Help needed debugging a schematic

Started by suryabeep, September 20, 2017, 11:42:11 PM

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suryabeep

Hi everyone!
I 'designed' a little Meathead rip off with an AMZ tone stage and recovery stage, it works in the simulator but I simply can't get it to work on a breadboard. I'm not sure why, since I've followed Meathead values for the most part with only slight tweaks. The tone and recovery stages work perfectly, it's just the first two gain stages that don't work. What's happening is I keep getting a heavily gated signal. I've attached the schematic below. My voltages are:
9.59 supply

Q1
e: 0
b: 0.36
c: 1.00

Q2
e: 0.36
b: 1.00
c: 0.45

Q3:
e: 0.99
b:1.58
c: 4.94

My theory knowledge isn't up to scratch, so I just can't figure out what's going wrong. Can someone point me in the right direction? Thanks!


Still in the process of learning, so bear with me if I ask dumb questions :P

thermionix

Q2c voltage is really low.  I suspect you have a wrong resistor or two on your breadboard.

rezzonics

#2
In your simulation, your input resistor R4 is 1 milliohm (1m) not 1Megohm (1meg)

antonis

The above pointed is a VERY common mistake in use of simulators..  :icon_biggrin:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

anotherjim

...and I'm sure you didn't mean to have battery neg connected via the input. Probably only works because of the 1millohm to ground. That simulated signal source has some fire power don't it!
Still left with bias issue. Transistor pin-out needs confirming.


suryabeep

thanks for the replies folks, I've changed that 1 milliohm to a 1 megaohm and changed that 9V supply thing (well that was stupid :P).
I'm going to check my breadboard again thoroughly in a bit and report back
Still in the process of learning, so bear with me if I ask dumb questions :P

suryabeep

#6
Weird, it works now. I haven't changed anything though, just one slightly wobbly jumper was pushed in further. Two new issues (?):
1) signal cuts out when I roll the 1KB pot to max fuzz. It gets fuzzier, fuzzier, and then cuts out.
2) neck pickup on the strat + tone knob rolled back gives an octave up? Is this good? Should it be there? Do I want it?

edit: I upped the 200R on Q2e to 330R, which gave back all the range on the 1kB pot. Added some 3mm LEDs between Q1c and Q1b, which did cool stuff. Placed a 47u filter cap, which gave back some highs
Still in the process of learning, so bear with me if I ask dumb questions :P

PRR

> In your simulation, your input resistor R4 is 1 milliohm (1m) not 1Megohm (1meg)
> ...and I'm sure you didn't mean to have battery neg connected via the input. Probably only works because of the 1millohm to ground.


It works in sim because V1 will happily deliver 1,000 Amps of signal, and pass the DC current out of V2 with dead-zero drop.

And always use "Meg" or "1,000K" or "1E6". The milli/Meg ambiguity could be solved with lower/upper case, except the earliest forms of SPICE were in FORTRAN on potentially upper-case-only terminals.
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