vol pot comparison Q

[tubenit]

On my Tweed Overdrive Special, I keep the volume pot set at around "5" about 95% of the time.

So I measured the 1MA vol pot to ground and it's about 136k.

I'm thinking I don't need a 1M pot and can use a 500k instead. And with 136k to ground on a 500k, that there will be less resistence going into the pot.

In other words, I am thinking that a 500k (136k to ground) will actually be louder and/or brighter than a 1M (with 136k to ground)?  The 1M only becomes louder when it has more than 500k to ground.

Am I thinking thru this correctly?

With respect, Tubenit

[jeff]

Set to 136K to ground and try jumpering a 629K resistor across the hot side and wiper of the volume pot. That'll be the same thing(for this setting).

[RicharD]

Your plan seems logical to me.  Your AC loading is the 120k plate resistor in parallel with the switchable tone stack in parallel with the volume pot.  Depending on the switch position, your tone stack can be the greatest load.  Going from a 1M to a 500k may allow you a little more clean headroom, but it isn't drastically affecting the load.  Certainly no harm in trying.  A 250k pot may even be better.

[tubenit]

Thanks guys!

I think I need a 680k resistor paralleling instead of 629k. But I understand the point and will try that. 

The other 5% of the time, I may exceed 250k to ground so I'll work with the 500k. Good idea though.

With respect, Tubenit

[jojokeo]

Tubenit, I posted this a month or two ago in that I've stopped "blindly" using 1MA pots for volume and gain controls for a while now because of this very issue. I dislike always feeling the need to put a treb bleed cap across the pot's lugs and this actually creates an unbalanced condition which I find unfavorable for most conditions. When the vol is set about in 2 to 4 range it becomes abnormally bright and the brightness gets more balanced the further up you go on your setting but you don't always want to play at higher settings. Sometimes the brightness is just too much for the tone & sound or clarity you're after and w/out the cap it's too dark. Many times the added brightness also brings in too much humm and/or hiss to the noise floor too? So for these situations I will first try either a 250ka or 500ka pot or for the treb bleed method put a resistor in series w/ the cap which also will work nicely in a lot of situations. Start w/ a 47k in series w/ a 500pF across the vol pot's lugs and see it brighten up but still keep some hiss away and the brightness isn't over the top.

The other way to look at this is taking the minimalist approach is always best in using less parts count and getting your parameters set up right so as not needing a bunch of extra components when it's not necessary.

Lastly, more than the resistance value you measured corresponding to your vol level, it's the voltage divider that's created btwn the two values of your measurement (together w/ the 1ma pot) that's important. Likely your vol position may actually stay the same but you'll have the added brightness/clarity w/ the lower value. Use my voltgage divider spreadsheet and you'll see this new value change to be even less when re-measured for the same output using a lower value pot. This will result in even more benefit "to brightness & clarity" when it comes to changing the values.

[jeff]

If you really want an A/B switch, get a ganged 1M pot. Connect one section as normal and connect both wipers. Use a dpdt switch to connect/disconnect the outer lugs. Two 1M pots set to the same level with all lugs connected is the same as a 500K. If you like the 500K better try again with a ganged 500K and see if you like a 250K even better. This would give a nice A/B test at any volume setting. Instead of trying to remembering the sound before you unsoldered the old pot and resolderd the new pot and trying to compare from memory(hard to do).

I seem to remember using a 250K pot for volume after a tone stack(cuz that's all I had on hand) and not getting good bass responce. When I switched to a 1M I got more bass. So maybe the cap,resistor filter frequency will change with the different pot. Don't know much about that. Don't know if when you lower the pot you need it increase the cap, but maybe something like the second schematic is in order. Where the second caps value is the same as the original's.

[jojokeo]

I don't think this is necessary as your ears will let you know right away if you like it or not. You use alligator clips and don't even have to install the pot to get instant comparrison.
As for the pot's value vs freq response - yes it can impact it but not as much being the vol pot as if you changed values of the TMB pots or other components. It will have an impact "more or less" on impedance and signal loading depending on how and where you use it BUT in "most" cases this is simply not as significant as it may seem, IMHO.

[LooseChange]

Or do what I do. Strap a 1m resistor across the outer legs of the 1m pot and, BAM, it's a 500k pot.

[jeff]

When it's on ten. But I think it's different if you turn the knob. Especially with that cap across it.

[HotBluePlates]

I'm thinking I don't need a 1M pot and can use a 500k instead. And with 136k to ground on a 500k, that there will be less resistence going into the pot.

In other words, I am thinking that a 500k (136k to ground) will actually be louder and/or brighter than a 1M (with 136k to ground)?

I could understand brighter. I don't see how it could possibly be louder, though.

The load on the first stage is the volume pot in parallel with the tone stack's impedance to ground. If you make the volume pot a smaller value, you increase that load, which should reduce the gain and output voltage of the first stage.

Best test is to do what has been suggested and clip in a resistor to see how it performs for you.

[tubenit]

I changed the pot out to the 500k and it was somewhat brighter and as HBP stated it isn't louder. I found that I still wanted a 220p bright cap on it though.

With respect, Tubenit