Rangemaster Build Troubleshooting

[JMac26]

Hi there!

I am attempting to build a Rangemaster from the original schematic. I have created a layout I intend to use in DIYLC. I have everything set up on a breadboard at the moment, but the signal coming from the circuit is very quiet and in no way treble-boosty. I am using a germanium OC44 CV7003 Texas Instruments transistor. (link to the schematic below)

The voltages I have measured are:

Emitter -8.72v
Collector -4.1v
Base -4.1v

Getting quite a lot of buzz and a very faint guitar signal in the amp.

Any help would be much appreciated!

https://www.electrosmash.com/images/tech/rangemaster/dallas-rangemaster-schematic-parts.png

[GibsonGM]

Hi Mac,  can you post pics of the build, front and back of the board?

[PRR]

Check C3 shorted or backward.

[JMac26]

Hi Mac,  can you post pics of the build, front and back of the board?

It's just built on a breadboard at the moment. I've tried to upload pics but it keeps failing for some reason. I'll try again in the morning.

I saw in a previous RM troubleshooting post, someone mentioned that the polarised caps needed to be the other way round due to the positive ground (so that negative of the cap was going to negative of the battery). Otherwise the pedal would pass a small signal but not what was expected. I have tried this, but no success.

Also i've tested for continuity and there is continuity at every point expected in the circuit all the way to the output, but strangely not between input and output jack tips? But at the same time there is a small amount of signal passing...

I'll report back tomorrow with some pictures

[R.G.]

The voltages indicate something. For a bipolar transistor to amplify, the base and emitter voltages need to be separated  by only one forward-biased diode drop. For germanium, that's about 0.2V or so. So the base voltage should be a whole lot nearer the emitter voltage, not identical with the collector.

The schematic is kind of a mess. Where it shows +9V, it should have a ground symbol, and where it has a ground symbol, it should show -9V. Unless you run it from an isolated supply like its own supply, like a battery, it would short circuit 9V on its input jack and output jack to ground from any other pedals. I'm guessing that this was an attempt to run it from a more common +9V and ground, with the "ground" being the negative side of the power supply/battery and the emitter going to +9V to let you common up +9V and ground with other pedals. But the input and output jack signal grounds can't go to +9V and have this work right.

Presuming you swap the in and out jack grounds to the negative side of the 9V supply, it ought to bias up with the emitter up at, plausibly, near +9v.  But the base should not be more than 0.3V lower than the emitter, and you'd like the collector to be near where it is, +4 to +5V. 

The base being the same voltage as the collector can be several thing; one is a defective transistor with a base-collector short. Could be a slipped voltmeter probe shorting them together, too. Another is a bum breadboard. These used to get me all the time.

Ground the signal ground on input and output jacks to the negative side of your 9V, then measure again carefully.

[JMac26]

The voltages indicate something. For a bipolar transistor to amplify, the base and emitter voltages need to be separated  by only one forward-biased diode drop. For germanium, that's about 0.2V or so. So the base voltage should be a whole lot nearer the emitter voltage, not identical with the collector.

The schematic is kind of a mess. Where it shows +9V, it should have a ground symbol, and where it has a ground symbol, it should show -9V. Unless you run it from an isolated supply like its own supply, like a battery, it would short circuit 9V on its input jack and output jack to ground from any other pedals. I'm guessing that this was an attempt to run it from a more common +9V and ground, with the "ground" being the negative side of the power supply/battery and the emitter going to +9V to let you common up +9V and ground with other pedals. But the input and output jack signal grounds can't go to +9V and have this work right.

Presuming you swap the in and out jack grounds to the negative side of the 9V supply, it ought to bias up with the emitter up at, plausibly, near +9v.  But the base should not be more than 0.3V lower than the emitter, and you'd like the collector to be near where it is, +4 to +5V. 

The base being the same voltage as the collector can be several thing; one is a defective transistor with a base-collector short. Could be a slipped voltmeter probe shorting them together, too. Another is a bum breadboard. These used to get me all the time.

Ground the signal ground on input and output jacks to the negative side of your 9V, then measure again carefully.

Thanks for the info. I am getting a bit confused by this though. Do you mean that the input / output jacks ALWAYS go to the negative side of the battery, regardless of the circuit being positive ground? So they're not actually going to ground, just to negative battery.

Here's a list of where I have everything connected:

Negative side of the battery (-9V)

- Negative side of the 47uF Axial Cap
- Input and Output Jack Grounds
- 470k resistor
- Lug 1 of the 10k Pot

Positive side of the battery (positive ground)

- Positive side of the 47uF Axial Cap
- 68k Resistor
- 3.9k Resistor
- Positive side of the 47uF Cap (other side goes to the emitter of transistor)

With the I/O jacks connected to negative battery in this way, my new Q1 measurements are:

Emitter +8.16v
Base +7.72v
Collector +2.06v

I am getting a slightly louder guitar sound in the amp than previously. But with the pot cranked to full, it's only just about the same level as plugging directly into my amp. But it does sound like some low-end has been rolled off.

[antonis]

You need to double Collector current, hence double Emitter current..
For 9V power supply, that leads to Emitter voltage of about 7.44V, hence Base voltage about 7.0V..
(taking into account 440mV drop of your particular transistor - conclusion derived from your last measurements..)

You might have to tweak 68k/470k resistors a bit (not necessarily both of them) to set Base voltage at 7V..

P.S.
Exactly what is your battery/power source voltage..??

[JMac26]

I have switched to a different breadboard to make sure it's not that. I have connected the jack sleeves and lug 1 of the pot to the negative side of the battery, which seems to be working. But confuses me, because I thought the whole point of the PNP transistor was that I was using positive ground? But with the jacks and lug 1 connected to battery negative, they are connected to my -9v supply voltage? 

I'd say the guitar is now "trebly" and louder than when I directly plug into the amp, huzzah! I am having to crank the pot quite a bit though for an appropriate level boost, is this to be expected?

However, my voltages are still reading:  (black probe on jack ground, red probe on each leg)

E +8.18v
B +7.73v
C +2.12v

Based off the original post I am following: https://www.electrosmash.com/dallas-rangemaster
In the section called "the perfect bias point" the diagram shows that if I am referencing voltages to ground, I should have:

E +8.2v
B +8v
C +2v

Does this suggest I am about right, but just need to use a trimmer in place of the 3.9k to bias the emitter down to 8v?

Any advice would be much appreciated!

[Big Monk]

Take that schematic and everywhere it says +9v, replace it with a ground symbol. Then replace the ground symbol with +9v. Rewire the circuit and use a battery and report back.

[JMac26]

You need to double Collector current, hence double Emitter current..
For 9V power supply, that leads to Emitter voltage of about 7.44V, hence Base voltage about 7.0V..
(taking into account 440mV drop of your particular transistor - conclusion derived from your last measurements..)

You might have to tweak 68k/470k resistors a bit (not necessarily both of them) to set Base voltage at 7V..

P.S.
Exactly what is your battery/power source voltage..??

I'm using a new 9v battery as the power source. I've posted my current measurements above, which does give me a louder more treble-y tone. But i'm not convinced it's the right sound as it doesn't sound similar to clips i've listened to of originals / clones

[Big Monk]

Try this:

https://fuzzcentral.ssguitar.com/rangemaster/rangemasterschematic.gif

You seem to be getting messed up by that Electrosmash schematic. Rewire it per a more traditional positive ground schematic and report back.

I think your voltages are actually correct, I'm just not sure why you have power and ground references swapped.

[JMac26]

Try this:

https://fuzzcentral.ssguitar.com/rangemaster/rangemasterschematic.gif

You seem to be getting messed up by that Electrosmash schematic. Rewire it per a more traditional positive ground schematic and report back.

I think your voltages are actually correct, I'm just not sure why you have power and ground references swapped.

Thanks for the reply. The schematic you posted is how I have the circuit set up currently. The only difference I can see is that my jack sleeve lugs and lug 1 (i.e ground lug) of the 10k pot are connected to the battery negative. When I connect them to battery positive I get no sound at all.

[Big Monk]

Try this:

https://fuzzcentral.ssguitar.com/rangemaster/rangemasterschematic.gif

You seem to be getting messed up by that Electrosmash schematic. Rewire it per a more traditional positive ground schematic and report back.

I think your voltages are actually correct, I'm just not sure why you have power and ground references swapped.

Thanks for the reply. The schematic you posted is how I have the circuit set up currently. The only difference I can see is that my jack sleeve lugs and lug 1 (i.e ground lug) of the 10k pot are connected to the battery negative. When I connect them to battery positive I get no sound at all.

Well, you wouldn't connect lug 1 of the pot to positive. In the schematic it's connected to power which is negative. The jacks go to positive (i.e. positive ground), but not the pot.

[JMac26]

Try this:

https://fuzzcentral.ssguitar.com/rangemaster/rangemasterschematic.gif

You seem to be getting messed up by that Electrosmash schematic. Rewire it per a more traditional positive ground schematic and report back.

I think your voltages are actually correct, I'm just not sure why you have power and ground references swapped.

Thanks for the reply. The schematic you posted is how I have the circuit set up currently. The only difference I can see is that my jack sleeve lugs and lug 1 (i.e ground lug) of the 10k pot are connected to the battery negative. When I connect them to battery positive I get no sound at all.

Well, you wouldn't connect lug 1 of the pot to positive. In the schematic it's connected to power which is negative. The jacks go to positive (i.e. positive ground), but not the pot.

Thanks I missed that. But my understanding was that lug 1 of the pot would go to positive ground because when the pot is turned all the way to the left the signal will be grounded i.e no sound. But if this lug is actually going to battery negative, i'm confused how it is turning the signal down?

[Big Monk]

Try this:

https://fuzzcentral.ssguitar.com/rangemaster/rangemasterschematic.gif

You seem to be getting messed up by that Electrosmash schematic. Rewire it per a more traditional positive ground schematic and report back.

I think your voltages are actually correct, I'm just not sure why you have power and ground references swapped.

Thanks for the reply. The schematic you posted is how I have the circuit set up currently. The only difference I can see is that my jack sleeve lugs and lug 1 (i.e ground lug) of the 10k pot are connected to the battery negative. When I connect them to battery positive I get no sound at all.

Well, you wouldn't connect lug 1 of the pot to positive. In the schematic it's connected to power which is negative. The jacks go to positive (i.e. positive ground), but not the pot.

Thanks I missed that. But my understanding was that lug 1 of the pot would go to positive ground because when the pot is turned all the way to the left the signal will be grounded i.e no sound. But if this lug is actually going to battery negative, i'm confused how it is turning the signal down?

The "Boost" pot of the Rangemaster is wired as a variable voltage divider. Full clockwise, it sends full signal out the wiper because there is zero resistance between between the transistor collector and wiper. Conversely, when full counter-clockwise, you've decreased the resistance between the power rail and wiper, and a cutoff the output, i.e. no signal flowing through the collector.

Take the Fuzz Face for instance, which has a similar arrangement except it uses two resistors and taps the output cap of their junction. We know that as we increase the resistor that feeds the junction from power, the output of the Fuzz Face increases, i.e. you get more volume past unity gain.

[antonis]

But i'm not convinced it's the right sound as it doesn't sound similar to clips i've listened to of originals / clones

You can replace either 3k9 resistor with a 5k trimmer or 68k resistor with a 100k trimmer aiming for a higher Collector voltage (absolute) value..

[JMac26]

Ok thanks Monk, this makes a bit more sense. I think maybe the pedal is working as it should and I was just expecting a bit more of a boost.

[JMac26]

But i'm not convinced it's the right sound as it doesn't sound similar to clips i've listened to of originals / clones

You can replace either 3k9 resistor with a 5k trimmer or 68k resistor with a 100k trimmer aiming for a higher Collector voltage (absolute) value..

Thanks will give this a try!