Starting a "professional" audio lab (design and repair)

[iampoor]

Hi all

Im currently working on starting a lab for audio design, development and repair. I am currently not using much gear, but the times are a changing!

I working on guitar pedals, microphone preamps, tube amps etc. My focus is on designing professional audio products. I have been using some "free" tools in conjunction with a computer, but those have only been substitutes for the real deal. My primary objectives are to measure noise and distortion within the audio band (I am very interested in isolating and experimenting with distortion devices, but it has all been a "by ear" process. I want to see the nitty gritty and what circuit tweaks do in real time).

I already have a decent 100mhz oscilloscope, although it has a few finicky controls. I have been contemplating a nice lower bandwidth (maybe 20mhz) model, but am not really sure where to start. I am wary fo affordable digital scopes, due to the lower resolution displays/memory (Yes I have watched Daves videos on this, thanks!)

I am looking for cost effective, yet reasonable performance. Buying used/older gear is totally acceptable in my book.

Anyways, here is what I am looking at/not sure about!

Audio Analyzer: HP 8903B. I have heard good things and they seem affordable. This seems like a real stepup from a soundcard and using TrueRTA (WIth my interface being the limitation here). I am looking to minimize distortion and not have to worry about the test platform affecting it!

Distortion/Harmonic's measurement. I am lost here. Spectrum analyzers dont seem to be affordable.....not sure if its worth the cost. Any ideas here? I really want to see and understand distortion devices, but am a total newbie when it comes to test equipment :p

Signal generator-Ive been using my PC here, but would like a nice dedicated solution. Any good recommendations/ I just want something clean that works, only doing audio band work again.

What else should be on my list?

ANy other suggestions?

Thanks again, I love this forum and the blog! Has made me realize how there is to learn!!!!

[nowlan]

QuantAsylum QA400 ?
Perhaps someone here or on diyaudio.com knows more.

[GiskardReventlov]

Don't know where you're located but I saw a listing on los-angeles craigslist and someone was selling off all their audio related gear, it sounded similar to what you're describing.

[jancumps]

Tek Audio Measurement set

No affiliation.

Asks 1300€

[iampoor]

QuantAsylum QA400 ?
Perhaps someone here or on diyaudio.com knows more.

Seems great, but the input voltage appears limited

Im in the Norther California area

[commongrounder]

@iampoor:

I own and have used a Tektronix TS-4353 Distortion test set for many years.  It is composed of two SG505 10hz-100khz ultra low distortion audio generators, and an AA501 distortion analyzer, housed in a TM504 power supply housing.  This unit has a distortion product output jack that you can send to a scope or FFT/spectrum analyzer.  You can really visualize what signal impurities are composed of.  The test set jancumps posted is contains part of the system, but I've noticed that these systems get broken up and the modules sold separately, so you may need to track down the different parts.  It really is a great all in one audio analysis system.  Oh, the AA501 comes in different flavors, be sure to get a version with the "IMD" option.  It will accept an input of up to 300 volts peak.
Here is a link to someone selling a set:
http://dilette.com/main/dilettesales/Tek_TS-4353-U_Distortion_Analyzer.htm

[EEVblog]

An Audio Precision analyser is the holy grail of audio test gear. Own one, or lust after one, the choice is yours :->

[nickm]

I've got an 8903B and this biggest issue is the lack of computer connectivity.  It only has HPIB and you'll have to write your own scripts or use others (Pete Millet/s).  After using an Audio Precision it's amazing how much better it is with automated testing.  I think you should reconsider using a sound card.  If you get a good one that can measure out well past 20kHz you cant build a test jig to handle high voltages. 

I've got a HP 54645D that has the add on card for FFT functionality.  By plugging the output of the 8903 with the fundamental removed and running FFT on it, I can see the harmonics very well.

Older HP signal generators show up constantly and if they are the Wein-bridge type they will have very low distortion. 

[iampoor]

@iampoor:

I own and have used a Tektronix TS-4353 Distortion test set for many years.  It is composed of two SG505 10hz-100khz ultra low distortion audio generators, and an AA501 distortion analyzer, housed in a TM504 power supply housing.  This unit has a distortion product output jack that you can send to a scope or FFT/spectrum analyzer.  You can really visualize what signal impurities are composed of.  The test set jancumps posted is contains part of the system, but I've noticed that these systems get broken up and the modules sold separately, so you may need to track down the different parts.  It really is a great all in one audio analysis system.  Oh, the AA501 comes in different flavors, be sure to get a version with the "IMD" option.  It will accept an input of up to 300 volts peak.
Here is a link to someone selling a set:
http://dilette.com/main/dilettesales/Tek_TS-4353-U_Distortion_Analyzer.htm

WOw that looks great! How is the calibration? Have you ever had any issues? How accurate are they? Might be overkill, but a beautiful instrument!

An Audio Precision analyser is the holy grail of audio test gear. Own one, or lust after one, the choice is yours :->

As of now, its definitly a lust. I might be able to afford a used System 1, but those are pretty long in the tooth now. Not sure how great the advantage would be over a good soundcard setup

I've got an 8903B and this biggest issue is the lack of computer connectivity.  It only has HPIB and you'll have to write your own scripts or use others (Pete Millet/s).  After using an Audio Precision it's amazing how much better it is with automated testing.  I think you should reconsider using a sound card.  If you get a good one that can measure out well past 20kHz you cant build a test jig to handle high voltages. 

I've got a HP 54645D that has the add on card for FFT functionality.  By plugging the output of the 8903 with the fundamental removed and running FFT on it, I can see the harmonics very well.

Older HP signal generators show up constantly and if they are the Wein-bridge type they will have very low distortion.

Wow thanks for the heads up, didnt even think of that.
I have the option to use a decent audio interface, I just really wonder how it will compare to a dedicated older unit. Ive been thinking about getting an older Mbox and upgrading it possibly? What are your expierences with soundcards and measurements?

[commongrounder]

@iampoor:
The Tek test set has a system residual distortion of .0008%.  I admit I sometimes wish I had automatic computer controlled testing (Like Audio Precision or the Q400), but I have created boiler-plate charts on the computer and have become practiced at entering data.  I just like the feel of the unit.  It has proven to be very stable and reliable.  I think I had to replace the power switch on the PSU housing once, quite a while ago.  I send it out to a cal lab and it has required only the tiniest adjustment to optimize it.  Pretty good for gear of that vintage!

[HiTech]

Pretty much agree with the other's comments here. I also use an HP8903, two Tek SG505 plug-ins, HP & Tek scopes. If you're bent on a spectrum analyzer the Nicolette FFT audio unit is very nice but on the large size. From what you posted I get the hunch that you have much to learn before investing $$$ into high-end service/lab equipment. If you're not predisposed to having computer interfaced service equip. then most oledr HP/Tek stuff will suffice. For beginner's needs you can get by with Leader and B&K, Sencore grade equipment since it's plentiful and affordable.

[JuKu]

Dscope III is not bad at all for two channel work.