BOSS CE2 mod question

[bool]

I have a pretty old CE2 in need of maintenance and would like to perform some mods while at it.


1) I'd like to mod the input stage to be more like the one in CE3, i.e. converting it to a fet-input, with similar values of corresponding passive components. I was thinking of BF244/245A or 2N3819. Any objections to that?

2) I was thinking on "strenghtening" the pre and de-emphasis RC network, i.e. C3/R5 and C15/R23 from schem to values of 10nF/6,8k. In theory, this should keep the corner frequency (tonal) where it was but lowering the noise floor and whatever artifacts from the delay chip. Any objections?



3) I was thinking on putting it on 12V supply (and changing the zener diode D7 to a beefier one). The mod from pt.2 could require some more headroom as well ...

4) I noticed that the antialias filters aren't totally equal - the R15 is at 330k compared to R8 at 100k in the first filter. Why is that and would be there any benefit to having both at equal values?

5) How do you set up the VR3 and what the f* it _does_ in the grand scheme of things? (Surely I know it rebiases the whole pedal but what exactly is it there for? I mean WHY is it needed in the first place and WHAT should I do if I decide to put the pedal on slightly higher voltage.)

[Nikifena]

Fet for input is OK. I try to use fet's input and output with tubescreamer. Sounds verry little different (maybe I suggest myself).

VR3 is to set 1/4 from V.
Measure the voltage from GND to V+. If there is 9v, than the center tap of VR3 must have 4.5v - this called virtual ground.

[Dirk_Hendrik]

When replacing the transistor to a FET change R2 to a higher value too (say >1 Meg) for even better results.

[bool]

Thanks for the input.

I've fiddled with my unit (MIJ, 065500) and in the end decided to leave almost-as-is and instead build the tonepad clone ( http://www.tonepad.com/project.asp?id=53 ) with my intended mods included straight from the begining.


1) as for my original unit, I found that changing the C5 value to 47-68nF thickens the "syrup" and increases the "self" of CE2. Now, I decided to mod my unit to C5 value of 47nF and this will be the only "audio path" mod. The other mod will be to change the zener to the 15V one. This way I will comfortably power my unit with 12V supply, which will allow me to feed it hotter signal, in turn increasing effective relative s/n ratio of the path without modding the actual unit.

2) is setting the V/2 really really really the sole purpose of the VR3? FWIW it could be simply omitted ... Isn't there any more to it?

3) I decided to build the tonepad layout with the originally intended mods, i.e. FET buffer, "hardened" pre and de-emphasis (as I described in OP) ... BUT with use of MN3207/3102. Is there any way to calculate how would such emphasis circuitry impact the s/n ratio which is by default 7dB worse with MN3207?

From what I gathered via the internet, the 3207/3102 could be just "swapped in" into the existing circuit? What should I take care of? I know that going over 10V wouldn't be good ...