Since i absolutely LOVE 4049´s based distortions, i started to design my own preamp using these devices..
i want it to be a 3 channel, independent gain, volume and tone control for each channel (AMZ BMP tone + presence control)..
the basic idea (i took mark hammer´s advices) is an opamp gain stage as a first stage for all channels, with a gain of 10 or more--
channel one is a single inverter, with little gain, then tone control..
channel 2 is basically an opamp boosted red llama, with tone control at the end..
channel 3 will have 3 inverters..i´m still working on channel 2..
now.. my doubts:
this is the schem of the 2 first channels:
(http://diynoise.googlepages.com/galva.gif)
the output of the 2nd channel, before the tone control looks like this:
(http://diynoise.googlepages.com/gal1.gif)
wich looks so pretty- tube-ish compressed smooth top wave...
BUT..the wave after the tone control looks like this
(http://diynoise.googlepages.com/gal2.gif)
yikes!!!that wave looks to me like fizzy fuzzy splatty farts
the frequency response before (green)vand after the tone control :
(http://diynoise.googlepages.com/gal3.gif)
if i change the "body" control the post tone wave turns soooooo ugly!!!!!
now.. is that normal on tone controls or effectively the tone control is affecting the inverter so the output turns so ugly??
I think any change the tone control could introduce to the inverter stage, would be visible right at the inverter output.
Are you sure that's not how the waveform should look after that particular filtering you are applying?
Greetings
Miguel
Quote from: bioroids on September 20, 2008, 04:35:14 PM
I think any change the tone control could introduce to the inverter stage, would be visible right at the inverter output.
Are you sure that's not how the waveform should look after that particular filtering you are applying?
Greetings
Miguel
i´m not sure..that´s what i am asking..
i put the input signal through only the tone control, and the sinewave only changed its amplitute,
maybe clipped waves change forms with this filtering?
Quote from: dschwartz on September 20, 2008, 05:16:43 PM
i put the input signal through only the tone control, and the sinewave only changed its amplitute,
So that seems to be working ok. Weird
Did u try buffering? The input impedance of the tonestack looks pretty low to me...
Nos vemos el Viernes!
D.
there is a DC path from the outputs of U1 and U3 towards ground, if that matters?
Doug.. yes i used a buffer, and the same result..finally..since everything looks OK, i made a simple diode overdrive ( a la mxr dist+), and had the same kind od response..
i concluded that that´s the way the wave looks when is clipped and then filtered..only sinusoidal curves were unaffected in shape..
strange....
Does the weird waveform change in different positions of the filter?
That DC path, I don't know if it may cause this behaviour, but I'd try blocking it with a big cap going to the low-pass part of the filter
Saludos!
Miguel
dc bias shouldnt affect, apart from scratchy pots.. i tried blocking dc and the result is the same..
i´m working on a "cmos-lab" buard i designed, that includes the BMP tone control and the opamp gain stage..maybe in real life it still sounds good..
Quote from: bioroids on September 25, 2008, 04:14:01 PM
That DC path, I don't know if it may cause this behaviour, but I'd try blocking it with a big cap going to the low-pass part of the filter
Saludos!
Miguel
Yes, I'd definitely put a DC blocking cap on the output of the inverter.
The signal on the output of the inverter IS pretty square. It's possible that the waveform should look like that after the tone control, depending on the tone control settings.
Is this all simulation? The frequency response looks reasonable for that type of tone control (without calculating the response).
If you vary the level and/or frequency of the sine wave I think you'll find that the output waveform changes. Is the input a 1kHz sine wave? If you turn the tone control to the bass end and have the body control so it's not scooping the output should look closer to a sine wave.
You really need ears to test a tone control. I reckon if you build it and have a DC blocking cap there it will work fine.
Cheers,
Stew.
That waveform look just about right for a differentiator or high-pass circuit, assuming a square or rounded square input waveform. I'd reckon it looks a lot different when you turn the control toward the bass side.
Quote from: earthtonesaudio on September 25, 2008, 05:23:03 PM
That waveform look just about right for a differentiator or high-pass circuit, assuming a square or rounded square input waveform. I'd reckon it looks a lot different when you turn the control toward the bass side.
on the bass side it looks like a triangle wave (integrator)
grape fruit..the schem posted here is just for proof of concept.. on the real thing there will be dc blocking caps
Well congratulations, you have a perfectly working tone control :)
Since what you are putting in is pretty close to a square wave you have the correct output.
Cheers,
Stew.
Yes, those "tubelike" rounded-tops waveforms can look soft,
but: watch the slopes...
Daniel,
What software are you using for the simulation? I've been looking for something like that.
Stew.
Indeed, if you decrease the time divisions on the scope it becomes more obvious how square it really is.
Stew.
i´m using LTspice..it´s cool, it´s easy to use, and it´s FREE!!!
it´s like pspice, but free..you can simulate any kind of ckts..even tube amps
I know it's quite old thread, but I don't where else to ask: what parameters did you use to simulate CD4049B as amplifier? I tried similar schematic with default parameters (VDD=9 SPEED=1 TRIPDT=5e-8), but I get only HF oscillations.
I've found this model in Super Spice, so if anyone needs it, download Super Spice and it is there, listed as AINVERTOR_BUFFERED1_XN.
Some new design ideas aimed to improve CD4007UB-based overdrives.
***The article is in Russian. But, there are some sensitive items, so I think if somebody can translate it ...
http://forum.guitartonelab.ru/cgi-bin/yabb2/YaBB.pl?num=1514838111
(https://i.imgur.com/n6V2eb0.png)
This is really interesting overdrive design. I've modelled it in LTspice and it works fine. Breadboard is next!
Fitting source resistors to the 4007 X3,M3 pair like that carries a risk, since those pins are the chip Vdd and Vss connections. You must be sure none of the other pairs channels can have voltages exceeding those source voltages by more than 0.3v WRT Vdd or Vss or else the substrate diodes will start to conduct and you have unforeseen interactions going on - which might sound good, I don't know - I've always avoided it.
The internal diodes go from channel to P or N substrate and the appropriate power pin - not strapped to source as shown, which is of a conventional discrete MOSFET symbol.
Playing with CD4007UB I've found the following method to avoid the unwilling conductivity of substrate diodes:
1. Source resistors at X3 and M3 should be at least two times less than resistors at X1,X2 and M1,M2 sources (3.6k and 8.2k respectively);
2. Source resistors at X3 and M3 (pins 14 and 7) should be shunted with the big enough capacitance - 10...100 uF depending on the lowest signal frequency.
If so, there is no any interference between clipping and output (level compensation) stages.
*** By the by, the 8.2 kOhm source resistors in clipping stages seem to set optimal invertors' gain and current consumption (battery saving measure).
The picture shows schematic diagram of the output stage with 1MOhm volume control pot that is typically used with 3-knob tone controls.
This arrangement gives comfortable volume control curve.
(https://i.imgur.com/YYDPGif.png)
Dmitry,
If you have this already built (or on breadboard), could you please try to add a feedback loop like this:
(http://i66.tinypic.com/oicgh.jpg)
Simulation shows that with fixed resistor of 220k (which then sets minimum feedback) and 1Meg potentiometer, amount of overdrive could be nicely set from none to very much. I don't have parts at hand, so I can't test it yet.
Hi Rankot,
To my regrets, all of the gadgets have been sold out and I do not have possibility to check your idea.
At the same time I am sure that any feedback from the circuit output to clipping stage input will cause uncontrollable self-oscillations.
--------------------
By the by, you connected the output stage directly to the clipping stage, so the output stage will distort heavily. Hence you'll get sharp and "usual flat" distortion instead of "special MOSFET" sound.
I built this with feedback loop and interestingly - it sounds OK when using tone generator and small 2W amp for testing purposes, but when I connect it to real guitar and real amp, it starts to self-oscillate and the volume drops a lot. Without the feedback loop it works just fine!
With the feedback around the 3 sections, it could be a phase shift oscillator. The input RC networks on each section may need simplifying/rationalizing/omitting?
You're right, Jim, now I connected feedback only over the last stage and it works really nice! Thanks for a hint!
There's a schematic:
(http://i63.tinypic.com/21ahf69.jpg)