Tone linestage idea

[rman]

Hi all.

I am thinking about building this preamp and would like some input from some tube guru's. I found the basic ciruit here,
http://home.comcast.net/~stphkeri/tone_control.html
and changed it around a bit, using 12au7a's because I have two of them and I think the gain would be about right.

I figured if I put the treble first I can make it direct coupled as the tone network can act as a fixed voltage divider for DC bias to the next grid. Also maybe this will reduce the possibility of overdriving the next stage if the bass gets cranked up. I took 5 kohms off the upper r/c network resistors to compensate for the output impeadeance of each stage.

The first (50k) pott is meant for tweaking the volume if nessesary instead of using a lossy balance control.

This is only my second attempt at designing a tube circuit. My first can be seen in the post called "Yet another 6em7 amp"

Any comments and /or suggestions elcome.

 

[Geek]

Hi,

That's a split Baxandall. They really only work well with a low source impedance (2K or less) into the stack.

Check out this handy program
http://www.duncanamps.com/tsc/index.html

And I believe they call it a "James" in that one.

Cheers!

 

[rman]

Hi Geek.

Thanks for the turn on to that tonestack program. I had been using an Excell spreadsheet I made myself for the split passive.
It always did seem that no matter what I did, the separate bass control had alot of influence on the midrange. When I try the "James" circuit in Tonstack Calculator, and neutralize the treble section by selecting very low capacitor values, the same thing happens. Very interesting. The "james as shown when you open the program seems to work very well, maybe this a better way to go. That way I could paralell the tube sections for a lower Z out since it would only need one gainstage.

As for the other circuit in the program, all I can say is guitar amps are strange!

Thanks for the input.

 

[Geek]

No problem!

That way I could paralell the tube sections for a lower Z out since it would only need one gainstage.

I have found a cathode follower works well.

As for the other circuit in the program, all I can say is guitar amps are strange!

Indeed!

When I was comissioned to build guitar amps, I quickly discovered that I had to unlearn everything I learned about HiFi tube amps when approaching them.

Cheers!

 

[TubeHead Johnny]

Is this for a guitar or hi fi amp?

Some interesting tone control circuits can be found here:

http://www.angelfire.com/electronic/funwithtubes/Amp-Tone-A.html

I've built a modded version of "A Tone Control You Can Love" and it works great in a hi fi circuit.

~John~

 

[rman]

Hi.

This is for Hi-fi but I am not in a hurry to build anything. I am using a sand preamp that I really have no quarrels with. (Hafler 110) I sits with my source components, CD, Cassete, tuner, and turntable, then drives about 8 feet of cable to my power amps.

I just finnished an active crossover, Rod Elliot's poject 9. I think I will probably go back to using the original passive crossovers since i dont really hear any improvment except possibly when using my pc as the source. It would be nice to make an instant A-B comparison between bi-amped and normal, but I really can't see how this could be done.

The amps are SET 6em7 amps one is direct coupled desined by Gary Kaufman, The other is two 6em7's in series desined by me with inpiration from Gary's original and John Broskies site.

Thank's for the link. It will give me lot's mor to mull over before building something. I did have this one bookedmarked
http://www.angelfire.com/electronic/funwithtubes/Amp-Tone.html
But missed the other one.

Thank's guys.
Rolf.