WHA WHA "GCB 95" TRUE BYPASS = "POP" NOISE

[Rhandy]

Hi

I found this tread http://www.diystompboxes.com/smfforum/index.php?topic=91577.0

I have same pop noise.

I use this diagram

But I put resistor no Long Led part.

Now I disconnect led from the circuit, But I sill Have POP Noise When turn on and off.

[GibsonGM]

Hi Rhandy,

Is there a "pulldown resistor" on the input of the wah?  If you can post a schematic, please do. 

The pop is caused by the build-up of DC at the switch, from leaky caps.  When you switch, the DC must suddenly equalize and it makes noise.  A pulldown resistor will allow this DC to drain away to ground without affecting your signal.

When this happens, I have tried plugging in a guitar cable (to turn effect on), and connecting my DMM to read DC across the free end.   Then switch the effect off and on, and see if you notice a DC spike.    Installing a pulldown resistor will (hopefully) take this away.    1 Meg is a common value.

Search the forum for many examples of this.   

[Rhandy]

Hi GibsonGm

I dont have shematic I just found this tutorial http://stinkfoot.se/archives/546

I see lots of shematics of gcb-95 My is one modded = zw45. Diference is one cap with 0.22uf instead of0.1uf and use RED FASEL.

[GibsonGM]

Do you have resistors?   I would try connecting a 1Meg between Circuit Input and Ground.   You may choose to do this at the PCB, or try it with jumpers before you solder (jumper to switch terminal >resistor> jumper to chassis)  - because you don't want to heat the switch terminals too much!   If it works, you can make it permanent.

Remember, the switch will not be SILENT, just "pretty quiet".  There will be SOME pop, because it is mechanical.  A "CLICK" is ok, a "POP" is not...

That is why I suggested you measure for DC at the board input, to see if a leaky input cap is allowing DC at the switch.  Did you try that?

If it works well except for the pop, I believe you will find this is the issue...

[Rhandy]

Hi

I dont have any resistor on input to ground! I dont have any DC on input when Led is out of circuit. If I put Led. I can read some milivolts between input jack and ground. I try to change led resistor to negative but doesnt work. I dont have any 1M ohm resistor to test Jack Input to ground. But Tomorrow I try.  I measure Cable goes to input of preamp disconected from pedal and I have 24 milivolts AC.

[GibsonGM]

Hi Rhandy,

I can't see a reason for there to be any DC because of the LED, that would mean the switch is bad...we are not measuring AC now, only DC.    Loud POP is from DC suddenly having to adjust its level because you switch to a branch of different potential. 

I read the thread you linked to - the people there seemed to say the 1M resistor does not change the pop.  I would still try it - 470k will also work for now, or 680k, or what have you.   Just to test, you can insert 1M later if it works.

You can try to re-wire the switch using Layout #5 from this PDF:  http://www.tonepad.com/downloadWarning.asp?id=76
Other people have said they have trouble making your wah true bypass - maybe something with the buffer?

[Rhandy]

Hi GibsonGm!

Yesterday I put one 1m resistor on switch between green wire (main input) and ground.  Pop noise attenuate when I On Wha, And no noise when I off. Today I try diferent values.

You can try to re-wire the switch using Layout #5 from this PDF:  http://www.tonepad.com/downloadWarning.asp?id=76

Link doesn´t work.

[GibsonGM]

Good, that is usually the problem!!  1M is good...you may play with other values, but at some point you will begin to hear a difference.  I do not think the 1M adds too much noise...

Go back to the link...click the "offboard wiring" in green, which is difficult to see....on the page it takes you to, click "Layouts"  (offboard wiring PDF).

That is a file that everyone needs to keep!!!

[Rhandy]

Hi.
I rewire all switch using shematic number 5 .
Now I dont have dc on ground using led. I feel more signal loss, but is normal because I run two cables with 6 +5 meters.
Pop noise doesnt go away. I have to try in other Amp.

As you know my Engl is on the hands of one tech , and I´m using my JMP-1 marshall pre (tube pre) + Marshall 8008 power Amp (transistor amp). But I think I have to replace tubes from JMP1.

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Just one apart. I´m really susprised. Engl doesnt connect any ground to chassis. All boards,jack plug and capacitor are isolated from chassis. Pcb board use plastic support to chassis. The only ground he use is Earth groun Line.

I also put and remove 1m resistors because I cant see any diference with or without.
Thank you.

[Rhandy]

Hi.
I rewire all switch using shematic number 5 .
Now I dont have dc on ground using led. I feel more signal loss, but is normal because I run two cables with 6 +5 meters.
Pop noise doesnt go away. I have to try in other Amp.

As you know my Engl is on the hands of one tech , and I´m using my JMP-1 marshall pre (tube pre) + Marshall 8008 power Amp (transistor amp). But I think I have to replace tubes from JMP1.

Just one apart. I´m really susprised. Engl doesnt connect any ground to chassis. All boards,jack plug and capacitor are isolated from chassis. Pcb board use plastic support to chassis. The only ground he use is Earth ground Line.

I also put and remove 1m resistors because I cant see any diference with or without.
Thank you.

[GibsonGM]

I am surprised, too.  I don't like "floating" circuits...I connect at least one ground wire to my chassis. I prefer to have them all bonded together.  I don't know why Engl may not do this.  A wah is not so complicated as to require floating power 

POP comes from one of two places:  DC on the switch, or the small mechanical noise of the switch becoming amplified by the effect.  If there is something in the input section here that amplifies the signal very much, the pop CAN be amplified - others said they removed the buffer because of this.    It will not be QUIET, ever...but it should not POP due to DC...

You can also measure for DC leakage on your amp input by plugging  cable in, measure DC across it with nothing else plugged in...I have tested every device I use for this.   It is not common to find DC at inputs/outputs, but if an effect is modded it CAN happen.

** One last thing to try, Rhandy - cut the input wire to the PCB....add a resistor in series here.  I don't have a value to give you...try 100 ohms, 470 ohms, 1K or maybe even higher....there may be a value that will end the POP, and hopefully not change the sound.    You will have to experiment.   

If the noise is generated due to the switch contacts bouncing, a series resistor may help.   If it does not, you can remove the resistor and just put the wire back together, so it is easy to try...

[Rhandy]

Hi GibsonGm

In wha I complety remove buffer!!!

My Engl comes today, I replace all tubes for:

120€ total cost.

Preamp Tubes
V1 = JJ ECC83S GOLD PIN SELECTED
V2= TUNG-SOL 12AX7
V3 = JJ ECC83S
V4= JJ ECC83

POWER TUBES

4 MATCHED JJ 5881.

RESULTS

NO HUM NOISE !!!

WHA WHA SWITCH ON AND OFF MUCH MORE NOTICEABLE!!!

MUCH MORE BREAKUP ON AMP

JJ POWER TUBES 5881 ARE MORE LITTLE THAN ORIGINAL 5881 ENGL ( PEOLPLE FROM BANZAI MUSIC TELL ME ENGL USE SOVTEK TUBES)

I CONSIDER MANY TIMES TO CHANGE OR NOT TO JJ 6L6GC .

BUT I ORDER JJ 5881.

AMP IS AMAZING! MORE BITE! GREAT BREAKUP. I HAVE TO CONTROL GAIN IN AMP AND IN VOLUME POTS OF GUITAR. BUT FOR THE FIRST DAY. I REALLY LOVE IT!

[GibsonGM]

Great!  I do not change my amp tubes very often, but when it is time to do so, it does sound very good!!   

JJ's are good tubes - you probably will not need to re-tube for a very very long time now!

Now you need to choose which effect you will build next 

[Rhandy]

Next is one power supply with 10 isolated 9v output. One friend make transformers. I order one with 1primary and 10 secondarys. 230v input 0x12 v ac output.

Each output have 1 rectifier bridge. 1 470uf 25 v capacitor, 1 L7809 transistor.  1 100uf capacitor.