OCD with a tantalum cap

[ghostsauce]

So, I did a lot of searching and found that there isn't much difference between the cap types, and that tantalums are less reliable, but that it can matter in some situations. Anyways, the OCD circuit I'm about to build calls for one. Has anyone here built the OCD with/without it? I don't want it to be missing that 'special something'. I'd just order the tantalum cap as well, but I'd have to source it from somewhere other than the place I'm getting the rest of the order. Boo.

http://rapidriotboxes.blogspot.com/2009/02/fulltone-ocd-v4.html

[Johan]

the main reason for using a tantalum cap is to be able to use a large value cap in a tight space. if you have plenty of space, you might as well use an electrolyte. if not, go with tantalum.  I doubt you'd hear any significant differance. tantalum's will fail in spectacular ways if you reverse the polarity, but so will electrolyte if the voltage is high enough...use what you have and don't panic if not everything is exactly as spec.  it is after all "diy" and you can/will fix it later if you're not happy with the endresult
J

[Steve Mavronis]

So, I did a lot of searching and found that there isn't much difference between the cap types, and that tantalums are less reliable, but that it can matter in some situations.

What makes you say tantalum is less reliable? They are less leaky than regular electrolytics which is a good thing and save space on your board. MXR has used them since the beginning and they still hold up well today. I've used them with no problems. I'd say they are very reliable. If you reverse polarity to blow it, that's not the fault of the cap.

[ghostsauce]

Thanks for the info!   

@above:  I just meant that the tolerance tends to be higher. Maybe I don't understand correctly, but I thought that meant that it's not a tight sounding unit if you use a high tolerance, or it won't always sound the exact same.

[Steve Mavronis]

Oh, I see what you mean. I don't know if you could percieve subtle changes in part value on either type cap at 5% for example. If I wanted a certain value cap or any other part, I'd want it to stay that value as tight as possible within the rated tolerance. I'm still learning about this stuff too. Here are a couple blurbs about tantalum caps:

http://www.ehow.com/list_5936216_benefits-polymer-tantalum-capacitors.html

Tantalum capacitors are particularly desirable because they can store a great deal of electricity for their size and weight, so the capacitors can be smaller--an advantage that mobile phone makers have taken advantage of to produce smaller and smaller cell phones. They are used especially where saving space is a priority and when long life and reliability are at a premium.

In the past Tantalum were made of magnesium dioxide (MnO2) and prone to failure. That's why modern polymer tantalum caps that replaced them are better.

The other drawback was that the tantalum-MnO2 capacitors had a higher "electrical resistance" than capacitors made with other dielectrics.

By using a polymer for the cathode instead, engineers have been able to reduce the resistance inherent in the devices, as well, making them a better alternative. In fact, the conductive polymer developed as an alternative in the 1990s is 1,000 times more conductive than MnO2.

[skrunk]

Tolerance just refers to how close the actual value of the part could be to the value printed on the side.
for example, the actual capacitance of a 100uf cap with 10% tolerance could be anything from 90uf to 110uf (100uf +/-10uf)
or the actual resistance of a 1k resistor with 1% tolerance will be anything from 990R to 1.01k (1000R +/- 10R). 

the actual value isn't going to vary over time, a 98uf cap is always going to be a 98uf cap, not 98uf one day and 101uf the next.
using lower tolerance electros isn't going to sound better or worse than high tolerance, you won't hear a difference between a 4.7uf or 4.8uf cap say.
and it's still possible a 100uf cap with 10% tolerance could actually be closer to 100uf than one with 5% tolerance (less likely, but possible).

btw if the tantulum your referring to is the 1uf output cap, a 1uf film cap will work fine and may even sound better.
as Johan said, it was probably only used to save space.

[PRR]

Tants in _power_ applications have a reputation for exploding in 20 years.

The available power in a pedal makes explosion unlikely, though it may short.

But it isn't a "big" immediate problem. Maybe you get 10 or 30 years of great sound, and then you have to repair it. Hey, this is a DIY group, repairs are no big deal.

A reason TO use tant used to be lower leakage. But Aluminum electrolytics have improved a LOT since the 1960s, and are now generally as low-leakage as tants used to be.

Tolerance is no big deal. Electros (Al or Ta) are usually OVER-sized. Cost is low. Math says 4.567uFd for exactly -1dB at 82 Hz, stick in a 10uFd (doesn't cost much more than 4.7uFd) so the worst possible case will measure to spec.

And size, though Al caps have got a lot smaller since the old days.

[Liquitone]

I tend to go for film caps all along the audiopath, and found a few that are about as tiny as a electrolyte.
I've heard good things about the panasonic stacked metal film but havent used them yet.
I've used a little wima mks 1uF cap for my ocd built and it sounds great.
the wima's are actually a tiny bit smaller than the 1uF electrolytes I have and will take up about as much space on the board as a tantalum.
There's a lot of discussions about wether the cap types makes a difference to the sound,
some say the use of less hi-fi tantalum and multilayer ceramic cap in the original OCD might actually work better in this application for adding grit and top end harmonics.
I've A/B'd my build with a real one and was a bit dissapointed, my build with expensive caps didnt sound really different from the original at all.
the only difference i could hear was that mine had less low end, but that might have been cause i used a 68n and the real one a 100n (not sure cause i havent looked inside it)