anderton bi-filter again

[niftydog]

can you tell me what could be the problem

not from half way accross the world, no... but I can try and help you find the problem!  

But you DO know the problem. There's no signal coming out of the op amp. That's why I'm concentrating on getting that working first. It might be that the whole thing is working properly, but with no signal you'll never be able to tell.

both of the led's light up when i turn the power on.

Ok, but the LEDs are kind of unimportant at this stage.

guitar signal seems to have no effect to them

that is simply because the audio doesn't come out of the op amp. This is the first thing you need to fix.

Unplug your guitar and amplifier, then tell us what the voltages are that you are getting at the pins of the op amp?

This time, read the voltages directly from the actual pins of the op amp itself, just to be sure.

Try this; Disconnect one leg of each C9, R13 and R14. Now check the op amp output with your audio probe. (remember, probing the actual pins of the op amp!)

Anything?

After that, I'd perhaps start checking that the resistors are the right values in the right places. It's real easy to accidentaly put in a resistor that's a magnitude of ten away from the one you intended to use. We've all done it plenty of times!

[thomas2]

i'll do that.. thanks man!  :lol:

[thomas2]

Hey i got an idea!! maybe i'll send the pcb there and you'll debug it? heheh  

[niftydog]

better yet, send me a return ticket for two to Finland and I'll happily debug your bi-filter!  

Just work on getting some signal out of that op amp and we can go from there. small steps!

[thomas2]

i disconnected the two resistors and the one cap.. tried audio probe on it.. there's no output at all from the opamp. also checked the voltages from the pins of the opamp (not the ic socket this time).. pin 4 shows -8 volts and pin 8 shows 8 volts.

[thomas2]

well.. i had to order some parts anyway.. so i should get the right opamps and diodes in a few days. gonna continue the happy, happy debugging then  :lol:

[Mark Hammer]

One problem I have had in past (and a VERY annoying one when you finally find out about it) is an IC pin getting bent under the chip during insertion.  One of those things that drives you crazy because:
a) the board looks fine on the copper side
b) the chip looks fine from the top
c) all the parts are OBVIOUSLY oriented correctly, but
d) when you touch your probes to the chip pins, nothing reads like it should.

Pop the chip/s out and just verify this hasn't happened to you.

Since the few BFF's I've made were all made with CLM6000's (and believe me, every time I break a pin on one and have to discard it, I feel like I've murdered an endangered species), I obviously can't see inside them.  However, it is my understanding that the LEDs should be *dark* with no signal and light up when you pick, not the other way around (darker as you pick).  That, in itself, is not a problem since going from bright to dark should get you reverse sweep ("ow", rather than "wah"), but the fact that they ARE on right now suggests some sort of potential error in wiring up power.  Are you sure that all the places which should have +9v actually do, and all the places that should see -9v also do?  (Incidentally, this can sometimes occur if someone has made the "backwards version" of a board by using a photoetch layout for a Press-and-peel etch, or a PnP layout drawn on with a pen)

Finally, although it is common here for people to recommend very simple fuzzes (like the Tweako or Bazz Fuss) as first projects, I fully understand the feelings of someone who feels no obligation to make distortion.  I salute you for having chosen a first project as challenging and as "nonconforming" as this one.  When you get it working (and you WILL, or else we will find out where you live, come to your house, and hurt[/u] you!), you will have learned an enormous amount.  Not without some blood and pain - but you will be very nicely prepared to take on other projects.

If I drank, and if I was in your neighbourhood, I would happily buy you a drink at the end of this.

[thomas2]

hehee  :lol:
this isn't my first build. i have done many different projects before. but this is the first time i'm trying to build a filter pedal.. i will check the ic's again..
you don't have to come here and hurt me.. i will finish this someday..
and i don't drink alcohol at all, so no panic!  :shock:
i have no use for a distortion device because i don't play the guitar anymore.. i was going to use the filter effect to do something weird with my piano for example  :twisted:

[Mark Hammer]

Hmmm, glad you mentioned piano.  I'm not so sure this will be ideal for that application.  *Tonally* it might be interesting, but  unless you pick your LDRs carefully, the decay time (how quickly the filter sections re-settle) might be too long.

There ARE things you can do to make decay time a little shorter or longer, and LDRs do vary widely in how sluggish or speedy they are,  but LDRs generally fall back from minimum to maximum resistance more slowly than do FETs.  Certainly the slower response time is a help in terms of reducing unpleasant envelope ripple (one of the assets of the BFF, to my mind).  But notes tend to come more frequently on pianos than on guitars, and if the filter is still finding its way back from wherever it went, that can prevent you from getting a wah when you want, especially given the huge transients that pianos are capable of producing on chords.

I'm certainly not saying this isn't a terrific pedal, just that it may be suboptimal for piano.

I can't believe that after all that I'm discouraging you. :roll:

[thomas2]

man.. i do all kinds of weird music.. i may use it for percussion or bass too.. or melodica.. you never know how it will sound unless you've tried it  :lol:

[Mark Hammer]

Oh hell, then let's just keep going!! :lol:

[niftydog]

well, their just isn't much more it could be!

You've probed the input pin and got signal. You've probed the output pin and got nothing. You measured the supplys and gotten the correct readings...

Therefore, there must be something up around the feedback path to the inverting terminal. Check the resistor values.

Do you measure any DC voltage on the inputs and output?

[StephenGiles]

It's got to be that opamp - have you checked the pins as Mark suggested - happened to me many times. I'll have a think about this one.
Stephen

[thomas2]

i have.. i've tried several opamps too.. no output at all :roll:

[Mark Hammer]

If you are using dual op-amps, then you should get +9v (well, a few millivolts below what yo measure on the battery alone out of circuit) on pin 8 and -9v (same deal about a few mv less) on pin 4.

I'll bet you that either the power is connected wrong or that a short or break elsewhere in the circuit is corrupting the power in some manner, because:
a) if the input stage and board around it SEEMS fine except for lack of output, and
b) the LEDs are always on,

something is amiss with your power.  Do you have the power-supply decoupling caps oriented properly?

[thomas2]

alrighty then! got the right opamps and diodes.. i put them into their places.. nothing changed  :lol:  still no output at all from the first opamp..

[thomas2]

i have checked the voltages.. everything should be ok..

[MR COFFEE]

Thomas,

Since I presume you did check the DC voltages on the op amp pins and they are biased where they should be, that leaves out bent IC pins, bent over IC socket pins, problems in the feedback loop around the op amp, etc.

As a just-to-be-absolutely-SURE check of the op amp, put a DC voltage into the non-inverting op amp pin (+1.5 volts from a battery will do), and verify that the DC output voltage goes negative. It's OK if it pins it to the negative rail. If it changes in the right direction, you can be pretty darn sure the op amp is not the problem.

What is left, ...as Sherlock Holmes used to say, ... is the truth, no matter how bizarre it may seem.

You are not getting any output from your op amp because it isn't getting any input signal.
:idea:
Probe around the input to the op amp using your audio probe. Is signal getting to and through the input capacitor? Is it even getting through the input jack?

Frustrating though troubleshooting is, the victory will be sweet, Thomas.

[thomas2]

man..  read my posts about this earlier.. i have probed it several times just to find out that the signal goes into the first opamp, but doesn't come out anywhere.. the voltages have been checked many times, the ic pins have been checked many times, different opamps have been tested, i tried different diodes, different caps etc.. i'm not even sure i wanna get back to this anymore after i finished nurse quacky.. which is a very cool pedal btw  :lol:

[MR COFFEE]

Thomas,

I know your are frustrated, and I sympathize. And Yes,  I read every one of your posts, and thought about them at length.

But the reason everyone gave up on helping you is that you are insisting that what is logically impossible is reality.

Did you, in fact, do the DC amplification check I suggested, or are you simply in "I know that isn't the problem" mode?

Bipolar supplies can make seemingly OK DC voltages look correct, when in fact, because you are measuring with a high impedance voltmeter device, the voltage appears to be correct, when, again, in fact, the voltages you believe you are measuring are absent and you are measuring nothing. Nothing is the same as "Zero volts" in a system with bipolar supplies.

You are apparently new at this, and the troubleshooting aspect of building can be very frustrating, especially at first. I can relate.

However, if all you can do is express frustation, I will give up on helping you also.

The good news about troubleshooting electornics is that electronic circuits work perfectly when you (or I, whomever is the builder) have executed the circuit perfectly.

It is one of the unfortunate realities of troubleshooting electronic circuits that it is quite easy to repeat the same mistakes you have already made before - over and over again - in tracing out and troubleshooting the same circuit.

It's the "over and over" again that lead you to the same erroneous conclusion, and the assumption that "it has to work" when, in fact, it doesn't.

If you don't want to fix it, well, OK.

If you do, see if the op amp is amplifying, i.e., does it respond as you would expect when your provide it with a DC input voltage?

THEN, does it respond to what you are assuming is the AC input voltage. If it doesn't, then you have a VERY useful piece of information about where to look for the problem. If it does, you also have a VERY useful piece of information about where to look for the problem.

This is how troubleshooting is done. FWIW.

I am not stupid, and I assume you are not either. Frustrated as hell, yes,  I hear that, but not stupid.

If it's not worth the trouble anymore to you, that's OK, too.

It can be an awesome learning experience to overcome an "imposible" problem.