Debugging: Box of Rock

[MaxP]

hello guys,

I'm fairly new to building guitar pedals and I'm looking for help.
I'm building a box of rock clone with the tagboard lvlark vero layout.
Got the SHO side working!
The dirt side doesnt;


Here is the checklist to fill out:
1.What does it do, not do, and sound like?
The SHO part works fine, but the dirt side doesn't. There is sound coming through, but at a really low level, and it's clean.

2.Name of the circuit =
Box of rock

3.Source of the circuit (URL of schematic or project) =
http://tagboardeffects.blogspot.nl/2012/03/zvex-box-of-rock-complete.html

4.Any modifications to the circuit? No

5.Any parts substitutions? No

6.Positive ground to negative ground conversion? No

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => 9.36 (USING DC adapter)

I will fill this list later on, do not have the time to do the measuring tonight..

But, everything looks fine until the tone pot, getting almost no signal into and out of it..
Checked the 1uF cap, worked fine, but switched it for a new one (also tested, first putting some volts in it with the resistor function on DMM, then it dischargers to open circuit in volt setting)

It would be nice if someone could tell me if i missed something before the tone pot which is causing the problems.
I believe this is the same schematic as the vero board earlier on in this post(except for the 47u in the beginning):
http://3.bp.blogspot.com/-kq989pNrtME/TxQ5v0UVl8I/AAAAAAAAAkQ/tQV0VA6M2QQ/s1600/zvex_boxofrock_schematics.jpg

thanks in advance!


Well, the problem is, right after Q3, the problems start..
I've got normal readings everywhere on the voltage, until the - Leg of 1uF, then it goes to almost 0 V.. can't find a link to ground or something..   FIXED, Please read later on to the problems of Q2..


Update:
Checked everything, made some progres..

Swapped the 1uF with another, and the circuit is working now.. (have a nice voltage throughout the vero, from 9V to output )
But, I'm getting a very blatty/quiet sound out of it, and is not distorted at all...

If i'm right, something's not biased the right way..

Q1:
S 0.01 V
G 2.09 V
D 4.24 V

Q2
S 0.03 V
G 1.94V
D 8.15V

Q3:
S 0.27 V
G 2.39 v
D 4.79 v

D2:
- side 2.09 V
+ side 0 V

d3
- side 9.15 (but goes through 92R to 100uF to zero)
+ side 9.37

D1( SHO, not relevant)


If you need more values, let me know!

[PRR]

> Q2
> S 0.03 V
> G 1.94V
> D 8.15V

This can't be right if built correctly.

Re-re-re-check values of R7 R8 R10 R20.

[MaxP]

> Q2
> S 0.03 V
> G 1.94V
> D 8.15V

This can't be right if built correctly.

Re-re-re-check values of R7 R8 R10 R20.

I checken all of them, the 5k1, so r10 and r20 in series reads out a voltage of around 9, While q1 and q3 have Nice voltage drop from 9 to like 4,5,,

What causes the voltage to drop in half at the d side? This should be where the problems lies..
The gate reads out normall..

To be sure, ive switches some mosfets and they give good readings at q1, q3 and in the sho..

Greetings, max

[PRR]

> What causes the voltage to drop in half at the d side?

It doesn't. The MOSFET's Gate voltage is naturally about 2.2V. But this won't happen until the Drain puts about 4.4V across the 1Meg+1Meg resistor string to the Gate.

So it isn't half of 9V. It is twice the MOSFET Gate voltage, forced by the Gate resistors. (These were selected to put Drain near half of battery voltage.)

Mmmmmm. If there is a short to ground where C3 and R6 come togther, the extra 470K will force the Drain to rise near 9V to get the Gate voltage in the right zone.

[MaxP]

Thanks!

that was exactly what was happening!!

it worked now while testing 

Boxed it up and have the issue that the signal isn't distorted at all, volume is lower as should be.
Can i ask again for some suggestions?

[PRR]

> t worked now while testing  icon_cool
> Boxed it up and have the issue....

If it worked in testing, but not after you put it in the box, then something went wrong in the boxing. Broken wire, shorted jacks, parts knocked off... possibilities are endless.

(My favorite was a box that worked fine when open but shocked the user when closed. Took a while to figure out.)

[MaxP]

Thanks for all the advice,

I find something strange, when reading C6, the - leg has 0 volts, should this be?

so there is no voltage measurable on the tone pot...

[bloxstompboxes]

> t worked now while testing  icon_cool
> Boxed it up and have the issue....

If it worked in testing, but not after you put it in the box, then something went wrong in the boxing. Broken wire, shorted jacks, parts knocked off... possibilities are endless.

(My favorite was a box that worked fine when open but shocked the user when closed. Took a while to figure out.)

So what was it, man?!! Lol.

[MaxP]

> t worked now while testing  icon_cool
> Boxed it up and have the issue....

If it worked in testing, but not after you put it in the box, then something went wrong in the boxing. Broken wire, shorted jacks, parts knocked off... possibilities are endless.

(My favorite was a box that worked fine when open but shocked the user when closed. Took a while to figure out.)

Well measured everything through,

Everything looks good until i get to C6, the 1uF cap. The - leg goes to the tone pot etc. from this point on I lose the voltage at the cap leg.. Is there a reason which causes the voltage to drop to almost 0?
To be sure I didn't have any shorts I checked almost everything possible between the cap and the tone pot...

Please forgive me for my lack of knowledge on how caps work etc.

greetings,
Max

[PRR]

The - leg of C6 should show no DC voltage. From here on out there is no connection to the battery, all the "active" stuff is done, no need for DC power.

A next step is a Listening Probe. Someone here must have a link. In guitar-work you typically adapt a 0.1uFd capacitor to the end of an old cord, plug to your spare amp. Put signal into the sick effect, poke various points from input to output, and see where you stop getting signal.

[mcknib]

Some links:

How to build an audio probe a photo essay

http://www.guitarpcb.com/apps/forums/topics/show/7219163-how-to-build-an-audio-probe-photo-essay

How to use it

http://www.guitarpcb.com/apps/forums/topics/show/4814011-using-an-audio-probe-to-debug-builds


and how to trace the audio path

http://www.guitarpcb.com/apps/forums/topics/show/4897890-tracing-the-audio-path-a-how-to-tutorial

[bluebunny]

My favorite was a box that worked fine when open but shocked the user when closed. Took a while to figure out.

You can't leave us hanging like that, Paul!    Sounds like another great story.  We need the details!   

[bloxstompboxes]

My favorite was a box that worked fine when open but shocked the user when closed. Took a while to figure out.

I already asked that and got no answer. I believe PRR is trying to torment us.
You can't leave us hanging like that, Paul!    Sounds like another great story.  We need the details!   

[PRR]

The shocker-box is very distressing. I built a wall-power mike amp. One of the cover-screws hit the transformer, all the way into the windings. This was for student use, so I am very glad I checked for trouble and found it before it went into use.

[MaxP]

Well, I wanted to reply, but the forum was out of use or something like that...


got to give huge credit to PRR, got it working (also made 3 for my friends:) )

Working in eagle cad on a pcb for this, I'm eager on how it will turn out.

topic may be closed, thanks again!