Super basic question about biasing

[mkstewartesq]

Sorry for what is an incredibly basic question, but this is how we learn.

I’m about to start a Rangefinder build and, based on building a similar rangemaster clone before, I know I will need to bias at the very end to try to get to 7 V. My super basic question is how exactly do I do that with a multimeter? I understand that the positive lead is going to be measuring at the Collector of the transistor– but what am I doing with/where am I placing the black lead?

The one rangemaster clone I built before was an Aion kit, excellent for beginners, so that board simply had two test pads to which you touch the multimeter leads to do the biasing. So I’ve never really done a true “manual” biasing before. And every YouTube video I found always has the person doing the test say “and of course the other side is connected negative“ or the “other side is connected to ground” but they never actually show that connection in the video (It’s always obscured or offscreen).

Thanks in advance.

 

[DAJE]

Black probe goes to ground. Any ground will do as long as it's grounded. If the pedal is in the enclosure I just use the enclosure itself. If not, whatever ground is convenient, usually the in or out jack ground.

EDIT: Ground = negative in this case.

 

[mkstewartesq]

Thank you, exactly the information I needed. And I also had completely forgotten that when I needed to test something else, I used the enclosure as the ground just by putting the lead into one of the screw holes.

Mike

 

[mkstewartesq]

Okay, so a follow-up question:

For a Rangefinder(Rangemaster clone), the target voltage at the collector is 7v. However, even with the trimmer maxed out, I can't get above 6.84v when testing my Rangefinder build on my PedalPCb audition platform.

Oddly I had almost the exact same issue with an AionFX Rangemaster clone and some suggested a leaky capacitor was to blame, so when it came time to build the Rangemaster, I made sure to pay a fair amount extra and have Small Bear sell me a transistor (Mullard OC42) that they tested to have an hfe of 90 and very low leakage. (Interesting side note - I assume it's just different board designs but just in case someone finds it important: on the PedalPCB board, turning the trimmer counterclockwise raises the voltage while, on the Aion, the trimmer needed to be turned clockwise to do the same thing).

As far as power, I'm hooked up to a 1Spot Pro CS12 isolated power supply, reading 8.84 V as the power enters the board and about 8.65 volts at the IC.

So I'm a bit stumped. I get that 6.84 v may be "close enough for rock and roll" to 7v -but it just seems odd to me when videos on biasing show people accidentally overshooting 7 and having to dial it back down, and for Aion's pedal, their instruction also noted you could go beyond 7v for more gain, yet I can't get either of my my PedalPCB and Aion pedals to even hit 7v. Could it even be a multimeter issue?

Any thoughts appreciated.

 

[Big Monk]

Okay, so a follow-up question:

For a Rangefinder(Rangemaster clone), the target voltage at the collector is 7v. However, even with the trimmer maxed out, I can't get above 6.84v when testing my Rangefinder build on my PedalPCb audition platform.

Oddly I had almost the exact same issue with an AionFX Rangemaster clone and some suggested a leaky capacitor was to blame, so when it came time to build the Rangemaster, I made sure to pay a fair amount extra and have Small Bear sell me a transistor (Mullard OC42) that they tested to have an hfe of 90 and very low leakage. (Interesting side note - I assume it's just different board designs but just in case someone finds it important: on the PedalPCB board, turning the trimmer counterclockwise raises the voltage while, on the Aion, the trimmer needed to be turned clockwise to do the same thing).

As far as power, I'm hooked up to a 1Spot Pro CS12 isolated power supply, reading 8.84 V as the power enters the board and about 8.65 volts at the IC.

So I'm a bit stumped. I get that 6.84 v may be "close enough for rock and roll" to 7v -but it just seems odd to me when videos on biasing show people accidentally overshooting 7 and having to dial it back down, and for Aion's pedal, their instruction also noted you could go beyond 7v for more gain, yet I can't get either of my my PedalPCB and Aion pedals to even hit 7v. Could it even be a multimeter issue?

Any thoughts appreciated.

Did you use the resistors sent from Small Bear? Do they still provide those?

 

[mkstewartesq]

Ah, Big Monk, my ever-helpful friend:

They do still send them and, no, I did not use them (mainly ebcause I thought they were just for "proof we tested"purposes). Where would I use them on this board? I'd have to compare the actual resistors to a color chart to be sure but, based on the card they included, it looks like the resistors are 62K (Rb) and 4.3K (Re).

M

EDIT TO ADD - I do see that Small Bear's card states "this device is biased so the collector of Q1 sees + 6.8 to 7.2 volts", although i don't know if that refers to "with our resistors" or without. Maybe it's in spec at 6.84. I'm a bit ignorant on this point.

 

[mkstewartesq]

Just FYI

 

[Big Monk]

Ah, Big Monk, my ever-helpful friend:

They do still send them and, no, I did not use them (mainly ebcause I thought they were just for "proof we tested"purposes). Where would I use them on this board? I'd have to compare the actual resistors to a color chart to be sure but, based on the card they included, it looks like the resistors are 62K (Rb) and 4.3K (Re).

M

EDIT TO ADD - I do see that Small Bear's card states "this device is biased so the collector of Q1 sees + 6.8 to 7.2 volts", although i don't know if that refers to "with our resistors" or without. Maybe it's in spec at 6.84. I'm a bit ignorant on this point.

The resistors they send are what they biased the transistor with, in my experience.

If it sounds good, leave it. At this stage of the hobby for you, I would not recommend removing components, etc. It usually leads to disaster. In fact, it still occasionally does for me!

If you like the way the pedal sounds, it's a set and forget value on the RM so don;t sweat it.

 

[mkstewartesq]

The resistors they send are what they biased the transistor with, in my experience.

If it sounds good, leave it. At this stage of the hobby for you, I would not recommend removing components, etc. It usually leads to disaster. In fact, it still occasionally does for me!

If you like the way the pedal sounds, it's a set and forget value on the RM so don;t sweat it.

Thanks, Big Monk. I was hoping for just a tad more gain, hence my concern with not hitting the target voltage. But as I seem to have this exact same issue with two different Rangemaster clones, I guess I'll just chalk it up to "it's the nature of the beast" and leave it as an open question whether 'the beast" in question is the Rangemaster or me.