First, as it is my first post here, greetings to everyone here. Some of you I probably already know from BYOC. Now, to business.
I've built a Skreddy P19 using a Mudbunny board and when I fired it up it had issues with two of the pots. Sustain was working but Tone and Volume were doing nothing at all. I tried a different pot for volume, same issue. Eventually I redirected the ground wire from lug one off the board and directly to the output and volume finally worked as it should. So apparently there's something wrong with the ground on the board. Which might cause the tone pot to malfunction as well. My question to you fine gents is, where in the circuit might the culprit be?
The P19 is mostly a Big Muff with different values, but there are a few additions to the standard Big Muff circuit. TThere's an extra 2n cap between lugs 3 and 2 of the sustain pot (added to the pot), the cap and resistor between Sustain pot and Q2 are reversed from a normal muff (done to board), there's an extra 100r resistor between lug 2 of the tone pot and C12 (added between pot and board), there's the mid switch between the collector of Q3 and lug 3 of the tone pot and there's an additional 560pf cap between the output cap and volume pot going to ground (added to pot).
Finally a link to the P19 schematic:
http://1.bp.blogspot.com/-u2ndmxs2Eys/T47bHDJutuI/AAAAAAAABS0/v3r6znbrGtQ/s1600/skreddy_p19_schematic.gif
(http://1.bp.blogspot.com/-u2ndmxs2Eys/T47bHDJutuI/AAAAAAAABS0/v3r6znbrGtQ/s1600/skreddy_p19_schematic.gif)
Do you have photos of your non working build? I've made a P19 on a Mudbunny and it fired up ok.
Also, what transistors did you use? Did you make sure you were using the correct pin out? The mud bunny is set up for 2n5008's if I remember right.
I'll snap off some pics tomorrow (for now off to bed). The transistors I used were BC550C's, but I made sure to check out the pinouts and noticed right away that they were reversed from the Mudbunny layout. Then again a lot of BC series trannies seem to be reversed from the 2N series so I was expecting that at least.
Yep that's correct the BC550's should be reverse from the labeling on the mudbunny
Were you working from Juansolo's muff spreadsheet? If not, it could be worth crosschecking with it anyway.
Quote from: alanp on March 06, 2014, 03:49:55 AM
Were you working from Juansolo's muff spreadsheet? If not, it could be worth crosschecking with it anyway.
I used both the schematic I postred above and IvIark's vero layout on tagboard. Originally I wanted to do it as a vero layout, but of the four Muffs I built using vero layouts three had problems with the signal stopping at one of the transistors each time.
Here are some pics of the board:
(http://i140.photobucket.com/albums/r19/Muad_zin/2014-03-06115359.jpg)
(http://i140.photobucket.com/albums/r19/Muad_zin/2014-03-06115454.jpg)
(http://i140.photobucket.com/albums/r19/Muad_zin/2014-03-06115539.jpg)
(http://i140.photobucket.com/albums/r19/Muad_zin/2014-03-06115656.jpg)
I'm not looking at the spreadsheet, so there may be a good reason why you did this, but you've got a capacitor in the R8 (I think) spot.
Quote from: lincolnic on March 07, 2014, 04:21:24 AM
I'm not looking at the spreadsheet, so there may be a good reason why you did this, but you've got a capacitor in the R8 (I think) spot.
Yeah, according to the P19 schematic the normal sustain pot -> cap -> resistor -> Q2 is reversed. So I put C4 into R8's place and vice versa.
Looking at what I did I noticed that I hooked up the ground to the G+ lug next to the 9V and not to the G lug next to In. Think these changes would matter?
Quote from: Muadzin on March 07, 2014, 11:21:38 AM
Quote from: lincolnic on March 07, 2014, 04:21:24 AM
I'm not looking at the spreadsheet, so there may be a good reason why you did this, but you've got a capacitor in the R8 (I think) spot.
Yeah, according to the P19 schematic the normal sustain pot -> cap -> resistor -> Q2 is reversed. So I put C4 into R8's place and vice versa.
Looking at what I did I noticed that I hooked up the ground to the G+ lug next to the 9V and not to the G lug next to In. Think these changes would matter?
The ground you choose shouldn't matter. they are all ground. :P