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Posted: **Wed Feb 05, 2014 11:11 am**

Hi again, I was asked by a friend re adding a active tone control to a pre amp curcuit
he is using the bellow schematic.

: 6SN7_3.jpg (38.24 KiB) Viewed 4598 times

He was looking at a active tone control like this one.

Posted: **Wed Feb 05, 2014 11:47 am**

Can't go wrong with a Baxandall, but have a cap on that first tube's anode and keep the DC out of that bass pot

Have you tried this tool to model that control?
http://www.duncanamps.com/tsc/

Cheers!

Posted: **Wed Feb 05, 2014 12:24 pm**

Thanks for that but just so I can understand

is the Amp-Tone-4-A-A.jpg drawing a complete pre amp channel or is it something I incorporate into the above schematic?
For example at the start of the pre amp or at the end?

Posted: **Wed Feb 05, 2014 12:49 pm**

That tone control schematic has about 30db gain, a lot for a pre amp. At http://www.angelfire.com/electronic/fun ... one-A.html there's the A Tone Control You Can Love, that's basically the same circuit with the first 12AX7's output out of the cathode, so there's no gain, and lower impedance. It would go in front of the 6SN7, the 6SN7 would need it's own grid leak resistor too, about 470K to 1M. The tone control schematic used by itself would have a really high output impedance.

Posted: **Thu Feb 06, 2014 12:01 am**

: Amp-Tone-5-A-B.gif (13.89 KiB) Viewed 4557 times

Thank you for that I think I got it, I have made the change can you look at it and tell me? Does the volume pot stay as is?
Also the 6SN7 is drawing about 11mA what would the 12ax7 be drawing?

Posted: **Thu Feb 06, 2014 7:41 am**

I like to use a pot with push - pull switch on a tone stack.

I wire it up to lift the ground and bypass the tone control.

john

Posted: **Thu Feb 06, 2014 8:20 am**

6B4G wrote:Does the volume pot stay as is?

Yep, just attach volume pot to output of 12AX7. The 12AX7 might get loaded down by a 100K pot. You can fix that by installing a cathode follower, after the last 12AX7. There's an example a little lower on that page.

6B4G wrote:Also the 6SN7 is drawing about 11mA what would the 12ax7 be drawing?

1ma or a little less.

Posted: **Thu Feb 06, 2014 8:30 am**

A Tone Control You Can Love.
Figure 14 shows the tone control that I think has the best compromise between performance and tube count. Yes Virginia, everything is a compromise. It uses only two triodes per channel, one 12AX7 or your choice of other hi mu triodes, and it has a nice symmetrical looking frequency response curve. Its gain when set to flat is about -1 dB which is close enough to unity to not cause overload problems in a preamp or integrated amplifier. You could transplant the tube stages from Figure 18 below if inclined. The performance would be slightly improved.

Posted: **Thu Feb 06, 2014 9:59 am**

Thanks a million guys for all the help.

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