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dancelwerk
Joined: Aug 28, 2009 Posts: 93 Location: berlin
Audio files: 2
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Posted: Tue Aug 25, 2015 3:44 am Post subject:
VCO problems |
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Hi to all, I wanna write in the forum to say, heyyy I build three VCOs, and all is Ok, but that is not the true.
I build three VCOs, BC547 matched and I have problems with the waves, I try to set the trimmings but I can't, because when I connect the Saw, all is ok i have a Saw, but in:
oscillator 1
but when I connect the TRI, I have a Ramp, and with more amplitude (is a same SAW out but inverted and with more gain). When connect the Sinewave I have half sine and suddenly a total decay, start in negative and finish in positive and drop.
The pulse not sounds, only when you put the Pulse width pot at -5, and the you have a 25%, in -3 or above doesnt sound.
oscillator 2
the same but there is not Sinewave.
oscillator 3
in progress, not finished.
I cant get Stiroflex or silver mica, I put a picture later to the cap that i have.
T2 is 20k
R11 is 47k because I have a tempco of 2k and Yusynth suggest me change the original value to this value in one email.
R23 is 100k
Line Fm, Exp fm, sync, and pwm jacks works perfectly.
I hope your help.
Thanks in advance. |
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gdavis
Joined: Feb 27, 2013 Posts: 359 Location: San Diego
Audio files: 1
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Posted: Tue Aug 25, 2015 1:55 pm Post subject:
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Sounds like your saw isn't trimmed properly. You won't get a proper triangle or pulse until your saw is trimmed, and you won't get a proper sine until the triangle is trimmed.
One of the keys to properly trimming the saw is to make sure that your scope is set do DC coupling. This is important to make sure that the saw is symmetric around 0V (+5V to -5V). If your scope is AC coupled, it will remove the DC component and your waveform will always appear to be centered even if it's not.
Double check your scope to make sure it's DC coupled and make sure your saw is centered. If that doesn't get you going, post clear high res pics of both sides of your board. _________________ My synth build blog: http://gndsynth.blogspot.com/ |
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dancelwerk
Joined: Aug 28, 2009 Posts: 93 Location: berlin
Audio files: 2
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Posted: Tue Aug 25, 2015 10:48 pm Post subject:
Capacitor that I used to |
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Hey Gdavis, thanks for answer so soon, ok I check that, but I think that this is not the problem, I have a lot of synths and I know how to sound a Square or a Sine in my ears, you know what I mean, you don't need to see it,
I am checking now voltages, resistor values and all components, I made the three VCOs at the same time and I think that the mistake is the same in the three VCOs, I'll tell you later the progress.
This is the Cap that I have in my Pcbs,
220/1000 and in the other side 2.5
I don't know if this the reason. Other question is checking the schematics I saw in the Capacitor C7, in the layout of appears like 47p, but in the schematics and in the colored layout of components is 100p, I put 100p, is this correct?. Remember my VCO is BC547B version.
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dancelwerk
Joined: Aug 28, 2009 Posts: 93 Location: berlin
Audio files: 2
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Posted: Wed Aug 26, 2015 12:09 am Post subject:
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here we go with measures
oscillator A
+15V on pin 4 of the TL074 and -15.04V on pin 11 of the TL074 (both)
on the leg 10 ohm resistor next to the electro cap +15V postive rail
on the leg 10 ohm resistor next to the tranny +15.16V positive rail
on the leg 10 ohm resistor next to the electro cap -15.06V negative rail
on the leg 10 ohm resistor next to the tranny -15.17V negative rail
on pin 8 of the OPA2137 (I am using a TL072) +13.67V
on pin 4 of the OPA2137 -14.43V
on the long strap beside the 220pF cap : +4.52V
oscillator B
+14.98V on pin 4 of the TL074 and -15.02V on pin 11 of the TL074 (both)
on the leg 10 ohm resistor next to the electro cap +14.98V postive rail
on the leg 10 ohm resistor next to the tranny +15.16V positive rail
on the leg 10 ohm resistor next to the electro cap -15.03V negative rail
on the leg 10 ohm resistor next to the tranny -15.22V negative rail
on pin 8 of the OPA2137 (I am using a TL072) +14.42V
on pin 4 of the OPA2137 -13.75V
on the long strap beside the 220pF cap : +4.57V
all is correct, no? |
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dancelwerk
Joined: Aug 28, 2009 Posts: 93 Location: berlin
Audio files: 2
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Posted: Wed Aug 26, 2015 3:21 am Post subject:
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I have good news,
in Oscillator A all is working, I am making bad the trimming, now works all waves, but I have no linear FM.
in Oscillator B all is working, lin fm, all control ins, but only an issue, I have no Sinewave.
I am worried for sinewave in this oscillator, perhaps is the T4 trimmer I will change. |
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dancelwerk
Joined: Aug 28, 2009 Posts: 93 Location: berlin
Audio files: 2
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Posted: Wed Aug 26, 2015 3:50 am Post subject:
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t4 is ok
any ideas? |
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dancelwerk
Joined: Aug 28, 2009 Posts: 93 Location: berlin
Audio files: 2
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Posted: Wed Aug 26, 2015 4:15 am Post subject:
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ok the sine is here.
now I have only the problem on osc B with lineal fm |
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dancelwerk
Joined: Aug 28, 2009 Posts: 93 Location: berlin
Audio files: 2
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Posted: Wed Aug 26, 2015 4:17 am Post subject:
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hahaha, fuck to me, I have changed the sine in ground jack and ground of pcb in tip, fucking idiot, but is not the first time and too the last..... |
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dancelwerk
Joined: Aug 28, 2009 Posts: 93 Location: berlin
Audio files: 2
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Posted: Wed Aug 26, 2015 6:53 am Post subject:
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Lineal Fm working, was the jack, it was in short, I desolder and solder again and now its working.
I hope to have not the same problems with the third Oscillator.
Dancelwerk |
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