Rockdude discusses precision rectifiers and positional sens

[rockdude]

Ok so I've decided to try to build a precision rectifier:

I tried the firmware with my DIY 14" a to e snare but couldn't get any consistent results even though it should have a positive half wave of a signal.
I will certainly need some help to be able to build my precision rectifier. The first help would be to find the right components.
I tried to search for them on Farnells where you (dmitri) bought the opamp (LMC6034). I found that, but I'm to confused to find the rest.
Could you (dmitri) or anyone knowledgeable make a list of links to all the right components at Farnells? It would be preferable to order everything from the same place at least.

Just like my MegaDrum build log, this thread can be an idiots guide..but this time to a precision rectifier. Maybe it will help other confused souls and prevent further questions in the future

I'll start the list of components here and update it when people have helped me find the rest:
opamp:
http://uk.farnell.com/national-semicond ... tt=LMC6034

[mackanov]

But but... if you're using a DIY a-to-e converted snare, why do you need the rectifier? Mine works fine without it... as should all that give a positive half-wave. Try retuning your snare, I found that I though mine was very tight already, but it seems it can go tighter and tighter. It's so tight now I'm afraid it might explode on my face

Also, mine is not that well done, since it was put together really fast, with a sub-par not very well centered foam cylinder (not a cone, couldn't shave the foam to form a cone because it's too soft). It seems there's so much to do to improve my build (beginning with the multiplexers I can't find anywhere!) that I keep postponing the proper kit build.

[rockdude]

But but... if you're using a DIY a-to-e converted snare, why do you need the rectifier? Mine works fine without it... as should all that give a positive half-wave. Try retuning your snare, I found that I though mine was very tight already, but it seems it can go tighter and tighter. It's so tight now I'm afraid it might explode on my face

Also, mine is not that well done, since it was put together really fast, with a sub-par not very well centered foam cylinder (not a cone, couldn't shave the foam to form a cone because it's too soft). It seems there's so much to do to improve my build (beginning with the multiplexers I can't find anywhere!) that I keep postponing the proper kit build.

Can you do rolls from center to edge and get good positional results? Maybe it's just a configuration issue for me, but I tried all the options for positional sensing in MegDrum without success. I thought dmitri mentioned that precision would be even better with a rectifier. I don't know exactly what a rectifier does except making a negative first half wave positive, but I thought it also made the pad less hot and added precision in output.

[dmitri]

Can you do rolls from center to edge and get good positional results?

What is good "positional results"? The reason I'm asking is this: http://www.vdrums.com/forum/showthread.php?t=60406 - for some it may look excellent, for others - rubbish.

Maybe it's just a configuration issue for me, but I tried all the options for positional sensing in MegDrum without success. I thought dmitri mentioned that precision would be even better with a rectifier. I don't know exactly what a rectifier does except making a negative first half wave positive, but I thought it also made the pad less hot and added precision in output.

The rectifier doesn't add any precision. Also, if your DIY snare doesn't produce good signal for PS, it won't work with or without the rectifier on MegaDrum or a Roland TD-12/TD-20.

[rockdude]

Can you do rolls from center to edge and get good positional results?

What is good "positional results"? The reason I'm asking is this: http://www.vdrums.com/forum/showthread.php?t=60406 - for some it may look excellent, for others - rubbish.

Maybe it's just a configuration issue for me, but I tried all the options for positional sensing in MegDrum without success. I thought dmitri mentioned that precision would be even better with a rectifier. I don't know exactly what a rectifier does except making a negative first half wave positive, but I thought it also made the pad less hot and added precision in output.

The rectifier doesn't add any precision. Also, if your DIY snare doesn't produce good signal for PS, it won't work with or without the rectifier on MegaDrum or a Roland TD-12/TD-20.

What's good or bad is in the eye (or ear) of the beholder. The link below is how I would want it to operate (1.10-1.20 in that video):
http://www.youtube.com/watch?v=g9BRq8mW6AE&fmt=18

What's a good signal exactly? I've got a DIY A to E converted snare with a trigger in the center. I've added a 100k variable pot to reduce it's signal since it was too hot from the beginning. Now I get good dynamics when tweaked a bit in MegaDrum. I'm using DrumTec Design Mesh heads (Dual ply) with high tension.
I should add that I've built a combination of Roland cone triggering and the reflection plate design in my snare which triggers really well and reduces hotspots. Maybe I should convert another drum only using the traditional centered "Roland" cone and try it with the positional sensing feature.

[macca2004]

You can emulate the velocity postion effects (i.e vel >90 triggers a rimshot) using the new midi node function in Superior 2.2. I'm going to look at midinode function to improve my positional sensing problems..i.e good separation at low velocities but xtalking at higher velocity.

[Ken Forgettable]

Positional sensing works by measuring frequency, macca2004 is wasting his time by trying to map it to amplitude.

Finding a relationship between the two would be really cool though

[mackanov]

What's a good signal exactly? I've got a DIY A to E converted snare with a trigger in the center. I've added a 100k variable pot to reduce it's signal since it was too hot from the beginning. Now I get good dynamics when tweaked a bit in MegaDrum. I'm using DrumTec Design Mesh heads (Dual ply) with high tension.
I should add that I've built a combination of Roland cone triggering and the reflection plate design in my snare which triggers really well and reduces hotspots. Maybe I should convert another drum only using the traditional centered "Roland" cone and try it with the positional sensing feature.

I'm betting your reflection plate design messes with things a bit. I'm pretty sure it's very important to have as small and as centered as a contact point as you can get on your drum head for it to work well.

[rockdude]

What's a good signal exactly? I've got a DIY A to E converted snare with a trigger in the center. I've added a 100k variable pot to reduce it's signal since it was too hot from the beginning. Now I get good dynamics when tweaked a bit in MegaDrum. I'm using DrumTec Design Mesh heads (Dual ply) with high tension.
I should add that I've built a combination of Roland cone triggering and the reflection plate design in my snare which triggers really well and reduces hotspots. Maybe I should convert another drum only using the traditional centered "Roland" cone and try it with the positional sensing feature.

I'm betting your reflection plate design messes with things a bit. I'm pretty sure it's very important to have as small and as centered as a contact point as you can get on your drum head for it to work well.

Yes I'm afraid that might be the problem. I'll convert one of my spare drums with my "old" crossbar and cone design and do another try. I've removed all my earlier crossbar designs because I think they cause to much hotspots. But I guess I could live with one drum setup like that to get positional sensing working.

[rockdude]

Could someone do a little video or audio demo with the MegaDrum positional sensing feature? Kind of like the link I provided earlier in this thread.
dmitri's video was very cool and showed that it works, but it would be nice to listen to how it sounds when played with samples too.