BLENDER+RAT popping issue

[raziellycas]

Hi, I'm Raziel from Italy, please don't shoot me in face for this topic ^_^"""""  I know that tons of topic were opened about popping pedals but also if I've read a lot of them I still got my issue and can't understand how solve.

I'm a newbie so be gentle and try to speak me like you could do with a dummy

so I've used the layout in the pdf http://s27.postimg.org/fnt0zescj/Page_1_Express_SCH.jpg, it's a proco RAT with a buff and blend, I've wired it using the Gaussmarkov style http://gaussmarkov.net/wordpress/thoughts/wiring-up-a-1590b got the pop.

I've then used a switch called ABypass http://www.armonialibera.altervista.org/crbst_10.html, it doesn't pops, well... it still pops but using the transistor transient the pops doens't get thru the output and it can't be heard but the transient way still get issues with her, in fact the volume of the FX ramp up from low to standard due the capacitor discharge that it's used to keep the transistor enabled for few istants, unfortunately this ramp is really boring same as the pop itself.
The scheme shows 1uF as capacitor but it's a limit case, the developer itself suggest smaller value and I've used a 0,47uF. Pop bypassed ramp really boring, with 0,22uF still got the ramp and you got the pop too due the transistor isn't enabled for enough time.. so this is not the way.

Then I've used a millenium C bypass with 2PDT, got the pop too..

I have to admit that at first sight I thought that the pop comes from the led that's why I've switched to the millenium C but due I got the pop too, I've disconnected the led and it still POPS so it's not the led!

I don't know how proceed, the RAT has it's 1M resistor, the Blender has its own resistor with the couple 1M/1M ... I don't know maybe I have to increase them as 2M for each and increase the 100k on the output stage? I mean the ones connected to the ground..


any help will be appreciated!!

PS:forgive my english is not my mothertongue -_-"

[kaycee]

Best advice is to take a step back. Wire up the rat with your bypass switch and see if that pops on its own. If it doesn't then you know that the blend is the problem. There are lots of simple blend circuits out there, try a different one.

Have you used the millennium bypass successfully before? I have used it many times and it is good unless you have a high gain circuit that needs its input grounded in bypass to stop bleed through.

[duck_arse]

with the Q1 and Q2 buffers as shown, it should be poosible to adapt a boss style fet-switching for bypass, end your pop problems. have a look at geofex for technology of.

and welcome, raziellycas.

and I've just noticed the circuit you linked doesn't have an input blocking cap, putting 4V5 on whatever is connected to.

with the armnia libre thing, you might try a resistor to ground on the transistor base, let the cap discharge somewhere.

[raziellycas]

Regarding the mill bypass, I've used before, in a woolly mammoth and in a tube screamer TS808 replica in both case no pop issue.
The wolly mammoth has also the blender but passivated removing the 2N3819, the TS808 instead use the millennium C but don't have any blend.
I've made also a wolly mammoth with Gaussmarkov wiring with no issue too.

The only ones that gives me issues is the RAT witht he blender U__U

Kaycee I'm wondering is using the bass paralooper instead the buff and blend could solve issue.. unfortunately I've always use PCB and not the veroboards.. it's hard to modify -____-"" but probably I will try this, I'm not that happy to do it but temporarily removing all the blender components and connecting the paralooper instead using the same pad could works... at least on workbench due inside the enclosure another board won't fit..

Thanks Duck_arse , I've lurked here for a bit and then this was the moment to emerge ^___^
I prefer to avoid the fet bypass, it remove the pop but it's not true bypass, I know that maybe true bypass is overrated but this FX is not for my use and my friend ask me clearly for a true bypass rat with blend that's why I'm so busy to solve that issue.

Regarding the input blocking cap you mean something after the input and prior the 1M/1M voltage divider near the 2N3819? I could eventually use a  0.33uF for that installing it in the input path? and instead using the resistor to ground on the transistor BASE you means the GATE? due the 2N3819 is DGS a not CBE


maybe it's a stupid thing but if I use 2M/2M voltage divider instead it will increase the Z ?


PS: But... the voltage divider prior the 2N3819 what is used for? bias the signal prior the buffering? it's a must-do-it or eventually I could remove such divider and still get the blend?? forgive me if is a stupid question but I miss some knowhow regarding the electronic and also if I'm able to mod device following some basic rules I miss a lot of knowledge about why things work like they do... 

[duck_arse]

the gate of Q1 is connected to the R1//R2 divider, from 9V to gnd means the GATE sits at 4V5. no blocking cap means that whatever you in plug at the input will have 4V5 jambed up it. if it is a something with an output blocking cap, right at the output, no problem. if not, yes problem.

so, you put a blocking cap, your 330nF will be plenty big, to the left of the R1//R2, and add a 2M or so pull-down to ground to the open end of the new cap. now your input comes (from the bypass switch, obviously) to the new pull-down//new blocker, and the dc never gets in or out.

your 1M//1M "looks" to the gate like 500k; this is the input impedance of the Q1. your new 2M will (look) be in parallel with the 500k, so, you can up the 1M//1M to 2M2//2M2, and then use 1M as pulldown, works out the whole mess as ~500k.

the R1//R2 tells the fet gate to do what it's told, no messing about. it sets the source to a point for good output swing, both positive and negative, to feed the next stages transparently. if you look over at amz for the basic buffers and the mosfet boost pages, there is a lot of biasing stuff there. and geofex, of course.

I meant the resistor to ground from the base in this circuit .......
http://www.armonialibera.altervista.org/abypass.png?v=1hlzt816xnn7wp5b
you can try one on either side of the R1, just so the 1uF cap will be able to drain it's charge somewhere so the transistor will turn off. at the moment, all the charge goes through the 22k and the transistor.

[raziellycas]

 I'm really a noob -_____________- """""" absolutely a noob ..

I've replaced the 1M/1M with the 2,2M/2,2M and opened the FX-IN track on the board then made a couple of holes and added a 0,22uF (I thought of not owning any and instead I've found a couple of them ^_^ ) with a pulldown resistor of 1M .. seems that it doesn't pop anymore! ^_^
due here is 21:42 and I live in a condominium I've made a one try only with volume not that high but the pop previusly was really loud and this time instead I've noticed nothing so probably the issue is solved....

I'm embarassed  I suppose that this is a really stupid thing U___U""

Just to be sure... considering the scheme, if I'll remove the 1M/0,22uF (pair R7/C2) the original coupling cap and pulldown resistor, I'll get back the pop for the same reason? due the 100k/100k brings the 4.5v on the signal line for biasing the IC input? or instead the 2N3819 will stop it? maybe this is a silly question for expert ones but as I've reported previusly.. I need a for-dummies explanation ^____^"""""

[duck_arse]

there is an error on your circuit diagram! I don't think you've posted the board layout you are using, yes/no? your diagram at http://s27.postimg.org/fnt0zescj/Page_1_Express_SCH.jpg shows pin 2 and 3 shorted together. this is most definately WRONG. how did you wire yours?

in this diagram:
http://www.beavisaudio.com/schematics/Images/Proco-Rat-II-Schematic.png
shows the correct wiring. compare to your board.

you can't say you're a noob now, because you've already learnt something. no need for embarass. I've asked stupider questions. just last week ......

no pop - excellent. C2//R7 look like the original input parts for the opamp. if they were removed, you would not get a pop, because the dc voltages from the fet source and the R10 1M would fight each other, settle to some voltage, and just sit there, stable. C2 allows one side to have "a" voltage one side, and "another" voltage on the other, no fighting. the pop comes from uneven voltages meeting each other quickly, like in a switch. you are better-off reading something by RG Keen on popping, he really does know this stuff.

the R16//R17 yes puts the 4V5 bias voltage to the 1M R10. the 1M carries the bias to the opamp, and the opamp then sees the 1M as it's input impedance, so it doesn't load that which is driving it. R7 can be removed in this circuit as drawn, it does nothing, really. the C11 stops Q2 dc volts getting "out", and the C1 stops Q1 dc getting out.

[raziellycas]

regarding the opamp pins shorted is a drawing error they are not shorted on the pcboard 

many thanks for your great explanation regarding the circuit behaviour