Problem building Jack Orman's mini booster

[PCR]

Hi I am brand new to the forum and would appreciate help with my attempt to build Jack Orman's mini booster.  I am getting sound out of the circuit, but no gain at all, in fact the effect in sound is a bit lower in volume than the bypassed sound.  I followed the spec exactly except for using a 4.7uF capacitor in place of a 3.3 uF capacitor for C2 on the schematic  (connects Q2's D/Q1's S to Q1's G).  I could not find a 3.3uF cap locally. Also the cap I used was a film type.  The spec calls for a 3.3uF NP which I also could not find locally. 

Again, any help would be appreciated.  Thanks!

[GibsonGM]

Hi PCR, welcome to the forum!  The cap won't be a problem. What you should do is look up "What to do when it doesn't work" in the "Building your own stompbox" forum (it's a permanent topic at the top).   
Follow the instructions there, then post back when you have the info, such as voltages etc.  And posting a link right to the schematic is helpful, so we all know what you are looking at, since there may be more than 1 version of something!

It's probably a solder bridge (accidental short caused when you soldered) somewhere; you'll track it down and get it going!  98% of the time, we cause our own problems but eventually learn how to find them quickly!   Keep at it )

~Mike

[PCR]

Hi Mike,
Thank you!  Here is the schematic link:

http://www.muzique.com/amz/mini.htm

I found online:

http://www.singlecoil.com/docs/mini_booster.pdf

as per those instructions, I used a 2.2uF electrolytic with the positive leg to the junction between the D and S of the two transistors.  I did this, and the circuit gives a tremendous amount of gain.  What I am wanting is an extremely clean boost.  I would like to reduce the gain and have followed the instructions from the mod link above and have done the following:

Reduce Gain:

1. Take out C3 to reduce gain and to make the output more linear (I did this).

2. To further reduce gain, increase R5 to a value between 1k and 10k ( I went all the way up to 22k and it still is too much gain.  I am getting significant distortion with the 100k volume pot at maybe 25% of its range.

I also reduced C1 to .033 to try and cut the bass a bit.

I would appreciate any suggestions about how I can reduce the gain. 

Thanks!!!

[GibsonGM]

1)   This may fix the whole thing (or maybe not, ha ha).   C3, the .22u cap, is your output cap. You need that in there to block DC from going out to your amp or other pedals!!!  Measure your output for DC - if you've actually pulled C3, you will read some DC on there (probably abou 4.5v).   Put it back.   DC is not good for the pedals that follow, and will offset the signal enough that it will create a distorted sound.    Or, did you mean you pulled C2?  Perhaps THEY meant pull C2 and it was a typo on the PDF.....anyway, get something in there for an output cap.

2)  NOW play with R5 to try and reduce gain.  I'd set it back to 1k and then measure all my voltages at D,S,G, listed in a table like:  Q1  D= ?     Q2 D=?   .  Then we can see how the FETs are biased.   What FETs did you use, btw?  You sure their pins are oriented properly?  If either are 'backwards', you'll get weird trouble like you're reporting.

So, check that you have an output cap...that you have something in there for C2, that R5 is around 1k.  Then get voltages at all FET legs.    You can also audio probe thru the circuit's signal path (C1 to gate of Q1, D of Q1, top of volume pot, output).   See where the signal gets 'furry'.  Search for "audio probe" on here if you don't have one, make sure to use a cap before the input to your amp, and ground to the common circuit ground!

With that data, we can have an idea of what's going on.   I work nights, so won't get back on til tomorrow this time.  If nobody has helped, I'll look in on this topic again. 
Happy debugging!!!   You'll get it fixed, no worries...

[PCR]

Hi Mike,
Thank you!  I put the .22 cap, and 1 k resistor back in the circuit and tested the voltage at the transistors (2N5484's).  The readings were as follows:

Q1 
D= 8.27
S= 4.91
G= 3.94

Q2
D= 4.91
S= 0.841
G= 0 to neg .1

Thanks again!

[GibsonGM]

You do have C6 in parallel with the 1k resistor, right? That could be misread as "something to add later", just making sure - only the A and B labels are for something later, the cap needs to be there....

Does it sound any better by changing those parts back, or still less than unity?   If not, what I suggest you do is try the audio probe and see what you get for signal.     
When you audio probe, you may (hopefully) find a spot where it boosts, then the next spot is quiet again - leading you to the faulty section!!   Try it out...it's a nice booster when working!  Probably just a bad solder joint, something cross-connected. 

[petemoore]

  Is the transistor that sets bias on the drain of Q2.
D= 8.27  Connected to a power supply ~9v, check.
S= 4.91   Is middlish to being centered between 9V and Gnd.
G= 3.94   Should be the same voltage as the voltage divider [the 2 equal value, 1meg resistors which should set 1/2v between V+ and Gnd.
Q2
D= 4.91   Seems a suitable bias for voltage swings to be able to go +/- and not hit V+ or Gnd...ie provide boost.
S= 0.841  above Gnd. like a Jfet, biased, would be 
G= 0 to neg .1  Probably a DMM anomoly.
  So...looks like a boosty-bias, C6 is an AC bypass capacitor for the 1k, and should increase gain.
  The Minibooster tends to distort a little, a Jfet or other @12v would be clean boost, probably can be done @9v if the input signal X gain isn't too strong.

[PCR]

Thanks guys.  Yes I do have C6 in parallel with the 1 K resistor.  It still is quite distorted. I  hope to be able to work on it some more in a couple of days and will report back.  Thanks for all of the help!!!!!

[GibsonGM]

Sure.  Be sure you audio probe it to see where the distortion occurs tho, ok? It should have some "grit", but not necessarily very distorted!  Going thru these things makes us all better trouble shooters )