Ehx lob-1 loud pop

tpruitt · Post by **tpruitt** » 19 Jul 2016, 20:39

I have a linear power boost that pops when turned on and off in the fx loop.
I've did some research and this is what I have tried.
I have tried a 2m2 resister on the input and output jacks from tip to ground.
I then tried a wire from the negative end of the led to the pot to ground it to the chassis.
I even tried removing the led.
All with no luck.
Any ideas?

induction · Post by **induction** » 19 Jul 2016, 22:19

I have tried a 2m2 resister on the input and output jacks from tip to ground.

Pulldowns on the jacks don't do anything good. They are not connected to the input or output caps when the pedal is bypassed, so they can't bleed charge from the caps to ground, which is what they are for.

It would help if you linked to a specific schematic because there are variations on this circuit, but most of them have a volume pot on the output, so no output pulldown is necessary. Try an input pulldown between the input cap and ground on the board itself.

tpruitt · Post by **tpruitt** » 19 Jul 2016, 23:08

Thanks. I was thinking how and why someone posted that. The ground really goes nowhere.
I'm new to pedal stuff. What do you mean by pulldowns?
I don't have a schematic. The board says "ec-d12 rev.b" if that helps

tpruitt · Post by **tpruitt** » 19 Jul 2016, 23:18

induction · Post by **induction** » 20 Jul 2016, 00:57

tpruitt wrote:What do you mean by pulldowns?

The 2M2 resistors that you put between the jack tips and grounds are called pulldown resistors because they are intended to tie the voltage on the input or output caps to ground. When they're left floating, they can take on a non-zero voltage, especially if the caps leak current. Then when you switch the pedal on, the voltage instantaneously switches to zero. That sudden shift in DC voltage is what causes the popping sound.

I'm not intimately familiar with that particular PCB, but if you post a photo of the other side of the board, we might be able to tell you where to put the resistor. A photo of the lug side of the bypass switch would help, too.

tpruitt · Post by **tpruitt** » 20 Jul 2016, 10:09

Here is the back. I'll get the switch tonight.

tpruitt · Post by **tpruitt** » 21 Jul 2016, 10:11

Here is the switch

Intripped · Post by **Intripped** » 21 Jul 2016, 11:35

just for fun, i've traced again this very famous booster
here is the schematic - the components' numbering matches the PCB's

notes:
i don't understand why the ferrites and 100p caps are always on the signal path, even in fx-bypass; could this be the cause of the POP?
i ask this because i had another EH pedal with issues (bass big muff), and when i opened it i saw that these ferrites were burnt, so i removed them, and the 100p capacitors as well.

tpruitt · Post by **tpruitt** » 22 Jul 2016, 20:03

Well?
I found a webpage that says remove c4-5 and those two beads to make it true bypass. Guess I'll try that out tonight

induction · Post by **induction** » 22 Jul 2016, 20:17

tpruitt wrote:Well?

If Intripped's schematic is accurate for your unit, the circuit already has pulldown resistors on the input and output. You could try measuring the DC offset at the input and output while the circuit is powered. Measure it while engaged and when in bypass. If the readings are significantly greater than 0V, then that's the problem. If not, then it's something else. (Could be the switch itself.)

Questions:
1. You mentioned it pops in the FX loop. Does it pop when it's used inline with the input?
2. Is it the only pedal in the chain, or are there others, even if they are all bypassed?

tpruitt · Post by **tpruitt** » 24 Jul 2016, 00:55

Not sure how to measure the dc here.
Negative to ground and checking input/output jacks? Nothing.

I ended up removing c4 and c5 but didn't remove the beads and still popped.

tpruitt · Post by **tpruitt** » 24 Jul 2016, 01:32

It only pops in the loop. Tried it with a different amp and still pops. Both amps uses a metro fx loop.
It the only pedal I'm using in loop.

induction · Post by **induction** » 24 Jul 2016, 02:11

It's possible there is a DC offset in the loop itself, and the pedal is not the problem.

Do you have any other true bypass pedals you can test in the loop?

tpruitt · Post by **tpruitt** » 24 Jul 2016, 12:39

The only other pedal I know is true bypass is a ts808 clone I built. My first pedal build.
I just tested and yes it pops.
So I went and looked and the loop. Metro instructions claim while checking ground it should be close to 0 ohms.
I'm reading 3 ohms . I moved the ground from the buss wire straight to the chassis and it still reads the same.
I should add that I tried the lpb boost pedal in the loop of a 5153 and it did not pop.
So,I am totally assuming you are correct here.

I know this is a pedal forum but,do you have any ideas?
My voltage for the metro loop is right where it should be at 295. Calls for 285 to 310.
Again,assuming....the voltage is probably coming into the loop sign from the preamp?

tpruitt · Post by **tpruitt** » 25 Jul 2016, 00:31

Check voltage on loop
0 volts going in
.003 coming out

Intripped · Post by **Intripped** » 25 Jul 2016, 08:31

i would try and measure again the ground connection(s) of the metro-loop.
to make an accurate measure, check first the ohmic value between the two tips of the tester: just make the tips touch each other and read the value on the tester.
you will probably read 1 or 2 Ohms, this is due to the slight oxidation of the tips and connections with the tester.
subtract this value to the reading on the metro-loop

also, make sure that the bolt used for the metro-loop ground connection is tight

tpruitt · Post by **tpruitt** » 25 Jul 2016, 20:38

Ok this is what I have wrote down.
Volts out of loop - 003ma
Ground - .003 ohms

tpruitt · Post by **tpruitt** » 27 Jul 2016, 00:21

I am editing the original post so ....

On the ground you were correct and I am reading zero.

Now the loop and the voltage coming out is
Off-- zero
On--- it floats around.but while on the vdc 200m. Floats between .8 and 2.8ish millvolts.

I would think that is significant but I really have no idea here.