Lab Setup

[meconlen]

I currently have access to my school's lab but that will be ending Real Soon Now. With a budget of about $1500 (not hard, but not too soft either), I'd like a real oscilloscope & spectrum analyzer, function generator, and a DMM that measures beta without too much hassle (everyone I've ever used is a PITA), and a soldering station. I have a good DMM for pretty much everything else. I already have a good dual output power supply and a okay single output power supply.

Let's assume that I don't live in the Bay Area, NY, or anywhere else where used deals are generally available and I'm sketchy on buying used from eBay. I will order online however, probably from Mouser or something similar.

Any thoughts on equipment I should look at or if I can reasonably put a decent lab together on this budget?

Thanks

[Conrad Hoffman]

IMHO, you need to get eBay savvy or you'll end up with rather mediocre stuff, particularly the scope. Forget a dedicated spectrum analyzer on that budget, though a nice sound card and PC setup is no problem. Good DVMs typically don't do beta, but I'd rather have a small dedicated board to do that at whatever current I needed, and just calculate it out.

Get familiar with the various Tek scopes and Wavetec function generators to see what might fill your needs. For new equipment check out Rigol- they make some decent cost effective stuff.

CH

[meconlen]

I'm really kinda surprised the scope manufactures don't put a FFT chip in them and have a frequency analyzer function build it. It seems like it would be kind of basic at this point considering the first computers with built in FFT on the processor were somewhere around 1995.

[Conrad Hoffman]

I haven't kept up with it, but the early Tek digitals had FFT as standard. I think it was an extra cost option later on, or at least any reasonable SA features were. IMHO, the FFT function in the scopes is near to worthless. It often has only a linear frequency axis, not log, and log is about all I'd use for audio. The dynamic range is usually lousy, because it's a scope, not a spectrum analyzer, not to mention the 8 bit vertical resolution on the screen. Now, the more recent scopes are a vast improvement, but they're way out of the budget you mentioned. One of the new $8-12k Tek or Agilent scopes would be very pleasant on my test bench, but it's not happening in this lifetime.

Years ago I worked for a place that bought, I think, a Protek SA for emissions pre-compliance testing. It was only $1500 and worked surprisingly well. It was just like the inexpensive analog scopes of the day, but an SA. Not enough low end for audio, but probably more along the price/performance line you were thinking. It seems that SAs have held their value better than any other type of test equipment, so even the used market doesn't offer much joy. You can get a used HP selective voltmeter, which has exactly the same guts as the similar low frequency SA, and sweep it onto a scope. Works great up to 60 kHz, but, for me, too much trouble to bother with. A sound card and SA software like Visual Analyzer (free) has far more features and maybe even better performance.

CH

[tomchr]

Originally Posted by meconlen

I'm really kinda surprised the scope manufactures don't put a FFT chip in them and have a frequency analyzer function build it. It seems like it would be kind of basic at this point considering the first computers with built in FFT on the processor were somewhere around 1995.

Eh... Because they can make more money by selling the FFT module as an upgrade option.

My test equipment park is from eBay, Boeing Surplus, company surplus. I've gotten good deals by buying broken equipment and fixing it. But it's a risk. If you want to pay more, consider buying calibrated equipment.

Lab supplies are fairly inexpensive. The HP ones last about forever. I paid $150 for my calibrated HP 3478A 5.5-digit multimeter on eBay. About $100 for a working HP 3312A function generator. A Tektronix o'scope will set you back a couple of hundred. Get the gear now and verify it on the known good equipment at your school. Get the service manuals (eBay ID: artekmedia has excellent quality scans on CD; Manuals Plus - Test Equipment Manuals is another source).

~Tom

[jackinnj]

Originally Posted by Conrad Hoffman

IMHO, the FFT function in the scopes is near to worthless. It often has only a linear frequency axis, not log, and log is about all I'd use for audio. The dynamic range is usually lousy, because it's a scope, not a spectrum analyzer, not to mention the 8 bit vertical resolution on the screen.

I second that opinion.

Strange stuff happens on EBay -- meters like the HP3456, 3468, 3478 can be dirt cheap, Tektronix TM500 series plug-ins went for a song, now they're expensive.

For a scope, keep your eye on a 465 or 2465.

and a post-hoc thought -- HP Power Supplies -- invaluable.

[macboy]

Originally Posted by Conrad Hoffman

I haven't kept up with it, but the early Tek digitals had FFT as standard.

Not the really early ones. I have a Tek 468 on my bench to prove it. It has cursors, and averaging (an option!) but that is the extent of it. The only nice thing about that scope is that the cursors work in analog mode too. The digital mode is useless. But the analog mode is just like a 465, except with cursors.

Originally Posted by Conrad Hoffman

IMHO, the FFT function in the scopes is near to worthless. It often has only a linear frequency axis, not log, and log is about all I'd use for audio. The dynamic range is usually lousy, because it's a scope, not a spectrum analyzer, not to mention the 8 bit vertical resolution on the screen.

Log frequency? Well sure we are used to that in audio but an FFT has an inherently linear frequency axis. Displaying FFT with log frequency is a hack. Now, a log amplitude axis is an absolute must in order to see anything low level.

You do have a point, with scopes typically digitizing at only 8 to 10 bits, the inherent noise floor will hide distortion products from good audio gear. So the FFT facility is very limited, but that just means you need to be crafty and resourceful in how you use it. So if you look at the notch filter output (residual) of a distortion analyzer, then the signal is the distortion and you can get a very good representation of the relative amplitude of the harmonics and even noise, all well above the scope's noise floor. This is far from "near to worthless". I do this with my Philips PM3320A scope, and it makes me glad to have the FFT option.


For the original poster:

If you are set on new gear, others have suggested "OWON" and "Uni-Trend" as inexpensive scopes. I haven't tried either. The OWON brand seems to come with FFT standard and start at less than $300. With your budget there are not many options for new scopes.

I have a B&K Precision DMM, and I like it. I particularly like that it can measure very large capacitances, up to 50 mF, that's milli not micro. That can be useful for measuring power supply filter caps. It is not a Fluke mind you, but for the price, it very well for me. I also use a Keithley bench meter. Don't be tempted to buy an ultra-cheap off-brand DMM. But I don't suggest blowing your budget on a brand new Fluke either. There is a middle ground.

You may want to reconsider the spectrum analyzer, and spend that part of the budget on a distortion analyzer instead. For audio work, you can probably get more useful information from the combination of that and a scope having FFT, than from a spectrum analyzer.

[dangus]

Find out when the local amateur radio club(s) have swap meets. Many hams are getting on in years, downsizing and letting go of equipment and parts, often very cheaply if not free. I've arrived late for a ham swap and found good stuff in the dumpster outside, or had sellers tell me "you picked it up - it's yours now" when I looked at an old walkie-talkie.

For a lot of audio testing, a computer with sound card is a very powerful tool. Spectrum analyzer, distortion analyzer, function generator, impedance measurements, all with free software. Just build up a box to buffer and protect the inputs and outputs, maybe with a balanced input, or ideally using an ADC and DAC that are fed by S/PDIF and isolated from the computer chassis.

[woody]

Yes go to a amature radio swap meet other wise known as a ham fest. Do a google
for ARRL and then look at the hamfast locations. While on the topic of saving money
you might take the first of the amiteur radio exams as passing it qualifies you for an
amateur radio car tag in the U.S.A. this saves you a few dollars each year on a car tag!

[jackinnj]

Originally Posted by dangus

Just build up a box to buffer and protect the inputs and outputs, maybe with a balanced input, or ideally using an ADC and DAC that are fed by S/PDIF and isolated from the computer chassis.

Check out Pete Millet's web pages -- he's done exactly this with a very nice buffer/RMS converter -- I think he has boards for the project.