MIcro Drive misbiased transistor. What should the pinout read?

[aab0mb]

I'm building the Microdrive.   http://aronnelson.com/gallery/Marcos-Album/microdrive

The sound has the "blatty" problem and only comes on when the strings are hit at a particular volume level.  I read that this indicates a bias problem somewhere.

The transistor readout is

c- 0.10
b- 0.65
e-  0.0

OR if it is flipped around it reads

c- 8.17
b - .56
e-  0.0

Not sure which way is correct but the first way listed produces some sounds when the strings are hit hard and the LEDs light very shortly and then the signal dies out and cuts off.  The second way it produces no sound.

I didn't have a 560k resistor so a used a 470k and and 100k in series.  Is this close enough?

Any advice is appreciated. 

Thanks,
Aaron

[petemoore]

  A cap between the diodes and the collector..
c- 0.10
b- 0.65
e-  0.0

OR if it is flipped around it reads

c- 8.17
b - .56
e-  0.0
  check data sheet, I think that's an npn with hat-tag by the emitter, then base and collector pins.
  does your DMM have an HFe tester? set it for hfe and put the transistor everyway [the four each pins for NPN/PNP...use the NPN side, and try the transistor up/down one index, back and forth both ways..ervery way, you should see an Hfe reading that looks 'normal' [something between 100 and 500 I guess.
  Emitter looks to measure 0.0v = ground, ok.
  Base is above emitter by 'some...doesn't look too bad by itself but
 
  either way the collector is nowhere near biased,
  first thing to do is affirm the pinout of the transistor
  The debugging page is a great read, and outlines debugging in great detail.
  or, fill in where the '*' s are with your circuit information.
  ..actually it's a fairly simple schematic, I would go through it with the DMM and verify all markings on the schematic match what's on your board.
  ..Skip the opamp parts.
  Name and show link to circuit schematic.
  *Garfunkels accoustic pre-amp
  If you're using a layout or PCB post a link to that too.
  *GAPP layout
   Is there a connection between circuit power supply V+ and Gnd. under any of all power supply 'conditions' ie...is there shorting under and 'normal' switching conditions of input jack or DC jack or any other time?
  *YES   /    NO  [enter comments
  Measure battery voltage.
  *X.X2VDC
  Measure battery voltage with circuit loading
  *X.21VDC
If using a power supply, what does it say on it about voltage rating?
  *Xvolt
  Also name power supply type
  *AC  or DC output
  test the voltage of the power supply.
  *9.2VDC
  Test votlage of power supply with circuit connected
  * .22vdc
  Is the circuit npn-negative ground?
  *Transistor type [npn/pnp...jfet, mosfet, Ge, etc.
  *Circuit polarity [neg gnd. or pos. ground?
  *Opamp type [Dual, single, OTA, CMOS...other
  connect DMM to ground, and test for continuity at every point in the schematic with a ground symbol, from the most 'distant' [test points should be beyond all connections and solder joints].
  Test the cables that are plugged if they can be plugged in, at the plug sleeves which connect to guitar and amp
  Is there continuity at all 'distant circuit ground points
  Stage 2
  Connect power supply, if there is a large current draw [ie voltage drops by 10% or more, disconnect power and post that result].
  Is there a >10% voltage drop in battery when circuit is connected?
  *Yes  /  No
  What voltages are measured [using ground as reference voltage =O.0V], using DMM at all active component pins?
  *Dual opamp
*1  4.5v
*2  4.5v
*3  4,5v
*4  0.0v
*5  4.5v
*6  4.5v
*7  4.5v
*8  9v
-----
  *Single opamp
*1  NC
*2  4.5v
*3  4.5v
*4  0.0v
*5  NC
*6  4.5v
*7  9v
*8  NC
-----
*Transistor type
  *NPN
  *PNP
  *Jfet/mosfet/BJT/Ge?
  *Transistor part #
  *Data sheet pinout information
  Pin Voltage
  *D 9v         
  *G 2.2V
  *S  .21V
  Or substitue 'E/B/C if using bipolar transitor
  List any pertinent comments and questions.
  Stage 3
Audio probe, and list results and comments.
  Test that all stages are 'separated' by DC blocking capacitors,
  Can you physically see that a capacitor is properly wired to the input and output of each active component stage? ie signal path must go through the cap to enter or exit the active stage.
  The circuit debugging may have limited results if the answers with * are not known or posted.
  BTW the opamp pins for most distorters [gain stages] are more than optimal, bias is 'centered' at 1/2 the power supply, except for the power supply pins [the 9v and 0.0v ones.

 

[aab0mb]

If the C of the transistor isn't biased properly how would I get the correct bias?  I went to the debugging and FAQ right away but didn't find what I was looking for.

I'm laying it out just like the scheme.

I'm only using a battery.  It measures 9.2 volts

All the values of caps and R's match the scheme.  All of the grounds are good. 

I guess I just need to know how to get that C reading to be right.

c- .13
b- .65
e- 0.0

[aab0mb]

Should i try a different value  resistor leading to the collector?  It seems like 10k is pretty standard for NPN bias resistors for the collector.  If i have two diodes shunting to ground will it matter which direction they go as long as they are opposite?  I didn't think it did but perhaps that could be part of the problem.  please help w/ links or info.

I've read the FAQ and debugging pages multiple time trying to absorb any info during my two builds.  I really want to understand HOW to fix it not just get it fixed.  I'm loving this hobby, by the way.  Thanks to everyone at this forum and around the stompbox community.

also, on the scheme the .01 output cap and the 10k bias resistor are both  connecting to the transistor collector at the same junction, right? 

Any ideas,
A

[petemoore]

Should i try a different value  resistor leading to the collector? 
  Not necessary
  It seems like 10k is pretty standard for NPN bias resistors for the collector.
  YEs...good MOTR value.
    If i have two diodes shunting to ground will it matter which direction they go as long as they are opposite?   I didn't think it did but perhaps that could be part of the problem.  please help w/ links or info.
  clippping diodes are BTB [back to back ie one points up, one points down, both are connected from between signal path and ground].
  If these diodes are connected to the collector [I did that], they will drastically alter transistor bias [like pulling collector voltage near ground], the capacitor shown between the C and diodes blocks dc, therefore dc bias is then set by the...bias resistors and transistor.
  It looks as though the collector:
  A needs to be connected to V+ through 10k
  B Bias isn't DC blocked through the cap to diodes.
I've read the FAQ and debugging pages multiple time trying to absorb any info during my two builds.  I really want to understand HOW to fix it not just get it fixed.  I'm loving this hobby, by the way.  Thanks to everyone at this forum and around the stompbox community.
  You saw about taking readings from 'distant' points in the circuit..
  The DMM can be used to measure everything [except caps, which can generally be taken for granted as...they just work, almost invariably], including resistances, connections, non-connections, all ground points.
  When the board connections reflect exactly the schematic..the circuit has to work.
  see..I'll mention cause I'm too lazy to read through all ..
  transistor pinout verified ?
  Emitter grounded means that's ok [as long as the emitter pin on the transitor isn't confused with a base or collector].
  Base should have ~47k shown as measurement between transistor base pin itself, and - [small post] of the battery clip.
  Base should have ~470k measured between pin and V+ [at battery clip].
  Collector will be ~10k to V+.
  also, on the scheme the .01 output cap and the 10k bias resistor are both  connecting to the transistor collector at the same junction, right?
  Yupp, the collector 'node' is collector/10k/'DC blocking output cap' 
 

[aab0mb]

Name and show link to circuit schematic.
  *Marcos Micro Drive  http://aronnelson.com/gallery/Marcos-Album/microdrive
  If you're using a layout or PCB post a link to that too.
  *Same Perf layout as the schematic
   Is there a connection between circuit power supply V+ and Gnd. under any of all power supply 'conditions' ie...is there shorting under and 'normal' switching conditions of input jack or DC jack or any other time?
  *NO 
  Measure battery voltage.
  *8.8VDC
  Measure battery voltage with circuit loading
  *8.8VDC
If using a power supply, what does it say on it about voltage rating?
  *none
  Also name power supply type
  *none
  test the voltage of the power supply.
  *none
  Test votlage of power supply with circuit connected
  *none
  Is the circuit npn-negative ground?
     yes
  *npn
  *Circuit polarity=neg gnd.
  *Opamp type -  none
  connect DMM to ground, and test for continuity at every point in the schematic with a ground symbol, from the most 'distant' [test points should be beyond all connections and solder joints].
  Test the cables that are plugged if they can be plugged in, at the plug sleeves which connect to guitar and amp
  Is there continuity at all 'distant circuit ground points
  Stage 2
  Connect power supply, if there is a large current draw [ie voltage drops by 10% or more, disconnect power and post that result].
  Is there a >10% voltage drop in battery when circuit is connected?
  * No
  What voltages are measured [using ground as reference voltage =O.0V], using DMM at all active component pins?
  *Dual opamp- none
*1  4.5v
*2  4.5v
*3  4,5v
*4  0.0v
*5  4.5v
*6  4.5v
*7  4.5v
*8  9v
-----
  *Single opamp
*1  NC
*2  4.5v
*3  4.5v
*4  0.0v
*5  NC
*6  4.5v
*7  9v
*8  NC
-----
*Transistor type
  *NPN- 2n3904
  *
  *
  *Transistor part # 2n3904
  *Data sheet pinout information
        flat side up E,B,C
  Pin Voltage
  *e 0.0       
  *b .67V
  *c  .14V
  Or substitue 'E/B/C if using bipolar transitor
  List any pertinent comments and questions.

9v+= 8.8
collector/10k resistor/ .1uf cap node - measures .14  ( could the resistor be bad?)
all ground points test good for continuity from the point of the input jack sleave.
I've yet to construct the audio probe.
If there was in fact a bridge between the C and the B of the transistor might that cause the low collector reading.  That one node seems to be the only problem right now but I'm at a loss as to what will get it to the correct reading.  I'll try a change of the 10k resistor (even though it measures fine) and see what happens.  Maybe swap the cap and chack the whole node for a solid connection.

"It looks as though the collector:
  A needs to be connected to V+ through 10k
  B Bias isn't DC blocked through the cap to diodes. "

Would the second half of that contribute to the bad reading?

I'm such an ashamed noob.  Will the noobdum end soon? 

[aab0mb]

Changed the 10k resistor, the .1uf cap before the diodes and made good'n'sure that the collector node joint was solid as hell.  Same problem.


dangit.