Autoranger for soundcards

[jan.didden]

Balanced spoken for. Will PM you guys.

Jan

 

[Pizzigri]

Hi Jan,
one question: what series and size are the resistors and caps used in the PCB? I see that resistors are MELF but maybe also other SMD like 1206 may fit? I'd like to stick to proven design, so if you used MELF, I'd use what you did - also for caps. I wanted to order from Mouser the parts so that I am ready to build when the PCB comes in.

 

[jan.didden]

I went for the MELF based on measurements from Samuel Groner.
I would not substitute, neither the caps.

Jan

 

[Salas]

Almost there

 

[Salas]

And a question. How the header pin rows correspond between boards? I received wrong pitch terminated flat cable so I have to connect the headers with Dupont jumpers.

 

[Salas]

In other words which row to connect with another? Lets name the rows 1,2,3,4 to help clear answering.

 

[jan.didden]

See attached, will that help?

Also, for those of you who don't like to construct the flatcable assembly, these are available from both Digikey and Mouser, part number ISDCB84, manufacturer NKK. Around $ 9.

 

[Salas]

Thanks. So it follows the IDC ribbon cables keying for odd numbers-connector key side, even numbers-connector flat side. 1 to 3 & 2 to 4 in my example naming. What I was afraid of. Takes to cross the Dupont jumper rows.

 

[jan.didden]

Nick, look at the Construction guide to the pic of the flat cable.

Jan

 

[Salas]

I looked at it and it implies the same conclusion. When flat side of connector should face U1 (4) it connects with the bottom row of control board pins (2).

 

[Salas]

By the way, an alternative idea to avoid scratching the chassis for grounding the BNC's body via the front fixing.

 

[Salas]

Hey, it works. Dupont jumpers connected as discussed. Sacrificial TL082CN for U2,U5. TL052ACP for U3.
What do you know, even low spec opas for crude initial tests can give decent results in Jan's Autoranger.
Here's an FFT with MOTU M4 as signal provider and analyzer. Congrats Jan, a nifty device.
Now to put the OPA1656's on adapter boards and order shorter rainbow jumpers I guess.

 

[gpapag]

Jan's AR is a transparent specs-wise unit.
A great safe, time saver testing tool


George

 

[jan.didden]

Hey, it works.

Of course ....
Well done!

Jan

 

[Salas]

 

[Salas]

...One last thing. J6,J7 are to be jumpered vertically to engage those four clamping diodes across the output phases, right?

 

[jan.didden]

Yes. I don't think the jumpers can be fitted another way.
J6 pos phase, J7 neg phase.

Jan

 

[Salas]

Those are very low capacitance clamping diodes, do they increase the THD a little on extremely good analyzers though?

 

[jan.didden]

Very, very little and only with higher signal levels. They are pre-biased by D9 and D10.
I have not tested it, but with the jumpers it is easy. Measure with/without jumpers, see if there's a difference.

Jan

 

[Salas]

Will have to fit the 1656s first but I also doubt my humble MOTU M4 can see that deep. Others with RME, Cosmos, AP, featuring top tier analogue to digital specs would evaluate that aspect better.