Midibox CV - Button Noise, etc.

[bentron]

Hello everybody,

i´m new in the Forum and let me first say thanx to Thorsten for this great diy project!!

I've just successfully completed a Midibox CV with 4 AOUT_LC Boards, everything seems to work in terms of hardware and software - means i´ve tested all voltages, burned bootloader, uploaded mios & MidiboxCV App. All soldering points seem to be fine.

But when testing with my SH-101 and MS-20 i noticed some strange behavior:

When plugging the gate into the sh-101 i triggers the synth constanly with a weak gate signal.

The 4 buttons connected through DINX_1 make a very audible noise when pressed - on higher octaves it seems almost like the buttons are triggering/gating the synth.  ???

And while plugging the gate or cv cable to the Patch-Panel of the ms-20 (e.g. shorting the pins), the midibox cv reboots instantly.

Besides that, the triggers and cv's themselves all seem to work - but all with the problems named before.

I'm pretty sure i've set the correct output-curves, jumper settings, etc.

I´m pretty stuck with this problem, since my electronic knowledge ends when it comes to trace problems in a circuit   :-[

Any suggestions on this?

Thank you in advance and best greets from vienna,

Max

[bentron]

I forgot to mention, that i noticed a problem while calibrating:

on the second channel of every AOUT_LC board (CV2,4,6,8) i only got about 0,6-07V with the 1V setting - while all other voltages where ok.

HMM, while checking it right now, i notice that the 7805 on the core gets very hot - even though i swapped it with a new one and now using a 9VDC 200mA instead of 9VAC 800mA.

i don`t have any clue  ???

[TK.]

Hi Max,

this could be a configuration problem.

For the 8 gates at J5, you have to set ENABLE_J5 switch in main.asm to 1

Also the AOUT_LC modules need to be configured in main.asm, for 8*8 bit you have to set:

#define DEFAULT_AOUT_LC_1_RESOLUTION 2  ; 1st AOUT_LC module

#define DEFAULT_AOUT_LC_2_RESOLUTION 2  ; 2nd AOUT_LC module

#define DEFAULT_AOUT_LC_3_RESOLUTION 2  ; 3rd AOUT_LC module

#define DEFAULT_AOUT_LC_4_RESOLUTION 2  ; 4th AOUT_LC module

Thereafter build a new .hex file like described here: http://www.ucapps.de/howto_tools_mpasm.html

it's normal that the 7805 gets very hot, especially when a backlit LCD with full brightness is connected. So long the core doesn't reset randomly, this is acceptable. Alternatively you can reduce the backlight brightness, or add a headsink to the 7805

Reboot when pins are shortened - I would propose to add small resistors to the gates and CV outputs, e.g. 100 Ohm, in order to prevent a short circuit.

Please let me know if it helps

Best Regards, Thorsten.

[bentron]

hi,

after some failed calibration attempts i decided to completely finish the unit and put it in its housing to eliminate possible error sources. Well that was quite a success since the button noise, constant gate voltage and the strange rebooting are gone now, ye-haw  ;D  (must have fed some voltage to the ground with those alligator clips  ;) or something like that)

But one problem remains:

I've set the all cv channels to 8/8 bit, see a part of the code here (but i assume it`s correct):

;

; use PORTA and PORTE (J5 of the core module) for 8 additional gate outputs

#define ENABLE_J5 1

;

;

; define the AOUT interface which is used here:

;   1: one MBHP_AOUT module

;   2: up to 4 (chained) MBHP_AOUT_LC modules

; all other values invalid!

#define DEFAULT_AOUT_INTERFACE 2

;

;

; only relevant if one or more AOUT_LC modules are used:

; define the resolution configuration here

;   1: first channel 12bit, second channel 4bit

;   2: first channel 8bit, second channel 8bit

; all other values invalid!

#define DEFAULT_AOUT_LC_1_RESOLUTION 2 ; 1st AOUT_LC module

#define DEFAULT_AOUT_LC_2_RESOLUTION 2 ; 2nd AOUT_LC module

#define DEFAULT_AOUT_LC_3_RESOLUTION 2 ; 3rd AOUT_LC module

#define DEFAULT_AOUT_LC_4_RESOLUTION 2 ; 4th AOUT_LC module

;

;

; define the pin which should be used as external clock output here

; DEFAULT_EXT_CLK_LAT can be LATC (Pin 0, 1, 2, 4, 5) or LATD (Pin 4)

; The external pin is disabled with DEFAULT_EXT_CLK_LAT == 0

#define DEFAULT_EXT_CLK_LAT LATD

#define DEFAULT_EXT_CLK_PIN 4

;

; desired pulsewidth of clock output in pieces of 500 uS

; 0 -> 500 uS

; 1 -> 1   mS

; 2 -> 1.5 mS

; etc...

#define DEFAULT_EXT_CLK_PULSEWIDTH 1

but still i get some strange behavior on every second cv channel (e.g. 2,4,6,8):

While calibrating, the 1V setting cannot be reached - maximum possible is about 0,6 to 0,8 Volts - while the other voltages are ok (min, max, 2,4,8,)

When connecting a synth then, the octaves are like - it's hard to describe - cut in half. the 4 lowest notes of every octave are played twice, so when playing the complete octave, the notes are like this: c1, c1#, d1, d1#, c1, c1#, d1, d1# an then it continues with the same notes one octave higher.

I've tried with 8/8 V/OCT, Hz/V and 12/4 Hz/V with several analog synths but it`s always about the same, so the problem must source somewhere else.

And again, CV Channels 1, 3, 5 and 7 work perfect, without any trouble.

Any suggestions?

Thanks again & best regards,

Max

p.s.: any recommendations on a simple s&h ciruit to eliminate that zipper noise? i assume a part of the SHX8 would do, but as mentioned, my electronic knowledge is very limited  ::)  :-\

[TK.]

Hi Max,

the described effect sounds like there is a problem in the 12bit->8bit conversion, but my problem is, that I'm not able to test this so easily anymore, since my AOUT_LC modules are configured for 12/4 bit mode, and built into a case.

The register upload routine is located in cv_aout_lc.inc, CV_AOUT_LC_LoadAOUTx_8_8

It looks clean, and so far I remember, I tested this before the v1.1 release... :-/

Could you please doublecheck, that your AOUT_LC module is really configured correctly?

S&H: this would require a refresh of the S&H stages each milisecond. I never tried this with MIDIbox CV, but I fear that continuous register accesses would add some permanent noise.

In general I noticed that the digital noise is extremely low when MAX525 are used. I'm not an analog expert, but maybe there are possibilities to improve the circuit by adding filter networks (R/C/L)?

Best Regards, Thorsten.

[bentron]

hi,

well i´ve tested several configurations with all 4 AOUT_LC boards, but always the same effect. even if i swap the lc modules around.  :(

So i think the problem resides on the core.

The only thing that comes to my mind now is the crystal on the CORE. i´m not sure if it's parallel cut, since the datasheet doesnt give any useable info.

I don`t have another crystal to test, so before i start rippin the old one out and gettin a replacement:

Is it even possible that this causes my problem?

thanks for the info on the s/h, but i think that's getting too complicated in the end,.  ;)

since the zipper noise isn`t really a problem anyways, my ears are just very picky  ;)

Intentionally i wanted to build the midibox cv with the AOUT module but i had big trouble getting the MAX6007B shunt.

Any supplyers in EU or substitute parts known?

Thanks & best regards,

Max

[TK.]

I don't think that the crystal is the problem - you wouldn't be able to upload a program (wrong baudrate)

It sounds like a software problem (wrong data conversion), but when I look into the program, I cannot see an error, and unfortunately I'm not able to test this with my own equipment so easily (means: it could take weeks until I find the motivation to open the case and to resolder my AOUT_LC modules, just to test if the conversion is done correctly).

On the other hand: are you really sure, that the modules are configured correctly for 2*8 bit mode.

What happens when the CV outputs are controlled via CC events? Are you able to sweep over the whole voltage range? (compare with http://www.ucapps.de/mbhp/mbhp_aout_lc_res_options.gif

And another note: the Hz/V curve normaly requires a resolution higher than 8bit, otherwise it isn't accurate enough. You could try the 12/4bit resolution (with the appr. setup in main.asm) - this is the one which I've tested on a MS20

Intentionally i wanted to build the midibox cv with the AOUT module but i had big trouble getting the MAX6007B shunt.

Any supplyers in EU or substitute parts known?

I'm also interested in this - or in a substitute for the MAX6007B shunt (I'm not an analog expert)

Best Regards, Thorsten.