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Buchla 208r V2.1 (Blue) Build Thread
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page Previous  1, 2, 3 ... 20, 21, 22 [all]
Author Buchla 208r V2.1 (Blue) Build Thread
papz
Sorry but your descriptions and answers to my questions are not clear. This makes it very difficult to figure out what happens and help you.

What do you mean by "the above case is no problem" ?
Are the LPG2 and channel B working ? Could you trace the signal as I told you ? Which signal was it ? MO ? CO via LPG1 ? External ?
From your previous posts, I understood this output is not working but the MO works as a modulation source.

Can you post pics of your cards and of the oscilloscope displays, detailing where it was measured and the related panel settings ?
wedaman
I'm sorry for the late reply.

papz wrote:
Any value from 10k to 100k is ok but a faulty channel B pot could also be a cause.

When I checked with the scope, channel B pot is working.
Because, when channel B pot is CCW, the waveform becomes horizontal. And CW, the height of the waveform becomes maximum.


papz wrote:
With a signal routed to LPG2 fully open, you can check for signal with the scope from card 11 pin 3 and trace it untill card 12 pin 11 via the pot and R71 33k resistor on the MB.


I traced the MO signal.
The routing switch is centered, LPG 2 and channel B pot are fully opened.


The following are the images of the scope of each part.

at card 11 pin 3.



at channel B pot center pin on MB (fully opened).



before R 71 33 k resistor on the MB.



after R 71 33 k resistor on the MB.



at card 12 pin 11.



I think there is a problem with R 71 33 k resistor. But R 71 is a correct value.



I would like to ask your opinion.
Any advices are welcome.
papz
With the routing switch in central position, this sine wave is a bit surprising : the MO has no sine output. It looks like it's the CO output.
Is the routing switch good working ? The IC related to this switch is IC1 on card 11.
tarandfeathers
papz wrote:
With the routing switch in central position, this sine wave is a bit surprising : the MO has no sine output. It looks like it's the CO output.
Is the routing switch good working ? The IC related to this switch is IC1 on card 11.


I don't think the MO is producing any output (or it is not making it through the switches on the modulator), according to the scope traces that sine wave is over 28kHz so something in the MO signal path is unstable and oscillating. There shouldn't be any signal on the scope at card 12 pin 11 anyway, this is right on the inverting input of an op amp whose non-inverting input is tied to ground - an op amp always tries to keep its inputs equal so it uses its output to force the inverting input to ground as well.

Is there anything more sensible looking on card 6, pin 4? The signal levels mentioned earlier sound low to me, there should be around 7.5Vp-p at this point, wedaman reported getting only around 0.67V?
papz
Thanks tarandfeathers. 28kHz is high for the CO indeed.

Wedaman wrote the MO modulates the CO as it should, so the CV output is working and I assumed the signal output it's taken from is thus working as well, but it's good to doublecheck indeed.
wedaman
Thanks Guys.

I swaped IC 1 of card 11 five times. Is it still necessary to swap?
Do you know how to check whether the IC is OK or error?


These are waveshape images of card 6 pin 4.
I have not calibrated yet. sorry.

It's saw.



It's rectangle.(I understand not square, haha )


It's triangle.



Please let me know what you think.
Any advice will be of help to me.
tarandfeathers
Although the shapes and amplitude are approximately correct, the frequency is well outside the range of what the MO should be producing. Where were the frequency slider and fine tune pot set when these images were taken?

I think you need to remove card 6 and double and triple check all solder joints and values, maybe post photos? If you can get the card operating in the correct range then the waveshapes should be much better formed.

The LPG and output amplifier are almost certainly working okey, but the signal coming from the MO is completely out of band and will not be passed (it is low pass filtered to the sine-like wave you posted earlier), plus it is outside the range of human hearing so you wouldn't hear it anyway.
wedaman
tarandfeathers wrote:
Although the shapes and amplitude are approximately correct, the frequency is well outside the range of what the MO should be producing. Where were the frequency slider and fine tune pot set when these images were taken?

I think you need to remove card 6 and double and triple check all solder joints and values, maybe post photos? If you can get the card operating in the correct range then the waveshapes should be much better formed.

The LPG and output amplifier are almost certainly working okey, but the signal coming from the MO is completely out of band and will not be passed (it is low pass filtered to the sine-like wave you posted earlier), plus it is outside the range of human hearing so you wouldn't hear it anyway.


Hi tarandfeathers,
I appreciate your precise advice.
The frequency of MO is out of range. I understood.
Certainly the sound of my MO is like a mosquito sound.
I will go back home and check double triple card 6.
I will post the results.
papz
According to these previous reports the MO is able to oscillate at LFO rate. The out of range is likely due to a wrong setting of its preset and range trimpots on the MB.
I wonder if it's not a user problem rather than an electronic issue.

wedaman wrote:
<a.m.osc>
I moved the MO index sliders up. The sound of CO gradually became smaller. It is not completely quiet.

<f.m.osc>
I moved the MO index sliders up. The pitch of CO gradually down.


wedaman wrote:
When I increase the MO frequency, the CO pitch did't amplitude modulation well get faster.
tarandfeathers
You could also interpret those comments as meaning that the sound of the CO changes as the index slider is moved, but does not necessarily continue changing when the slider stops moving. Even with external CV, I'd be surprised if you could get the Mo up to that frequency in normal circumstances.
papz
Unlike the CO that is limited to about 2.5 kHz the MO is able to oscillate at high frequency above the audio range. On my 208, properly calibrated, I can drive it up to 30 kHz using the ToolBox frequency switch and panel input together as CV sources.
tarandfeathers
papz wrote:
On my 208, properly calibrated, I can drive it up to 30 kHz using the ToolBox frequency switch and panel input together as CV sources.


No doubt, but I wouldn't describe that as "normal circumstances" when troubleshooting a suspect module :wink:
papz
Indeed, but with the panel settings and trimpots all the way up, I wouldn't be surprised if the MO oscillates at 30kHz, I won't uncalibrate mine for test purpose only though wink

Improper calibration and panel settings upset effective troubleshooting, so we're likely not under "normal circumstances".

Hence my wondering regarding a user error :
- if the MO oscillates above the human ear audible range, it's normal not to hear it
- some measures, descriptions and answers of Wedaman are incomplete, vague, wrong or contradictory
- Wedaman doesn't seem to have a very clear idea of how the 208 works and what it's supposed to do
wedaman
Sorry, my English is not good.
Wait a while for the results. hyper
wedaman
I checked card 6 three times. But the sound of MO is like a mosquito sound.
I didn't swap only Q1 (2N4341) of card 6. I will swap as soon as parts arrive from mouser.

They are the images of card 6.
[img][/img]

[img][/img]


pa726.
[img][/img]

[img][/img]


Also the images of card 11.
[img][/img]

[img][/img]


Do you have any advice?
Thanks.
papz
What are the panel settings when the MO sounds like a mosquito ?

C4 on card 11 looks very big for a 1µF cap, should be the same as C5.
Same for card 10 just in case.
Sammus
papz wrote:
What are the panel settings when the MO sounds like a mosquito ?

C4 on card 11 looks very big for a 1µF cap, should be the same as C5.
Same for card 10 just in case.


C4 on card 11 is likely swapped as per the recommended mod on https://modularsynthesis.com/roman/buchla208v2/208spss.htm

Quote:
The MO is mixed to the signal output through C4 on Card 11. This is a 1 µF capacitor feeding a 10K potentiometer which is a high pass filter with a lower frequency cutoff of 15 Hz. I increased C4 to 47 µF with a capacitor on the rear of the card where there is more room. This allows lower frequency MO output to be passed through on the signal outputs. This scope image shows the mixing of a low frequency MO triangle with a high frequency CO which is not possible with the original 1µF capacitor.
papz
Thanks for the info, I didn't know this mod, the latest time I checked Dave's page in details was long ago.
wedaman
This movie is the MO sounds like a mosquito.
https://youtu.be/wrGz6U-hMk0

The channel A level is 2.5 but the channel B level is 10.
The channel B is very small sound.

Do you have any advice?
Thanks.
tarandfeathers
I think I have heard that people with fake uA726s found that their oscillators produced extremely high frequencies (relatively speaking). Perhaps there is a build error with the pA726 on the MO card or a faulty CA3046? You can try replacing the sub module temporarily with two 2N3904 (or any generic NPN transistor) and see if this improves the behaviour - tracking/temperature stability won't be good but it should oscillate at the correct frequency.
wedaman
tarandfeathers wrote:
I think I have heard that people with fake uA726s found that their oscillators produced extremely high frequencies (relatively speaking). Perhaps there is a build error with the pA726 on the MO card or a faulty CA3046? You can try replacing the sub module temporarily with two 2N3904 (or any generic NPN transistor) and see if this improves the behaviour - tracking/temperature stability won't be good but it should oscillate at the correct frequency.


Thanks tarandfeathers.
I have 2N3904s. I try your excellent advice ! hyper
Sammus
Hi!

I just finished casing my 208r build, almost everything is perfect, except the pulser doesn't trigger from the keyboard!

1) I have read Dave Brown's guide, and have install the missing link from SW8 to SW10 which I think is meant to solve this exact issue:
Dave Brown wrote:

A 218 V1 will sometimes not trigger correctly as the pulse output is only about 6V. You can parallel a 240K resistor across R56 on the back of the motherboard to change the pulse in threshold from 10V to 5V. This changes the threshold for the Pulser, Sequencer, and Envelope Generator. However, the Pulse input will NOT trigger the pulser when Keyboard is selected. There is a run missing to SW10. Add a wire on the motherboard rear between SW8 and SW10 as shown below.


2) 218 I'm using is a V2 with a "proper" pulse output, and the pulse successfully triggers the envelope and steps the sequencer if set to.

3) I have checked the pulser switch continuity as per the part number, and it is functioning as it should. I checked all before installing them, and then again now I have noticed this issue smile

4) Double checked panel settings smile the bottom pulser switch is is set to "triggered" and the top one is set to "keyboard".

Any guidance here would be much appreciated! thanks!
kashmir
Hello everyone,

I was extensively calibrating my recently finished 208 (big thanks to all builders for sharing the tips and mods!) and I was wondering how should the timbre circuit perform. I'm able to get enough of folds and have no unwanted oscillations but still there are some "pops" in the sound when increasing timber slider at higher frequencies. On the scope the waveform is smoothly shaping and then suddenly jumps forward a bit, it is usually at the moment when the rising peak is changing to dip. This happens more with higher frequencies (say 500hz above) and higher slide range (6-10). It pops usually 2 3 times between 6-10 on the slider and always at the same spots so it is not random. I tried different resistor changes on various recommended places and all possible calibrations, but the combination of few folds+higher pitch+ strong timbre always causes it.

Is this behavior usual or the timbre can work smoothly at all settings?

Another thing that no one mentioned is that the spring reverb oscillates a lot, sometimes it howls really loud, so no speakers or headphones are needed to hear the easel smile anyone has simillar issue?
keithwin
Hi All,

Looking to buy a Music Easel Infinite Sustain Module by Dunnington Audio, anyone got a spare?

Many thanks

Keith


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