On 3/13/2017 4:26 AM, 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