74HC04 vs SN7404n notice

zjuyzj / OPL2LPT-Replica

A re-designed, simplified version of OPL2LPT Adlib-Compatible sound card working on printer port.

MIT License

23 stars 4 forks source link

74HC04 vs SN7404n notice #2

Open zhblue opened 3 years ago

zhblue commented 3 years ago

a second hand IC maked "sn7404n england" works fine with 470 ohm resister but a brandly new IC maked "74HC04" from JLC market need a 4.7k ohm resister to work with. i have no idea about why , just post here for people who might need it.

zhblue commented 3 years ago

the extra 470 ohm resister can be used parallelly on the outer two pin of volume control, make volume adjust more smooth.

AidenShaw2020 commented 2 years ago

I had same issue, that me get almost crazy, but resolution is pretty quite simple :) Only what you need is change oscilator circuit from this: , to this:

After that, you get perfectly stable frequency +/-1Hz.

dekkit commented 2 years ago

Interesting i had a batch of SN7404n (ordered 5) ..4x worked with 470R.

..but 1x pcb needed both 470 replaced with a 4.7k.

I suspect anything above 1k will work more consistently.

Note (new builders):

if building the circuit the first time - becareful and pay attention to the dots and chip orientation (as labels written on the pcb arent necessarily orientated the correct way)

badass-boss commented 1 year ago

These values must still be just downright incorrect. This card doesn't work right at all using all original mouser parts linked in the BOM. 1K resistors paired with a 100pf cap generate a TON of random noise and loud glitches and the FM music gets all corrupted at all times. When changing resistors to a higher value, the issue is fixed and I think this card works best with 4.7k resistors. What are these resistors even supposed to achieve and what is the configuration of the original Adlib card?