some help with this 4049 based preamp..

[dschwartz]

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:



the output of the 2nd channel, before the tone control looks like this:



wich looks so pretty- tube-ish compressed smooth top wave...

BUT..the wave after the tone control looks like this


yikes!!!that wave looks to me like fizzy fuzzy splatty farts

the frequency response before (green)vand after the tone control :



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??

[bioroids]

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

[dschwartz]

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?

[bioroids]

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

[zencafe]

Did u try buffering? The input impedance of the tonestack looks pretty low to me...

Nos vemos el Viernes!

D.

[snap]

there is a DC path from the outputs of U1 and U3 towards ground, if that matters?

[dschwartz]

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....

[bioroids]

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

[dschwartz]

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..

[grapefruit]

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.

[earthtonesaudio]

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.

[dschwartz]

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

[grapefruit]

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.

[puretube]

Yes, those "tubelike" rounded-tops waveforms can look soft,
but: watch the slopes...

[grapefruit]

Daniel,

What software are you using for the simulation? I've been looking for something like that.

Stew.

[grapefruit]

Indeed, if you decrease the time divisions on the scope it becomes more obvious how square it really is.

Stew.

[dschwartz]

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

[rankot]

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.

[rankot]

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.

[DDD]

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