Putting a Pot in series with a resistor in commercial PCB?

[bazzwazzle]

How would I go about putting a pot in series with a resistor on a commercial PCB?

[dolhop]

Lift one end of the resistor, connect it to terminal 2 of the pot, then connect termial 1 or 3 of the pot (depending on how you want the pot to work)  to the pcb location where you lifted the resistor.

[bazzwazzle]

i have just finished but when i turn the knob i notice no difference whatsoever in sound. What I am doing is the external pot mod to my dunlop crybaby on the bottom of this page: http://members01.chello.se/pastorn/fx/mods/dunlop.htm

[bazzwazzle]

just to tell you what i did:

I desoldered one end of the resistor, i connected that end to the middle lug of the pot. then i connected one of the side lugs to the hole where that end of the resistor would have been. It also says to connect the unused lug to the middle lug to reduce crackles, so i did that also. When using it, i noticed no difference in sound when turning the knob.

[petemoore]

Me neither...er at least I think were talking about the same mod...
 External pot changes Q or something
 I found out 'this' mod makes no difference if the inductor is not a 500mh or so...I left the mod as is, because it made no difference, and someday plan to try out an 'improved' inductor.

[dolhop]

which wah do you have?  What is the value of the resistor on the board?  What is the value of the pot you are using?  Is it a log or linear pot?  Use an ohmmeter across the resistor + pot (while the battery is disconnected) to ensure that the pot  changes the resistance from the reistor value to the resistor + pot value.  You may need to disconnect the third lug of the pot from the board to do this.

If you have a GCB-95 wah, replace the 33k resistor with a 10k and use a 50k linear pot for optimum results.  It worked well for me.

[bazzwazzle]

sweet cause i'm using the GCB-95 with a 50K pot, but let me try the different resistor value to see what happens. thanks for the information.

[bazzwazzle]

i still BARELY notice the difference. It's extremely slight. although it does show slightly more.. should i purchase a better inductor?

[markr04]

i still BARELY notice the difference. It's extremely slight. although it does show slightly more.. should i purchase a better inductor?

Lemme guess... the "vocal mod". I did every mod on that page. That's how I got hooked on this stuff. That mod was the one I was hoping would make the most difference, but it is minor.

The resistor in question, on the gcb-95, is a 33K. You leave it in series to prevent the pot from taking it lower than that. But a 50K pot isn't going to make much - if any - difference to the ear. You should go to a 100K pot. Make sure it's "audio taper" or "log" (different stores name them differently). It's still not much though.

I have a slew of those Dunlop HotPotz, BTW. All brand new, with the gear. If anyone has a scratchy wah and is interested, let me know. A well-known internet site is selling them for $25. That's absurd.

[dolhop]

How much are you selling the hotpotz for and where are you located?

I found that the resistor change made a huge difference with the Q.  Check out this page:

http://users.chariot.net.au/~gmarts/fx-wah.htm

[markr04]

How much are you selling the hotpotz for and where are you located?

I found that the resistor change made a huge difference with the Q.  Check out this page:

http://users.chariot.net.au/~gmarts/fx-wah.htm

$12.00 + actual shipping ($1-ish?). I'm in Dallas, TX USA. I'm not in business selling these things. I just got them dirt cheap, compared to the 'other place', and I can pass them on.

[bazzwazzle]

should i consider going higher than 100K pot?

[markr04]

should i consider going higher than 100K pot?

No, not higher than 100K. The usable area is within 33K-100K. Above and below that (the reason for the 33k being in series), you'll get no change. 100K is best here.

You may want to change that .01 uF cap too. I like the difference. But then I want an extreme effect, nothing subtle.

I've tweaked the heck out of mine. After I finished, I saw one of the newer, higher priced Crybabys, and it has the knob in the same place as mine...lol. I'll post some pics when I get the time.

Besides the stompboxes I'm working on, I'm also shielding my guitars' cavities. I'll be posting sound clips of the noise reduction difference too.

[vanhansen]

I'm planning on moding my GCB-95 as well.  One thing I did notice in mine compared to the pics at http://members01.chello.se/pastorn/fx/mods/dunlop.htm is I don't have that input buffer section below the input jack.  Not sure why.  The jacks are soldered on the board.  I've had it for years, probably since the late 80's.

[bazzwazzle]

You may want to change that .01 uF cap too.

Did that, I wanted higher frequency so i went to a 0.0066 uF cap.

I'm planning on moding my GCB-95 as well. One thing I did notice in mine compared to the pics at http://members01.chello.se/pastorn/fx/mods/dunlop.htm is I don't have that input buffer section below the input jack. Not sure why. The jacks are soldered on the board. I've had it for years, probably since the late 80's.

You probably have an earlier revision. I think it says when they started putting the buffers in, early 90's or something? I'll be receiving the 100K pot soon, so i'll try that. Hope it works out!

[vanhansen]

You probably have an earlier revision. I think it says when they started putting the buffers in, early 90's or something? I'll be receiving the 100K pot soon, so i'll try that. Hope it works out!

I knew it was earlier than a 90's model.  The board says WF6 and then under it says ECB-25e.  I'm guessing this is Rev. E.  The jacks are soldered to the board and it has the 8-pin hookup at the top.

Can the same voice mods be done with this rev?  Is there anything special I need to do to the board when putting in the true-bypass mod?

[vanhansen]

I was able to confirm that my Crybaby has PC Board Revision E.  I found the info on the Dunlop web site.

I'd still like to do some mods to it though.

[bazzwazzle]

did dunlop have a picture of the REV. E board? I think you'll be able to to still do most of the mods. I'm not sure about true bypass though. a picture of your PCB would help alot!

[vanhansen]

did dunlop have a picture of the REV. E board? I think you'll be able to to still do most of the mods. I'm not sure about true bypass though. a picture of your PCB would help alot!

No, they didn't have much.  Just a description.  The part number wasn't even available.  Weird.  The info is here:

http://www.jimdunlop.com/support/faqs/elec_parts.html

I found in the GCB95 faq that mine is a 90-91 model actually.  Man, I can't even remember when I bought the thing.  :roll: It was the first rev to have PC mounted jacks.

I'll get some pictures so you can see it.

[bazzwazzle]

thanks, I'll check out that link right now.