Info on spectrum analyzer, signal analyzer, etc (HP 3561A)

[nsubulysses]

I've always wanted a spectrum analyzer but have never got one because they are so expensive. After this thread my desire has been renewed (Scope image interpretation).

I have just started researching these and have come across signal analyzers that seem to do what spectrum analyzer does and more. I have been looking at the HP 3561A. From what I understand it functions as a scope as well as a spectrum analzyer, and can also give amplitude and THD measurements and certainly many other measurements I don't really even understand. It seems like this would be the ultimate tool as it is so many things in one. Seeing the amplifier output on the screen along with the harmonic profile and THD % has me wanting one bad.

Does anyone have any advice on this type of purchase or things to look out for or avoid? I have just started researching but it seems like the HP 3561A signal analzyer is among the cheapest () pieces of equipment that can do these types of functions. Anyone have info on other models or brands that could be good. Sometimes the HP 3561A sells for quite a bit but also I see it sell on ebay for $250-700. Still expensive but I have many amps laying around that barely get used. I'm really itching to sell one and get this signal analzyer!

Any info or insight appreciated. I'm raring to jump in and buy, but trying to be patient and make a smart purchase

Link to completed listing

HP 3561A info

[olddawg]

Back in the day...... every manufacturer from Akai to Zenith required you to have one to be an authorized servicer for warranty repair. I think I actually used one 2 or 3 times in 30 years. (And I didn't really need to then) My theory was that they figured if you invested in one you were probably serious about your business and not a fly by night knucklehead, lol. I used to joke with the reps about it all of the time.

[nsubulysses]

I know Enzo has two HP distortion analyzers that were required by Crown that he has never used also

[gbono]

Spectrum analyzer is needed to check and see if signal generators are still putting out a clean test "tones" without harmonics. Also a good tool for looking at harmonics (even and odd order) to baseline performance of gear before making repairs or modifications or make real time measurements to do diagnostics. Not as handy as a scope but a SA can be a useful tool (many new scopes will do the "math" to convert time domain data into frequency).........

[nevetslab]

I had always thought HP's 3561A was the best Audio Spectrum Analyzer in their lineup. I never had the funds to spring for one, and had other instruments to cover what they put into one box. I use my HP 3580A...a hetrodyne sweeping 0-50kHz SA, whenever I need a better look at something in the frequency domain. My bench doesn't have the space to leave it set up, or I'd probably use it more often. Is it a daily-dirt instrument? Not usually, unless you adopt procedures that make it so. I used to use an FFT based instrument (HP 3582A) in biasing tape machines, as you'd get a good feel for the system linearity as a function of over-bias. Same would probably hold true with biasing tube amps....vs using a distortion analyzer. I normally don't..usually park the bias in a normal 'comfort zone, and am more concerned with getting multiple tubes to match.

For your first spectrum analyzer......an excellent instrument....assuming all works. I've been buying used test gear for years, and I have had my share of bad luck....sometimes I never succeed in getting it fixed, but more often I do. As for the 3561A's scope function.....I'd rather be using an analog scope, and not have to read between the digital lines of signal purity that you can always see on a proper scope. This is a great time to find normally expensive gear....it's a buyer's market out there.

An alternative to the traditional Spectrum Analyzer is the Wave Analyzer. HP's 3581A is such an instrument. Same 85dB dynamic range on the same hetrodyne architecture as the CRT-based 3580A. I have one of each. It displays the waveform on a large analog meter, calibrated with a 0--90dB range, or 10dB range, with a frequency counter to tell you where it's tuned...does the same automatic sweeping...and if connected to an XY plotter or an XY storage scope, you're seeing the same thing as the 3580A shows you on it's CRT. I bought one of those for around $50 years ago, in PERFECT condition!

A sleeper of an instrument that only some folks know are the Analogic / Data Precision D6000 with a 611 4-ch plug-in. It's essentially a 4-channel 100kHz digital scope, with a tone of signal processing, 14-bit converters so when you do FFT with it, you're good for better than 80dB dynamic range....if your signal magnitude is optimal. Like most digital scopes that do FFT, it's always reading in time domain, and you have to send it into frequency domain with a captured time-domain signal....so not quite as handy if you want continuous Frequency Domain display. These instruments can be found inexpensively. I have full documentation on them in my manual library, and always had good luck with them.

If the auction is an AS-IS, no refunds offered or exchanges....then I'd want more confidence than 'it powers up, lights come on, but beyond that, I don't know enough about it"....sort of statement. Buyer beware.

[TimmyP1955]

Our OWON SDS6062 does real time FFT display.

One could also use Studio Six Digital's FFT app on an iPad with a camera kit or other interface widget.

[trobbins]

I also haven't got the space or had the incentive to spend $ on a scope/analyser.

Over time though I've gone the soft route. I collated 'parts' rather than purchased commercial items, and there are many paths to take. For amp assessment, I am impressed by what can be achieved with an old soundcard preamp kit, a $2 USB soundcard, a $40 USB isolator and software like REW and VA32 and TrueRTA. If I need better than 80-90dB SNR then I use an ebayed E-MU 0404 to get excellent SNR and to remove some USB related artefacts. The convenience of TrueRTA is super, and the excellence of REW is amazing.

But I do miss he convenience of a dual probe CRO with phosphor screen, as the persistence can come in handy when looking at V-I anode loadlines, and dual probe for phasing. That said, there are modern USB multi-probe CROs around.

It is quite easy to damage an expensive sensitive analyser. Anyone that has done that usually doesn't own up to their accidental faux pas.

[drewl]

I'm always in favor of more test equipment, and my lab at work would make you guys drool!
I know I've worked on 8561's in the past but I really don't think you "need" one for audio frequencies.
I have to have a spectrum analyzer for RF at work, but hey if you got the cash go for it.

A Tektronnix digital scope might be more practical as it can also analyze the signal, provides THD and can capture glitches or random occurring events.

[nsubulysses]

Hey thanks for all the replies. Sorry I have not been back to this thread. Unfortunately something bad happened and it derailed my eagerness to buy.

I had a working Sunn 1200s that I wanted to sell for this purchase. I had the heat sink stability brackets installed by a shop (Fender would not sell the part to me becaseu I'm not authorized repair center) because it was a free warrantee repair. I figured hey, why not, it will be better for future users, and it's free. That was about 3 months ago. I turned it on for the first time since to give it a little test drive before selling and it lasted about 5 seconds and shut off. All the output transistors and many of the driver transistors are shorted. They must have cracked/broken some solder connections when installing the heat sink brackets Unfortunately I think I'm SOL since I let this sit for months after the warrantee repair. This will be fun to fix.......


Anyway, I am starting to look into some of the other HP gear mentioned as well as the Tek digital scope. Would you mind mentioning a few specific models Drewl if possible? My sadness at the fried 1200S that was gonna pay for this has passed and I'm ready to research this again

[nsubulysses]

Still on my research quest. I went from HP 3561A to the cheapest Tektronix with FFT, TBS1052B, which is $550, to the Rigol DS1054Z for $400 that has way better specs than the Tek scope. I was on the verge of buying Rigol DS1054Z but I kept researching and finally started getting into the HP 54500 series. Anyone have experience with these scopes first hand. Nevetslab?

The 54510/54512 (same scope, just 2 ch vs. 4 ch) looks pretty awesome as well as the 54520. They can both be had for around $200-700 which isn't bad and they have FFT capability. There is an ebay seller who claims to be a retired HP scope designer, selling refurbished and cal'ed ones.

HP 54520
HP 54510B
HP 54506B (4 channels!)

Guess I'm just looking for a little reassurance before I buy something for hundreds of dollars that I've never seen in person before if anyone has any insight to share. Maybe it's time to just jump in. I'm sure if I buy any of the gear mentioned it will be very helpful and I'll probably just fall in love with it.

[TimmyP1955]

It's old and big (deep), but the quality should be superb.

But, given how the cost of digital stuff has come down (and modern displays Vs a color CRT), I wonder if it's really better than an Owon or Rigol (that's much smaller and lighter) in the $400 range?