Vintage SCRIPT vs Vintage BLOCK logo MXR Phase 90

[cyberpunk409]

i just bought a vintage BLOCK logo MXR PHASE 90 off ebay (haven't got it yet). The year of manufacture, according to the seller/pot code is 1979.

 

Here is a picture of the circuit board:

 

Now here is a picture of a vintage SCRIPT logo phase 90, made in 1977

 

What the heck is the difference?

 

The later vintage BLOCK logo boards (still owned by MXR - pre-dunlop) did look different, something like this (circa 1979):

 

And the even later BLOCK logo boards (still owned by MXR - pre-dunlop) got a complete overhaul, dropping the single 6 opamps and replacing them with 3 dual opamps, among other things:

 

so my question is... what exactly have i purchased? cheers to anyone who can shed some light on the matter

[cyberpunk409]

i should probably also add, that this is an EVEN older circuit board, from 1974:

 

So does this mean that there was a transitional period where SCRIPT and BLOCK logo Phase 90's had the SAME circuit board/same chips?

 

i'm thinking maybe late '77 to early '79 ?

 

If so, does that mean that there are varying levels of "collectability" among vintage SCRIPT logo Phase 90's themselves?

 

this is all doing my head in

[andreas]

Yes, it was never as clear-cut as script = six single opamps, no feedback; block = three dual opamps, feedback resistor. As you noted, these changes were made in steps, gradually. Initially, the circuit didn't change at all after the switch to block logo, and at some point (possibly when they ran out of already-populated circuit boards) they added the feedback resistor to make effect a little stronger. At a later date, they revised the entire design using three dual op-amps instead of the six singe ones used earlier.

 

So there are "transitional" block logo pedals with script logo circuit boards in them. Also, the batch produced between the addition of the feedback resistor and the redesign can be easily modified to script logo specs - after all, the only real difference is the added feedback resistor, so it's just a matter of taking it out. Later models (using the three dual op-amps) can also be modified of course, as the circuit works the same as the older one, but it will not be 100% correct.

 

Yup, it's a jungle out there...

 

/Andreas