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Solid State Amplifiers => Preamps and Effects => Topic started by: shinychrome0 on August 05, 2010, 07:33:51 PM

Title: Custom LPF build is distorted
Post by: shinychrome0 on August 05, 2010, 07:33:51 PM
I've been working on designing and building a 5 cascaded stage low pass filter , and it doesn't exactly do what i want it to.  The schematic is attached.  There is some output, but it is sputtery and badly distorted.  Is there something in the schematic that shows a design problem?  I've been staring at this thing and prodding with my meter all over to make sure its built exactly to the schematic, and nothing is touching or shorted where it shouldn't be.  The schematic is attached.
Title: Re: Custom LPF build is distorted
Post by: J M Fahey on August 05, 2010, 08:38:14 PM
Well, yes, a couple ones.
1) It's not biased, and ground is unrelated to + and - rails.
You have an end to end 9V power supply, which is floating.
You fix that by wiring a , say, 10K resistor from the positive end of the battery to ground, and another from the negative side to ground.
*Now* you have +4.5V and -4.5V rails. Also wire 100uF capacitors from each rail to ground (pay attention to polarity).
*Now* U6, your first op amp, is biased to ground, *if* your sound source/generator provides a resistive path to ground and does not have a DC component.
I'd wire a 1 M resistor from U6 + input to ground.
All other Op Amps, being direct coupled, will follow it.
2) I have a doubt with the value of R2/3/nn/5 (nn=unlabeled) ¿are they 100 r (ohms) or you meant 100Kr?
R6 is labeled 10000 which I think means 10Kr.
3) Did you mean to wire R1 to -V (-4.5V)?
Good luck and correct those small doubts.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 05, 2010, 09:24:09 PM
1) well the battery is stupidity on my part.  I was planning on running off of a 9v DC adapter, but i was just using a battery for testing, and COMPLETELY forgot about the adjustments.  Would the 9v supply also need the resistors and capacitors to make it a bipolar supply, or can i just use it directly?  And what exactly do you mean about biasing?  Do i just need the 1 meg resistor to ground on the first stage to have everything covered?
2)the first 4 resistors are all 100r, and the 10k is a 10k log pot.
3)there is no r1.  I don't know what it was but its apparently no longer there.
Title: Re: Custom LPF build is distorted
Post by: J M Fahey on August 05, 2010, 10:14:46 PM
Hi Shinychrome.
1) Yes, *everything* needs to be biased, which really means "where do I stay when there is no signal present?"?
Op Amps are simplest to bias but even they need to be provided in certain approppriate pin a certain voltage.
Besides, voltages always exist referred to some other point, that's why meters have two probes which go to different places.
You always measure voltage (more precisely difference of potential) between two points.
For comparison, you measure temperature or pressure or magnetic field intensity or PH ... etc. on a single point.
2) This type of circuit calls for two voltage rails, referred to a third wire called ground.
If you do not use a battery but an external single supply, you will still need to "split" it into 2 rails.
3) Your input jack will have a hot pin connected to the input and another to ground.
Your output jack will do the same, but connected to output pin.
100r is the minimum resistor that can usually connected to a regular op amp output. It'll be happier with, say, anything above 470r or 1K. Your capacitors will be smaller (cheaper) too.
4) You need that 1M in the input for when you unplug your guitar or whatever.
5)Congratulations for getting your feet wet.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 05, 2010, 11:07:55 PM
Ok cool. So my last question then is how do i split that supply?  Something like this, with the 9v from the wall wart going where the battery is?

http://www.generalguitargadgets.com/richardo/distortion/bias2.gif

or this?

http://www.generalguitargadgets.com/richardo/distortion/bipolar.gif
Title: Re: Custom LPF build is distorted
Post by: teemuk on August 06, 2010, 03:51:06 AM
4 stages to achieve -3dB @ 32 kHZ and then the final 1st order filter stage where it all goes to -3dB @ 320 Hz.

This design doesn't make any sense to me. Not one bit.


What's the application? If the goal was achieving the steeper curve from the summing effects of series filters then why not just go straight to using second order active filters and cut down the component count drastically? If the goal indeed was the -3dB @ circa 320 Hz then you effectively do it in a single stage (pretty much with a curve of a plain 1st order filter to add), so what's up with the rest four stages that only introduce only -5 dB above audio range? They seem pretty pointless to me.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 06, 2010, 08:57:22 AM
It was more of an experiment than a practical application, but i'm still going to use it.  And yes the steeper curve was the idea, using the simplest circuit possible.

However, i still have the same problem with distortion, even with the updated power supply, and 1 meg resistor to ground on the input of the first stage.  Could it have anything to do with using 100r resistors on the outputs?
Title: Re: Custom LPF build is distorted
Post by: phatt on August 06, 2010, 09:55:33 AM
Hi shinychrome0,
I'll take a stab here,
I'll bet it worked on the sim and you assumed it would work in real life. ::)

*** Be very aware Sims are not bullet proof ***
Quite often they give a result that might look really good on screen but
in real life are impossible. :'(
Very powerful tool but can easy lull a novice into a false sense of security.

You do need to do some homework and read up so that you have a reasonable idea of *basic circuit function*.

I'm saying this because Like You I was learning and making these kinds of mistakes not to many years back. Be patient, Google the terms you read so that you develop a solid basic circuit understanding.
(And of course ask these wonderful chaps who've posted above me as they are a treasure trove of knowledge :tu:)

As has already been said the circuit is way off and there are much easier ways to achieve what you wish.

I'll also assume you are trying to get a very sharp rolloff?
If so then Google  *Ed Rembold Marshall Simulator*
(Ed's circuit is a simlified version  found in Marshall JTM Amp schematics)

Or hunt down the *LXh2 cab sim* stuff.

LXH2 is complex but Ed's sim is about as easy as it gets and it does it's job well.

If you wish I will post my Marshall Cab sim circuit for you to work with,
you can even tweak some of the values to your liking on screen to see how each part changes the rolloff.

At least you know it will actually work when you put it together! ;D
Phil.
Title: Re: Custom LPF build is distorted
Post by: teemuk on August 06, 2010, 10:01:01 AM
e.g. 2nd order low-pass (a.k.a. "Sallen-Key")
(http://freecircuitdiagram.com/wp-content/uploads/2008/09/low_pass_filter_lm833.gif)
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 06, 2010, 10:02:14 AM
Yeah i'd love to see your circuit of the cab sim.  And for the purposes of learning from my mistakes, i'd still like to make this build work, even if its not quite what i was going for.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 06, 2010, 10:07:11 AM
teemuk, what is the circuit you posted?  Is that the marshall cab sim?
Title: Re: Custom LPF build is distorted
Post by: teemuk on August 06, 2010, 10:15:58 AM
No, it's an active second order low-pass filter. You likely find two or more of these basic circuits connected in series from most cab sims.

Basic "workhorse" filter circuits such as this are pretty well covered in electronics literature, with all the applications and mathematic equations for component values included. There's no need to reinvent the wheel.

You can turn the same circuit to 2nd order high-pass like this:
(http://users.cscs.wmin.ac.uk/~wooda/components/opamps/opamp-sk-hp-filter.png)

And even combine the two in series just using a single OpAmp. You simply don't need buffers for every stage.

Here's the same thing with discrete components:
(http://www.vk2zay.net/calculators/sallen-key-high-low-pass.jpg)
and a calculator for values:
http://www.vk2zay.net/calculators/sallenKey.php

Here's the OpAmp versions shown with neccassary biasing arrangements, if you plan to power them from a single-sided power supply such as battery:
(http://www.simplecircuitdiagram.com/wp-content/uploads/2010/04/Low-and-High-Pass-Single-Supply-Sallen-Key-Filter.gif)
Notice how the inputs need to be referenced to a DC potential that is exactly half of the rail-to-rail voltage (Vcc/2).

With a dual-rail supply you could just use ground as reference because half of the rail-to-rail voltage is zero volts.

You will need to provide this reference to the OpAmp stages because otherwise their inputs will "float" and the stages won't operate correctly, they may even clamp the output to one of the power supply rails. All AC coupled stages will need the reference, DC coupled can be series connected assuming you provide the reference to at least one of them. But in latter case you got to watch for DC offsets that real-life OpAmps generate. Those offsets may cause the reference to drift from the exact point and again compromise the operation.

Note that simulated circuits tend to work too well because they use ideal components and often they are not hindered by deficiencies that exist in real life. The schematic you posted works well in a simulation, badly or not at all in real-life.

To get it to work in real-life you need to address the issues of at least:
- Creating a properly working power supply
- Creating proper DC references for the OpAmps
- Handling DC offsets that series connected stages may generate

J M Fahey is right on the money with his previous posts.

If you plan to build something with OpAmps, even electronics stuff in general, I suggest you learn the theory behind before rushing straight into making something. You have much more chance of success. Most analog electronics theory books cover the 101 stuff in an easy-to-learn format. Plenty of learning material can also be downloaded for free.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 06, 2010, 10:20:42 AM
Is there a way to make a filter like that adjustable?  Otherwise it won't help me out a whole lot.
Title: Re: Custom LPF build is distorted
Post by: teemuk on August 06, 2010, 10:26:39 AM
Adjustable, as in what way?
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 06, 2010, 10:29:35 AM
adjustable cutoff frequency.  I found one article that says to use a dual ganged pot to keep the Q the same, but that means using two dual ganged pots to get a four pole filter circuit.
Title: Re: Custom LPF build is distorted
Post by: teemuk on August 06, 2010, 10:42:20 AM
I don't think there's an easy way around it. It's an RC filter after all, so for four of them it makes sense you need to vary four "R" 's.

Possibly you could replace the ordinary resistors with a resistive element that you can control "remotely" (e.g. LDR, solid-state device, etc.) with just a single control but that will make the circuit rather complex.

Some parametric EQ circuit tweaked to operate only at proper low frequency, on single band, and only in "cut" mode, likely is a better alternative than the convential filter circuits. Those will often feature a "gyrator" circuit - a simulated inductor - that allows to tune the L of a LC filter, hence making possible the adjustment of both frequency and Q of the filter.
Title: Re: Custom LPF build is distorted
Post by: DJPhil on August 06, 2010, 01:42:57 PM
Just wanted to throw in my 2pf.

I've been neck deep in filter literature lately for one reason or another. It seems that as a general rule analog filters represent a trade-off of adjustability, performance, and component sensitivity. As I learned more I remember thinking that the engineers were crazy, after all, a simple tone stack is a bare handful of (usually cheap, low performance) parts. They were lamenting the need for several precisely matched capacitors and resistors per circuit. Ok, we don't need that level of precision, but something's off.

In studying some of the passive tone stacks I found that often the settings were interdependent, i.e. one filter's settings could change the response and basic function of another. The engineers would find this messy heaving of load around a circuit to be insanity, but the early amp designers didn't care about precision. They just wanted a low parts count circuit that'd be as flexible as possible. I suspect a lot of their work was experimental 'see what it sounds like' sort of exploration, and when you could get six components and two pots together to make an interesting range of tone it was time to celebrate.

It was a bit of a revelation to me, but in hindsight it should have been obvious that these two camps had different goals. I'm sure I've read exactly this sort of breakdown before, but it didn't sink in for me until a few days ago as I was trying to make different values of pot work in a tone stack.

Hope that helps. :)
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 08, 2010, 04:37:39 PM
How about a design like this then?  I'll play with values on the first stage on a breadboard first, and then just have two knobs on the second stage(the 10k resistors) for adjusting that one.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 08, 2010, 05:33:01 PM
ok new problem now.  I layed everything out on a breadboard just to test, and i didn't have the right value caps, so i made it according to the schematic below just to test with.  Apparently, i'm getting some sort of HF oscillation, as the opamp quickly became to hot to touch and stopped making any sound.  It worked right for about 5 seconds though.  How do i fix the oscilation?
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 08, 2010, 08:47:12 PM
ok i put  68 ohm resistors in the feedback loop to kill the feedback(and replaced the chip, which was apparently fried) and now it works great!  I'll just have to play with some capacitor values to find the right cut off point, and then i'll be ready to solder!
Title: Re: Custom LPF build is distorted
Post by: DJPhil on August 08, 2010, 08:58:53 PM
Quote from: shinychrome0 on August 08, 2010, 08:47:12 PM
ok i put  68 ohm resistors in the feedback loop to kill the feedback(and replaced the chip, which was apparently fried) and now it works great!  I'll just have to play with some capacitor values to find the right cut off point, and then i'll be ready to solder!

Excellent! Here's a calculator that might help. Sallen-Key Low-pass Filter Design Tool (http://sim.okawa-denshi.jp/en/OPseikiLowkeisan.htm)

There's a bunch of good filter calculators on that site.

Hope that helps.
Title: Re: Custom LPF build is distorted
Post by: J M Fahey on August 09, 2010, 08:49:43 AM
Well, just off the top of my head, no calculators, your close shave3 looks like an 8KHz, 24dB/oct lowpass.
Is that what you are trying to achieve?
By the way, it should not oscillate, being that each stage is unity gain, so your problem must be another one.
Using 68r resistors in the feedback loop , or a piece of wire, is the same.
If anything, you can use that 68r (the "standard" one would be 100r) between the last op amp output and the output jack, as to isolate it from output cable capacitance.
Active filters are fascinating subjects, study them because they are one powerful mean of tweaking sound, specially in "speaker simulators"
There's an old, yet "the Bible" type reference book: "Active Filter Cookbook" , which has it all between 2 covers; you can buy it cheap, used, from Amazon.
There is also another similar reference book: Op Amp Cookbook.
Best stuff. :tu:
Title: Re: Custom LPF build is distorted
Post by: phatt on August 09, 2010, 08:56:54 AM
hi Shinnychrome,
               Once you grasp what is needed I doubt you will have any need for adjustable stuff.

Once the toneshape is created the rest can be done with simple stuff.

ToneBrake circuit;
I built 6 of these some years back and sold all bar 1 unit which I still have.
This one worked wonders after my old Quadraverb unit.
Worked best in a recording situation. Most of the big name rack stuff will benifit greatly when recoring.

On clean sounds it's hardly inspiring,, but gezz once you get into heavy OD's it really becomes obvious.
You need to insert this **AFTER** Dist or raky gear, not before.

I found this thing to be a great learning tool ,,not only for the electronics but you start to realise just how critical tone shaping is.
As one chap stated with eyes wide open after using it for some recordings.
"WOw I never realised just how much Hi Freq crap just destroys good guitar tracks,
an that magic box cleans up the mess".
This chap owned Masses of expensive recording gear BTW.
Needless to say he asked me to build one for him.:)
One thing I would change (Now that I've learnt a little more) is the output really needs a buffer.

If you wish for more things to look at check my Schmo page here;
http://www.ssguitar.com/index.php?topic=1648.0
The *DDC* there is both an OD unit and Cab sim all in one neat little circuit,
though a little more complex.
Cast an eye over the PhAbbTone circuit ,,delivers up to 30Db notch cut @ 400Hz  8)

One thing you might find useful is wedging in a simple Graphic EQ after the Cab sim.
This will give you access to many of the sounds you may wish to nail.
GEQ without the Cabsim box *first* will not be as convincing.

GEQ before cab sim will help but I've found it much simpler to run an old fashioned passive EQ stage before dist/OD >> then Cab sim >> then GEQ.

Truth is there are just so many ways to do it and some will be better than others but for me the home made equipment I've assembled/ collected over the last 10 years is all basically cheap and simple gear.

I personally refuse to lay down big money on gear that is often only marginally better than what I've built for very little outlay.

BTW I'm not alone in this manner of thinking as there are many pages on this at Amptone;

Try starting here; http://www.amptone.com/index.html#eqconcepts

It will take forever to read,, ALLLL TEXT (sorry no fancy stuff) and I must say hard to keep track of,
a little too wordy in places but a 100 ideas to give you insight as to how to approach things.


Heres' a little snippit I took the liberty of lifting for you.
________
EQ concepts and pre-distortion EQ
John Murphy, chief engineer for Carvin Corp., wrote "the pre-clipping frequency equalization and post-clipping EQ are absolutely critical adjustments. Once you have a well-behaved clipper -- even if it's just simple diodes, as in the stomp boxes -- it is the precise combination of pre- and post-clipping EQ that mostly determines how an amp sounds. The 'secret' of the best sounding guitar amps lies in the pre-clipping EQ response curve."

Van Halen's guitar tech recommends an EQ pedal above all, as the most valuable pedal, in his book Guitar Gear 411: Guitar Tech to the Stars Answers Your Gear Questions, pp. 75-76.
________

Now I'll just add this to give you a head start;
The trick is NOT about making the BEST tone circuit (i.e. I've just built the best EQ circuit on the planet)
and expecting it to deliver gold.

The best results will be found in a combiation of different circuits and shapes.
What you hear from the speaker is combination of many shapes all imparting their particular alteration to the sound produced.

Hence my simplemans approach is old styled passive tone in front> Dist> Cab sim> GEQ > Main Amp.
Have Fun,, Phil.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 09, 2010, 09:18:40 AM
For the moment i've got all the tone shaping i could ask for.  I use a pod xt live as the heart of my rig, and run it through a power amp into an actual cabinet.  However, i prefer a very smooth mellow sound, Carlos santana style, and love the effect i can get with a low pass filter after the POD.  I just have a passive single pole filter i use now, with some caps on a six position switch.  I don't need much adjustability, its mostly a set it and forget it effect in my rig, but sometimes for recording i'll sweep it around while layering guitars, some with more grit, some with hardly any.  So if i can just find a cut off point that is slightly below where i want it, i can then back it down by turning the two 10k pots, and find the absolute tonal sweet spot.  So adjustability is more for the sake of having it than for any actual necessity.
Title: Re: Custom LPF build is distorted
Post by: phatt on August 10, 2010, 08:24:38 AM

I don't have a Pod handy but I doubt a passive setup could even come close to what the above circuit (or Similar) can do.

I'm only offering advice having been there done all that,,if you catch my drift? 8|
Phil.

Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 10, 2010, 02:56:19 PM
Yeah the passive filter was a good start, but its not quite good enough. 

Ok so here's where i'm at.  I just finished getting everything transferred to a board, and i must be close but not quite right.  There is a big volume drop when i kick in the filter (probably from those 68r resistors that i put in.  I'll be removing those shortly) and it does not appear to be cutting anything.  Its passing everything as far as i can tell.  It should be fairly obvious if it is cutting or not.  The cut off point should be at about 3000 hz with both knobs dimes.  Any suggestions?  I'm confused how it could be just acting as a buffer without also acting as a filter.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 10, 2010, 08:54:44 PM
Here's the updated schematic by the way.  Just the Capacitors and the power section have been changed to make use of a DC adapter.

There's a considerable volume drop when the pedal is first engaged,(even without the feedback resistors) and then it comes back up slightly after a second or two, but not back to full volume.  Isn't this supposed to be a unity gain circuit?  And shouldn't the maximum setting be pretty obvious?  With a cutoff of 2.3khz, i would think it would be.  I can tell there is a slight cut, but it sounds like its way higher up than it should be.  I'm a little lost here.
Title: Re: Custom LPF build is distorted
Post by: phatt on August 10, 2010, 10:49:57 PM
Hi SChrome,
                You have no gain block only a filter which is lossy by nature.

Take a look at the Tonebrake, the 2nd stage is where all the gain happens.
Without that it's worse than a passive setup :(
Phil.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 10, 2010, 11:24:57 PM
Wow.  Well thanks for mentioning that now that i have no space left on the board.  It would have been nice to know something like that a week ago.  Another project for the scrap bin.  Its useless as it is now.
Title: Re: Custom LPF build is distorted
Post by: J M Fahey on August 10, 2010, 11:41:46 PM
Hi shynicrome.
Your schematic is basically right ... maybe the Protoboard real world version has some real mistake.
Some doubts (I understand you drive it with your Pod, it's impedance is low for a passive guitar connected straight and that would cause an important level loss)
1) The frequency is right, around 3400Hz, which is very audible, specially on distorted sounds.
At 24dB/octave even more audible.
Will sound similar to using a 15" bass speaker for your guitar.
2) To "engage it", it should always be connected to the Pod output, and a switch should select between taking signal from the input jack or from the output of the filter.
3) For now forget about making it tunable, just get it working and after that, change whatever capacitors you need, but leave it for a second version.
4)Get it working on Proto first.
Good luck.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 11, 2010, 09:59:59 AM
I'm going to try to salvage this by integrating it into a tube preamp i built last year.  I figure i can run it off the spare 12v secondary on the transformer if i put in a small rectifier.  The tubes will give the extra gain i need.

Will a full wave rectified signal be good enough without extra smoothing caps since they will go through the 1000uf caps in the power section anyway?
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 11, 2010, 03:29:14 PM
Alright that didn't work.  I had everything hooked up and it sounded good for about ten seconds.  Then my signal slowly gave way to a loud hum.  I'm done.  I have no idea what happened, what fried, whatever.  And i don't have the time to find out.  I leave for college again this weekend.  So the soldering iron is off till christmas.  But i'd still like to know where the hell i went wrong.  Any ideas?
Title: Re: Custom LPF build is distorted
Post by: J M Fahey on August 11, 2010, 05:33:07 PM
Your schematic is good, so the problem is in the actual gadget.
Triple-check everything, measure voltages.
Post clear pictures of what you did.
Aren't you counting the IC pins backwards?
There's a zillion small mistakes possibles.
After you find it, you'll knock your head against a brick wall, saying nooooooooooooooooooooooooo !!!!!!!!!!! , *that* was all the problem ?????
Don't worry, we've all been there before.  :-[ :-\
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 11, 2010, 07:54:06 PM
Well thats the problem.  I HAVE triple checked everything, and can find nothing wrong.  Actually, before combing the LPF and the preamp, both worked fine, except for the volume drop that was a design error, not a build error.  The only problem that i can find is that there may be too much ripple in the dc supply, but is there really any way that could harm any components?  Its only like a +/- 6v supply.  Its not anywhere near the limits of the opamp, or anything else for that matter.
Title: Re: Custom LPF build is distorted
Post by: J M Fahey on August 11, 2010, 11:18:32 PM
No, ripple is not a *big* problem, only a nuisance.
Juat a thought: so far you have been posting the PCB software drawing, which is very specific.
1)Post a picture or two of your Protoboard.
2) Draw *by hand* the *real* schematic of what you actually have built, including input and output jack drawings, the power jack, wire colors, etc.
Forget the "official" schematic, draw with only the board before you.Also show your switching.
3)Last but not least, post the voltage on pin 6 on each op amp, as well as on pins 4 and 7. Also on pin3 of op amp 1, with and without the Pod plugged there. All referred to ground.
Also check continuity between input and output jack grounds as well as with the power supply centerpoint.
Well, that's all for now.
Good luck.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 12, 2010, 10:11:01 AM
its a dual package opamp.  Are those still the same pins you want voltages for?

And i'll try to get some pics and a drawing up later today if  i can manage it.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 12, 2010, 02:21:27 PM
http://www.flickr.com/photos/26826525@N05/4885957996/sizes/l/

here's the board.  I'm still working on drawing up a schematic.
Title: Re: Custom LPF build is distorted
Post by: J M Fahey on August 12, 2010, 02:51:32 PM
Hi shinychrome.
Then THAT is your problem !!!
The LT1001 is a SINGLE package op amp, with industry standard LM741 pinout !!!!!
What IC did you actually use?
Edit: Now I've seen your picture.
I see parts bent to different angles (to avoid shorts and problems they should basically be vertical, at least with this layout), plus you should try to find a cleaner wire layout.
I would get the thing going on regular plug-in ProtoBoard first, for easier debugging (and even pulling everything out in frustration and re-starting from zero) and only after satisfied I would put it in a Proto-similar PCB.
Wish you a pound of good luck and a ton of patience..
EDIT2: and what are those Germanium point contact diodes doing in your board????
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 12, 2010, 04:01:30 PM
Sorry i should have mentioned that sooner.  I used a TL082 opamp, but i just used a random opamp for drawing up the schematic.  I wish there was a cleaner wire layout, but with these stupid rat shack boards, it was the best i could figure out.  I know it sucks.  And i had already done the whole thing on a breadboard, except it was powered by a battery, and this was supposed to be the permanent build, not another troubleshooting phase. 

Here is the Schematic i've drawn up from the board.  I found and fixed two errors, one in the power supply (the 1k resistors were in series with the voltage rails, rather than with one end to ground) and another that should have stopped the whole circuit cold.  There was n connection from the output of the first opamp to the input of the second.  I have no idea how any got any sort of sound out of it before, but i don't anymore.  Fixing both of those things still has done nothing though.  nothing but hum city.

And the GE diodes were all i had around to build a bridge rectifier with.

http://www.flickr.com/photos/26826525@N05/4886278694/sizes/l/
Title: Re: Custom LPF build is distorted
Post by: J M Fahey on August 13, 2010, 01:24:01 AM
Now you see that drawing by hand what you actually built is better than any packaged solution.
1) The filter schematic is basically correct, just replace the two pots by fixed resistors, leaving both halves the same.
Make it work and then add the frills.
2) The PSU part is wrong.
a) As drawn the upper rail is negative, the lower one positive, the opposite of what you need.
b) *As drawn*, the upper electrolytic is reverse-biased, which being an electrolytic means it becomes some kind of short too.
You will hardly have more than 1V there, because reverse charged electrolytics have *very* high losses..
3) As drawn, the lower electrolytic is correctly biased ... but it supplies positive voltage into the negative rail.
4) Please replace those 1N34 with 1N4002.
Well, enough for today, good luck and post often.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 13, 2010, 08:56:03 AM
Ugh.  Stupid mistakes.  I'll try to get to them before i leave for school sunday.  But i can't guarantee anything.  It would be nice to get it working though.
Title: Re: Custom LPF build is distorted
Post by: joecool85 on August 13, 2010, 09:45:08 AM
Quote from: shinychrome0 on August 13, 2010, 08:56:03 AM
Ugh.  Stupid mistakes.  I'll try to get to them before i leave for school sunday.  But i can't guarantee anything.  It would be nice to get it working though.

It's ok, those stupid mistakes are the ones that always trip me up too.  By "school" I take it you mean college.  Where are you going/what are you going for?  I just graduated 2 years ago from UMaine with a BA in New Media.
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 13, 2010, 01:59:37 PM
Yeah.  I'm at cincinnati christian, majoring in classical guitar performance.
Title: Re: Custom LPF build is distorted
Post by: bry melvin on August 13, 2010, 03:48:29 PM
Isn't Music a second major there? or has that changed?
Title: Re: Custom LPF build is distorted
Post by: shinychrome0 on August 13, 2010, 10:59:34 PM
what do you mean?