Incoming Project: DCR320

[Synthbuilder]

New rack effect module. I've been asked to do a clone of the SDD-320 (Dimension D) for some time but with Klark Teknik's, ie. Behringer's, cost effective attempt last year I was a little wary. However, I thought I'd add something to the pot with all the important parameters brought out to the front panel.

It also features a standard Juno style stereo chorus mode too.

Boards are available now. Documentation and sound samples should be available by the end of the week.

http://www.oakleysound.com/DCR320.htm

Tony

[Synthbuilder]

The preliminary version of the Builder's Guide has now been uploaded. This contains only the complete parts list, or BOM if you must, and more detail will be added to the document over the next few days.

[Leverkusen]

Looks great with all those additions - looking forward to the sound examples being uploaded. Hopefully shipping to mainland europe will smooth down soon!

[terjewinther]

This looks great. Already ordered. The only thing missing is a user manual, telling us where to put the knobs to get preset I - IV on the Dim D, just like in the old days when analog synths came with knob settings :-) "Put the knobs here to get a realistic saxophone. Use some amount of mod wheel" :-D
Seriously: great rack effect!

[magicdust]

This looks great. Not a builder but may have to start

[terjewinther]

Planning for parts, some question came up for me:
All the filter caps, do they need to be close tolerance parts, like 5% and not 10-20% tolerance? Or maybe matched?
There is no mention of matching transistors either in the building docs.
Also, any place where polystyrene caps would be of interest, as in the original?

[Synthbuilder]

All the filter caps, do they need to be close tolerance parts, like 5% and not 10-20% tolerance? Or maybe matched?

For the polyesters: 10% would be fine. 5% is better but I doubt you'll hear much of a difference. 20% is just terrible - avoid these because they will probably be poor quality devices.

For the C0G: 5%, 2% or even 1% will be just fine.

There is no mention of matching transistors either in the building docs.

There's no need to match any transistors.

Also, any place where polystyrene caps would be of interest, as in the original?

I don't think there are any polystyrenes in the original apart from the two VCO timing capacitors. They've been replaced by C0G in the DCR320 which will behave effectively the same as the original devices.

Tony

[Synthbuilder]

The only thing missing is a user manual, telling us where to put the knobs to get preset I - IV on the Dim D, just like in the old days when analog synths came with knob settings.

I hope to have something just like that in the User Manual. It'll not be in the first revision coming tomorrow since I need to work out how best to actually create suitable graphic images to represent the positions of the controls.

And it may not be that accurate since, being analogue, everyone's DCR320 will behave slightly differently.

That said, the beauty of the DCR320 is that it doesn't have just four presets (actually 6), so you can go well beyond what the original does.

[terjewinther]

Great - thanks for the answers.

[Synthbuilder]

Just a heads up on PCB stocks. Although I still have a few of the first run of DCR320 boards left in stock, I have sold out of RPSU boards. More RPSU boards have been ordered and should be with me before the end of this month.

Thank you to everyone who has bought a board. The interest in this project has been more than expected.

[Leverkusen]

Hey Tony - just wondered how it is going with the sound examples?

[Synthbuilder]

... just wondered how it is going with the sound examples?

Not done them yet. It's not one of my favourite tasks so I've been putting it off. Plus the fact I've sold out of RPSU boards so there isn't an immediate demand for them.

I'll try and get them done in the near future though.

Tony

[MattyT]

I just got my big box of parts from mouser. Would it be helpful to pre-trim the potentiometers to certain values to mark where the original circuit settings might be before I populate the boards? This way I can mark on my faceplate where those values fall. Or will there be a different procedure for finding the stock setting?
Thanks

[Synthbuilder]

Would it be helpful to pre-trim the potentiometers to certain values to mark where the original circuit settings might be before I populate the boards?

I don't think this would help. Because of the analogue nature of the design each DCR320 built will be slightly different from one another. So although I should be able to give some hints at where the front panel pots will need to be for a particular SDD-320 preset, it will very rough.

Another thing to bear in mind is that in the original devices there was quite a variation between units. There is no calibration in the original to set the various parameters that you now have available on the front panel of the DCR320.

I think the best way will be to use your ears when tweaking the front panel controls - different sound sources will often suit different settings.

[MattyT]

That makes sense about none of the units being exactly the same. I still think the fixed values of the original circuit would be a good starting point for getting the stock setting. So whether you go that route or find a different method for locating the stock setting, i look forward to some guidance

[Synthbuilder]

I still think the fixed values of the original circuit would be a good starting point for getting the stock setting.

Ah, I think I understand what you are saying now. That there is a way to replicate the actions of the SDD320 by setting the front panel pots of the DCR320 to the same resistances used in the SDD320. Is that right? If so, this isn't possible. The DCR-320 has the same BBD circuitry and clock drivers as the original. It also has the same noise reduction system and unusual EQ in the audio pathway. Everything else though is different.

The variation between the settings in the original device is set with various resistors, a multigang switch, and FET switches. This is not copied in the DCR320 so as to allow for variable control over those parameters. So instead of resistors in the modulation oscillator we now have a fully voltage controlled LFO. The effect mix and balance controls use a different type of mixing circuit, and the circuitry that controls the delay time is made more complex to allow for the delay time to be manually controlled.

Now these additional complexities don't change the sound of the effected signal, but they don't make matching between the SDD and DCR a simple case of selecting resistor values. What should be possible is to match the sound by simply putting the DCR320's pots in the correct position. This is something I have already done but I need to find a way of showing it in the user manual. Hopefully you won't have to wait too long.

[MattyT]

That makes way more sense. Thanks for the explanation.

[eljay]

Hi Tony, a couple of questions/observations on the front panel overlay FPD file.

The overlay thickness in the file is 2mm not the 1.5mm you mention at the bottom of the web page description, if the value is amended to 1.5mm in the FPD file a warning message is displayed that states the panel is too thin for it's size - please contact Schaeffer if this is really what you want. Did you contact Schaeffer and specially request a 1.5mm thick panel or did you in fact get a 2mm thick panel?

Just to confirm the hole diameter for the Power Switch is incorrect and is just a place marker, the hole diameter needs to be amended to the size required by the power switch selected. I have identified a Multicomp switch from Farnell, part number 1634642 that requires a 20.2mm diameter front panel hole. This is a clip-in type switch and will fit a panel up to 3mm thick hence it would be necessary to drill a bigger hole in the rack enclosure front panel of 24mm to provide clearance, which seems quite big. Should I look for something smaller?

[Synthbuilder]

The overlay thickness in the file is 2mm not the 1.5mm you mention at the bottom of the web page description...

Sorry. That's a mistake. It should be 2mm. I wish it was 1.5mm as it would be better I think. I've never had the courage to ask Schaeffer whether they would do a 1.5mm one.

Just to confirm the hole diameter for the Power Switch is incorrect and is just a place marker, the hole diameter needs to be amended to the size required by the power switch selected.

It's not so much incorrect but, as you say, just a marker for your chosen switch. Power switches come in many shapes and sizes and availability (especially at the moment) varies from country to country. And it will also depend on whether the builder is using a DPST or SPST which is determined by the type power supply they are using.

I have identified a Multicomp switch from Farnell, part number 1634642 that requires a 20.2mm diameter front panel hole. This is a clip-in type switch and will fit a panel up to 3mm thick hence it would be necessary to drill a bigger hole in the rack enclosure front panel of 24mm to provide clearance, which seems quite big. Should I look for something smaller?

I used a smaller one. Rapid part: 75-0057. Like that Farnell one it's only suitable for the internal mains transformer, or a very beefy single phase wallwart.

I did have to make the hole behind the overlay slightly bigger than the hole in the overlay to accommodate the spring clips.

[Synthbuilder]

That Rapid switch also needs a notch taken out of the side of the mounting hole to stop it rotating over time. That's pretty scary to do on a nice new Schaeffer panel. I used a narrow file and taped up the front of the panel to prevent me from scratching it. I made the hole bigger with a conecut drill bit.

Incidentally, my first DCR320 overlay panel that Schaeffer sent me had obvious tooling marks around the smaller holes. Thankfully, they dealt with the problem very swiftly and I had a perfect replacement panel delivered just two days later.

Note that the overlay is printed and not engraved like my others. I thought I'd give it a go as it was cheaper. It's actually quite good. Not perhaps as clear as the engraved one but certainly good enough.

[eljay]

Many thanks Tony. That Rapid switch is a much more sensible size, I will amend my copy of the FPD file to have the hole diameter set to 15.2mm (the size for that switch), this should save any extra drilling in the panel. I have a set of small files so should be able to file the small notch out without too much trouble.

[Synthbuilder]

I have added some example settings to the User Manual that should allow builders to get close to the original four presets of the SDD-320. Each DCR320 will be different though, so may need slightly different settings to mine. I've included the LFO speeds and delay time spread for each preset in the descriptions, so if one has access to a scope it will be possible to match the settings more closely.

[MattyT]

Bet you cant guess my favorite color...
I turned the overlay into a full front panel for my 1ru case
The case I had is steel and has a vented top, not aluminum so I used separate heat sinks.
Ive got the voltages correct, after that step I cant do much else. Unfortunately i dont own a scope or know how to use one so now I gotta try and find someone local to help me calibrate it

[waldenpotato]

Bet you cant guess my favorite color...
I turned the overlay into a full front panel for my 1ru case
The case I had is steel and has a vented top, not aluminum so I used separate heat sinks.
Ive got the voltages correct, after that step I cant do much else. Unfortunately i dont own a scope or know how to use one so now I gotta try and find someone local to help me calibrate it

This looks good! Is this an altered .fpd file?

[Synthbuilder]

Ive got the voltages correct, after that step I cant do much else. Unfortunately i dont own a scope or know how to use one so now I gotta try and find someone local to help me calibrate it.

Calibration is good but it's not essential if you just want to get on and use it. Just set all the trimmers to their mid points and enjoy.

It is worth getting a scope though. Even the cheapest ones are good enough for audio testing and repair.