suitable inductors for alephX supply

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nobody special

nobody special

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Joined 2002
#1
I have been looking critically at my supply lately, and have found that I really need an inductor to get rid of some of the ripple at the output. The problem I'm having is that my transformers are only delivering about 13.5 volts UNLOADED, and I am biasing the amp at 7A. When I use a reasonably-sized air core inductor of about 2 mH, I get quite a drop in the output voltage. This is even using a 14ga. air core with a resistance of .310 ohms! I have seen iron core or ferron core type inductors with less resistance per inductance. Are these suitable for use in an amp that will be drawing a constant 7 amps? Will they saturate? Can anyone recommend a suitable part?

Here are the specs on my supply...
per rail:
12V (13.5V unloaded) rated 20A transformer.
35 A bridge pack
inrush suppressor after the bridge- .5ohms cold resistance- .04- .05 with 7A current through them (CL-101)
(10) 6800µF capacitors
inductor- to be specified
(10) more 6800µF capacitors

I will eventually be going with a different transformer- one that will get my rail voltage up to about 16V. For now, I want to get all the voltage possible out of my cheapo transformers with as little ripple as possible.
Any suggestions will be appreciated.
Also, I'm in the US, so keep this in mind when recommending a part's source.
Thanks.
-NS
 
#2
Hi NS,

I'm been thinking of the same problem. Given the high
current draw of the Aleph-X, the DCR of the inductors
is a big concern. From what I've read here and elsewhere,
the torobar from Intertechnik looks very interesting.
Unfortunately I haven't located a source for them in North America. 🙁

Dennis
 
#3
I have also thought about this and have been considering winding my own using a kit some companies sell. Also, I have been talking to a couple of motor winding repair shops and one said to stop by next week for some pointers. Some thing to consider... I don't know if this is really do'able, considering time/effort vs return.
 
#4
Dennis,
Yeah, someone recommended those to me before, but it's not worth it to me to try and get one shipped overseas.
Given the high
current draw of the Aleph-X, the DCR of the inductors
is a big concern
Click to expand...
Absolutely! And also considering the low rail voltages... a couple volts with a 35 volt rail aleph isn't such a big deal. When you are talking 12-15 volts, and you are running a balanced amp, it starts to really cut into your output capabilities.

Philo,
Rolling your own may be the way to go... let us know if you decide to do it, and how it "turns" out (pun intended, ha ha). :clown:
I wonder how big a 12 ga. 2 mH inductor would be physically?

I did consider going with a CRCRC type filter, but it cuts into the voltage just as much, and the results aren't nearly as good.
 
#5
One shop gave me a guestimate of "a little smaller than your fist" for 12AWG 2.5mH (which was an "off the cuff" rating guess for what I might need). This sound a little large but probably not far from the truth. I am going to try and put together a couple of sizes and test them. Not using "Perfect Lay" type square or flat wiring also has a size impact. I need to get my final gainclone together this weekend and finish putting my DIY heatsinks together before I try this project. A friend agreed to loan me his home-built winder for the project. I am hoping for an attempt next week but don't wait on me. It always seems something comes up right when you having the most fun...
 
#8
What about these unit used in cars and boats

<a href="http://www.allelectronics.com/cgi-bin/category.cgi?category=945&item=NF-10&type=store">AUTO/MARINE RADIO NOISE FILTER <br>
<img src="http://www.allelectronics.com/images/gold/full/NF-10.jpg" ></a>

American International # S-10-ACL. Reduces and eliminates ignition and alternator interference (noise that increases or decreases with engine speed). For stereos, amps, equalizers and CB radios up to 10 Amps , 150 Watts. 4" x 2.27" x 1.9" high.
CAT# NF-10
Your Price: $2.50 each

Aren't they Just A choke and Cap in a flashy box

Radioshack also has/had the following
270-030 Basic Noise Eliminator 4A
270-051 10-amp Noise Filter
270-055 20-amp Heavy-duty Noise Filter

Specs for the 10 Amp Noise Filter
270-0051 Specifications Faxback Doc. # 9546<pre>
Input Voltage:........................16.0 VDC Max.
Input Current:........................10.0 Amps Max.
Voltage Drop at 10 Amps:..............0.4 VDC Max.
Attentuation:........................1000Hz: 22 dB Min.
4000Hz: 38 dB Min.
DC Resistance:........................0.04 Ohms Max.
(ALL-01/26/95)</pre>

The 270-030 looks like this
<img src="http://www.radioshack.ca/images/RadioShack/27/2700030l.jpg">

I haven't been able to find any specs for inductance


Regards
James
 
#9
Nobody special,

What about just using a .2 ohm resistor and a big cap like they use in car pro audio?

Or let me have an e-mail from you I may have a pair of inductors
that fit your need. (( at a real real good price))
 
#10
James,
I think that those type of filters are only effective at higher frequencies, like what would be generated by alternator noise. 120Hz needs a fair amount of inductance, which I'm sure that these type devices don't offer. Thanks for the suggestion though.

Bob,
Inductors are much more effective in getting rid of the ripple... I was originally going to go with an RC network, but found that I would cut the ripple from 80-100mV down to about 5-6mV by using an inductor.
I decided I will just have to put up with the dc drop and use some heavy gauge air coils. Transformer upgrades may be in my future.
-NS
 
#15
If you have the space you can parallel two inductors. That will cut the dcr in half and any heat the inductor produces will also be shared and lowered per inductor. You have to make sure the inductors are not too close together or they will vibrate. How close to place them depends on the design of the indcutor. You just have to experiment a little by moving them towards each other until they vibrate too much.
 
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