Carlos AD815 preamp PCB

[PierreG]

Gcollier and knabsol,

Do you have a PCB for the PSU reg and the offset null circuit as per Carlos plans?

[Gcollier]

Originally posted by knabsol
Thank you very much Gcollier!
So is this somewhat what you mean by shorting the feedback? I used smd resistors there instead. Better?


I have planned to try carlos nulling circuit or maybe with none at all. that´s why I got the jumper there so i can take it away without resoldering anything.

That's pretty much it. I don't know that I would bother with SMD for that part, just give youself enough clearance for the pads. Some times I put the pads for an SMD part right under the through hole version, just to give myself a few options. Also, you might as well move R5 and R6, right next to the feedback resistors.

I don't have a PSU or nulling circut myself, but Tobias has a very nice design that uses the servo, I'm sure he will share the eagle files with you. If you wan't to try the "Carlos" nulling circut you could likely fit it at the top of the board near where you have the jumper. You could still leave yourself the option of switching it out of the circut. The big problem with the nulling circut is that it does not work across the entire range of your pot.

I am not actually using this preamp myself...to be honest I prefered my OPA627/Buff 634 combo better...the AD815 sounded grainy to me...as usual everyone will have their own preferance. I am looking to give this or something similar another try.

G.

[tobias_svensk]

Hello G and knabsol

Well, it's the Carlos nulling circuit I'm trying to do a layout for. But for a servo it would look the same just the servo OPamp would go right under the AD815 and the nulling circuit would be omitted from the PSU-board.

http://www.ettnet.se/~tobias/diy/ad815/smd/

Stacking the two boards on top of eachother with the PSU on top.
And I would connect the two boards with the pins from the output el. caps from the regs.
Also some vias connecting heatsink areas in both layers.

Haven't done the boards yet so I don't know how it would work.

Did a "DIP" version long ago to, but it isn't finished. The groundplane has to be redone.
http://www.ettnet.se/~tobias/diy/ad815/dip/

Cheers

[knabsol]

Pierre, yes I got a board for Carlos null and reg power supply. I´m testing it tomorrow I hope..

Thanks everyone for the opinions!

[Gcollier]

Originally posted by tobias_svensk
Hello G and knabsol

Well, it's the Carlos nulling circuit I'm trying to do a layout for. But for a servo it would look the same just the servo OPamp would go right under the AD815 and the nulling circuit would be omitted from the PSU-board.

http://www.ettnet.se/~tobias/diy/ad815/smd/

Stacking the two boards on top of eachother with the PSU on top.
And I would connect the two boards with the pins from the output el. caps from the regs.
Also some vias connecting heatsink areas in both layers.

Haven't done the boards yet so I don't know how it would work.

Did a "DIP" version long ago to, but it isn't finished. The groundplane has to be redone.
http://www.ettnet.se/~tobias/diy/ad815/dip/

Cheers

Hey Tobias you sent me the eagle files for that desing a while back. I was tinkering with it to make it possible to use for us self etchers. I didn't look too closely at the PSU design, at the time I was more interested in your implementation of the opamp. I still think that this chip holds some promise as it is highly regarded by most who build it (then again what isn't around here). In anycase I am planning to use a WM8816 to control the gain. Because the microcontroller will know exactly what the gain is I should be able to reliably predict the offset and use the microcontroller to null the offset, maybe with a smoothed PWM signal, or even a really simple DAC. I suspect this will be a complicated project, so it may take a while.

G.

[amichalik]

This sounds like a really interesting project, and I'd love to know how the boards turn out. I'd like to build an intergrated GC and on one hand, don't want a passive linestage, but on the other hand, don't want a complex (expensive) preamp section.

I'm particulary interested if anyone makes a run of these boards. I'll certainly sign up for a set.

[Holger Barske]

Just one simple question:
Did someone ask Carlos for permission before starting this one...?
I somewhat doubt he will be amazed.

[peranders]

Permission of using a non-inverting configuration, model 1A Hardly any rocket science.

[Holger Barske]

That's not the point, and you know that very good.

[Franz G]

Holger

I like your intervention!

Permission of using a non-inverting configuration, model 1A Hardly any rocket science.

Peranders: maybe, you are right.

But: could you explain me, why this project / thread is sailing under the name Carlos? And why a group buy including his name is planned?

Is this fairplay?

Franz