General question about transfomers & psus (jlm stuff included)

[atticmike]

Howdy there,

I'd like to gain a little more knowledge on the juice side of builds.

Here are my question:

1. Basically, in order to almost have no head dissipating from your power section, you'd be needing to draw the AC * 1.4 exactly on the board, having the transformer's A capacity spread all over the rails?

2. The JLM Powerstation & AC/DC kit speak of at least 15 VAC input. Does this mean I could run those with a 30 to 50 VAC transformer at 12 V secondary voltage and set the rails to 15V? At this point, I wouldn't need the +48 v pump rail.

3. To what current is the 48V pump rail trimmer supposed to be set? Is there a default for supplying phantom power because as far as I know the 48V phantom power are not really 48, rather somewhere over 30 and 35V?

4. If your build had apart from +/- 18 V draw one nother rail of -24, would you have to go 18 at the secondary voltage just because the -24 foils the balance? Or could you also draw it with a 15 secondary voltage? Guess not right?

Thanks in advance, hope someone can answer my question.

Mike

 

[JohnRoberts]

Howdy there,

I'd like to gain a little more knowledge on the juice side of builds.

Here are my question:

1. Basically, in order to almost have no head dissipating from your power section, you'd be needing to draw the AC * 1.4 exactly on the board, having the transformer's A capacity spread all over the rails?

generally unregulated PS has some extra headroom to account for mains voltage variations and the like.

2. The JLM Powerstation & AC/DC kit speak of at least 15 VAC input. Does this mean I could run those with a 30 to 50 VAC transformer at 12 V secondary voltage and set the rails to 15V? At this point, I wouldn't need the +48 v pump rail.

don't know

3. To what current is the 48V pump rail trimmer supposed to be set? Is there a default for supplying phantom power because as far as I know the 48V phantom power are not really 48, rather somewhere over 30 and 35V?

Phantom power is 48V DC.

Thanks in advance, hope someone can answer my question.

Mike

JR

 

[atticmike]

Howdy there,

I'd like to gain a little more knowledge on the juice side of builds.

Here are my question:

1. Basically, in order to almost have no head dissipating from your power section, you'd be needing to draw the AC * 1.4 exactly on the board, having the transformer's A capacity spread all over the rails?

generally unregulated PS has some extra headroom to account for mains voltage variations and the like.

2. The JLM Powerstation & AC/DC kit speak of at least 15 VAC input. Does this mean I could run those with a 30 to 50 VAC transformer at 12 V secondary voltage and set the rails to 15V? At this point, I wouldn't need the +48 v pump rail.

don't know

3. To what current is the 48V pump rail trimmer supposed to be set? Is there a default for supplying phantom power because as far as I know the 48V phantom power are not really 48, rather somewhere over 30 and 35V?

Phantom power is 48V DC.

Thanks in advance, hope someone can answer my question.

Mike

JR

thanks mate, most appreciated

How much dc need those psus at least to pump up the 48v?

If I was to take a guess, I'd say 17.5 by the 1.4 rule of thumb?

 

[abechap024]

Hello,
I think you might be over-thinking it a bit. I think there is a little bit of a language barrier but you might be confusing "Voltage" and "current". Both are 2 very separate things (as you probably already know!)

The JLM power supplies use a voltage doubler/tripler. Its needs to be fed AC for this to work. Basically you WANT to give the regulators some extra voltage to work with. So if you get a +/-15V transformer, after you rectify and smooth it you will get about 20V or so and that is perfect for the regulators to then smooth to +/-15. Does it have to be a 15V transformer to get 15v?

No

Its very possible to use higher voltage, but that equals more heat dissipation from the regulators, and I've also squeezed some +/-15v rails from a 12V power transformer for a personal build, and it works fine but not usually good practice if you can help it.

if you needed +/-18v and also 24V just have the transformer feed all 3 regulators.

 

[atticmike]

is it actually possible to do the negative doubler rail mod with the +48 rail as a regular with the ac/dc kit from jlm?

 

[abechap024]

is it actually possible to do the negative doubler rail mod with the +48 rail as a regular with the ac/dc kit from jlm?

sure you might need to cut some traces though, or depending on how its grounded you could flip the polarity. but probably easier to just get what you need until you read up on it.

 

[squib]

I agree you are mixing up a few terms and concepts.

you want + and - 18v and +48v (phantom) and -24v.

is this to power SSL5000 modules?

If so, the -24v does not need to be regulated. A well filtered supply will be fine.

You can get all these from a 3 rail JLM PSU if you use a transformer with dual 18v secondaries.

You will need to tap the raw -v pre-reg voltage on the pcb and bring it off the board to an additional filter consisting of a 22R series resistor and 2,200 uF of capacitance. This will then be your -24v rail. If you don't understand how to do this I can draw you a diagram.

Now comes then question of the VA ( watts ) of the transformer used. This is determined by the current draw by what you have hooked up to the power supply but is also limited by the specifications of the JLM module ( if this is what you are using ). To power two SSL5000 modules a 30VA transformer will be fine.