Budget distortion analyzer/signal generator

I need to get some kind of professional audio analyzer. I need something that has choices for different signal generator output loads, like 150/200 ohm for mic preamps (I build a lot of those) and 600 ohms for vintage gear.

My head is a-spinning with the possibilities:

- AP System 1 or 2. Yeah, it's old, but so am I. Hell, I'm still running ProTools 5 on OS9....

- Sound Technology 1710A. Old but it does have 150 and 600 ohm outputs.

- Quant Asylum QA401. The new version is available with differential in and out. Not sure how to get the 150, 200 and 600 ohm outputs I require - pads? Pardon my ignorance.

- RMAA with 24/192k USB interface.

I appreciate your sharing experience with which of these tools you've had good luck with recently.  Thank you!

You can converte a low-impedance output to 600 Ohm by adding series resistance. It should be easy to make an external box with a switch.

You should think about the analog performance and digital features (e.g. sample rates) you need. Note that the APs come with various features (purely analog up to full mixed-signal versions) which makes a lot of difference in price and versatility.

If you can live with basic digital functionality (e.g. no high sampling rates), the requirement for an older operating system and good, but not top-notch analog performance, a fully equipped mixed-signal System One would probably offer excellent value.

Samuel

I have a 1710a that I absolutely love - if you can find one that has been cared for you can't really go wrong - especially for the price they go for these days...

the precision signal generator is super handy - and it works as a dBm meter as well.

I don't feel its really a substitute for and Audio Precision or a Prism DScope - but if you don't need or don't want to pay the entry fee into the digital world - the Sound Tech's are great.

I have a QA400, for which I made an interfacing box here.  Works OK.  Would I like to get an AP?  Certainly, but this is a lot cheaper and works well enough for hobbyist needs...

Reading this thread about low cost audio analysers prompted me to fire up the Quantum QA400 I bought ages ago. I had only used it a couple of times and then went back to using my Lindos. I first upgraded to the latest software and found it to be rather more responsive on my old 32 bit Vista laptop than it was when I first got it. First I checked out its calibration by feeding 1KHz 0dBu from my Lindos via a 10K:10K Sowter into the QA400. 0dbu read as -2.46dBV - close enough. I then did some distortion measurements on a Classic mic pre in a lunch box. Nice to be able to see the harmonic content rather than just a THD figure.

Lastly I decide to compare its noise measurement with that of the Lindos. As expected, with the gain fully up at 70dB and the input shorted, the Lindos measures output noise at just better than -52dBu which means the EIN is comfortably below -120dBu which I reckon is quite good for a tube mic pre. I then hooked it up to the QA400 and got very similar results. What was interesting was to see the spectrum. Fairly flat throughout with little evidence of 1/f noise at the low end. What was interesting was the 50Hz and 100Hz peaks which were not far south of -50dBu. Turning down the gain control dropped the noise as expected but also dropped the hum which implies it is getting into the first stage. I wondered if this was the old magnetic radiation from the mains toroid problem so I unhitched the mains transformer and moved it around but it made no difference at all. The Classic module was right near the power supply so I moved it to the other end of the lunch box far away from the mains toroid and tested again. No difference. I moved the output transformer around in case some was getting in there but again no difference.

I also noticed that flipping the HPF switch on the Classic would lower the hum a couple of dBs - further proof it is entering the amp somewhere. Interesting thing though, it made no difference to the Lindos reading - proof that a spectrum is a handy thing to have. Then I noticed the 'A' weighting button on the QA400. I pressed it, the hum dropped by 25dB and the overall noise dropped below -66dBv! That makes the A weighted EIN better than -134dBu. Looking at the spectrum, there is some reduction in level at high frequencies but mostly the difference is down the low end. So I switched back to flat response and pulled the mains plug. The heaters are still hot and the HT holds up for more than 30 seconds so you get a good idea of how good the performance could be. Not as good as with A weighting but noise below -60dBV which makes the potential EIN around -128dBu. Repeating this test with the Lindos gave no difference in measured noise so the Lindos weighting curve must already remove most of the hum components (it measures noise to the ITU-R 468 standard which includes a weighting curve that is rather different to the A curve but clearly similar at low frequencies).

From this I conclude that the QA400 is actually quite a useful tool. It gives readings not too dissimilar from the Lindos but provides a depth of additional information not available with the Liindos. With a 10K:10K Sowter at the input it handles balanced signals with no possibility of ground loops and I already have a 600 ohm load and 20dB balanced attenuator so getting it to handle big signals is no problem. I think I will be using it a lot more from now on. Now to track down that hum!

Cheers

Ian

AP Sys 1 or S2 if you can find one cheap.  You'll never look back........
Best,
Bruno2000

bruno2000 said:

AP Sys 1 or S2 if you can find one cheap.  You'll never look back........
Best,
Bruno2000

Click to expand...

Finding one cheap seems to be the dilemma. I didn't realize the going price to be $1000+.

The Quant Asylum QA401 is starting to look pretty good, especially in light of Ian's comments above.

AusTex64 said:

bruno2000 said:

AP Sys 1 or S2 if you can find one cheap.  You'll never look back........
Best,
Bruno2000

Click to expand...

Finding one cheap seems to be the dilemma. I didn't realize the going price apprears to be $1000+.

The Quant Asylum QA401 is starting to look pretty good, especially in light of Ian's comments above.

Click to expand...

If you are patient and quick, you can get them on eBay for much less.  I have purchased sys 1s for $500.
Best,
Bruno2000

bruno2000 said:

AusTex64 said:

bruno2000 said:

AP Sys 1 or S2 if you can find one cheap.  You'll never look back........
Best,
Bruno2000

Click to expand...

Finding one cheap seems to be the dilemma. I didn't realize the going price apprears to be $1000+.

The Quant Asylum QA401 is starting to look pretty good, especially in light of Ian's comments above.

Click to expand...

If you are patient and quick, you can get them on eBay for much less.  I have purchased sys 1s for $500.
Best,
Bruno2000

Click to expand...

I'm good with quick, struggling with patient!   I need something soon. Amazed I've managed to do without something like this for so long.

bruno2000 said:

AusTex64 said:

bruno2000 said:

AP Sys 1 or S2 if you can find one cheap.  You'll never look back........
Best,
Bruno2000

Click to expand...

Finding one cheap seems to be the dilemma. I didn't realize the going price apprears to be $1000+.

The Quant Asylum QA401 is starting to look pretty good, especially in light of Ian's comments above.

Click to expand...

If you are patient and quick, you can get them on eBay for much less.  I have purchased sys 1s for $500.
Best,
Bruno2000

Click to expand...

Hi All
The AP System's are a great investment in lasting performance and super bench tool.

Purchasing a System One typical will cost about $2500 in total or more. Buying a CHEEP  Ebay System may not only get the System, but may need service, Interface card & cable. I do sell Systems and  they are fully working. I have had several clients that have purchased Systems and they end up in my shop.

Duke

I use an Amber 5500.  Less known but quite nice.  The designer went to AP after closing down Amber!  Has 50/150/600 ohm source, 100k/600/150 ohm load.  Balanced and unbalanced, filters, RMS/average/quasi-peak.  Does freq, level, thd+n, has options for sweeps, IMD, and more.  Bought mine for around $500.

Lindos does some great testing equipment. I'm not sure about the load capabilities but you should definitely check them out!

http://www.lindos.co.uk

I ended up purchasing the Quant Asylum QA401. Will report back on how it works out for me.

Forgot that I said I would reply back regarding the Quant Asylum QA401. For the price I've found it quite useful. I made some cables with resistors for specific loads I needed (200 ohms for mic preamps) and have used it a lot. Very handy for determining Zobel values on a mic pre I'm working on.

I requested measurements in dBU, and it was included in the latest software release. The QA people have been very responsive to questions and suggestions. I'm a happy customer.

An alternative to the Quant Asylum products is a free software program called REW:

http://www.roomeqwizard.com/

Although designed for room EQ, it is a very good general purpose measurement tool. Coupled with a decent USB audio interface (I use a Focusrite 2i2) it can do everything the QA401 can and more. One advantage is that it is platform independent so it will work under Linux, Windows and OSX. It has a built in generator that can produce white or pink noise as well as frequency sweeps. The FFT display is very good and it can take more samples and apply a lot more averaging than the QA products (very handy when measuring noise). The one downside is all its measurements are in dBFS so you have to calibrate it so you can convert form dBFS to dBu but other than that it is now my go to measurement tool. I built a passive interface box for it that provides me with a transformer isolated signal, zero or 150 ohm terminations and 40dB or 60dB signal attenuation on the source side, and a 600 ohm load and a switched 20dB pad on the return side so I can measure distortion at high output levels.

Cheers

Ian

If you are going to measure dBu or dBV the usb-soundcard stuff is lacking. while the interfaces can be calibrated, I is a common source of error, specially if your gain knob is not all the way up / down during calibration / measurement.

the  usb interfaces also lack a significant gain / attenuation range, but this has been nicely taken care of Ian with his front end.

an alternative (other then what has been discussed already) is Audiomatica's clio system. quick, easy to operate and with decent near realtime capabilities.

- Michael

I looked at CLIO, but it was a lot more money than the QA401. It does more though. But it was stuff I didn't need. YMMV

If you are really talking budget, Terrasonde Audio Toolbox has one that actually works well, with a comprehensive signal gen (and lots of other features).
Seen 'em go for $100

ruffrecords said:

An alternative to the Quant Asylum products is a free software program called REW:

http://www.roomeqwizard.com/

Although designed for room EQ, it is a very good general purpose measurement tool. Coupled with a decent USB audio interface (I use a Focusrite 2i2) it can do everything the QA401 can and more.

Click to expand...

Hi Ian,
I had installed REW a few years ago, and I came to the conclusion that, although it seemed really good at what it was designed for, namely room EQ for home-video systems, it was not taht great for general audio test use.
I use occasionally RMAA, and, like most of the free programs, I think it is lacking in two departments: amplitude sweeps and graph overlay. That's also my main beef regarding QA400, which I use as a door stop now
How does REW perform in these territories?

we should  brainstorm the A400's possibilities to do quick sweep / multitones as this is the most lacking part, now that there is a front end for it. mine is also sitting in a box, ashamed of itself.
there is a SDK or programming language but their examples never made me want to start learning programming....

we would need quick frequency response, 1/12 1/6 1/3 1/1 octave intergation, dB lin, dBA and dBC  calculations, some sort of buffer for a number of traces, say 12 or so. averaging and smoothing might also be nice of course.
THD stuff is already implemented, so that's good.

did I mention exportcapabilities?

the list is going to be long.... duh!

- Michael