[minima] Re: Linear Output Filter Switching

  • From: Mark G0MGX <mark.g0mgx@xxxxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Thu, 06 Feb 2014 18:31:55 +0000

I'm going to have my first bash at the filters and switching tomorrow; I only have some tiny single pole relays plus small ceramic caps - we shall try that first and see what we see!

I'll definitely be using a bigger than needed DIL socket for the CMOS chips! I've also got some of those Darlington transistor pairs in a DIL package that was suggested as the drivers (ULN2803A) so will try them too. Also I hadn't considered that we don't need to switch the lowest frequency filter so lots learned and lots to play with!

Unfortunately I'm off to the Middle East on Saturday morning for a week or so, which means I'm running out of play time :-(


On 06/02/2014 18:25, Wayne McFee wrote:
Hi Dan,

Sure you can definitely use single poles and lower value caps for lower power.

But it doesn't cost much more to build the output filters for higher power than you think you are going to use, so that you don't have to rebuild them when you want to switch out your lower power amp for another one.

Actually the 200V caps should be good for up to 20-25 Watts, for 50 watts they should be higher yet, say 500V units.

But it is all up to the individual builder, and this is really a neat project for experimenting and hacking.

I'm really enjoying all the comments,


On Feb 6, 2014, at 9:46 AM, Dan Reynolds <on30ng@xxxxxxxxx <mailto:on30ng@xxxxxxxxx>> wrote:

Great work Mark. That will get me started for sure. My Si570 should be here today.

Wayne, I think it's a good idea to double the contacts for higher power but I'm probably not going to have a power amp higher than 10 watts or so.

Dan -- KB9JLO

On Thu, Feb 6, 2014 at 5:52 AM, Mark G0MGX <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> wrote:

    Hi Team

    I've done a bit more work on the output filter switching using a
    4028 (which arrived today!).

    The wiki is updated:


    Including a link to a simple sketch to try and illustrate how it
    works and enable others to prototype the ideas as I have.

    There will be more on this topic from me....


Other related posts: