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Re: couldnīt make it happen..

7/19/2000 1:18 PM
Mark Hammer
Re: couldnīt make it happen..
The distortion I mention is entirely due to something about the audio signal path, and is NOT due to ripple in the envelope voltage, as many people have found with different commercial units (Ibanez Auto-Wah, Dr. Q). The audio signal path itself is pretty simple: a one-transistor buffer, and a (Sallen-Key?) bandpass filter. I am going to have to check the transistor, since it was cannibalized from something else. I hope there is no heat damage. Maybe that is my problem.  
Once you get the design working and finalized, it would be good to include a brief note on the schematic about including a fixed resistor or trimpot on the emitter of the range-setting transistor.  
"you can get it to work with a momentary push-button switch to go wahwah by pressing the switch"
I don't think this would do much for a guitar player, but DJ's would find it interesting. One company (Electrix) has already had a great response to its filter module, BECAUSE it includes a big momentary switch.
And now, a word from our sponsors:

7/20/2000 7:59 AM
Hemmo P.

"I hope there is no heat damage. Maybe that is my problem."
No, the design really stinks.. breadboarded version was suffering from bad sound even with a 47k before the filter and 100k in FB-loop.  
"Once you get the design working and finalized.."
I honestly have to say that Iīve pretty much given up the circuit, I canīt get nothing good out of it,  
not even anything that would be īweirdī in a good sense.  
The push-button Wha would be something that i would like as a consumer, youīd have to see the circuit to know whatīs really happening there..  
The envelope section consists only two resistors and one big elco cap, and I streched it to have SIX POTS, just the envelope itself plus gain pot and two momentary switches.. with these you can really control the effect.  
But of course envelope filter would be much simpler to handle in a commercial kinda way.. I think you were right about different envelope types, I should try the Mutron III(possibly with the env. driving tranīs instead of LED/LDRīs)  
Weīll see..
7/20/2000 3:33 PM
Mark Hammer

Don't give up yet.  
The envelope extraction part doesn't seem to have any obvious problems. The only real problems seem to be in the audio path, and perhaps some issues to be solved in selecting transistors and biasing components.  
I like the way it responds to my playing. I just wish it wasn't so distorted. Could you try a simple op-amp buffer on the input?
7/21/2000 8:03 AM
Hemmo P.

"Don't give up yet."
Ok, I wonīt, but I am VERY frustrated on the circuit..  
Reason for the transistor buffer is to make the ouput non-inverted, it also gives a bit boost but it īdistortsī even without the buffer, so it doesnīt really matter.  
It may be difficult for you to replace parts if you did it on a perfboard(and tightly packed?) but try replacing the gain making resistors, one before the IC and and in series with the pot, both into 47K or the series R into 1K.(unless you already have)  
BTW I noted that the envelope is(or isnīt?) missing a resistor and a cap in the op-amps inverting input to GND..(if we refer the schem on slow gear attack decay)but that probably wonīt matter either.  
hanging on, Hemmo P.
7/21/2000 1:53 PM
Mark Hammer

Thanks. I'll try what you mentioned. I'm using some cheap magnifying reading glasses I bought at the bargain store (3.5x) so it's easier to inspect and work in those little places now. I should be able to get at it. (I think the secret is NOT to use 1/8w resistors on their ends!).
7/24/2000 7:03 AM
Hemmo P.
made it happen..
I think I got it working, just a few minor tweaks  
and the tone came good.  
I replaced the buffer with IC one, and took off some gain and reduced all the caps in the audio path.  
You can try to replace input cap, and one in the middle to 100nF and the output cap to 470nF.  
I think that this limits the available signal some degree.  
Hemmo P.
7/24/2000 4:23 PM
Mark Hammer

Thanks for your perseverance. I hope to try the changes this week.

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