New module: Discrete Ladder Filter

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Post by Synthbuilder » Fri Jul 15, 2016 3:53 am

mooneh wrote:It would be great if you could do more dry demo someday. Its easier for me to hear the character.
Dry did you say... without delay? :deadbanana:

How's about this then?

https://soundcloud.com/takla-makan/oakl ... s-sequence

[Sorry for some weird reason it's not linking properly in the embedded player]

A very simple sequence of three notes repeating. The patch is the standard subtractive thing: Two VCOs, one discrete ladder filter, VRG for filter envelope, ADSR/VCA for final volume control.

As the sequence is playing I'm tweaking the cut-off, resonance, drive and input levels to the filter.

Tony

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Post by mooneh » Fri Jul 15, 2016 12:58 pm

Thanks sounds great. Must have :party:

I guess the sound around 1.36 is made with the drive knob to overdrive the filter? So nice.

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Re: New module: Discrete Ladder Filter

Post by Noiseconformist » Tue Jul 19, 2016 6:18 am

Synthbuilder wrote:It's not terribly ground breaking but I'm trying out some ideas with printed circuit board design
that I thought I would try in 5U before I start putting them into a completely
new series of 5U, 19" and Eurorack designs that I'll be working on later in the year.
In fact, that's what I'd consider a major teaser! 8-)

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Post by Synthbuilder » Mon Aug 08, 2016 3:54 am

Issue 2 boards should be available later in the month and the price for the bare board will be 20GBP. Issue 2 PCBs will be nearly identical to issue 1 boards but will allow the pots to be mounted as normal. If you want an issue 1 board to save a bit of money and don't mind the extra hassle in mounting the pots now is the time to get a board at the current cheaper price.

Tony

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Post by emi2345 » Mon Jan 16, 2017 2:20 am

Hi there. I am planning my first modular and am pretty set on the Oakley system. I've built guitar amps and pedals before. I'm a full-time musician in a band. My favourite synths that I've played are (rather unoriginally) the vcs3, minimoog and arp 2600.

I'm thinking of a simple starter package around 12U, with a view to future expansion to around 20U, along the lines of:

mididac, vco controller, 2x vco, filter, adsr, multimix?

I'm trying to decide which filter and format I should go for. Would the discrete ladder filter be the most appropriate for minimoogy/early arp2600 sounds or the transistor ladder filter? Is there much difference, apart from obvious features? And the other question I had was, are there any advantages to the 2U format DLF? Could I use it as a distortion/mixer unit if the filter is fully 'up' or will it always sound to some extent 'filtered'?

Thanks for the help and apologies if I've posted this in a bad place, I can't make a new thread yet.

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Post by Synthbuilder » Mon Jan 16, 2017 7:57 am

emi2345 wrote:mididac, vco controller, 2x vco, filter, adsr, multimix?
I'd add another ADSR or, my favourite, a VRG.
I'm trying to decide which filter and format I should go for. Would the discrete ladder filter be the most appropriate for minimoogy/early arp2600 sounds or the transistor ladder filter? Is there much difference, apart from obvious features?
They do sound different and the Superladder does have the rather useful one pole and bandpass modes. But for older synth sounds I'd take the DLF.
And the other question I had was, are there any advantages to the 2U format DLF? Could I use it as a distortion/mixer unit if the filter is fully 'up' or will it always sound to some extent 'filtered'?
The 2U DLF behaves much like a 1U DLF with a simple passive mixer in front of it. Personally, I'd have the 1U DLF and an additional Fourmix module. Having the mixer separately allows for filter free (and therefore very clean) mixing and allows flexibility later on when you add more filters to your system. The Fourmix also has an interesting overdrive mode as well as a useful way to add constant voltages to your audio which can create asymmetrical distortion.

Tony

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Post by emi2345 » Tue Jan 17, 2017 1:25 am

Thanks for the reply Tony!

That slope/bandpass pot in the TSL is really cool, I'm assuming it wouldn't be easy to implement it in the DLF instead of one of the CV depth pots?

One thing I'm not quite clear about the DLF is the way the CVs work, I'm guessing they both control the frequency and not the drive or the resonance like the TSL? Couldn't the same effect be produced by mixing two CVs together using a multimix and then patching that into one CV input?

The VRG is definitely on my long-list, I just want to get a simple system up and running first and then I can add each new module one at a time and learn it really well instead of having a tonne of complex stuff to learn in one go.

One final thought, and this may not be the best place to ask, does anyone know of a simple 2U or 3U loudspeaker/amplifier/headphone module I can get in the 5U format? I've been searching and I can't find one. One of the things I love about the VCS3, 2600 and Gleeman Pentaphonic is you can sit in a corner of the studio away from everyone else working on a patch without hogging the main studio speakers and making everyone else get itchy feet. They are complete instruments you can take anywhere and play without any external stuff. I'd be happy to try to build one from a schematic.

Thanks for all the help.

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Post by Synthbuilder » Tue Jan 17, 2017 10:53 am

emi2345 wrote:That slope/bandpass pot in the TSL is really cool, I'm assuming it wouldn't be easy to implement it in the DLF instead of one of the CV depth pots?
It would not be a trivial modification since you'd need another differential amplifier and a crossfader circuit. There's not a huge sonic difference between the sound of the TSL and DLF though - they are both clearly Moog ladder filters.
One thing I'm not quite clear about the DLF is the way the CVs work, I'm guessing they both control the frequency and not the drive or the resonance like the TSL? Couldn't the same effect be produced by mixing two CVs together using a multimix and then patching that into one CV input?
Yes. Neither drive nor resonance are voltage controlled on this one. If you have a Multimix summing your cut-off CVs then the extra CV input on the DLF is superfluous. However, with the simple need for just envelope and keyboard CVs to control the filter there is no need for the Multimix - just plug them direct into the DLF and save that mixer for other duties.
One final thought, and this may not be the best place to ask, does anyone know of a simple 2U or 3U loudspeaker/amplifier/headphone module I can get in the 5U format?
Inbuilt speakers and me don't get along well. I'd always settle for a nice little monitor speaker sat on top of my modular rather than one internal one taking up module space and which would inevitably not give the sonic results worthy of the modular connected to it.

A headphone amp and output module has been on the cards for some time.

Tony

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Post by Blake Smith » Thu Jan 19, 2017 10:48 am

A headphone amp and output module has been on the cards for some time.
That would be very handy.

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Post by emi2345 » Thu Jan 19, 2017 11:27 am

Well it seems like the best solution would be to get the DLF and then add a diode ladder later, which I think is similar to what the VCS3 has.

A 1U headphone output module would be great!

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Post by trebmonster » Wed Jan 25, 2017 1:02 pm

I'm a newbie so I'm not allowed to start a new thread...!
I'm just starting to build a DLF for use with my Moog Voyager. I shalln't be building a separate modular system but may add a couple of VCOs later. So I need to insert the DLF between the Voyager's mixer and filter. Moog kindly provide a jack for this purpose but the signal lever from it seems too low. I've not hooked up the scope yet but a DVM shows about 0.5v (AC) with all 3 VCOs on. My understanding is that the Oakley (and other MU systems run with analogue signals at around the 10V peak level. Is this right? So do I need to add an op-amp amplifier with gain of say 10 at the front and an attenuator at the end?
Many thanks :)

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Post by Synthbuilder » Thu Jan 26, 2017 9:35 am

trebmonster wrote:I've not hooked up the scope yet but a DVM shows about 0.5v (AC) with all 3 VCOs on.
The DLF is designed to work with signals ten times that, ie. 10V peak to peak. The input 'mixer' of the DLF will start to overload at around 8V peak to peak. Ideally then you need to amplify the signal with something like your mixing desk or an EFG module. Bear in mind that the output of the DLF will also be ten times what the Voyager wants on the way back in. So you'll need to cut it down a bit; a -20dB passive attenuator would be best. Not entirely straightforward then...

Alternatively, you could make the following resistor value changes to the DLF:

R18 220K, R24 15K - this will increase the input sensitivity by a factor of ten or so. I think this should work without introducing too much instability.

R27 3K3 - this will reduce the output by a similar amount.

I've not tested this so do let us know whether you get the results you are looking for.

Tony

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Post by trebmonster » Thu Jan 26, 2017 3:47 pm

Thanks Tony. I'll change R27 as you suggest, but as I may add some VCOs in the future, I'll leave the input sensitivity as it is and boost the Voyager with an Op-amp instead. Cheers.

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Post by trebmonster » Thu Feb 02, 2017 5:58 am

All perfect. op amp giving gain of 10 on the input and your 3k3 change works spot on. Levels with Voyager just right. DLF calibrated perfectly - all trims to 0.000 V :) Sounds great. Love how you get resonance AND bass end at the same time. Many thanks.

905 clone reverb being built now when the tank arrives. But what next...???

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Post by kdjupdal » Mon Jun 25, 2018 4:43 am

Hi

I just got the Discrete Ladder Filter, and it sounds great. (I did not build it myself).

One question just to be clear on the "drive" pot: Could you explain how drive would normally be patched in a filter that don´t have this pot?

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Post by Synthbuilder » Mon Jun 25, 2018 5:57 am

kdjupdal wrote:Could you explain how drive would normally be patched in a filter that don´t have this pot?
On the DLF the Drive pot works by increasing the volume of the signal going into the filter, but post CP3 mixer, and decreasing the volume of the output coming out of the filter. The maximum signal gain on the way into the filter core being around six times more than the lowest gain.

Most analogue filters will be non-linear to some degree. This means they behave differently depending the signal level going in. A completely linear filter will behave identically irrespective of the signal level and would normally be described as sounding clean. At points near to self oscillation even a perfectly linear filter will behave differently with different signals levels simply because the amount of self-oscillation is not dependant on the signal level. However, in most analogue filters self-oscillation is affected somewhat by signal level.

A filter will generally behave more linearly with lower signal levels. But lower signal levels also mean more unwanted noise as all filters are noisy. So there is a sweet spot to obtain the best signal to noise ratio.

All these complexities in a real analogue filter mean that selecting overall input level is important to getting the right sound. Simply having level controls on the input signals is enough to do this. This can be done with a mixer on the input, or under voltage control with a VC-Mixer or VCA following a standard mixer.

But changing the input levels will also change the output level. If you want to make up for the gain loss when driving your filter at low levels then you need to amplify the signal up after the filter. This is done in the DLF by the drive pot (which is a two gang pot). However, you can do this with another VCA that works in tandem with the VCA on the input signal. As one VCA increases gain the other reduces it. This is easily done on a dual-VCA module that has an inverting CV input. eg. Oakley Dual VCA.

Tony

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Post by LED-man » Wed Jul 17, 2019 3:57 pm

Here is my own Panel design for the DLF.
Compared to the yusynth ladder sounds this VCf better in my ears.

Image

Image
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Post by Bodo1967 » Fri Oct 25, 2019 11:46 am

Darn. Mine behaves totally weird and doesn't work :waah: :ripbanana: .

The input signal passes through it more or less unaltered. The input mixer pots have no effect at all :hmm: , and neither have the cutoff frequency nor drive pots.

Resonance has some effect - however, I don't (or hardly at all) see it change the signal until it goes into self oscillation (that bit actually works and responds to the cutoff frequency pot).

I'd be glad for any ideas on where to start searching...
... why buy it for $100 when you can build it yourself for $150?

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Post by LED-man » Fri Oct 25, 2019 11:51 am

Check LK1 jumper - must be installed
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Post by Bodo1967 » Fri Oct 25, 2019 11:53 am

LED-man wrote:Check LK1 jumper - must be installed
It is (I used the 10k pot for resonance), but I'll do another checking round later in the evening :confused: .

Danke jedenfalls schon mal - und das Bier für die TTSH-Hilfe seinerzeit hab ich nicht vergessen ;).
... why buy it for $100 when you can build it yourself for $150?

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Post by Synthbuilder » Fri Oct 25, 2019 12:17 pm

Bodo1967 wrote:The input signal passes through it more or less unaltered. The input mixer pots have no effect at all :hmm: , and neither have the cutoff frequency nor drive pots.
Do you have Dotcom (MU) or MOTM power? If Dotcom then make sure that the middle two solder pads of the four way header PSU are linked together with a bit of wire soldered to those pads.

Tony

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Post by Bodo1967 » Fri Oct 25, 2019 2:45 pm

Synthbuilder wrote:Do you have Dotcom (MU) or MOTM power? If Dotcom then make sure that the middle two solder pads of the four way header PSU are linked together with a bit of wire soldered to those pads.
:doh: to myself, and :hail: :tu: to you!

And millions of THANKS!

... filter is working now and sounding great :nana: .
... why buy it for $100 when you can build it yourself for $150?

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