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Old 22nd August 2012, 09:43 AM   #1
Mnvizb is offline Mnvizb  Lithuania
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Default tone stack buffer

Hi guys. I am planning to add a tone stack to my diy amplifier, but it will reduce output, of my preamp. could you recommend any schematics for a buffer (best if it used 9V supply, cause i have that). I am going to use a marshall style tone stack.
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Old 22nd August 2012, 03:05 PM   #2
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Simplest is probably an emitter follower
Im sure theres plenty of diagrams online, bias the base to 4.5v via potential divider, connect the emitter to 9v, emitter to a 10k resistor, and resistor to ground, take output from the emitter with a coupling capacitor.
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Old 22nd August 2012, 05:04 PM   #3
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Note that the better Marshall solid state amps (AVT) use only one tube, and that's a cathode follower that comes before the tone stack.
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Old 23rd August 2012, 12:03 AM   #4
Minion is offline Minion  Canada
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It"s going to be quieter no matter what ..... a Passive tone stack can only cut frequencies not boost them , instead of a buffer I would suggest a makeup gain stage after the Tone stack .....
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Old 23rd August 2012, 02:57 AM   #5
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With the controls set to "flat" (1, 9, 1) there's only about -7dB insertion loss.
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Old 23rd August 2012, 07:30 AM   #6
Mnvizb is offline Mnvizb  Lithuania
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oh, sorry. when I wrote buffer, I meant gainstage which would compensate for any loses. I don't want any complex EQ, just a simple three band and an either opamp or transistor/FET gainstage. I hope you could give some design, because I'm quite bad at designing circuits. Or any literature, which could help me do it. Thanks
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Old 23rd August 2012, 10:11 PM   #7
Minion is offline Minion  Canada
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If your going to make a gain stage/buffer then you might as well build an active tone controll that way you dont need makeup gain and you get to boost frequencies as well as cut frequencies , it wont take many more parts and you overcome some of the drawbacks of passive tone controlls ......
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Old 26th September 2012, 12:47 AM   #8
Struth is offline Struth  Canada
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Hi Guys

Minoin's idea is a good one. On the other hand, Mnvizb did not say what technology his amp is: tube or solid-state?

Just as a point of interest, typical tone stacks cut the signal by a factor of 5-10, so you need make-up gain of a similar range. A single triode, BJT, jfet or mosfet easily produce this much gain, but you have to know the signal sizes involved to make the right choice.

Another point of interest with respect to cathode-driven tone stacks in guitar and bass amps: everyone copied Fender, who in their Bassman head experimented with a CF. This was to improve how well the active mixing stage could drive the feedback loop and the EQ. This was a very early model before the version Marshall copied.

The feedback loop around the second stage was removed but the wiring was already being done with the CF, so the CF stayed. The follower is a "remnant" of a discarded Fender design.

Cathode-driven EQs tend to lack adjustment range and sound lifeless. Plate-driven EQs are far more dynamic and the controls _do_ something. If you rewire the follower in a Marshall to either be bypassed or to double the stage preceding it, most players will find the amp more lively and smoother sounding. As with all myths that are widely believed, if you then say you bypassed the follower, the player will appear less happy - since belief in a myth is more important than belief in one's hearing.

Have fun
Kevin O'Connor
londonpower.com
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Old 26th September 2012, 09:14 AM   #9
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Thanks Kevin. Thought that's what I heard but the myths wouldn't go away...
Cheers
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