Good resistors,right value,right place,still bad voltage on tranny bias...

[momo]

So I guess this is a spinoff of my other debug thread, it seems like I have a re-occuring problem on a HWY 89, and 2 Big Muffs that im debuging right now. Thanks for the help...

I just dont get it, can a resistor which is used to reduce voltage from 9v to 4v lets say, not work,even if it tests out right?

A simple example would be R13 on the Hwy-89, it goes from 9v to collector of Q3, im supposed to have about 4.5v if im not mistaken on the collector. How in the world can I end up with .9v!!, almost nothing, there are absolutly no shorts, cold solders, if I check on the resistor lead before the resistor, everything is fine, I get the batt voltage,after the resistor, .9v for (8.66V).
http://aronnelson.com/gallery/album76/Highway_89_LAYOUT_b?full=1

I get the same problem of 2 muffs at some trannys....

[mac]

I bet your problem is that nice girl ... keep your eyes off her and look at the schem!!

If  vc3=4.5v then ic3= 0.45ma and ve3=0.45v. Then vb3=1.05v supposing vbe3=0.6v. ib=ic/500=assuming that a 5089 has a gain of 500. The voltage across r12 is v12=ib*r12=0.009v almost zero. So ve2 must be vb3 IF ic2>>ib3. ic2=1.05v/100k=0.001ma, almost ten times ib3. vb2=1.65v so i10=1.65v/1000k=0.00165ma ? i9. Then r9=(9-1.65v)/i9=4454k=4.45M. If you used the correct resistors and high gain trannys about hfe=500 this should work.

mac

[petemoore]

  I just dont get it, can a resistor which is used to reduce voltage from 9v to 4v lets say, not work,even if it tests out right?
  There's more. The transistor and related bias resistors all figure in the equations of what voltage is appearing at these gain stages collectors.
    Ah..here it is ! Required reading.
 
  From R.G.
http://www.geofex.com/

What to do when it doesn't work:

The following is a "how-to", step by step procedure for getting the most help fastest when your newly soldered up effects circuit just doesn't work. The material is copyright 2005, R.G. Keen, and is displayed on diystompboxes.com by permission. Permission is not granted for redisplay from other web sites without permission in writing from the author.

Gather the things you'll need

A full set of information about what you built
1.Name of the project: Example: Neovibe, from General Guitar Gadgets.
2.Links to the source of the project web site with the schematic or project, layout and wiring diagram. Example : Neovibe
3.Some candid admissions about how closely you followed the suggested layout, if any. If you just perfboarded it, say that, and if you can, include a picture of the board. Scanners do a GREAT job of making pictures of PCBs, by the way.
4.Any parts substitutions or modifications you made to the original. If you didn't have any 10uF caps and used 22uF, say that. If you had to use a 2.7K resistor instead of a 2.2K, say that. If you used a BC109 instead of a 2N3904, say that. By the way, if you substituted any transistors, it's a sure bet that the first question you get asked will be "Did you check the pinout of that transistor?" Delight the questioner by saying (truthfullyâ€) "Yes, I did a google search on that part number and check the pinout against how I soldered it in." If you can't say that, chances are good that you've already found your problem, all by yourself.
5.Whether or not it's a positive ground circuit like a PNP fuzz or a Rangemaster that has been hacked to work with negative ground. This is a special case, but a common one. "Positive ground" means that the positive/red lead of the battery clip is connected to signal ground. "Negative ground" means that the negative/black lead of the battery clip is connected to signal ground when the effect is operating.
6.What it does and does not do how it works; partially or not at all. For instance, if it lets no sound through; or if it makes a harsh, distorted sound only when you strum hard on the strings at full volume; or if everything is really, really low volume.

An electronic meter capable of reading 0-20Vdc and with an ohmmeter scale. This can be analog, but digital ones are available for as little as $10.00. I've seen them as low as $2.99 here in Austin Texas in 2005. If you have to, borrow one. There is really very little anyone can tell you that would help if you can't measure and tell them what voltages you get. It will be much easier if your meter has some way to clip the negative/black lead to circuit ground instead of having both leads with only points. Most meters do. If yours doesn't, you could use a clip lead to do this, if you have a clip lead. Here's a quick guide to how to use a meter in simple laymans' terms. (to be added RGK)

A non-dead battery. Measure the battery with the voltmeter. If it's not over 8.0V, it's going to gum things up and give you inconsistent results. Get a fresh one. Using a DC wall wart is problematical. What if it's the wall wart that's bad? Get a good battery.

A calm, open mind. I don't like to admit this in open company, but one of the deepest episodes of rage I ever felt was when I had been flogging this one poor circuit board to death and even though all the hookup wires and parts were in the right place, nothing worked for hours. I was almost speechlessly angry until I noticed that I was debugging the bottom side of the board for access to all the solder points and had neglected to put the ICs in the sockets. The madder I got, the LESS capable I was of noticing the real problem. You gotta clear your head first.
Being absolutely certain that everything is correct and it still won't work is not good preparation for noticing an errant solder thread, for instance. Mother Nature does not lie, but she is a stickler for details. If it was put together perfectly, it would work. It not working is Mother Nature's way of telling you that you made some tiny error, and it's no reflection on you if it's not perfect the first time.

When you have everything gathered, but before posting, get the specific information you'll report.
1.Hook up the DC power to the circuit (no input signal or amp needed) and clip the meter black/negative lead to signal ground. Probe **every** pin of each IC, transistor and zener diode (if any), and also the battery at the clip and where the battery wires come onto the board. Make a written list of the voltages. Below is a helpful starter list of the minimum things to measure.
2.For extra credit search the forum archives for problems with the same circuit. Someone else may have had exactly the same problem.

(d) Now post. Post all of your gathered information along with the list of voltages along with a request for help interpreting them. Chances are, someone will spot the section that's not running correctly right away. Then a few more secondary tests will likely have it nailed. You'll be posting it to a forum where most of the people there will have been through exactly the same situation. They want you to be successful, and they don't think you're stupid or not cool for having a problem with it.

(e) Learn. There are certain things that always determine what's working and what's not. Read the postings of others that have posted their voltages and find out what happened to them. That way, you get the benefit without having to make the mistakes. Search the archives for problems with the same circuit. Read the debugging page for the indicators about what voltages indicate about function. This last takes a long time, but it's the most rewarding. If I had had a similar forum to learn debugging in when I started this, I'd have wasted a LOT less time in my life.


That's the procedure.

Here is the checklist to fill out:
1.What does it do, not do, and sound like?
2.Name of the circuit =
3.Source of the circuit (URL of schematic or project) =
4.Any modifications to the circuit? Y or N
5.Any parts substitutions? If yes, list them.
6.Positive ground to negative ground conversion? Y or N
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? =>
Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead =
Voltage at the circuit board end of the black battery lead =

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Q1
C =
B =
E =

Q2
C=
B=
E=

IC1 (or U1)
P1
P2
P3
.
.
.

D1
A (anode, the non-band end) =
K (cathode, the banded end) =

D2
A =
K =

Z1 (zener)
A =
K =

And so on until you get through them all. Having gathered the data, post a tidy list of it on the forum, and you'll most likely have a working effect soon.

For extra credit, while you're waiting for someone to tell you what they see, probe the pins of each of the electrolytic caps, verifying that the voltage on the (+) pin is more positive than the voltage on the (-) pin. If it's not, that cap will eventually fail, whether it's the immediate cause of the thing not working or not.

Yes, it is a pain. But it is a time tested, effective, highly productive pain.

Do this a few times, and you'll start to know ahead of time when something is wrong. You'll be far down the road on learning.

-- more additions:

http://www.geofex.com/effxfaq/fxfaq.htm
http://www.diystompboxes.com/pedals/debug.html
http://www.diystompboxes.com/cnews/FAQ.html

 
 
 

[momo]

  Man, thats how I felt after getting the dreaded "read up on how to debug" post!.....Pete, sorry about that, I have read up on the procedures, I just did not want to bore you guys with what I thought unesasary details. I had narrowed down the problem to bad collector voltage after passing thru a simple resistor, But you are right, there are more details acting on this and so I should have posted accordingly.

That said, I put the Muff down and started to debug/modify my FuzzFace. I put trimpots on both Q collectors and read up on how to bias this. That was great, I think that this will be my way of learning.
I know that the math/equation part is very important for what we are doing, but for me, reading up on what I see as heavy math(Im am the worst math guy on earth!) is like doing the dishes, I really have to put my mind to it and even then, its not sure that it will be completely done....

So anyway, I know I have to read all this, Ill just take it at my pace.
Back to the FuzzFace,I ended up, fiddling with the two trimpots so that I could push the Q1 into its sweet spot, and then adjust Q2 for 4.5V. I must say, if I was doing some math there, well thats how I want to do it!....it was fun!
I really liked hearing the math!
Now I might just order some Ge's from small bear just to compare, but I know I will have to rebias, but thats great, the more I do it, the more my brain will accept this new reality
I liked the sound I had, that made me realize, that its not too far from a Muff, the low end does not compare, but my FuzzFace sustain is I would say 70% of what you can get on a Muff.
If I understand this right, the distortion on the FF is a feedback technique giving particular impedence characteristics a bit like the Rangemaster, where as the Muff is stage related gain, and has "normal' high impedence.
Please correct me if im wrong on this.

OK, Ill  make myself some great coffee, put a chair in the garden....and try to read up on some of those amazingly detailed tech papers.....
Cheers

[mac]

(Im am the worst math guy on earth!)

well, after 6 calculus, 2 algebras, 2 numerical calculus, 1 estatistics, etc,... i still use my caculator to do 2+2

mac

[petemoore]

If I understand this right, the distortion on the FF is a feedback technique giving particular impedence characteristics a bit like the Rangemaster, where as the Muff is stage related gain, and has "normal' high impedence.
Please correct me if im wrong on this.
  I'm no math whiz, but I have hacked through some equations, half the battle is the terminology, what the letters mean can be a whole nuther study, and how the math works, using combination calculator and shoot from the hip maths...
  I put some reads RG typed, on the subject of math working, in 'addition to the FAQ, I think it's still near the end.
  The 'actual' equations are usually somewhat forgiving, at least in fuzzes, close works fine.
  The FF is different than the Muff, it's got the feedback loop / gain controlled at guitar volume / pickup loading thing going on. The BMP has numerous gain stages so any signal present tends to become 'big', near as big as what the diode clippings will pass hence the 'sustain tag', which is really compression via gain/clipping...so it won't clean up much.

[momo]

OK thanks petemoore for that info,
Mac, for some reason, I picture you with a huge protruding bump on the back of your head... , where that math part of the brain has just grown out of control .
How you went thru so many years of calculating is, well, um, I cant find the words.. I guess!   ha ha!

At your level, you could decide to go spend 75 dollars at he groceries, not a penny less or more....and do it easily
Cheers

[momo]

He He , well I debugged my green rusian Bigg muff. I learned in the process... it turns out the diodes on a Muff dont directly go to ground, they are pulled to ground thru a 100K first! I mis interpreted a link to ground on the layout....once that was fixed,everythng is great!
I really love the tone knob, plus the sustain rolloff develops some kind of phasing! just great and not too noisy,but you dont use a muff for quiet music anyway
thanks for the help, now ill try to debug my triangle muff, different layout so I think the diodes are alright...

[mac]

Glad to hear that.

Mac, for some reason, I picture you with a huge protruding bump on the back of your head... , where that math part of the brain has just grown out of control  .
How you went thru so many years of calculating is, well, um, I cant find the words..   I guess!   ha ha!
At your level, you could decide to go spend 75 dollars at he groceries, not a penny less or more....and do it easily

Did I mention 2 quantum physics, 2 electromagnetism, 2 quantum statistical mechanics, thermodynimics, classical mechanics and all that stuff? Yeah, my friends say that my head is bigger after college. If you see my avatar you'll realize why I'm wearing a hat

Now seriously, maths needed here are pretty simple. Also most distortions can be somehow disected with the aid of some basic eqs, ie  like 2.Pi.f=1/RC which is used a lot in the forum, and understanding how a diode, resistor and cap  work. Also transistor bias are not that difficult to estimate. Tech students have some advantage, but anyone can understand basic stuff reading and googling.
Now more complex circuits like phasers or compressors require more understanding. Elect eng and techs look circuits and figure out what's going on quickly. In my case, even though my formation, I need some time and a lot of coffes to get a picture of how many circuits work.

I recommend some old physics books, like Sears. They cover the basic EM theory. Some integral and partial derivatives are need to get some results, but most of it is just daily math. At least you can get a general picture.

------------
One way to see why the BMP is not touch sensitive is that hugh amount of gain. If a fly stands on a string, most likely that mV generated at the pick up will be "hyper amplified". But because the batt is just 9v the signal will distort a long time until the guitar sends a wave weak enough to be less than 4.5v. Add diode clipping. This is a very rough idea.

The FF has that feedback resistors. My bet is that a low gains the effect of the feedback resistor is bigger than at high gains. Not sure.

mac

[petemoore]

  Most of the time the DMM and audio tests can debug a circuit, but a little intuition can reduce the 'DMM Dogma' of seemingly endless testing.
  At a safe 9v, I like to connect my thumb to signal path bipolar transistor pins as a 'reverse audio probe', looking for the base to be louder than the collector on a gain stage, and ~1 to 1 unity on buffers.
  For RAProbing [or audio probing] Fets, substitute Gate for Base, and drain for collector.
  ...testing with connections to guitar and amp, circuits powered, starting from output to see where a possible drop in signal occurs, in signal path...working my way point to point, [also across caps/resistors/other] starting on the right [at output jack tip] and working left, toward input, controls set half way at first, or verified as being wired so CW rotation increases gain or volume...a pot wired backward and turned all the way 'up' [which'd be ATWDown] ..can really throw things off.

[momo]

Again Pete thanks for the clarification, but in doing so, you have opened up another question .....I really dont get how you use your thumb to hear which leg of the tranny is louder?? I cant wait to hear this one!

[petemoore]

  Not for use with HV circuits, safe @9Vdc though.
  when you touch the tip of a 'hot' cable [connected to live amp] to the carpet or your thumb [press your thumb across the sleeve/tip] you hear a buzz.
  I call it the 'thumbuzz debugger' technique.
  Now plug that live cable to the output of your stompbox, touch it with your thumb, you should hear about the same buzzing sound [maybe a little quieter because some signal goes to ground through a 100k pot usually].
  If your switch wiring for output is incorrect, you won't hear any buzzing on the circuit side of the switch, and that'll need fixed [1 debug so far].
  K, now you've got thumbuzz the same on the circuit board output as the output jack tip [signal is making it this far], now try on the last transistors collector 'inside' the output cap [we'll say it's a gainstage we're verifying or debugging at this step], we still get buzz, possibly slightly attenuated if the cap is small value enough to do so [and also because DC is removed]...so the cap is good, and the collector buzzes, the base should then BuZZ, louder than the collector because the collector is an amplified version of the base signal.
  It's just a simple, very basic way to introduce 'any' signal into a circuit for debugging purposes, you could use a toy organ, with a key taped down so it produces signal, and a shielded/grounded sleeve connector, tip connection through a DC blocking cap...
  But I find 'any' signal is enough signal for basic debugging purposes, and since I always try to keep my thumb handy, I can connect it easily to any point in the circuit through a small screwdriver or any other conductive metal prod, I just connect my thumb to the lead, connect the lead to where I want signal to appear, my thumb has enough output to satisfy the signal requirements, I find it's quite useful and much easier and quicker than setting up some other type of signal injector.
  Enjoy at your own risk ! [ie no risk @ 9vdc, not for use with HV circuits].

[momo]

Wow, using the thumb as a third hand!, that great, one of the things I really hate in debugging is not checking voltages or stuff like that....its hearing that same "regular tuning open strumming chord" that I had to endure because the guit was on a stand, that "chord" on a Muff is just hell!
I was holding the DMM lead,in one hand and strumming the awful "chord' repetitevly with the other...Ill have to try the thumb trick!

Since Im here, I have to say that my comprehension of what is going on as far as tranny biasing is getting much clearer, and just as any other DIY job, you can read as much as you want, it wont get real clear till you actually mess around with things.....anyway thats my experience.
Yesterday, I had a breakthrough!, I had a 2 different muffs not working, and the Hwy-89 not working.Now I got a major confidence boost when I realized that the reason it was not working was other than bad connections, in other words, psyically speaking, my builds are very clean and tidy.
So the problems turned out to be others...one Muff had the diodes soldered to ground....I missread a layout. The highway -89 had a cold solder on R10, which was critical because no connection was made to ground with the 9v for base of Q2. So now Im left with debugging the Muff Triangle, should not be too hard, now that ive got a debug routine established!
Check voltages,if good, use audio probe, if not good,check bias resistors,by then, you should be close...

Oh and just a little note on the actual tones....First I have to say how I monitor....this has been the best way consistantly to monitor sound quality:

I always first pass the circuit into a high quality computer interface into a studio quality monitoring system. That gives me a flat response to really hear the pedal. Everytime ive had a great sounding pedal on the computer, plugging it on an amp was always the cherry on top. Plugging a bad sounding circuit nicely revealed in the pro monitors, onto an amp, always gave less than great results compared with a great box.
So anyway, now that you know how I differentiate different tones...

The Highway-89 sounded OK to me, but not as great as the clips posted. Im using 3904's though, so yea, I think the 5089's will give me the "cream" that is missing...its ok now, but I say just like a regular dist, so I want  type distortion!!

The Russian Green BigMuff is a beast! and I say that after playing with 3904's!, so I cant wait to drop some 5088 or 89's. The tone pot is wierd though, ill have to check if I missread a value on the tone stack caps, what I dont like is the high end values. I dont know if this green Muff is designed like that, but at full treble, it buzzez like a fat bee!, it has lost all content below say 6K and has accentuated high-mid buzz.
Well I know I dont like it!, its just not versatile enough, it could be interesting for an effect, but it also seems to keep the high-mid buzz that is a bit agressive.
Ill check for mods on taming or changing tone on the high end.

[mac]

Pete's trick is very effective. When I'm testing circuits, I always change caps and resistors with the circut and amp power on, so I'm used to that loud buzz. I prefer the noise than turning up and down the amp volume a hundred times.

BTW, I never use the layouts or pcbs posted. Just use my own.

I always first pass the circuit into a high quality computer interface into a studio quality monitoring system. That gives me a flat response to really hear the pedal. Everytime ive had a great sounding pedal on the computer, plugging it on an amp was always the cherry on top. Plugging a bad sounding circuit nicely revealed in the pro monitors, onto an amp, always gave less than great results compared with a great box.
So anyway, now that you know how I differentiate different tones...

I only have my chinese DDM and my ears.

The Russian Green BigMuff is a beast! and I say that after playing with 3904's!, so I cant wait to drop some 5088 or 89's. The tone pot is wierd though, ill have to check if I missread a value on the tone stack caps, what I dont like is the high end values. I dont know if this green Muff is designed like that, but at full treble, it buzzez like a fat bee!, it has lost all content below say 6K and has accentuated high-mid buzz.
Well I know I dont like it!, its just not versatile enough, it could be interesting for an effect, but it also seems to keep the high-mid buzz that is a bit agressive.
Ill check for mods on taming or changing tone on the high end.

The tone stack is hated or loved... Play with the 10nF and the 22/39k to gnd from the pot. See the prescence control at muzique.com.

mac

[petemoore]

I prefer the noise than turning up and down the amp volume a hundred times.
  I debugged the volume control on my testamp many times, then figured out how to never turn it down <10% volume...
  Kinda funny spending hours debugging on a circuit because nothing is coming out of the speaker because the volume control on the amp is ATWay CCWise.

[mac]

That happens. Sometimes I forget to turn the PS on. Or even worse, the speaker cable of my amp is connected to my lm386 mini amp.

mac