Single trun Vs. Multi turn trimmers

[Mike Nichting]

What is the difference/advantage/disadvantage of the single turn trimmer vs. the multi turn trimmer??

  Is there a clear advantage to always using a multi turn over a single??

Thanks,
Mike N.

[R.G.]

You use multiturn when you need very, very fine gradiations on adjustment. Usually proper attention to design detail means you can use the less expensive and more reliable and always cheaper and smaller single turn variety.

[aron]

About the only time I have used multi-turn was for biasing circuits.

I have used those locking pots as well for amplifier biasing pots. $$

[Paul Perry (Frostwave)]

In making a run of stuff, sometimes there is so much variation in components (eg transistor gain) that you need a multiturn for fine adjustment. If you are just building a single unit & have the time, you can usually just tack in a pot temporarily & than make one up with selected resistors at the end of a smaller pot as R.G. suggests. I found I had to use a multi turn in my ring modulater, also handy fr tweaking the resonance section of some filters. Bob Pease hates them with a vengance, but I have had very very little trouble (less than one per 200).

[Mark Hammer]

One of the advantages of multi-turns is that you can bludgeon the chassis to death with your Doc Maartens, and the trimpot value won't move very much.  The same amount of jostling and trimpot movement in a single-turn  might result in greater trimpot error/drift over time.  But remember we're talking worst-case scenario here.

Like Paul, I found a multi-turn was immensely helpful in nulling out the on-board VCO signal in my Anderton/EPFM Ring Modulator.  IN that case, the trimpot is used to get rid of something annoying, as opposed to adjusting something so that it works well enough or sounds good enough.  Under those latter conditions, a single-turn is generally more than sufficient.

Also, as Paul suggests, you can increase the "precision" of a single-turn by narrowing down the range you want it to adjust over, and using a fixed/variable combo.  So, if the schematic calls for a 10k trimpot, and you have a pretty good sense that it might only need to be adjust in the zone close to 10k, you could sub a 6k8 fixed resistor and 5k trimpot in series.  That way, instead of maybe only 10 degrees of trimpot rotation being any use to you, adjustment would be spread across maybe 40-60 degrees of trimpot rotation, which lets you zero in more accurately.  You end up with less precision than a true multiturn, but way more than a conventional single-turn.

[Mike Nichting]

hey Thanks all~!!  That makes complete sense to me~!! I was afraid I would get these out of this world explanations and end up in the same boat as when I started. Which happens sometimes :-)

  I now think back on a circuit that I had to bias the transistor voltage and couldn't get it close enough with a single turn pot. I kept missing by about .3-.4 volts no matter what I tried.

I will keep the rsistor/trim pot idea handy and I might just try a couple of multi turns on my next few projects.
It wouldn't hurt to use a multi turn even if you didn't need one would it??
That would fall under "better too much than too little" wouldn't it??

Thanks again~!!!!!!!!

Mike N.