Fantasy TOS Needs your contribute

[kagliostro]

This is the result of my thinking about a TOS Stand Alone Preamp

In my version I've put some mods to the schematic (it definitively will not sound the same as a TOS I or a TOS II - however I was thinking this will happen anyway for more than one reason)

for the clean channel I've think to a James Tone Control with added Shift control

for the OD channel I've think to a Tilt Tone Control

I've put the OD Level of the TOS II after the DPDT switch to be used as a Master Volume for both channels

the Fatness Control of TOS I now is "splitted" in two volume controls, so I can choose how many signal go to V1b (12AY7) and to V2a (5751) independently and can have a mix of any level of the two tubes or only the 12AY7 or the 5751 tube engaged

I added a fourth tube (a 12AX7) and use it for the CF of the 5879 and for the CF that acts as FX Loop sender to have a very low output impedance, also I added an output transformer to have Balanced Output

Need your help to revise schematic and your council about any aspect of the circuit

I draw a red circle with a number near any <ground connection>, please can you give me help about which <ground connection> must be grouped and where they must be connected to the ground ?

Does exist an XLR connector with incorporated switch, something that acts at the insertion of the male connector, as to eliminate the "Balanced Out on/off" switch that must be acted separately ?

Thanks

Kagliostro

[DummyLoad]

interesting. would be cool on a well designed PCB. how about sub-miniatures? 

--pete

[tubenit]

I like your design!  I thought about trying a James tone stack in the clean also but never got around to trying it. Those James tone stack can get reasonably mid scooped  AND  mid boosted.  Nice idea.

I think this will be a cool sounding amp!

I'd tie 1-17 to a buss ground just like on Hoffman's grounding scheme.  I am not smart enough to know about 18-20?

With respect, Tubenit

[kagliostro]

@ Pete

There will be a PCB on this preamp circuit, the filament and relays power supply (see attached PCB)

but about the preamp it will be a turret board

today I'm trying (my first time) Visio for the layout (GREAT PROGRAM), but at the moment I think it will be better to abandon this idea and try to draw using Jschem that I know much more, to me is quite difficult to try to draw a decent layout, and if I use a software that I don't know I think it is too difficult

may be it will be less difficult to me to draw the layout using Autocad, also if I don't use that program since some years ago

@ Tubenit

Thanks for your comments and indication about ground connections, I think the connection #18 may be considered as the cathode connection of the final tubes in an amp, but not sure, about #20 ?? may be I'll connect the same place of #19

about the layout of the pre, I've think to have the components of the tone controls out of the board, directly connected to the pots, this way the board will be smaller, but above all I do it as to have some flexibility about the choice of the Tone Controls

Happy you like the idea of the James Tone Control + Shift, I'm convinced this will be a good choice

What do you think about the Tilt control at the output of the OD ?

I have think to that as it is an only one knob, do you think it will be better to use a more sophisticated Tone Control there ?

Kagliostro

  

[tubenit]

Kagliostro,

I got to looking at the values you have in the James Tone Stack and I think you're going to have way too much bass when the OD is engaged.

I think it's going to end up too muddy sounding.    I plugged in your values into the Duncan Tone Stack Calculator and saw what it did. Lots of lower mids and not much treble.

http://www.duncanamps.com/tsc/

I have attached a schematic showing my favorite JTS values (& I have tried ALOT of different values) for a clean tone.

So, I have offered a suggestion that is a good compromise between your tone stack and the one I prefer the most.  

I would NOT use a .0047 in the "upper" bass position, I definitely would go lower.   IF you look at the spdt switch, it will give you a very nice mid boost with the paralleled cap.  I think this will work OK with the OD engaged?

Anyhow,  food for thought.     I still like the JTS idea but I think when the OD is engaged, it's not going to sound right.

with respect,  Tubenit

[kagliostro]

Hi Jeff

thanks for your contribute

as I told, the tone control components will be attached to the pots, not on the board, so I can try and if necessary also change completely the tone control

thanks for the suggestion of the values to be try


Franco