Filter Caps Coming Off 9VDC

[BrianS]

Up front please don't crucify me for not being an electronics guru because I am not. I can put these things together and quite often they work.  I bought a Rabbit Hole and was doing some reading on the different variations to try and figure out which one to build.  I was reading a thread on the TDPRI forum and one of the commenters wrote:

"One last trick that I've gotten a lot of mileage out of is to make the filter cap that comes off your 9VDC source as big as you can. I now make it 470uF always, and I've seen at least one builder (Dice Works) use 1000uF. BJT transistors in these old crude circuits can be fantastic hum amplifiers with the sustain control all the way up - the big filter cap REALLY helps."

Most every gain pedal I built has so much hiss/hum that I end up not liking it. I know this is for the most part their nature.  But if I could go in and place a bigger filter cap on these pedals am I going to get a reasonable result as mentioned above without jacking something else up as far as sound goes? 

[galaxiex]

Bigger filter caps *might* help. Like so many other things, it depends...
That said, it won't hurt anything. You could always socket the cap(s) and test different values to see if it makes any change.

[madbean]

The Muff certainly is prone to some noise and hum. I built my RH to Civil War specs and it is actually pretty quiet, if that helps. Most likely that is due to it being less gain than some of the other versions. But, you are not going to be able to fit a large cap like that (470uF or 1000uF) on the Rabbit Hole. There's just no room. If you are using a well-regulated power supply like the PP2 or whatever, the 9v rails are already filtered quite a bit, too.

[BrianS]

The Muff certainly is prone to some noise and hum. I built my RH to Civil War specs and it is actually pretty quiet, if that helps. Most likely that is due to it being less gain than some of the other versions. But, you are not going to be able to fit a large cap like that (470uF or 1000uF) on the Rabbit Hole. There's just no room. If you are using a well-regulated power supply like the PP2 or whatever, the 9v rails are already filtered quite a bit, too.

Brian I know you're real busy and if you can't answer this perhaps someone else can. You built the Civil War version and the only difference  that I can see between it and the Green Russian (used this because its on the same page) is the 430p caps.  So C2, 5 and 8 are basically determining the gain level between the two versions?  And the Triangle and Creamy Dreamer would have the most gain since they are 560p (I know there are different parts used/omitted on these also).  I am just trying to understand the process here.

And this question wasn't so much directed to the Rabbit Hole but in a whole towards the other gain/distortion pedals I've built that have so much hum/hiss that to me they're just not usable.  A lot of these were earlier builds when I first started and maybe soldering and part selection wasn't the best.  I know there are many variables that can contribute to this.   

Thanks for the answers. 

[m-Kresol]

If you have a noise problem with all/most of your pedals, the first question is: what power supply are you using? that really can make a big difference here to have a well regulated PSU. Do your commercial pedals also hiss and produce more noise than you'd expect? Than it's most likely the PSU.

Other stuff that *might* help, that many of the designs here already incorporate is a low pass filter at the power input, i.e. a low resistance resistor (eg 33-47R) before the smoothing cap. This will get rid of some of the low-frequency humming assuming you have a bad ripple current in your power supply. Making the cap bigger could certainly help too. You could use one of your too noisy pedals, desolder the cap, socket it and try various other values to see if it actually helps.

But don't forget that many drive pedals are noisy anyways. you could also use a noise gate... (there's one in the etchers paradise, Lectric-Fx has one and I could hook you up too)

[BrianS]

Even when I run some of them off a good wall wart by themselves they still make noise.  I run everything off a OneSpot and I've been looking at getting a better power supply.  I just saw the the post on that particular forum and just wanted some advice from those of you that are way smarter than me if the bigger cap would make any difference at all.  I will do as you said on a couple of the high noise pedals and socket the cap and see if that does anything.

[thesmokingman]

the caps you're referring to in the big muff don't set gain of the transistor. see http://www.electrosmash.com/big-muff-pi-analysis to understand their function.

also, while I do contribute to the tdpri forums, they're not always a reliable source of information.

[solderfumes]

Brian I know you're real busy and if you can't answer this perhaps someone else can. You built the Civil War version and the only difference  that I can see between it and the Green Russian (used this because its on the same page) is the 430p caps.  So C2, 5 and 8 are basically determining the gain level between the two versions?  And the Triangle and Creamy Dreamer would have the most gain since they are 560p (I know there are different parts used/omitted on these also).  I am just trying to understand the process here.

R23 also differs.  It's 2k7 on the Civil War and 2k on the Green Russian.  That resistor affects the gain on the final transistor stage.