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hoby
Joined: Jan 30, 2018
Posts: 21
Location: Copenhagen
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 Posted: Fri Mar 09, 2018 10:42 am Post subject:
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| gdavis wrote: |
Based on that, off hand I'd say double check C7 (100pF), that both emitters of J4 are connected to R15, R15 is not shorted and that the base of J4 that should be connected to ground actually is. |
I have gone through the points, and it looks as it should. C7 is the right value, and the base one the right J14 is connected to ground, and both emittrds to R15.
Also probed around U5, and connections and values seems to be right. I get around 500k when I measure across R19. |
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gdavis
Joined: Feb 27, 2013
Posts: 359
Location: San Diego
Audio files: 1
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| Posted: Fri Mar 09, 2018 11:16 am Post subject:
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| hoby wrote: |
I have gone through the points, and it looks as it should. C7 is the right value, and the base one the right J14 is connected to ground, and both emittrds to R15.
Also probed around U5, and connections and values seems to be right. I get around 500k when I measure across R19. |
Ya, that was the next area I was thinking of looking. R19 may not read accurately in circuit because of the other components connected to it, but if it's low that could cause problems. You could try removing it and see how the circuit behaves. You'd lose the hysteresis but it should still function.
I'm curious what the actual voltages are at U5 pin 2 and the gate of the JFET (probably need to scope them because of the pulsing) as well as the signal at U5 pin 3 (should look like U6 pin 7 but I'm curious what voltage the bottom of the saw is at).
Some of the reset circuity is pretty sensitive so you need to measure carefully here.
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My synth build blog: http://gndsynth.blogspot.com/ |
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hoby
Joined: Jan 30, 2018
Posts: 21
Location: Copenhagen
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| Posted: Fri Mar 09, 2018 1:12 pm Post subject:
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| gdavis wrote: |
I'm curious what the actual voltages are at U5 pin 2 and the gate of the JFET (probably need to scope them because of the pulsing) as well as the signal at U5 pin 3 (should look like U6 pin 7 but I'm curious what voltage the bottom of the saw is at).
here. |
Ok - I started measuring at U6 Pin7 on channel 2, and U5 pin2 on channel 1
At 51 Hz
 [/url]
At 203 Hz
 [/url]
and at approx 1 kHz
 [/url]
U5 pin 2 is around -0.1V throughout |
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hoby
Joined: Jan 30, 2018
Posts: 21
Location: Copenhagen
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| Posted: Fri Mar 09, 2018 1:24 pm Post subject:
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And the same but U6 pin7 against U5 pin3
They are identical
50 Hz
 [/url]
100 Hz
 [/url]
1 kHz
 [/url] |
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gdavis
Joined: Feb 27, 2013
Posts: 359
Location: San Diego
Audio files: 1
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| Posted: Fri Mar 09, 2018 6:13 pm Post subject:
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Oh, sorry, you need to turn your coupling from AC to DC so we can see what the DC offset is. This is also necessary for adjusting T3 and T4 which may explain your tri and sine wave shapes, but not the tuning instability.
Also, U6 pin 7 doesn't look right, the amplitude doubled. You sure that wasn't pin 1?
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My synth build blog: http://gndsynth.blogspot.com/ |
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hoby
Joined: Jan 30, 2018
Posts: 21
Location: Copenhagen
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| Posted: Sat Mar 10, 2018 3:30 am Post subject:
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| gdavis wrote: | Oh, sorry, you need to turn your coupling from AC to DC so we can see what the DC offset is.
Also, U6 pin 7 doesn't look right, the amplitude doubled. You sure that wasn't pin 1? |
Ah my mistake, sorry.
Here is the measurement setup for (U6 p7) and (U5 p2)
And the DC coupled measurements at 1 kHz
and 50 Hz
and just to make it complete (U6 p7 ) and (U5 p3)
Ill remember your point about DC when I get to adjusting the shapes. |
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gdavis
Joined: Feb 27, 2013
Posts: 359
Location: San Diego
Audio files: 1
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| Posted: Sun Mar 11, 2018 2:46 pm Post subject:
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Why do all the images show 1.00 V/ except the last one which has 2.00 V/? Is that the volts per division or something else?
If everything is actually 2V/div then these last images look pretty OK. The curve is much less pronounced than in the earlier images, has anything else changed?
Your U5 pin 2 measurement is actually connected to c10. In theory this should give you the same reading since they are connected together. The thing is, the circuit isn't behaving as it should which means something may not be connected as it should be, so it's important to measure the specific points of interest. If you've already checked both points and confirmed that they match then that's fine, but just wanted to mention it to make sure.
What's going on at U6 pin 7? Looks kind of funny but I can't really see in the image. Is the socket broken or obscured by the probe or something?
You may want to try trimming everything up again and see how it looks.
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My synth build blog: http://gndsynth.blogspot.com/ |
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hoby
Joined: Jan 30, 2018
Posts: 21
Location: Copenhagen
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| Posted: Sun Mar 11, 2018 4:12 pm Post subject:
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| gdavis wrote: | Why do all the images show 1.00 V/ except the last one which has 2.00 V/? Is that the volts per division or something else?
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Yes it is the voltage division. The pictures were not taken in the order I have presented them, and I may have been fooling around in between them, zooming in and out to get of the best resolution, but always having ground or 0 volts in the centre. I should have mentioned that.
| gdavis wrote: |
Your U5 pin 2 measurement is actually connected to c10. In theory this should give you the same reading since they are connected together.
The thing is, the circuit isn't behaving as it should which means something may not be connected as it should be, so it's important to measure the specific points of interest.
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Yes, it is a bit hard to get to the legs on the chip with my probes without risks of shorting, so I made sure beforehand that there was zero resistance between the U5 pin2 and C10.
| gdavis wrote: |
What's going on at U6 pin 7? Looks kind of funny but I can't really see in the image. Is the socket broken or obscured by the probe or something?
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Nah, the socket is fine, it is just the large probe tip getting in the way in the picture, and perhaps the funny angle with the camera. It does look a bit funny. On U6 I could actually get my large probe directly on pin7 without any problem as it was the outer leg. |
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hoby
Joined: Jan 30, 2018
Posts: 21
Location: Copenhagen
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| Posted: Mon Mar 12, 2018 4:01 am Post subject:
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And the recalibration did not change the behaviour.
As I have three boards with the same issue, it think is is unlikely (but not impossible) that I did the same mistake three times.
Perhaps it would make makes sense to look at changing the components like J111/112 and the LM311 as the boards behaves as they should above 200Hz - both in terms of tracking and wave shapes. It is only at low frequencies something is going on.
On that note, I just noted that Yusynth site specifies a LM311N - mine does not have the "N" in the type name. Could it be as simple as that? |
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hoby
Joined: Jan 30, 2018
Posts: 21
Location: Copenhagen
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| Posted: Sat Mar 17, 2018 1:07 pm Post subject:
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| ok - so got to change the j111, the LM311N and the OPA2137 with fresh new components today as new parts arrived. Sadly it made no difference. |
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