[Photostory] 8 channel THAT1512 Micpreamp

[rkn80]

Hi,

some time ago I designed an 8-channel mic preamp based on THAT 1512 but I never built it, too bad. But then another thread here inspired me to build it just now and I can use it next year for some recordings.
It is quite a simple design. Just a THAT1512 with everything around to get it working, a DC-Servo added, gain setting by a potentiometer, +48V phantom power, balanced outputs on SUB-D  and the option to connect an ADC pcb. That's it.
So, let's start with the empty board.

R.

P.S. This photo story should also show that it is not so difficult to work with SMDs …

 

[rkn80]

First all ICs are populated.

 

[rkn80]

Then all 0805-capacitors…

 

[rkn80]

… followed by 0805-resistors, 1206-resistors and finally the 1812-capacitors.

 

[rkn80]

Now the diodes in MELF-packages are populated.

 

[rkn80]

And with the electrolytic capacitors all SMDs are done and it is time to clean the board from flux with a PCB cleaning spray.

The through-hole devices will follow soon…

 

[rkn80]

All through-hole parts mounted. Now it is time to put the main board on the side for a moment and to make the control panel.

 

[michal_k]

looks good! you haven't thought about placing all the decoupling caps on the other side of the board to make the layout less crowded?

 

[rkn80]

Yes I have thought but did not because the power rails are on top and by placing the decoupling caps on top, too you get a very solid ground plane on the bottom.

R.

 

[rkn80]

The control panel is finished. Now it is time to connect a few cables to a Lab-PSU, connect it to a signal generator and to a scope, cross your fingers and turn everything on….

 

[rkn80]

No smoke and a nice sinus on the scope. 
Only the inputs of the dc servo a connected with inverted polarity.  :  :-X
Will fix that on all 8 channels tomorrow.

R.

 

[bremusound]

Great but i really really want those PGA2500 based pres you wrote about in another thread:
http://groupdiy.com/index.php?topic=52530.0

Cheers

 

[rkn80]

Well then I have some bad news for you. The PGA2500 PCB is currently delayed. There was some trouble to get the AD-Converter used on that board, so a redesign is needed. Therefore, I decided first to build THAT1512 based preamp because I had already the design and I need some extra preamps soon. But the PGA2500 is still in the pipeline, probably after the main board with the UAC2 interface.

R.

 

[rkn80]

DC-Servo is now working properly. Next step: The final PSU. Here I decided to use the PSU I designed for the AD/DA-project. Therefore, I copied it from the main board to its own PCB. Benefit: I can test this already now. Hopefully the transformer and the switchers will arrive soon (but there is enough stuff to do on another project while waiting…  ).

R.

 

[rkn80]

PSU finished. There was a bug in it: The transformer have been connected wrongly. 
It works with a wall wart and generates via switchers: +48V +/- 15V +/-5V (or alternatively another +/- 15V pair), +5V and +3V3. Everything you will ever need for Opamp-based circuits.
Now it is working. Next step: Metal work for a nice housing.

 

[Rochey]

i envy how you are able to get so much stuff done!

 

[rkn80]

Thanks, but don't overrate it. Most of my projects are running over a long time…