Caps for MXR Distortion Plus

[natron_mn]

I was going to build an MXR Distortion + clone using the layout below, but was wondering about those 1uF caps. In this layout, they show no polarization. So, can I use some 1uF film caps? Or should I use polarized caps?

I was also going to use a 500k reverse log pot for the distortion, as I've heard that is what they used in the originals.

[mimmotronics]

If there's no polarization given I might default to film caps. Though, if polarized caps are used for bypass purposes, I've always seen the positive end being used as the "input" side for the signal and the negative end as the "output" side.

[slashandburn]

I think you can use a non polar and it'll be fine. If you opt for a n electrolytic, positive end the IC I think.



Someone more informed will be along soon enough. I think this cap is just for DC blocking.

[mimmotronics]

Now that I've had a better look at the board it seems as though the 1uF cap on the far right is being used as stabilization for the 4.5V bias. For that I might lean towards a polarized (because thats what I've seen in most voltage stabilization applications, especially in power circuits). The other 1uF cap looks like a bypass/DC-blocking cap for the output signal from the 741. For this I've seen both types used. As far as which is better here, I'm not entirely sure.. I'd love if someone with more experience could lay down some knowledge on this topic.

[GibsonGM]

I've built them with polarized electro's, + towards IC as noted (the other "+"  would of course be towards +9V at your bias network). 
Yes, they use them a lot in power supplies like this, as they are common, cheap, and effective. 

No issues at all, no need for worry or having to find special caps   

If you wanted to use "hardcore engineering rules', yes, the AC-passing cap at the IC's output would ideally be a NP, or perhaps a poly type (Wasn't the original a tantalum, tho??) as polarized electro's 'aren't really for AC'.     Maybe that helps the Dist + sound the way it does, tho!   It is not something I personally would worry about here; mine sounds fine w/electros, has for a decade.   

You COULD use 2 - 470n poly types in parallel there if it makes you feel better....  *shrug*

[bluebunny]

I would tend to go for a film cap at the output of the opamp, although it's unlikely to fit in the space it's been given on that layout.  Or try an MLCC?  The type of the one at the far right isn't important, for reasons already mentioned.

[anotherjim]

If you google "MXR D+ schematic" you will find several drawings that do show those cap polarities.

[GibsonGM]

If you google "MXR D+ schematic" you will find several drawings that do show those cap polarities.

Anyone have an original?  I'd bet dollars to donuts it was just a 1u tantalum or electro in that era, tho not 'wonderful engineering'.   
That wouldn't bring out the ultrasonic hi-fi quality of the 741, ha ha....

Here: http://www.generalguitargadgets.com/pdf/ggg_dist_plus_sc.pdf

[antonis]

There always been the option of using 1μF Non-Polarized electrolytic caps..

[natron_mn]

Naive question, but what is the purpose of non-polarized electrolytic caps? Do they function the same as film caps, or any other non-electrolytic cap?

[anotherjim]

Both of the caps in question will have a proper polarising voltage across them. One is from Vb to 0v and the other is op-amp output ( at Vb) to 0v. I would have no hesitation using polarized caps.
The only time the non-polarized electro caps must be used is when there is no particular constant DC across them. Between op-amp stages and both ends are at Vb. That's the only time the likes of Boss fit them.