to ...trim or not to trim?...

[alderbody]

Do you keep the trimmers on your projects,
or you replace them with fixed resistors as soon as you find that "sweet spot" value?

For instance, would you keep the trimmer on the Collector resistor of Q2 in a Fuzz Face circuit?

or, the two biasing resistors on a rangemaster?

OK, i would never leave the trimmer on, unless it's there for biasing.

or am i wrong anyway?

EDIT: what's the best thing to do, tonewise?

[petemoore]

  I've used a socket for 'that' resistor.
  sticking a Variable resistor pot [whatever value pot will allow the range of R needed to find bias point], adjust the pot to find the resistance desired, then carefully removing it to not re-adjust the setting, measure the resistance that provides the bias you want, and then insert a fixed resistor to the socket...then your pot [linear wiht wires from wiper and an outside lug] can be used over and over.
  To get a wire into a socket lug, tin the end, then if you have flat jaw pliers you can make a flat 'spatula' lead end that goes in the socket easy.

[R.G.]

Tonewise, it does not mattermuch unless the trimpot is a truly sorry, low quality one.

Trimmers are a two edged sword. They let you adjust it ... just right... when you do the initial setup. But they also let the next guy - or you, after you've forgotten the details - maladjust the pedal some time later. I would never leave a trimmer on a project unless it needs periodic tweaking, for instance to correct thermal drift in a ring modulator. Correcting thermal drift in the bias of a Fuzz Face is marginal. A Rangemaster, I would not leave a trimmer in.

I guess my internal rules are
1. If you mess with it all the time, make it a front-panel control; if you do this, limit the control's sweep so it doesn't make the effect get into non-functional regions of operation.
2. If you have to adjust it now and again to correct drift, make it a trimmer.
3. If you can find a magic setting that you never want to change, remove the trimmer.

But then my history is in the commercial world of electronics where a manufacturer will go to great lengths to NOT put a trimmer in. It costs too much to have someone set the trimmer, and the customer can then mis-adjust the trimmer themselves - service calls, warranty costs, drift, etc.

[burnt fingers]

I left the trimmer on my fuzz face.  I have it set too where it sounds good to me.  I suppose a good option would be to mark the trimmer with a sharpie when you find the sweet spot.  then if you or someone else has the urge to tweak later you can still go back.

Scott

[petemoore]

  Sometimes these trimmers are touchy, I tend to have trouble hitting the teeny spot on them which is the correct resistance to set up bias voltage for the application.
  Using stop resistors + smaller trim values to equate a resistance often makes the trim set task easier to do.
  For a FF Q2CR as trimpot, I'll often pick a resistor around 5k and add that as a stop R to the 10k trimpot, this allows adjustment between ~5k to 15k.
  [With a 20k pot used as V/R for FF bias, I've found the desired resistance sometimes is near a touchy spot on the pot and/or isn't available...could be crappy pots.
  ..I also used this method to find sweet spots and limit [the top box mounted] pot as Q2CR with stop resistors and pot value/taper resistors [across some potlugs] to limit variable resistances that were within mostly good operational ranges, if the pot got inadvertantly turned, the device would still work, and usable bias range would be spread out over the 0-10 settings of the pot.

[Sir H C]

Not as much a problem with most of these circuits, but often the tempco of the trimmer will differ from the other resistors in the circuit and so you could have issues where your sweet spot goes away as the temperature changes, worse than it would if the resistors matched tc's.

[The Tone God]

Trimpots can be handy but I tend to try to reduce their use and use them only in settings that can change from unit to unit. Otherwise I tweak the value and use tight tolerance components.

Temperature stability is an issue. If the trimpot is unsealed then humidity can affect things as well. Another thing that irks me sometimes is the force required to turn the trimpot can throw off the reading. As you find that "sweet spot" under rotational tension when you release the pot it will change settings slightly. Some trimpots have the same issue in their physical design laterally so when you press on the pot it's value changes. Headaches all around.

Andrew

[MartyMart]

I get through many dozens of trim pots, all the Jfet sims have 100k's and all my fuzzes have
50k/20k trimmers too. ( makes bias very easy )

I've never removed any of them !! ( never thought about it ! )

I quite often have to "adjust" so I just swollow the 50p each one and forget 'em

MM.

[petemoore]

  I know I'm gonna wanna swap transistors...so I do the same thing, I like having the dials on the board, and so do people who look inside the boxes....lol.

[Stephen]

I guess in the perfect world you can trim, than use a fixed resistor...

I have never really seen, as  I have watched voltages where a germanium transistor will not drift with temp ..age..etc....

I am thinking of leaving trims in my projects and also transistor sockets..I never did before but am getting to notice it is a convience and WHY not??? 

Beats unsoldering and resoldering ...WHAT a MESS !!!!!!!

[MartyMart]

I am thinking of leaving trims in my projects and also transistor sockets..I never did before but am getting to notice it is a convience and WHY not??? 
Beats unsoldering and resoldering ...WHAT a MESS !!!!!!!

The only two projects I have without sockets, was when I ran out once !!

( I soldered VERY carefully ) 

MM

[petemoore]

  It was cool when I put my finger on a GE and watched the bias change quickly and alot, try it sometime.
  I think I also noticed bias changes after playing through certain transistors after a while, it feels like they lose their 'bite'?
  I wonder if a buncha trimpots on drains in a row might cause noise, I had noises in amp sim[?s] that could be eliminated by bomping the box..

[alderbody]

Thanks for sharing your thoughts and practices with me!

As mentioned above by many, i also socket my transistors (especially the Ge) and use Multi-turn precision trimpots,
so the issues about humidity or difficulty in finding the sweet spot are off.

Yes they might cost much more, but i do it for me and for my pleasure,
so any "budget" restrictions and stuff or a possible mis-adjustment do not really apply here.
Nobody touches the guts of my pedals... 

And as i wrote before, i only use the trimpots for biasing and never in the signal path.

btw, it's really fun to watch the reading on the DMM while playing with a Ge loaded pedal and see the values drift with time/temp/etc

As for panel mounting, i utilized this practice in quite some times.
A great example is my WahWah pedal which has external resonance and mid controls (plus an inductor selector),
while in the inside there is a trimpot in Q1ER for gain adjustment of the ...Ge transistor