HELP WITH A CHUNK SYSTEMS AGENT 00 MARK II

[DOND]

I am trying to help my kid out (i am the worlds cheapest roadie) with this pedal.short and sweet this thing sounds like "ass" when activated and when switching sweep (up/down) switch,it sort of works (pedal sound wise) one way and not the other but overall pedal is not working (i have checked out the demo video's).i have checked all the resistors,diodes, capacitors,and tracks and they all seem ok.there are 3 ic/op amps in this pup.LM13700N,TL074CN,LM324N.
  since i joined this forum i learned about checking data sheets on the various circuits.where i am confused is on the V- circuits.when i check these pins on the various chips i am getting positive (+)..i am assuming the negative (-) voltages are biased voltage.when i look at the datasheets i see - voltage specs of like -5 to -15,but i have no - voltages on any of these amps.am i missing ground somewhere or am i chasing my ass?
                                         example: on the LM13700N on input - i have 4.75 volts
  i have tried to find a schematic for it but the only one i found i can barely read,but i am more concerned if i am missing biased voltage(if that is - voltage in these circuits)...i know if you loose biased voltage in a tube amp the tubes glow so bright they will melt down..
                                                            once again...thanks in advance for any help/input/education
fwiw,the only thing i did find weird is that there was a diode that i found that had continuity in both directions (thought i had found issue),but when i checked it out of circuit it showed fine so i assume my reading was due to what was in that track

[thermionix]

The "-" inputs are inverting inputs, not really anything to do with negative voltage.  In a typical 9V system, you'd expect to see about 4.5V there.

[DOND]

cool...thanks for the education ....than that eliminates that theory.back to the drawing board...just running out of options.....ready to toss this in the s**tcan but I figure I need to learn to fix something that's already up and going before I attempt doing it from scratch

[tonyharker]

This looks like the circuit.




Cant seem to get the schematic saved at high enough res.

[DOND]

tony,that's the one, only I can't get it to print so I can see it.also doesn't have any values.thanks though,appreciate the help

[tonyharker]

The original pdf has all the values. If you PM me your email I'll send it.  The system will not let me post pdfs

[PRR]

Have you tried with a battery? Or with a dedicated 9V pack NOT shared with other pedals?

This thing, neither battery lead is "common".

[PRR]

Even without part-values, many voltages can be figured from the topology.

[ElectricDruid]

Did you mean that, Paul? you put "All voltages relative to input jack shell", but that looks like the battery negative connection to me, which means those "0V" are 4.5V and those "-4.5V" are actually 0V.

I realise it doesn't matter much in the grand scheme of things, but it's going to confuse the OP!

[duck_arse]

Did you mean that, Paul? you put "All voltages relative to input jack shell", but that looks like the battery negative connection to me, which means those "0V" are 4.5V and those "-4.5V" are actually 0V.

I realise it doesn't matter much in the grand scheme of things, but it's going to confuse the OP!

I read it this way too. [all those ground symbols would read +4V5 relative to sleeve.]

[PRR]

I may be confused. Let's see if Mark agrees.

[DOND]

just wanted to thank everyone trying to help me out here.just getting back to this...looking at what PRR posted,no where in this pedal do I find -4.5 vlts. I have tried running this on a power supply and battery,stand alone and all it does is sound like ass...I am going to sit down later and start from the beginning,but looking at all the diagrams it looks like a simple circuit but I am beginning to feel like a dope now but so far this is what I have:
                                                          LM13700-SUPPLY VLT-9.45
                                                                         INPUT =/-..4.75
                                                                         AMP BIAS-1.72
                                                                         DIODE BIAS-.98
                                                                         OUTPUT-5.69
                                                                          BUFFER IN-5.69
                                                                          BUFFER OUT-4.60
   
                                                             TL074CN-SUPPLY-9.46
                                                                       OUTPUT #1&2-4.76
                                                                       INVERT #1&2-4.76
                                                                 NON-INVERT #1&2-4.76
                                                                        OUTPUT #3-5.00
                                                                        INVERT#3-4.75
                                                                  NON-INVERT#3-4.75
                                                                        OUTPUT #4-3.82
                                                                         INVERT #4-4.75
                                                                   NON-INVERT #4-4.75

                                                             LM324N-SUPPLY-9.46
                                                                          OUTPUT #1-4.21
                                                                           INPUT #1-4.22
                                                                           INPUT +/-..4.16
                                                                         INPUTS 2 THROUGH 4 BASICALLY MIRROR #1

                               

[DOND]

PRR..i am assuming on your topology..i am assuming where you have -4.5 volts in reality I should have 0..correct?

[ElectricDruid]

PRR..i am assuming on your topology..i am assuming where you have -4.5 volts in reality I should have 0..correct?

Yes, correct.

Voltage is all relative. The middle bias voltage is also known as a "virtual ground". If you regard it as just that, a ground, and then measure voltages from there, you get -4.5V and +4.5V at the battery negative (jack ground shield) and positive. Alternatively (and entirely equivalently) you can regard the middle bias voltage as a bias voltage, in which case you'd measure from the battery negative and jack ground, which gives you 0V, 4.5V and 9V. That's what you've got, and the readings look pretty good.

It's two different ways of looking at the same thing, but it is the same thing.

[DOND]

thanks electricdruid...that's what I thought but for the life of me I can not find what's wrong with this thing.voltages check out,etc.but this thing still sounds like residual ass.i started thinking outside the box and did find that this unit will pick up outside frequencies.example.if I type on my laptop I can hear it come through the pedal and out to the amp.same if someone calls or texts me,the pedal picks it up (if I eliminate pedal and go straight guitar/amp all is good)...only thing I can think of is I have a ground issue in it somewhere....also noticed if I check return voltages  of pots 2-3-4..nothing changes but pot 1 will go from 4.75 vlts to 3.28 when moved...pots themselves are fine.

[ElectricDruid]

Could I be a pain and ask if you could re-do your voltage measurements just based on pin numbers around the ICs? (anticlockwise, the usual way)

Eg.

TL074
1- 4.5
2- 4.5
3- 4.5
4 - 0

etc etc

While your style, naming the functions, is certainly equivalent and just as valid, it's not what I'm used to seeing and that makes it much harder to spot obvious errors. I visualise the chip in my mind's eye, and I know what voltages I'm expecting to see on each pin. Without the pin numbers, that's surprisingly hard to do. Maybe some others here feel similarly.

Thanks. I realise that's a pain in the neck since it's repeating work.

T.

[DOND]

no pain at all...but...I see you're asking me to do the vlt checks "just based on pin #'s around the IC (counterclockwise.the usual way)..exactly what is the usual way ? didn't think/know there was a usual way...the way I have been checking the voltages,i have been looking at the datasheets,knowing the notch in the top of the ic is forward, pin 1 and 8 are closest to the notch if it's a 8 pin IC..is that what you mean with "counterclockwise,usual way"?,,not being a douche,just that I am winging this and learning as I go...lmao..

[duck_arse]

I got a slap from antonis last time I posted this, but I don't care, I'm posting it again.

this is the usual way, anticlockwise from left of the notch, to count the IC pins. then, you just say ...

..... well, same as ED said.

and there are no "no readings", tell what shows on the meter, please.

also, for some reason, we haven't yet asked: can we see some photos of that which you have built, please?

[DOND]

duck...that's what I thought..once again I am new to this and if I am asking dopey questions I apologize.on the pedal..i didn't build it.it is a actual chunk pedal.

[DOND]

as request by electricdruid...my voltages of tlo74
                                                 pins 1/2/3=4.76
                                                 pin 4=9.48 (with 9volt adapter)
                                                 pins 5/6/7=4.76
                                                 pin 8=5.02
                                                 pins 9/10=4.76
                                                 pin 11=0 (grd)
                                                 pin 12=4.59
                                                 pin 13=4.45
                                                 pin 14=3.84