QuantAsylum QA400 Audio analyser

[niner]

yes, that's what i ended up with.  final schematic is attached to this post.  i've been using it for the last couple months and it does what it should.  my pcb layout is more cramped than it should be for optimal usability.

rotary switches are from grayhill & toggles from e-switch.  xlrs are neutrik d series, and bnc connectors are from molex.

the limits are set by the qa400's unbalanced connections;  it wouldn't hurt if the interface had a balanced input from the qa400, and maybe some sort of ground-canceling output.  for now, this works ok.  eventually i might have another go at it.

What do you use as FB1 and FB2?  If you have a part list, would you mind share it? 

 

[dfuruta]

What do you use as FB1 and FB2?  If you have a part list, would you mind share it?

Just standard through-hole ferrite beads, like this:  http://www.digikey.com/product-detail/en/28C0236-0BW-10/240-2491-ND/806594 .

I don't have a parts list.  Besides what I posted before, it's just standard parts.  Anything specific?

For the next step, I think it might be wise to use a differential input from the QA400.  That connection seems to be the weak link.  My PCB layout is also a little bit cramped.  There's enough room for everything and all the controls are accessible, but it might be nice for fat fingers if they were spread out more.

 

[niner]

Thanks for the info.

I'm trying to find switches that are perfect match with the PCB, especially SW 3, 5, and 7.

BTW, where did you source THAT ICs?  I have problem finding those.

 

[niner]

Never mind, I found those THAT ICs at Mouser.  Thanks anyway.

 

[dfuruta]

Thanks for the info.

I'm trying to find switches that are perfect match with the PCB, especially SW 3, 5, and 7.

BTW, where did you source THAT ICs?  I have problem finding those.

The toggle switches are from E-Switch, from their 100 series.  SW 3, 5 and 7 are rotary switches from Grayhill, from their 71 series - if you look on Digikey for switches -> rotary switches and then filter by grayhill -> pc pin termination -> right angle orientation, just choose the switch with the right number of poles/decks.

If you end up building one of these, I'd really like to hear your opinion.  Maybe I'll try to do another revision sooner or later.

 

[niner]

Thank you!

Yes, I planned to build one.  I already ordered PCBs from OSH Park.

I have an AP System 2 at work, which I will compare QA400+front-end board to.

 

[siavash]

Thank you!

Yes, I planned to build one.  I already ordered PCBs from OSH Park.

I have an AP System 2 at work, which I will compare QA400+front-end board to.

I know it's been a couple of month. I was wondering what are your thought on QA400 after using it for a while.
Thanks

 

[abbey road d enfer]

Thank you!

Yes, I planned to build one.  I already ordered PCBs from OSH Park.

I have an AP System 2 at work, which I will compare QA400+front-end board to.

I know it's been a couple of month. I was wondering what are your thought on QA400 after using it for a while.
Thanks

After playing with it for sometime, I've ditched it because it doesn't do the basic things I expect from a piece of audio test, such as have a reconfigurable scale and mainly the capability of overlay. Their service dept told me that I could write plug-ins for that; they gave me examples of existing plug-ins that were supposed to tell me how to write my own. I looked at them and decided it was too obscure for me. I showed that to the engineer in charge of software at my company; she said it would be difficult for her.

 

[dfuruta]

I've also not used this much recently.  It's better than nothing, but it's not particularly quick or fun to use.

At some point I'd like to do another revision of this front-end, as I think I could do better on the noise performance (and, after having used it, I think it could benefit from balanced connections to the QA400).  No clue when I'll have the time, though.

 

[ricothetroll]

Hi there,

Sorry for digging this old post.

I'd like to build a front end for using with my RME Multiface. The only difference with dfuruta's interface would be to have balanced in and out because the soundcard will be a few meters away from the front end. I thought about using THAT1200 and THAT1646 for input and output connections. The main goals of the front end is to get rid of the influence of the cable length, and also to provide protection for hasardous voltages from the DUT to the soundcard.

So I have a few questions :

- your talked about updating the schematic for lower noise. Did you do it ? What were the problematic noise sources in your original schemo ?

- About the output PAD : I don't understand why you chose 68R in series with your -40dB PAD and 62R with your -60dB PAD, while without PAD you chose 47R. That gives about 135R output impedance for -40/-60dB and 94R without PAD. Maybe there's something I missed here.

Thanx a lot for your work anyway !

Best regards

Eric

 

[dfuruta]

I think balanced ins and outs are a good idea.  My main problem with this unit is 60Hz hum pickup, which seems to mostly be picked up by the BNC cables to and from the qa400 (as moving them around quite noticeably changes the amount of hum).

I haven't done any work on this since, and I unfortunately lost my kicad files in a computer crash some time ago.  So, I'm not likely to revisit this soon.  Even with a front end I don't find the QA400 terribly pleasant to use, and so I'm not very motivated to improve it...

I can't remember what I was thinking with the output pad;  quite possibly my math was off.

If I remember correctly, I should have used a THAT1206 for unity gain instead of a 1200.

Hope it'll be of some use to you, anyway!