Topogram - noisy output

Hi,

I know it’s a legacy product, but wanted to ask about the noise I’m seeing in Topogram. I got mine used, but it is in absolute mint condition. I’m seeing diagonal lines in the output, especially evident in the darkest portion of the picture.

At first I thought maybe it was an issue with the unit, or maybe the power. But then I saw that the noise is present in Johnny Woods’ “3 Patches” video posted three years ago. It’s most evident at around 4:30.

So, is this a known issue? Any chance of getting a clean output? I’m totally willing to pay for repair or modification.

Thanks

Another screen capture from official video, showing the icky noise, with just an LFO going into Topogram source input

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I am sorry you are finding the lines distracting. Legacy LZX modules are sensitive to power supply noise. Modules with high gain functions amplify power supply noise more than others. This is what inspired the shared module-based power supplies used by Gen3 modules–our latest attempt at making the cleanest signal possible in analog video.

Thanks Chad! Power is coming from Doepfer PSU3. Any ideas on how to reduce the noise?

Would it be possible to construct an adapter, or modify a legacy module, to accept power from DC Distro? Would that make any difference?

I have my Topogram in same Doepfer PSU3 case! I’m wondering if the Trogotronic m05/silencer would help…

^just tried an m05/silencer…no noticeable improvements.

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I think it is just the nature of the beast–and the reason we had to slay said beast with the new modules. Johnny is using the best/quietest power supply option in the video, designed by LZX and employed in our old Vessel case.

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Not surprising the m05/silencer didn’t work. It’s almost certainly designed to get rid of noise in the audio range, not the video range.

That makes sense!!! Least now we can rule out that option.

Hmm. OK. Well, since Topogram is so incredibly awesome, I anticipate that there will be some iteration of it in the Gen3 lineup. Down the road, of course.

I’m finding that the level of visual noise in my Topogram is severely limiting my creative options. I can only use certain color combinations and modulation speeds to mask the noise. Pretty disappointing, especially considering how expensive the module was. Frankly, I’m surprised that this made it out the factory door in its present state. Either no one noticed the design flaw, or it was knowingly released with the design flaw. All the more reason there should be an updated Gen3 version, or module with similar functionality.

Thanks.

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Topogram takes a signal and sends it to a bunch of soft keyers, the outputs of which are all tuned to not overlap with one other. This can be accomplished with new LZX modules by multing your signal (using Sum/Dist) to as many FKG3’s as you need, dialing in the desired threshold and softness of each keyer, and controlling the thresholds simultaneously (using Matte).

The edge distortion visible in the Topogram 3 Patches video only happens when the gain is at its highest. This is a bit of overdrive that Topogram allows and it can be useful, if that’s what you’re after. The edge distortion goes away when you turn down the gain (or attenuate external control voltage). This is the nature of an Expedition-series high-gain sequential soft keyer. It is the character of the module–much like the character of an analog audio filter module, which might distort or break up at certain settings.

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Thank you Chad. Before this particular Topogram became available on the used market, I was contemplating the multi-FKG3 workflow. Unfortunately, that is beyond my budget at this point.

Please note that, at least with my Topogram, the noise issue occurs even when the Gain is at 12 o’clock. Not just at high Gain settings. This is what I was talking about, how this issue limits my creative options. If I want anything close to a hard edge, I have to choose my color palette very carefully to mask the noise. And modulation needs to be very fast; once again, to mask the noise. Slow or no modulation makes the noise stand out like a sore thumb.

Maybe once I have the financial wherewithal, I might think about doing something with Keychain x3. That should be good for a four-level sequential hard edge key. Video multed into Keychain inputs, all three thresholds set by a single Matte channel.

But in a best case scenario there would be an updated Topogram, or similar sequential keyer, in the Gen3 lineup. It really is one of the coolest modules I’ve seen, and it’s so sad that it has a near-fatal flaw.

This is how most of the Expedition era felt like for me, with EuroRack power in general, any time we tried to do higher gain circuits. Does your Topogram have the copper shield installed between the two boards in the rear? There should be one in there – if not, no wonder you’re seeing some noise.

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Mine does have the copper shield installed!! Never knew what that was for until now!

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@creatorlars, I do see a copper shield around the vicinity of the power ribbon header. It’s not shielding the entire middle board, which I presume is the logic part of the sandwich.

Would it make any sense to try to enhance that shielding? E.g. wrap the whole middle board in some kind of insulated metal foil? I guess some EM radiation is always gonna leak through the spot where the power ribbon header contacts the rear and center boards.

Thanks!

Moving the entire power entry/supply to a separate PCB has been the best approach (as done in the Gen3 power packs.) I would not try to further modify the existing copper shield.

Thanks, so I guess you’re saying that the power circuit isn’t on a separate board for pre-Gen3 modules, and issues such as this were one of the motivations for the current design. Isolating the power circuit to a separate daughter board cuts down on noise as well as streamlines the manufacturing process.

Yes, those aren’t all of the factors involved, but that’s all correct! We designed the Gen3 architecture with an “aquarium” ecosystem in mind: create an ideal 12HP or 8HP tank to hold the fish (aka the video circuit.) The power supply backpack is like having all the water filtering happening in an external unit, so that only the cleanest water ever enters the aquarium. If you have power entry/filtering on the board with the circuit, you are potentially dealing with dirty power and analog circuits in the same place – now crosstalk and noise can pollute things. Standard EuroRack power circuitry (basic filtering, no internal power supply) is like a pet shop where the water supply is shared across all the tanks – a dead fish in one tank may pollute the rest.

These are terrible metaphors. :slight_smile:

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LOL Those are great metaphors!
I can understand it without thinking :thinking:

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