Adding 3-Way Switch for Tone Bypass and Bright Bypass

[MarkF786]

I have an amp with a 5F2A-like tone control:



I'd like to add a 3-way switch to do the following (in no particular order):

- Tone Pot and Bright Cap (C1) Enabled
- Bright Cap (C1) Bypassed
- Tone Pot and Bright Cap (C1) Bypassed

I drew a diagram out on paper that I think would work; I tried to find a schematics tool that to use on my Mac to draw it, but didn't have luck. Since I can't share a schematic, I'll try to explain what I'm thinking. Obviously I'd be using a 3-way DPDT switch, but I think I'd need to use an "on-on-on" switch that works like figure D below in the center position:



So my plan is to have one leg of the switch toggle the connection to the top of C1, and the other leg of the switch toggle the connection to the middle terminal (2) of the tone pot. This should create the following switch positions:

- Tone Pot and Bright Cap (C1) Enabled - the switch would have both connections "closed"
- Bright Cap (C1) Bypassed - the switch would have the connection to C1 "open" and the connection to the tone pot "closed"
- Tone Pot and Bright Cap (C1) Bypassed - the switch would have both connections "open"

My questions are:

1. Would this work, ie. would having "open" connections at these points properly bypass the components, or is it not good to have "dangling" connections like that?

2. Is there a more efficient way to wire it?

I know other people have done this mod before but I haven't found a schematic, and also I've seen different switching options (for example, "On"/"Off"/"Bright") which makes me think there are other ways to wire it.

Thanks for your advice!

Kind regards,

Mark

[Tonewood]

Lifting c1 & #2 on the tone pot is fine, no problem dangling.

I believe that when people talk about a "bright cap", they are talking about a cap across legs 1 & 2 (in your diagram) of the volume pot to maintain treble at low volumes.

scott

[MarkF786]

I believe that when people talk about a "bright cap", they are talking about a cap across legs 1 & 2 (in your diagram) of the volume pot to maintain treble at low volumes.

Yup, and that is exactly what C1 is doing

If you trace the path, C1 connects between legs 1 & 2 of the volume pot, though the tone pot is also in series. When the resistance of the tone pot is between legs 1 & 2 zero, C1 is acting exactly as a bright cap. As you adjust the tone pot, it varies the effect.

The way I look at the circuit, C1 boosts treble and C2 cuts treble; by adjusting the tone pot, you vary the effect of the two. Ideally they would cancel each other at 50%, but that doesn't happen; instead there is a treble boost and cut simultaneously occuring but with different corner frequencies. I find the effect of C1 to be too bright at times, thus my desire to add the ability to bypass it.

There was a discussion on this topic in another thread: http://music-electronics-forum.com/t18949/

[Tonewood]

Thanks for pointing that out-i didn't catch that if the tone pot is full on, c1 is a standard bp cap.

I'm working on a small size amp and with a one knob tone and would like to hear what you think of your mods.

Also curious about the type of pickups and speaker you use with the amp as it will help me understand the tone talk.

Thanks
scott

[MarkF786]

I've manually tried what I'm proposing. With the bright cap removed, the amp is not as bright sounding; the tone control no longer can boost highs but only cut them, similar to the tone knob on your guitar. Some people might think the amp would sound dark, but it has enough high-end without the bright cap.

With the entire tone control removed, the amp is similar to a Champ. Also, the signal becomes a little boosted when it's bypassed.

The amp has a 12" Mojotone BV-30H in it, which is modeled after a Celestion G12H30. I have a variety of guitars (my favorites are my Hamer Talladega, Koll Superior, and D'Pergo AVC) with humbuckers or single coils (including P90s). Lately I've mostly been playing my humbucker guitars but I go through phases.

Mark