Choke input PSU...


I would like to try a choke input supply instead of my current capacitor type.

The output voltage is now around 50V and minimum current is 2.6A (idle current for two class A channels).

The current transformator is 36Vrms, and this must be changed to about 60V for same DC output voltage. Then I need a choke of approx. 25-33mH and able to handle 3A...where can such a part be supplied?

And, if output current exceeds the 3A, output voltage will go up....this might be good for dynamics in short musical passages?

And, if output current exceeds the 3A, output voltage will go up....this might be good for dynamics in short musical passages?

When I tried simming a choke input in PSU2 for an F5 I got the voltage going so high and so low on different current draw that I feared for both power-caps and transistors in the amp. You need CLC to keep the voltage stable. Only a few amp-circuits with absolute constant current draw is suitable for choke input. (I am no expert, just my findings based on some discussions and sims).
I am using a choke input filter at ca. 55V 2A for a ZENV4 and it works like a charm. My coils are a bit "on the big side" with 300mH and 4A rating (do not ask how I arrived at that value), size is 150b, weight 10+ kilo a piece, and they where custom made by a local manufacturer.

Thye X-over coil you showed "looks" to be a bit small. I found a formula on the WEB on this page Tauscher chokes (also in English). They calculate the energy requirement for a coil as E = 0,5 L I² and you can then look up the necessary size for a given coil type. With a normal EI type E96 core you would be in the right ballpark. Maybe you find E96 coils for crossover networks that have the right inductance. Otherwise you would be better off having them custom made. Btw., having a higher than necessary inductance does not do any harm.
Hello Doug,

DC resistance is 0.7 Ohms, low enough that they do not warm up noticeably at 2A load. I started off with some wrong assumptions/plans, hence more inductance than I needed, but it turned out that more inductance does not do any harm (except the higher cost). The only problem is getting the whole (outboard) PS assembled into one box.
Can anybody in the UK, or elsewhere, recommend an air cored choke suitable for a monoblock F5 that does not cost an arm and a leg, as I'll need four? I get very confused when faced with the range available and would appreciate some expert advice. Most inductors seem designed for crossover use rather than power supplies and might be adequate, but I'd rather not risk stressing them or causing a bonfire!
To design a choke input supply, here are some of the required equations:
To get the Q required (1 or less) = 1/Rdc *(sqroot(L/C))
L (minimum) = Vin rms / Imin = .01 H= 30V rms / 2600 mA
For 1 channel using a LL1694 Q = 1/.9R (Sqrt(.08H/.18F)) = .73
Minimum Choke goes to .02H for a single channel F5.

The required capacitance and inductance is truly enormous. I would hate to see a .02H air core with a low dcr. CLC are much more practical. What fun is that? :)

Many thanks for your rapid response DougL. I now realize that my question might have been misleading. I intend to use around 90,000 uF capacitance per rail, but having read some of the discussions would very much prefer to employ an inductor (as well as some resistance) to couple them CLCCRC..... Using PSUD to model the PSU shows that a very low ripple can be achieved this way. I had innocently assumed that 2mH would have been the required inductance, but clearly have a lot to learn. Any suggestions for a suitable inductor at a realistic price?
For a CLC or CLCRC type supply, you have a lot of flexibility in choosing inductor values. in an LC or LCRC, having a high enough inductance is critical for success. The equations I posted are for LC, not CLC.
For a CLC, a standard crossover air core will melt before it saturates, and it would take a lot more current than you are using to melt even a 20 gauge one. From looking at parts express, you are looking at $8 to $12 each. Not insignificant, but not outrageous.


Thanks Doug - you have reassured me a lot. There are many coils available, but they all seem to be for use in crossovers or SMPS so I was anxious that they could be dangerous in an F5 even in monoblock form. Do you have any advice on value in this format or is it simply bigger is better as elsewhere 2mH seems to be the preferred choice for two channel F5 power supplies? Nick