Never Buy a BK 4003 Function Generator (or scope)

I have spent so many, many, many days trying to figure out why my circuits have crappy overshoots and ringing problems even after they had mojo feddback and have been compensated into hell. It turns out that the BK function generator makes completely ill formed square waves. Unfortunately, I have a BK scope as well and I could not see most of the overshoot and ringing because that scope is a piece of crap too, and has no resolution whatsoever. Anyhow, I have borrowed a Tektronics scope for an afternoon after suspecting what was going on. My second-hand Heathkit generator ($20) puts out square waves that are far better than the two hundred fifty bucks BK generator.
:evil: :evil: :evil: :evil: :evil:

Note to self: Stop buying cheap measurement instruments. Take a deep breath, and repeat...

Tamas

Part of the crabbiness is that I have been having a sinus infection for two weeks and I don't know if I am hearing something or the mucus is commuting from one side of my cranium to the other.

Is the TEKTRONIX 475 a decent scope?

While I am venting. How come there are no more places to go to and buy a piece of instrument, put your hands on it, test it out, etc.? Everything is online now!

Tamas... now I'm worried. I'm planning on getting a signal generator in a few days.

http://www.testequipmentdepot.com/ezdigital/audio.htm

This one is about the same price as the BK.

Question to everybody: Is is better to get the above unit? or something like this???

http://www.testequipmentdepot.com/instek/signalgenerators/gag-809and810.htm

This particular unit is almost exactly the same in layout/design/configuration as a $30 used TENMA I saw in eBay.

I know that the BKs use an IC for all the functions (ICL8038 or variant like XR2206). They are crapola...a good one might get to 0.5% on a good day. We have had good luck buying the Leader LAG120 used on evilbay. They usually go for around $40 to $50. That Instek looks like and is spec'd like this model of the Leader. You could get one, find a place that does instrument calibration and ask them to check the THD for you. They might charge you $50, but you will know whats up with your sig gen!

In general, BK makes junk...that's why its cheep.

HTH!
Charlie

I don't know if this might be a viable approach, but for low-THD testtones, how about digitally generated stuff from a hi-spec (>16bit)soundcard ? You might have it around already.

This is a different approach and might definitely be undesirable for several applications, but how about a simple function generator with tweakable knobs for the simple tests - and use the computer-stuff for generating a higher spec signal.

Please correct me if this isn't going to work - I'm just wondering and haven't tried. Who knows a decent test-CD on a decent CD-player may already work for certain signal-generating jobs... :roll:

Peter

Tamas,

Neutrik has a virtual generator you can download from their website: http://www.nt-instruments.com/default.asp?pLngCateId=217&pIntLevel=4&pLngPageId=276

I don't know if you would find it useful, but it's free!

:thumb: :sam: :green:

This virtual thingy is great!

If you load down any generator too much, the square wave goes to hell, so check your load before you blame the generator.
But yeah, BK is not my favorite brand.

I tested it with several loads from 10k and down. At 1k ohm the overshoot and ring were better, but not nearly as good as the Heathkit square wave (loaded or unloaded). More loading tends to round off the signal instead of creating overshoots in my experience. I was testing at 22KHz.
It is amazing how low tech is the Heathkit, and how well it performs compared to this far more modern counterpart. The BK even has a fan to keep the components at the same temp for frequency stability yet pumps out jaggedy-poop.
The Heathkit has about six transistors in it and runs off two 9V batteries. :thumb:

I remember a while ago someone debating between buying a used tektronix and worrying about the reliability, and buying a new BK Precision 2120B...

There were recommendations both ways, but I have tek at home and at work, and at work we have about fifty BK 2120's.

I'll take an eBay Tek over a brand new B&K any day of the week.

Cleaner focus, better linearity, better reliability, parts are a dime a dozen on eBay, and it just feels better in your hands, like the difference between an upmarket Mercedes and an econobox Ford.... In fact I think that was an analogy that I made at the time... nothing wrong with Ford, but they build down to a price, whereas the top Mercedes are built up to a standard.

Think of the difference between a taiwan wrench and a Snap-On tools wrench. Both do the job, but one is so-o-o-o-o much nicer to own!

Keith

[quote author="jrmintz"]Tamas,

Neutrik has a virtual generator you can download from their website: http://www.nt-instruments.com/default.asp?pLngCateId=217&pIntLevel=4&pLngPageId=276

I don't know if you would find it useful, but it's free!

:thumb: :sam: :green:[/quote]

currently using a virtual signal gen right now, but it's a hassle since my workbench and PC are two separate areas, and my studio DAW is another separate area. So I have to carry my scope, and stuff and junk to be near the PC to use the PC signal gen.

So I really wanted a benchtop signal gen for convenience.

Check your scope probe also.
I just found out that I get a lower self resonance frequency when testing transformers with the probe set to 1:1 instead of 1:10!
For now on I will be testing transformers with a 1:10 probe setting.
The extra capacitance or lower impedance of the1:1 setting is to blame.
:thumb:

Thanks CJ. I was always wondering what that little switch did on the probes. Maybe Santa will get me a nice Tektronix scope in 2008. :grin: