Polypropylene Vs. Electrolytic: results.

[bobbletrox]

I've been experimenting with a Bass Fuss style circuit and finding components/tranny combinations that sound best to my ears.  My perfed version used electrolytics, but I've been itching to use these high quality Polypropylene caps so I designed and etched a PCB that would accomodate their size.

I used a Fender P-bass to compare both circuits and the main difference I could hear was that the electrolytic circuit seemed to lose definition and be farty on lower notes (especially on drop-D).  The Poly circuit, however, seemed to maintain the same note/fuzz definition all over the neck -including drop D.  Another suble difference was that the electrolytic circuit sounded a bit on the dull side.  

Now, it beats me whether the differences I described are even physically possible from just using different capacitor materials...but the Poly circuit certainly seemed to sound better on the low notes.  Either way, it was a good excuse to use big yellow capacitors!

This is the poly circuit (ignore the text -it was just a reminder to myself):

[bobbletrox]

A set of $600 knobs would probably improve the bass response even further.

[Peter Snowberg]

Your observations match mine in amp building 100%. Electrolytics just have a "dull" sound to them. Try tantalums out too if you can. I find those to have a less dull tone, but with a sharp "grit" to them. Film caps are still my all around favorite.

When using film, I don't think the $600 knobs will help. The only way to improve that would be to use 2% silver solder and have your board assembled by a virgin on a full moon as she eats garlic.

Cool looking board BTW.

Take care,
-Peter

[Paul Perry (Frostwave)]

peter, any virgin assembler eating garlic by the full moon deserves to remain a vigin,..and probably will

[aron]

I think one of the toughest things is to figure out whether there are differences in the capacitance of the capacitors. It's too easy to say that a film sounds better than an electrolytic in this case (but it probably does!). I wonder what the differences are if you measure them?

[bobbletrox]

I wonder what the differences are if you measure them?

Unfortunatly my DMM is dead right now!  I'd say the Poly caps would at least be closer to their marked values than the electrolytics though.

Your observations match mine in amp building 100%.

Great!  So I'm not just hearing things  

I know pedals aren't really supposed to be hi-fi circuits, and the grittyness of the components give them character -but poly caps seem to work well in this circuit.  At least bass players can play those low notes without having to worry about their tone going mushy!

[Peter Snowberg]

Great!  So I'm not just hearing things  

I could be hearing things too.  

I've seen XY scope traces showing distortion with a sine wave applied and the differences in distortion there are very obvious, but I would love to see a detailed spectrum analysis of white and pink noise run through some caps at different voltages. I think that should show something dramatic.

I'm willing to bet that many of the parameters will vary with frequency and I wouldn't be surprised if that variance is non-linear.

take care,
-Peter

[niftydog]

Check this out, goes some way to explaining the differences.
http://members.aol.com/sbench102/caps.html

IMO, it all depends on WHERE in the circuit the caps are, what value the caps are and what their job is.  It even comes down to the difference in equivalent series resistance (ESR) between caps.

A large ESR in series will attenuate the AC signals, and the ESR may be non-linear, thereby attenuating high frequency more than low frequency or vice versa.

Another factor is the different PC board design.  PCB tracks in close proximity produce capacitance and other reactances.  It's entirely possible that there is some tiny capacitance affecting the circuit.

A large cap (say 100µF) has hardly any effect on audible signals, however, a tiny "stray" capacitance (say 1picofarad) could have a huge effect on the signal.

Thankfully, most of the time, this stray capacitance exists between tracks (ie; in parallel), and the humungous reactance present is actually a good thing.  If such a reactance were presented in series with your signal it would stop the signal in it's tracks!

[petemoore]

And minute...but an Electro lytic for input cap on the FF seems upon extended playing to exhibit the slightest differenct to film...but it is probably the shiney outside that makes it sound that way...
 I was gonna type " I swear I hear it anyway"  as a contradiction to what I've read...just figured it couldn't be so...still I think it Is so...So it is...I got as far as trying to decide if I like that...the 'electrolytic-ness' of it...without a way to measure what the actual values are of individual caps it's hard to conclusively say what it is I think I might be hearing.

[niftydog]

A set of $600 knobs would probably improve the bass response even further.

it is probably the shiney outside that makes it sound that way

hey, it's like the story I read once in New Scientist...

big Hi-Fi demonstration fare, a lot of expensive, hi-tech speaker cables on offer... apparently anything up to US$30,000/metre!!!!

One stall was embarrassed when it was revealed that, rather than relying on their expensive speaker cables to set up their demos, they had dashed across the road to the local hardware store and bought several orange, heavy duty outdoor power extension cables and snipped off the plugs and sockets!

None of the audiophools noticed the sound, but the bright orange cable gave it all away!

After all, wasn't this test done in a fuzz box?  Well, do you want distortion x or distortion y?  It's all relative.  Another guy might like the muddy sound!

I wonder what the differences are if you measure them?

Unfortunatly my DMM is dead right now! I'd say the Poly caps would at least be closer to their marked values than the electrolytics though.

Your DMM will only show you how two caps of the same value are never quite the same value!  Try your tests on a humid day, then stick your fuzz box in the fridge for half an hour...

[bobbletrox]

You're quite right that there are many, many variables...and my test is far from scientific (I used my ears!) -but Polypropylene caps seem to sound good in this circuit.

Might I also add that my main moviation for trying them was that they were big and yellow.  

[bobbletrox]

Try your tests on a humid day, then stick your fuzz box in the fridge for half an hour...

lol...I'll have to give that a go one day!

[niftydog]

but Polypropylene caps seem to sound good in this circuit.

They'll also last a lot longer!

[bobbletrox]

I didn't think of that!  

Good point.

[Ge_Whiz]

Looking back through earlier threads, and at numerous hi-fi sites, I can now tabulate the following opinions expressed:

Carbon composite resistors sound 'dirty'
Metal film resistors sound 'metallicky'
Ceramic capacitors sound 'brittle'
Silicon transistors sound 'shiny'
Old electrolytics sound 'dull'
Tantalum capacitors sound 'small'
Cheap vacuum tubes 'suck'
Polyester capacitors sound kinda 'plasticky'
Old polypropylene capacitors sound 'big and yellow'
...and anything outrageously expensive sounds 'fantastic' - to the owner

[niftydog]

...and red wine has a hint of;

plum
cherry
leather
oak
earth

and white wine has a hint of;

grape
honey
butter
crispness
fruit


Hey, you never know, maybe poly caps increase your soundstage and musicality!