Do ceramic disc caps add to the script-logo MXR Phase 90s mojo?

[Humbucker]

Do ceramic disc caps add to the script-logo MXR Phase 90s mojo?

Apparently the original Script-Logo MXR Phase 90 had a Texas intruments UA741CP op amp, carbon comp resistors, and some NOS ceramic disc caps. Many boutique pedal builders replace all the ceramic disc caps with metal film, but in the case of the Phase90, don't the ceramic disc caps play a huge part in the tone of the original script versions?

[R.G.]

Do ceramic disc caps add to the script-logo MXR Phase 90s mojo?

Apparently the original Script-Logo MXR Phase 90 had a Texas intruments UA741CP op amp, carbon comp resistors, and some NOS ceramic disc caps. Many boutique pedal builders replace all the ceramic disc caps with metal film, but in the case of the Phase90, don't the ceramic disc caps play a huge part in the tone of the original script versions?
Why would you think so?

[Mouthurst]

Do ceramic disc caps add to the script-logo MXR Phase 90s mojo?

Apparently the original Script-Logo MXR Phase 90 had a Texas intruments UA741CP op amp, carbon comp resistors, and some NOS ceramic disc caps. Many boutique pedal builders replace all the ceramic disc caps with metal film, but in the case of the Phase90, don't the ceramic disc caps play a huge part in the tone of the original script versions?

Just my opinion but I would say Absoulutley. I think those pedals are meant to "add or change" the tone and probably evolved from the simpler original original "Phase Tone". I have one and its the only way I can get Dave Gilmore's early sound.
From the marketing Ive seen I beleive the boutique guys dont want to change the tone but have the effect transparent.

[Humbucker]

Well, the reason I'm asking is that I was thinking of getting a BYOC Phase 90 kit, they have a "block-logo" Phase 90, which probably has better quality caps but then there was this "script-logo" Phase 90 kit which has a Texas intruments UA741CP op amp, carbon comp resistors, and some NOS ceramic disc caps.(This Script-Logo kit is actually $10.00 more then the "Block-Logo" kit)

I was debating which one to order and I ended up just ordering the Script-Logo, I'm sure it'll rock!

Thanks for your replies!

[R.G.]

Well, the reason I'm asking is that I was thinking of getting a BYOC Phase 90 kit, they have a "block-logo" Phase 90, which probably has better quality caps but then there was this "script-logo" Phase 90 kit which has a Texas intruments UA741CP op amp, carbon comp resistors, and some NOS ceramic disc caps.(This Script-Logo kit is actually $10.00 more then the "Block-Logo" kit)

I was debating which one to order and I ended up just ordering the Script-Logo, I'm sure it'll rock!

Thanks for your replies!

You do know that you can get the ceramic disc caps for about $0.10 each from Mouser, right? And you do know that one meaning of "NOS" is "stuff that wouldn't sell when it was new" right?

I personally would be amazed if you could tell the difference more accurately that blind guessing between two otherwise identical units which differed only in having ceramic caps and carbon comp resistors.

Carbon comp resistors do not show off their special nature under about 50V of signal swing - hard to do in a 9V pedal.

[Mark Hammer]

Because MXR did not have the luxury of small pots or small-footprint stompswitches "back in the day", and because they made the corporate decision to use the same small-size Eddystone (equivalent to Hammond 1590B) boxes for all their first series of pedals, they were faced with the challenge of making very low profile circuit boards that could fit in the box over top of the pots. The end result of that was that they used caps that could be bent over flat, which meant ceramics for nonpolarized, and often tantalums for polarized. When a shift in packaging occurred several years later, they adopted "normal" plastic caps and electrolytics as the default choice. We have a much wider array of component choices now in 2006, and can probably find medium-value electrolytics that sit lower on the board than bent-over picofarad ceramics did in 1976, and for half the price. I am confident that if MXR were starting out nowadays, they would have made entirely different choices in component types.

As for "mojo", it sometimes occurs because of happy accidents that diverge from the stated specs and nominal values of the components. Ceramic caps are often less precise than their plastic cousins, and these may easily shift the corner frequency of this or that as a result.

You will also find many small-but-critical design or component-value changes over the years that have influenced the sound. Chalking up the results of those differences to the composition of the parts is an error in inference.

[David Schwab]

The script logo unit and the block logo unit are quit different on the inside. MXR made several changes to the Phase 90 over the years. The newer units have more feedback for a more resonant tone than the originals. I like the old ones best.

I had an original script unit... it had about 8 or 9-741 op amps. Mine was in a Budd case.

Some of the kits I've seen online, like from buildyourownclone.com, are NOT the same board as the original script unit. That one uses 4 op amps... probably dual units?

I have a drawing of the circuit board and the schematic I made back in the early 80's. I could scan it if anyone needs it.

[R.G.]

...
I had an original script unit... it had about 8 or 9-741 op amps. Mine was in a Budd case.
...
I have a drawing of the circuit board and the schematic I made back in the early 80's. I could scan it if anyone needs it.
Yeah, I'd like to see an 8 or nine 741 version of the P90.
Could you scan those and perhaps email?

[dai h.]

I thought it was six single (741) which was later changed to 3 dual (TL062) plus a bit of difference in circuitry. I'm not sure I'd read too much into the carbon comp thing, since I think MXR just used what resistors they had since you see a mix and more or less of them depending on the unit. Resistor type difference would be inconsequential compared to changing a block type circuit to "script specs".

[David Schwab]

It's been a while since I looked at the scematic/board drawing... but I seem to remember it was more than 6 op amps... but I could be wrong. I'll dig it up this weekend.

I had a friend who had one that stopped working (as later did mine) and I figured it was a bad 741. So I removed all of them and installed sockets, and plugged in new ones. Seemed like a brute force kind of way to fix it, but it worked.

We then replaced the 741's with TL071's. Gave it a more "open" sound.

[David Schwab]

I thought it was six single (741) which was later changed to 3 dual (TL062) plus a bit of difference in circuitry....

Yep, you are correct... six 741's. I was remembering four in a row on one side and just assumed it was two rows of four...

Anyway, here's the diagram I made. I could only find the drawing of the circuit board and parts layout... but I had figured out the circuit schematic from this at the time.

This drawing is from 1977, when I was a young lad of 19... :)

http://www.sgdlutherie.com/images/phase90.gif

[dai h.]

nice diagram! That's what I should've been using (graph paper, lol...).

[David Schwab]

nice diagram! That's what I should've been using (graph paper, lol...).

Thanks! Pretty sloppy, but not bad for using a flair marker! As long as you line up the pads to the parts, it works fine...

I used to copy a lot of pedals this way. I actually made a Phase 90 by hand drawing the circuit board (sharpie makers resist the enchant well) ... boy when you are young and don't have a lot of money, you find time for such things! By the time my Phase 90 quit working I just didn't bother to fix it.

I mostly used to make Distortion+ clones with TL071's.. a LOT easier!

[dai h.]

actually I mean to say it is quite neat since I was doing the same thing by eye--judging the distances between parts--which obviously was not a particulary efficient way to go compared to graph paper. DIY ghetto methods...lol

[David Schwab]

actually I mean to say it is quite neat since I was doing the same thing by eye--judging the distances between parts--which obviously was not a particulary efficient way to go compared to graph paper. DIY ghetto methods...lol

What I used to do, besides using graph paper, was to start off with a piece of tracing paper, taped to the board. I pressed it so the ends of the soldered components would poke through the paper. Then I would draw in the traces with a pencil. Once I got a good tracing, I transfered that to the graph paper, usually by poking a pin through the holes left where the pads are, and then using a flip book type technique, where I would flip up the graph paper to see the line, draw a bit, flip, draw, etc.

I transfered that to the circuit board by using a center punch to make dimples where the wholes would be drilled. I used perf board as a guide to get the IC holes right.

I used to love making PC boards by hand. :D

Now I do everything photo-mechanically...

[dai h.]

hmm... now that I think about it, I never tried copying a pcb, just made them from magazine articles and this one book, most with that whatchamacallit light sensitive stuff. I suppose it'd be easier with a scanner now.

[Mark Hammer]

I use to simply photocopy the board, tape the photocopy to a piece of copper board, and use my spring-loaded centre-punch to make the dimple holes, then connect the dots. Made a couple of MXR clones this way back in the day.

[jaysg]

David,

My old P90...(foolishly sold off), was that layout. Does that mean it was a Script logo? I bought it between 1973 and 1977 -- can't recall or find the reciept. My 78 D+ is block. (I recall trying someone else's P90 in 1979 and I hated it.)

[David Schwab]

I use to simply photocopy the board, tape the photocopy to a piece of copper board, and use my spring-loaded centre-punch to make the dimple holes, then connect the dots. Made a couple of MXR clones this way back in the day.

Photocopying... great idea. Didn't occur to be back then! I also used a center punch... probably just a plain kind. I remember having one of those spring loaded ones. Forgot all about that!


David,

My old P90...(foolishly sold off), was that layout. Does that mean it was a Script logo? I bought it between 1973 and 1977 -- can't recall or find the reciept. My 78 D+ is block. (I recall trying someone else's P90 in 1979 and I hated it.)

Probably. Mine was a script logo. I bought it new at the time, so that's how they all were. I think I still have the case somewhere... don't know where the board went ... :(

[Zoe_N_Iain]

I mostly used to make Distortion+ clones with TL071's.. a LOT easier!

(Iain) Me too. Had to put the RAF's PCB unit to some productive use. :)

I think I used every pin compatible opamp, surplus capacitor and suitable resistor I could find in the bottom of a drawer to knock up those things.

I used to have a really sweet one that used an opamp (the type escapes me now) that looked like a metal can transistor with 8 legs. I just bent the legs until they lined up with the holes and put bits of stripped insulation on each one.

The thing that used to really irk me was having to buy the 9V battery connectors. :D

[Humbucker]

Thanks for all of your replies to my post guys!

BTW, the BYOC Script-Logo Phase 90 kit now comes in a "new 6 opamp version".

Linky:
http://www.buildyourownclone.com/phaser.html