Please help with one knob tone control

[Markusv]

Folks
I recently completed this amp:
Sounds great and I wish I had built it ages ago
http://www.18watt.com/storage/18w%20Schematic.gif

Changes are:
I am running EL34's as the power tubes
The PI values (cathode and tail resistor) were changed to drive those tubes harder
I have a 330 pf brite cap on the Volume control
Reduced V1 cathode bypass cap to 10 uf

Challenge:
I am getting increased treble as I turn the tone knob on the normal channel clockwise. But I wish at the same time it would cut a bit of the low mids/ bass.
Doesn't seem to do it enough
Do you have any suggestions for different values in the tone circuit?
I don't want to reduce coupling caps because sometimes I want to retain the fat mids and I'm concerned the amp would sound anemic

Question:
Is what I want even achievable with a single tone knob?

If anyone would indulge me- please also explain the RC dynamics and how I could predictably alter them in future. For instance:
Impact of pot resistive value
Impact of capacitance values in relation to pot value
etc....

Thanks in advance

Markus V

[diagrammatiks]

might want to try the baxandall.

You can put it on a dual knob and it'll work a bit like the orange amp's shape control.

[Markusv]

Thanks, Diagrammatics!

"Insertion loss is lower than the standard Fender tone stack, but obviously higher than 1 knob controls"
From Adam's Pages

This is my concern: that something more complex may reduce the already limited drive to the PI

Thoughts??

[diagrammatiks]

Well, insertion loss is always going to be an issue if you want more complex shaping.

How is it now? is it enough to bring the poweramp to overdrive?

[Markusv]

It is enough to overdrive the poweramp nicely
And I would not like to see too much of a reduction

I was wondering if the 100K resistor on the one leg of the tone knob sets the slope for the tone shaping as is the case of a slope resistor in TMB tone stacks?
Perhaps that is where I may start?

Just speculating here...



Markus V

[Richie]

A few things come to mind on the 18. Most like the trem channel tone circuit more than the normal channel. Also listen close to 18 watters,when in the normal channel if you go to about 8 on the vol,it stays fairly constant. Between 8 and 10 you will hear a subtle loss in volume.

You can also use a more fender type tone circuit. There should be a modded version to use in the normal channel.

Also look at the 6g3. Earlier than an 18,but its very similar to an 18 in some ways.I'd almost call its leo's american version of an 18 watter..lol

Look at the normal and bright tone controls. The normal channel uses a .01 off the tone pot,and has a snubber on the plate resistor for that channel. Now look at the bright channel. It doesn't have the snubber and uses a .02 off the tone pot.
I'd suggest using the bright channel tone circuit in your 18 watter. Its very similar to the 18 trem channel circuit. Pot values are 1M over 500k in the 18.

Another option is change the PI to more like the 6g3,[without feedback] and take out the tone pot,and use a cut control for your tone control.

The easiest is to change it to the 6g3 bright channel tone circuit. I think you will like that much better over the 18 normal channell.


http://ampwares.com/schematics/deluxe_6g3.pdf

[tubeswell]

Folks
Challenge:
I am getting increased treble as I turn the tone knob on the normal channel clockwise. But I wish at the same time it would cut a bit of the low mids/ bass.
Doesn't seem to do it enough
Do you have any suggestions for different values in the tone circuit?
I don't want to reduce coupling caps because sometimes I want to retain the fat mids and I'm concerned the amp would sound anemic

Question:
Is what I want even achievable with a single tone knob?

Thanks in advance

Markus V

Hi Markus

You could try a tilt control, like a Big Muff, but scaled for a geetar tube amp.

If the pot and resistor values are kept between 470k and 1M, you will minimise the insertion loss and keep the resistor noise to an optimum level.

I have used these resistor and cap values before with great success, and that was being driven by an EF86, (set up for a gain of 100 - but still with high-ish output impedance -so it was a lossy combination anyhow) and it worked fabulously.

(Plus its a simple circuit - just two extra components (in this case 2 x 1M resistors) over and above a tweed princeton tone stack) so its quite easy to convert from a 5F2A tone stack to this and vice versa)

[jjman]

You could add a switch to change a cathode cap to a lower value to cut the lows and low mids. Maybe switch the 10u with a 1u or 0.1u.

[Markusv]

Many thanks to all who responded. You are awesome and generous with your knowledge and that is why this is by far the best forum I know of
Looks like I have a wide variety of options!
I will have time this weekend and try out some of the strategies

Markus V

[diagrammatiks]

I second that big muff control.

you'll have to change some of the values to make it work for an amp but it's a real spiffy control.

[tubeswell]

I second that big muff control.

you'll have to change some of the values to make it work for an amp but it's a real spiffy control.

FWIW the values I've used there are for a tube amp

[diagrammatiks]

ah ya. I was thinking of the default one from the duncan calculator.

[tictac]

Here's what I used for a 1 knob TC; It's basically a BF Fender circuit installed on a 100k pull-pot. When you pull the knob the slope/bright circuit changes from 100k/250p to 50k/500p....

The 100k pot changes the midrange level and so acts like a gain control and a tone control at the same time. CCW rotation is the glassy Fender tone with a big mid dip, at full CW rotation the mids get fatter and gain increases....

The values of the resistors can be changed to suit your favorite BF tone settings. Most people set it and forget it anyway so who needs 3 knobs?

You could go with a 250k pot if you want a bit more gain...

TT

[Markusv]

OK

Thanks to everyone who helped here

I went with the Big Muff control and it is VERY interesting!
Though the amp lost some drive to the PI I think I may be able to live with it
The control seems to add a lot of what I can only describe as "presence" to the tone and you can really dial the mid-range nicely

I may want to introduce a bit more bass to the stage and thus may return the V1 cathode bypass cap to the original value of 50 uf
Right now I have a coupling cap of .02 uf coming from the plate of V1 and that is already up from .005 that I had in there originally.

The amp's cleans are spectacular and I can't wait to finish my treble booster (rangemaster) to really push it over the edge

Any comments welcome please

Thank you all for the help

Markus V

[diagrammatiks]

OK

Thanks to everyone who helped here

I went with the Big Muff control and it is VERY interesting!
Though the amp lost some drive to the PI I think I may be able to live with it
The control seems to add a lot of what I can only describe as "presence" to the tone and you can really dial the mid-range nicely

I may want to introduce a bit more bass to the stage and thus may return the V1 cathode bypass cap to the original value of 50 uf
Right now I have a coupling cap of .02 uf coming from the plate of V1 and that is already up from .005 that I had in there originally.

The amp's cleans are spectacular and I can't wait to finish my treble booster (rangemaster) to really push it over the edge

Any comments welcome please

Thank you all for the help

Markus V

grab the duncan tone stack calculator.

It's got the big muff tilt in it.

and you can use the coupling cap calculator at pentodepress.com to calculate your -3db roll-off for your stage.