insert a tube amp between the DDS and the gear you are
testing...

--

Rick C