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rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Tue Aug 27, 2019 3:19 pm

I think the diodes D1 + D2 on Cap C16 is better for protect Hard- and SoftSync input.

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alfa
Learning to Wiggle
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Location: Latvia
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Post by alfa » Tue Aug 27, 2019 10:27 pm

Dear Rolf
If it works , then it is Ok!
But now Sync input may overload source and may cause
problems for other recipients/modules of these signal. It looks better
at first buffer/shift Sync input to avoid such possible problems.

ixtern
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Posts: 160
Joined: Mon Jan 22, 2018 4:34 am

Post by ixtern » Wed Aug 28, 2019 10:12 am

Good idea with OP07 for the sine buffer. Due to very low slew rate (typ.0.3V/us) it works like additional low pass filter, smoothing eventual spikes. Of course sine on 20-30 kHz will be rather triangle but those are not very useful frequecies.

tubeohm
Learning to Wiggle
Posts: 30
Joined: Sun Sep 07, 2014 2:29 am

Post by tubeohm » Mon Nov 11, 2019 7:31 am

ixtern wrote:Good idea with OP07 for the sine buffer. Due to very low slew rate (typ.0.3V/us) it works like additional low pass filter, smoothing eventual spikes. Of course sine on 20-30 kHz will be rather triangle but those are not very useful frequecies.
Hello , Rolf has already worked on something. Since I wanted to build an oscillator anyway, I have now developed a circuit board with the basic functions of the AS 3340 (Alfa ) / V3340 (Behringer) and CEM 3340 (Curtis). This board can be used for all 3 IC's. At the same time a sub-oscillator was implemented -1/-2 Oct.
The PCB design is such that it can also be plugged onto a breadboard / hole=2.54mm. So only the control elements and the buffer amplifiers are needed.

The special features of the board are :
LDO power supply 10 V and stabilized reference voltage.
This serves frequency stabilization.
Suboscillator -1/-2 oct at the PWM . If the PWM is 0 then the sub is also 0.
4x 1V/OCT, SYNC , Softsync and LIN FM in. All components are trough hole - so easy to assemble.
OUT RECT,SAW,TRI, RECT-1 Oct, RECT-2 Oct

The board was tested with the AS 3340- because I just ordered 2 from Thonk.

Now the test report.
The board was equipped and connected to +10 V -12V.
(I had not ordered a LDO 10 V regulator yet )
The VCO worked correctly - but first without a square wave signal.
After the connection of a potentiometer for the PWM, the VCO now also delivered the square wave signal which could be controlled by PWM. (clear , 0V PWM =zero PWM)

** The following info. The square wave signal has overshoots in the lower frequencies from 400 Hz. The sub-oscillator did not run correctly. The lower the frequency, the more overshoots can be seen on the oscilloscope.
Why overshoots ?
Well, the control voltage for the PWM is a bit noisy. The comparator triggers into a small range several times. The lower the frequency, the larger the time window and the more overshoots there are.
The solution is as follows :
a:)To be on the safe side you should connect a capacitor to input Pin4 1..10 nF
b:) and of course the 1 M Ohm resistor between pin 4 and 5. This prevents the overshooting by pulling the PWM control voltage over the 1Mohm downwards. This results in clean
Switching states.

Unfortunately this is not described in the Alfa manual, but it is in the original Curtis manual. These overshoots can be avoided by soldering a 1 M Ohm resistor from AS 3340 PIN 4 to Pin 5.

( The resistor is of course on the board - but as SMD component - which I didn't have available yet. OK didn't have all parts on stock - then I soldered in a normal resistor )

Very interesting for me was the thermal behaviour of the AS 3340.
To anticipate - the difference between cold ( not switched on)
and warmed up (approx. 5 minutes on) was at 1000 HZ approx. 2..3 Hz.
A wandering of the frequency as it happened with Rolf I could not notice. On the contrary, a once set frequency remains constant even after 30 minutes. Currently the oscillator runs at 6400 HZ and 6V.

0 Volt is 100.9 Hz. As you already suspected I calibrate the IC straight and proceed as follows.
At 0 Volt my set frequency is 100 Hz.
then the voltage is increased in 1 volt steps.
1V =200,2V=400,3V=800,4V=1600,5V=3200,6V=6400,7V =12800
The calibration I have now carried out up to 7V - flawless - I am impressed.

Very important is also the jumping behaviour. The IC tracked cleanly between 0V =100Hz and 7V =12,82Khz. It came to no frequency tracking.

For testing a RIGOL power supply DP832, resolution 1 mV and a Fluke 77 - resolution 1 mV was used. The frequency was measured with a TEKWAY DST 1062 .Image
ImageImage

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rolfdegen
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Location: Wuppertal (germany)

Post by rolfdegen » Sun Dec 01, 2019 3:18 pm

Hallo everyone

My next step is an audio miniscope for my Eurorack (see pic). The basis is a microcontroller board STM32F103C8T6 (BluePill).

BluePill Board with STM32F103C8T6
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My Prototyp
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Circuit diagram
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Based on a small STM32 board with the name BluePill STM32F103C8T6, the Scope the waveform and frequency are displayed on a small 0.89 "OLED display. The" IN "connector is on Input for the audio signal. Via "OUT", the input signal reaches the outside unbuffered. The potentiometer adjusts the level of the input voltage. For measuring purposes serves the "CV / OSC" output. It supplies a control voltage from 0 to +8 volts or an adjustable
oscillator frequency eg 440Hz.

The scope has a 16-bit DA converter with two output channels. I have it for the circuit Development soldered to a SOP-8 board. Output A is for the utput of a DC voltage. Of the Output B outputs a 440Hz tone. Both DAC
outputs have a tristate function and are switched alternately. As a result, I do not need a second OP for the output of a measurement tension.

The input voltage for the scope can be regulated via potentiometer R8. IC4a limits the input voltage at the AD converter. IC4b is switched as a comparator and for triggering the waveform responsible. The power supply (+ 3.3V) for the STM32 processor board provides the + 12V voltage over K1. Have a second butterwoth filter integrated for the DA converter. The
calculated Filter frequency is 10KHz. The STM32 board corresponds to the dimensions of the connection pins exactly one 40-pin IC socket.


Fontpanel
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My Eurorack
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Video
[video][/video]

See next. Rolf

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