Rod eliotts Sweep Eq

[Reno]

Hi I have been playing with various types of EQ's recently and came across the esp Parametric Equalizer, and thought I would give it a go as I have built very similar gyrator circuits with good success.
The first thing I done was omit the input buffer as this was not needed but everything remained the same. However the circuit is not performing exactly right, everything works except the Lin sweep pot does not seem accurate it sweeps within the right frequency range 35hz - 150hz. But the pot only works to mid point meaning if the pot is turned anticlockwise fully it will peak at 150hz but will peak at 35hz under mid point and if its fully clockwise nothing. I just need away to spread the frequency through out the potentiometer if its possible, all suggestions would be highly appreciated thanks.

 

[ronsimpson]

Which pot are you having trouble with R4 or R7?

 

[Reno]

Hi I am having trouble with R7 the sweep pot

 

[ronv]

It doesn't look like In1 (ground & R7) is tied to ground.

 

[Reno]

Sorry you cannot see the ground plane in the pic but they are connected on the board ill try to add another picture thanks for your respnse

 

[ronv]

Silly me. If I would have kept looking I would have noticed the other grounds. What are the values of the pots and caps? Maybe you could take a few DC measurements around the op amps?

 

[ronsimpson]

But the pot only works to mid point meaning if the pot is turned anticlockwise fully it will peak at 150hz but will peak at 35hz under mid point and if its fully clockwise nothing. I just need away to spread the frequency through out the potentiometer if its possible, all suggestions would be highly appreciated thanks.

Is the pot linear or log? Pull the pot from the board and mount it on the other side of the board. This will swap which end of the pot you are using. If the pot is log or damaged it will make a difference. If the pot is linear it will not effect anything.

 

[Reno]

Hi the pot I am using is Linear, I already tried to mount it the other side but as you said nothing happend. regarding cap values and pots the original circuit is here **broken link removed** thanks thanks for the replys

 

[ronv]

It simulates ok. The 1 uf at the input could be a little bigger to get the gain up at 30 Hz.

 

[Reno]

I wonder if I have a dogy potentiometer I will check and see if this is causing the problem, what do reckon I should raise the 1uf cap to ronv?

 

[ronv]

I just changed it to 10Ufd. Here are the response curves.

What does it do when the pot goes bad? no sound or? It seems there is still an output no matter what the pot is though the frequency response is screwed up.

 

[Reno]

Hi ronv when the 10k pot is at full gain and the 1m pot is swept fully to the right it peaks at the 150hz and peaks at the 35hz when the pot is half way instead of when fully anticlockwise so the sweep is very tight, So half the potentiometer is having no effect at all

 

[ronv]

Ahh yes, I see. Try a log pot. I think it will feel better.

 

[Reno]

Ok thanks ronv I will give it go tomorrow