DIY - Elektor Vocoder - General Build Thread

[nologin]

Yes, i removed it and soldered another, 7905, still the same problem. I'm going to try one on another circuit, maybe they are faulty. It's strange.

[KSS]

Verify that you actually have a 7905 regulator and not a 7915?

And that you don't make the common mistake of thinking the tab/back of 79xx is GND. It is on the the 78xx, so these cannot touch each other -typically through shared H/S- or wierd things can happen. Keep your 78xx isolated from any 79xx.

[nologin]

Yes KSS, if i had done that reversal 78xx/79xx, regulators would have burned out.
Here, i've got this at IC20 and no short circuits:

[elmegil]

Test another 7905 from that batch separately. It is labelled correctly but depending on your supplier, it could conceivably be mislabelled.

The other thing I would look for would be a short between the -5 and -15 rails.

[KSS]

Yes KSS, if i had done that reversal 78xx/79xx, regulators would have burned out.

I didn't say anything about reversal. I said if there is contact between the tabs of 78xx and 79xx, weird results can and do show up. And this does not necessarily blow the Vregs. It's as much a reminder warning for anyone reading this thread asfor you personally. It's happened enough times to others besides you to beworth mentioning when 78xx and 79xx share a PCB. /fix typos

[Croodey]

so,... now after many hours because i dont undrstand the adjustment instructions i hope i did anything right with the adjustment on the filters. it is very suspicious that I have to turn the trimmer for the "DC offset" all the way down to the stop in order to achieve the minimum output level. did I do it right at all? (Solved: the reason was, i took the 1m resistors on r200 and r201 AND a 10k trim too )

I'm currently at the "Switching interface adjustment".
my first questions:

Bridges of G-H and I-J? (Yes No?)
Signal in carrier?
Voice and Out 100%?
what should I adjust to what? optical signal on the LEDs, or acoustic?
acoustically silent with "s" sounds or with noise?
is a hum normal when "a" and "s" are audible? (ok,... i think i have the hum fixed with the grounded case)

why is there no audible crackle for me, no matter what the settings on the dedecting board are?


please help me to finish this nice project

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[yan6]

I hope you are able to push forward with this project and help document the deficiencies in the calibration documentation. I fell flat on the calibration and could never figure it out, now mine sits in a bin

[Croodey]

Yesterday i got some infos in german lenguage. I will test it and translate it
But for the first loint yesterday i have seen, i made the fixing mod for the offset wrong. Now i must start again to adjust the bandfilters.

[Croodey]

Now, i have read the instructions from the elektor magazin 1980. The instructions on the page from this DIY is the same and really good. In the magazin are maybe a little bit more infos witch helps to understand (in case of my own).
Yesterday i did step 1 and step 2 of the filtercalibration.
For step one i take the noise from my SH-101 into the voice inputterminal of the elektor with inputlevel on max volume. No carrier. On the outputterminal (level max) i put on my oszilloscop and adjust the trimpotis between 20mv and 40mv.
The next step is to connect a mic into the voice terminal and the outputterminal to your mixer and send 200mv on the point "in" on the boards. I turned the gain to the point, where i hear a little bit noise. Than i turn the trimpoti on the filter for the second step so far to the point where it comes a loud noise. Turn it back to the nearly point where it is between qiuet to get loud.
The 3rd step is easy.

I hope i does it right. But it looks like.
I will see it in the afternoon, when i adjusted the voice/unvoice and noise.



EDIT:

it is easyer if you turn all trimpotis to the centerposition before you start to adjust.

[Croodey]

Next Vocoder, next problems

Does someone got this version of circuitboards? It is without the places R200 / R201
Maybe there you have a old BOM or buildinguid.
I changed now on p1 (offset) the 100k to 10k but it doesnt work really good an have 27mv and more

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[nologin]

My problem solved, my -5VDC power problem was because of 7915 that were labeled 7905. It's the first time in my life that I've seen this... It's ST they're labeled L7905CV 99205. Replaced by a motorola MC7905CT, problem solved. But i wonder how it's possible that a manufacturer could make such a mistake and let this go.

[Alfrede]

Hey Croodey, look at this perhaps it helpes: http://www.emusic-diy.org/Schematics/Effects

[Croodey]

Hey Croodey, look at this perhaps it helpes: http://www.emusic-diy.org/Schematics/Effects

Thanks a lot

[bluestang]

Is the kit still available for purchase?

[nologin]

Hello, there are 2 resistors that i don't see in the BOM. R42 on the switching board and R36 on the highpass board.

[nologin]

There's no one who can tell me about R42 and R36? Because i don't know how many ohms they are, i can't find them in the BOM...

[elmegil]

Much earlier in this thread....

[nologin]

I had watched the whole thread, i don't know why i didn't seen.

[zephyrin]

Hello i m trying to do the Step 2 - Preset voltage to current convertor for the OTA’s
It'sworking fine for all filter excepted for High Pass.
test voltage is very low around 10 mv (9- 11) for the other bands it's between 60mv and 120 mv

I have see on the original magazine that there an other way for setting the preset voltage
what I the best way for this adjustment ?

[KSS]

Look for a resistor wrongly placed. Or wrongly read. Some 1 and 2% resistors give 'valid' codes read both ways.

If you're dealing with a kit and you find this, then you have to look for -and find- the complementary wrongly placed or identified resistor.

Wrong resistor ID or placement is number one SDIY fault. Right before poor soldering.

[zephyrin]

I have check the Resistor and all are ok.

I have something strange for the filter:
For 2 boards i don't have any signal on the output of vocoder : 265 Hz and high pass filter

For the other 8 I have3 boards with the signal output lower than the 5 others.
I have detected for this 3 boards that the input signal is lower for carrier just after After Resistor R1!

For this 8 filters that seems to work I can't scope the signal on pin 6 of 741

I think that there something wrong !

[zephyrin]

Fetchie could you please give us the informations about your modification around the 741 , I have several trouble with filter that I don't have with original board that I have made.
I wanted to return to original schematic without resistor R200 201 AND R202 , because I see that it's work better without that !

[Fitchie]

For this 8 filters that seems to work I can't scope the signal on pin 6 of 741
I think that there something wrong !

Might be useful for builders who may have similar problems, hereby some instruction how to ‘follow’ the signal though all filter cards.

Scope step by step on the places indicated by the red circle.
As soon as you don't see a signal, something is wrong.

[Fitchie]

Fetchie could you please give us the informations about your modification around the 741 , I have several trouble with filter that I don't have with original board that I have made.
I wanted to return to original schematic without resistor R200 201 AND R202 , because I see that it's work better without that !

All commercial sold vocoder kits are upgraded with the patch for offset compensation (R200, R201 & R202). This is necessary using HA-4741 OpAmps. Only 2 prototype sets without the patch were distributed to testers and they are aware of this.

Using “modern” OpAmps (TL-series), the upgrade offers no real benefits. Just check the bias (pin 6), as long as you are below 0,1 volt do nothing, in case the bias is significant different, try the exchange the OpAmp.

[Fitchie]

Does someone got this version of circuitboards? It is without the places R200 / R201 / R202

All commercial sold vocoder kits are upgraded with the patch for offset compensation (R200, R201 & R202). Only 2 prototype sets without the patch were distributed to testers and they are aware of this.

But as mentioned, the patch is only useful while using old HA-4741 OpAmps. It doesn't really matter if you use modern OpAmps (TL series).