Easyface question

[brett]

In standard trim the Easyface has a 250k pot control of "Pregain".  The wiper of this pot is connected directly to the base of Q1.  Therefore. at low Pregain settings the base of Q1 is grounded.  Surely that doesn't make much sense (or does it??)  Looking at an old PCB of an Easyface I built years ago, I see that for some reason (probably habit), I put a DC-blocking cap between the pot and the base of Q1.

Was I doing something smart, or just messing up the mojo???

To cap or not to cap; that is the question...

[Ansil]

hmm i will look again but the pregain is just wired up as a simple volume pot on a guitar or the output of the fx.. it was done this way to simulate turnign your guitar down,  if i rem correctly the top of the pot is the inpu the middle is going to the base and the bottom is grounded.  this is just like all other volumes i have seen,  but i will look again just to be sure :D

[brett]

Looking at the Easyface project at Tonepad, there is an extra "Tone?" pot in the circuit, and the base of Q1 is DC isolated from the Pregain pot.  

So which is better - DC blocking cap on the base or not?

[Ansil]

what you are looking at on the tonepad site it the input pregain and the blend pot,,  u always want a cap there,. this just blends the two caps one for more bass one for less in every pedal there should be input and output caps...  so if you dont' use the input bledn then yes stick a cap inthere.

if you look at the generalguitargadgets  site you will notice the input is conneted into a cap before the pregain
where as on the input blend one we are connecting after wards ie in other word both are connected with a dc coupling cap just done two different ways.. so as long as you have one somewhere between the input jack and the base you will be fine..

[brett]

so as long as you have one somewhere between the input jack and the base you will be fine..

Except that it will sound different if the base of Q1 is biased by the Preg-gain pot.  In the GGG schematic, the base of Q1 is brought down to ground as the Pre-gain pot is turned down (and at some stage it would even turn the transistor "off").  Whereas in the Tonepad schematic the Pre-gain pot has no effect on the voltage at the base of Q1.

(I think I'll make mine up the Tonepad way - it just seems more conventional to have a fixed bias on Q1)

[Ansil]

yep i understand the theory on it,  but i have done both and had no real noticable differences, i see what you are getting at, but in my personal version i didnt' add either one so that could account for my lack of hearing a diference..

have fun   :)


damn it whats up with the smileys not working ????