Saw tooth wave not 150 Hz

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MrNoPain
 
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Joined: Sat Jun 16, 2012 4:23 pm

Saw tooth wave not 150 Hz

Post by MrNoPain »

Hi,
Im building my first x0xb0x kit, bought it from x0xsh0p.de
Soldering electronics is not new to me but using an oscilloscope is.

I have come to the VCO part in my build and so far everything have worked out fine.
Im at the point where im supposed to measure the saw tooth wave for the first time and Im not at all familiar with my old scope.

I am getting a saw tooth wave on my scope but there are som readings that are a bit off i think.
(Tried to upload an picture of the wave but it did not work)
The voltage is 5.8V peak to peak and the frequency is about 34.6Hz and not 150Hz as in the online build manual.
The saw tooth wave changes when i turn VR2.
Dc bias is 8.08.

I also tried the headphones listening test but i could not hear anything.

After reading a nother post with problems hearing the wave i also took some measurments.
Q26:
1=5.332
2=5.333
3=4.705
4=7.96
5=5.383

IC 11
1=1.825
2=5.335
3=5.334
I only measured pin 1-3 as suggested i the post.

Q28
Left to right
8.10 7.96 11.94

Q24
Left to right
5.349 0.027 0.018

What do you guys think?
Should i continue with the build or is there a problem with the saw tooth wave?
Maybe im just worrying to much.

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mmm
 
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Re: Saw tooth wave not 150 Hz

Post by mmm »

You didn't mention if you applied the 3v as control voltage.

Basically if you're getting a sawtooth and if its frequency is changed by VR2 you shouldn't worry too much because the VCO basically works. If the listening fails this could have something to do with the fact that 34Hz is a very low frequency that the headphone may not transmit properly.

(On the other hand if you actually applied the 3v we may want to debug the problem right away).

MrNoPain
 
Posts: 4
Joined: Sat Jun 16, 2012 4:23 pm

Re: Saw tooth wave not 150 Hz

Post by MrNoPain »

Thanx for your answer.
This would explain why i didn´t hear anything from the headphones.

I did apply a 3V control voltage to R90 while testing.

Maybe i also should have mentioned that when i received the x0xb0x kit there was a note included that reccomended me to change Q28 transistor.
Instead of using the SK30A-0 i should use SK118-0 in Q28.
The note says that "SK118 produces a far better squarewave".
I did get the SK30A-0 as well if a wanted to use the original transistor instead.

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mmm
 
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Re: Saw tooth wave not 150 Hz

Post by mmm »

MrNoPain wrote: I did apply a 3V control voltage to R90 while testing.
In this case please measure pins 5 and 7 of IC11 (while the 3v are connected).

MrNoPain
 
Posts: 4
Joined: Sat Jun 16, 2012 4:23 pm

Re: Saw tooth wave not 150 Hz

Post by MrNoPain »

Ok this is the voltages on IC 11 with a 3V control voltage on R90.
1= 2.581
2= 5.333
3= 5.331
4= 0
5= 3.0
6= 3.001
7= 3.001
8= 11.93

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mmm
 
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Re: Saw tooth wave not 150 Hz

Post by mmm »

That all looks good.

I'd probably continue with the build; and if there really is an error I'd try to debug it later (especially once the digital part works and the oscillator can be controlled from the keys).

MrNoPain
 
Posts: 4
Joined: Sat Jun 16, 2012 4:23 pm

Re: Saw tooth wave not 150 Hz

Post by MrNoPain »

Ok thanx alot for your advise.
I will continue the build tomorrow.

And also trying to become better friends with my old scope :?

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