4049 gating

[aron]

For you guys using the CD4049UBE, how are you guys getting around the gating? No matter what, I hear a slightly unbiased gating sound in the tail of the note. Even when I apply a DC bias to the input, I still hear it. I remember having this problem with the Insanity (subsequent versions). I wonder if it's the make of the chip. For you guys not getting gating, where did you get your chip and what brand etc...??

[MartyMart]

I seem to be fairly unlucky with cmos builds ! ... however the best results I've had are from using
TI chips ( 4049UBE ) these are from Smallbear.
I also have some 4069UBE's with an " ST " logo, ( ST Microelectronics ) which seem to be fine.
I think these came from ESR.

My recent UBE-screamer for instance, when set for high gain produces a sort of gated/digital cut off
But low to medium gain is 100% perfect ! ?

MM.

[puretube]

OK, I used , and found this schemo.
Haven`t ever built it, but the large 10µ cap at the inverter`s output might give it a hard time to charge/discharge it with the limited inverter`s drive-capabilty/high output-Z.
I`d try 100nF.

just a thought...

[JisforJustin]

I think it has something to do with the supply voltage, or possibly the supply current. If I use a fresh 9V battery to power it, at high gain settings I do notice the trailing effect. However, if I use a battery that is maybe half drained, the trailing seems to go away. I think it could be more of a current issue, though, because I noticed if using sections as oscillators the pitch is affected by supply current, not voltage.

Justin

[aron]

If I use a fresh 9V battery to power it, at high gain settings I do notice the trailing effect. However, if I use a battery that is maybe half drained, the trailing seems to go away.

Interesting. I am using a low ohm resistor to limit current. I will try different values. I will also try a reduced voltage and see what happens.

I am using a Ti CD4049UBE. I am not making the Insanity. I am trying to breadboard a more simple design as a test.

Thanks!

Aron

[JisforJustin]

That would be a great test. Let me know what you find.

Justin

[MartyMart]

If I use a fresh 9V battery to power it, at high gain settings I do notice the trailing effect. However, if I use a battery that is maybe half drained, the trailing seems to go away.

Interesting. I am using a low ohm resistor to limit current. I will try different values. I will also try a reduced voltage and see what happens.
Thanks!
Aron

I just tried using a battery reading 6.4v and it made no difference .... hmmm ... onwards !
( I just had less overall volume )

MM

[JisforJustin]

I just tried using a battery reading 6.4v and it made no difference .... hmmm ... onwards !
( I just had less overall volume )

Yeah, hmm.. I just tried it too, and this time it did not work. Maybe I'm just an idiot.

Justin

[aron]

I won't have time to test until tomorrow. This is very troubling. I wonder how Mark Hammer's pedal works.... is there gating?

Are you guys direct coupling the stages or are you bypassing with a capacitor? I wonder if that makes any difference? (Doubt it).

[The Tone God]

Are you guys direct coupling the stages or are you bypassing with a capacitor? I wonder if that makes any difference? (Doubt it).

You can either way depending on the circuits needs. If you need to you can rebias the signal on the input either through changing the feedback amount or putting on a dedicated bias control like in the schematic Puretube linked to.

Andrew

[Mark Hammer]

I won't have time to test until tomorrow. This is very troubling. I wonder how Mark Hammer's pedal works.... is there gating?

Are you guys direct coupling the stages or are you bypassing with a capacitor? I wonder if that makes any difference? (Doubt it).

I've never knowingly experienced any sort of gating with 4049-based pedals.  I'm not saying I don't encounter it, just that I've never noticed it.  Is this the sort of thing that studio quality sound/levels would be required to detect?

I brought one to a store on Saturday for Hairyandy (from the forum here), the guy who makes the Retro-Sonic pedals, and the guy who owns the store to try out.  They played it through some sort of boutique-ey Tweed Deluxe and nobody reported any sort of odd nuances to the tail of the notes.

[puretube]

You used the same circuit, Mark?

[Mark Hammer]

I used this but without the frequency booster segment, and with a 1-10uf cap between points A and B.
http://img.photobucket.com/albums/v474/mhammer/Forty-Niner.gif

[puretube]

ah: it`s got the inverters decoupled by a 0.1µ...

[aron]

If you need to you can rebias the signal on the input either through changing the feedback amount

Andrew,

Can you elaborate on this? Do you simply mean changing the feedback resistor?

Mark,

I directly coupled 3 stages together, used 100K resistors as feedback resistors. I tried with 1M input resistance to ground and without (like yours).  I am assuming your 9V+100uF cap is to pin 1 for supply voltage.

I didn't try decoupling yet.

Thanks,

Aron

[aron]

One more question - how DO you bias this chip? Is it internally biasing or? AFAIK Mark's schematic and others do not apply any DC bias to inputs.

[Mark Hammer]

Mark,
I directly coupled 3 stages together, used 100K resistors as feedback resistors. I tried with 1M input resistance to ground and without (like yours).  I am assuming your 9V+100uF cap is to pin 1 for supply voltage.

Yes on the last question.
I've actually never built anything using 4049's without the decoupling.  What does the old Hot Tubes use?

[aron]

The MXR uses coupling.

http://www.montagar.com/~patj/mxrhott.gif

OK, WHY am I not coupling? 

[puretube]

I can`t contribute to all those known "TSF" & "HT" circuits that flood the web,
coz I never tried them.

But I read that the inverters are automatically biased to Ub/2 by the feedback R from out to in. (Datasheests, App-Notes, & RayMarston).

Also I read that they work like inverting opamps with an (input) series-R
and a feedback-R.

Now when you don`t use a series-R, you`re attempting to rise the gain to infinity,
which doesn`t work with this chip.

The other thing I can imagine is,
that if additionaly to not having a series-input-R
and there being no decoupling cap between the stages,
the individual inverters *might* have slightly different "mid"-voltages
they are trying to bias to with the help of the feedback-resistor,
but that the slight difference between those "mid" voltages is the "threshold"
below which the signal gets "gated".

[puretube]

yes: I designed a couple of CMOS inverter based circuits over the past year,
but these aren`t comparable in topology with those "wellknown" pedals...