Some Shruthi 4PM XT build issues/questions

Discontinued products Shruthi
#1

So I was waiting on a single voltage regulator from Mouser in order to be able to finish my Shruthi 4PM XT build. Good news is it came today, so I finally got everything put together this afternoon!

The good news is the 4PM filter works and the XT board is great to use as a Shruthi controller. The bad news is that a few functions aren’t working as well as I intended:

1) Scrambled LCD

When I tested the naked Shruthi XT my LCD (recommended Newhaven part) looked picture perfect. I was so excited to get everything built and housed in the case that I must have shorted something on the LCD or bent the bezel somehow when assembling (the XT metal face makes direct contact with the LCD bezel but as far as I can tell there is not a large amount of force being placed on the LCD). There are a few tabs on the bottom of the LCD which don’t make contact with any points on the PCB, except for one tab which I didn’t notice previously (which hovers over the solder points for the MIDI connector. I’ve been able to bend the tab back so it doesn’t touch anything but I guess the damage has already been done.

Anyway, now my LCD display is all scrambled. I’m going to resolder the connection tonight but I have a feeling I will need to buy a new LCD. Is there any saving this display?

2) Filter+ modes aren’t working correctly?

This was something I thought I had fixed initially but I still feel is not working 100%. It also could be due to being new to the 4PM filter, but it seems as though some of the different filtering options under the Filter+ page do not have an affect on the sound. When I switch to the MS style, Wobble, etc I do hear a difference in the way resonance is handled but when I switch between LP4, LP3, etc I do not notice any change in filter characteristics. Here’s a quick sound demo I made of the first 3 patches:

https://soundcloud.com/portervance/shruthi-4pm-filter-test-1

I sweep the regular filter from 0 to 127 then back to 64 or so with some reso and env set then I switch to Filter+, set the filter to Wobble (as opposed to liquid), set the filter to about half with some reso, and then at the end of each sound I slowly pass between the different filter types. As you’ll hear, the sound is very stable in the last bit of each sample (no change in sound despite selecting different filter types). I am assuming there should be some change in how the filter sounds when you select these different types. PS: listen at a lower volume, there are some squelchy resonance spikes when MS filter type is engaged for a second.

Also I’m wondering if the general sound on the demo is consistent with how the 4PM should sound or not. When my filters are open all the way it sounds a big too light and airy (obviously the filter is open 100% but I feel my sound sounds different than some of the demos I’ve heard).

3) Interior 4PM LEDs

For my interior LEDs on the 4PM board I soldered a red and green LED directly to the board with 2x 220ohm resistors for current limiting. The LEDs light up when I turn the unit on but it is my understanding that they should pulsate or turn on or off depending on how the filters are set. My LEDs just remain on all the time. Is this correct?

I’m going to touch up some solder joins and see if that make s difference with the LCD. Will report back.

#2

Is the 1x6 board connector installed between the two boards?

#3

Yes I’ve soldered the 1x6 header on the “output expansion” area. I think the connection on this area might not be the greatest (pins are almost too short in terms of making a connection with the filter board) which may be contributing to the issue.

I noticed this initially when I had an Arduino header placed in between the filter board port and the male pins (to extend their length). The pins on the extra header were a little too short and I’d notice changes to the sound and LED turning on/off when I put more or less pressure on that area of the control surface. I’ve since added a different kind of socket in between the pins but this also does not make as solid of a connection (though the LED is consistently lit now).

I have a strip of headers with longer pins so I will try replacing the current 1x6 pin strip with those to ensure a better connection. Do “filter modes” like Wobble get handled over this connect or is it only “filter types” and other communications?

#4

> Do “filter modes” like Wobble get handled over this connect or is it only “filter types” and other communications?

Resonance modes are 50% - 50% through the connector and through scaling the resonance CV.

Filter modes are all going through the digital expansion port. Check that pins 15 and 1 to 5 of the 595 on the 4PM filter board change when you change filter modes.

#5

I swapped out the shorter set of 1x6 pins for a longer set and that has fixed the filter types issue :).

Volume is also a lot louder among other things. It’s sounding much more like a 4PM Shruthi now.

I touched up the solder on the LCD but this did not solve my problems. I’m assuming the LCD is completely busted. Putting pressure on different parts of the display changes nothing as far as pixels or brightness goes.

Luckly I bought 2 Newhaven displays from Mouser so I can probably swap a new one in there. 2 questions before I go this route:

1) I’m assuming the XT metal panel put too much pressure on the LCD bezel and caused this issue or a component shorted the LCD and it’s scrambled due to that. Beyond bending some of the metal tabs on the back of the LCD, what other precautions should I take to avoid ruining another display?

2) The LCD part is NHD-0216K1Z-FSW-FBW-L. You’ve tested this LCD in another post I came across. I’m wondering what current limiting resistor value you used for this display. 68ohm?

#6

1. I can’t speak about that one - I tried building a XT with a LCD and ruined it :smiley:

2. Newhaven LCDs do not need current limiting resistors.