Big Muff Pi- review/questions

[tennisdude]

Hey guys

Today I build a triangle Big muff with the layout at www.tonepad.com. I must say i'm not sure if its working perfectly well, or if its just a quirky pedal.

the tone control has a huge impact on the tone of the pedal. maxed out it sounds fairly bright and pretty wimpy. at 0 it sounds very muffled and fuzzy, and the whole range in between.

the sustain control is wierd. it doesnt add sustain, it just adds volume. and with the sustain control at 0, there is no sound. the volume control is the same.

even with all that extra volume, the pedal BARELY (if at all) reiches unity gain with both volume and sustain maxed out.

It definately adds some fuzz-- im not getting that buzzsaw sound though.

I did a test with my audio probe (thanks RG!) and everything seems fine... i am very curious as to what's going on.

thanks!
John

[petemoore]

even with all that extra volume, the pedal BARELY (if at all) reiches unity gain with both volume and sustain maxed out.
  Doesn't appear to be working. Read 'what to do when it doesn't work', at near top of the thread page<.
  Follow the instructions, don't forget to include battery voltage.

[tennisdude]

ok:

only modification was substituting two .047 uf caps for two .05 uf caps, and a 4.9, 2.4, and 1.5 resistor wired in series for the 8.2 resistor in series with the middle sustain lug

ill get some readings in a sec

john

[tennisdude]

forgive my ignorance with the DMM, i've only used it a few times.

if its on on the 20 V mode and you get a reading of 1, how many volts is that?

[pyrop]

forgive my ignorance with the DMM, i've only used it a few times.

if its on on the 20 V mode and you get a reading of 1, how many volts is that?

if the 1 is on the right it means 1volt. if its on the left it means its out off range. if its out of range try the setting either side.

pyrop

[petemoore]

  You can test the 8k2 resistance using the DMM on Resistance mode, probably has a 20k range, but will read pretty good on 200k range or something.
 You can check the Resistor ranges using resistors and just checking their values against the DMM readings, anyway is measure every resistor before installing it, for a whiile, it makes it easier to get used to color codes and using the DMM.
 
 only modification was substituting two .047 uf caps for two .05 uf caps, and a 4.9, 2.4, and 1.5 resistor wired in series for the 8.2 resistor in series with the middle sustain lug
 Substituting a .047uf for a .05uf is not noticable or at least not a work/no-work scenario...should provide about exactly the same voicing, put a .1uf and you'll probably notice some difference.
  It's a good idea to get used to measuring with the meter, voltages, resistances at least, current too, so that you'll know what to look for...a 10k resistor'll probably read like 9.86k when measured, within the +/- 5% or 10% tolerance or whatever for that part.
 f its on on the 20 V mode and you get a reading of 1, how many volts is that?
 1v...but measure some 9v batteries or 1.5v batteries, see if you get some 'normal' readings ont he DMM.
 Measureing voltage at transistors pins E/B/C in the case of the BMP, from ground is detailed in the thread I mentioned...basically clip the DMM black lead to ground rail, measure withe the DMM set to 20v range, contacting the red lead to emitter [take/note V reading] base [note that] and collector. Post those and the measurement of battery voltage when connected to the circuit, and we'll probably be able to narrow the search for the problem.

 

[tennisdude]

Q1: backwards D orientation
top: 9 volts
middle: .018 volts
bottom: 0 volts

Q2: D orientation
top: .10
middle: .71
bottom: 1.29

Q3: backwards D orientation
top: 4.45
middle: .73
bottom: .16

Q4: D orientation
top: 1.28
middle: 1.75
bottom: 3.91

D1
not black stripe: .47
black stripe: .71
D2
black stripe: .47
not black stripe: .71
D3
black stripe: .72
not black stripe: .49
D4:
black stipe .49
not black stripe: .72


thanks, hope this helps.

john

[tennisdude]

i dont have a good 9 volt battery, but the power supply is 9.5 V btw

sorry about the shitty readings, im not sure about the EBC stuff

[dadude]

Of course read the usual troubleshooting guides (found here etc.).  I do not have a lot of time tonight to get you through it, but it sounds like your problem lay in the area of the sustain control, meaning the PCB layout or maybe the soldering on those resistors in series, When I say the layout I mean it's possible that you have a short or an open some where in that area. I've seen this in the past. @ Zero the sustain control still lets signal through. If it were something on another section of the board you would still be getting a signal through (that is if the circuit was not completely dead). Using the audio probe and setting the sustain control on zero I would probe to find your open or short in this area.

[dadude]

Also check out where your pot's at...

Er, um not that pot stupid! Check out the wiring on your board to the pots make sure all is wired up and spot on.

[petemoore]

Q1: backwards D orientation
top: 9 volts [I can't assume this is the collector]
middle: .018 volts
bottom: 0 volts

Q2: D orientation
top: .10
middle: .71
bottom: 1.29

Q3: backwards D orientation
top: 4.45
middle: .73
bottom: .16

Q4: D orientation
top: 1.28
middle: 1.75
bottom: 3.91

D1
not black stripe: .47
black stripe: .71
D2
black stripe: .47
not black stripe: .71
 Look up the data sheet on the transistor type[s you're using for the project.
 It may take some study, and work, but following the instructions completely on 'what to do when it doesn't work' is essential, I'd list:
 Schematic [specify Neg Gnd .... better yet provide a link]
 Voltage readings with transistor pin designations
 But I'm sure I'd miss something...all the digs are in the read and the work that follows, without these things, the meat and potatoes of debugging, staring at schematic and following traces on the board and comparing them, reading resistor color codes to determine correct values is the only recourses...I'd welcome 'new' ones, if they'd work, these circuits all abide by mother nature and ohms law though, he gave us solutions to find all our problems, finding the solution may require more effort.
 I can't tell what's what with the readings, the emitter in a gain stage should be near ground, about a volt or so, the base must be at least .6v above the emitter, for max swing on the neg and pos of the signal amplification, the collector should be at about 1/2v of supply [4.5 of 9v, ... or 5v of 10v depending on PS voltage].

[tennisdude]

thanks for the help so far guys
ill provide more info in a sec, im doing a little troubleshooting (the tone pot might have had a cold solder joint, but why that would affect anything is beyond me.

[pyrop]

Posted by: tennisdude 
Insert Quote
Q1: backwards D orientation
top: 9 volts             C
middle: .018 volts    B
bottom: 0 volts        E

Q2: D orientation
top: .10                  E
middle: .71             B
bottom: 1.29           C

Q3: backwards D orientation
top: 4.45                 C
middle: .73              B
bottom: .16             E

Q4: D orientation
top: 1.28                 E
middle: 1.75            B
bottom: 3.91            C

If you have done the "gran mango 3.1416" layout from tonepad the tranny pinouts are in red above

pyrop

[tennisdude]

Q1: backwards D orientation
top: 9 volts [I can't assume this is the collector]   C
middle: .018 volts                                             B
bottom: 0 volts                                                 E

Q2: D orientation
top: .10                                                          E
middle: .71                                                    B
bottom: 1.29                                                   C

Q3: backwards D orientation
top: 4.45                                                          C
middle: .73                                                     B
bottom: .16                                                      E

Q4: D orientation
top: 1.28                                                     E
middle: 1.75                                                B
bottom: 3.91                                                C

http://www.tonepad.com/getFile.asp?id=94

[tennisdude]

i just figured that out... thanks!

[tennisdude]

strangely enough my resistor mesaurements are totally skewed... i think my multi meter must be wrong, because i'm getting measurements like 260k ohms for a 390k resistor, and 90 ohms for a 150 ohm resistor... so wierd

[tennisdude]

again, nevermind... i got different readings with the power on/off

[petemoore]

strangely enough my resistor mesaurements are totally skewed... i think my multi meter must be wrong, because i'm getting measurements like 260k ohms for a 390k resistor, and 90 ohms for a 150 ohm resistor... so wierd

Actually you're most probably reading through the alternate path the circtuit provides when the resistor is in circuit.
  To read the actual resistance, you'll need to pull one end of the resistor or do some calculating or figure it's probly 'right', it just can't be 'read' while it's connected at both ends....readings lower than the marked value of the resistor are subject to this 'in circuit', readings larger...you can't have that...if that resistor is supposed to be 470k, and you read say 510k or larger across it, in circuit or not, the resistor is wrong.
  Measuring resistors is a good way to find a wrong value in a circuit, but as you've discovered, and I probably should have typed about, is subject to 'rules'.

[tennisdude]

yes! YES!

stupid resistor mistake. it sounds sick now

thanks for the help guys. you rock.

[petemoore]

yes! YES!

stupid resistor mistake. it sounds sick now

thanks for the help guys. you rock.

I hope I haven't misled you into changing resistors unnecessarily.
  I should have stated the 'caveats' to in circuit resistor reading.
  I'm not at all sure those 'suspect' resistors were wrong value, if the color code is correct, there is about a .007 % chance they are 'faulty'...hardly ever do I come across a faulty non active component, resistors being near bottom of list near wires, at least using 1/4w R's @ 20v's or so.
  First I would find the data sheet on the transistor, or at least state what type[s you are using.
  Next I'd take a look at the voltages again. This is something bias requires, for the transistors to operate as intended, they must be sitting at operational voltages.