Oscillator leakage into Journeyman Filter (5U Variant)

[eljay]

I've noticed recently that there appears to be some tiny bleed through of my SVCO oscillators to my Journeyman filters, without any connection from the Oscillator outputs, to anything else. I have a small rack of Oakley modules that includes three SVCO oscillators, two journeyman filters and a 904A and Diode ladder filter. I have only noticed this 'feature' when the output of the Journeyman filter(s) are connected to my mixer, there doesn't appear to be any bleed through from anywhere else. The level of pick-up is very faint and it is only really noticeable when nothing else is playing however I have noticed it and that it clearly changes pitch when I vary the pitch of the oscillators.

My question is : is this a 'feature' of the journeyman design, that it picks up local oscillators without a physical connection. Or are there components that I need to check or is there some other explanation that I should investigate. As previously stated I can observe this feature from both the journeyman filters and nowhere else.

The modules all use an Oakley power supply and dizzy for power distribution.

[Synthbuilder]

The two main mechanisms by which one module may affect another without patching are via the power supply wiring, and proximity. If both Journeyman modules are similarly affected then we can rule out proximity, as if this were the case the filter nearest the oscillators would have the worst bleedthrough. This then leads me to think it is probably the power supply wiring. This could come via either of the +/-15V connections (although I would suspect the +15V first for the Journeyman) or the 0V.

To minimise power supply related crosstalk or bleedthrough, ensure that the leads feeding the Dizzy from the PSU are as short and thick as possible. You may also wish to move the modules' power leads around on the Dizzy. Put the SVCOs on one branch of three (and nearest the power supply inlet if you have an older Dizzy). And put the two Journeymen on a different branch of three.

The Journeyman is more susceptible to power supply noise because it uses very small signals in the filter core. These are then amplified up considerably before they output the module. I wonder if increasing C2 to 220uF, 25V would improve things.

Tony

[eljay]

Thanks for the response Tony.

I have experimented further and the Resonance level pot very clearly affects how much of the bleed through is heard. I've changed C2 to 220uF on both filters and although it doesn't eliminate the bleed through it has almost completely gone so in practice is a non-issue. My power leads are longer than they need to be so at some point I will shorten them to minimise the power cable crosstalk.

I do love the twin journeyman filter configuration, it does sound spectacular and I wouldn't have mentioned the above issue except I am so used to a totally 'noise free' Oakley System.

[Synthbuilder]

I've changed C2 to 220uF on both filters and although it doesn't eliminate the bleed through it has almost completely gone so in practice is a non-issue.

This is good to know. I will update the Builder's Guide to incorporate this change.

My power leads are longer than they need to be so at some point I will shorten them to minimise the power cable crosstalk.

I don't think 'Dizzy to module' power lead length would have an affect in this case. But the 'PSU to Dizzy' wiring most certainly does.

[Flareless]

This is good to know. I will update the Builder's Guide to incorporate this change.

So we can now take this change as permanent (C2 = 220uF instead of C2 = 100uF)?

Would it please be possible to include the Builder's Guide version numbers in their link description (instead of just for example; Journeyman issue 2 Builder's Guide). It would be much easier to quickly see if a module has had a build modification.

Perhaps even a sticky thread up top where build changes can be listed.

[eljay]

Just to confuse the picture more, I built my journeyman filters a while back (Issue 2 PCBs) and used Builders Guide V2.0.3, in this C2 was given as 22uF, so I have made the change to C2 from 22uF to 220uF, it is therefore possible I would have noticed the same improvement if I had moved from 22uF to 100uf which is the value given in Builders Guide V2.5. In any event I'm sticking with the 220uF value Tony has suggested as it appears to minimise the oscillator bleed through. I may also re-calibrate the resonance sensitivity to bring it down a notch or two - but as always "If it ain't broke, don't fix it!" so I'll probably leave it as is.

[Flareless]

Wow. I'm liking the idea of a changelog sticky thread even more.

Thank you eljay for your help in determining the optimum cap value.

[Synthbuilder]

So we can now take this change as permanent (C2 = 220uF instead of C2 = 100uF)?

I've not tried it but there should be no problems increasing C2 to 220uF. Whether there is a noticeable difference to 100uF I couldn't say. The law of diminishing returns will no doubt be true in this case. Within reason the bigger the better here - with the limiting factor being the physical size of the capacitor.

Would it please be possible to include the Builder's Guide version numbers in their link description (instead of just for example; Journeyman issue 2 Builder's Guide). It would be much easier to quickly see if a module has had a build modification.

That does make sense but I'll probably not change the name of the file or link. Changing the name of the file may lead to dead links if someone has come from a search engine or other external link. The latter may well become very important if I do decide to offload the retail side of my business next year.

A change log would be a good idea and should have been done years ago. But I've been too disorganised to sort it out. My advice is always download the latest version from the website before you build - the issue number is on the front page.

[Flareless]

Thanks Tony!