Well, I think I need to re-approach this this with a lager power transformer (as suggested over on the Pass Labs forum where I posted originally) with 18v secondaries so I don't have to drop so much voltage. And a choke with much less dc resistance. PS filter caps. Oh and the bridge!
Other than that, I got most if it right!
This is the cost of the alternative I've used with success before.
It just doesn't seem to be heavy enough. Not enough iron!.
Other than that, I got most if it right!
This is the cost of the alternative I've used with success before.
It just doesn't seem to be heavy enough. Not enough iron!.
FWIW: I don’t do class A (at all) but low power AB and D amplifiers with regulated linear PSUs with very good results. When using low power amplifiers with relatively low current demands things get a lot easier.
Your 3A continuously makes it a harder challenge. I don’t have any knowledge of Pass designs but the ACA needs 19V isn’t it? Anyway you want lower voltage drop and very low ripple voltage.
Your 3A continuously makes it a harder challenge. I don’t have any knowledge of Pass designs but the ACA needs 19V isn’t it? Anyway you want lower voltage drop and very low ripple voltage.
The ACA originally came out with 19v, but the current version can take 24v. That is 24v at 1.5 amps continuously for about 8 watts per channel!
I have a 100 watt transformer, but sounds like I need 24v x 1.5A x 2 channels x 2, which is closer to 150 watts. Digikey has a 18v primary 180 watt Hammond for $80!!!!
Maybe I will buy a 35A rated Graetz bridge just to see what happens. But I still have the issue of the under rated choke.
We'll see.
Thanks,
Dan
I expect the 20v CT is 10-0-10. I am using across the entire primary and not using the center tap.
Thanks,
Dan
Rather than go full-bore switching supply, as you already bought your iron, consider using a buck regulator to get full use from your existing trafo. I'm getting good results with something similar to this : https://www.aliexpress.com/item/1005005535867374.html
One to play around with.... default models, click and run. I'm sure someone can make the transformer model better.
FWIW I think the use of SMPS for the ACA is 100% the optimal solution in all regards for this amp and it offers the best performance for this amp considering cost, weight, heat generation and ultimately any noise and ripple at the speaker output. YMMV 🙂
Yes, it was an experiment to check out a CLC power supply filter. It has gone wrong, and there is really no reason to spend money to fix it.
But not able to completely let go, I have some heavier duty rectifier diodes in my parts bin (MBR735 7.5A), so I had to give those a try this morning. And that didn't even make a difference.
So now I can really throw in the towel.
I already have one of those Meanwell power supplies on the shelf, guess I need to spend $20 to finish the 2 ACA bridged monoblocks.
Thanks again,
Dan
MBR735 is also too tight with regard to maximum reverse voltage. Sorry.
You use Schottky diodes meant for low voltage switching power supplies.
You use Schottky diodes meant for low voltage switching power supplies.
Yes, in both cases the reverse voltage of the bridge diodes is too low and they will break down briefly on every cycle.
When the diode breaks down it conducts in reverse which lowers the voltage on the first filter cap and the rest of the output circuit.
The diode PRV needs to be a minimum of 2 x the peak unloaded transformer secondary voltage plus some headroom for AC line voltage fluctuation
In this case 2 x 22.1Vrms x 1.4 = 62V
Use 100V or greater diodes.
For a 2-diode, center-tapped rectifier yes.
For a bridge rectifier, 1 x Vpeak is theoretically sufficient
For a bridge rectifier, 1 x Vpeak is theoretically sufficient
FWIW I also learnt to use twice the peak voltage when using Graetz bridges. No explanation given but probably to be safe in all possible conditions and scenarios. Diodes used to be so cheap overdimensioned ones were chosen anyway.
Let’s say that people that do like that never run into such issues 🙂
Let’s say that people that do like that never run into such issues 🙂
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