Presence Control seems not to work too well

[dude]

 
I've been trying to get this 18 watt 6V6 Super Lite's Presence Control to work better. Seems the control cuts a lot of the highs too fast. (Seems to only work at at last 1/4 turn)  I have to turn it all the way on to get close to the brightness I want.

I changed a lot a values and drew this schematic of what I used.

Possibly the R to the speaker is too low on the Presence pot...?

Any changes to make the treble and presence work better, both seem to be always on full to get to the tone I like. I use a strat with clean vintage p/u's so I should be closer to ice pick tone.

Tone not bad but just want that presence to work better.

Any suggestions welcomed,
al

[SILVERGUN]

You could try it like this:

[SILVERGUN]

In your hand drawn schematic it looks like you've got the cap connected from one side of the pot to ground in series with the pot. I don't see a wiper connection drawn.
If that is the case then the pot is just varying your total NFB resistance by 5K, and the cap is always 'all-in'.

[dude]

In your hand drawn schematic it looks like you've got the cap connected from one side of the pot to ground in series with the pot. I don't see a wiper connection drawn.
If that is the case then the pot is just varying your total NFB resistance by 5K, and the cap is always 'all-in'.

I didn't open the amp to look how I wired it, I know I didn't draw it correctly. I kind of made up the schematic from several schematics.
I might have just wired the pot wrong, also I read somewhere that the resistor feeding the pot needs to match the speaker ohms.

The 27K I used from a Marshall plexi schematic but it was connect to the 16 ohm tap, perhaps a 39K would be better as I have only an 8 ohm speaker tap.

I'll check the wiring again. I think from memory I put the .1 cap on the wiper to ground with the other leg of the pot, which I think is correct, if so changing that 27K higher does what?

al   

[SILVERGUN]

In your hand drawn schematic it looks like you've got the cap connected from one side of the pot to ground in series with the pot. I don't see a wiper connection drawn.
If that is the case then the pot is just varying your total NFB resistance by 5K, and the cap is always 'all-in'.

I didn't open the amp to look how I wired it, I know I didn't draw it correctly. I kind of made up the schematic from several schematics.
I might have just wired the pot wrong, also I read somewhere that the resistor feeding the pot needs to match the speaker ohms.

The 27K I used from a Marshall plexi schematic but it was connect to the 16 ohm tap, perhaps a 39K would be better as I have only an 8 ohm speaker tap.

I'll check the wiring again. I think from memory I put the .1 cap on the wiper to ground with the other leg of the pot, which I think is correct, if so changing that 27K higher does what?

al

Raising the value of that resistor lowers the NFB voltage (just as you would imagine)

Swithching the tap requires changing the value to get the same result....i.e.:
27k on the 16 = 19k on the 8 = 14k on the 4

[sluckey]

Just copy this...

http://mhuss.com/Plexi6V6/Plexi6V6c.gif

[jojokeo]

That schematic always seems to pop up here & there. Mark's a good dude. I built an amp using a couple of his ideas in that schem years back & he was always more than helpful.

[alerich]

I used Mark's JCM800 schematic to build my 2204 clone. Clear, easy to read and sounds better than the real thing.