Phase 45 Mod Question

[Paul Marossy]

I tried doing a search, but couldn't find an answer to this, so here goes:

On this schematic here http://www.lynx.bc.ca/~jc/phase45modded.gif , what is the point of the two 8.2K resistors in parallel? Does it change the speed?

[gcme93]

That's an odd one :s

I found the value to be 7.5K by googling the original MXR schematic (I'm sure you've done the same) which suggests the mod just takes the Speed resistance range to 4k - 504k.

I guess it justs makes the slowest speed slower or the fastest speed higher depending on which way the pot works. Funny that it says two 8.2K in parallel rather than a 3.9K or something? Perhaps it creates quite a high current at this stage if you drop the resistance down, so its sharing the power loss over two 1/4 watt resistors.

[Paul Marossy]

That's an odd one :s

I found the value to be 7.5K by googling the original MXR schematic (I'm sure you've done the same) which suggests the mod just takes the Speed resistance range to 4k - 504k.

I guess it justs makes the slowest speed slower or the fastest speed higher depending on which way the pot works. Funny that it says two 8.2K in parallel rather than a 3.9K or something? Perhaps it creates quite a high current at this stage if you drop the resistance down, so its sharing the power loss over two 1/4 watt resistors.

I think the modern schematics use 8.2K because it's easy to get. A 7.5K resistor is an odd duck in today's world. I'm assuming the end result is as you suggest. I guess I can try it out tonight and find out for sure.

[pinkjimiphoton]

call me crazy, but i swear sometimes two resistor in parallel to get  a required value "sound" different.
on my toneblaster, i used a 100k resistor and a 100k pot in parallel so i could dial in a total load of around 22k ...

i tried it with various resistors, it seemed to sound best with the two in parallel as opposed to the next closest value alone as a resistor.

[gcme93]

call me crazy

Okay, you're crazy.

Haha I can't really see how that makes any difference in an engineering sense (it really should be identical) but one thing that seems most apparent from reading countless pages of this forum is that to know for certain, you have to try it. And if you've tried it Jimi, then I trust that you can tell a bit of a difference.

Maths can only get you so far, ears will get you the rest of the way i guess

[pinkjimiphoton]

well, now that we've established me being nuts...lol

seriously. it indeed sounds different, and i bet there's a reason for it.

i mean...4  8r 12's in series parallel is still 8r...

but it for SURE sounds different. obviously, there's a lot more speaker area and all, but...

i'll stick with me being crazy!

[gcme93]

well, now that we've established me being nuts...lol

seriously. it indeed sounds different, and i bet there's a reason for it.

i mean...4  8r 12's in series parallel is still 8r...

but it for SURE sounds different. obviously, there's a lot more speaker area and all, but...

i'll stick with me being crazy!

And using the same analogy of parallel resistances, I guess the difference here is a lower power loss on each branch causing a slightly different tone by having parallel resistors? We'll put it down to less heat on each resistor, or some slightly fudged reason like that

Jimi, if we had no crazy people in the world, we'd have no interesting ideas, no experimentation and no progress. Stay crazy.

[pinkjimiphoton]

lol.... eddy currents or something. beats me george!! lol

btw...that vero i did for the bbd?s you bet.

[Paul Marossy]

Just for the record, making that 8.2K (7.5K) resistor half as big seems to double the speed. Might be a useful mod I suppose as the slowest setting is way too slow IMO.