Author |
Message |
LektroiD
Joined: Aug 23, 2008 Posts: 1018 Location: Scottish Borders
Audio files: 2
G2 patch files: 2
|
Posted: Fri Jul 17, 2015 4:54 pm Post subject:
Vocoder issues... |
|
|
I emailed a similar message, but thought I'd repeat the post here, as it may be useful to others, if this gets resolved.
I only hear white noise coming from the output. With no external cables attached, I connect my scope to the inputs. Attached pictures show what I see with the scope at the inputs and outputs.
Description: |
|
Filesize: |
58.98 KB |
Viewed: |
674 Time(s) |
This image has been reduced to fit the page. Click on it to enlarge. |
|
Description: |
Measured at the output with 50% gain. Frequency increases with gain. |
|
Filesize: |
55.86 KB |
Viewed: |
610 Time(s) |
This image has been reduced to fit the page. Click on it to enlarge. |
|
_________________ LektroiD |
|
Back to top
|
|
|
LektroiD
Joined: Aug 23, 2008 Posts: 1018 Location: Scottish Borders
Audio files: 2
G2 patch files: 2
|
Posted: Fri Jul 17, 2015 6:16 pm Post subject:
|
|
|
Now I feel rather silly...
I forgot to ground the PCB to the panel components. _________________ LektroiD |
|
Back to top
|
|
|
LektroiD
Joined: Aug 23, 2008 Posts: 1018 Location: Scottish Borders
Audio files: 2
G2 patch files: 2
|
Posted: Fri Jul 17, 2015 7:02 pm Post subject:
|
|
|
I would like to say that there is one small issue... the lowpass band bleeds into the output. I built the individual band level controls, and the only way to get around it is to shut that band off completely. But it would be nice to have it working properly. Any ideas how to prevent this bleed through? _________________ LektroiD |
|
Back to top
|
|
|
Shock_Hazard
Joined: Jul 17, 2015 Posts: 16 Location: Gwynedd
|
Posted: Sat Jul 18, 2015 10:07 pm Post subject:
|
|
|
signal bleedthrough can be caused by capacitive coupling of cables, make sure you have some power supply filter caps aswell, you could even calculate them to cancel out the kind of frequencies you are working with.
Shielding is the usual solution for blocking out outside/unwanted signals. |
|
Back to top
|
|
|
LektroiD
Joined: Aug 23, 2008 Posts: 1018 Location: Scottish Borders
Audio files: 2
G2 patch files: 2
|
Posted: Sat Jul 18, 2015 11:45 pm Post subject:
|
|
|
I placed the specified value caps as per the BOM, and used shielded cables on every connection, unless otherwise stated in the build docs…
It's just the lopass which has the bleed. All other bands work as expected. _________________ LektroiD |
|
Back to top
|
|
|
Shock_Hazard
Joined: Jul 17, 2015 Posts: 16 Location: Gwynedd
|
Posted: Sun Jul 19, 2015 12:27 am Post subject:
|
|
|
hnmmm weird... I'd have to get a look inside to really tell you more, you seem to have done everything well.
By capacitive coupling I didn't mean anything to do with the capacitors- it's really that unintentional capacitors are created by close together cables, allowing the passage of AC signals between cables, but if shielded, as you have done, that problem should be prevented. |
|
Back to top
|
|
|
elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
|
Posted: Sun Jul 19, 2015 11:01 am Post subject:
|
|
|
Does the lowpass section have any traces that have long(ish) parallel runs next to the output traces? That's the most common way for coupling to happen. The rev 1 TTSH's had that problem with VCOs 2 & 3, had to cut a trace and run the signal a different way with a shielded cable. |
|
Back to top
|
|
|
LektroiD
Joined: Aug 23, 2008 Posts: 1018 Location: Scottish Borders
Audio files: 2
G2 patch files: 2
|
Posted: Sun Aug 09, 2015 6:08 am Post subject:
|
|
|
What's interesting is the problem is only evident when the modulation source (mic input) is set to 'mic', when switched to 'line', it works as intended (no bleed). _________________ LektroiD |
|
Back to top
|
|
|
elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
|
Posted: Sun Aug 09, 2015 7:17 am Post subject:
|
|
|
LektroiD wrote: | What's interesting is the problem is only evident when the modulation source (mic input) is set to 'mic', when switched to 'line', it works as intended (no bleed). |
That's not surprising: a mic level signal needs more amplification, which means it's more likely to pick up low-level bleed. |
|
Back to top
|
|
|
LektroiD
Joined: Aug 23, 2008 Posts: 1018 Location: Scottish Borders
Audio files: 2
G2 patch files: 2
|
Posted: Sun Aug 09, 2015 8:05 am Post subject:
|
|
|
elmegil wrote: | LektroiD wrote: | What's interesting is the problem is only evident when the modulation source (mic input) is set to 'mic', when switched to 'line', it works as intended (no bleed). |
That's not surprising: a mic level signal needs more amplification, which means it's more likely to pick up low-level bleed. |
I'd understand that, but the bleed comes from the carrier (synth). It is still present when the modulator is turned fully anticlockwise, so the signal is ground zero. When I switch the modulator to line and turn the dial to maximum, no bleed.
The bleed only comes from the hipass and lopass bands (I did the individual band mod, so it was easy to determine). _________________ LektroiD |
|
Back to top
|
|
|
LektroiD
Joined: Aug 23, 2008 Posts: 1018 Location: Scottish Borders
Audio files: 2
G2 patch files: 2
|
Posted: Fri Mar 02, 2018 3:34 am Post subject:
|
|
|
I'm still no further with this... As a workaround, I have been using a mic pre and running it through line, but would be nice to have it all self contained... _________________ LektroiD |
|
Back to top
|
|
|
Bodo1967
Joined: Aug 10, 2016 Posts: 15 Location: Germany
|
Posted: Mon Mar 12, 2018 7:13 am Post subject:
|
|
|
LektroiD wrote: | I'm still no further with this... |
It's exactly the same as in mine. As far as I can tell, the problem sits in the onboard mic preamp.
I have constant 260 mV on pin 1 of IC1 resulting in about 1.4 V on pin 7 of that IC when the audio toggle switch is set to 'mic', no matter how I set any of the pots. I double checked all the component values in that section but couldn't find any mistake on my side.
LektroiD wrote: | As a workaround, I have been using a mic pre and running it through line, but would be nice to have it all self contained... |
That's exactly what I do as well .
LektroiD wrote: | but would be nice to have it all self contained... |
Absolutely! |
|
Back to top
|
|
|
LektroiD
Joined: Aug 23, 2008 Posts: 1018 Location: Scottish Borders
Audio files: 2
G2 patch files: 2
|
Posted: Wed Dec 19, 2018 5:20 am Post subject:
|
|
|
Did anyone manage to solve this? _________________ LektroiD |
|
Back to top
|
|
|
|