CD4049UBE....is it inherently noisy?

[powerplayj]

I tried out the Mr. EQ and like its versatility.  I haven't put it in an enclosure because it is quite noisy and I wasn't sure if the enclosure would quiet it down a bit or if the chip is just inherently noisy.  If it is inherently noisy I may just salvage it into a 3-Legged Dog or something that I want to be a little noisy in the first place.

[jmusser]

I'd guess it would be just the opposite, that the hex inverter would be inherently quiet. I would guess that any noise problem you have ought to subside once you box it up. I've built a couple 4049 circuits, and never had a noise problem.

[Joe]

CMOS chips are noisy, especially with 4 stages. You could build the circuit with inverting opamp stages instead with a little modification.

[markm]

I have found ocillation to be a problem with the CD4049UBE at times

[A.S.P.]

http://www.diystompboxes.com/smfforum/index.php?topic=47736.0

[powerplayj]

any capacitor >22p (<10n) from out-to-in will astound you... 

I don't understand....care to explain?

[markm]

any capacitor >22p (<10n) from out-to-in will astound you... 

I don't understand....care to explain?

The cap helps to remedy ocillation.

[A.S.P.]

http://www.diystompboxes.com/smfforum/index.php?topic=47736.0

[alteredsounds]

Coincidently I was going to ask a very similar question.  I love the Red Llama build but it does seem to have a large amount of hiss, more so than normal high-gain hiss.  That also uses a CD4049UBE.  Please anymore info on 'any capacitor >22p (<10n) from out-to-in will astound you...'.

Cheers,
Nick,

[A.S.P.]

http://www.diystompboxes.com/smfforum/index.php?topic=47736.0

[alteredsounds]

Thanks a.s.p Mr Hammer in your great wisdom could you shed some more light on this

[powerplayj]

when you are saying output to input are you talking about the the chip itself?  Maybe using this schem as an example would help explain it to me.

[Transmogrifox]

Most of the stages in the Mr EQ have what was mentioned.  It's just like the 100p capacitor connected from pin 6 to pin 7.  The only place you could add one in this circuit where there isn't already is beteen 3 and 2.  I would recommend going on the 10p side--maybe 47p your maximum before the high frequency content goes away altogether.

If you're having "hiss" noise, then it won't get much better in a box.  MOSFETs in general are noisey at audio frequencies (CMOS is just a complementary pair of MOSFETs).  That's just the nature of using CMOS logic inverters as an amplifier.

If you're getting hum and buzz noise, then you'll want to filter your power supply better, and it's not the CMOS chips.  For me, the noise that would be generated by Mr. EQ would be tolerable into the clean channel on my amp, but quite atrocious into the high gain channel.

[Connoisseur of Distortion]

look at U1-b. There is a 100p capacitor in the feedback loop of that stage. what it's doing, combined with the resistors in parallel, is forming a HPF allowing the high frequencies to return to the input. In truth, the stage would be called a LPF, simply because the highs are only being returned to the input to be eliminated. The other cap (to ground) I do not recognize, but it looks like it's forming a LPF with the 'left' 270k for about 800 (check this, i'm not very good with numbers) Hz to return anything lower than that corner frequency to the input, and form a HPF stage. (We really do need someone else here...!)

Basically, take the input of a single inverter, and place a small capacitor to the ouput of that same inverter. simple!

[A.S.P.]

http://www.diystompboxes.com/smfforum/index.php?topic=47736.0

[B Tremblay]

I'd try putting it in an enclosure before modifying the circuit.

Mine's quiet, if that counts.

[Peter Snowberg]

looking at that circuit, I`d use metalfilmresistors to limit noise-generation.

+1

The higher the resistor value, the more thermal noise you get. The only resistor I wouldn't consider normally is that 1K.

[bioroids]

Hi!

At what resistance values does the noise starts to become important?
I'm currently using metal films for all values greater than 100k, should I got lower?

Luck!

Miguel

[Peter Snowberg]

It depends on the amount of current passing through the resistor. I generally like metal film for everything over (and including) 100K too. 

[bioroids]

That's good to know, thanks Peter!

Miguel