Megadrum 32 input - Input problems!

[stellari81]

Hi all!, I begun to build my MD about the beginning of this year and then for work reasons I had to stop a few months.

Now I took the whole thing and started out again. I preferred to build some input PCB rather then solder jacks directly to the 40pin ide connector.

I re-designed the 4051 input board to accept 4 4851 (without diodes) then I designed 4 boards to place the jacks. I double-checked all the schematics, connections, PCB tracks and soldering and all is fine except this:

(in pseudo-order):
Bassdrum WORKS!
everything alse SUCKS!

for example, snare does nothing, ride activates a few input together! some inputs make a repeating fast tamtamtamtamtamtam sound (I mean, when connected to a MIDI synth) and so on...

Can faulty 4851 be the problem? is there a way to test if all 4 4851 are working?

Thank you all!

[Pete Predictable]

Is the clasic tamtamtamtamtamtam sound generated from the synth' using the hihat controller output?

+ Read the documentation to reset (initialise) your megadrum.

+ Remember Megadrum uses channel 10 (percussion) so make sure the note assignments of this MIDI channel correspond to your synth'/sampler instruments.

[Firelord]

I re-designed the 4051 input board to accept 4 4851 (without diodes)

Did you replace the 32 input 100R resistors with jumpers?

Bassdrum WORKS!

Can faulty 4851 be the problem? is there a way to test if all 4 4851 are working?

If the kick input is fine chances are that everything else on that MUX is also in order. Still, it is VERY unlikely that you managed to kill off 3 out of 4 MUXes somehow. Plug the kick to different channels and see if it works there.

Or else remove all the MUXes except the one you consider working (which muktiplexes the kick channel) and place it into other sockets, see if that changes anything.

[jman 31]

If you are using Synthex's inputs with Dmitri's board you will have problems. They are not meant to work together.

[stellari81]

First of all, thank you for your interest.
Now, I completly designed input board and jack boards from scratch to be fully pin compatbile with original dmitri version.

I re-designed the 4051 input board to accept 4 4851 (without diodes)

Did you replace the 32 input 100R resistors with jumpers?

No, I didn't, I only removed diodes from design but kept the resistor as input current limiter, I may try removing them but I don't think a 100ohm resistor can completly kill an input.

Bassdrum WORKS!

Can faulty 4851 be the problem? is there a way to test if all 4 4851 are working?

If the kick input is fine chances are that everything else on that MUX is also in order. Still, it is VERY unlikely that you managed to kill off 3 out of 4 MUXes somehow. Plug the kick to different channels and see if it works there.

Or else remove all the MUXes except the one you consider working (which muktiplexes the kick channel) and place it into other sockets, see if that changes anything.

Kick input is THE ONLY INPUT WORKING in the first 4851 IC! I must try (when I'll have time) to write down the behaviour of the *most-working-IC* and swap them to see if it behave same way (working pins keep work and viceversa) or if it changes something. If it's the same it means that likely i've fuc**d up all non working inputs and I must replace all 4851 IC, otherwise may be something else.

Now I buyed 4 new 4851 from synthex and as soon as they'll arrive I'll test all again.

In the likely event that all works I will share my boards schematics and PCB drawing wich I did like this:

1 x analogue mux board (4x4851 ICs, no diodes)

4 x Input sockets board in (listen well!) 3 format each:
- straight 6 pin switched audio jacks (input on left 3 pins, grounds on right 3 pins, PCB mount)
- reversed 6 pin switched audio jacks (input on RIGHT 3 pins, grounds on LEFT 3 pins, PCB mount)
- enclosed 7 pin swictched jacks (6 "circular" pins plus 1 ground, originnaly panel mouted but I soldered them)

Those 3 configuration (or a mix of them, like I did 'cause I had only a few jacks per kind) will allow a lot of flexibility in the case construction allowing you to decide where to place what, and, eventually, avoid bad connections from jack to pin.

Thank you all!

[mackanov]

Check your analog board for hairline shorts between mux pins 9 and 10, since I had almost the same problem as you and that was it. Still got the tamtamtam though, and will check for more shorts tomorrow since by sunlight it should be easier for me to see!

[mackanov]

"Tamtamtam" is probably a short between VCC and the input. Was in my case.

[stellari81]

Thank u all for the kind replies!

Unfortunaly actually I'm alway on travel to work and don't have much time to spend on the project (doh!).

I'll check all your suggestions on my board and let you know if I'll get down to the problem.

Thankyou all!