Follow-up: My Rangemaster voltage readings are WAY off -- HELP!

[msb69]

Well, I tried measuring the voltages on each of the pins of my OC-44 transistor in my Rangemaster clone.

Here are the steps I took:

1. Set multimeter (DMM) to read DC voltage

2. Connect the black lead from the DMM to ground

3. Insert cord into pedal input jack

4. Turn pedal on

5. Touch the red lead from the DMM to each of the OC-44 pins (individually).

My (very bad) results:

C = 2.00v

E = 8.09v

B = 7.95v

The battery I am using measured at 9.01 volts.

On the OC-44, I assume the red dot marks the Collector pin, the middle pin is the Base, and the third pin is the Emitter.

I purchased the OC-44 from Small Bear.  Steve sent the appropriate bias resistors, which were 56k (for Rb) and 3.9k (for Re).

HELP!

[tcobretti]

I would guess that two components are touching that shouldn't be, and I would say that the next step is to start measuring resistances to try to isolate the problem.   Disconnect the battery first - it'll cause problems when you're measuring resistances.  Very carefully compare what you have built to the schematic, and make sure everything is put together right.

It's great when you finally get them working, but be patient - you'll figure it out if you stay at it.

Also, If you haven't, read this link.
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Good Luck.

[msb69]

I should also note that I have built my PNP Rangemaster with the negative ground configuration.  Could that be affecting things?

[msb69]

I think I found my answer.  An old post from RG Keen:

Builder:  "I'll see if I can spell this out so it makes sense. I'm using GGG's PNP negative ground layout, so I thnk I was measuring right. Attaching the neg. lead to the "-" side of the battery and measuring with the positive lead."

RG:  "Actually, that's 99% of your problem. Using a negative ground version of this circuit means that you are measuring voltages from what would be the power supply of the Rangemaster circuit at GEO. That means that you want a collector voltage of 2V, not 7V on a 9V battery.  With your 9.48V battery in the negative ground circuit, you ought to see maybe 2.2V on the collector. Try that.  What you call ground does make a difference."

So it looks like I'm supposed to be seeing roughly 2 volts on the collector.

m

[petemoore]

PNP Rangemaster with the negative ground configuration.
  These [pnp, pos gnd.] PS Schemes are not recommended...