Positional sensing testing

[dmitri]

Hi,

I built the precision rectifier circuit following the schematic on the first page of this thread and using an MCP604 op-amp. It's stated that if it's 'unity gain stable' (this one is), then C3 and C4 can be omitted - I figured C4 should be left out entirely (not bridged), but should C3 be bridged?

I use MCP604 and it's variants. C3 and C4 can be omitted, i.e left out and not bridged.

On the other hand, I didn't have 15k or 12k resistors, so for the 15k I soldered two 10k resistors in parallel followed by another 10k in series, and for the 12k I used 10k followed by 2k2 in series. My multimeter just died on me recently so I couldn't see the actual values that resulted from this fix, but the resistors are rated at 1% tolerance so they *should* be close enough to the right values, except for the 12k which is nominally 200 ohms over the mark. Would this be a problem?

If the values are withing 1-3% it should be fine.

I'm describing all this because when I tried the board out, the first thing I noticed was that the snare has lost a lot of sensitivity. It has a trimpot to cool it down (it was way too hot), but with the rectifier board I had to completely open it and even so high level is now at around 250, when it used to be at 990. Is this normal?

Yes, this is how it should be. The precision rectifier cools down a connected pad but it also reduces noise somewhat so the Gain can be raised and Threshold can be lowered.

[ignotus]

Yes, this is how it should be. The precision rectifier cools down a connected pad but it also reduces noise somewhat so the Gain can be raised and Threshold can be lowered.

Cool, thanks Dmitri. When I get the chance I'll try to fine tune it. Oh, and another thing - I see that only half of the chip is used for one input, so the other half could be used (replicating the circuit) for another input, couldn't it?

[dmitri]

Yes, this is how it should be. The precision rectifier cools down a connected pad but it also reduces noise somewhat so the Gain can be raised and Threshold can be lowered.

Cool, thanks Dmitri. When I get the chance I'll try to fine tune it. Oh, and another thing - I see that only half of the chip is used for one input, so the other half could be used (replicating the circuit) for another input, couldn't it?

Yes, of course. This is how it is done in the Positional sensing addon board.

[ignotus]

Well, I found time to have a fiddle: it's working grand! I need to raise minscan to about 80, but to be honest I don't notice any negative effects on performance - on the contrary, I've been able to lower threshold, retrigger, dynlevel and dyntime to pick up lighter and faster hits without double triggering. I'll even go so far as to say that it works even better than in the demo video Dmitri posted in this thread! Positional sensing kicks in at about 1/4 of the way from the centre and reaches CC127 about two cm from the rim on a 10" pad, great stuff!

Next: try to get it to work with the ride...

[angr77]

Hi!

I had an wilde idea regarding positional sensing. I just wanted to check again with the forum the following:

All MD channels do support PS, if the centralized piezos first half wave is positive?

The PS board do support PS on 5 channels, channel, 4 , 6, 8, 10, 12 with rectifier functionality

To give you a hint on my idea...positional sensing not only on drums..the ride cymbal and also the...hihat!

Best Regards

ANGR77

[angr77]

Hi again!

After been reading the forum regarding positional sensing...i see the PS board covers channel 4, 6, 8, 10 and 12 and the rectifier function. One post also mentions that the hihat channel 2 has the op amps for handling high/low impedance but my question is if this channel also are covered with the rectifier function?

Best Regards

Anders

[dmitri]

With the Positional sensing addon the Alt (High impedance) HiHat pedal input has an opamp buffer which allows to use both high and low impedance pedals. It doesn't rectify signals and it doesn't need to - signals from pedals are always positive.

[angr77]

Aha, i get it. The op amp covers the hihat pedal. Just be sure...the hihat input for bow (which i believe is input 2) has no op amp on the PS board. Right?

[dmitri]

Aha, i get it. The op amp covers the hihat pedal. Just be sure...the hihat input for bow (which i believe is input 2) has no op amp on the PS board. Right?

Correct. But it doesn't matter - you can assign any input as a HiHat cymbal input.

[alexmcintosh]

Configuration Questions:
For Snare Drum (cake-pan, QuartzTrigger)
Type = Dual [Dual or 3way Yamaha; 3rd Zone = 0 (Disabled)]

1.)Should.. SnareH & SnareR both have the same 'PosLevel', 'Pos Low' & 'Pos High' values?
a.) seems like they should but there's no documentation I can find.
2.) What CC values get sent out?
a.) I think it's CC 1 (for the snare drum), but I'm not 100% on this
3.) What CC values are sent out for the other Positional Sensing pads? (Ride, Tom's,etc.)
3.) What is MidPoint Width? How is the cause & effect described?

If I can get all my questions answered I would be very grateful.
Sincerely; Alex M.