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

[Sun King]

Could it just be that without the grounding to PIN 1 of the XLR that it's not working with a condenser mic?

.........

All Pin 1 XLR inputs should connect to chassis

Chassis should connect to Earth Pin on Power prong

0V on PSU should connect to 10r (2watt) resistor in parallel with 0.1uf (63v) cap and then to Chassis

0V of  each Mic Pre PCB separately should connect to 0V on PSU

Can I check what exactly is the 0V connection?  Am I right in thinking that it's the ground connections on the preamp PCBs and PSU PCB?

Also, would a 10R - 3 Watt resistor be ok?  That's what I can get locally.

Cheers

 

[Harpo]

Ben, it seems your previous questions have been answered in the other thread, your 1st post already refers to. Do your PSU questions still relate to your 18-0-18V + 48V transformer from that thread, or what (voltage and VA-rating) type of transformer do you use now? Leaving out C11 and C12 in the voltage doubler section obviously relates to your seperate 48VAC transformer  winding from that thread as well.

 

[Sun King]

Hi Harpo,

This is the mains transformer I am now using as per Whoops' advice.

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

Regards

Ben

 

[Sun King]

Ok, great I understand now.

Thanks so much for all of your help.  It would have been impossible for me to get this far without the help from Harpo and Whoops, and also Mark and Greg!  And of course Fabio, and all of the useful stuff on various different threads!

You guys are ACE! 

Ben

 

[Whoops]

I dont think you need to change the LM317, just change the resistor and check voltages

 

[Sun King]

Hi Whoops<

I have changed the resitor R7 for 220R and am now getting 47.9VDC, so that's great (thanks Harpo).  I left the LM317 in for REG48.

I've soldered in the LM7812C for REG_SW, and I'm getting 2.6VDC 

Is it due to the resistors I have in place for R10 & R11?

R10 is 470R wirewound (I couldn't get the 450R wirewound in the BOMs that you shared for the PSU)  :-\

R11 is 470R.

I hope it's these, and not something else!  How do I calculate what the values should be to get 12VDC?  I know it's simple Ohm's Law, but as you know, I'm a complete amateur!

Regards

 

[Harpo]

Ben, what type are your 12VDC relais exactly?
The -from schematic- left side of R10 now connects to the junction of D1/D2/R1/C1 instead of +48VDC out ? (R10 could get substituted with a piece of wire, as already shown in the modded psu schematic ...)
Value of R11 probably better would be (12VDC supply - 2V LED Vfwd) / 0.01A allowed current thru LED = 1000 ohm current limiting resistor needed, when assuming about 2V forward voltage from your LED (might differ depending on type and colour of LED) and allowing for maybe 10mA in order to not build a headlight. For high efficiency LEDs you maybe only allow for 2mA, so adjust numbers in previous formula by your parts parameters. Your 470R and previous example values would allow for (12V-2V)/470R=0.021A=21mA that already might exceed your LEDs parts limits if the 12VDC rail would be operating correctly.

 

[Whoops]

follow Harpo suggestions
R10 is not used in the modded schematic, so a pice of link wire (could be a resistor leg)
R11 - use 1K

When you have a problem with a rail always post voltages at the input of the regulator, so what voltage do you have between ground and the 7812 input (pin1)?

Do you modded the PSU correctly? please re-check that, I think that might be your problem

 

[Sun King]

Hi guys,

Thanks for the response.  Sorry, I have only just got back to my computer to check these.

I hadn't performed the MOD, so that is probably the problem. 

One thing I'm not sure about, is that the modified schematic seems to show PIN 1 of REG_SW connecting to the junction of R1, C1 & D1.

Should I be doing this, or just putting a jumper wire in place of R10?

In this picture, should it be the red or the green?

Cheers

Ben

 

[Sun King]

Could it just be that without the grounding to PIN 1 of the XLR that it's not working with a condenser mic?

Yes, because it's not receiving phantom power, there's no ground reference.

All Pin 1 XLR inputs should connect to chassis

Chassis should connect to Earth Pin on Power prong

0V on PSU should connect to 10r (2watt) resistor in parallel with 0.1uf (63v) cap and then to Chassis

0V of  each Mic Pre PCB separately should connect to 0V on PSU

Hi Whoops,

Does 0V mean the ground plane on each PCB?

Cheers

Ben

 

[Harpo]

..Should I be doing this, or just putting a jumper wire in place of R10?
In this picture, should it be the red or the green?

Only the green wire.
Don't populate the red jumper wire (a 7812 voltage regulator with its 35VDC abs.max. input rating probably won't survive for long when fed from +48VDC).

 

[Sun King]

Thanks Whoops,

I was just about to post this reply, so yeah, you've answered it.

Ben, what type are your 12VDC relais exactly?
The -from schematic- left side of R10 now connects to the junction of D1/D2/R1/C1 instead of +48VDC out ? (R10 could get substituted with a piece of wire, as already shown in the modded psu schematic ...)
Value of R11 probably better would be (12VDC supply - 2V LED Vfwd) / 0.01A allowed current thru LED = 1000 ohm current limiting resistor needed, when assuming about 2V forward voltage from your LED (might differ depending on type and colour of LED) and allowing for maybe 10mA in order to not build a headlight. For high efficiency LEDs you maybe only allow for 2mA, so adjust numbers in previous formula by your parts parameters. Your 470R and previous example values would allow for (12V-2V)/470R=0.021A=21mA that already might exceed your LEDs parts limits if the 12VDC rail would be operating correctly.

Hi Harpo,

Thanks for your response.

The relays are TQ2-12V.

As i mentioned earlier, I hadn't done the mod. 

Is it just a case of having a wire/jumper going from Pin 1 of REG_SW to the junction of R1, C1, D1/D2 ?  And no longer having a connection between REG_SW and 48VDC at all?

Regards

Ben

 

[Whoops]

Is it just a case of having a wire/jumper going from Pin 1 of REG_SW to the junction of R1, C1, D1/D2 ?  And no longer having a connection between REG_SW and 48VDC at all?

Yes, follow your modded PSU schematic, the goal of the mod is not  having the feed to the 7812 from the 48V rail.
Follow the schematic

 

[Sun King]

Ok chaps,

All done with PSU mod.

Measurement I am getting on Pin 1 of REG48 is 46.6VDC and on the 48VOUT is 47.9VDC

Measurement I am getting on Pin 1 of REG_SW is 28.3VDC and on the SWOUT is 11.8VDC

This is correct, yes?  It seems to be.

Whoops, I just wanted  to check about the resistor and capacitor in parallel for the mains?

Could it just be that without the grounding to PIN 1 of the XLR that it's not working with a condenser mic?

.........

All Pin 1 XLR inputs should connect to chassis

Chassis should connect to Earth Pin on Power prong

0V on PSU should connect to 10r (2watt) resistor in parallel with 0.1uf (63v) cap and then to Chassis

0V of  each Mic Pre PCB separately should connect to 0V on PSU

Can I check what exactly is the 0V connection?  Am I right in thinking that it's the ground connections on the preamp PCBs and PSU PCB?

Also, would a 10R - 3 Watt resistor be ok?  That's what I can get locally.

Cheers

 

[Whoops]

Measurement I am getting on Pin 1 of REG_SW is 28.3VDC and on the SWOUT is 11.8VDC

You want 12V out, so the output voltage is good. You need to Heatsink that regulator otherwise it might run too hot

if you have 28.3VDC after the rectification it means your transformer has a 12,5% tolerance

18VAC x 1.125 (tolerance) x 1.4 (rectification ratio) = aprox 28.v VDC

Measurement I am getting on Pin 1 of REG48 is 46.6VDC and on the 48VOUT is 47.9VDC

You want 48V out, so the output is alright although I can see a problem there.
The LM317 needs at least 1.25v more voltage at the input than the output voltage it's suppose to regulate
So you need at least 49.25 volts at it's input

By my calculations you should have more voltage after the rectification

18VAC x 2 (secondaries)  x 1.125 (tolerance) x 1.4 (rectification ratio) = aprox 56.7 VDC
Or without the tolerance the minimum should be 50VDC (36VAC x 1.4)

that 46.6 VDC after the rectification seems too low to me for the transformer you have,
are you sure you are measuring it properly?

 

[Harpo]

Measurement I am getting on Pin 1 of REG48 is 46.6VDC and on the 48VOUT is 47.9VDC

You want 48V out, so the output is alright although I can see a problem there.
The LM317 needs at least 1.25v more voltage at the input than the output voltage it's suppose to regulate
So you need at least 49.25 volts at it's Input

The problem is the wrong assumption, this 317 vregs pin1 would be input. All vregs in this psu (7812, 317, 337) have a different pinout. Have a look at the parts datasheets.

 

[Sun King]

You are very good to me Harpo! 

It was per the schematic with its pin labellings (that must be wrong) that i tested.  I will do as you say, as looking at the pinout, they are differently numbered.

Thanks for pointing it out my friend!

And thanks again Whoops.  You guys are sound as a pound!

Ben

 

[Sun King]

Harpo,
Because of your advice, the preamps have been running flawlessly, for coming up to 10 years!
Thank you so much for your help!
Benny