Measurement Equiptment?

[Chris Prosser]

Hi Folks,

I like to build amps, mainly from kits. Some of them sound awful, others are OK. This site has inspired me to want to actually measure their performance. I came across this thread which has some recommendations on hardware: http://techtalk.parts-express.com/forum/tech-talk-forum/1381828-basic-diy-amplifier-measurements

I have built a chip amp, so I need a ADC that can deal with a differential input. I already have a USB based scope (an older bitscope thats approx 8-10 bits), and an old HP analog scope.

The two items listed are the:
Scarlett 2i2 (https://us.focusrite.com/usb-audio-interfaces/scarlett-2i2)
Behringer UMC202HD http://www.musictri.be/Categories/Behringer/Computer-Audio/Interfaces/UMC202HD/p/P0BJZ

So, does anyone have decent measurements of those, or something in that category they could recommend?

Thanks!
--chris

 

[DonH56]

Amir has tested one of the Behringer units as a DAC and it was pretty good. I think someone (Blumlein88?) may have tested the ADC side. Focusrite. MOTU, etc. have good reps and would probably be good.

What USB DSO do you have? I keep looking at the Pico units (mainly the high-res models) but haven't gotten anything. Keep vacillating between those and a conventional bench model like the Rigol or Tek models. Then I realize how little money and time I have for such things and just go back to posting inane content on Internet fora...

 

[amirm]

I tried to use the UMC202HD for measurement once and was unhappy with it showing a lot of mains hum. After that, I did not bother to test it more.

I hope to test the Quantum Asylum Q-4014. It costs a few hundred dollars and I think is a better option than a sound card if you can afford it.

 

[Blumlein 88]

https://www.audiosciencereview.com/forum/index.php?threads/comparing-aliasing-in-three-adcs.3272/

I looked at aliasing in this thread above. I can provide more info if you wish like THD, IMD and SNR. I looked at the Focusrite Scarlett 18i20, the Focusrite Forte, and the Antelope Audio Zen Tour ADCs.

I think on the ADC side the 2i2 is a better choice than the 202. The 2i2 Scarlett is not necessarily equivalent to the Scarlett 18i20 I have. There are some differences.

The Quant Asylum looks really good, but I was concerned with the fact it appears to let the noise floor get pretty heavily modulated by input signal level. I'm not sure I fully understand what all it is doing however. It may be automatically changing gain based upon signal level making it less clear what is actually going on with it. I think @BE718 has it and might give some input.

Now you could get a second hand Forte like I have for $200 or sometimes a bit less. They turn up some on ebay or on www.reverb.com if you keep an eye out for them. They are discontinued, but are nice units.

I think the Quant Asylum can take high voltage inputs. With these other ADCs you'll need to pair up a couple resistors to reduce signal level unless your chip amp only puts out a few volts. I've intended to build such a box to use myself, but haven't gotten around to it. Also if your chip amp is class D it has high frequency max voltage switching at the outputs. You'll need to reduce level with the resistor pair for that before sending to an ADC or put a filter of some sort between the ADC and load resistors being measured. Most of these ADC can take about 7.75 volts max input. The 2i4 can take about 15 volts. Might be worth getting it or looking for a 2nd hand one of those. Also the 6i6 Scarlett according to specs would take 15 volts input, and it has better SNR, and THD specs similar to the 18i20. If your chip amp is not over 25 watts it might work with no attenuator though using one would be safer.

 

[andreasmaaan]

Someone measured the Scarlett 2i2 here. If the measurements are reliable then it looks good apart from a weird artefact at multiples of 8KHz that's nevertheless about 110dB down in level.

 

[Blumlein 88]

Someone measured the Scarlett 2i2 here. If the measurements are reliable then it looks good apart from a weird artefact at multiples of 8KHz that's nevertheless about 110dB down in level.

Doesn't look too bad. The 8 khz artifacts are likely USB packet noise. That is on the output as a DAC though. Wish he had done the line inputs as well as mics, but generally Focusrite gear in my limited experience does meet the basic specs claimed. Which btw are here:

http://us.focusrite.com/usb-audio-interfaces/scarlett-2i2/specifications

While not state of the art, it is good enough to show if an amp is basically operating correctly.

 

[andreasmaaan]

While on the topic, at some point soon I'm gonna be looking for a cheap (say under €200) ADC with mic preamps. The 2i2 is one that I'm looking at. Do you know of any others that have been measured here or elsewhere @Blumlein 88? Or have any recommendations?

 

[SIY]

While on the topic, at some point soon I'm gonna be looking for a cheap (say under €200) ADC with mic preamps. The 2i2 is one that I'm looking at. Do you know of any others that have been measured here or elsewhere @Blumlein 88? Or have any recommendations?

I've posted some measurements of the Behringer UMC404HD. Except for the relatively low output (1V), it's quite good. None of the mains issues that Amir saw.

 

[andreasmaaan]

Thanks @SIY. I wouldn't be using it as a DAC at all actually so that's fine. Just mic/line pre + ADC.

 

[SIY]

You'll also be concerned with the DAC because test signals need to be generated.

You might want to investigate front ends to go with whichever ADC/DAC you choose. Jan Didden's Autoranger is a great choice here.

 

[andreasmaaan]

You'll also be concerned with the DAC because test signals need to be generated.

You might want to investigate front ends to go with whichever ADC/DAC you choose. Jan Didden's Autoranger is a great choice here.

Ah, crossed wires. I'm not planning on using this to test anything. Just live recording. Sorry, now I see I've hijacked the thread. Will let you get back to it @Chris Prosser & co...

 

[SIY]

Live recording? I've used the Behringer, but the Scarlett 2i2 gave me a lower noise floor. Works superbly well, very good mike preamps.

 

[andreasmaaan]

Live recording? I've used the Behringer, but the Scarlett 2i2 gave me a lower noise floor. Works superbly well, very good mike preamps.

Nice That's what I suspected. GTK

 

[Blumlein 88]

While on the topic, at some point soon I'm gonna be looking for a cheap (say under €200) ADC with mic preamps. The 2i2 is one that I'm looking at. Do you know of any others that have been measured here or elsewhere @Blumlein 88? Or have any recommendations?

Measurements are hard to come by. Even in that price range performance is pretty good generally.

Do you plan to use dynamic or condenser (or ribbon) microphones?

The gen 2 Scarlett 2i2 doesn't have much microphone gain. Some dynamic microphones might barely work with them. Ribbons mostly wouldn't work. Condenser microphones have more output and would be fine.

The 2i2 only has 50 db of microphone gain which is rather low. The 2i4 has 55 db of mic gain which is about normal in these type interfaces. So it might be worth the extra 50 euros or so.

I don't know the gain of the UMC204HD or 404HD as it isn't listed anywhere. The Tascam US 2x2 might be worth looking at though I've not used it. 57 db of microphone gain.

The Audient ID14 if available where you are would be a really nice choice. Real nice specs and 66db of gain. But I'm thinking that stretches the cost out to 300 euros.

Also if you are doing recording you'll need a DAW. Some of these come with DAW software included and some don't.

If you are on windows you need ASIO support for these which a DAW will do. You can record simply with Audacity or similar. But Audacity does not support ASIO and you'll be going thru some portion of Windows which may mean it isn't direct to and from the interface. You can try Reaper DAW for free which is $60 on the honor system. If you like it and use it, I'd think you should eventually pay for it though you don't have to.

If you are using a Mac then Audacity can directly record from the interface. For some purposes it isn't as nice as a real Digital Audio Workstation, but for a couple of channels it is fine.

Don't get too hung up on the interface. In recording the microphone is what makes the big differences. Rather like on the other end it is speakers that matter the most.

 

[SIY]

I actually got pretty good results using ribbons (mine are about 2.6 mV/Pa) with the 2i2. If more gain is needed, something like the Simply Sound SS-1 will give you another 26 dB or so with very low distortion.

 

[andreasmaaan]

Thanks guys

@Blumlein 88 primarily I'd be using it to record the line output from a mixer, so the mic gain is lower priority than line level ADC.

But it would be nice to have direct mic input too for some flexibility. Good to keep in mind what you say about the low mic gain. Although we're using dynamic mics atm, it's for close-mic'd vocals only, so I'd imagine we might get away with 50dB. What do you think?

Already have a DAW.

Looking at the 2i2 the mic input/ADC measures perfectly adequately I think and has a SNR of 100dB, so maybe that's the one to go with. Will check out the Audient too though, it seems it sells for around double the price of the 2i2 here.

A

EDIT: miked, mic'd, or miced???

 

[DWPress]

I use a Scarlett 2i2 & Dayton EMM-6 mic for measurements via REW and FuzzMeasure on my Mac and have had no issues or problems. Here's a really good article by John Reekie on using the Scarlett along with a few measurements of it.

 

[DonH56]

My relatively old experience with Behringer has been the mic inputs are a bit noisy.

Mic and mike are used interchangeably but I and most folk I know use mic since it is short for microphone (no K, at least not in my language).

 

[Chris Prosser]

Thanks for all the replies. I have to admit, I like the flexibility of the Scarlett 2i2 for some possible future project ideas. I also have a Topping d30 and d10 kicking around, so that would clean up the 8kHz spikes on the DAC side of things. Though I must admit, the QA401 scratches my test equipment itch. That said it's running at $450 whereas the Scarlett is $150 from amazon. I'm thinking it's best to go the middle road until I hit the limits of my test gear, and I'm pretty sure my amps won't be near that.

What USB DSO do you have? I keep looking at the Pico units (mainly the high-res models) but haven't gotten anything. Keep vacillating between those and a conventional bench model like the Rigol or Tek models. Then I realize how little money and time I have for such things and just go back to posting inane content on Internet fora...

I have an older Bitscope 120 (http://www.bitscope.com/product/BS120/). I think I've only used like 10% of it's capabilities. I don't need it very often, but when I do, nothing will substitute. I just realized I'm having an intermittent problem with a internet remote I built for my AC and I should wire it up and try and capture it failing in action.

 

[March Audio]

I have just received a Motu Ultralite MK4 so will be performing measurements over the weekend and seeing how it stacks up against my 8A.