Decent Parts?

[ricach]

I've run out of old stock I had lying around for years - pots and jacks mainly. I needed to replace a scratchy pot so I drive to Radio Shack and buy one. What junk. The first 1/4 turn I get nothing, then like an on/off switch - boom comes the volume. So I figure I'd order from one of our favorite suppliers of tube amp parts. That pot is just as scratchy as the 50yr old one I'm trying to replace. And 1/4" jacks I bought are cheap looking, and the nut appears to have been stamped out of a huge sheet of metal. What gives? Anyplace offer consistant - good quality parts? I don't mean pots from one place, jacks from another, toggles from a 3rd.

[Paul P]

Having almost finished buying a whole bunch of parts for my soon to
be built amp I can say it's not possible to buy everything from one place.
Not everyone carries the same parts and there can be big differences
in prices. The best example of this is a Carling 110-P push-on push-off
switch as used in foot pedals. Mouser sells these for 17.93$US ( !! I've
talked to them about it), Digi-Key sells them for 8.26$US and you can
find them from small places on the net for 6.00$.

Mouser's prices can be ok for most stuff and they have a huge selection.
But Mouser doesn't sell good pots and Digi-key does (by Precision Electronic
Components). Digi-key also sells wire in less than huge rolls and they carry
the Hammond stuff.

Little things, like good Fender pilot lamps, can only be bought from small
internet operations.

I try to buy as much stuff as possible that's made in North America, which
is usually a good way to ensure quality.

My order of preference is Mouser -> Digi-Key -> Little Guys.

It's amazing the amount of time that you can spend hunting down parts
on the net.

Paul P

[Jag]

What junk. The first 1/4 turn I get nothing, then like an on/off switch - boom comes the volume

It sounds to me like you got a linear pot instead of audio. If so, it wouldn't be the fault of the part or supplier.

A pot can sound scratchy if there is DC on it. My guess is you have a leaky coupling cap and it's passing DC from the previous stage. Check for DC on the input to the pot and, if you find it, replace the coupling cap from the previous stage. I'd probably check the other coupling caps too.

I do agree, however, that there are a lot of crappy parts out there.

[ricach]

The caps and resistors are all new in the preamp section, but I did reuse the existing pots. So when I decided to replace the one, I replaced it with the same thing it was - linear. However, I now notice my newly designed preamp was supposed to use audio-taper.

Why would linear cause this problem? Brings up a another question, is there a specific reason to use either linear or audio in volume and tone controls? I would guess audio is good for volume so you have more control, but linear in the tone pots. However, I notice Fender TMB use audio as well.

[Enzo]

Radio Shack?

Would you expect to get a top quality steak at 7-11? Or an Armani suit at K-mart?

Radio Shack sells cheap stuff for kids to play electronics with. I go there for fuses or maybe an emergency diode.

You get good parts at good parts suppliers. That is why we are always referring to places like Mouser, Allied, Digikey, etc.

[Chuck H]

I pine for the days when I could drive to my local mega electronics store and buy almost everything I needed to build an amp.

I watched that store go from a booming business, then to a clearing house, and then to a single counter in the corner of a 1/2 acre building where you could place an order from a couple of catalogs. The rest of the building was in the process of being leased out to pool supply and furnature vendors. Then gone. All over the course of 5 years. Maybe I'm getting old and stubborn, but I don't think as a population americans are as contented in this information / E-comerce age as we were before.

Now I have to Email 9 people, wait for a response and open a new PayPal account every time anything about my service changes just to buy parts that typically arent as good as what I used to be able to get "down the street".

FWIW the name of the store was Quement Electronics on Bascome Avenue in San Jose California.

JM2C...Sorry for the rant

Chuck

[ricach]

Well Enzo,
When I just need a pot, and don't have a list of things I also need and then wait for days after I order it, I thought I could get away with just a simple part at Radio Shack. My worse case scenario thoughts were that it just won't last as long as a good one. Didn't imagine it would be unuseable. But I will again drive to my Radio Shack and buy and audio-taper pot and see if that works.

Jag, I'm still curious how you pegged it being a linear pot. I can't figure out why that would create that scenario. It wasn't that it ramped up quickly, it went from zero to 4 completely passing over 1,2 and 3.

[MWJB]

"it went from zero to 4 completely passing over 1,2 and 3." Zero to 4 what? 4 pounds, 4 inches, 4 gallons, 4 dancing elephants? :-) These are just arbitrary numbers either painted on a knob or face plate - they are not values of anything that your amp actually understands. Even audio taper pots have varying tapers, where one 1Meg pot might read 22K at say 9 0'clock, another audio pot might read twice that. The circuit that the pot is in may also affect the effective taper.

You can tweak pot tapers by putting a resistor in parallel with the relevant portion of the pot (wiper to ground on a volume), however the total value of the pot in ohms will be just the value of the resistor rather than the original pot value. Do this sometimes with amps used for harp that are too "touchy" and will never be used flat out. OK if you only ever played the original pot at somewhere less than flat out, no good if you need to play the amp as if it were wide open with the old pot.

[ricach]

"it went from zero to 4 completely passing over 1,2 and 3."
Zero to 4 what?

Just speaking metaphorically.

[MWJB]

I know...it's just one of my pet peeves, gets me all irrational. :-)

When guys say things like, "I always set my controls to 5"...it's meaningless - a manufacturer may have used a 10% taper pot on one amp, if they ran out/new stock came in then they may have used a 30% taper, maybe even a linear on the next one (before we even consider other factors like instrument, speaker etc). Setting an amp's controls "by eye" just seems totally mad to me, I try and get folks to take "the leap of faith", shut their eyes and set by ear.

[Steve Conner]

Yes, that's why the "11" thing in Spinal Tap is funny.

[Enzo]

Well, that's one louder, innit?

[Chuck H]

Rob: "Well...Why couldn't you just make 10 louder and make that be the loudest number???"

Christopher simply says: "These go to 11."

God I love that movie.

The guy who now sings with Creedence Clearwater Revisited (in John Fogertys absence) is my brother in law. Doug Cliffard and Stu Cook continue to tour (Elliot Easton from the Cars played guitar for 'em for a long while). I quote that movie sometimes in his presence and he says "I don't get it. It's just not that funny 'caus thats how it really is with these guys on the road." His stories are just as funny and amazing as the movie, I swear to god.

Chuck

[PRNDL]

Why would linear cause this problem? Brings up a another question, is there a specific reason to use either linear or audio in volume and tone controls? I would guess audio is good for volume so you have more control, but linear in the tone pots. However, I notice Fender TMB use audio as well.

The problem you describe is characteristic of linear pots, which is why they use audio pots in both volume and tone circuits.

The basic reason is because audio is a logarithmic function in both frequency and volume.

Radio Shack parts aren't really that bad.
They're not great, but I'm really glad they're around.

[gwbdopesmoker]

A tube tester in every hardware store !