THD claims of audio signal generators

mc · Jan 2, 2006

My ancient Heathkit audio signal generator, which uses 3 tubes and a light
bulb in an oscillator circuit, claims to produce sine waves with a total
harmonic distortion less than 0.1%.

My semi-ancient Hewlett-Packard HP202B oscillator only claims to produce THD
less than 1%.

I would have expected the HP instrument to have considerably better
performance specifications because of its much more elaborate circuit.

Are we simply looking at pessimistic vs. optimistic ratings?

Phil Allison · Jan 2, 2006

"mc"

My ancient Heathkit audio signal generator, which uses 3 tubes and a light
bulb in an oscillator circuit, claims to produce sine waves with a total
harmonic distortion less than 0.1%.

** Err - at what frequency/s ???

Betcha that is true only above 50 Hz and below 20kHz.

My semi-ancient Hewlett-Packard HP202B oscillator only claims to produce
THD less than 1%.

** The 202B is a very low frequency design - operates down to 0.5 Hz.

If it manages < 1% THD at that frequency, using bulbs to stabilize the
level - it is tops.

........... Phil

mc · Jan 2, 2006

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:41ru37F1frc05U1@individual.net...

My ancient Heathkit audio signal generator, which uses 3 tubes and a
light bulb in an oscillator circuit, claims to produce sine waves with a
total harmonic distortion less than 0.1%.

** Err - at what frequency/s ???

Betcha that is true only above 50 Hz and below 20kHz.

I think that's right.

My semi-ancient Hewlett-Packard HP202B oscillator only claims to produce
THD less than 1%.

** The 202B is a very low frequency design - operates down to 0.5 Hz.

If it manages < 1% THD at that frequency, using bulbs to stabilize the
level - it is tops.

Would the THD be appreciably lower at the mid audio frequencies?

Phil Allison · Jan 2, 2006

"mc"

"Phil Allison"

My ancient Heathkit audio signal generator, which uses 3 tubes and a
light bulb in an oscillator circuit, claims to produce sine waves with a
total harmonic distortion less than 0.1%.

** Err - at what frequency/s ???

Betcha that is true only above 50 Hz and below 20kHz.

I think that's right.

My semi-ancient Hewlett-Packard HP202B oscillator only claims to produce
THD less than 1%.

** The 202B is a very low frequency design - operates down to 0.5 Hz.

If it manages < 1% THD at that frequency, using bulbs to stabilize the
level - it is tops.

Would the THD be appreciably lower at the mid audio frequencies?

** Depends on that " if ".

BTW

If you cannot tell what the THD is, then it don't matter to you.

........ Phil

Jan 2, 2006

mc wrote:

My ancient Heathkit audio signal generator, which uses 3 tubes
and a light bulb in an oscillator circuit, claims to produce sine
waves with a total harmonic distortion less than 0.1%.
My semi-ancient Hewlett-Packard HP202B oscillator only claims
to produce THD less than 1%.
I would have expected the HP instrument to have considerably
better performance specifications because of its much more
elaborate circuit.
Are we simply looking at pessimistic vs. optimistic ratings?

if I were buying a low-distortion oscillator, neither would
be amongst my consideration.

What you're seeing is that a THD spec, all by itself, does
not the performance of an oscillator describe.

Compare the other specifications of the two oscillators,
e.g.:

* Response flatness: I would expect the HP to be
substantially better in spec and actuality

* Settling time after aburpt frequency change, I would
expect the HP to be FAR superior.

* Short-term amplitude stability vs time: I would, again,
expect the HP to be much better

* Long-term amplitude stability vs time: ditto for the HP.

* Phase noise/jitter: guess what? I'd expect the HP to be
much better.

If you need to build a simple, cheap, easy-for-someone-
of-unknown-skill-to-build oscillator, you make one set of
design choices. If you need to build a rugged, highly
stable, dependable unit which will has better short- and
long-term stability, can be swept rapidly in frequency while
maintaining that stability, and so on, you make a different
set of choices. Both choices have costs and consequences.

If I wanted cheap (at original prices only), I'd consider
the Heath, but I'd have to be willing to live with the fact
that I can't depend upon it as a source of stable,
dependable sine waves. If I needed a lab instrument that I
could depend upon to not have the amplitude bounce
substantially when I swept frequency, that I could
implicitly trust for amplitude flatness over the full range,
that would maintain its calibration for a long time, I
wouldn't buy the Heath.

But if I wanted dependably low distortion, I'd have
something else entirely.

Arny Krueger · Jan 2, 2006

THD as speced by the manufacturer is not the only measure of equipment
quality. For example, a lot of the HP equipment would meet spec near
their end of life or the end of life of their tubes. while Heathkit
equipment might meet spec only if routinely maintained.

HP's audio signal generators were renouned for their relatively high
power output, on the order of 1 watt for some models.

When you look at THD specs, you have to consider the whole operational
environment, including the power level, the impedance of the rated
load, and the frequency range.

Asimov · Jan 2, 2006

"mc" bravely wrote to "All" (02 Jan 06 00:39:09)
--- on the heady topic of "THD claims of audio signal generators"

mc> From: "mc" <look@www.ai.uga.edu.for.address>
mc> Xref: core-easynews rec.audio.tech:185968
mc> sci.electronics.design:536317 sci.electronics.repair:353509

mc> My ancient Heathkit audio signal generator, which uses 3 tubes and a
mc> light bulb in an oscillator circuit, claims to produce sine waves with
mc> a total harmonic distortion less than 0.1%.

mc> My semi-ancient Hewlett-Packard HP202B oscillator only claims to
mc> produce THD less than 1%.

mc> I would have expected the HP instrument to have considerably better
mc> performance specifications because of its much more elaborate circuit.

mc> Are we simply looking at pessimistic vs. optimistic ratings?

Some designs take the output at a different location and/or extra
filtering to achieve better distortion numbers. It also depends on the
circuit design, for example using a Wein Bridge configuration instead
of multiple RC phase shifts, etc...

A*s*i*m*o*v

.... Which sparks some mnemonic circuitry.

Bret Ludwig · Jan 2, 2006

Arny Krueger wrote:

THD as speced by the manufacturer is not the only measure of equipment
quality. For example, a lot of the HP equipment would meet spec near
their end of life or the end of life of their tubes. while Heathkit
equipment might meet spec only if routinely maintained.

The HP generators derived from the Model 200 will run forever, or at
least more than one human lifetime. There are no proprietary parts that
are likely to wear out with normal use. If needed the transformers and
the tuning capacitor could be repro'd for far less setup costs than
having a replacement IC taped out, masked and a run made such as would
be needed on many solid state units using proprietary ICs.

Everyone should own and care for one of these things. They were
manufactured until 1986 and represent the antithesis of all that is
wrong, immoral, indecent, and generally fucked up in the electronics
business today. (And most will run on 220 balanced power with only a
flick of the voltage switch...)

Bret Ludwig · Jan 2, 2006

Phil Allison wrote:

"mc"
"Phil Allison"

BTW

If you cannot tell what the THD is, then it don't matter to you.

....... Phil

A fucktard and spaznerolli like always.

Phil Allison · Jan 3, 2006

"Brat Ludwig" = PSYCHOPATH

** The grandiose pile of psychoses needs dealing with.

......... Phil

Tim Williams · Jan 2, 2006

"mc" <look@www.ai.uga.edu.for.address> wrote in message
news:xZ2uf.88196$k76.51068@bignews6.bellsouth.net...

Are we simply looking at pessimistic vs. optimistic ratings?

Idunno. Evidence that tubes are better? ;-)

Sounds like the HP202B is the same old RC lamp-controlled oscillator, same
as the Heathkit you describe (and an Eico 377 that I have, that has a
terrible 20-200Hz band!), so there shouldn't be any fundamental difference
between them. Maybe the ratings are as you say.

Thing about the HK, I bet, is it may not be tuned to low distortion (however
you might do that), while the HP I would imagine came set from the factory.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Jan 3, 2006

Yes, I had a HP 220CD, if I remember the model number correctly. And it
was wonderful to look at inside. It got left behind on one of my moves.

Today, for practically any purpose that I can imagine in my home shop,
the audio output on my PC sound card rules. A decent voltmeter tells me
the output level.

Michael A. Terrell · Jan 3, 2006

Arny Krueger wrote:

THD as speced by the manufacturer is not the only measure of equipment
quality. For example, a lot of the HP equipment would meet spec near
their end of life or the end of life of their tubes. while Heathkit
equipment might meet spec only if routinely maintained.

HP's audio signal generators were renouned for their relatively high
power output, on the order of 1 watt for some models.

When you look at THD specs, you have to consider the whole operational
environment, including the power level, the impedance of the rated
load, and the frequency range.

I had a version that used a pair of 6V6's for about 20 watts output.
It was built to test telephone lines and carrier current loops. Add the
right transformer to the output, and it made a great 120 VAC variable
frequency power supply. I had some of those large 24 VAC school clocks
and used one with the carrier loop generator to vary the speed f the
clock. Would would tell a pesky salesman he could have 15 minutes, then
I would turn up the frequency to only give him four or five minutes,
then slow it down and tell him his time was up, then point to the clock
over his head. They never caught on. ;-)

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Bret Ludwig · Jan 3, 2006

As an aside Jim Williams of Linear Technology has written very
intelligent pieces on HP Wien-bridge oscillators and building an
improved solid state version. I doubt it is on the web but you may be
better at finding it than me.

Arny Krueger · Jan 4, 2006

"Bret Ludwig" <bretldwig@yahoo.com> wrote in message
news:1136248029.822553.230810@g49g2000cwa.googlegroups.com

Arny Krueger wrote:
THD as speced by the manufacturer is not the only
measure of equipment quality. For example, a lot of the
HP equipment would meet spec near their end of life or
the end of life of their tubes. while Heathkit equipment
might meet spec only if routinely maintained.

The HP generators derived from the Model 200 will run
forever, or at least more than one human lifetime.

If you use them a lot, the tubes wear out.

There
are no proprietary parts that are likely to wear out with
normal use.

Tubes have always been proprietary parts. OK, you HP 200C has say a 6SN7 in
it. Which manufacturer's 6SN7 is the right one to use?

If needed the transformers and the tuning
capacitor could be repro'd for far less setup costs than
having a replacement IC taped out, masked and a run made
such as would be needed on many solid state units using
proprietary ICs.

The tube-bigot lie here is that most ICs in good audio test equipment are
standard parts, or can be readily replaced with standard parts.

Arny Krueger · Jan 4, 2006

<elephantcelebes@yahoo.com> wrote in message
news:1136262642.278391.35950@g44g2000cwa.googlegroups.com

Today, for practically any purpose that I can imagine in
my home shop, the audio output on my PC sound card rules.

Most PC sound cards vastly outperform legacy audio signal generators, both
for low distortion and flatness. They also have excellent settling times.

A decent voltmeter tells me the output level.

The trick is finding an inexpensive one with good frequency response. My
best meters are Flukes (not cheap) or the ProTek 506 (flat enough but not
wonderful and still not exactly cheap).

Tim Williams · Jan 4, 2006

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:qKKdnaxtnbfeVSbenZ2dnUVZ_s-dnZ2d@comcast.com...

Tubes have always been proprietary parts. OK, you HP 200C has say a
6SN7 in it. Which manufacturer's 6SN7 is the right one to use?

Uh..!? Tubes from different manufacturers are _massively_ better matched
than any two transistors or ICs from the _same batch_!

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Jim Thompson · Jan 4, 2006

On Wed, 4 Jan 2006 09:43:45 -0600, "Tim Williams"
<tmoranwms@charter.net> wrote:

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:qKKdnaxtnbfeVSbenZ2dnUVZ_s-dnZ2d@comcast.com...
Tubes have always been proprietary parts. OK, you HP 200C has say a
6SN7 in it. Which manufacturer's 6SN7 is the right one to use?

Uh..!? Tubes from different manufacturers are _massively_ better matched
than any two transistors or ICs from the _same batch_!

Tim

480)460-2350 | |
| E-mail Address at Website Fax

Arny Krueger · Jan 4, 2006

"Tim Williams" <tmoranwms@charter.net> wrote in message
news:s3Suf.165$dj3.88@fe04.lga

"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:qKKdnaxtnbfeVSbenZ2dnUVZ_s-dnZ2d@comcast.com...

Tubes have always been proprietary parts. OK, you HP
200C has say a 6SN7 in it. Which manufacturer's 6SN7 is
the right one to use?

Uh..!? Tubes from different manufacturers are
_massively_ better matched than any two transistors or
ICs from the _same batch_!

Thanks for permission to summarily dismiss any and all posts on
rec.audio.tubes mentioning equipment sonics dependent on brand of tube used.
;-)

As far as matching of SS parts goes, in practice parts matching is not the
issue for SS that it was for tubes. This is especially true of ICs.

Richard Crowley · Jan 4, 2006

Uh..!? Tubes from different manufacturers are
_massively_ better matched than any two transistors or
ICs from the _same batch_!

It usually takes several weeks into a new year before we
see things so remarkably clueless.

THD claims of audio signal generators

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