Balanced to unbalanced board

[ti5002000]

30 minutes ago, mypasswordis said:

A little breakout board for the AD5254 digital potentiometer... so I can dynamically bias the Dynalo through my phone (through a uC). 256 step resolution but lowest full wiper resistance seems to be 1k so 3.9 ohm per step. 

Very nice! i have been looking for something like this.

[kevin gilmore]

if you are going thru all that effort (and its a good idea) might as well add some hall effect devices on the power rails to monitor the bias current.

something I did in the uberamp quite a while ago and that made the bias super stable, set it to what you want and it works. then if you want to get super silly, add dynamic bias

[mypasswordis]

I remember you mentioning the same thing awhile back, but didn't get a chance to do anything until now. I have I2C temperature sensor prototypes working (simple tmp36 to92 devices with ADC for now) and will definitely look into current monitoring as well. 

[mypasswordis]

Very slowly coming along... just noting the size difference.

What is everyone using for the right angle headers? I bought some 4 pin headers for the main 4 pins but ground pin is off to the side, maybe just airwire that one? Also are you socketing the headers or directly soldering? If socketing what are you using?

Edited July 8, 2017 by mypasswordis

[cspirou]

Hey @mypasswordis, do you have a BOM available for the ubal board and diamond buffer?

[mypasswordis]

I literally split the parts across like 8 different orders... give me a few days to compile a BOM

[cspirou]

Do the SMD boards use 1206 size resistors and LEDs?

[mypasswordis]

My bad. Yes they do. For the current source LEDs pick a forward voltage and matching resistor to get close to 4ma and you can use the vishay tnpw like from earlier builds or I used yageos. 

Also the decoupling caps on the opamps are 0603

Edited July 12, 2017 by mypasswordis

[mypasswordis]

So I did end up using a female header socket and air wiring the ground. The part number for the 4 pin right angle header is 68016-404hlf. The leds I used are extremely bright orange-red, glad once i case it up it will be harder to see. I am measuring about 3.95ma after a few minutes warm up but the thing lights up like a Christmas tree. Will do further testing hopefully over the weekend 

Edit: the diamond buffer boards are getting really toasty

Edited July 13, 2017 by mypasswordis

[luvdunhill]

I have a discrete opamp that is unity gain stable that sounds quite nice. Once you get this up and running and familiar with the sound, I would appreciate a comparison. Will send samples for positive review only though. K thx bye.

 

Actually, it would be a PITA - mine are dual opamps on a single board. So, would probably need a new board.

[kevin gilmore]

Put a heatsink on the back of the buffers

[mypasswordis]

Got some old RPi heatsinks I can stick on if need be. Gotta check with temperature probe 

19 hours ago, luvdunhill said:

I have a discrete opamp that is unity gain stable that sounds quite nice. Once you get this up and running and familiar with the sound, I would appreciate a comparison. Will send samples for positive review only though. K thx bye.

 

Actually, it would be a PITA - mine are dual opamps on a single board. So, would probably need a new board.

Okay let me know whenever!

[luvdunhill]

Put a heatsink on the back of the buffers

 Could you be persuaded to modify the board? Basically would need a SIP-10 pinout for the dual opamp and usual external resistors.

 

Pinout would be:

 

1 - signal ground

2 - OUT_A

3 - -IN_A

4 - +IN_A

5 - -23V

6 - +IN_B

7 - -IN_B

8 - OUT_B

9 - +23V

10 - psu ground

 

Drop-in replacement for something like NJM4558E, pin 1 and pin 10 are omitted (one of the advantages to a discrete opamp is handling ground properly/differently/carefully)

 

http://akizukidenshi.com/download/NJM4558.pdf

 

Also, would need to note changes to the external circuit for slightly higher rails.

 

 

[kevin gilmore]

the opamps are strictly the servo's, not sure there is any reason to change that part of it.

the diamond buffers are strictly the output buffers, unity gain, the servo's are on the main board

[luvdunhill]

Right - so I am proposing to replace the two diamond buffers with a single SIP-8 pinout with external resistors that can be shorted to run the discrete opamps as buffers. Then the existing buffer boards could be made double sided (stereo) if desired.

[mypasswordis]

To answer the question, yes they do need heatsinks. Measuring 50-52 C with the sinks in the pic. Don't have part number, just RPi heatsinks from ebay

[cspirou]

Are you using +/-20v? Can you run it without heat sinks at a lower voltage?

[mypasswordis]

I'm using +-18V straight out the PS of the Dynalo mini. Actual measured voltages +17.96, -17.92. I tried it at 16V on a GRLV and it still got quite hot, didn't measure temps. 

[swt61]

Those look really nice Justin!

[mypasswordis]

Thanks, Steve! And many thanks to Kevin for the design and layout!

[Kerry]

Nice Justin!

[mypasswordis]

What wasn't nice was the first negative regulator working perfectly, then my ham-fistedness shorting it to ground with my probe when measuring voltages and then having to order and put in a new one  

[Kerry]

^ Been there to many times...

[Pars]

So I did end up using a female header socket and air wiring the ground. The part number for the 4 pin right angle header is 68016-404hlf. The leds I used are extremely bright orange-red, glad once i case it up it will be harder to see. I am measuring about 3.95ma after a few minutes warm up but the thing lights up like a Christmas tree. Will do further testing hopefully over
Edit: the diamond buffer boards are getting really toasty

A few questions:
1) The air wires I presume are grounds? Ground(s) aren't accommodated in the connector pin pattern? (I didn't look at my boards obviously)
2) How did you attach the heat sinks?

Thanks!


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[mypasswordis]

You'll know once you look at the boards, there is a gap between ground and the other 4 pins. If it's just a standard 2.54mm gap then potentially you could use a 6 pin header (if you cut the end off the gap header), though the socket end would still need to be 4 and 1, and the unused gap header would just be dangling. 

The RPi heatsinks already have some 3M adhesive squares so just stick them on.  I wasn't sure if they were electrically insulating so just to be safe, I avoided the vias on the bottom of the boards. 

Edited July 20, 2017 by mypasswordis