Rangemaster biasing

[rangermaster]

Hi.

I made a rangemaster pedal but now i'm having some troubles biasing the oc44.

Right now i had to lower the 470k to 13k to get 7v on the collector.

But i have this now
C: 7.04v
B: 6.84v
e: 7.04v

What can i do to get the right voltage everywhere? The other resistors are still 3.9k and 68k.

Thanks.

[duck_arse]

percyhornickel rangermaster - if you have built a circuit with pnp transistors, and with positive ground, all your voltages should read negative. for consistency, we ALWAYS put the black meter probe to ground [no matter pos or neg ground, always ground] - and we ALWAYS ground the sleeve of our jacks, so that's a good place to put your black probe to avoid confusions. and when you post those voltages, you should include the minus sign.

[Rob Strand]

Right now i had to lower the 470k to 13k to get 7v on the collector.

But i have this now
C: 7.04v
B: 6.84v
e: 7.04v

What can i do to get the right voltage everywhere? The other resistors are still 3.9k and 68k.

I agree with duck_arse about reporting the voltage.  The base voltage being below the collector and emitter is confusing.

It's had to make a suggestion because we don't know where the meter -ve is connecting to.

If I had to guess I'd say you might be trying to get 7V with the wrong set-up and it's screwing everything up.

[iainpunk]

i think you might be trying to get 2-ish volt bias, not 7-ish, due to negative ground.

cheers

[rangermaster]

I will measure again today and add some photo's

Thanks for the replies

[rangermaster]

Right now i have wired it like this.

Here are the CBe  voltages on photo.








It has to be positive ground and it will be powered by a battery. Like the original rangemaster. To keep the best performance of the pedal they say ?

[PRR]

I don't see a Collector resistor?? (Originally they used the pot, but you gotta have something, maybe 10k fixed.)

[rangermaster]

I don't see a Collector resistor?? (Originally they used the pot, but you gotta have something, maybe 10k fixed.)

You're right. 10k between C(collector) and 470k right ?

When i look at the original schematic the + and - battery lead are reversed on mine ?

[rangermaster]

Like this ?

[rangermaster]

I wired it exactly like the original. With a 10k pot. Now i have the collector bias as on the photo.

Base is: -7.72v
Emitter is: -7.88v

When i try to adjust the bias with a 100k pot where the 68k resistor is normally i can't get it higher then -2.89v

[Rob Strand]

When i look at the original schematic the + and - battery lead are reversed on mine ?

According to your hand drawn circuit the battery is around the wrong way.

Put meter + lead on the rightmost point on that circuit ie. where the 68k + 3.9k join.   That should be battery +.
Put the meter - lead on the collector.
Should read -7V.

[rangermaster]

See leads and voltage. I have wired the dc jack with the red lead on the center pin and the black lead to the sleeve. (Positive ground right) if i do it backwards it's + volts

It's getting a really messy board now.. i think i'll have to resolder everything when it works to get it nice and clean.


Here a photo with the dc jack leads reversed as you said.. + side on the 3.9/68k




I use a 100k pot instead of the 68k resistor for the bias value

[Rob Strand]

Here a photo with the dc jack leads reversed as you said.. + side on the 3.9/68k


I use a 100k pot instead of the 68k resistor for the bias value

The set-up looks good

All you need to do is to decrease the value of the 68k resistor/pot.  The collector voltage as you are measuring it now should increase as you decrease that resistor value.

If the transistor has a lot of leakage you will need to decrease the 68k resistor.

[rangermaster]

Yeah but then the voltage is +7

It has to be -7v right ?

And this way it's wired negative ground...

[Rob Strand]

Yeah but then the voltage is +7

It has to be -7v right ?

And this way it's wired negative ground...

The way you have the meter leads the meter will show positive voltages - that's fine nothing wrong.   If you can get +7V with the set-up in your last pick  - it's working man!

The negative voltage is when you connect the meter - lead to battery + lead then measure the collector with the meter + lead.

[rangermaster]

Yeah but then the voltage is +7

It has to be -7v right ?

And this way it's wired negative ground...

The way you have the meter leads the meter will show positive voltages - that's fine nothing wrong.   If you can get +7V with the set-up in your last pick  - it's working man!

The negative voltage is when you connect the meter - lead to battery + lead then measure the collector with the meter + lead.

Ok i thought positive ground was reversing the battery leads.. and it can't be used with a standard 9v adapter

But i have to wire it like a normal negative ground pedal

[Rob Strand]

Ok i thought positive ground was reversing the battery leads.. and it can't be used with a standard 9v adapter

But i have to wire it like a normal negative ground pedal

The process of setting up can be separated from how the grounds are wired.

As for the grounds,

The way that pedal is normally wired is called positive ground.  In this case the ground goes to the point where the 3k9 and the 68k join.  Positive ground wiring isn't compatible with other pedals so you will need to wire it as negative ground.   The important thing is you don't change the battery connection you change the ground connection.

If you go here, then to section 5.1 near the bottom.   The one you want is the negative ground version in the middle,
 
https://www.electrosmash.com/dallas-rangemaster

Here's another example of the changing the ground with another pedal,
http://www.muzique.com/lab/fuzzface.htm

[rangermaster]

Yeah i will keep positive ground and use battery's. I have made a switch to turn on and off the battery. To prevent battery drain.

So correct me if i'm wrong. All the ground with positive ground goes to +9v(red lead). Black - lead goes to the far left of my circuit board and the red + to the far right(3.9k/68k)

This way my DMM shows a voltage of +7v right? Instead of -7v ...

I can use the pedal with other pedals in chain but i havr to use this one with a battery.

[Rob Strand]

So correct me if i'm wrong. All the ground with positive ground goes to +9v(red lead). Black - lead goes to the far left of my circuit board and the red + to the far right(3.9k/68k)

This way my DMM shows a voltage of +7v right? Instead of -7v ...

Yes, it's just that.

[rangermaster]

Thanks for all the great help. I'll try rewiring it tonight