312 preamp in my way (Now with pics)

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HappyTom

Well-known member
Joined
Jun 7, 2004
Messages
144
Location
Sweden
Hi!

I might do a presentation for my project.
8 channels.
Lundahl 1538 for input transformer.
Cinemag CMOQ-2S for output transformers.
Fabio Baumans 2520 DOA
48v
Pad
Phaseswitch
Instrument In on 2 or 4 channels.
All pcb's are 100x60mm.

I got a Shaeffer case. I don't know what the style is called but I call it boardslotcase, the ones you slide the board in just like an api lunchbox.

I got the boardsdesigns done, just need to prototype and test them.
This project is for learning and have fun.
Thats why I don't buy ready made pcb's.

Here are the files:
http://www.rollingthunder.se/saker/api/
Files gets updated with the progress of my project.

First question:
Is my PSU any good.
I've lended bits and pieces from Peter C's greenpre psu and Fabios 312PSU.
Is the capacitance OK on the rails?
Any other designflaws in there?

I know i probably wouldn't do this project because of my none or very little knowledge in electronic design, but that's what this board is for, isn't it?

More to come..

HT
 
I forgot to mention Handcrafted Tone who helped me to understand Eagle.
Thanks!

No comments on above question?

HT
 
I´d increase (lets say double) the capacitance in front of the regulators. If you have more C over there the regulator has an easier life. Rule of thumb is 1000uF/A in non-audio applications, hence more for us.
I don´t know the exact current draw of your modules but I guess it might be around 100mA/each. This would give 800mA in total which seems to me a hard job for the standard LM317 regulator. Make sure you have good heatsinks and get a version which is capable of higher currents (3A?). After the regulators you might possibly decrease the caps, no problem here. Bypass caps in the PSU can cause oszillation since they form a parallel resonant circuit with the big ´lytics. I´ve learned (a thousand years ago) not to do this. But other people say different things, just my 0,02$.
+48V rating is 10mA per channel which would give you a total of 80mA. Since this voltage has to be very clean add some capacitance here (C16,C15,C17), too.
The schemo looks good to me, but I didn´t check your layout.

Good luck and fun with your project
:guinness:
 
[quote author="jensenmann"]I´d increase (lets say double) the capacitance in front of the regulators. If you have more C over there the regulator has an easier life. Rule of thumb is 1000uF/A in non-audio applications, hence more for us.[/quote]
Ok, didn't know that.
I added 2 caps on each rail.
The reason why I use these 670uF 50v is because I got a bag with them.

[quote author="jensenmann"]
I don´t know the exact current draw of your modules but I guess it might be around 100mA/each. This would give 800mA in total which seems to me a hard job for the standard LM317 regulator. Make sure you have good heatsinks and get a version which is capable of higher currents (3A?).
[/quote]

My plan was the TO3 version (1.5A) with big heatsinks.
When I had read your post I looked for better regs and found a positive one, LM350K (3A). But no negative.

[quote author="jensenmann"]
After the regulators you might possibly decrease the caps, no problem here. Bypass caps in the PSU can cause oszillation since they form a parallel resonant circuit with the big ´lytics. I´ve learned (a thousand years ago) not to do this. But other people say different things, just my 0,02$.[/quote]
I didn't know this either.
I will think of this when testing the board.

[quote author="jensenmann"]
+48V rating is 10mA per channel which would give you a total of 80mA. Since this voltage has to be very clean add some capacitance here (C16,C15,C17), too.[/quote]

I raised them from 47uF to 100uF.

[quote author="jensenmann"]
The schemo looks good to me, but I didn´t check your layout.
[/quote]

Can I run into problem if the layout is bad?


[quote author="jensenmann"]
Good luck and fun with your project
:guinness:[/quote]

Thank you very much for the help!
:thumb:

HT
 
My plan was the TO3 version (1.5A) with big heatsinks.
When I had read your post I looked for better regs and found a positive one, LM350K (3A). But no negative.

You can just use 2 positive regs. Make 2 seperate 0v to +v PSUs. connect the + of one to the 0v of the other which becomes your 0v. Then you have a + & - above & below it. This is how AMEK do their PSU for their desks but with LM338k which do 5A. I copied their supply for my trident & it works very well.
 
I read the Datasheet for the 2520 and the currentdraw was between 18 an 85 mA dependant on supplyvoltage and load.
Then i guess the diodes have some small currentdraw..??

This might add up to less than 100mA.
That's 800mA.
And the regs is good for 1500mA.

Isn't that enough?
Do I need to overrate the regs moore?

You can just use 2 positive regs. Make 2 seperate 0v to +v PSUs. connect the + of one to the 0v of the other which becomes your 0v. Then you have a + & - above & below it. This is how AMEK do their PSU for their desks but with LM338k which do 5A. I copied their supply for my trident & it works very well.
Thanks but I don't really get that. hehe

HT
 
It's not just the total current, it's the power dissipation in the regulator you have to design for. If you have, for example, 25V dc on the reservoir caps at maximum line volts supplying a 1A dc load at 18V, then the power in the regulator is (25-18) * 1 = 7W. This needs a big heatsink, and I would also not consider using less than a 2A regulator part.

The point about using positive regulators for both + and - output rails is that you build two identical floating 18V PSUs using 2A or 3A positive regulators fed from two separate secondaries on the mains transformer. You then connect the - output of one of them to common (ground), and the + output of that supply is the +18 rail. For the other supply, you connect the + output to the common, and the - output becomes the -18 rail. You can't use a single bridge rectifier with centre-tapped transformer as on your original schematic, although you have drawn it as two windings joined in the middle as a centre-tap.
 
I found a schematic online with a psu of 2 LM338 and I guess i messed up some things..
All is going to be fixed tonight.

HT
 
I guess I might be wrong..
Those language barriers(?)..
I'll post a link to the schematic and would love to see another schematic of a psu of this type. Anyone got a link?

Heres my:
http://www.rollingthunder.se/saker/api/PSU-sch.jpg
I think you got the diode bridge in the -18V PSU wrong way round. It should be the same as the +18 PSU.

I find that sometimes I need reverse diodes across the output rails to ensure regulator start-up after a short absence of power, especially if the load circuits have unequal bulk capacitiance to ground on the + and - power rails.
 
Yeah, I didn't translate your post right.
And I guess I wont get the new post either.

I read on a audiophool-forum that using many caps instead of, say one big might cause motorboating, and that's bad i guess.
Is that true?
I don't know what motorboating is but I'll search.

HT
 
Hi again!
Now my psu is working, i guess.
It measures right anyway.
Now I'm trying to get the preampboard to test ok.

Thanks guys for the help!

And some pics:

PB170008.jpg

PB170010.jpg

PB170012.jpg


HT
 
Thanks!!

I found it at work.
Used to be some sort of automationthing.
I had to mod it quite a bit to make things fit.

HT
 
Let me guess, you could get some info at the folowing telephone number: 0586 81000.
Those are my secret agent skills at work :cool:

Nice work, we want more moduls.
MORE! :green:
 
Thats right Regis but I don't think the support is valid anymore.
I want more modules aswell.
Some work left to do.

HT
 
[quote author="Handcrafted Tone"]Wow that looks great Tom!

where did you get that case?[/quote]



Try RS Components part# 1198861, they look very similar. The brand is Rittal

OR

part# 4182339, made by Schroff
 
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