converting passive Tone control to active?

[fatecasino]

well, my theoretical background is not my best, but I tried to improvise with a problem and now I have another problem
I try to build my amp http://www.dx.com/p/y148-audio-amplifier-module-93121#.Vy3aXGF95cZ using Y148 Audio Amplifier Module and I decided to add a passive tone control


However I had a noticeable loss of signal, and  due to the lack of certain fragments of knowledge I decided to add an active mixer (with only 1 channel) so I re-obtain the signal level.


However I found very difficult to set the R1 - R2 values relation. When I used the values of the schematic the volume was low. When I increased R2 the volume came loud again but I got an annoying wind blowing sound too! There's another thing with the wind in the amp that's a bit strange. When I play the guitar, the wind sound goes low. When I stop play the wind blows stronger within the next few seconds of silence. It sounds like a compressor!

So,

• can you suggest a modification to make this thing work?
  
• Otherwise, is there any other schematic to regain the volume loss after the passive tone control?
  

[GibsonGM]

Hi,

Typically, if one is going to add a tone control to the front end of a circuit, you would first amplify the signal above the noise floor (the WIND sound!), then send it through your tone control, and finally re-amplify the signal to restore its level.

Search for the Big Muff Pi schematic, and note how this is done, with the final transistor re-amplifying the signal...there are 100 ways to do this but this is a very simple one!

[fatecasino]

So you mean that the conversion of the the passive tone control to active happens by adding two op amp modules,
one before the passive tone control and one after it.
I know that there must be 100 ways to do this but can you suggest a simple schematic for these two modules?
The big muff Pi is too popular to locate what I exactly need for my case

[slacker]

This is a good circuit to look at http://www.runoffgroove.com/tonemender.html, the first opamp is a buffer before the tone control and the second one is a boost after the tone control. You could swap the two opamp stages round to give a boost before and a buffer after or use boosts before and after.
If you replace their tone control with yours then you would connect the bottom of your tone control to Vref instead of ground.

[TejfolvonDanone]

However I had a noticeable loss of signal, and  due to the lack of certain fragments of knowledge I decided to add an active mixer (with only 1 channel) so I re-obtain the signal level.

So you added a gain block. The circuit is essentially have 1.5 gain. If you increase R2 you get more gain (and it amplifies the noise as well hence the "wind" sound).

The big muff Pi is too popular to locate what I exactly need for my case

If you search for a big muff pi schem you will get plenty of good explanations on how it is working.
http://www.pisotones.com/BigMuffPi/psst/schm-triangle-1.jpeg
If you look at the schem above you might notice a pot named "tone". That's the tone control. Q4 after it is the gain block GibsonGM was talking about. Because the BMP is a distortion pedal all the other transistors are the "front end" of the tone control.
The gain of a common emitter amp (the Q4 and the four resistors near it) is collector resistor divided by the emitter resistor. In this case it's around 4.4.
The tone control has a maximum of -6 dB damping (pot in the middle) and the Q4 stage has more gain than the loss in the tone section.

Search for the Big Muff Pi schematic, and note how this is done, with the final transistor re-amplifying the signal...

I just want to add that it also eliminates loading effects.

If you want to have this gain stage -> tone -> gain stage type of circuit you to consider some things:

• What type of output will be plugged in?
• What type of input will it drive?
• What type of gain do i want? FET? BJT? Op-amp? Tube?
• How much gain do i need? Do i only want to compensate the loss in the tone control or do i need more?

Just to list a few.

[GibsonGM]

^  Yep.  As slacker said, you can also use a buffer (or 2!) for this.    Remember, when you run a signal thru passive components, you get what is called INSERTION LOSS.  The components "don't act right", and take more power to do their thing than you have available.   Resulting in the sound of crap, ha ha.   

A pre buffer (or gain stage, with its own set of input and output impedances, a WHOLE other topic but one to keep in mind here...AC resistance...) helps to keep your signal level up, noise down, and also to match the impedance to avoid/lesson insertion loss.    You will always lose SOME signal, tho, so you often will use a gain stage post-tone control to re-amplify back to a good level.  Not all circuits need this, but many do.   
As stated, depends what you want to do (see Tej's list).

It is, and it isn't, very complicated.  As you can see from the answers, there are some things you need to be thinking of, but after a while it becomes second nature and isn't very involved.    "Getting" the initial concept is the challenge...

[fatecasino]

You could swap the two opamp stages round to give a boost before and a buffer after or use boosts before and after.

what would it be the  difference in the sound when swaping the opamp stages?

If you replace their tone control with yours then you would connect the bottom of your tone control to Vref instead of ground.

So, to understand clearly,
*the first stage start with In and ends at 1, at exit of U1a?
*the second stage starts just after the 1M resistance - 5th pin of the U1b?
*does the level pot decide how much gain I have at the exit?
Generally I aim to the largest headroom and lowest noise floor.

connect the bottom of your tone control to Vref instead of ground.

*do you mean that in my passive tone control, I disconnect every single ground and connect it to the Vref?

[J0K3RX]

Have a look at the datasheet for the YDA148... Should help you get this setup.
http://download.yamaha.com/api/asset/file/?language=ja&site=jp.yamaha.com&asset_id=46252