Double D Help

[Moo]

I built the Double D from Runoffgroove, and although it works (slightly), I have problems. The output level is way too low (less than unity even at max gain + volume). The jiggle channel sounds ok, but the bounce channel sounds "blatty" and doesn't have nearly as much gain as the clip has. The gain isn't much more than the jiggle channel's gain. I tried swapping CMOS chips, but with no effect. Does anyone else have that problem, and can anyone help?

[Peter Snowberg]

Welcome Moo,

I'm just wondering from your comments if your 4049 has a U in the suffix?

The 4049 comes in two versions. The version with a U in the suffix is the unbuffered version and this is what you want for analog use. The regular version of this chip uses three inverters in a row and it will sound really bad if you try to use it in an analog circuit.

Another question worth asking is have you checked the voltage from your battery or power supply? I really don't like the sound of lots of circuits when the power gets too low. Just an idea.

I have not built the Double-D myself, but when everything is in place you should have no shortage of output level and it should sound really good too. I've been very happy with the CMOS inverter curcuits I've built.

Keep on working at it. The solution is out there.

-Peter

[will]

Hi Moo,

I built that circuit and the bounce channel should have considerably more gain / volume than the jiggle.  If the jiggle side sounds good, then you know that over 60% of the circuit is ok.  I would expect the 4049 is ok and the power to the chip and the FET's are ok.

I would start by checking the gain & volume pots for the bounce side. I had a similar experience with building the fat gant & the blues breaker. A batch of 100K pots that I purchased were bad. I would check all of the connections to ground for that side and the values of the resistors. Also check your 4.7uf cap the negative side should be towards the volume control. If you used a tantalum cap incorrectly it is probably toast. Also check your layout weed out any part placement errors. Also check your soldering, a cold solder joint or an unwanted solder bridge will always cause problems.

I hope you find the problem fast. This is a good sounding petal.  


Regards,
Will

[gez]

The jiggle channel sounds ok, but the bounce channel sounds "blatty" and doesn't have nearly as much gain as the clip has

Are you sure all the inverters are biased properly?  Check the voltage at the output of each stage, they sould be round about half the supply voltage.

[Peter Snowberg]

One more idea.... Do you have the input to the unused inverter grounded?

CMOS chips are subject to a condition called "latch-up" which happens when parts to the base chip structure start acting like parasitic transistors. This odd condition causes power to flow through the structure of the chip where it shouldn't, resulting in malfunctioning of the chip. I get it all the time on breadboards when I forget to connect all the inputs or to ground the unused ones.

-Peter

[Moo]

The part number is CD4049UBE. Both channels are at less than unity gain when cranked up. I haven't measured the CMOS voltages, but the supply is 9.0 volt regulated, the drain on FET1 is 5.0 volts, and the drain on FET2 is 8.9 volts. Would that be any help?

I'll try resoldering everything pretty soon, unless there is a more immediate solution. Thanks.

[gez]

There are no dividers at the outputs of this circuit, so with the volume pots cranked up the ouput should be huge!  Check all connections, pin-out of both FETs, wiring of pots and measure voltages at the output of each divider (edit: I meant inverter...sorry!).

[Mark Hammer]

I think we can pretty much promise that it's gonna be something that will result in the butt of your hand striking your forehead.  Just the gods way of keeping us humble. :wink:

[Gary]

Moo,

Double check the pinout of the 4049.  It sounds like you may have an input and and output of an inverter mixed up.  I've had this happen in breadboarding.  It can sound much like you describe.

When you sort your problem, the output is very big.  You'll have to run the volume knobs under 12:00 for unity gain.

Good luck!

[Moo]

Boy am I stupid.

The first try, I had the CMOS in, but nothing came out. I switched the direction of the chip and it worked, but with problems, and then posted on this site. I flipped the chip back around like Gary said, and replaced it with a spare chip. It worked. Beautifully.

The first chip I had was a dud. What a pitiful solution for a pitiful problem.

By the way, would having the working IC flipped around and 9V connected to some random pin have damaged the IC in any way? Output level is huge, but is noise performance affected?

Another thing--would putting a resistor from effect output to ground for millennium bypass affect tone? And what size resistor if it doesn't affect tone? I have a mil2 bypass in it, and the LED (blue) slowly turns on when bypass is engaged sometimes, and I heard that a resistor helps. Thanks.

[gez]

By the way, would having the working IC flipped around and 9V connected to some random pin have damaged the IC in any way?

Put it this way, whenever I make wrong connections (especially with MOSFET stuff) and only realise once I've powered the thing up, I'm amazed if it works at all once the thing is wired correctly!

Another thing--would putting a resistor from effect output to ground for millennium bypass affect tone? And what size resistor if it doesn't affect tone? I have a mil2 bypass in it, and the LED (blue) slowly turns on when bypass is engaged sometimes, and I heard that a resistor helps. Thanks.

You need ‘pull down’ resistance of some sort at the output in order for the Millennium to work.  The Double D is buffered so this resistance doesn’t have to be enormous.  

Why not stick a 100k pot at the output instead of a resistor to act as a master volume? (would allow you to overdrive the FET for even more sonic mayhem).