EHX LPB1 Build Not Working

[sk8rc13]

Hello, so I have been trying to build a clone of the EHX LPB1 with no luck. The schematic I followed for the full build was the one found on Pedal PCB

The circuit layout I followed for the sections relating to input, bias, and the common emitter amplifier was from a vero board layout, pictured below.



After completing the build I plugged it in and...nothing. My footswitch works and bypassed signal goes through, but when engaged my light turns on and my signal disappears. The potentiometer has no affect on the signal. I've gone in and tested all my connections with a multimeter and everything seems like its connected and signal can flow.

In my attempts at troubleshooting I've
- Flipped the pin 1 and 3 of the potentiometer thinking I've made a mistake there. Flipping pin 1 and 3 of the potentiometer had no change.
- Thought its was my positive power line (a piece of cable had melted accidentally) so I cut the line and removed the melted section. This had no affect.













Ive tried to make as simple as possible but Im still at a loss as to what I've done wrong or what I can do to correct the circuit and build. Any help with this project would be greatly appreciated.

[GibsonGM]

Hi Sk8r, welcome!  Can you go here, copy the questions and post them back here w/as much info as you can provide?
https://www.diystompboxes.com/smfforum/index.php?topic=29816.0
Hopefully you have a DMM? (digital multi-meter)

I can say from some experience, it's MUCH easier to debug a board you've just made by testing it, using jumpers to hook up the battery and jacks, before you add switching!  Often times, the real problem is in the switching.  We'll know more directions to point you when you post the info and let us know what level you're at in building/electronics.   We'll get you going.

[sk8rc13]

Hey Gibson, thank you for responding!

Here are the answers to the questions you directed me to.

1.What does it do, not do, and sound like? No sound coming out when engaged. Occasionally if I fiddle with things on the circuit I can get an extremely fuzzy/distorted sound that will cut in and out. But mostly no output.
2.Name of the circuit = EHX LBP1
3.Source of the circuit (URL of schematic or project) = https://docs.pedalpcb.com/project/APB-PedalPCB.pdf
4.Any modifications to the circuit? No
5.Any parts substitutions? No
6.Positive ground to negative ground conversion? No

I got a little confused on the directions listed for measuring things as I am not building this for use with a battery, only wall power supply. And as far measuring the diode and transistor I'm a little confused on how to measure these. Do I need to have power plugged into the pedal when measuring? Also what am I measuring(which setting on the DMM)?

My experience with building is maybe middle of the road. I've taken several electronics classes in college and I've built loads of kits through out my life, but have never built a circuit from scratch. I can't tell you why a certain part needs to be there, but I can put that part there, lol. Basically a very rudimentary understanding of the subject. With my knowledge I thought I'd try with the LPB1 as it is seemingly a very simple circuit that I could construct with the parts at my disposal. Another reason was that the LPB1 circuit seems to be a good one to begin with when trying to learn the understanding of pedal circuits and how they work. 

[bluebunny]

I got a little confused on the directions listed for measuring things as I am not building this for use with a battery, only wall power supply. And as far measuring the diode and transistor I'm a little confused on how to measure these. Do I need to have power plugged into the pedal when measuring? Also what am I measuring(which setting on the DMM)?

Welcome.  The power source doesn't matter, just tell us how much is getting to the circuit at the point it would arrive from the battery or DC jack.  To do this - and the other voltage measurements - connect the black lead to a ground point on the circuit and use the red probe to jab (carefully) at the various test points.  Set your DMM to DC volts.  If you have multiple ranges, choose 20V or something close.

[antonis]

Hi & Welcome..

Can't trace your layout with all those board flying wires so check for DC voltages as follows:



P.S.
You should post not-mirrored pictures..!!

[GibsonGM]

Also, if you're measuring voltages, you want the power on, and a plug inserted into the input jack if you have wired it up as a power switch (the typical input jack setup). Have to be careful not to short things together with your meter probe, and keep the board on a non-conductive surface so you don't short to something like a screwdriver on the workbench...

If measuring resistance, you don't want any power applied, EVER (it can burn up your meter's fuse, or the meter itself in some cases).   To be 'proper' about measuring resistance, one leg also has to be unsoldered from the board, but don't worry about that now. Doing that too many times will ruin your board, not part of this right now. 

Same for diodes- to measure the actual diode, power would be off - but for basic debugging we are looking for voltages before and after a diode (which will tell us if it's working).   We look for the voltage drop through components due to current flowing through them.   

We only need power off to check for continuity (connection between parts), and only unsolder something to test its actual value, which is sometimes needed if a circuit works but not the way it was meant to.

[bluebunny]

Also, if you're measuring voltages, you want the power on, and a plug inserted into the input jack if you have wired it up as a power switch (the typical input jack setup).

Ah, yes.  I knew I'd forget something important. 

(Looking at my post time, I would only have had one coffee at that point...)

[GibsonGM]

It's a team effort, Marc!     I should keep a running list of all the things I forget, ha ha. 

I think it has more to do with having developed an 'auto pilot' in these things; we learn to first have a good battery, known working cables, the amp is on, yes it's plugged in, check that we put ICs in sockets and so on...and forget to tell the newcomer because they're so ingrained after all this time.

[ElectricDruid]

they're so ingrained after all this time.

Are they?!? Why did no-one tell me before now?!?  I *still* get that sort of stuff wrong all the time - thinking about something else, and miss the really obvious.

[antonis]

Another reason was that the LPB1 circuit seems to be a good one to begin with when trying to learn the understanding of pedal circuits and how they work.

A very loose ideal CE amp aproximation: 



Voltage gain:
(loose) A = R4 / R5
(more realistic) A = [R4 x VOLUME/(R4 + VOLUME)] / [R5 + 0.025/Ic]
Input impedance: Zin = R1//R2//R3//[(h_FE+1)x(R5+0.025/Ic)]
Output impedance: Zout = R4 // VOLUME
(where // means "in parallel")
IN HPF corner frequency: 1/(2π*C1*Zin)
OUT HPF corner frequency: 1/[2π*C2*(R4+VOLUME)]
(where 1/2π = 0.159)

[antonis]

thinking about something else, and miss the really obvious.

Τhe fatal loneliness of genius..

[sk8rc13]

Hello All! Thank you for the responses. Apologies I haven't gotten back sooner, have been working nonstop since my last post.

Im still a little confused on what to do exactly for testing. Does a plug need to be plugged into the input jack for all testing? Does a guitar need to be on the other end? Do I need power or not, at least for this test? Sorry

I went ahead and tested with no cable in input, power plugged in, and the recommended DMM settings. Here are the results

Q1 - 2N5088
C - 8.22
B - 0.59
E - 0.05

I tested again with a cable plugged into the input and the results were the same.

[GibsonGM]

I suspect your jack/switch wiring is off. Go back over it, refer to a diagram and make sure which contacts on the jack are tip, ring and sleeve, and that the proper wires are connected to each.  You should ensure which terminal is what using your meter. 

This is why it's good to test the board using jumpers before you put any jacks or the switch in!  Then you know it works, and any errors after are almost certainly in that wiring. 

[sk8rc13]

Alright, I've gone ahead and ordered some jumper cables, lol. When they arrive I'm going to disconnect some of the connection points and experiment a bit.

[GibsonGM]

In for a penny, in for a pound      We'll have input, output, common ground and power on just about every build we do.  I use little jumpers to connect jacks (mono; no ground switching yet!) and took a 9V battery clip and added alligator clips to it.   All grounds go back to battery "-".   

Actually, that's the old school way. I've since built a box that does all this, with internal (always 'known working') bypass switching and power, an audio probe, that interfaces w/my breadboards, but that's another topic!

In my experience 85% or more of the time in a non-working build, the switching has been to blame.

[antonis]

Q1 - 2N5088
C - 8.22
B - 0.59
E - 0.05

What is your power supply voltage..??

[sk8rc13]

Im using a 9V power supply.

I cut some lines and used the recently purchased jumper cables to reconnect. Went through and experimented trying to find a weak spot in the build. Noticed that my potentiometer was acting funny so I switched out the A100K potentiometer to a B100K and I finally GOT SOUND! But...it's a super fuzzed out tone.  Any reason it would be a fuzz tone instead of the boost?

[antonis]

Any reason it would be a fuzz tone instead of the boost?

This..

C - 8.22

P.S.
Plz, read post #9 to find out what proper C-B-E voltages should be..
Then, check for proper resistors values and connectivity..