Umble Schematic vs. PCB

[ECDavis]

Hello, this is my first post.  I performed a keyword search and read every post containing "Umble" but could not find a discussion about a particular issue concerning the Mid tone control portion of the circuit.

I purchased a kit from Officially Licensed Circuits that included a PCB, and I downloaded the Build Guide http://www.olcircuits.com/olc_umble_buildguide.pdf

The schematic shown on Page 3 of the guide shows the 47nF capacitor connected to Lug 1 of the 100K Mid potentiometer, the wiper Lug 2 connected to Lug 3, and Lug 3 going to ground. At full CounterClockWise, the signal would go straight from the cap to ground, and at full ClockWise the signal would see the full 100K resistance of the pot.

However, the pads on the PCB connect Lug 1 with Lug 2.  When wired as shown on Page 17 of the build guide, the effect of the wiper's rotation on the signal is reversed:  at full CCW the full 100K resistance occurs between the cap and ground, and at full CW rotation the cap is bypassed and the signal goes straight to ground.

My question for the friendly experts here is: Are the Mid frequencies "cut" when the pot's resistor is bypassed and the signal goes straight to ground?

If so, then without altering the PCB, could the Mid frequency cut be made to occur at full CCW by simply swapping the placement of the wires between the PCB and Lugs 1 and 3?  Thanks!

[pappasmurfsharem]

Hello, this is my first post.  I performed a keyword search and read every post containing "Umble" but could not find a discussion about a particular issue concerning the Mid tone control portion of the circuit.

I purchased a kit from Officially Licensed Circuits that included a PCB, and I downloaded the Build Guide http://www.olcircuits.com/olc_umble_buildguide.pdf

The schematic shown on Page 3 of the guide shows the 47nF capacitor connected to Lug 1 of the 100K Mid potentiometer, the wiper Lug 2 connected to Lug 3, and Lug 3 going to ground. At full CounterClockWise, the signal would go straight from the cap to ground, and at full ClockWise the signal would see the full 100K resistance of the pot.

However, the pads on the PCB connect Lug 1 with Lug 2.  When wired as shown on Page 17 of the build guide, the effect of the wiper's rotation on the signal is reversed:  at full CCW the full 100K resistance occurs between the cap and ground, and at full CW rotation the cap is bypassed and the signal goes straight to ground.

My question for the friendly experts here is: Are the Mid frequencies "cut" when the pot's resistor is bypassed and the signal goes straight to ground?

If so, then without altering the PCB, could the Mid frequency cut be made to occur at full CCW by simply swapping the placement of the wires between the PCB and Lugs 1 and 3?  Thanks!

It should respond like a typical 3 band eq if it's backwards just swap 1 and 3

[J0K3RX]

My question for the friendly experts here is: Are the Mid frequencies "cut" when the pot's resistor is bypassed and the signal goes straight to ground?

If so, then without altering the PCB, could the Mid frequency cut be made to occur at full CCW by simply swapping the placement of the wires between the PCB and Lugs 1 and 3?  Thanks!

Yes, it cuts mid frequency... The lower the resistance between the 47n cap and ground the more mid frequency is cut.

Swapping the wires between lugs '1 and 3' or '1 and 2' will make the pot adjustment/orientation backwards.

lugs 2 and 3 of the 100k/B pot should be connected to the 47n cap and lug 1 should be connected to ground for correct orientation.

[pappasmurfsharem]

My question for the friendly experts here is: Are the Mid frequencies "cut" when the pot's resistor is bypassed and the signal goes straight to ground?

If so, then without altering the PCB, could the Mid frequency cut be made to occur at full CCW by simply swapping the placement of the wires between the PCB and Lugs 1 and 3?  Thanks!

Yes, it cuts mid frequency... The lower the resistance between the 47n cap and ground the more mid frequency is cut.

Swapping the wires between lugs '1 and 3' or '1 and 2' will make the pot adjustment/orientation backwards.

lugs 2 and 3 of the 100k/B pot should be connected to the 47n cap and lug 1 should be connected to ground for correct orientation.

I believe he currently has the connection backwards as he stated that pin one is connecting to the 47n

[ECDavis]

Thank you all for your prompt replies!

"I believe he currently has the connection backwards as he stated that pin one is connecting to the 47n."

Just for my own clarification (sorry . . . I took Electronics in high school and one semester in college, but that was 30 years ago. . .) I need to make certain I correctly understand the schematic symbol for a potentiometer: When wiper Lug 2 is pointing UP, Lug 1 is on the LEFT side of the resistor and Lug 3 is on the RIGHT side.  If this is correct, then rotating the symbol 90 degrees clockwise -- as it's shown on the Umble schematic -- would indicate Lug 1 (on top) is connected to the 47nF capacitor, Lug 3 (on the bottom) is connected to the ground trace of the PCB, and Lug 2 (pointing right) is connected to Lug 3/ground.

In any case, the wiring diagram for the pots also shows Lug 1 connected to the cap and Lug 3 connected to the ground trace. However, the PCB is constructed so that Lug 2 is connected to Lug 1 (capacitor) instead of Lug 3 (ground).

Wired as shown on the Build Guide, wouldn't the construction of the PCB cause the Mid frequencies to be cut as the knob is rotated Clockwise i.e., as the knob is turned "UP?"

[pappasmurfsharem]

Thank you all for your prompt replies!

"I believe he currently has the connection backwards as he stated that pin one is connecting to the 47n."

Just for my own clarification (sorry . . . I took Electronics in high school and one semester in college, but that was 30 years ago. . .) I need to make certain I correctly understand the schematic symbol for a potentiometer: When wiper Lug 2 is pointing UP, Lug 1 is on the LEFT side of the resistor and Lug 3 is on the RIGHT side.  If this is correct, then rotating the symbol 90 degrees clockwise -- as it's shown on the Umble schematic -- would indicate Lug 1 (on top) is connected to the 47nF capacitor, Lug 3 (on the bottom) is connected to the ground trace of the PCB, and Lug 2 (pointing right) is connected to Lug 3/ground.

In any case, the wiring diagram for the pots also shows Lug 1 connected to the cap and Lug 3 connected to the ground trace. However, the PCB is constructed so that Lug 2 is connected to Lug 1 (capacitor) instead of Lug 3 (ground).

Wired as shown on the Build Guide, wouldn't the construction of the PCB cause the Mid frequencies to be cut as the knob is rotated Clockwise i.e., as the knob is turned "UP?"

Not 100% but it may just be misdrawn. Otherwise you would be correct.

No worries you've probably forgotten more than I'll learn in this hobby I'm only 24.

[J0K3RX]

Thank you all for your prompt replies!

"I believe he currently has the connection backwards as he stated that pin one is connecting to the 47n."

Just for my own clarification (sorry . . . I took Electronics in high school and one semester in college, but that was 30 years ago. . .) I need to make certain I correctly understand the schematic symbol for a potentiometer: When wiper Lug 2 is pointing UP, Lug 1 is on the LEFT side of the resistor and Lug 3 is on the RIGHT side.  If this is correct, then rotating the symbol 90 degrees clockwise -- as it's shown on the Umble schematic -- would indicate Lug 1 (on top) is connected to the 47nF capacitor, Lug 3 (on the bottom) is connected to the ground trace of the PCB, and Lug 2 (pointing right) is connected to Lug 3/ground.

In any case, the wiring diagram for the pots also shows Lug 1 connected to the cap and Lug 3 connected to the ground trace. However, the PCB is constructed so that Lug 2 is connected to Lug 1 (capacitor) instead of Lug 3 (ground).

Wired as shown on the Build Guide, wouldn't the construction of the PCB cause the Mid frequencies to be cut as the knob is rotated Clockwise i.e., as the knob is turned "UP?"

You are correct about the symbol... The schematic is kinda strange  but, if you look at the perf board layout on ROG lug 3 is connected to the 47n cap... http://www.runoffgroove.com/umble.html

Looks like 3 is connected to the 47n cap and 2 and 3 are connected to ground. In any case, if you turn your pot clockwise you will want it to dial in more mids, right? If you install the pot with lug 3 to ground it will work backwards. Build it and see, if it's backwards then you will know what it is...

[ECDavis]

Yes, I agree that the perf board layout is correct, i.e., with Lug 3 connected to the 47n cap and Lugs 1&2 grounded.  The perf board is essentially opposite from the diagram shown on OLC's Build Guide.

Thanks again!

[waltk]

ECDavis - welcome to the forum!

I've built a ton of Umbles - love the sound.  Early on in my pedal building, I thought there was serious mojo to be had by finding the right circuit, and using some "special" components in it (and who wouldn't want a Dumble amp, after all).  I thought it was best pedal of its type until I tried the BSIAB (not dissing the Umble).  If you get as hooked on building as some of us have, you might want to try the BSIAB next.  There's also a variation on it called the Spitfire (by Rob/DeadAstronaut).

It seems that you've sorted out the issue with the pot wiring, so I won't comment on that.  If you still have any difficulties, post here, and I'll dig out some old working builds to answer your questions.

Again - welcome, and good luck...

[ECDavis]

WaltK,

Thanks for the suggestion.  I just found the perf board layout for the BSIAB 2 (by  Ed Guidry & Xavier).  I'll start gathering the parts.

I have to say the genious in spacial relations demonstrated by the guys who lay out some of these boards is remarkable!

[ECDavis]

So I just completed the build.  I wired the Mid pot like the wiring diagram -- not like the schematic -- and the control definitely acted as a mid frequency cut as the knob was turned clockwise, i.e., "up."  Counterintuitive, yes, but that's the way it worked.

I simply pulled the #1 and #3 wires on the PCB and swapped them, leaving the #2 wire alone.  Now the Mid control definitely acts as a mid frequency boost as the knob is turned "up"  Or, one migh say the control acts as a Mid freqency cut as the knob is turned down/counterclockwise.  In either case, by reversing the wires to the #1 and #3 lugs, the control now works as expected.

I biased the transistors to about 4.68 volts.  It was impossible to bias at precisely 4.5V. The trims were just too jumpy.  Trying to bias down from about 4.65V caused the voltage to make a quantum jump down to about 3.5V.

Also, I fried the LED.  The build guide said to place the supplied 4.7 ohm  (not 4.7K ohm, but 4.7 ohm) resister in series on the + lead of the LED.  The guide said if you hear a *pop* when switching, use the supplied 15K ohm instead.  Well, neither a 4.7 ohm nor a 4.7K was supplied, so I used the 15K. When I switched on, the LED did not emit light.  So I replaced the 15K with the only lower valued resistor I had, which was a 10K.  Still no light.  So I decided to just short the LED across the battery terminals to see if the LED was good.  You guys with experience will know that I just fried the LED when I did that.  So I'll acquire another LED and a 5K ohm and see if that combination works.