Pop noise when effects turn on (not the typical I guess)

[Labaris]

Hi,

I know about the typical noise that you get form true-bypass circuits when you turn on any pedal. So, that is fixed in my four pedals...

BUT

I decided to put the AMZ Super Buffer in front of the chain and I'm getting the pop noise when I turn on any of my effects.

I connected the fourth plug (the las one) of a daisy-chain to that circuit. My power supply is 12V/300mA and my pedals areonly DIYones: SmallClone, DS-1, Guvnor, DynaComp.

I wonder if the reason for the pop is that the PS is working near its limits or what could be the reason for the noise.


Suggestions? Thanks in advance

[GibsonGM]

Questions: 
- does it pop with JUST the AMZ buffer?
- Can you measure the current draw with all your pedals on?
-  You say no pops until you put the AMZ buffer in there?  How about if you change its location in the chain?
-  Have you measured the output of the buffer for DC? (leaky cap maybe)
- got an LED circuit in that buffer? Could that be causing it? Do the other pedals pop if the buffer is in-line but OFF?
Tell us all you can! 

Weird sounding issue, man.  I'm willing to bet it's simply an error somewhere in the buffer. 

[Labaris]

Answers:

- does it pop with JUST the AMZ buffer?

Yes, my pedals never pop before

- Can you measure the current draw with all your pedals on?

I can, but not today. Maybe tomorrow (pedals not at home)

-  You say no pops until you put the AMZ buffer in there?  How about if you change its location in the chain?

You mean the DC chain or the guitar-signal chain?

-  Have you measured the output of the buffer for DC? (leaky cap maybe)

Good idea, I'll do it when I meassure current draw

- got an LED circuit in that buffer? Could that be causing it? Do the other pedals pop if the buffer is in-line but OFF?

I forgot to say the circuit is now on a proto-board, and it has no on/off switch, it's always on. And yes, the proto has a LED


Thanks for the help

[GibsonGM]

No problem, everyone here likes to help )

I would say go thru and do the things above that you couldn't try out.  I do mean changing the position of the buffer in the signal chain...but while you are at it, try moving it in the DC chain as well (?) maybe it will show you something.

With the buffer in, you should not have any troubles.  So it sounds to me like something may be miswired on the protoboard, or the output cap could be in backwards or faulty.  The 'DC in the signal path' after the buffer test is important here, as is finding out how much current you are drawing.  It doesn't seem like should be exceeding 300mA, though!

[Labaris]

I have about 1.5V DC at the output 
I replaced the output cap and the noise was still there. I removed the cap and the noise disappeared.
With 1uF (polyester this time) it jus pop for about 2 seconds (charge time of the cap I guess), then it stops.

So that may sound like a great solution, but the cap is there to bring a full-range response to the circuit which is important in this case. I didn't notice an "obvious" bass loss with the new 1uF cap, but maybe it's there...

[GibsonGM]

Ok, recheck your connections, Labaris.  I just looked at the schematic; C2 and C3 are isolating any DC from the output, if properly wired.  Do you have the pulldown resistor, R7, in the right place??  If not, that would tend to increase the pop factor by allowing the DC level to float around between pedals. 

C2 and C3, the output capacitors, are splitting the work here.  The little one is letting through the highs to give 'shimmer', and the big one allows the low end thru.  Both of them also block DC, so you should be reading no more than millivolts, IMHO. 
That DC is the source of your trouble.  Could be bypassing those caps due to a wiring error.  ;o)

[merlinb]

Either one of the output coupling caps is leaky, or you simply need to give it longer to charge up, i.e., you measured 1.5V too soon after switch on. (That 2.2M discharge resistor could easily be lowered to 1M).

[GibsonGM]

??

There should be NO DC on the output, no matter what = bad cap(s), or miswiring.

[merlinb]

There should be NO DC on the output, no matter what = bad cap(s), or miswiring.

Depending on what the buffer is plugged into, there may be DC on the output for over a minute until the output cap is fully charged to 4.5V. Since clean buffers need big output caps, this is quite normal.

[GibsonGM]

True, Merlin - a steady-state measurement is needed.  I'd definitely make that pulldown 1M, anyway, to bring that time constant down. 

I'd expect that Labaris would have had more than 1 minute's worth of playing with his switches to know if it will pop all the time, or if it's just for the first 1 or 2 minutes?

[Labaris]

I haven't wait more than 1 minute to see if it's still happening, I'll check tomorrow.

Thanks

[merlinb]

I haven't wait more than 1 minute to see if it's still happening, I'll check tomorrow.

Hook your voltmeter up and then turn the buffer on. You should see the voltage jump up at first, then slowly decay towards zero.

[Labaris]

I haven't wait more than 1 minute to see if it's still happening, I'll check tomorrow.

Hook your voltmeter up and then turn the buffer on. You should see the voltage jump up at first, then slowly decay towards zero.

Ok, I'll do that


Something I noticed yesterday is that the pop is very low when the other effects of the daisy-chain are on. The more effects activated the less pop noise.
And I had the power-supply switched on for more than a hour, and the pop was the same...

[Labaris]

I replaced the 10uF cap with 2.2uF, and the output resistor is now 10K.
The pop is over, but it seems to be a little loss of highs. I know the buffer is working, because without it the high are even less. Could be the changes I made at the output the cause of the loss of highs?

GibsonGM said that clean buffers always use big output caps, why is that? I don't notice an obvious loss of bass...

So, two questions in one

PS: Didn't measure yet what you suggested (DC on the output). But before the changes the pop was for hours there (actually it never stopped)

[gtudoran]

Hello guys,

I had the same problem with amz buffer... and no solution till now; changed the putput cap changed the pull down resistor... nothing still pops with other pedals after it and it's not about the pedals (tryed both diy and commercial and it's the same thing).

Best regards,
Gabriel Tudoran
Analog Sound

[merlinb]

The pop is over, but it seems to be a little loss of highs. I know the buffer is working, because without it the high are even less. Could be the changes I made at the output the cause of the loss of highs?

No, only less bass. You're probably imagining it- everybody thinks it sounds different after they've modded something!  

GibsonGM said that clean buffers always use big output caps, why is that? I don't notice an obvious loss of bass...

Large output caps are used:
1) To ensure full bass response even when driving a low impedance device, such as a mixing desk.
2) To maintain a low output impedance at low frequencies so that mains hum doesn't couple into the output cable easily.
3) To eliminate capacitor distortion (this is not really a big deal for guitar though)

[Labaris]

No, only less bass. You're probably imagining it- everybody thinks it sounds different after they've modded something!  

Ok! I thought I was maybe imaging it 

Large output caps are used:
1) To ensure full bass response even when driving a low impedance device, such as a mixing desk.
2) To maintain a low output impedance at low frequencies so that mains hum doesn't couple into the output cable easily.
3) To eliminate capacitor distortion (this is not really a big deal for guitar though)

Thanks for that info!