Cool a hot trigger, gives divider or 1 resistor same effect?

[Rovalo]

I read many threads on cooling down hot pads, or by voltage divider (2 resistors or potmeter) or 1 resistor in line with the piezo signal.

I read somewhere that the latter is actually a voltage divider as well because MD would use a pull down resistor on each input as well. I do not see one on the schematics but is could be within the input IC. If so then what value?

I also understood from posts that the divider (potmeter) is easier and will provide more accuracy in finding the optimum resistor values in case you replace the potmeter by cheaper resistors. Finding the single in-line resistor value might require more effort.

My question is: will both methods give exactly the same behaviour of the cooled trigger once the equivalent resistor values for both methods are used?

[dmitri]

Pull down resistors on the board are 4.7k + 2.2k = 6.9k.
You can use either method for "cooling". I think it is easier to just use a small trim pot resistor inline with a piezo (signal) without a pull down resistor. With a trim pot you can adjust how much the signal is to be "cooled".

[Rovalo]

Thanks for giving the values of the MD board pull down resistors.

With that I did some calculation and with 50k 12-turn trim pots I can do both accurately.

I go for the option of putting the trimpot inline with the piezo signal because one less wire and do that in each pad.

Hopefully I can adjust all 5 DIY pads to give the same high levels and response.

[Kabonfaiba]

What trim pots are you thinking of buying Rovalo?

I was thinking something like this would be easier to solder?



Is it possible to get away without connecting up the ground pin?

If the trimmer needs to the grounded, I've seen these longer trimmers that might fit nicely above each TRS jack, although I haven't measured this yet.

[Rovalo]

I use these with 12 rotations

https://www.conrad.com/p/vishay-74x-50k ... ter-423840

[Kabonfaiba]

Semi on-topic; but is it possible to universally cool all inputs at once with a single in-line resistor somewhere?

For example, replacing one of pull down resistors?

[dmitri]

Not without modifying the main board. But you will also (severely) reduce sensitivity on all inputs on the same MUXer.

[Kabonfaiba]

For those interested, here's a picture of my new trimpots installed on my duel piezo inputs. Boy was the soldering a messy PITA.

IMG_20190408_175553.jpg

So far very pleased! Nothing is broken and it's so much better to adjust on-the-fly.

My 3-zone triggering has improved significantly, that rim-shots are a joy, now they are more reliable. TBH I think my trimpots should be in the default kit but I understand that's a lot of extra soldering for Dmitri (perhaps an optional premium? )

I was able to do lots of experiments with variable resistance.

Key findings:

1. Input 8 is indeed ridiculously hotter, it needed around 48k to bring it in-line with the rest. Nothing hot about the drum.
2. Cooling all the rim piezos slightly (2-5K) helped with crosstalk (between inputs and the head piezo on the same input) even though they are very insensitive. Gain 7 and HighLevel 64 remains the best setting with Gain 8 introducing too much noise. Very dynamic even so. It's just the design of the trigger at the end of the day.
3. Adjusting the trimmers had no affect on other inputs (duh) but I had to prove it to myself.
4. No "crazy spontaneous self triggering" on the rims yet but I've only had it on for an hour. Point 2 might have helped.
5. Tom 1 was very rim happy and there was nothing I could ever do about it in MDM, to stop the false triggering. Turn the trimpot slightly and problem solved, couldn't believe it! This was something that couldn't be calibrated out MDM.
6. Still got self triggering aftertouch messages on both my cymbals. So obviously the next job will be to apply some trimpots to those inputs as well and hopefully eliminate this problem once and for all.

If I solve point 6 and if the "crazy spontaneous self triggering" never comes back, it'll be serious cause for celebration as those have been issues for years!