Capacitors and trimpots for Haible String Filter

Resynth · Joined: Jan 20, 2019 Posts: 4 Location: UK

Hi

I'm building a Haible String Filter and currently sourcing components.

Jurgen specified "Wima MKS, Siemens MKT or similar". I'm using Mouser who stock Wima MKS but they don't make them in the 1.5nf to 10nf range. No huge drama as there are Kemet PET caps in those values but it got me thinking...

Why does Jurgen specify PET caps when PP and PPS types are known to have lower distortion are readily available at a similar price. Of course I'd be inclined to trust the designer, clearly he was a clever man and must have had a reason? Is it simply a case of PCB space or is there some reason not to use PP or PPS?

Also, I'm shocked at the prices of buying 40 multiturn trim pots from the quality makers such as Bourns, Vishay, TT. The Suntan trimmers from RS are a 3rd of the price so very tempting but I'm concerned about quality.

Have people had good/bad experiences with Suntan?

Has anyone tried building a string filter without trimmers, ie using 1% caps or fixed resistors sized for each filter?

Only other issue is availability of LM394 or SSM2210 matched NPN pair. I'm going to try a SSM2212 on a SOIC to DIP adapter but thought I'd mention it incase anyone with experience has comments on this?

Cheers
Ben

Boerge · Joined: Sep 02, 2009 Posts: 80 Location: Germany

wackelpeter · Posted: Mon Feb 11, 2019 3:40 am Post subject:

I usually stick to these trimpots from Reichelt:

https://www.reichelt.de/praezisionspotentiometer-25-gaenge-stehend-1-0-kohm-64y-1-0k-p2711.html?&trstct=pol_14

Regarding the Suntano, are they of better quality? Asking because i had some faulty ones from that other brand (maybe approx. 1 out of 20 or 30) and when soldering i find they don't make good contact with solder, contrary to all other through hole parts i use... haven't tried any other solder or temperature as i use for other parts, maybe some more temperature would solve this, but i doubt it and wouldn't want to heat them extensively...

Resynth · Joined: Jan 20, 2019 Posts: 4 Location: UK

Thanks for your replies.

Boerge - Good to hear the Suntans are fine and Reichelt have them as well as the wima caps. Reichelt have cheaper TL072's too so I'll use them.

That AS394 looks very nice with it's gold plating, blingin!

Wackelpeter - My understanding, from reading around the web is that the Suntans are better than the cheap unbranded trimmers. It's always hard to tell from reading what others have to say though, many say only the expensive brands are any good but good to hear Boerge has good results with Suntan.

Ben