GGG BMP build help

[raycroft]

Hi.  I built the BMP tonight- first time cranked it- LED lit and very faint, fuzzy sound.  Sounded great, only too quiet.  I double - checked all my solder joints (I used their solder- not used to it-probably better than the ratshack stuff I've been using), as some of them were suspect for cold joints.  Re-touched every joint.  Also found 2 places where the schematic called for 8.2k resisitors and I put in 82k (little color blind).  Fixed all that and triple checked every pin-out; the only elec cap is in correct and more voltage on + than - ;  verified all resistors and caps correct.  I used only parts from their kit-no substitutions.  I built the GGG Tuned version  http://www.generalguitargadgets.com/pdf/ggg_bmp_wiring.pdf
http://www.generalguitargadgets.com/pdf/ggg_bmp_ggg_sc.pdf

In the process, my led burnt out, and I replaced it w/ a green one I had lying around.  I fired it up and it is about 3/8 quieter than the clean guitar signal out of my amp.  What signal is there sounds great!  I cranked my amp up halfway (line6 flextone duo-100 watts- never have turned it up that loud- I'd be deaf) just to hear it, coz it's sooo gooood. 

Anyway- audio probing shows me that my signal drops proportionaly from q1 to q4.  By the time it hits Q4- it's barely audible, but normal at Q1. 

Q1   C 3.58  B .58   E .03            Q2   C 3.55    B .58     E  .03       Q3   C  3.55    B  .58   E  .03     Q4   C 8.55   B   1.58   E   1.13

D1   A  .40   K   .58     D2   A  .58   K   .44       D3     A   .58     K   .56     D4   A   .58   K   .47


Oh, there is 1 thing- instead of the linear pot suggested in the layout- they sent logarithmic, so I'm using that.  The  volume on this thing seems to only work in the top 1/4 rotation, by the way.


I did a search on this issue and found people have had very similar issues w/ low audio- I couldn't find the one that matched my situation.  I've been troublshooting this thing since 7:00pm  -  it's now 11:20 pm.

Thanks for your help, everyone!


One more thing, just in case it makes a diff- using the audio probe- I touched it on my 3pdt where the input from the stereo jack is- it's distorted.  The side of the switch from the circuit output is soldered to is clean (?).  I figured it would be the other way around.  I checked my wiring at least 5 times.  Thanks again.

[Michael Allen]

it should be the other way around on the 3pdt. somewhere your wiring is messed up. All your voltages look good, it sounds like you just have a wiring issue in your offboard connections. Try redoing all the switch wiring.

[raycroft]

I keep waiting for that "aHA" moment; but it's just not happening.  Here's some pics.

  ( this looks like the yellow input touches the led post on the way to the top right post- it doesn't .  It misses it by about 1/8".)






any help is appreciated.

[petemoore]

Q1   C 3.58  B .58   E .03       
Q2   C 3.55    B .58     E  .03     
Q3   C  3.55    B  .58   E  .03     
Q4   C 8.55   B   1.58   E   1.13
  Collector is near the top rail, can't swing up from there, Q4 is misbiased.
  Measure the resistance between the collector and V+.

[Michael Allen]

ah yeah Q4, missed that. Its collector is too high. I just built one and I think the collector sits at about ~4V. Base is 1.7V and Emitter was 1.2V

[raycroft]

yeah, I did some more searching this site and found some BMP voltages (they were in de-bug process, so they could've been wrong).  Mine is nowhere near theirs on Q4.  So , I was thinking that same thing, and checked for literally the 4th time and made sure r24 (collector resistor) was in fact 10k and not 1k.  It's right, 10k.  I guess I'll go home and pull it out and see what the heck is going on.  Would that cause this problem?  If their's that much voltage being fed into it, it'll oversaturate it, correct?  Thanks for your help!

[raycroft]

measuring R 24 it's 8.72 which is my battery voltage.   

I took it out- it was intermittently measuring a few ohms w/ my dmm.  I grabbed another 10 k and threw it in, and it's slamming loud! 

It didnt' really change Q4's voltage, though.     C 8.63   B  7.95   E  8.30

Getting ready to box it up and see if my hummmmm goes away.

Thanks!

[raycroft]

Final post for this one:   It's great.  I love it.  This is what distortion is supposed to sound like, according to me.  I highly recommend the Generalguitargadgets kits, it was my favorite build so far.  Thanks for the debug help;  it was 1 bad resistor.  Peace, out.

[petemoore]

 C 8.63   B  7.95   E  8.30
  Dohh..lazy typer I am...
  The emitter looks like it's floating, and should be 'near' ground, measure emitter to ground resistance.
  @@ Rate there's a bias problems with #4 transistor, and diddling with it [measureing, testing continuities etc.] 'till the voltages pop into place [ie: collector has room to swing up/down, base is ~a diode drop or so above emitter, which means emitter needs to be 'near' Gnd.]

[raycroft]

Pete, thanks for the help.  I'm not positive I know what you mean about measuring emitter to ground resistance;   I put my negative lead on ground and dmm on ohms and checked emitter and got +2.19.  Don't know if that's right.  No battery attached of course.  same reading on emitter resistor till it hits g, then 0.00.



wait a minute..      I just re-checked Q4-  (w/ battery) I got    c  3.45   B  1.58  E 1.12.  That's better!  I don't know what did that.