choke input power supply filter

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#21
I am using a choke input power supply for my ZEN V4 (outboard, with IXYS diodes and RC snubbers a la Hagerman) and my horn speakers have 104dB sensitivity. However, the amp is absolutely dead quiet, no hum, no buzz, no nothing. So maybe your problem is somewhere else?

Note that switching noise can also create RFI and can couple directly into your amplifier circuits. You should try and move the power supply away from the actual circuit, and also minimise the loop sizes in your PS.

Lastly, especially if you intend to optimise the power factor, you should increase the input choke to beyond the critical value, e.g. by swapping the 3mH and 120mH inductors. If L is below this value it is strictly speaking a capacitor input supply. My 5 cents ......
 
#25
Hi Firestorm....

This thread is a bit old...so I reviewed it...

I gather that 2.5mh of inductance is not enough to reach critical inductance with the amount of current being drawn...

but the Aleph 30 Amps have been working...sound very sweet...remember, that I had some large Signal Transformers that were almost free. Their voltage was too high...so I was looking for a way to get to 25 volt rails. Choke input seemed to be a way to cut down the voltage, and seemed to have some other advantages.

So choke input worked for me...
 
#26
I'm just reviving this thread yet again - no doubt it's always of interest. I have some chokes which are 280mH and 2.7A. Could be used singly or in parallel. I've used them for DC filaments for DHT tubes like 300b, but not for a solid state amp. What do I have to worry about with turn-on spikes with larger value chokes like this? Can somebody explain how pure choke input, choke input with small cap in front (like 220uF) etc. works with regard to spikes? I have a multimeter but not a scope, and I don't know if a spike would show on a multimeter.

I note the original Nemesis used a similar size choke. One version has 150mH at 2.5a and another 200mH.

andy
 

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#28
I don't think that Andy suggested the above circuit to have a choke input power supply.
Omitting the 33mF/40V before the choke would make the power supply choke input (clear enough) and drop the final DC supply to about 25 V with the same power supply transformer.
Enough to be found on behavior of choke input supplies with regard to current spikes IMO.
 
#29
Yes - Pieter is right here, I'm basically asking what to do with the 280mh chokes I have. Whether I can use them for pure choke input, or with a small cap or with a large cap depending on what the behaviour is regarding spikes. A friend of mine uses chokes in his power supply for a JLH amp and his opinion what that 280mH is unusable because of the spikes it would cause, so I was including the Nemesis to show a similar size choke being used. In this case the input cap is 33,000uf as stated, so does that mean a smaller cap or pure choke input was rejected as unsuitable?

Andy
 
#30
I am using 300 mH (nominal value) chokes in a PS with 2A load and I do not get any turn on spikes at all, or turn-off spikes for that matter, even if there where spikes the heavy load would dampen them.

220uF in front of the choke is not such a good idea I would say. It somewhat defeats the purpose of the choke, can cause ringing and may not be able to manage the ripple current. Try to simulate your PS in PSU designer, I found that it is pretty accurate and should even show you the start-up behaviour.
 
#33
Thanks for that - I'll look into that.

I just tried out some chokes in the PSU to my little digital amp - 280mH + 22,000uF in the positive and negative legs coming from a bench supply. You can clearly hear a difference in the sound. Not the same kind of amp, but still it shows chokes can make an improvement. Must look into this some more.

Andy
 
#34
andyjevans said:
No doubt followed by 50,000uf or something.
Click to expand...
It is an LCLC, first cap bank is 33 mF, followed by a 1,5mH choke (all outboard) followed by 30 mF inside the power amp. I am currently redoing the outboard PS after I finally managed to find a trafo case that can hold everything. It is going to be LCLCRC, 3 times ca. 28-30 mF. I know it is completely over the top but then I had some space left in the trafo case and enough caps to fill that space.
 
#37
andyjevans said:
You mean 300mH > 33,000uF > 1.5mH > 30,000uF. That's pretty nice. Does the 1.5mH do something useful here?
Click to expand...

Hello Andy,

It acts as another low pass filter, will further reduce ripple, and should also filter out any switching noise and line noise that still gets through the choke (up to its resonant frequency which I believe lies somewhere in the 100KHz range) - 1,5 mH because I had, otherwise I would have put in a higher value, say 2,2mH - 4,7mH depending on DC resistance and current handling.

what kind of heavy duty chokes do you use in the input? 300mH seams a little bit to much for 2 A.
Click to expand...

Hello Peter

I am using 150Nb/65 cores, they were custom wound by Experience Electronis here in Germany some years ago. Actually they can handle 4A and at 2A they do not buzz and do not even get warm. The PS is running at 55V loaded which becomes some 85 Volts unloaded; originally I wanted to use 63V caps, so this would have required a bleeding resistor as a precaution in case the nominal load got disconnected. This and some misunderstanding how a class A amp and its power supply act when playing a signal.

I ended up using 100V caps so no need for the bleeding resistor. If I had to do it again I would probably get smaller and cheaper chokes though the higher value does not do any harm. As a matter of fact the resonant frequency of the PS will go down with increased inductance which is a good thing. Lastly, I was toying with the idea of getting Mundof chokes but now my personal choice would be to contact trafo manufacturers and ask for custom built chokes. There are quite a few around so you might get exactly what you need at a reasonable price.
 
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