What test equip do I need?

[user 37518]

There is a plot in the data sheet.  Seems to be -3dB at70kHz, and around -0.2dB at 20kHz.

Anyone compared it directly with other sound cards?

I find the choice of BNC connectors rather curious for something designed to measure audio.

the only good thing about BNC connectors is if you are using BNC to alligator clips, for instance when testing prototype gear, otherwise, having an XLR to dual BNC cable seems like a complication to me.

 

[user 37518]

I was also going to say a thing or two about the old HP 8903 audio analyzer, I have one of them, you can find them on e-bay for around $500 USD, they are good solid units, I connected mine via GPIB to my computer and made a MATLAB program to control it with the PC, but you can also try and download Pete Millet's software for it which never worked for me which is why I ended up doing my own programs, you need a GPIB to USB interface which is not cheap.

You can measure Power, THD, SINAD, swept frequency response and SNR. The only downside I see with these units is that their distortion residual is not very low, -80dB if I recall correctly, thats equivalent to 0.01% THD, which is ok for many things but a bit high for testing today's ultra low distortion equipment, for tube gear it may be ok, if you have an external low distortion oscillator you can measure lower distortion single frequency figures but if you plan on using the 8903 oscillator, for instance to do sweep measurements the lowest you can get is 0.01% THD. You can try using something like Cordell's distortion magnifier but in the end I think a QA401 is cheaper and easier to use.

 

[abbey road d enfer]

I find the choice of BNC connectors rather curious for something designed to measure audio.

These people who have designed the QA are geeks, not audio engineers. They don't understand the needs and habits of the art.
I've been one of the first users of the QA400; I found there were so many quirks I communicated with them and understood that they come from too far away.
I guess thay took an academic view of the challenge and said "yes, we can code that", but it's not enough.
I believe they have learned along the way, but they are not there yet IMO.
BNC's were acceptable on the QA400, but when they went balanced on the Q401, they should have put XLR's.
Some may argue that unbalanced measurements are often done in the course of tuning up a prototype.
I had an adapter with a BNC receptacle on a male XLR that I used regularly on the Audio Precision, in conjunction with a 'scope probe., 1:1 of course, since a 10:1 would not be compatible with the AP's input impedance.

 

[ruffrecords]

From the QA web site it seems to me they are oriented more towards production testing of consumer products, the vast majority of which are unbalanced. Using their products for pro audio work is probably outside their intended main market.  I think it can still be used as a good tool for economic pro audio testing, in the same way that REW is primarily intended for testing speakers and rooms but it also makes a pretty good job of testing audio hardware. AP is undoubtedly the best for pro audio work but for most of us here it is not economic.

Cheers

Ian

 

[Bowie]

In the interest of saving space, I've been looking into getting a laptop and running a USB scope but it seems that most of them have input voltage specs too low (around 50v) for the work I do. Are there PC based scopes that can be used in tube power sections?

 

[john12ax7]

I would advise against a computer / usb scope.  If space is a consideration the newer digital based scopes take up very little spaced compared to the old analog ones.

 

[Whoops]

I'd really rather get actual hardware to run tests on my bench as dragging opened gear over to my studio PC is not ideal.

The problem is not the PC solution, the problem is that you need to get a PC for your Bench.

Ask around you friends/family circle, you will see that there's someone that probably has a PC laptop that doest use any-more and that will be glad to give it to you, and that older PC would run windows 7 and totally capable of being a good workshop tester

 

[ruffrecords]

The problem is not the PC solution, the problem is that you need to get a PC for your Bench.

Ask around you friends/family circle, you will see that there's someone that probably has a PC laptop that doest use any-more and that will be glad to give it to you, and that older PC would run windows 7 and totally capable of being a good workshop tester

I used to use a laptop but it is too big and heavy and the screen is not right where I need it to be when testing. So I just bought one of these tiny things:

https://www.amazon.co.uk/gp/product/B07PDB6Q9Y/

It comes with a VESA bracket so you can fix it to the back of a monitor or to the wall. I have an old monitor without VESA fittings so my little box will be fitted to the wall behind my bench. It is smaller than the Scarlette interface I use with it. It runs Windows 10 with ease and boots up in about 30 secs from it internal SSD. As well as REW, I have also loaded Kicad and LTspice onto it. I use  a wireles mouse and keyboard with it.

Cheers

Ian

 

[bluebird]

Wow, that's a sweet little unit. And "fanless" as well. Thanks Ian!
For better or worse, technology is getting so cheap. I recently got rid of 4 old flat panel monitors in the garage I was "saving" because they occupied some sort of value space in my brain. The cost back when I bought them still hurts today! I have boxes of stuff like that...

 

[ruffrecords]

Wow, that's a sweet little unit. And "fanless" as well. Thanks Ian!

And I forgot to mention it comes with Win 10 preinstalled. Set up was a breeze, just fill in your location, time zone and keyboard style and that was about it.

This is the later version of the one used by QuantAsylum in there minimum system test.

Cheers

Ian

 

[abbey road d enfer]

I would advise against a computer / usb scope.  If space is a consideration the newer digital based scopes take up very little spaced compared to the old analog ones.

I have bought a Hantek scope for the same reason, replacing my Hameg CRT scope. I am very disappointed with it. The trace is never clean, the effects of quantization on noise I believe.
Just recently I bought a Bitscope, which uses 12-bit ADC, so the trace is much cleaner.
I ise it with standard switchable 10:1/1:1 probes, which give me 120V capability. Using 100:1 probes would allow me working on tube amps.
I use it with a 10" tablet that I bought second-hand for the purpose. The picture is larger and more legible than that of a DSO, however, the tactile screen is too taxing on my eyes and fingers, so I will add a mini BT keyboard that's been used as bookend until now.
It definitely takes less space than the DSO when I move aside the keyboard, that I don't need constantly.

 

[abbey road d enfer]

I used to use a laptop but it is too big and heavy and the screen is not right where I need it to be when testing. So I just bought one of these tiny things:

https://www.amazon.co.uk/gp/product/B07PDB6Q9Y/

It comes with a VESA bracket so you can fix it to the back of a monitor or to the wall. I have an old monitor without VESA fittings so my little box will be fitted to the wall behind my bench. It is smaller than the Scarlette interface I use with it. It runs Windows 10 with ease and boots up in about 30 secs from it internal SSD. As well as REW, I have also loaded Kicad and LTspice onto it. I use  a wireles mouse and keyboard with it.

Cheers

Ian

That's also a very nice solution. I haven't adopted it because I wanted to have a dual-screen arrangement and I could not find monitors small enough (maybe I haven't looked hard enough?), and I already had one notebook with REW, RMAA and Audiotest on it.

 

[Bowie]

Thanks for all the additional replies.

In the interest of saving space, I've been looking into getting a laptop and running a USB scope but it seems that most of them have input voltage specs too low (around 50v) for the work I do. Are there PC based scopes that can be used in tube power sections?

Back to this Q, does anyone know if there are USB/PC scopes that can handle tube circuit voltages?

 

[ruffrecords]

That's also a very nice solution. I haven't adopted it because I wanted to have a dual-screen arrangement and I could not find monitors small enough (maybe I haven't looked hard enough?), and I already had one notebook with REW, RMAA and Audiotest on it.

Surprisingly it is capable of running a dual monitor system. It even asks the question when it sets up Win 10. One monitor output is HDMI and the other is a good old fashioned VESA? DB15 socket.

Cheers

Ian

 

[john12ax7]

Back to this Q, does anyone know if there are USB/PC scopes that can handle tube circuit voltages?

Abbey offered a possible solution, get a 100:1 probe.

 

[Whoops]

That's also a very nice solution. I haven't adopted it because I wanted to have a dual-screen arrangement and I could not find monitors small enough (maybe I haven't looked hard enough?)

I have a small flat screen monitor that I dont need and could give it to you in case you need it.

 

[user 37518]

Abbey offered a possible solution, get a 100:1 probe.

Better yet, get a HV differential probe, it will probably cost more than the scope thou.

 

[abbey road d enfer]

Surprisingly it is capable of running a dual monitor system. It even asks the question when it sets up Win 10. One monitor output is HDMI and the other is a good old fashioned VESA? DB15 socket.

Cheers

Ian

Interesting. The challenge would be to find smaller than 10 inch monitors...

EDIT: Not so mucha challenge, actually:
https://www.amazon.fr/TOGUARD-Ultra-Mince-Haut-Parleur-Compatible-Surveillance/dp/B06WWHQ6Z9/ref=asc_df_B06WWHQ6Z9/?tag=googshopfr-21&linkCode=df0&hvadid=186761974072&hvpos=&hvnetw=g&hvrand=15073827579531724401&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9056208&hvtargid=pla-360316864487&psc=1

 

[ruffrecords]

Interesting. The challenge would be to find smaller than 10 inch monitors...

EDIT: Not so mucha challenge, actually:
https://www.amazon.fr/TOGUARD-Ultra-Mince-Haut-Parleur-Compatible-Surveillance/dp/B06WWHQ6Z9/ref=asc_df_B06WWHQ6Z9/?tag=googshopfr-21&linkCode=df0&hvadid=186761974072&hvpos=&hvnetw=g&hvrand=15073827579531724401&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9056208&hvtargid=pla-360316864487&psc=1

That is interesting. I am thinking of relocating my test area to my larger bench which is big enough to take a small mixer for testing. I was thinking of adding a shelf to hold my scope, audio interface and the little PC plus chunky monitor, but with neat displays like that I could probably just fix most of it to the wall and have the scope on the bench. Hmmmm.... food for thought.

Cheers

Ian

 

[Bowie]

Abbey offered a possible solution, get a 100:1 probe.

Thanks, I had missed that part.