Muff's Modules & More

[daverj]

A few thoughts:

Inputs to op amps are more sensitive to noise and inductance than the outputs. If you are going to stand resistors up you should reverse the direction of R1, R3, R5, and R6 so their bodies are connected to the inputs of the chip and their leads that are up in the air are facing away from the inputs.

Move R1 and R3 closer to the chip so there isn't so much copper trace between the chip and the resistors. R2 and R4 placement is not critical. They can go wherever they fit.

The ceramic bypass caps should be as close as possible to the chip. The electrolytics and 10 ohms are not so critical placement. They can be further away than the ceramics and other parts.

The ground connection for the ceramic cap going to pin 8 should be short and direct to the ground connection of the ceramic cap going to pin 4.

[DGTom]

this thread keeps on giving!

Great tips thanks! I wasn't aware of the critical nature of placing upright resistors.

I always put the electro/10ohms right next to the power connector as every synth PCB I've seen does this.

Thanks again

[daverj]

The ceramic caps pass high frequencies much better than electrolytics, which is why the ceramics need to be as close as possible to the chips. They kill spikes and oscillations. The electrolytics pass the medium and low frequencies which the ceramics don't, so their placement is less critical. They kill ripple.

The resistor gives isolation from the power supply and helps the caps to act as low pass filters.

If there is only one 10 ohm and electrolytic for the whole board, and there are multiple chips, then the resistor and electrolytic would go by the power connector and each chip would have the ceramics right at the chips. If there's only one chip on the board, then might as well put them closer to the chip.

Another school of thought is to put a ceramic, electrolytic, and resistor at each chip. In that case they would all be near their chips. In general that is overkill, except on some really noisy chips or chips very sensitive to power noise. Most op amps aren't so sensitive to power supply noise, so one set of electrolytics and resistors for the whole board is usually fine (maybe more electrolytics if the board is large).

If a chip draws a lot of fluctuating current, then having it's own electrolytic (in addition to the ceramic) is a good idea.

[Funky40]

it was just a first try with lochmaster, and the first try with a stripboard layout

[DGTom]

yeah heaps of my DIY modules have no de-coupling & prob. break every rule daverj has outlined. To begin with its just fun to get something working & play around, I think its a good idea to know, even just in theory many of the rules, even if you don't understand them or always use them

vital knowledge when, at some point, things start misbehaving!

hey Funky, maybe we should have a Lochmaster thread to swap tips & tricks etc. I've found it very usefull in getting cleaner & faster protoboard builds up & running

very cool little app.

[daverj]

I wasn't trying to say things won't work if you don't follow layout rules. Lots of circuits work great without any care for the rules.

But at least being aware of them removes some of the "black magic" that confuses people when they get noise or crosstalk they didn't want.

Understanding them even helps when you do want extra noise and crosstalk.

[Moog$FooL$]

[wetterberg]

"I'd like to build an inverter..."
"Oh no you wouldn't!"


- ahem, sorry, lame joke

[Funky40]

[SOFTWIRE]

so can someone tell me the difference from the 4069 inverter and the 40106 schmitt trigger inverter or can they be used interchangably?(not the chip itself, just the function)
Thanks

[DGTom]

As I understand it.

The 4069 is *just* an inverter whereas the 40106 is a little 'smarter'

http://en.wikipedia.org/wiki/Schmitt_trigger

I think its actually 3 inverters + the schmitt, so the output is really, really square. I have read of people having problems with the 4069 as a standard inverter w/ less than clean input signals.

the 4069 makes a great fuzzbox tho & as I've found out, a great (albeit crunchy) low pass gate!!

[SOFTWIRE]

thanks it makes alot more sense now.

[frijitz]