Quick question about powersupplies

[API]

I am racking a pair of old Cadac modules and have previously bought the Fivefish 2448 powersupplies using them with 2x15v transformers.
Setting the voltages i have no problem (24v plus 44v) but when i connect the modules the audio power drops to 40v.
So my question is, do i need to up the ampere rating of my transformers or should i up the voltage as well?

 

[pucho812]

how are you measuring your PSU's sounds like there is no load when you measure them?

 

[API]

Maybe i was not clear enough.
I easily can set the +44v without any load but when i hook the modules up the voltage drops to about +40v and i can not trim the voltage up any higher.

 

[pucho812]

I would look for failed parts in the cadac modules, dead caps perhaps

 

[API]

The modules are likely not the problem.
I have tried with about 10 different modules, all recapped, and they all work but the voltage drops every time.
I suspect that the powersupply can not deliver enough juice to power them.

But would love to hear any more theories.

 

[Harpo]

..but the voltage drops every time.
I suspect that the powersupply can not deliver enough juice to power them.

Assuming you try to power your modules from the two positive rails of the 5fish psu, there is insufficient power from the phantom voltage rail (designed to supply 4 condenser mics, IE 40mA, worst case 56mA). Main bottleneck here are the two 100uF caps at the voltage doubler. Next bottleneck is your 30VAC center tapped transformers secondary voltages. You won't get clean 24VDC out (the voltage regulators want about 3V more in to maintain regulation) and the 44VDC out would need a voltage tripler in front from 15VAC in to get there.
I'd get a piece of perfboard and build a different psu with a different mains transformer. If you still want to use the 5fish psu in an at least mindbending way, you don't use the phantom rail but use the positive rail set for +20V and the negative rail set for -24V from the 5fish psu. The 5fish V- out now being your 0V reference voltage, 5fish Gnd your +24V and 5fish V+ out your +44V in respect to 5fish V-, the offsetted/new reference voltage. Use insulated standoffs, so a once-was-gnd on pcb doesn't short to your case ground. Still a dual 22-25VAC or 44-50VAC center tapped transformer in front needed with sufficient (AC) VA rating to deliver the (DC) current demand (factor 1.8 for fullwave bridge rectification).

 

[API]

Not sure if we are looking at the same psu, therre are no 100uf caps in the 2448mkII psu.
This was designed to power Yamaha modules and not only condensers with the 44-48v rail and the 24v and 48v path are exactly the same.
Either way, i found the full pdf for the modules online and 5fish recomends at least 2x18v for these so will mot likely get 2x22v transformers and give that a try.

 

[kato]

Yep, that is correct. No one should have ever told you that you can get to 48v with a 15+15 secondary. The math doesn't work out. (At least without a voltage tripler.)

Joe Malone added a jumper to his PSUs to select between doubler and tripler depending on whether you have >18v transformer or <18v.  Much interesting discussion at JLM audio on the subject...