Fabio R312 (X 2) & Fabio PSU Build - Final Couple of Steps - Please Help Noob !!

Hello everyone one and all,

I'm in really urgent need of some help finishing my two Fabio R312 preamps in 1U case. I have gone with Fabio 312 boards and also the Fabio PSU. The op amps I am using in each of the preamps are gar2520s.


PSU312 V1 FILES
psu312bom_v1
psu312parts_v1
psu312sch_v1
psu312solder_v1

MODDED VERSION OF PSU psu312sch_v1_mod

R312 REV3 FILES
R312bom_rev3
R312parts_rev3
R312sch_rev3
R312solder_rev3

OPAMP
gar2520

SERVO
I used the OPA604 for the (SERVO ), as on the BOM for the R312bom_rev3. So, 1 on each R312 pcb, 2 in total.

The input and out put transformers I am using on both boards:

INPUT TRANSFORMER(S)
In both cases I have gone with the Ed Anderson EA2622 from Classic API for TF1.

OUTPUT TRANSFORMER(S)
In both cases I have gone with the Ed Anderson EA 2503 from Classic API for TF2.



I successfully etched my own boards and am happy with the result.

I have stuffed all of the components in both boards and also the PSU.

After initially posting on here in a different thread which is Fabio PSU312v1 Resistor values question, I had a great response from Harpo who gave me lots and lots of information which I really appreciate, but alas, a lot of the information is somewhat beyond my understanding  :-\

He mentioned that my mains transformer is not "beefy" enough to run both preamps with phantom power, along with the fact that he recommended using 12V relays instead of the 5V relays (which I currently have installed), as per Greg's otherwise extremely useful mouser BOM.

Here's the Mains Xformer that I did buy ORIGINALLY (i'm in the UK so I am running off 240V mains power):

MAINS TOROID TRANSFORMER
I have the CA-18-VT31284  purchased from Carnhill. Here is the closest thing I have to a Data Sheet for that model. For quick reference,
Primary: 110v-0-110v
Secondaries: 20.95v-0-20.95v @ 0.27A and 50v @ 0.023A

And here's the Relays I currently have installed:
RELAYS
There are 4 relays on each R312 pcb.  They are RL_HZ, RL_LINE, RL_PAD & RL_POL.  In each case, I used the TQ2-5V.  So 4 on each R312 pcb, 8 in total.

One of the key questions that I need answering if anybody would be so kind, is what spec mains transformer should I be looking to get if I replace the relays with the 12 V ones (which is what I need to do right?), and also, whether I can use the "two coil latching" types of relays (?), which are the only ones I can currently obtain, which are these TQ2-L2-12V.


The other conundrum that I have faced is that there were missing resistor values for R1, R2, R10 & R11 on the PSU schematic and BOM.

MODDED PSU SCHEMATIC
Harpo pointed out that there was another schematic for the PSU which was a modification of the original design.  Here it is:
MODDED VERSION OF PSU psu312sch_v1_mod

By carrying out this mod, which I've yet to do, I can see that I then do have some of the resistor values, R1 and R2 are marked as 22R/5W apart from R11 , still marked as "??" which I think I understand will be calculated as a result of the voltage of the mains transformer that I use (?) and connect to the PSU board.  R10 is thankfully no longer used as a result of the mod  ;D

Can anyone help this newbie with suggestions of what mains transformer voltage rating etc that I should get along with whether I can use those type of relays?

Lastly......Harpo mentioned something about leaving out the voltage doubler caps C11 and C12 on the PSU.
Also, Harpo said "better use a TL783 or at least a LM317HT instead of a LM317 for REG48 and for +48VDC out instead of +44VDC out use 220R instead of 240R for R7". 
So if/when I should do this, where will I connect the power for the 48V phantom power?

Once I have established this, all I need to do is wire it all up, drill my case and then I will finally be able to take to an experienced friend of mine who I trust to wire up to the mains etc so that I don't electrocute myself!  Then I can install into my studio!!  I'd love to get this done before Xmas, when I have some recordings planned!! 

Any help with this would be very, very much appreciated beyond words guys.  I'm a musician who has dabbled with something far beyond my understanding here. As opposed to an electronics expert who is dabbling with music (although I'm trying to learn).

Please be gentle with me, as there are certain calculations that without explanation, I simply  don't know what they represent, even though I have tried to research the best I can to understand Ohm's law, and Kirchhoff's 1st and 2nd laws. I really want to learn, and this is my first ever project of any kind of electronics apart from a little portable headphone amp in a mint tin! 

I have bought many books but it is difficult to even be able to look something up that you don't even know what the terminology is for what you are trying to achieve in the first place.  I've searched high and low on GDIY too, but just can't seem to find the answers I'm looking for.....


Kind regards and a HUGE thank you and kudos for any advice whatsoever and anyone who's helped thus far.


Ben

R11 is a simple LED Resistor,
you can calculate it using this:

http://led.linear1.org/1led.wiz

Thank you Whoops!

So, so helpful.

Thank you so much!

Any recommendations on mains xformer? 

In Layman's terms?

Cheers again! 

Hello Ben,
if you're a newbie to the forum and this is your first project let me tell you that unfortunately you choose a difficult project to start.
Not because an API type circuit is difficult , but because the Fabio boards and layouts were used a long time ago and has no one does them nowadays there's not much info and support ready available.

You would be better doing the Access 312 pcb that's a really simple design with updated information and people doing that project at the same time as you, so its easier to ask questions and have support.
And also using an JLM PSU or even the SSL9K PSU,  a lot of people uses those, their simple and info also highly available.

Saying this I will try to help you finish your project.

But dont forget to read the API thread and other relevant threads.

As for the PSU I found these 2 BOM's in my archives, hope their helpful to you

Another BOM

MAINS TOROID TRANSFORMER

Yes your transformer is not beefy enough for this application, you will need at least the double of that amperage.

You will be fine with a transformer with 2x18V secondaries at 30VA,
them you will have aprox. 833mA per secondary and thats quite beefy for 2x 312 preamps
get one of these:

http://uk.farnell.com/multicomp/mcfe030-18/transformer-30va-2-x-18v/dp/9531742?ost=9531742

https://www.banzaimusic.com/Talema-TRT30218.html


Are you using the PSU inside the preamp case of are you building it in an external enclosure?

About the input transformer,
remember the Fabio schematic you have was specific for a circuit using a Jensen JT110K input transformer,
if your're using the EA2622 transformer you Zobel network needs to be different.

Check the tips of Jeff from Classic API>

"Hey all,

The original schematics for the 312 and for my 536 input channels in my board all show 5.1K and 220pf for the Zobel. In reality, my boards were populated with a 10K R and the 220pf cap. Ed has confirmed the 10K R on the 312 card he used when he was working on the EA2622 design. BTW, suggested load R after the Zobel network is 150K when using a 2622, new or old. 

Also, I have noticed that many of the 312 boards that are in existence these days, don't have the input x-fo primaries in parallel. This must be done with a new or old 2622 for good performance(1:7 ratio). 3nity's Access boards have an optional jumper for this which is cool. Otherwise, just solder a small jumper from pin 1 to pin 2, and another from pin 3 to pin 4 (under the PCB) after the 2622 is solder normally into position. 

Also Use 1000pf for decoupling before the 2622 primaries.
One on the Hi side and one on the Lo side. Primaries
should be in parallel as previously noted. Recommended

Best regards, Jeff
"

You can check how the 1000pf  decoupling caps are connected in the API 312 schematic, they're on the primaries of the input transformer

I redraw your Reliquia Schematic, with the Zobel  modifications you have to do for the EA2622 transformer.

Check this against you reliquia schematic and you will know what to do

Hi Whoops,

That's fantastic!  I really can't thank you enough for your help with this, thank you, it's very much appreciated

Really useful info and documents.  I've attached a photo I knocked up with some markings on it to see if I'm understanding correctly about the making the EA2622 input tranny's primaries parallel, and also about the correct placement of the 2 X 1000pF decoupling caps?



As for the Zobel network modifications, can I check whether this is a case of replacing  the current RL of 100K with a 150K resistor?  Replacing the current RC of 31K with a 10K resistor? And replacing the current CC of 56pF with a 220pF capacitor?


I took your advice and have just ordered the http://www.farnell.com/datasheets/1906771.pdf}MULTICOMP  MCFE030/18  Toroidal Transformer, 30 VA, 2 x 18V, 830 mA, Chassis

I have been planning to install it and the PSU board inside the same 1u case that the pres are going to be housed in.

Is this recommended?

I also ordered the resistors at the same values as in those BOMs (wire wound), as well as some LED clips etc and the resistors and caps for the Zobel networks and the decoupling caps.

Thanks to your help and advice, I'm starting to nearly see a glimmer of light at the end of the tunnel!

Many thanks for your support!

Ben 

Hi Ben,
hope you are able to finish and use your preamps soon.
I will try to help with what I'm able.

As for your questions,

EA2622 inputs
- yes you got it right, connect Pin 1 to Pin2 , and Pin3 to Pin4

Placement of the 2 X 1000pF decoupling caps
- I thing the connections you show in your pics are not right, you are connecting a 1000pf cap between Pin1 and Pin4, and another one from pin 4 to Pin5.
What you need is to connect the Cap from Pin 1 to ground , and another one from Pin 4 to Ground
I dont know the Fabio board, never used on, but I guess Pin 8 of the input transformer is connected to ground (please check that), if so You connect one Cap from Pin 1 to Pin 8, and the other one from Pin 4 to Pin8

"As for the Zobel network modifications, can I check whether this is a case of replacing  the current RL of 100K with a 150K resistor?  Replacing the current RC of 31K with a 10K resistor? And replacing the current CC of 56pF with a 220pF capacitor?"

Yes, that's it

"I have been planning to install it and the PSU board inside the same 1u case that the pres are going to be housed in.

Is this recommended?"

Some people prefer external PSU's because of transformer noise inductance in the audio path, I always do my Mic Pres with the PSU inside the case because I cant carry around a lot of external PSU's,  I prefer it this way.
Although you should do 2 things:
1) don't know if you ever used and toroid transformer, but after you install it you should rotate it while listening the output of the  Mic pre that is more close to the transformer, there will be a position were the noise is reduced a lot, after you discover this screw the toroid in this  position.
2)After that install one  transformer shielding sheet around the torroid, keep the overlapping of the shield sheet in the section that is closer to the mic pre pcb. you can buy trafo shielding sheet here:
https://www.don-audio.com/trafo-shield
After these 2 steps transformer induced noise should not be a problem at all.

Thanks again Whoops! 

Here is how I have connected/modified the input transformer circuit (caps are on other side of board, as well as a jumper which is marked with dotted yellow line - which i used to connect one of the caps to ground via an unused trace).  I think this should be right?



I replaced the components in the Zobel config. as per your advice, also as well as removing all of the 5V relays and replacing with 12 V ones.

One question I have regarding fastening the output xformer to the board.  Is it okay to use plastic washers, so that the bolts/nuts (the smallest i could find) don't connect to copper traces that they shouldn't?  I'm assuming that the red lead of the transformer connecting to ground is all that is needed?



I'm getting closer.......



Cheers

Ben

Your Connection of the Caps it's correct,
although I would not do it that way.

The Cap from 4-3 to ground in fine but the other one you complicated a little bit, there's no need for the jumping wire.
I would connect the 1-2 Primary to the Aground trace directly using the CAP legs, using shrinking tube on the legs.

See attached pic for the way i would do it , it's the black Line

in this pic you can see how I did it in an Access 312 board with shrinking tube on the legs of the caps.

Sun King said:

One question I have regarding fastening the output xformer to the board.  Is it okay to use plastic washers, so that the bolts/nuts (the smallest i could find) don't connect to copper traces that they shouldn't?  I'm assuming that the red lead of the transformer connecting to ground is all that is needed?

Click to expand...

Yes, it's fine

You can also reverse the screw, have the head of the screw side under the PCB the Nut tightens on top os the transformer.
I think that way you don't have the problem of shorting ground with the neighbor traces.

Hi Whoops,

Yeah, it's not the way I wanted to do it.  I wanted to do it with just the caps legs, but unfortunately I accidentally ordered different type of caps (not ceramic), so the legs weren't long enough, so chose to go over the top of the board.  Here's the top view, the white wire is the jumper.  Do you think this could create problems with the signal?  If so, I'll get some more caps.

Ok,
if you dont have other caps just connect a small wire under the board from the unused pad to the place you connected the cap from 4-3.  It's much more elegant than the big wire on the pcb's top

see attached photo is the Pink connection

Ok yes, I understand, cheers Whoops! 

Sun King said:

...I accidentally ordered different type of caps (not ceramic), so the legs weren't long enough, ...
...this could create problems with the signal?

Click to expand...

Size of caps looks more like >1000pF / 1nF.  Maybe only optical artifact. (maybe/better use 100pF...1000pF c0g/np0).  The length of cap legs probably will be sufficient when soldered to the right place.
These two caps are for keeping RF out. They will not be on this preamp pcb. These caps are located close to the (max.1" apart where signal enters the unit in order to be effective, better directly at the) XLR input connector between XLR-1/2 and XLR-1/3 with XLR-1 connected to shield/case-ground by the shortest possible connection.
As always YMMV.

Harpo said:

Sun King said:

...I accidentally ordered different type of caps (not ceramic), so the legs weren't long enough, ...
...this could create problems with the signal?

Click to expand...

Size of caps looks more like >1000pF / 1nF.  Maybe only optical artifact. (maybe/better use 100pF...1000pF c0g/np0).  The length of cap legs probably will be sufficient when soldered to the right place.
These two caps are for keeping RF out. They will not be on this preamp pcb. These caps are located close to the (max.1" apart where signal enters the unit in order to be effective, better directly at the) XLR input connector between XLR-1/2 and XLR-1/3 with XLR-1 connected to shield/case-ground by the shortest possible connection.
As always YMMV.

Click to expand...

Hello Harpo thanks for joining,
The 1000pf caps are Decoupling Caps and not RF filters. These Caps should be placed in the 2622 transformer primaries.