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 Forum index » DIY Hardware and Software » fonik's place
5-channel Attenuverting Mixer 2nd run
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fonik



Joined: Jun 07, 2006
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PostPosted: Fri Mar 19, 2010 3:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

BZX85 is just the series and the 0 might be a C actually (BZX85/C ZENER Diodes)?
anyways, i would go through the circuit step by step, starting with measuring the voltage at the switching tip of the input sockets to see what's the offset voltage (ZENER controlled).

BTW did you already check the continuity of all connections of the non-working channels? without pondering too much i just smells like a wrong wired potentiometer (however it is funny that two channels behave the same way - but things happen and the both channels are not connected to each other, so...).

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wmonk



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PostPosted: Fri Mar 19, 2010 4:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, measuring the input voltages:
Channel 1: 0V, Channel 2: 0V, Channel 3: 0V, Channel 4: 0V, Channel 5: 0V
The voltage across the Zener is 6.28V
All potentiometers have 6.4V across, with, from backside view, pins downward, the left panel positive pin on multimeter. Except for channel 1, there it is 5.9V across.
Checked all jacks, and no problems there.

Thanks for the help Matthias! Smile

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fonik



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PostPosted: Sat Mar 20, 2010 1:15 am    Post subject: Reply with quote  Mark this post and the followings unread

seem to be okay, so far. the differences in the voltage at the CW of the potentiometers is due to the measurements in a living cicuit, i'd say (remember there are also trimmers involved).

next step would be to measure the voltage at the potentiometers wipers (middle pin) and to check if the potentiometers CCW is connected to GND.

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PostPosted: Sat Mar 20, 2010 6:26 am    Post subject: Reply with quote  Mark this post and the followings unread

The CCW ends of the potentiometer are all connected to the ground.
The voltages of the wipers 4 depends on potentiometer of 1? That is strange....
pots 2, 3 and 5 go from 0V to 6.4V.

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fonik



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PostPosted: Sat Mar 20, 2010 9:32 am    Post subject: Reply with quote  Mark this post and the followings unread

wmonk wrote:
The voltages of the wipers 4 depends on potentiometer of 1? That is strange....

interaction, that should not be.
and what do you measure?

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PostPosted: Sun Mar 21, 2010 12:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Voltage across pot 1: outside pins.
Potentiometer to the CCW end: 0V, halfway: 6.86V, CW end: 7.32V, about the same for the wiper value.
Pot 1 to the CCW end, measure at Pot 4, wiper with reference to ground. CCW: 0V, halfway up: 0.01V, CW: 0.02V
Pot 1 halfway up, measure at Pot 4: CCW: 0V, halfway: 3.94V, CW: 7.17V.

In fact, all other pots act the same as pot 4, the values depend on the setting of pot 1.

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fonik



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PostPosted: Sun Mar 21, 2010 2:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

tomorrow i will have the time to ponder upon your measurements.
however, from a 1st look at your measurements and observations i would say: replace and rewire potentiometer 1.
it should work as a voltage divider, so the voltage at CW should always be the reference voltage from the ZENER, whilst the voltage on the wiper should change from 0V to reference voltage (CW).
maybe there is a short between CW and wiper (inside the pot, or at the board). then the potentiometer would act as a variable resistor, not as a voltage divider. this would cause a change in the reference voltage, as far as i can see now (without looking at the schematic and thinking more about it), thus affecting the other channels...

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PostPosted: Sun Mar 21, 2010 3:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the help. Replaced the pot, and now channel 1, 2, 3, and 5 are working great. Channel 4 remains on 5.81V whatever setting of the pot, and the mix out remains at -9.3V
Time to track down those problems Smile

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fonik



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PostPosted: Sun Mar 21, 2010 11:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

great. one problem solved.
what about the 4th potentiometer. what do you measure now at it's pins?

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PostPosted: Thu Mar 25, 2010 12:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

any news on your side, wmonk?
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PostPosted: Thu Mar 25, 2010 12:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh sorry Matthias, I can't work on modules on monday to fridays, as the modular is at my parents (have more room there)
I'll measure the other pins on friday evening Smile Thanks for the help!

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PostPosted: Sun Mar 28, 2010 8:29 am    Post subject: Reply with quote  Mark this post and the followings unread

All pots on the 0 (center) position. Potentiometer 4 in the CCW position, voltage across wiper and right pin: 0V. Center position: 3.2V, CW position: 6.4V
Whatever the position of pot 4, the output voltage of channel 4 is 5.89V.

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fonik



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PostPosted: Sun Mar 28, 2010 9:38 am    Post subject: Reply with quote  Mark this post and the followings unread

wmonk wrote:
All pots on the 0 (center) position. Potentiometer 4 in the CCW position, voltage across wiper and right pin: 0V. Center position: 3.2V, CW position: 6.4V

this is what you measured for the other pots, and this is as it should be: it's working as a volage divider.
Quote:
Whatever the position of pot 4, the output voltage of channel 4 is 5.89V.

so we should take a closer look at the other path the voltage goes. check all connections (continuity) of the trimmer T4 and it's accossiated parts. compare the voltages you measure here (behind the trimmer) with those of the other working channels (same potentiometer settings). the opamp is trying to balance the difference between the both inputs, so since the potentiometer side is okay, the error will be at the trimmer/feedback side...

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fonik



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PostPosted: Thu Apr 01, 2010 3:56 am    Post subject: Reply with quote  Mark this post and the followings unread

wmonk, i just wanted to let you know, that i will not be available for the next 10 days.
nevertheless, keep on looking for faulty joints, wrong values around the trimmer...

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PostPosted: Sun Apr 04, 2010 7:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, got channel 4 fixed, the opamp didn't work, and there was no voltage across the trimmer. Still the mixer doesn't work. Tim to fix that Smile
Edit: near the C9 capacitor is a white line on the silk screen. Should that be a wire connection? Embarassed

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fonik



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PostPosted: Sun Apr 11, 2010 4:19 am    Post subject: Reply with quote  Mark this post and the followings unread

wmonk wrote:
Ok, got channel 4 fixed, the opamp didn't work, and there was no voltage across the trimmer.

great. you seemed not to have much luck with the parts you're using.

Quote:
Still the mixer doesn't work. Tim to fix that Smile
Edit: near the C9 capacitor is a white line on the silk screen. Should that be a wire connection? Embarassed

hehe. indeed. a wire jumper to connect the channels to the mixer... i did not call it out as a jumper, since for me it was clear. sorry for causing confusion.
so you will have a working module soon!?

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PostPosted: Sun Apr 11, 2010 4:25 am    Post subject: Reply with quote  Mark this post and the followings unread

It does work now! Thanks a lot! Smile
Fixed it last week, very nice.

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emdot_ambient



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PostPosted: Sun Apr 18, 2010 7:43 am    Post subject: Reply with quote  Mark this post and the followings unread

So.......with the VCPS PCB coming soon, isn't it time for the annual limited run of Attenuverters? Very Happy

Even if no new features were added, I'd be up for 4 of these.
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fonik



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PostPosted: Sun Apr 18, 2010 11:31 am    Post subject: Reply with quote  Mark this post and the followings unread

emdot_ambient wrote:
Even if no new features were added, I'd be up for 4 of these.

what features would you like to see?

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PostPosted: Sun Apr 18, 2010 1:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't requre additional features. I just noticed some people earlier had mentioned some and my post was intended to say "the current module's feature set suits my needs perfectly well."
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LektroiD



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PostPosted: Thu Aug 26, 2010 9:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Just wiring up now, and I notice there are no diagrams and not even a description on how to wire the 3 pole switch in the documentation.

Looking at the board so the text on the switch section of the board is facing myself: There are 3 U shaped indicators on the board relating to the switch. the way I have it wired is the first, third and fifth (the left of each U) connect to the bottom row of the switch, and the 2nd, 4th and 6th (the right of each U) connect to the centre row on the switch.

I don't know if that is correct or if it is related, but the fault I have is when all the pots are centred (and nothing connected) the +LED is glowing softly. If I turn any of the pots clockwise it goes off, if I turn them anticlockwise it glows brighter, and the more pots anticlockwise also brings the -LED on at the same time.

Plugging something into the output disables the pot associated with that output, and moving the trimmer does nothing.

Does anyone have a wiring diagram for the switch, or does it look like I have wired it properly and my fault maybe lies elsewhere?

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fonik



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PostPosted: Fri Aug 27, 2010 12:20 am    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
Looking at the board so the text on the switch section of the board is facing myself: There are 3 U shaped indicators on the board relating to the switch. the way I have it wired is the first, third and fifth (the left of each U) connect to the bottom row of the switch, and the 2nd, 4th and 6th (the right of each U) connect to the centre row on the switch.

correct. if the switch is open, the module is in AC mode. the LEDs shall not be lid then. if the switch is closed, the passive filter on the summed output is bypassed, and the module is on DC mode. the LEDs should work in this mode.

Quote:
I don't know if that is correct or if it is related, but the fault I have is when all the pots are centred (and nothing connected) the +LED is glowing softly. If I turn any of the pots clockwise it goes off, if I turn them anticlockwise it glows brighter, and the more pots anticlockwise also brings the -LED on at the same time.

there is something wrong. the +LED should get brighter when any pot is turned clockwise, and darker when any pot is turned counter clockwise.

Quote:
Plugging something into the output disables the pot associated with that output, and moving the trimmer does nothing.

plugging any single out should just remove this output from the sum (thus you won't see any effect on the LEDs then). however, the pot should still work for this channel/single out.

Quote:
...fault maybe lies elsewhere?

i believe so.

IMHO most errors are wiring related. some suggestions:
just triple check the pots wiring.
check the orientation of the +LED.
each input is normalled to 5V. check and follow this voltage of a channel throughout the entire circuit using a multimeter (does it appear on the switching contact of the input socket? does it appear on the single output socket? does it appear at the summing stage? does it appear at the LED driver?).
try to follow the calibration instructions.

hope that helps.

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LektroiD



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PostPosted: Fri Aug 27, 2010 5:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
check the orientation of the +LED.


Problem solved! Embarassed

That's the last time I'm using heat shrink cable sleeves before everything is tested!

Thank you.. I need more of these, lots more!!!

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fonik



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PostPosted: Sat Aug 28, 2010 2:50 am    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
fonik wrote:
check the orientation of the +LED.


Problem solved!

Cool

Quote:
Thank you.. I need more of these, lots more!!!

it's now available as ready built module:
fonitronik at schneiders
fonitronik at analoguehaven

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LektroiD



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PostPosted: Sat Aug 28, 2010 5:08 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
LektroiD wrote:
Thank you.. I need more of these, lots more!!!

it's now available as ready built module:
fonitronik at schneiders
fonitronik at analoguehaven


Does this mean you're no longer making this module (or others) available for DIY?

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