THD claims of audio signal generators

Ya, because they have that fun little exponential Vbe curve. Beta is to transistors what Gm is to tubes and FETs, and you know it...

Tim

-- Deep Fryer: a very philosophical monk. Website:

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.

So far, so good.

Yes, and the Vbe curve relates very closely to the standard definition of transconductance, right?

Huh?

No Arny, the trick is to ante up once and buy a good one from a first or at least second tier manufacturer whose specs well eclipse the job at hand. Second tier manufacturers are sometimes better because they use off the shelf parts where Agilent and Tek used their fab capabilities to make wonderful chips....that no longer exist. And they are not making more.

If commodisumo PeeCee hardware were test grade National , Aeroflex, Agilent and others would not be getting the hemmorhoid-splattering prices they do for CompactPCI and VME/VXI hardware. A peecee is not a core piece of test equipment. Yes you can do a few things with a sound card, but a Audio Precision box is NOT a sound card in a fancy box.

This is why they still make'em.

My experience is the box works with any of them. Probably one yields best case distortion or dial tracking. I have never had it be an issue.

IIRC the 8903 has a proprietary diff amp that is close to unobtanium. HP solid state RF gens use a lot of proprietary silicon-8640s are slowly dropping, which is a shame, they are the low phase noise solution even today. The Ollies couldn't copy this stuff on their own, or they would-they need Western capital and management. Too bad, I'd love seeing Agilent hoist by their own 35 year old petard!

Bullshit on stilts. McIntosh, ARC, Julie Labs and many others have made tube amps with THD and intermod specs comparable to any popular solid state and bandwidth up to at least 25 or 30 kHz, surely you can't hear above that. Tube amps do a good job from perhaps 16 Hz (they are down some there usually) to 20-22 kHz (and if they are down a little over 15 kHz that's OK as long as it is not too sudden a slope) and because the type of distortioon differs. .1 THD is OK on tube amps whereas .01 may NOT be on solid state. Subjectively tube amps of a given specification often (not always) sound better than solid state amps of better spec. Russ Hamm proved it in 1973 with his paper which appeared in JAES and it has not been contradicted. Arny talks a lot but he knows it's true and will be until they change the laws of physics.

We got Cal a copy of the book "An Evening with Marilyn" by Douglas Kirkland for Christmas. There's a hi--fi system in the background in the loft where the shoot takes place. (Looks like an Altec amp and a big Altec bass driver-the horns are out of the picture. There's a big dust cap-it's not a 604....but who would have cared?) You know when Frank Sinatra, Arthur Miller, JFK, and DiMaggio were on top of THAT situation the music was playing just fine with no silicon involved. You know what? It still does. (The music. The people, they're dead.)

My experience with several dozen HP 200's does not match yours. Yes, they all oscillate, but amplitude stability and phase noise is tube dependent.

If you recall, the 8903 is a fairly rare beast in and of itself and hardly constitutes an example supporting your claim. I have an entire wall of audio test equipment from HP, ST, Techron, GR, B&K, Leader, and so on, and there's nary a proprietary IC in any one of them.

Now the exception is my old, trusty GR 1390B random noise generator which uses a proprietary noise diode. if it goes, the unit is worthless. WAIT! It's a vacuum tube, not an IC! Fancy that, a proprietary, non-replaceable vacuum tube.

Lessee, HP 8640: signal generator with a range of 500 kHz to

i have probably just been lucky. Also I pay little attention to the dial markings, I use my freq counter to set frequency. And I don't use them for scope cal, there are precision level gens that are used for that.

Oh no! They were sold by the truckload because they replaced the 339. Then they went to *ucker in trade for....used 339s....because they weren't. Potomac IIRC essentially cloned the 339, but in two boxes, a gen and receive, and charged more for either than HP had for the 339. So 8903s are common as sin. However, barring abuse, they run forever.

and

Well, then I guess an FM tuner isn't an "audio unit".

What - I mean, WHAT?

Pearce Consulting

I would take it , then, that you have not seen more than maybe a couple of these units, yes? So, you hardly speak from a position of authority. Having run an electronics calibration lab, and seen quite a few, I might huimbly suggest my experience trumps yours.

Fine, but that doesn't deal with drift, amplitude instability, and all the rest.

And how many of them are solid state>

You obviously missed my point, or chose to completely dance around it with irrelevancies. The 8903 is merely ONE example of audio test equipment. It is not representative of the realm of equipment as you might suggest it does. Besides, you have already demonstrated pretty narrow experience with HP200's, and you did qualify your claims on the 8903 with "IIR," yes? SO you have yet to provide any substantiation to your claim.

How in any way, shape or form is this at all relevant?

Which seems to contradict you earlier point.

A point you failed to address.

A point you failed to address.

I should also add that of all the equipment I have, the tube0based stuff has been the most difficult to support, because it's becoming increasingly difficult to find suitable tubes, any ol' fire bottle just won't do. But , even though the tubes ARE easy to extract, they WILL have to be replaced at some point, absolute guarantee.

Whether or not any of the solid state units have proprietary parts that will be hard to replace, I don't know: not a single one of them has failed.

Last time I checked, the part that an HP 8640 would test isn't.

I'm afraid it's true. Discrete power transistors vary much more than tubes of a given type and manufacture run. That's why construction or repair of high power solid state amps requires either factory-matched sets or the use of a curve tracer to sort through piles of them.

Of course, the transistors come in N and P channel or NPN and PNP types whereas tubes are not complementary. So it's apples vs. oranges.

Are apples or oranges better?

and

It may or may not be a crock, but no one has submitted a rebutting paper to the AES for consideration in 32 years. So I am inclined to believe it myself.

Utter bullshit. In any normal application, IC matching is vastly superior to valve matching.

Only because the design sucked in the first place (*). Probably designed by a "tooobz" engineer ;-)

I have yet to see a single design that demonstrated the proper way to do a stable A-B bias.

I know how but I ain't talking ;-)

I like mixed fruit salad myself... apples, oranges, grapes, Kiwi, and maybe some Pomegranate ;-)

...Jim Thompson

Given that I mentioned a first tier vendor (apparently you never heard of Fluke, Brat) I've got your "buy a good one" covered. Given that I mentioned ProTek (apparently you never heard of them, either) I've got the lower tiers covered as well.

BTW Brat, for your future reference, here's some much-needed info for you about who Fluke is:

Not in terms of parameters that matter.

That would be a misapprehension on your part, Ronnie.

Prove it:

MC275, their only tubed amp - rated THD = 0.5% out of the running

Julie Labs

No evidence on web

Only contradictory evidence can be found.

There's no need to, just like all the other JAES papers that now contain obsolete information.

Take it up with the manufacturer - its gratuitous.

In fact audio generators with rediculously low residiuals have been made using nothing more exotic than NE 5532s.