TS Headroom/Volume

[jcknowles89]

Hello All! First Post! love y'alls stuff!

Should be an easy question. So I have done lots of tube amp mods and I am getting into Pedal building and mods. I know that in a tube amp when you increase the Size of a pot (say from 100k to 200k) it increases the Gain/volume as less signal is sent to ground. If I were to do the same thing in a TS style pedal increasing the Pot from 100k to 250k would I get the same volume boost I would in an amp?

Thanks,

[ElectricDruid]

Welcome!

If you increase the value of the volume pot in a Tubescreamer, it won't make any difference. That's because the pot is wired up as a potential divider not a variable resistance, so the value is less important. Instead, the wiper is tapping off a percentage of the signal.

If you increase the value of the gain pot, you'll get more clipping, but it won't really boost the level, because the level is limited by the clipping threshold of the diodes, and you've reached that already when you're at max gain. Plus the pot is already 500K, so it's a pretty high value.

If you wanted more volume from a screamer, you'd probably have to start swapping the diodes for something that would raise the clipping threshold. But it's pretty loud already - those diodes are supposed to have a 1V forward voltage.

HTH,
Tom

[jcknowles89]

Awesome! thank you for the info. So would that mean the inverse would be true as well? If I decreased to Say 10k would it decrease volume/Headroom?

Thanks,

[MJ_Sound_Cubed]

Well if you want clean head room, make the clipping diodes switchable. Here is a cool article:http://www.geofex.com/article_folders/tstech/tsxtech.htm

If you neeed datasheets and other useful links, check below.

[ElectricDruid]

Awesome! thank you for the info. So would that mean the inverse would be true as well? If I decreased to Say 10k would it decrease volume/Headroom?

Reducing the value of the volume pot won't have much of an effect either for the same reason as increasing it won't (although there is a 1K resistor in series which will start to reduce the volume if the pot value gets small).

Reducing the gain pot will give you a milder version of the pedal. If you dropped it to 100K, you'd essentially get all the sounds you can find on the first 20% of the gain knob, but spread out over the whole range, so you could get into the detail a bit more. But you won't get any more or less level.

That level limit is set by those clipping diodes, and as MJ says, if you want more clean headroom, you should look at add switchable options for the diodes. There are loads of possibilities for this - series pairs of "normal" silicon diodes, unbalanced sets of diodes  (two one way, one the other) for assymetrical clipping, LEDs for higher level (blue LEDs tend to be loudest of all, but won't clip much unless the gain is similarly high), MOSFETs, etc etc. You'll find a ton of stuff on this online.

[antonis]

Just to add/remind that Volume(OUT) pot value DOES matter when dealing with circuit output impendace and output high pass filter..
(the resistance between upper & middle lug should be considered as source resistance for whatever it feeds where the resistance between middle & lower lug should be considered in parallel with the impedance of whatever comes next - I presume there isn't any need for output filter definition..  )

[ElectricDruid]

+1 agree with Antonis.

What I said was based on the assumption that whatever comes next in the chain has a high input impedance of at least 500K and hopefully much closer to 1M. If it doesn't, you will start to see interactions and both tone and volume will be affected.