Magnus Dallas Rangemaster not "boosting"

[duck_arse]

squirrel - you don't want to measure continuity across a transistor junction, you want to measure continuity between the transistor legs and the parts they are supposed to be connected to. if you reverse the probes, you will probably get no continuity across that same transistor junction.

and magnus - I don't want to sound like a total duck, but your switch is drawn as an on-on-on. if you want to convey it's on-off-on-edness, you'd leave the centre position dot unconnected with the swinging/arrow pointing to it, and the cap that is allays in circuit (C1?) would then connect from the Q1 base around the switch to its common.

[Magnus]

Hello,

@duck_arse:
Thank you - good to know - I can read and convert schematics, but I'm more the layout guy 


Greetings
Magnus

[Squirrel Murphy]

Did you try another transistor?

btw: Don't solder germanium-transistors, they don't like too much heat...

Sorry... been out of town for a week. Back now.

Didn't solder... tranny is socketed.

I just tried another and discovered that I've had the tranny in BACKWARDS all along! I had checked it previously, so I'm not sure how that happened.

With them in backwards, the pedal plays smoothly and the frequency ranges are clearly differentiated when toggling between them. But unity seems to be past 10 on the pot (i.e., the pedal is an anti-booster).

With the tranny flipped (collector to pot3 and emitter to R1), the sound is louder, but it's crackly, sustain fails quickly, and it seems unstable. Sounds terrible. It's very sensitive to attack... super loud at the first of a strong attack and then very rapid drop-off or empty spaces in the note. More fuzz/distortion than the other way around. The input-cap toggle switch seems to still work the same, but it's not as obvious because the signal breaks up easily. It can sound OK with the amp pushed to distort, but I'm mostly testing on clean so I can hear what the pedal is doing.  I think it may be that it sounds OK with the amp distorted because the distortion is covering up the signal problems with the pedal.

New measures using a wall-wart (instead of battery):

C: -6.51V
B: -6.51V
E: -6.64V

Emitter is where it should be now...

Might just be bad soldering / weak connection at this point? Maybe time to build an audio probe.

[Magnus]

Hello,
try a second build on perfboard as you had planned 


Greetings
Magnus

[Squirrel Murphy]

try a second build on perfboard as you had planned 

Actually, I think I'm going to build a stock Rangemaster first so I can clearly see how it's supposed to behave. Then I can build another Magnus / continue to troubleshoot this one.

I was going to use this layout because it seems like it'd be difficult to fail. 

I'll post results back here...

[Squirrel Murphy]

squirrel - you don't want to measure continuity across a transistor junction, you want to measure continuity between the transistor legs and the parts they are supposed to be connected to. if you reverse the probes, you will probably get no continuity across that same transistor junction.

This is incidental. I do check from part to part (to test for good solder connections where they are supposed to be). What I was doing was looking for a solder bridge on the board where it wasn't supposed to be. So I probe between the solder blobs for continuity. With those two points, I got weakish continuity which I assumed was going through the circuit (because I couldn't see a bridge and wasn't hearing a strong beep). I later pulled the tranny and checked again and there's no continuity at all between solder points. So I was getting continuity THRU the tranny which is not what I wanted to measure as you indicate. But there ain't a solder bridge either and I now know that.

It's habit of mine to use a convenient point that I already know is continuous with where I want to measure. So am guilty of measuring from the actual tranny leg too. I figure I'm testing "from the horses mouth" by including the tranny leg + socket + solder blob instead of starting from the solder blob itself. It seems that this could get me into trouble. I do the same with ground, often opting for the enclosure because it's super easy to find a good probe point (i.e., everywhere).

Bad habits?

[duck_arse]

testing from the transistor leg instead of from the solder blob may well be a good diagnostic tool. you do want continuity all the way to the tranny, after all, and sockets are just another potential problem in the chain.

[PRR]

> C: -6.51V
> B: -6.51V
> E: -6.64V
> Emitter is where it should be now...

No. It can't amplify audio with all three pins at the *same* voltage.

You expect B and E near each other and C several volts different.

C and B at the same voltage within 0.01V strongly suggests a short.

[Ben Lyman]

C and B at the same voltage within 0.01V strongly suggests a short

Paul, that's what I was thinking. For the sake of my own learning, is there also the possibility of a transistor going bad and shorting internally?

[Squirrel Murphy]

No. It can't amplify audio with all three pins at the *same* voltage.

You expect B and E near each other and C several volts different.

C and B at the same voltage within 0.01V strongly suggests a short.

Maybe it was me and my testing... somehow screwed up. I retested using a wall wart (at 9.28V).

C: 6.51V
B: 9.16V
E: 6.64V

Different numbers. I guess I probed B as C last time because there's no short there (checked a few times). But this isn't B and E near each other either.

I'm going to look for an incorrectly sized resistor or cap. This thing plays all farty...

[Squirrel Murphy]

I hope you guys don't mind "learning along with Squirrel"....

I built and boxed this version over the last two nights. It took me a while to figure out how to wire for positive ground but I got it. Works great and I really like the sound although I don't think it sounds best biased with C at 7V. I did it to compare to the broken Magnus so I know what to expect from a working circuit. I soldered in the OC-44 and it's my last one... so I can't easily swap it into the Magnus as "known good".. but I don't think that's the problem anyway (I previously swapped this one in).

Measurements using -9.43V battery:

B: -1.09V
E: -0.99V
C: -6.85V

This matches what PRR says I should expect and I can easily bias C to 6.5V to 7.2 or so with the trimpot.

Input cap is different than the Magnus (4.7nF versus 5.5nF (2.2+3.3)) and R1 is variable with the trimpot.... but otherwise it's the same circuit so should work similarly despite the very different layouts.

I am noticing that C5 and C6 are oriented the same way in both circuits... so maybe I have the caps in the Magnus backwards after all.

[Magnus]

Hello,
very good - be proud of it 

Do you try to get my layout working or do you install this new version into your enclosure?

...I would be interested to see the final pedal 


Greetings
Magnus

[Squirrel Murphy]

Do you try to get my layout working or do you install this new version into your enclosure?

...I would be interested to see the final pedal 

I plan to enclose both (2 pedals). I will post results here for you to see.

I think my soldering is sometimes inconsistent and this can be causing me troubles. I have 3 wonky pedals at the moment.

[Squirrel Murphy]

Fixed!

I've been having troubles with intermittent circuits that work when jostled, but otherwise are flaky. Wiggle wires and they wake up until bumped again. I thought it was maybe my soldering technique. Someone suggested I dump the 15W iron for a hotter one. In the closet sits a 50W variable station that I don't use because the 15 is always handy. I pulled out the hotter iron and re-flowed all of the connections, adding a little solder here and there. Boom! the pedal first up and seems to work great! It still doesn't boost as much as the simple version I posted, but it boosts and it sounds great! I didn't even bother to measure the voltages yet...

Add C7 to combat noise and cased it...

Thanks all! Special thanks to Magnus for offering up the layout, specs, instructions, and guidance.

I'll post pics once I finish the enclosures... but it might be a long time. I work slowly.

[Squirrel Murphy]

Hi everyone. We had some warm weather this Feb so I could go outside and spray. This allowed me to finish these pedals. As promised, I'm posting here.

First the fully working and wonderful Magnus. I run it with a power supply and no battery and it runs quietly. Here's a general description:

Dallas Rangemaster treble booster using the Magnus circuit design. Germanium OC-44 PNP transistor; switchable input capacitors for a variable high-pass filter ranging from treble boost to full-range. "Classic" matches the original 1960s design. Designed for a negative ground circuit. Socketed transistor so I can try different transistors. Yellow LED.

I had some trouble with the waterslide (my printer skipped and smeared a little). It was consistently doing it, so I decided to live with it rather than keep wrecking waterslide paper. It also rippled a little after drying. I call it vintage spray clear over it anyway. I think I'll try an etch next time but I feel like I should pretty much expect a high fail rate there too.



Gut shot. I use a business card under the circuit board to keep from shorting on the pot. The same with the top side. I need to shrink-wrap the LED lead because it's a good shorting opportunity. But otherwise I think it's fairly solid albeit not very professional.

[Kipper4]

Nice one Squirrel.

[Squirrel Murphy]

Here's the other one I built to compare to the Magnus' functionality. Modeled after the original in terms of face color, font, and labels.

Dallas Rangemaster clone using original circuit design as per Tagboardeffects. Germanium OC-44 PNP transistor. Positive ground circuit. Kept it simple with battery power and no DC jack or LED. Biased to 7V with the 5k trimmer.

I had the same waterslide problems. Not much smearing on this, but you can see the skips. I'm hoping it will age nicely and have a vintage-ish vibe. The tranny legs should probably be wrapped to prevent shorts. I purposefully left the legs long so I can bend it over and get the back cover on. They don't short, but there's a risk for down the road. Trimmed business cards are sitting loose under and over the board to prevent shorting on the back cover or the pot. Not super professional, but effective.

[Magnus]

Hello,
nice to hear from you my friend - great builds 

...and my name on your pedal 


Greetings
Magnus