Shared Tone Stack

[C Moore]

Can I do this.? A friend has me working on his Fender SF Bassman. It is a gut job. I am trying to put two separate inputs on the "bass" channel, so I need to separate those channels between the plate and entry to the tone stack.
In the picture is the B+ feed (150k and 100k). Can I just add a slope resistor to the plate of the "second" input, and by doing that, I feed that separate channel into the tone stack.? Is that Kosher.?
Thank You
below is the stock schem and photo of my "circuit"
http://www.el34world.com/charts/Schemat ... _AA864.pdf

[Kagliostro]

try to post a schematic of what you want to do

Kagliostro

[C Moore]

try to post a schematic of what you want to do

Kagliostro

Wish I knew how to create a schem on the computer. All I could do is hand draw one and take a picture. Don't know how well that would work.
This is for a friend. He bought a beat to heck Fender SF Bassman, and wants me to make it "better".
So I am trying to take advantage of the one, un-used triode in the preamp. On the Bass Channel, I am separating the input jacks, and sending each one to its own triode of the AX7.
Then I can use a different cat resistor and cap for each input.
I can also use a different plate resistor value for each input.
Then I can use a different value slope resistor for each input as I feed it into the tone stack. That is my theory anyway.
Do you guys see any big problems with me doing that.? Should I hand draw a schem and then take a picture of it and see if I can post that.?
Thank You

[Hellhammer]

Wish I knew how to create a schem on the computer.

I use Paint! If you use an existing schem it's very easy to just cut and paste and move around, and then tie everything together using straight lines.

[Kagliostro]

you can also use an existing schematic, draw your mods by hand and scan (or make a photo) the result to post it into the forum

Kagliostro

[C Moore]

[quote="Kagliostro"]you can also use an existing schematic, draw your mods by hand and scan (or make a photo) the result to post it into the forum

Kagliostro[/quote
Yeah.....OK, I will just hand draw one, take a picture(s) and see how they look.
Thanks

[tubeswell]

Hi hired hand

You can download one of the free schematic drawing programs like express Schem or JSchem http://dhost.info/jschem/ (if you have a mac)

[C Moore]

Hi hired hand

You can download one of the free schematic drawing programs like express Schem or JSchem http://dhost.info/jschem/ (if you have a mac)

Really appreciate that link. I have HORRIBLE computer skills. But when I have time, i will certainly see what I can make work for my Dell with XP.
So I had to resort to a hand drawn schem. I have really lousy drafting/artistic skills. Sorry about that.....did the best I could, believe it or not. So it is my friends idea to make the Bass Channel on his old head, more guitar friendly. He wants 2 separate inputs with different values of components in the plates, cathodes, and slope resistors. I can play around with values if they do not turn out the way he wants.
But what about the way I have it wired.? Do you think this should accommodate the 2 channels.? Am I on the right track.?
All the same pic. I took 3, in the chance that one might be easier to read than another.
Standard AB165 is also linked below.
Thank You
http://www.el34world.com/charts/Schemat ... _AB165.pdf

http://i111.photobucket.com/albums/n143 ... hem001.jpg
http://i111.photobucket.com/albums/n143 ... hem002.jpg

[plexitone]

I'm no expert but I don't see how that can work right. First, the slope resistors are not in the correct place (between the treble and bass cap inputs). Second, high frequencies now have an additional path to ground back through the filter cap.

It may be possible to "hardwire" it but if not, you could always put the different tone stack components on a switch.

I don't see much benefit in having those tone stack values anyway since they are so similar. There's not going to be much difference in sound between the two.

[C Moore]

I'm no expert but I don't see how that can work right. First, the slope resistors are not in the correct place (between the treble and bass cap inputs). Second, high frequencies now have an additional path to ground back through the filter cap.

It may be possible to "hardwire" it but if not, you could always put the different tone stack components on a switch.

I don't see much benefit in having those tone stack values anyway since they are so similar. There's not going to be much difference in sound between the two.

Wow....this is much worse than I thought.
I really tried to just copy the Fender schem, and add a second input.
I am looking at the drawing.....OK, I see what you are talking about. I have it wired correctly on the board, but I surely have it wrong on my schem. Thanks for pointing that out to me. I will make the change and repost the pics.
As far as highs feeding back through the filter cap, you have lost me there. May be above my level of understanding. Or will that be corrected when I fix my drawing.?
Component values are not a worry. I can change those to whatever my friend might want. Especially as you say, if he cannot hear a difference between the two.
Thank You

[Firestorm]

Yeah, that won't work. Slope resistors need to be in between the tone caps (dividing signal between them); you've got them in front, so it's just a series resistance. You've also got your treble caps wired in parallel, so it's just like one 600pF. But since there's no slope resistor, the treble cap and control will do absolutely nothing.

I'd suggest getting your channel variation from different cathode bypass caps and different plate resistors as you do now (I think you'll find you want a bigger difference than 100K/150K on the plates) and then put a dual gang pot to mix the two channels together into a single tone stack.
You can have a switchable slope resistor, switchable treble cap and so on there if you want.

[selloutrr]

am i missing something? the volume is after the Tone stack in the bassman so you wouldn't have control over the individual channels that feed into the tone stack. Sort of pointless to have both balls out... why not just use an A/B/Y pedal and keep the amp stock. or put a toggle on the inputs jacks.

[C Moore]

Yeah, that won't work. Slope resistors need to be in between the tone caps (dividing signal between them); you've got them in front, so it's just a series resistance. You've also got your treble caps wired in parallel, so it's just like one 600pF. But since there's no slope resistor, the treble cap and control will do absolutely nothing.

I'd suggest getting your channel variation from different cathode bypass caps and different plate resistors as you do now (I think you'll find you want a bigger difference than 100K/150K on the plates) and then put a dual gang pot to mix the two channels together into a single tone stack.
You can have a switchable slope resistor, switchable treble cap and so on there if you want.

I posted a new drawing above.
Maybe I will raise that 150 to 220.
This is just a partial drawing. Not complete at all. I was just wondering if the amp will work as I had it laid out.
The owner wants me to make the Deep Switch into a bright switch. He wanted two separate channels, and make them a High and Low input separately for different guitars. Will it be a big deal if the inputs are not parallel.? I guess what I am asking is, is it better to make the cat and plate variations switchable, than it is to just just have to change from one input jack to another.?
He also did not want to add any holes, pots or switches. I was just trying to give him two different/separate channels he could plug into on the bass channel that he never used anyway.
His amp still has the Normal channel also. I am sure I will have to make some changes for him, but I first wanted to make sure the amp will at least work the way I have it wired. Then I know I have a working amp I can do something with per my friends desires.
I really appreciate all the help and suggestions from everybody. I do not play guitar, so I Really Do Appreciate the input. Feel free to make any other suggestions you feel would help.
Thank You

[C Moore]

am i missing something? the volume is after the Tone stack in the bassman so you wouldn't have control over the individual channels that feed into the tone stack. Sort of pointless to have both balls out... why not just use an A/B/Y pedal and keep the amp stock. or put a toggle on the inputs jacks.

Sorry, I do not understand. If you are only using one channel at a time, isn't it OK to have the Volume after the tone stack.?
Thank You

[selloutrr]

am i missing something? the volume is after the Tone stack in the bassman so you wouldn't have control over the individual channels that feed into the tone stack. Sort of pointless to have both balls out... why not just use an A/B/Y pedal and keep the amp stock. or put a toggle on the inputs jacks.

Sorry, I do not understand. If you are only using one channel at a time, isn't it OK to have the Volume after the tone stack.?
Thank You

why would you need two channels into the same tone stack that are pre any sort of volume control when the one input has two jacks. I guess I just don't see the useful function. The reason for seperate ch. would be to adjust one ch differently. if all you want to do is use two guitars. plug both in and turn the volume down on the one you aren't using. if you want to switch it with your foot use and A/B box if you want the both option use the A/B/Y box. IMHO It just seems pointless.. what is the function?