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Old 17th November 2012, 09:00 PM   #1
vasko is offline vasko  Czech Republic
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Smile Tone control preamp

I need simple (preferably) pentode/triode or triode/triode preamp with bass, mid, treble and gain control. So simple, two valves. Input will be guitar. Output will be small SE 3W tube amp that I already have, or headphones. If both isn't possible then just SE amp. I expect tone controls are between valves, not at the end.

I want pentode first to pick up signal, because with low input signal is not likely to saturate triode behind. If there is some amount of clipping it's acceptable, it's for guitar.

So it's pretty common demand, if you know of schematic of something like this?
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Old 17th November 2012, 10:03 PM   #2
kevinkr is offline kevinkr  United States
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Moved to I & A per forum policy regarding guitar amps.
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Old 18th November 2012, 07:18 AM   #3
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How about this:

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Old 18th November 2012, 09:30 AM   #4
vasko is offline vasko  Czech Republic
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Yes, something like that. Two things:

1. I'd like that gain pot is after first tube.

2. I don't see what resistors are pots, in bass, mid, treble controls?
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Old 18th November 2012, 10:54 AM   #5
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If gain adjustment is after first voltage amplifying stage, then a cathode follower must be added between volume potentiometer and tone control stage.
Tone control stage reguires steady source impedance which volume potentiometer is not.
Why do you want the volume control before tone stage ? I see no difference if it is after tone stage.

R5 and R5 form 500 k treble adjustment potentiometer (now on middle position), R7 and R5 is Mid. and R9 + R10 is Bass.
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Old 18th November 2012, 11:43 AM   #6
vasko is offline vasko  Czech Republic
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Quote:
Originally Posted by artosalo View Post
If gain adjustment is after first voltage amplifying stage, then a cathode follower must be added between volume potentiometer and tone control stage.
Tone control stage reguires steady source impedance which volume potentiometer is not.
Ok.


Quote:
Originally Posted by artosalo View Post
R5 and R5 form 500 k treble adjustment potentiometer (now on middle position), R7 and R5 is Mid. and R9 + R10 is Bass.

You mean R5 nad R6, R7 and R8?

How about limiting end values of pots with additional resistors? Is it ok if pot goes 0R at end positions?
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Old 18th November 2012, 11:53 AM   #7
vasko is offline vasko  Czech Republic
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Quote:
Originally Posted by artosalo View Post
Tone control stage reguires steady source impedance which volume potentiometer is not.

How about gain after tone controls?

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Old 18th November 2012, 12:37 PM   #8
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Judging by your posts, I'm a bit surprised that you're even asking. It seems to me that you know what you want and how to find/design it.

What you've shown there is essentially a standard Fender pre-amp, which is what I was going to suggest in the first place. It's simple and proven. Add a voltage divider with a pot on the bottom to control your output level and that should be all you need.
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Old 18th November 2012, 12:53 PM   #9
vasko is offline vasko  Czech Republic
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Ok.
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Old 18th November 2012, 01:21 PM   #10
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Sorry for misprints. Yes, R5+R6 Treble, R7+R8 mid, R9+R10 bass. All pots 500 k linear.

Without limiting resistors at the end of potentiometers the max. lift/attenuation is some 15 dB.

The frequency response of your circuit (=Fender) is confused and hazy.
This is not a real tone control, it is just a "tone control".
Different controls have interaction.
Adjusting bass will effect to treble etc. Also there is not real flat position.

In my example all the these defects are avoided.
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