Posted by
Kalimna on
Jul 23, 2017; 11:39pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/Another-request-for-assistance-this-time-a-Green-Rhino-tp39219.html
Greetings Folks,
I'm afraid I am after a little more assistance in debugging a pedal. This time it is the Way Huge Green Rhino from this blog,
http://tagboardeffects.blogspot.co.uk/2016/05/way-huge-green-rhino-mk-ii.htmlThe issue is a loud high pitched whine and stuttery distortion that develops after 20 or so seconds of the effect being engaged. Initially the sound is rather nice indeed, but it seems to develop the whine when the controls are adjusted, especially the 'curve' control. In fact the whine stops if the curve is at zero, but there is still a negative effect on the tonal quality (sorry can't explain it better than that).
I have triple checked component values (including the pulldown resistor which I had at 10k, now corrected) and placement, as well as the cuts and links. As far as I can tell, there are no errors there. I have also knifed the tracks, so I don't think there are any solder bridges.
Here is a list of the pin voltages, which seemed rather invariate as there was almost no difference in readings whichever position the controls where in. It also struck me as odd the similarity between several of the IC pins - though I fully accept my own knowledge is more likely at fault here. Supply voltage was 8.94V from my PSU
Transistors Q1-Q4 all reading the same :
E- 4.08v
B- 4.38v
C- 8.94v
Transistor Q5
E- 4.64v
B- 5.26v
C- 8.94v
LM833 (pins numbered 1 at top left, running anti-clockwise)
1 - 5.28v
2 - 5.27v
3 - 4.98v
4 - 1.1mv (inc to 1.4mv with control at max)
5 - 5.26v
6 - 5.27v
7 - 5.28v
8 - 8.94v
LF347
1 - 5.28v
2 - 5.28v
3 - 5.28v
4 - 8.94v
5 - 5.28v (dec to 5.24v with control on max)
6 - 5.28v (dec to 5.24v)
7 - 5.28v (dec to 5.24v)
8 - 5.28v (dec to 5.20v)
9 - 5.28v (dec to 5.24v)
10 - 5.29v (dec to 5.24v)
11 - 1.1mv (dec to 0.9mv)
12 - 5.29v (dec to 5.19v)
13 - 5.29v (dec to 5.21v)
14 - 5.29v (dec to 5.21v)
Nothing appears to be getting hot if left on for 10-20mins.
My thoughts are
1 - incorrect component placement/value or solder bridge
2 - faulty (or damaged) IC or transistor (most of the 2n2484's measured about 450-500 hfe, but one was about 200)
3 - as the pedal works initially, maybe a capacitor related issue
I do have spare IC's, so I will check those. I do not have any more of the 2n2484 transistors, but have plenty of other NPNs - what would be a suitable replacement?
Again, any thoughts/help is greatly appreciated, before I populate a new board.
Cheers,
Adam