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The Slow Gear/Lazy Sprocket circuit is capable of longer swell times, but requires a higher resistance Attack pot to attain them. In discussing this with fellow forum mod mmarsh, he told me he had found that the maximum usable value is somewhere around 75 - 80 Kohm; above about 3 o'clock on a linear taper 100K pot, you start to get noticeable volume loss.

Well, obviously a B75K is a pretty rare beast to try to find, so I started thinking about how to work around the problem. What I came up with is to solder a 220K fixed resistor across lugs 1 and 2 of a B100K pot. This parallel resistor configuration gives a maximum resistance according to the formula Rp = 1/(1/R1 + 1/R2) where R1 and R2 are the two individual resistance values and Rp is the overall value. Plugging in the values of 100K and 220K for R1 and R2 gives a composite resistance of about 69 Kohm--pretty close to the 75K I wanted. The pot response isn't quite linear, but it's reasonably close. And I get a really nice, long swell with the pot "dimed".

Here's a shot of the modified B100K pot--just needs to have the excess leads of the resistor trimmed off and it's ready for installation.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

The DV-Man is D Man!

I tried this on mine and it works really well. I use the stock .68 tant cap and the 100K pot because I like the feel of the release with that combo rather than a larger value tant cap, which mucks with the release too much for my taste. But as duhvoodooman says, you can't use the 25% or so of the travel on the 100K pot. His solution is devilishly clever.

Thanks!

Mike

Hello gents

I am a total novice at electronics, but am going to attempt this mod. I live in the UK and just need to check which kind of resistor to use.

http://www.maplin.co.uk/Module.aspx?Mod ... Code=M200K

Is this right? I'm not sure about 'metal film' (I've seen carbon film as well) as I don't even know what this mean!

Same for wattage. Is 0.6W right?

Thanks in advance.

Hey Brainy,

That web link ought to be just fine. Be sure to select the 220K value, not the default 200K. The 0.6w rating is higher than you need here, but since the resistor is the same size as a 1/4w, there's no problem there. Chances are very good you'll never need anything bigger than a 1/4W rating for pedal building. That doesn't mean you can't use a bigger value, but why spend more money? Plus components increase in size along with the wattage/voltage ratings, and we like to stay small.

The important difference between metal film and carbon film resistors is manufacturing tolerance. The brown carbon film ones, like DVM pictured above, are typically accurate to within 5% of their stated value. Metal film resistors, usually blue, are typically accurate to within 1% (or sometimes 2%) of their stated value. It has been my experience that when values are off-spec (which they nearly always are), the resistance is usually lower than the stated value, and almost never higher.

Metal film also is said to introduce less noise into audio circuits, while carbon film resistors are sometimes said to be "hissy". I've never noticed a difference, really. You may also see carbon comp resistors from time to time, usually in builds advertised as having lots of "mojo". These are the old-school resistors that look like a big brown tube. They are often only accurate to 20% of their stated tolerance! In fact, most carbon comps will be a minimum of 10% off -- because resistors with tolerances better than 10% were kept aside and sold at a higher price by some of the major manufacturers.

Lastly, I think the color codes on carbon film resistors are easier to read, because the last band is a metallic paint that signifies tolerance. In the case of the one pictured above, it's a gold band to denote 5%. On metal film resistors, it's often assumed that you know the tolerance is 1%, so the color bands are printed without it. This can lead to reading the codes backwards - another reason it's good to measure your components with a DMM before installing them.

That's probably more info than you wanted... but that's what this forum is about, right?

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Thank you, Captain, the info is spot on. I would just reiterate to make sure to choose the 220K resistor. This is an easy mod and works really well. Good luck!

Mike

Thanks very much Captain, that was all useful info to someone like me, not too much at all, really helpful!

I forgot to ask also about making sure I got the right pot to do the mod. My local electronics shop won't have them in for another 6wks, so I've resorted to ebay. I can see there are differences on the shafts of these two, but would either work? Or, in other words, which one should I use?


http://cgi.ebay.co.uk/100K-Potentiomete ... 20b4dffdab

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT

PS
Thanks for pointing out the 220k not 200k - that's exactly the kind of mistake I would make!

brainy, those are both B100K pots, and either one would work for DVM's mod. If it were me, though, I'd go with the one that doesn't have a shaft that would stick up 3" out of the front of my pedal.

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What? I actually DON'T want one pot sticking up 3"?

God, I'm more of a novice than I thought!!

Thanks again for your advice, the one with the shorter shaft is also cheaper. I shall pop off now and buy one, and try my first ever mod!

You can actually hack-saw that off, so that would not have been a fatal error I've had occasions where those were the only availables and the hack-saw on aluminum is easy...

If your target resistance is 75K to 80K a better combo would be with a 300K in parallel.

100K // 300K = 75K

100K // 330K = 76.7K

100K // 360K = 78.3K

100K // 390K = 79.6K

// = in parallel with

_________________
"It’s your soldering."

Ok, so the same pot (that I've now bought) and just buy a 300k resistor and put it in exactly the place that this mod starts off by showing?

That is what Stephen is saying, although DVM did say that he played around with values and found 220K to be pretty optimum. This mod is easy enough to try both, though if you're ambitious, and neither Stephen nor DVM would steer you wrong

*EDIT* I've done the mod with 220K and I can say that the 100K pot is usable now the full radius of travel, FWIW.

To be fair, if I'd had a 300K resistor around, that's what I would have used. But I had a 220K handy, did the parallel resistor calculation, and figured 69K was plenty close enough for my needs. But if you have a 300K or something close to that, it will probably give you even a bit more dwell than I got. AAMOF, 330K is a pretty common resistor size, and that would work out to 77K.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Hi all

I did this mod, but sadly, had a rather amateur time doing so.....


It worked - after making an error wiring up the power adaptor jack. It wasn't pretty.....there was some collateral damage.......and now.........

the original power adaptor jack is very dead.


Being a total novice at electronics, I don't know how to make sure I buy the correct replacement in the UK, or from where. (Maplin being the usual place to start in the UK)

Any guidance gratefully accepted.


PS
I did post this question in the sourcing parts thread, but have had no replies, so thought I could try here. Apologies if this is not correct forum etiquette...

Hi brainy -

I am indeed sorry to hear about your woe

Here are the specs on the jack:

DC power jack
2.1mm plastic
Fits 1/2" opening

Maplins for sure has them.

Mike

Can't point you to a UK source, but this is what comes in the BYOC kits:

http://www.pedalpartsplus.com/mm5/merch ... y_Code=JAC

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Thanks very much both, I should be able to track one down now.


Not sure about maplin, looking at their website (which is spectacularly lazy of me, as there is a maplin shop about a mile from mt flat......but I trust you good people more than the people in the shop, to make sure I get the right part....)

Are these right? They look it, but just not sure where it's saying about clearance. The pedals I could be using this for are: reverb, large beaver, classic OD, classic compressor

http://www.doctortweek.co.uk/shop/artic ... m-(plastic).html?shop_param=cid%3D49%26aid%3D92%26

I followed that link but did not see a DC jack...this one with fit, but it does not say if it is switching: http://www.doctortweek.co.uk/shop/artic ... m-(plastic).html?shop_param=cid%3D49%26aid%3D92%26

Thanks mmarsh, I must have cocked my link up - that was the item I was linking to. I'll buy one and see what happens...(cos also I don't what it means to be 'switching'! I really know pretty much nothing about electronics, although I am on about my fifth BYOC build, with only one failed build....)

The other thought I'd had is that I've just finished my tone bender build, and was thinking that to prevent any accidental plugging it into a daisy chain, I could just remove the dc adaptor from that, as I intend to only ever power it by battery. But the battery snap is connected directly to the dc adaptor, so not sure how to rewire it....

I did this mod as Voodoo describes and it works a treat and gives just the swell I need but you have to get the sensitivity right.

Cheers
Fez

I tried this but it didn't work so I just put my old pot back in and it works like normal, with the volume drop off. Adjusted the trimpot, sensitivity, and of course the swell, but no change. With the sensitivity all the way counterclockwise, there was some gating, but the trim and swell did nothing. Seems weird since it is a simple mod and it works fine with the old pot.

One other thing worth mentioning, about a year ago, I tried to put in a different swell pot so I got an A100k pot because that's all Radio Shack had. It stuck out like a foot from the pedal and had to hack it off. First, I tried putting 3 100k resistors on this pot, but it didn't work. It had the same result as the B100k pot: just the gating on the sensitivity knob.

Any suggestions?

Thanks,
Keith

Oh, and this pedal was put together by BYOC, so I know it's not screwed up in some other way.

-Keith

Please post a picture of you modified pot. It should look like DVMs. And BTW, BYOC does not build pedals, you probably got yours from Axw And You Shall Receive, just as a clarification to others reading this post

Mike

I got some new resistors today, the 1/4 watt ones instead of the 1/2 watt ones that I had used the other day. I used 3 100k resistors and it worked fine this time. I don't think the 1/4 watt would make a difference, but it worked this time. Nice mod!

And thanks for the clarification. I bought it used and the guy said BYOC had made it, so that's why I thought that.

-Keith

Cool, it is a great mod. Enjoy the pedal, and glad you got it working!