Em Drive not working

[mattlee0037]

Hey guys, this is the 3rd (and easiest) circuit I've built so far. I built the Emerson Em Drive using the compact layout found here http://tagboardeffects.blogspot.com/2013/01/emerson-custom-guitars-em-drive.html

I cannot for the life of me figure out why these 6 little parts won't work. I've never had to test voltages before, but I borrowed a multimeter in hopes that it would shed some light on the situation (although I admit, I'm not sure what they do or mean).

Anyway here are some voltages I've got are
9v is 9.45v
Sleeve is 0
Output is about 0
Input iis about 7.5
Negative LED is 7.5
Positive LED is 9.45
Transistor Collector is about 0.23

So I think somethings wrong with the transistor and LED. Anyone think I killed the transistor?

[mattlee0037]

Alright this is my first time, but I found a data sheet I think and I used the DMM to check the HFE and it's like 360 and the range I think is supposed to be 70-200. So does anyone think a new NPN transistor would make it work?

[Jdansti]

Welcome to the forum!

There's something not right with your voltage readings. For example, your negative LED reading should be 0 if you're using the meter correctly and it's connected properly. Do you have the black DMM probe on ground and the red lead on whatever you're checking for all of your readings?

How is the LED connected?

[mattlee0037]

Hey thanks! Right I wouldn't be surprised as its my first time! Uhm I put the black probe on the DC jack ground and touch the red to wherever I measure. The LED is just hooked up to the top rowof the 3pdt switch as per standard true bypass schematics with a 4k7 resistor on the positive end (I've heard it doesn't matter which end). And I used a cell battery to test that the LED lights normally.

[PRR]

> won't work

What does it do, or not do? Doesn't play like Clapton? Doesn't distort at all? Doesn't pass any signal? Sets off the smoke alarm? Observe everything.

> Negative LED is 7.5

There's no LED on that plan. What are you measuring here? Or do you have another plan with LED?

You do have one *excellent* observation:

> Transistor Collector is about 0.23

It's slammed; pinned to the ground like a losing wrestler.

If you read the article (BTW the theory is dubious) you see a suggestion of 2V at collector.

> HFE and it's like 360

Bingo!!

This design is *VERY* sensitive to hFE. Since hFE is the most variable parameter of transistors, it might be called a "poor" design for mass production (or for duplication by non-geeks).

You don't throw-out 10 good transistors to find one that happens to work in a poor circuit. (At least we didn't back when transistors cost money.) There's always a circuit change that will get some use out of any non-dead transistor.

Lessee... 2Meg and 4k7.... 2000k/4.7k= 425, so hFE of 425 or more will slam it. You are actually not knock-out slammed, which is typically 0.1V. But an hFE of 360, in a circuit that slams solid with hFE>425, sure will be pretty unwilling to move.

Change 4k7 to 3k3, 2k2, something like that. (If you have a spare 4k7, carefully stack it on top of the existing 4k7, just tack the leads to try it.)

[mattlee0037]

Sorry for leaving out info! It won't pass any signal bypassed it engaged. The LED was just the off board wiring LED I just read somewhere that is should sit at about 2v so I thought it may be pertinent info. And ok I will try a 2.2k resistor change tomorrow. Also the LED doesn't light up when turned on as well.

[Jdansti]

Make sure your switch isn't rotated 90 deg.

Here's the bypass scheme I use.



If you still think it's all wired up correctly, it would be best for you to post some photos showing both sides of the board and all of the off-board connections.

[mattlee0037]

Ok so I changed the resistor to a 2.2k and the collector is now about 4.8v. Also, now when plugged in it makes a low pitched buzz noise that changes slightly when the volume on the pedal is changed, and bypassed it passes no signal. I've attached some pictures of the board.






Thoughts?

[Jdansti]

I think I see several problems with your wiring. Looking at this photo, the ground through both jacks is switched such that when the plugs are in the jacks, the path is open (no continuity through the switch). There should be no reason to switch the ground if you're not using a battery, and when you do, it's normally only on the input jack, using a stereo jack, not a switching jack.

Also, what appears to be your output jack has metal parts touching the enclosure.



Looking at the switch, I don't see how the signal input and output can be switched to go through the board.  And in what should be bypass mode, the input gets switched completely out of any path and at same time the jumper that should be connecting the input jack to the output jack is connected to ground on one end and to the output jack tip on the other.  I can't see what's connected to the very center terminal of the switch.



I honestly can't see how any of the switch and jack wiring would work. Have you wired other builds using this exact same wiring plan?

[mattlee0037]

Sorry if you could explain a bit more on the grounds being switched? Also to clarify, its hard to tell from the pictures but input tip is going to centre row centre column circuit input output and led are in the top row with jack in jack out and ground in the middle and the connector on bottom (which if I'm honest I Dont know what that connector does at all). The thing I Dont understand is bypassed it should definitely pass signal as its only going input ground and output right? Also to ground connections I'm not exactly sure how to do them. I just connect them to the closest ground really most of the time I just run it to the sleeve if it says ground. Lastly, when I play it those metal contacts Dont touch the enclosure. That jack is a temporary thing as its a 2 in 1 enclosure but I'm testing the circuits separately to dtermine the problem.

[mattlee0037]

Come to think of it idk what a switching jack is?? I thought these were just regular stereo jacks with easier solder terminals 

[Jdansti]

Sorry if you could explain a bit more on the grounds being switched? Also to clarify, its hard to tell from the pictures but input tip is going to centre row centre column circuit input output and led are in the top row with jack in jack out and ground in the middle and the connector on bottom (which if I'm honest I Dont know what that connector does at all). The thing I Dont understand is bypassed it should definitely pass signal as its only going input ground and output right? Also to ground connections I'm not exactly sure how to do them. I just connect them to the closest ground really most of the time I just run it to the sleeve if it says ground. Lastly, when I play it those metal contacts Dont touch the enclosure. That jack is a temporary thing as its a 2 in 1 enclosure but I'm testing the circuits separately to dtermine the problem.

I should have used this photo. I've properly labeled the contacts, so let's see what happens in each switch position.



Here's what I see:

Pin 1= board input
Pin 2 = ground
Pin 3= jumper to pin 9
Pin 4= LED neg leg
Pin 5= guitar input
Pin 6= not connected
Pin 7= board output
Pin 8= output to amp
Pin 9= jumper to pin 3

When the switch is in the "up" position the top two rows of lugs are connected. So in the up position, you have:

Pins 1 and 2 are connected = ground and board input are connected. Bad
Pins 4 and 5 are connected = guitar in and LED neg leg are connected. Bad
Pins 7 and 8 are connected = output jack tip and board out are connected. Good

Now lets look at the other position:

Pins 2, 3, 9 (via jumper), and 8 are connected = ground to jumper to output jack tip. Bad
Pins 5 and 6 are connected = guitar input is connected to nothing.  Bad
Pins 8 and 9 are connected = same as pins 2 and 3 above. Bad

Use the switch configuration I gave you earlier and you'll get it working. Be careful desoldering everything.


Now for the jacks. The terminals from one side to the other form normally closed switches. When you insert the plug into the jack, the metal fingers raise up and open the circuit. Look at one carefully and insert and remove the plug and you'll see. If you're not using a battery, ignore the center terminal (ring) and just use the sleeve and tip according to my switch diagram. Connect all of your grounds and sleeves together at one point, and connect the jack tips per my diagram. There are two jumpers on the switch. One between pins 3 and 6, and another between pins 1 and 9.

It would be a good idea for you to go through the same exercise of seeing how things are connected in both switch positions using my diagram. You'll see how the guitar signal travels into the switch, then to the board, then back to the switch, then to the output jack when the effect is not bypassed. Likewise, you'll see how the signal goes from the input jack, through the switch, and then to the output jack, bypassing the circuit. Draw the switch lugs on a piece of paper and draw the paths. It will help, I promise!

[tca]

As PRR says,
>This design is *VERY* sensitive to hFE. Since hFE is the most variable parameter of transistors, it might be called a "poor" design for mass production (or for duplication by non-geeks).

You should breadboard it first... I've tested similar circuits with different resistor values and BJTs,  it works fine. Experiment, experiment, experiment,...

Cheers.

[nocentelli]

***edit - Sorry, just realised the information about switching jacks is contained in the posts above.

[mattlee0037]

Wow! Thanks for all the help guys!! 3pdt switches have always been explained to me that ALL the two rows are connected not just the two, so now the jumper on the bottom makes sense and now I understand the switching jack! I never would have figured that out, so I'll try to do this today and report back.

[mattlee0037]

Ok, so good news and bad news! Good news first is that I got the whole circuit working and it sounds great thanks so much! Now the bad news, I added the second board which is
http://tagboardeffects.blogspot.com/2013/03/bearfoot-baby-pink-booster.html the bottom one on here. Bypassed it passes signal, and when turned on the LED goes on, so I'm assuming the power section, and the bypass section work fine so it has to be somewhere on the board.
The drain measures about 0
S measures 0
Drain is 9.15

The diode has 9.2 on the negative side and 9.45 on the positive side

Also the LED only lights up when something is plugged into input and output. I have board ground to DC jack ground and sleeve to the ground of the 3pdt switch

When the effect s switched on I get a super fuzzy/farty noise. ALMOST DONE haha I have too much time in this circuit right now....

[Jdansti]

Ok, so good news and bad news! Good news first is that I got the whole circuit working and it sounds great thanks so much! Now the bad news, I added the second board which is
http://tagboardeffects.blogspot.com/2013/03/bearfoot-baby-pink-booster.html the bottom one on here. Bypassed it passes signal, and when turned on the LED goes on, so I'm assuming the power section, and the bypass section work fine so it has to be somewhere on the board.
The drain measures about 0
S measures 0
Drain is 9.15

The diode has 9.2 on the negative side and 9.45 on the positive side

Also the LED only lights up when something is plugged into input and output. I have board ground to DC jack ground and sleeve to the ground of the 3pdt switch

When the effect s switched on I get a super fuzzy/farty noise. ALMOST DONE haha I have too much time in this circuit right now....

Probably time for more photos...   

[mattlee0037]

[Jdansti]

Thanks. I'm working on it.

[Jdansti]

Pin 1= Board input
Pin 2= From Pin 8 of other switch. (Can't see-please verify).
Pin 3= Jumper to Pin 9
Pin 4= LED neg leg
Pin 5= Ground*
Pin 6= N/C
Pin 7= Board output
Pin 8=Output jack tip
Pin 9= Jumper to Pin 3

*I think your problem is that you don't have the output sleeve connected to all of the other grounds. Run an additional ground wire from wherever you tied all of the others to your output jack sleeve.

I couldn't tell, but I assume that the board's ground is also connected to the common ground point. If not, it should be.

On future boards, it would be better if you inserted the off-board wiring from the top of the board instead of soldering the wire flat on the traces. It's neater, less prone to bridges, mechanically stronger, and less likely to cause a trace to separate from the board.