2sc1583 on minimoog vcf?

capicoso · Joined: Nov 19, 2012 Posts: 128 Location: Argentina

Hello. Can i use 2sc1583 instead of match the bc547s? The only problem I see is that on the bc547 a 47n cap is between each emitter. But the 2sc1583 has only one lead for the emitter...
thanks

gdavis · Posted: Tue Feb 11, 2014 6:39 pm Post subject:

Well, that one problem is pretty significant since the caps between the emitters are what make it a filter Wink

I've built a few of these without bothering to match the BC547's. If they're from the same batch they should be fairly close. The filter will still function if they're mismatched, the cuttoff just won't be as sharp.

I wonder if the BCM847 would work. I think it's basically a dual matched version of the BC547. Shoot, now I'm really curious to try it.

capicoso · Joined: Nov 19, 2012 Posts: 128 Location: Argentina

I see, thanks.
So having them matched would make it better to play the filter auto oscillating with a keyboard just like in the minimoog i guess. How good is your tracking? I bought like 30 bc547, i suppose they're from the same batch

gdavis · Posted: Tue Feb 11, 2014 7:12 pm Post subject:

hmm, I don't know how the matching of those transistors would affect the tracking, they're not making an expo converter like the matched transistors in a VCO.

I think the tracking is more dependent on Q1 which isn't temperature compensated anyway.

From what I've gathered, the tracking is actually more a factor of the log compliance of the transistor and the scaling of the CV input. Matching affects the temperature stability of the overall tuning.

I only put a little bit of time adjusting the tracking. It really wasn't very good compared to the VCO, but might be able to get better with more effort.

capicoso · Joined: Nov 19, 2012 Posts: 128 Location: Argentina

Thanks.
I'll try to match them, anyways I don't know how well I can match them with a cheap multimeter...

marfoski · Joined: Jan 26, 2011 Posts: 36 Location: Italy

capicoso · Joined: Nov 19, 2012 Posts: 128 Location: Argentina

Thanks, matching them right now Smile

and to gdavis
on that link someone asked

ultrashock wrote:
there are also BCM847 and BCM857 transistors (M at the end means matched). And I noticed they are also cheap (out of stock at Digikey now). So, could they be used for our purposes without matching as such a ".1%" transistors?

Yes they are definitely useable in expo converters but be aware that they are SMD components not thru-hole.