The Popping Brian May Treble Booster

[Elijah-Baley]

Hello guys.
My last achievement is a Brian May Treble Booster, Sabrotone layout.
These are the links: http://www.sabrotone.com/?attachment_id=3212. You can see, it is based on GGG schematic: http://www.generalguitargadgets.com/pdf/ggg_geb_bmay_sc.pdf. It has the volume control, I used a 2N2222, and I added a three way switch for select different combinations of the input capacitor. Everything works.

I have a pop problem when I turn it on and off. At the beginning I thought it was because the led, and I noticed a reduction of the pop volume after a while I play, keep engaged and using the toggle switch. But after some tests I discovered it have the pop also without led, and also without psu. Further, the pop volume is rather variable, sometime it comes back after a while, especially when I keep it off.

Then I read this: http://www.generalguitargadgets.com/pdf/ggg_geb_all_instruct.pdf.
«Bypass Switch Click
While working with DIY replicas of all these different boosters we noticed one thing
that they all had in common: they are all very susceptible to bypass switch pop. We
added a pull down resistor on the input and output of all the versions and this
stopped the pop and also doesn't effect the tone as far as we could tell. That is to
say that we didn't notice any tone differences in the testing we did. It should be noted
that if you use a volume control modification, then you don't need the pull down
resistor on the output (R11) and due to the pot on input of the Orange & Apollo
Boosters, they don't need a pull down resistor on the input (R8).»

In this schematic we have a very low pulldown input resistor, 120k. The layout used by me don't the pulldown resistor.

I used the lead test to add a 1M resistor on the input tip and the box (ground). The same thing on the output jack. (Not the two things at the same time).

What I should to do?

Thank you, guys!

[antonis]

First of all you can disconnect the LED to verify if it's an LED popping sound..
(which IMHO it isn't)

The low value of the pull down resistor is not critical (the less the bettter - NOT for the input impedance  )

Best practice is to connect BOTH IN & OUT to GND via the 3PDT switch in Bypass mode (possibly you have to modify input capacitor selector such as left side of capacitors is connected to input via main selector which in turn is connected to GND via the ON/BYpass switch..)

A better but more complicated solution is to connect to EVERY input cap a pulldown resistor AND connect them like above described..
(this has to deal with capacitors allways connected to GND despite of your selector position..)

[induction]

I used the lead test to add a 1M resistor on the input tip and the box (ground). The same thing on the output jack. (Not the two things at the same time).

If you connect pulldowns to the input and output jacks, they are disconnected from the circuit in bypass, which means they don't do anything to prevent pops. However you wire them, make sure they connect the relevant side of the input and output caps to ground when in bypass.

[antonis]

 
You've been on point, induction..

(maybe I should read more carefully..)

[Elijah-Baley]

I forgot to say that I used (for the first time) the madbeanpedal wiring.

And I used this method for input capacitor selector: http://3.bp.blogspot.com/-UTu9z3raSz0/TdytG0slKVI/AAAAAAAAAmM/udp2p9Uvx8o/s1600/Brian%2BMay%2BTreble%2BBooster.gif

By the way, I tried to disconnect the led, but only the positive side, then I stoped because I found some popping info about this pedal.

About some further pulldown resistor, I saw that, I and tried to do that. Never tried it early.
http://s440.photobucket.com/user/devnulljp/media/ANTI-POP-1.png.html

In this topic http://www.diystompboxes.com/smfforum/index.php?topic=27422.0 there's a suggestion about the pulldown output resistor,
If you see the sabrotone layout I could put the resistor (1M?) on the column 5, from row B to row C. After the output resistor.

I'm afraid I need some instructions step by step about where I should or could connect these pulldown resistors and how I should wire the DPDT toggle switch for the input capacitor.

Thanks for your help!

[induction]

If you see the sabrotone layout I could put the resistor (1M?) on the column 5, from row B to row C. After the output resistor.

I'm afraid I need some instructions step by step about where I should or could connect these pulldown resistors and how I should wire the DPDT toggle switch for the input capacitor.

Thanks for your help!

Column 5, row B to row C is actually before the output cap, so that won't work. You need to connect the other side of C2 (Sabro numbering) to ground with the pulldown. There isn't room for it on the vero as shown. You can connect it between the bypass switch lug that connects to the circuit output (the one connected to Sabro layout column1, row E, or the top right switch lug on madbean standard wiring) to any ground point that is not disconnected in bypass (the lower left lug on madbean's switch wiring would be fine, or the input or output jack ground lugs).

[Elijah-Baley]

Thanks for the correction, induction. I lost the output!

So, in few words, and if I got, I can put the output pulldown resistor directly on the footswicth, from lug top right (output) to lug bottom center (ground). Of course I'll try it with the test leads, and see what happens.

[duck_arse]

I'm lost - the sabro shows the pulldown at the input - R8, the ggg the same, even the cap switching sidetrack shows the 120k attached to the outside end of the input cap. and they have a pot on the output cap that will serve the same purpose. where else can you add pulldowns?

the cap switching diagram suggests that those caps will pop when you work the switch, because both ends of the caps are floating. it would be better to common one end of each cap, and add discharge/leak/pull resistors across the switched end/s.
imho.

[induction]

I'm lost - the sabro shows the pulldown at the input - R8, the ggg the same, even the cap switching sidetrack shows the 120k attached to the outside end of the input cap. and they have a pot on the output cap that will serve the same purpose. where else can you add pulldowns?

The Sabro layout has the traditional Rangemaster volume control feeding the output cap, which floats in bypass.

[Elijah-Baley]

What about the cap switching diagram? Could be the mods the cause of the pop?

[induction]

What about the cap switching diagram? Could be the mods the cause of the pop?

No. That could (but might not) cause the cap selector switch to pop, but it won't cause the bypass switch to pop.

[duck_arse]

the caps would/might pop when the mod switch switched, but should be quiet otherwise.

[Elijah-Baley]

Ok, I got it. (Anyway, I can hear no, meaning at least, pop when I switch the caps.)

So, I'm gonna try with the pulldown resistor on the footswitch.

Thanks for the moment!

[LightSoundGeometry]

I have recently taken a few pedals apart and finally realized with the help of mark hammer ..popping is the nature of the beast ..has to do with layout design like the wiring, or now even putting the foil side of caps to the low impedance end of the circuit as demonstrated by mr carlson in his video ..proper grounding etc ..all adds up

[PRR]

> a three way switch for select different combinations of the input capacitor.

Draw this out.

"Floating" caps are prone to POP.

The GGG plan clearly shows proper de-pop for the one input cap, but you changed that with your 3-way switch. We need to see JUST what you have built, not what it is based on.

[Elijah-Baley]

I did exactly like in this layout:

I HAVE NO USED THIS LAYOUT.

I soldered on the board the "stock" 4,7nF cap. Regularly. From every side of this cap come out a wire, (one for each hole). These wires goes to the center poles of a DPDT toggle switch On/Off/On. So, I have soldered a 4,7nF cap on one side of the switch and a 22nF on the other side of the switch. That's it.
I have pop in every position of the switch, but not when I switch it.

If it is not enough clear I can make some image.

[PRR]

[Elijah-Baley]

Oh... .
Ok. I trust in you.
But there's something I can't understand. I have to add two resistors and two jumpers?

I'll try with the test lead, if I can .

Thank you!

[antonis]

You need to have all input capacitors continuously grounded (via 10M & R3 resistors) despite of their specific "activation"...
(On/Bypass or Switch selection..)

Paul draw this for saving extra columns for grouding resistors on PCB and additional cables from switch caps..

[PRR]

> and two jumpers?

You never needed the double-pole switch, one on-off-on pole would do the electrical problem.

(However the DP does give you a place to mount the far ends of the caps.)

We need to bleed all ends of all caps all the time. Wired double-pole that means four resistors. Single-pole means two resistors. I figure the cut-off resistor leads can be your jumpers to defeat the second pole without major trauma.