New Product Idea - Stereo Trimpots - Page 1
Forum section: electronics / projects

author: German_EE
author_rank: Super Contributor
timestamp: June 25, 2017, 01:33:57 pm
content: Another idea for a product which is not (yet) manufactured, you can get stereo or dual track potentiometers but not dual track trimpots. I was setting up an audio amplifier this afternoon after I repaired it and had the idea after adjusting the separate left and right audio gain trimmers.A stereo device might be a little taller (maybe 10mm or so) but I don't see any problems in manufacture. Yes, I know that I could use two digital potentiometers but I want something to tweak,

author: Ian.M
author_rank: Super Contributor
timestamp: June 25, 2017, 02:06:07 pm
content: That's when you use a subminature dual gang vertical PCB mount pot with a slotted stub shaft and a shaftlock collar. Alternatively, some of the rectangular enclosed trimpots are adjustable from either side and are stackable if you have tight fitting X section shafting to gang them.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 25, 2017, 02:08:01 pm
content: What's an audio amp need trimmers for?More broadly: what does anyone need trimmers for? I use them very rarely.Tim

author: German_EE
author_rank: Super Contributor
timestamp: June 25, 2017, 02:10:54 pm
content: In this case to set the bias on the final stage, as an adjustment to eliminate crossover distortion and to set the audio path gain per channel. Three trimpots per channel. Don't blame me, speak to Pioneer.

author: fcb
author_rank: Super Contributor
timestamp: June 25, 2017, 02:13:57 pm
content: I think if there was a need for a ganged trimmer it would have existed - along long time ago.

author: jeroen79
author_rank: Frequent Contributor
timestamp: June 25, 2017, 04:09:17 pm
content: Isn't the purpose of trimmers to adjust for variations in other components?It would be unlikely fot both parts of a stereo to have the same variation.I agree with fcb.Looking at the construction of trimmers making a dual version would not be that complicated so if there was demand for them they would have been made.

author: Fungus
author_rank: Super Contributor
timestamp: June 25, 2017, 04:26:17 pm
content: The whole point of a trimmer is to compensate for the variations in all the other components in the path. You NEED to adjust each path separately.

author: DaJMasta
author_rank: Super Contributor
timestamp: June 25, 2017, 05:19:22 pm
content: Yeah, I think trimmers are usually a cost cutting device in a design. You put a few in your design to allow you to compensate for wide tolerances of cheaper components and less stringent assembly requirements. Instead of paying the premium for 0.1% resistors, top notch soldering jobs, and 2oz copper (for example), you spend a little on trimmers and you go with 5% resistors, regular soldering, and a 1oz board and just pay someone to tweak the trimmers in the final testing stage (which you're doing in either case). Or instead of using a controlled impedance substrate and measuring your hand wound inductors, you use FR4 and 20% inductors and just trim it up to spec (again not a fantastic example, but the point is there).I think the difficulty of a stereo trimpot lies in manufacture.... they're not super consistent because of the mechanical wiper aspect, and with trimmers, generally your adjustment range is smaller and using a smaller range will be harder to match between the two channels. Then if you get like two 1% trimpots in one package.... how do you make them track to the same value? Even if they track completely linearly, you're likely to get one that it slightly offset from the other, so you'd just need another trimpot to compensate for the offset thus defeating the purpose.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 25, 2017, 06:52:25 pm
content: Quote from: DaJMasta on June 25, 2017, 05:19:22 pmUp until you need a tech to hook up test leads and turn a screwdriver, perhaps!This application sounds 100% like something that can be completely and positively solved in design. Toss in a couple more transistors to servo things, or just use properly temperature matched bias networks, or a thermistor or what have you. It's lazy design, and not the good kind of lazy (fixing things in the design so you don't have to have techs poke at your circuit!), just bad design.And, therein lies the best answer to the OP, I suppose -- a good design avoids trimmers altogether; or if some sort of adjustment is always required, it should be taken out to a CV (control voltage) and adjusted by DAC (in which case, ganged adjustments are trivial: run them all from the same CV!), or perhaps a digipot or MDAC if it has to be proportional (but not wideband, since those parts tend to fall off around 200kHz). Other situations can be handled by more specialized chips (scope front end ICs, RF PGAs, or analog switches, for digitally variable gain). More specialized applications, especially at lower quantity where the NRE is comparable to production cost, can handle the bother.Tim