Pots! What brands are good?

[makinrose]

What brands of pots do you guys use?  I lots of builder seem to favor the old style CTS pots but I've been using Alpha with no complaints for years.  There a lot of good prices on pots on AliExpress but I'm not sure of the quality. Does anyone have any experience with those brands? Thanks guys!

[K O'Connor]

Hi makinrose

For the most part, most brands of pot are pretty reasonable and the cost=quality notion is itself not entirely reliable. This means you can get a 25-cent pot that works well for decades and a very expensive one that fails or becomes noisy. Sometimes it is just a bad sample.

When I started building amps, I used whatever pots were available to me from local suppliers, or from broadline vendors as I found out about them. A lot of custom stuff and mods were done using "no name" pots. When I started building amps as company products, I standardised on PEC pots because they were needed for the Power Scale circuits I was using at the time. These are 28mm with smooth shafts as standard - no options for knurled shafts, just for shaft length when buying quantities.

PEC went a bit nuts with their pricing, so I designed them out and switched to 16mm pots everywhere. My local suppliers carried Alpha-Taiwan pots but the shaft lengths would vary with the pot value and taper. Needless to say, you want pots with uniform mechanical characteristics so you can use one style and type of knob. I found a Chinese supplier that I still use today and I can get the shaft length I prefer with knurled shafts that match the knobs I use.

When choosing pots, you have to keep in mind what knob you want to use. For example, when modifying Marshalls, you can buy Marshall knobs that have a set screw and fit 1/4" smooth round shafts, and knobs that are push-on to fit a T18 knurled shaft. This allows you to mix pots that are physically different. I'm seeing more styles of knobs that come in both set-screw and push-on forms, which greatly alleviates some of the problems amp builders and modifiers have finding such things.

For the hifi stuff I build, I use 1k linear and log pots from Bourns that are 9mm. I get these from Mouser.

[makinrose]

Hi makinrose

For the most part, most brands of pot are pretty reasonable and the cost=quality notion is itself not entirely reliable. This means you can get a 25-cent pot that works well for decades and a very expensive one that fails or becomes noisy. Sometimes it is just a bad sample.

When I started building amps, I used whatever pots were available to me from local suppliers, or from broadline vendors as I found out about them. A lot of custom stuff and mods were done using "no name" pots. When I started building amps as company products, I standardised on PEC pots because they were needed for the Power Scale circuits I was using at the time. These are 28mm with smooth shafts as standard - no options for knurled shafts, just for shaft length when buying quantities.

PEC went a bit nuts with their pricing, so I designed them out and switched to 16mm pots everywhere. My local suppliers carried Alpha-Taiwan pots but the shaft lengths would vary with the pot value and taper. Needless to say, you want pots with uniform mechanical characteristics so you can use one style and type of knob. I found a Chinese supplier that I still use today and I can get the shaft length I prefer with knurled shafts that match the knobs I use.

When choosing pots, you have to keep in mind what knob you want to use. For example, when modifying Marshalls, you can buy Marshall knobs that have a set screw and fit 1/4" smooth round shafts, and knobs that are push-on to fit a T18 knurled shaft. This allows you to mix pots that are physically different. I'm seeing more styles of knobs that come in both set-screw and push-on forms, which greatly alleviates some of the problems amp builders and modifiers have finding such things.

For the hifi stuff I build, I use 1k linear and log pots from Bourns that are 9mm. I get these from Mouser.

That's very helpful.  I'm largely building and repairing vintage-type amps for customers so I'm often using set screw style pots and the smooth shafts with 3/8" bushings. My experience has been positive with the 16mm pots but customers often balk at "mini-pots". I'm going try out few different brands and find what I like.

[K O'Connor]

Hi makinrose

As TUTs say, magazine reviewers and most players lack the technical knowledge to state categorically that any specific component is "bad" let alone that an entire class of component is "bad". In your relationship with your customers, YOU are the technically knowledgeable party so it is YOU that decides if a pot is good enough for you to install. You end up either hand-holding your clients, or just do the job and do not discuss parts other than that parts you use are what you know to be good.

Some techs let the customer dictate component choice and let the chips fall where they may. This is particularly sad when $$$ parts like transformers are in question. Of course, if a customer like that comes along you are not obliged to accept their work.

Speculators on the internet are simply that: speculators, which in this case means "guesser", "gossiper", "parrot" - take your pick.

[makinrose]

Hi makinrose

As TUTs say, magazine reviewers and most players lack the technical knowledge to state categorically that any specific component is "bad" let alone that an entire class of component is "bad". In your relationship with your customers, YOU are the technically knowledgeable party so it is YOU that decides if a pot is good enough for you to install. You end up either hand-holding your clients, or just do the job and do not discuss parts other than that parts you use are what you know to be good.

Some techs let the customer dictate component choice and let the chips fall where they may. This is particularly sad when $$$ parts like transformers are in question. Of course, if a customer like that comes along you are not obliged to accept their work.

Speculators on the internet are simply that: speculators, which in this case means "guesser", "gossiper", "parrot" - take your pick.

I totally agree.  It's been challenge for me.    After I read the TUT series a several years ago I realized how many little things I could do better with my builds and started to employ those changes over time.  The switch over to Galactic Grounding, better filtering,  better layouts, and more use of radial caps have all improved the sound and performance of my builds enormously but have also forced me to answer lots of questions from customers. I've stopped posting pictures of the inside of my amps. In fact  I've gotten to point where I don't allow customers to pick out parts at all but I still get lots of questions.  The question I get a lot is: "Is it exactly like the original amp?".   I don't mean to complain but it's wearying process contending with "internet experts" and the advertising people buy into.  

I'm definitely going to try out few different brands of pots and see what I think is good.  Thank you Kevin.  As you know good information is hard to find and I appreciate your advice.

[jmcd]

I like to use alpha pots with 8mm bushings. I like to use anti-rotation tabs, and the ones on the 8mm-bushing pots are more substantial (yet possibly a bit thinner). And the body of those pots seem to make better contact with the chassis.

I also like the feel of the alpha pots on amps. They have a nice feel (and audible swoosh, if you listen closely).

[K O'Connor]

Hi Guys

Jmcd: In other words, you are using 24mm pots. 16mm pots have about a 7mm bushing.

An "audible whoosh" is just from the noise in the circuit... you hope...

For either size, but likely more usual on the smaller pots, the bushing is cast aluminium along with the bushing and front face of the pot.i always use the anti-rotation tab, which requires drilling a small hole beside the hole for the bushing. The mechanical drawing for the pot you wish to use will give correct dimensions, or just measure the pots once you have them in hand.

Have fun

[jmcd]

Hi Guys

Jmcd: In other words, you are using 24mm pots. 16mm pots have about a 7mm bushing.

An "audible whoosh" is just from the noise in the circuit... you hope...

For either size, but likely more usual on the smaller pots, the bushing is cast aluminium along with the bushing and front face of the pot.i always use the anti-rotation tab, which requires drilling a small hole beside the hole for the bushing. The mechanical drawing for the pot you wish to use will give correct dimensions, or just measure the pots once you have them in hand.

Have fun

Yes, 24mm pots. But with the smaller-diameter bushing.

The audible swoosh is mechanical and doesn't come through the speaker. It's due to the stiffness of the wiper, I guess. I like it on my amps but not on my guitars

[Champ81]

I thought most of the alpha pots were carbon track element. 
I got some alphas from mouser for bias adjustment and realized they are of metal element.  Always used to carbon  pots. Are there any differences?  I'm not going to go into audible differences with bias pots. Is metal better in terms of reliability or other factors?
Really want to know your thoughts.. or if this even matters for my circuit.

[K O'Connor]

Hi Guys

There are no "metal element" pots, you must be referring to ceramic or plastic elements. The plastic element is usually the longest life-cycle.

When setting bias in push-pull set the first side of the circuit by meter so you know the idle is safe, then set the other side by ear for minimum hum with NO SIGNAL into the PA. The bias pot may make a noise while being rotated if the track is dirty. The noise is related to the DC shift and the unevenness of the track.

[Champ81]

I'm not sure but this has got me confused. Attached is a screenshot of the pot in question. Specs on mouser.

[K O'Connor]

Hi Champ81

Please provide the actual part number.

A search at Mouser shows many Alpha pots listed under the filter "metal element", but the data sheets for what comes up say they have a metal shaft but do not actually state the track material type. 15k-cycles is typical for carbon.

[Champ81]

I ordered several of them. 
All of them say "metal" as the element.
Unless they mean cermet which consists of ceramic and metal particles 


RV16AF-10-15R1-B50K-3CLA
Linear B50K


RV170F-10-15R1-B50K-0021
Linear 50K


RV120F-10-15F-B50K-0075
Linear D-Shaft 50K


RV16AF-10-15R1-B50K-3DLA
Linear B50K Solder L


RV16AF-10-20R1-B50K-LA
Linear 50K Solder Lu


RV170F-10-20K-B50K-3021
Linear Knurled 50K


The last two pots have an interesting look to them. The back of the body is black plastic and the pot casing is the same diameter as the ones you provided bit the width is a bit smaller. The solder lugs are spread out instead of parallel to each other. However the lug holes and lug are small and it would be difficult to solder 4 pieces to it (in this case 2X20awg wires, a resistor lead and capacitor lead). The lugs for these two are very thin compared to the others. These are rated 1/10W.

Also interesting and one ive never seen before.
RV16AF-10-15R1-B50K-3CLA has a centre detent. So when I turn the pot it "snags" or "catches" in the middle. Notifying you when you are mid way. This might be a useful thing to have to know when the pots are at mid point when biasing.

[K O'Connor]

Hi Guys

Cermet is what I referred to as ceramic.

The pot with a center detente is intended to be used in audio as an EQ control or balance pot.

For bias control, you do not want a pot with detentes.

The detentes actually interfere with setting the pot near the detente point, as the metal spring that makes the detente forces the wiper to settle at the detente point only or anywhere far away from it. A range of setting positions is then lost. This has a lot to do with how the manufacturer implements the detente, which can be quite gentle or require significant force to rotate into and past.

You can get pots with up to 40 or so detentes. These are used as an inexpensive replacement for a multi-position switch and resistor stack for feeding preset voltages to computer circuits (ADCs). They are not that useful in audio as direct controls.

As far as mounting / wiring several components to the pots: Where the convenience of simply hanging everything off the pot lugs is undeniably appealing, it will often be more useful and easier to service / modify in many situations if the components are mounted elsewhere, on a terminal strip or eyelet card, then just single wires tie to each terminal on the pot. Think about how easy / difficult it is to undo any of the pot connections. Think about the bulk and weight of the added components. Think about if you need to change the pot or any of the related components.

[Champ81]

Thanks Kevin

Thats precisely also what was in the back of my head. Serviceability. And was contemplating on adding a couple of small terminal strips onto the chassis so only the components. In this case the 500k resistor and cap in parallel are soldered onto the terminal strip lugs with wires leading to the pots themselves. In that case it would be a heck of alot easier to unsolder and remove just the components if need be.