[BUILD] 1176LN Rev D DIY

[tommypiper]

I'm building 2 channels in one box. Looking closely at the power supply options.

Option1:
Onboard PSU, run two boards supplied by one torroid power transformer. What transformer ratings would we need?

There's no regulation on the -10v onboard supply. I don't quite understand how this works. Is it a complete supply as is?

Option 2:
It might be better to use one of the little outboard PSU to supply two channels, instead of the onboard supply.

If so, how do we build it to get +30v and -10v? Isn't that over-stressing the regulators by forcing such widely different voltage supplies? Wouldn't we need like a higher voltage transformer?

Isn't there a potential for crosstalk if the regulation feeds two channels? Is the supply adequate for two channels?

The size of the caps are double on the onboard. So, I'm wondering how can we run TWO channels with half the reservoir cap values (outboard) as ONE channel onboard PSU? That's essentially 1/4 the value per channel.

Is anyone else using the outboard PSU? I've seen no posts on it. I've looked everywhere, does anyone have a schematic for the outboard PSU?

:guinness:

 

[edanderson]

input and output transformers now sold out.

ed

 

[Stagefright13]

Wow Mnats thanks for the free board! I think I owe you a beer! And Ed too! :grin:

As far as the external PSU I believe Mnats mentions it can supply up to 1.5 amps. And the board only uses 40 milliamp. I am going on memory here so correct me if I am wrong. I'm gonna build my external one as a lab supply for goofing around...

If ya check the purple schematic they spec a pretty small transformer. I personally used a 60 centertap. 1.3 amp but that is WAY overkill even for 2 boards.

And I did check my onboard ps when I first fired it up and had +30 and -10 volts where appropriate. I think r81 82 drop the voltage

John

 

[tommypiper]

Thanks, John. The Purple shows 23VA.

Do you have any info or a schematic for the external PSU?

I'm not sure how to get the wide range of voltage.

cheers, :guinness:

 

[ap123]

[quote author="tommypiper"]The Purple shows 23VA.[/quote]

http://www.groupdiy.com/index.php?topic=22073&highlight=y236106

I have an avel lindberg Y236107 (30va 30+30) running two independently regulated rev d boards. This seems kind of hokey to me...but I built one rev d and decided to build a second a couple weeks later. I might convert my 2-1176 to use it as soon as someone tells me what I've done (two psu on one transformer) is a bad idea. There is an option to use trim pots for the adj legs of the regulators. The -10 is regulated by the 337.

 

[tommypiper]

Thanks. Glad to hear you can run two boards off one transformer.

Yes, I know the regulator will control the -10v on the outboard PSU. But I think controlling it from 30v AC from the transformer to -10v DC is over stressing it.

I believe a resistor is needed somewhere to get the voltage closer. Does anyone have a schematic for the outboard PSU?

 

[Stagefright13]

Here's a quote from Mnat's docs:

"The power supply is taken from a later revision. It uses a three-terminal regulator for the +30V 50mA rail rather than a hard-to-get power zener. The negative supply is unchanged."

Sorry no schematic here for the external one.

As for the external PS board all the values are on the board except R1 and R2 wich are step down resistors to drive leds. You would have to calculate them any way depending on output voltage... And also VR1,2 and R3,5. R3 and 5 would be the fixed values for the adjustable regulators to supply the required voltage. And VR1 and 2 would be used if ya wanted a variable supply. Don't know those values off hand but you should be able to look them up.

As far as going from -34 volts ~ after rectification with a 30-0-30 transformer to -10 volts... I'm not sure. Also the -10 supply may use very little power. But I don't know this for sure. Maybe someone more experienced with this could chime in.

John

 

[tommypiper]

[quote author="Stagefright13"]
As for the external PS board all the values are on the board except R1 and R2 wich are step down resistors to drive leds. You would have to calculate them any way depending on output voltage... And also VR1,2 and R3,5. R3 and 5 would be the fixed values for the adjustable regulators to supply the required voltage. And VR1 and 2 would be used if ya wanted a variable supply. Don't know those values off hand but you should be able to look them up.

As far as going from -34 volts ~ after rectification with a 30-0-30 transformer to -10 volts... I'm not sure. Also the -10 supply may use very little power. But I don't know this for sure. Maybe someone more experienced with this could chime in.

John[/quote]

Thanks, John. Yeah, I see the part info on the boards. But I don't really understand how it works or how to figure out what value resistors to put in there. I've read other posts in my searches that say you can't use the LM3x7 regulators to move the voltage more than a very small amount, so I'm wondering why, how this can work to create +30 and -10 at the same time. :? The resistors must set the voltage to a close range, then the regulators do the rest. How do we figure out these resistor values?
Is it me, or is it strange that we have these boards but there's no information. And no one seems to be using them. Why do they have LEDs, for example? Is that part of the circuit function, or is that for our front panels?

 

[nerd]

I am doing a dual using the Avel Lindberg Y236106 (30VA 25 + 25). I built up the Mnats "Little PSU" as described on his site using the variable resistors to set the voltages. It seems to work fine (PSU only, I am not done putting the whole 1176 thing together yet).

The Neg regulator gets warm, but I put a double sized heat sink on it. I think it will be fine.

 

[Stagefright13]

The external psu is for building a supply for 2-1176 or for experimenting. I built a single and works great. But I am very happy to have the extra boards to experiment with! And I will when I have some money for another transformer.

Building a 2-1176 is a bigger project in my opinion. And may require a bit more knowhow and money. I personally wouldn't try a stereo unit without at least building a single first. The biggest fun for me is learning new stuff.

I think I remember in the 80's Radio Shack had those Engineering handbooks or whatever they called them. With circuit snippets including the LM series voltage regulators with schematic examples. And lots of other stuff. Wonder if they still sell them? Hint?

But now I guess the internet has that stuff...

John

 

[nerd]

About the Little PSU: In case I wasn't clear, it works fine at +30, -10.


As for building the dual - This is my first DIY in many years and certainly the biggest DIY I've tackled. I've come across issues building the dual, but probably not what you would think. Aside from the usual FET matching, which was no big deal actually, the biggest problem I am having is jamming all the stuff in one case, trying to find two of everything (o-12s, attenuators), getting knobs that fit and look right with the pre-made case I purchased.

Of course, I am not finished yet, so I am bound to run into a few more things, but I don't anticipate anything major.

 

[mnats]

[quote author="tommypiper"]Is it me, or is it strange that we have these boards but there's no information. [/quote]
I don't possess any special knowledge about electronics and would never consider myself a "designer". That's why my outboard power supply is based on an off-the-shelf adjustable regulator.
[quote author="tommypiper"]I've looked everywhere, does anyone have a schematic for the outboard PSU? [/quote]
I have to ask - but have you looked at the data sheet for the LM317/337? Aside from a few 1N400xes to protect against input and output shorts and the initial full-wave rectification and filtering, the PSU is based on the same schematic in the data sheets. That's why I have never bothered to draw it out. If someone would like to redraw it and host it somewhere, please feel free.
[quote author="tommypiper"]How do we figure out these resistor values?[/quote]
As you will see, I'm no artist either. Here is the basic schematic of the regulator circuit sketched out on the back of an envelope:

Looking at the data sheet, the typical reference voltage of the regulator is 1.25V. The adjustment pin current is typically 50uA. Calculating the current through the 120 ohm resistor: 1.25V/120R=10.41mA. Add the current from the adjustment pin: 10.41mA+50uA=10.46mA. That's the current that will flow through the bottom resistor.

Calculate the resistor for the desired voltage and round the figure to the nearest available value. Let's say you need 30 volts: 30-1.25/10.46mA=2749 ohms. Use a 2.7k resistor.

Or use the values posted on my draft PSU page. Or just put a trim pot in place of the fixed resistor and dial in the voltage you need.

Hopefully I don't get busted by the real electronics people on the forum, but I think the above is correct.

[quote author="tommypiper"]There's no regulation on the -10v onboard supply. I don't quite understand how this works.[/quote]
There is regulation of the onboard -10 supply. Try doing a search for "zener regulator".

 

[okgb]

Sometimes the searches are not always that easy BUT gotta appreciate
having a board as nice as your's and gaining a little more electronics
knowledge won't hurt us as we figure it out.

The sreening i really appreciate , and of course the Black is too cool too

thanks for everything so far [ haven't got mine together yet so i'll be back ! ]

regards Greg

 

[mnats]

[quote author="okgb"]Sometimes the searches are not always that easy [/quote]
I agree with you. But you reminded me of something I wanted to add: don't limit yourself to searches of this forum.

BTW, fixed some of the mathematics above...

 

[tommypiper]

[quote author="mnats"]
Or use the values posted on my draft PSU page. [/quote]

Ah! So this is what people have been referring to. I've been searching and could not find that. (That page is linked only from the Gyraf 1176 clone page, BTW, not the Rev D, so if you only read the rev D you won't find it).

EDIT: OK, I've found some better datasheets that cleared this up and actually I was able to look at the indentations on the little PSU card to follow the traces and figure out what you had included and not included from the various set-up options. That made things clearer. For example, you are using the diode protection, but not the bypass cap (which is not needed because the 1000 uF are close by).

I actually had forgetten zener regulation, thanks for pointing it out. I feel like a dolt.

Is there a concern about cross talk with single supply off board regulation for two channel boards?

Which is better, running two boards from the little PSU? Or the onboard supplies fed by one toroid?

Cheers.

 

[ap123]

I linked to the LM337 datasheet in my previous post but it wasn't that obvious enough a link. I had a feeling I could find one of these and I did...it's a voltage divider calculator made for the LM317 and 337:
http://spazioinwind.libero.it/andreabinello/lm317-lm337/index.html

 

[tommypiper]

Edited: redundant

 

[Stagefright13]

Finally done WOHOO! Sounds awesome. Here's a pic:

Thanks Mnats and ED!!   :green:  :thumb:  :thumb:

 

[dissonantstring]

hey stagefright,
nice and clean build! :thumb:
i'm just starting mine so i'm jealous! :green:
whats that honkin' resistor coming off of the AC input to the main board?
-grant

 

[Stagefright13]

A 5 watt 220 ohm to drive the Sifam 12 volt meter lamp. And thanks. I'm warming it up for final calibration now.