xoxshop.de squarewave not in spec

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wonky
 
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xoxshop.de squarewave not in spec

Post by wonky »

Hi,
I'm definately a beginner synth diy-er. So far I've built a few modular kits and had no problems. My soldering is good and I'm careful to use the right parts (slow).
XOXBOX is the first thing I really needed to test as I went along so I got hold of a scope to do it properly. TBH I dont really understand the scope properly yet, other than to know that what I'm seeing isn't what should be there.
I have done the sawtooth wave in the VCO section and that looks spot on. Unfortunately when I came to checkout the Squarewave its not looking right. I have double checked the components that went in this section and they all look right. Please have a look at scope images below. Any advice would be much appreciated, thanks in advance
SAWTOOTH
Image

SQUAREWAVE
Image

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wonky
 
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Re: xoxshop.de squarewave not in spec

Post by wonky »

I should add more info!

Here is what it should look like

Image

so thats 4Vpp and 7V DC bias.

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antto
 
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Re: xoxshop.de squarewave not in spec

Post by antto »

at what frequency was the square oscillating on that photo?
could you try making another photo of it at some high-ish frequency, at least 50Hz or more

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wonky
 
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Re: xoxshop.de squarewave not in spec

Post by wonky »

Hi antto

Its says 121.9hz on scope. Is that the right freq? I clicked stop on scope to hold the waveform. (Like i say im buskin with the scope and learning as i go)

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MoFe
 
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Re: xoxshop.de squarewave not in spec

Post by MoFe »

Hi,
i also got a xoxbox from xoxshop.de this week and started assembling today. Im have expirience in soldering and testing complex circuits and i also should know how to measure.
Unfortunately analog circuit debugging is not one of my skills :)

I have excactly the same problem! + my reference voltate can not be driven to more that 5.29V, Have you also got this second problem wonky?

When i measured the signals in the pictures, all potentiometers on main board were set to middle position, The reference voltage adjustment potentiometer was turned all the way up to come as close as possible to 5,333V. Measurement Equipment: Rigol DS5060MA, UNI-T UT61D

Vref(5,333) = 5.328V
V12V = 11,80V


SAW
VSawBias: 8.5V
VSawPeakToPeak = 5.5V
fSaw = 81.97Hz
IMG_1968.JPG
IMG_1968.JPG (71 KiB) Viewed 1625 times


SQUARE
fSquare = 81.97Hz
tOff = 2ms
tOn = 9.6 ms
VHigh = 11.2V
VLow = ~200mV
IMG_1967.JPG
IMG_1967.JPG (62.59 KiB) Viewed 1625 times
Maybe there is a faulty part in our shipping? I checked everything twice in the last hours :/ Please tell me any signal to measure, i will post screenshots ASAP as long as im awake :)

Dear community, Please help us finding the problem!
Thanks in advance . . .

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antto
 
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Re: xoxshop.de squarewave not in spec

Post by antto »

i wasn't sure about that 121Hz ... if that was really that high - then something is definately not right
same goes for MoFe - at 80Hz the square shouldn't really look like that

the inability to set the 5.33V reference to 5.33V has occured before, and there is info about it on the forum

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MoFe
 
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Re: xoxshop.de squarewave not in spec

Post by MoFe »

Hi,
thanks for your reply, im currently searching through the forum to find some hints about the voltage, but didnt find any thread yet. The faq couldnt help me.

You (antto) say that the square wave doesnt look right at 80hz. Does the saw wave looks right? Can 80hz be ok? i dont really know where to start the search but i will continue at the power supply board now. . .

All i realized so far is that if i measure the voltage between any pin of D25 and GND the Square frequency changes heavily or the system even stops oscillating.

thanks,
MoFe

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antto
 
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Re: xoxshop.de squarewave not in spec

Post by antto »

here's one example: http://forums.adafruit.com/viewtopic.php?f=12&t=8641
another one: viewtopic.php?f=12&p=25290
see if you can find anything familiar to your situation there

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MoFe
 
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Re: xoxshop.de squarewave not in spec

Post by MoFe »

Hi!
I was analysing the schematic around LM336Z-5 and when you send me this link i swapped R5 from 2.4k to 1.5k, now i can ajust my VRef from ~5.2 to ~5.5V. So this problem is solved. . .
Thank you antto, maybe i use the search in a wrong way. . .

I will continue on solving the VCO Problem (Unfortunately it wasnt solved by the rise of 0.004mV on VRef :), If you have any additional hints for me please let me know!

Thanks,
MoFe

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MoFe
 
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Re: xoxshop.de squarewave not in spec

Post by MoFe »

Hi!
Placing R36 solved the problem for me, after that the square wave looked normal. This is not in the tutorial, but i think R36 is important for getting a correct square wave

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wonky
 
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Re: xoxshop.de squarewave not in spec

Post by wonky »

Hi mofe

I went out dancing to square waves and now have a big headache, but it looks like my xoxbox headache may be solved. Wow! I will install the r36 and see what i get...

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MoFe
 
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Re: xoxshop.de squarewave not in spec

Post by MoFe »

Looking forward to your answer. It seems to me that some essential things are missing in the fab manual, This is not a no-brainer unfortunately :)

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wonky
 
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Re: xoxshop.de squarewave not in spec

Post by wonky »

Hey Mofe. I fitted r36 and now have a better wave, bias and pp are right, looks a bit more like a 'lump wave' than a square at the mo but i guess adding the rest of the oscillator section should sort it...

Thanks all for the input. Press on!

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MoFe
 
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Re: xoxshop.de squarewave not in spec

Post by MoFe »

Good to hear that but watch out! In my kit from xoxshop.de they messed up some ics! And the 1.5M Ohm resistor was a 1,5k resistor. Is yours ok?

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antto
 
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Re: xoxshop.de squarewave not in spec

Post by antto »

MoFe wrote:Looking forward to your answer. It seems to me that some essential things are missing in the fab manual, This is not a no-brainer unfortunately :)
the square wave shouldn't look like that normally
R36 can surely be used to change the effective pulse width of the square, but that doesn't fix the actual problem

i would suggest checking each component, including resistors, for proper values before putting them in
i know it takes ages that way, but it's easier to do it once and to be sure than to just solder everything and then wonder which component is responsible for the given problem

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