Calrec PSU question

Just before I build the Calrec EQ PSU - just one question that is really having me scratch my brain cells
On Jakobs site - it mentions using
"
Use a 2x15V transformer and 7815/7915 for +/-15V or a 2x18V transformer and 7818/7918 for +/-18V.
"
I have read all the posts here about regulators needing a bit more voltage than specified to work..
Should I be using a 2x18v transformer and 7815/7915 for a +/- 15v - to leave enough extra volts for the regulator to work..

Or have I got totally the wrong end of the stick...

Both will work.

with 15V transformers you'll get 15x1.4142V=21.2V unloaded, which is enough for 7815/7915 to work. But with 18V transformers you have extra margin - and some extra heat.

Jakob E.

Many thanks
I was going to heatsink the regulators anyway
I have a 30VA 18v and I was going to feed four of them with it...

That should work nicely..

> regulators needing a bit more voltage than specified to work..

Transformers are rated for the RMS of a round-wave, while most DC power supplies charge-up to the peak of the wave.

15V AC into the standard rectifier-capacitor will give about 21V DC.

My rule of thumb is VAC = VDCreg+3V. So for a regulated 15V supply I "should" use 18VAC. But I am very conservative, and a "15VAC" transfomer may run 17-18VAC when lightly-loaded.

So for small supplies over maybe 12VDC, just use VAC=VDCreg.

For large supplies, or low-volt supplies where the rectifier drop is not "negligible", add 3V.

If, like me, you have years where the "120VAC" is closer to 109VAC (the city's main power station exploded 2 years ago and they fed the city on temporary feeders), always round-up. And use extra sinking in case the 109V bounces to 129V.

What do I need to watch out for if I am powering 4 units?

Should I regulate each one seperately?

How many volt amps will I need in the transformer?

d./

I found this part at digikey.

TE62084-ND is is 50VA. If that is overkill..
There is a TE62064-ND that is 35VA.

Thoughts?

Do I need to regulate each channel seperately?

I am using a 30VA transformer - and Jakobs design for the PSU on the Gyraf web site.
I drew the circuit using a etch resist pen but at the end of the circuit where you have the 18-0-18 (or 15-0-15 depending on your regulator)
The original looked a bit like this....

|......|......|
X.....X.....X


The Xs were the holes for the outputs..
All I did was keep the lines going... (so only 1 regulator was used)

|......|......|
X.....X.....X
|......|......|
X.....X.....X
|......|......|
X.....X.....X
|......|......|
X.....X.....X

Then I just put in three way molex connectors into each bank of holes (i.e. 4 of them) and connected the molex connectors to 4 x 5 pin XLRs to each Calrec box (I am using 5 way because I am sending +24v/0V from another transformer to power some relays and illuminated lamps)
Note - I think I know what I am doing - I am just learning and taking advice from the fellows here...

What are the relays for?

[quote author="thedug"]What are the relays for?[/quote]
i am planning to replace the 4 pole and 2 pole switches with one push button switch that illuminates when switched on...
The relay will from one on/off switch - switch 4 conatcs in and out of the circuit - I can also hang the lamp voltage from the relay circuits as well
I am in the process of drawing up the PCBs - will post when I have time (in the next few eeeks ) I will have a go at doing the handmade PCBs

Hey Guys I'm building a Stereo unit with a 18V transformer.
I built Jakobs Mini PSU.. what is the best way to get power to both units?

Is it as easy as taking 3 pairs of wire (2 wires from 0. 2 wires from +15. 2 wires from -15.) from the output of mini PSU board. Or do I daisy-chain them some how.

Clueless!

I measured one channel about 130mA (65mA each rail +/-).

Looks like a 30VA transformer can feed the whole calrec desk :green: :thumb:

Hi,

so, 15VA, 2 x 18V, is enough to run two channels of eq at 15V? Also, do the regulators of the mini-psu (gyraf) require heatsinking? I noticed they're getting pretty hot when feeding just one channel...

It sounds great by btw! :guinness: :thumb:

thanks,
corneel

15VA is enough for two channels. The regulators needs heatsinking if they get hotter than they can be touched for a second or so..

Hey guys;

I'm losing my marbles.. I can't figure out the correct wiring for the power transformer to mini PSU. I know its essentially the same as the PSU on the GSSL. I have built 2 different mini PSUs in many different configurations with different components and still its not right. I was wondering if someone could tell me how to wire this puppy.

I have been trying to wire both AMVECO transformer - 62063 (2 X 15, 832mA) and 62064 (2x 18, 694mA)

Here my 2c..

For 115V do the following:

Input:
Connect the Yellow and Red wires and connect Black and Violet. These are for you mains-input.

Output:
Connect Red and Brown, this is your center 0V, Green and Blue are your AC lines that will feed the regulators of the mini-psu.. Worked for me.

Adios,
Corneel

Thanks that cured my first issue.

Much appreciated! :thumb:

I am having issues with wiring up the PSU and xlr connectors. I included a link with a pic of the layout of the board. Could somebody possibly check out the layout and paint the correct wiring of the calrec?

Thanks,

Pax


http://www.geocities.com/paxworth21/calrec.html

Hey Guys;

easy question for you. is the mini-PSU considered a Dual power supply or split power supply?

are dual power and split power supplies the same thing?