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 Forum index » DIY Hardware and Software » YuSynth
LFO Problems
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Sebo



Joined: Apr 27, 2007
Posts: 538
Location: Argentina

PostPosted: Fri Feb 20, 2009 12:44 pm    Post subject: LFO Problems
Subject description: Waveforms and frequency are wrong
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Hi Yves:
I have some problems with the LFO.
First of all I have the range switch inverted, I wired exactly as the picture.
Not a big problem just have to rewire it, I mention it because could lead
to the solution of the other problems.
Second, the frequency is to high, with the switch in X1 the frequency
goes from 500Hz to 10000Hz, and with the switch in X0.1 the frequency
goes from 50Hz to 1000Hz.
I used a tantalum 10uF cap and poliester 1uF, in the BOM is not especified
so I bought it poliester, lately when I start the calibration process, I read
in the calibration instructions that it should be tantalum too. I don't think
this can cause such a big frequency shift.
Finally the waveforms are strange:
The SAW is a little bit trianglish (I post a picture to show what I mean).
The TRIANGLE have a portion inverted and is a little bit sinish.
And the SINE have the same portion inverted.
Also the waveforms looks diferent depending of the postion of the range switch.
This is the first Yusynth module I have problems with.
To be honest I'm so tired at this moment to do a serious trobleshooting,
but I checked for posibles mistakes and found nothing.
I will retake the work tomorrow, but if you (or somebody else) could point me
in the right direction will be great.
Thank you.

EDIT: I forgot to mention that the pictures of the waveforms are after calibration.
That are the best I could get.

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Last edited by Sebo on Fri Feb 20, 2009 12:52 pm; edited 3 times in total
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Sebo



Joined: Apr 27, 2007
Posts: 538
Location: Argentina

PostPosted: Fri Feb 20, 2009 12:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Last picture...
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Sebo
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Sebo



Joined: Apr 27, 2007
Posts: 538
Location: Argentina

PostPosted: Fri Feb 20, 2009 12:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Last picture...
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Sebo
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yusynth



Joined: Nov 24, 2005
Posts: 1222
Location: France

PostPosted: Fri Feb 20, 2009 4:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Here are some possible mistakes : the fact you have very high frequency can be due to a common error with this module either you used a BC547 for Q1 instead of a BC557. If this is not the case and you are already using a BC557, check that it is a BC557B as specified in the BOM and not a BC557C. A BC557C provides a to high charging current. If you were already using a BC557B then you'll have to heck the values of R1,R3,R5(100K),R6(27K) and R7 (820). Make sure R7 is correctly soldered on both sides.
Check also that your soldered all the jumpers.

By the way what are the settings of your scope ? y : V per square ? Is the middle horizontal line indicating 0V ? What is the frequency of the wave shape you show ?

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Sebo



Joined: Apr 27, 2007
Posts: 538
Location: Argentina

PostPosted: Fri Feb 20, 2009 4:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Yves:
I don't have the LFO here, I will check tomorrow. I don't think I used a
BC547 instead a BC557, but I'm not sure about the subfix.
About the settings at the scope, the middle line is at 0V, 2V per square,
and the frequencies are the states in my previous post:
The first 3 pics with the switch at X1, frequncy: 10KHz
The last 3 pics with the switch at X0.1, frequency: 1000Hz
Thank you.

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Sebo



Joined: Apr 27, 2007
Posts: 538
Location: Argentina

PostPosted: Sat Feb 21, 2009 1:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Yves:
I checked Q1 and is a BC557B, also I checked R1, R3, R5, R6 and R7 and
are correct values (at least reading the colour code). I checked the that R7
is correctly soldered at both sides. Also looked for shortcircuits or broken
tracks, and all seems OK.
The only error I found was the wiring of the range switch (I stated it was
correct, but a better look today, being fresh, shows that I swaped 2 wires).
About the strange waveforms, I discovered that D1 and D1 looks a bit
different than all 1N4148 I have (shorter and rounder), and ar unlabeled,
so may be wrong diodes, I will change them to see if that correct the
waveform problem. But the frequency problem is a mystery by now.
If I can find the problem I will change all resistors in the summing opamp
section and Q1.
Thank you.

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Sebo
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yusynth



Joined: Nov 24, 2005
Posts: 1222
Location: France

PostPosted: Sat Feb 21, 2009 3:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK check the voltages at the output of the 741 (pin 6). First adjust T1 to have 0V at its wiper pin. Then when cranking the frequency pot from min to max you should measure a voltage varying from 0V to -7V. Next measure the voltage at the base o Q1, there you should get something a voltage from 14,55V to 14,35V, that is a variation of 0,2V. If you have values significantly diffrent from these then the problem comes either from R1,R3,R5,R6,R7 or U4. If these voltages are correct then the problem is either coming from Q1, C1 or U1 (7555).
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yusynth



Joined: Nov 24, 2005
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PostPosted: Sat Feb 21, 2009 3:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Which version 1 or 2 hdid you build ?
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Yves
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Sebo



Joined: Apr 27, 2007
Posts: 538
Location: Argentina

PostPosted: Sat Feb 21, 2009 5:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Yves:
I build version 2 of the LFO.
I will measure the voltages on monday.
Thanks a lot for your help.

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Sebo
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www.myspace.com/cosaquitosenglobo
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yusynth



Joined: Nov 24, 2005
Posts: 1222
Location: France

PostPosted: Sat Feb 21, 2009 11:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sebo wrote:
Hi Yves:
I build version 2 of the LFO.
I will measure the voltages on monday.
Thanks a lot for your help.


In that case remove the BS170 to run the tests.

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Sebo



Joined: Apr 27, 2007
Posts: 538
Location: Argentina

PostPosted: Mon Feb 23, 2009 6:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Yves:
Things are getting better.
When I was trying to set T1 to 0V, I realized that I can't reach 0V, I replaced the Trim and now all seems to work more or less right.
I measured 0V to -6.28V at pin 6 of the LM741 and 14.4V to 14.2V at base of Q1.
The frequency is still a little bit high, with the range switch at X1 the max freq is 143Hz and with switch at x0.1, max frequency is 15Hz (T1 is at 0V).
I was using a borrowed oscilloscope, and don't have it now, so I can't measure the minimum frequencies.
I don't know how to lower the frequency, or if I should, but now it works as an LFO at least.
Also the waveforms look as should be (after some tweaking), but the triangle and the sine, both have a glitch in the middle of the positive half cycle (the negative half cycle is OK), could I do something to get rid of it?
Finally the sync wasn't working, I didn't check before I remove the BS170, so maybe I fried it, but after I relocated it, the sync did nothing. I changed the BS170 for a BC547 (I didn't have another BS170) and the sync started to do something, but not what I was expecting. The incoming pulse syncs the LFO but also gates it, so the LFO works while the pulse is active. I tested it using the LFO of my MS-10 (wich has variable pulse width) as sync source, and when the sync pulse is too narrow the LFO stops working. Is all this normal? should I try a new BS170?
Thank you.

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yusynth



Joined: Nov 24, 2005
Posts: 1222
Location: France

PostPosted: Tue Feb 24, 2009 12:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi
All you describe looks normal. Normally you should adjust the lowest frequency with the trimmer T1. If you wish to get lower try different BC557B or even a BC557A for Q1.

Concerning the glitch in triangle and sine this normal and it should be very brief such that you should not notice it when you use the LFO to modulate the VCO. Normally the capacitor C5 is there to filter out the glitch you may increase its value up to 220pF in order to minimize the glitch.

Concerning the SYNC, it should also work with a BC547 but not as efficiently as with a BS170. The circuit is designed to sync the LFO (reset the sawtooth to it's start on a rise up at the input) not to clamp it (blocks oscillation as long as the input is high). The korg LFO you mention does clamping . If you want to obtain clamping instead of synching then you simply bypass cap C6 (which acts as differentiator).

Cheers

Yves

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Last edited by yusynth on Wed Feb 25, 2009 12:23 am; edited 1 time in total
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Sebo



Joined: Apr 27, 2007
Posts: 538
Location: Argentina

PostPosted: Tue Feb 24, 2009 7:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Yves:
The BC557B I used has an hFE of 336, I changed it by the one with the lower
hFE (320) in the batch I have, but it only lowered 5Hz the max frequency
to 138Hz. I will try a BC557A if I find one (belive it or not, at the local stores
don't separate transitors by subfix, they have what they have, all mixed up).
I'm happy with the frequency now, but I want to get closer to the label on
the front panel Smile
Also, you where right about the glitch, I modulated a VCO and I didn't notice it.
Thank you very much for your help.

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joshco



Joined: Nov 14, 2008
Posts: 48
Location: germany

PostPosted: Wed Feb 25, 2009 4:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Then i can go on with some troubleshooting Laughing

I have built version1 with the inverted output.
There is only a steady Voltage at the output, the LED is not blinking, its glowing the whole time.

I have checked:
Traces and solder points
changed the IC´s
no IC´s getting hot
no shorts (i´ll check it again)

maybe someone knows to localize the error...
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joshco



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PostPosted: Thu Feb 26, 2009 5:46 am    Post subject: Reply with quote  Mark this post and the followings unread

furthermore i have checked the +-15v voltages at the ic´s and the grounding points, and resoldered the pads


Quote:
First of all I have the range switch inverted, I wired exactly as the picture.

what does inverted mean?

Thanks!
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yusynth



Joined: Nov 24, 2005
Posts: 1222
Location: France

PostPosted: Thu Feb 26, 2009 2:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Joshco

I am back from a long trip, I will answer your questions tomorrow.

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joshco



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PostPosted: Thu Feb 26, 2009 3:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

allright, thank you Yves, take your time, there´s no hurry Very Happy
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yusynth



Joined: Nov 24, 2005
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PostPosted: Fri Feb 27, 2009 12:17 am    Post subject: Reply with quote  Mark this post and the followings unread

joshco wrote:
Then i can go on with some troubleshooting Laughing

I have built version1 with the inverted output.
There is only a steady Voltage at the output, the LED is not blinking, its glowing the whole time.

I have checked:
Traces and solder points
changed the IC´s
no IC´s getting hot
no shorts (i´ll check it again).


OK do you have normal signals at the direct outputs (the non inverted) ?
Have you connected R43 (not on the PCB) as shown in the wiring diagram ?

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joshco



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PostPosted: Fri Feb 27, 2009 4:19 am    Post subject: Reply with quote  Mark this post and the followings unread

at the direct outputs is also a steady voltage
square -5,6v
saw triangle and sine -15v
i have only a cheap multimeter, no oszilloscope
the resistor R43 is connected

i also have adjusted the offstet trimmer and bias but it has no effect...
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yusynth



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PostPosted: Fri Feb 27, 2009 5:56 am    Post subject: Reply with quote  Mark this post and the followings unread

joshco wrote:
at the direct outputs is also a steady voltage
square -5,6v
saw triangle and sine -15v
i have only a cheap multimeter, no oszilloscope
the resistor R43 is connected

i also have adjusted the offstet trimmer and bias but it has no effect...


OK then this means that it doesn't oscillate at all, therefore we will have to check the heart of the circuit. Can you make the voltage measurements I mentioned in a previous message for Sebo ?

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joshco



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PostPosted: Fri Feb 27, 2009 6:40 am    Post subject: Reply with quote  Mark this post and the followings unread

yusynth wrote:
OK check the voltages at the output of the 741 (pin 6). First adjust T1 to have 0V at its wiper pin. Then when cranking the frequency pot from min to max you should measure a voltage varying from 0V to -7V. Next measure the voltage at the base o Q1, there you should get something a voltage from 14,55V to 14,35V, that is a variation of 0,2V. If you have values significantly diffrent from these then the problem comes either from R1,R3,R5,R6,R7 or U4. If these voltages are correct then the problem is either coming from Q1, C1 or U1 (7555).


ok, i´ve adjusted T1 and measurred a voltage from 0 to -8v
at the Base of Q1 is a steady voltage of 15V

R1,3,5,6,7 have the value from the BOM
I´ve also tested different tl071, 7555 without success...
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joshco



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PostPosted: Fri Feb 27, 2009 6:47 am    Post subject: Reply with quote  Mark this post and the followings unread

C1a is a 1µ polyester, had also tested an elco
C1b is 10µ tantal, maybe i change it with an another one, but switching has no effect
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yusynth



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PostPosted: Fri Feb 27, 2009 6:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
ok, i´ve adjusted T1 and measurred a voltage from 0 to -8v
at the Base of Q1 is a steady voltage of 15V

R1,3,5,6,7 have the value from the BOM
I´ve also tested different tl071, 7555 without success...

OK with T1 adjust to 0V, yous should obtain a continouous variation (when tweaking the frequency pot) from 14.2 to 14.5V at the base of Q1. If not, check that you have a variation from 0 to -6.5V at pin 6 of the TL071.
If you don't have these values at pin 6 of the TL071 then there must be either a short cut somewhere or a dead component.

C1 has nothing to do with the problem apparently.

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joshco



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PostPosted: Fri Feb 27, 2009 7:15 am    Post subject: Reply with quote  Mark this post and the followings unread

at pin 6 i have the full range from 0 to -7v when turning the rate pot
at the base of the transistor i have a small variation, as far my multimeter can deteced it from
from 0,3v
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yusynth



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PostPosted: Fri Feb 27, 2009 7:28 am    Post subject: Reply with quote  Mark this post and the followings unread

joshco wrote:
at pin 6 i have the full range from 0 to -7v when turning the rate pot
at the base of the transistor i have a small variation, as far my multimeter can deteced it from
from 0,3v

OK up to the base of Q1 all seems correct.

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