Ripple in unregulated supply for class-A amp

[agdr]

I think the ferrite core on those will go into saturation if used in differential mode. Here is some info, 5th paragraph down:

Application Notes: How To Select And Use Ferrite/Nanocrystalline Common Mode Chokes : CWS Coil Winding Specialist, manufacturer of transformers, inductors, coils and chokes

But those CM chokes are cheap enough you could give it a try! Whatever impedance they wind up producing may be enough to do the job.

Another thought is just one 0.25 ohm 20W resistor between the two 40mF cap banks, rather than the 3 0.1Rs. The results are nearly as good.

[IG81]

I'll be trying some of these common-mode chokes, a couple of these are already on they way to me. They're pretty cheap in any case. I'll see if they work, but I get it now that the core might indeed saturate in differential mode.

They Hammond chokes have too much DCR for my application, I would have to had planned for them from the start or to lower my power output as it stands.

If the CM chokes don't do it, I wonder if the primary or secondary winding of a small transformer might do?

IG

[IG81]

The common-mode donut chokes do seem to be saturating. They have some effect, but no where near what simulation predicts. Tiny power resistors do help out, but not enough on their own. It's kind of hard finding something that'll happily pass the 8 amperes required. The secondary winding of a small Hammond 166L24 transformer I have has under 1ohm DCR and I measured its inductance at ~43mH. This one worked really well and took down ripple to ~20mV. It was unfortunately on the fast track to heath-death and would not have lasted more than a few minutes IMO.

IG

[AndrewT]

try using a transformer out of a dead microwave oven.
Use the existing coils. take off the existing I of the EI and re-attach using paper as a gap filler in the EI.
You now have a gapped EI choke. and it cost you nothing.
Vary the gap to see what effect it has on inductance and saturation, if any.

[IG81]

Originally Posted by AndrewT

try using a transformer out of a dead microwave oven.
Use the existing coils. take off the existing I of the EI and re-attach using paper as a gap filler in the EI.
You now have a gapped EI choke. and it cost you nothing.
Vary the gap to see what effect it has on inductance and saturation, if any.

That's where my thinking was leading me, large salvage transformers, microwave sounds good for this. I might have a couple of regular cheap power transfos to try first though.

~30mH and up might be good and DCR should stay below ~1.5 ohm.

IG

[epicyclic]

post 7 .......demeterart


+1

[AndrewT]

the two microwave oven transformers I have salvaged do not have interleaved laminations.
They have all the I's on one side. That makes them very easy to dismantle and just as easy to reassemble.

[IG81]

Originally Posted by epicyclic

post 7 .......demeterart


+1

I might consider this down the road, but killing the hum at the source seems like a worthy first step IMO.

IG

[AndrewT]

CRC or CLC instead of C alone.

I always use the analogy of rCRC rather than omitting the leading r.

When you use C alone that missing r when replaced gives rC. You are using a filter with very little filtering effect due to the small r.

When you put in a real and useful R, the filter attenuates the hum much more.

[IG81]

Originally Posted by AndrewT

CRC or CLC instead of C alone.

I always use the analogy of rCRC rather than omitting the leading r.

When you use C alone that missing r when replaced gives rC. You are using a filter with very little filtering effect due to the small r.

When you put in a real and useful R, the filter attenuates the hum much more.

I had some mild success with some CRC attempts around 1ohm last night. I also have burn marks on my fingers. 8 amperes is a lot for anything above 0.1ohm.

IG