CD4049 circuit driving me nuts... why is it doing this!?

[Connoisseur of Distortion]

ok. i know how to use this chip (i think). i have a 5 volt regulator, the chip is a 4049UBE, the unused inverter is tied to V+, and it KINDA works. what i am looking for is a solution to a chip-related issue (again, i think)

i power it up and hit an open chord. it starts with oscillation, but then releases a huge, thick distortion that is absolutely breathtaking (i am using a FET stage followed by 5 inverter stages, if you follow). as it fades away (kind of fast, things considered) i continue playing. to my dismay, it is getting quieter and weaker.

it seems that my guitar signal is no longer as powerful as it was, almost as if the chip is anticipating my pick attack and then setting it as the new threshold. if i absolutely slam the strings, a blip of sound gets through, but even that is gone now.

any ideas? please, i am absolutely tapped.

[gez]

Schematic?  Voltage readings? 

[MartyMart]

Which circuit ?
Or, is it one of your own ?
I've had similar problems and some that "almost work" some that flat out
just "don't work at all" !!
I got my "Three legged dog" to work perfectly, Craigs "Tube sound fuzz" would
just stick on "high gain" permanently and the "Hot Harmonics" and "Red Lama"
I just could not get to work.
All these were with 4049UBCP and 4049UBE
Three legged dog has a 4049UBCP in it ....... !!!

Perhaps they are more prone to "static" problems than we think ?

Marty.

[JimRayden]

Exactly the same problem as my Whisker Biscuit a while ago. Couldn't track it down though...


PS: Is it just me or there's a huge interest in 4049 circuits lately.

---------
Jimbo

[MartyMart]

Exactly the same problem as my Whisker Biscuit a while ago. Couldn't track it down though...


PS: Is it just me or there's a huge interest in 4049 circuits lately.

---------
Jimbo

The Interest has "reappeared" but I dont think it ever went away !!
My guess is that these chips are "hyper-sensitive"  !!

Marty.

[gez]

My guess is you're making a mistake somewhere.  Hard to believe, but it happens! 

[Stevo]

 You said it works once when you power it up than nothing...Do you need to power it up again to make it work?  One thing in a thread a while ago 2-3 stages is enough with modest gain structure than you need, anymore is asking for trouble they said!! ,, Seems you have a pulldown on the circuit now I am just throwing out ideas!!  Is the fet functioning properly that is the input to the chip it needs biasing good ground etc......jump a connection off the fet output to the output jack do you get sound than the fet is working?? The wiring must be intense for 5 stages but is it grounding out somewhere a problem?? I would use 3 stages at tops but you want this to work now I say this is a problem too, 5 stages? Do you have a gounding cap say 100uf maybe it is bad? Just bypass it to test? Are you looking at the chip in the right angle 1 is power 8 is ground and the input outputs to the chip are different on one side?  Sure sounds like a gounding problem a short or cold joint maybe a joint on the jacks?? use some jumpers to test .........Good luck

[remmelt]

What happens when you use the audio probe? At what stage does it start this behaviour? If you haven't, you should really try the probe, it saves lives. Seriously.

[R.G.]

Things that show fading in or out, and especially when they fade so only stong chords cause a blip are almost always related to a bias fading problem.

I'd have to see your circuit to point out the particular parts to you, but I think you have the thing set up so that the bias changes with signal and never recovers.

[Connoisseur of Distortion]

i wouldn't mind posting a schematic, but i don't have an editor on hand, so i'll just describe as best i can.

the input stage is a mu-amp. no, it's not precisely a minibooster, but very similar. i used it so that i could have a ready bias on hand with different voltages (from adapters). it seems to be working properly, as i get half supply voltage (not from regulator, btw) at the drain of the amplifying FET.

from there, it couples into the first stage. the first stage uses a 1M feedback pot, and 1M input resistor (goes to ground at input). the second stage uses a 100k feedback R, and a 1M input R. third stage uses 2.2M feedback R, and 100k input R. fourth stage has 1M feedback R, no input R. fifth stage uses 100k feedback R, and 4.7M input R

all stages are coupled using .01 uF caps. i have not yet applied low pass filters into the feedback loop, but i intend to (to keep off the oscillations).

my mu-amp was made with a pair of NTE458s.

my power section is not currently using a power cap (i pulled it) and uses a RS bought 7805 for the voltage supply. yes, it works fine. it puts out an amp, too, so i think that it can safely be ignored.

R.G. , i have never heard of a bias fading problem. how would the bias continually change with the signal? is it related to ripple? can you identify potential problems based on my (lame) description?

remmelt, i have used an audio probe before, but i don't know what benefit it would do me now, as the issue is one that changes with time. i might entirely miss the event that is causing the problem. i just feel that the probe would cause me more frustration than relief. has saved me on a number of other builds, though...

stevo, i think i will try bypassing the 4049 for now, to see if it is the problem child. i think i'll put back my power cap and i'll try that, too. i have the pinout right, though. i had a data sheet next to me for the whole build, because i didn't want to mess it up.

gez, firstly, SCREW YOU I DON'T MAKE MISTAKES ( ). i would be happy to post a schematic, but i don't have software to do so (speaking of which, what's the norm around here?). i will post voltage readings after i try some suggestions.

and i agree with everyone that there has been interest in the 4049 lately. i have been throwing this thing together (that is drawing schemo, then breadboarding) in spare minutes over the summer, and some of my previous results have been very satisfying. for some very stupid reason, i chose to perf this version, because i though that this would be the defining version. it sounds incredible in the 5 seconds it works, believe me.   

[gez]

gez, firstly, SCREW YOU I DON'T MAKE MISTAKES ( ).

Actually, my comments were in relation to this quote:

My guess is that these chips are "hyper-sensitive"  !!

But please feel free to tell me to screw myself Marty!

the first stage uses a 1M feedback pot, and 1M input resistor (goes to ground at input).

Why does it go to ground?  Are you trying to create asymmetry or something? 

Bypass the 4049 like you said and see if the input stage is working.  If so then post voltages for the 4049.

[Connoisseur of Distortion]

actually, i just got back and the input stage is NOT working properly! this could be easier than i hoped! thanks for tips, will post updates!   

[Stevo]

So there hopefully is a pulldown on your circuit in the fets?? Man you have some helacious gain structure for your stages if I read them right... I would like to know if you can keep it from oscillating with so much gain in the chip? Lets us know what you did and how it sounds? Stevo

[Connoisseur of Distortion]

in the minibooster lookalike i threw together, i kind of made do on some parts, dropped things that didn't look important, and added things that i thought would be beneficial.

one thing i wildly butchered was the capacitance between the grid and source of the top FET. could this be a problem? mines closer to... 33 uF 

[Stevo]

I think the mini booster circuit is a stand alone scheme.. In other words I dont think you could drop something or add anything to make it better.. In fact it probably wont work unless it is built to spec.. I would try and build one to spec and than connect to your chip.. you peobably will have a better chance of it working...You can change the caps in the gate to source in the middle to a lower spec but I wouldnt go higher than the 3.3 non polar it calls for!!!! It would need to be non polar like a .1uf or .22uf but that would be around a good range if you do go polar put the negative towards the bottom fet......

[Connoisseur of Distortion]

i think i am going to take a break on this for a bit...