Arp 2600/Odyssey/Pro Soloist 4072 to 4034 Filter Mod?????

[dzlvs8]

I am about to get an Arp Pro/DGX. I am under the understanding that all Pro/DGX's (even the older styled ones) have the non moog filter (4032) in it. Instead they have the 4072 filter like the Arp Odyssey MK3's and newer Arp 2600's.

Does anyone know of any instructions on how to modify the filter on the Arp Pro DGX so I can have the better 4032 filter? I assume there HAS to be instructions out there for this somewhere. All I could come up with was this and its an improvement but not a mod to the 4032 style ladder filter.

http://www.arpodyssey.com/filter-mod.txt

[schmidtc]

It's a totally different design, so it's not really a mod that you can do. The size of the 4072 PCB's is the same as the rat shack protoboard, so if you can solder and read schematics it should be pretty straightforward.

[Kitevent]

My Pro/DGX has a 4034 - exactly the same filter as my Pro Soloist. I think most Pro/DGX units have a 4075 though.

The 4034 is awesome. I would best describe it as having the balls of a Moog with the liquid squelch of a Jupiter 8.

[dzlvs8]

My Pro/DGX has a 4034 - exactly the same filter as my Pro Soloist. I think most Pro/DGX units have a 4075 though.

The 4034 is awesome. I would best describe it as having the balls of a Moog with the liquid squelch of a Jupiter 8.

Yeah I ran into a few people that said they had the 4034 in their DGX. I wasnt sure if it were true or not. I have an Arp Omni 1 and the filter in that thing sounds awesome. Does anyone know if I can just swap the filter boards of my Omni and DGX????????????? I have no idea if the filter is even its own separate board. I havent looked yet. Any ideas

[Kitevent]

I'm really not sure if they can be swapped, but I would guess not.

I've never had my hands on an Omni, but the Quadra (which I think is meant to have some of the same parts as an Omni) has totally different boards to the DGX. There must be other people here who are more familiar with the insides of these instruments than me though.

My DGX with the 4034 is a model 2722 with a very low serial number. It says "Pro Soloist III" on the serial number plate. It is the version with wooden sides, although there was an identical one pictured in Performing Musician magazine than was said to have a 4075.

[Micke]

Interesting! I wasn't aware of that some early Pro/DGX's had the 4034 filter, I thought all of them had the 4075 seeing that
this model was released in the spring of '77, several months after the Omni mk I --and afaik all Omni's came with the 4075.

[Kitevent]

Yes, it definately has the 4034 and it is encased so I don't see how anyone could have got in to change it. Maybe ARP were using up left over parts because they were compatible?

The calibration procedure on these instruments calls for one of the trim pots to be adjusted for the "best sound" which, being highly subjective, may account for some differences when comparing models. I calibrated my DGX side by side with the Pro Soloist and can confirm that most presets (including the Fuzz Guitars) are the same on both synths. A few presets on the DGX sound as if their settings have been tweaked. I would say the Tuba and English Horn are improved on the DGX but I prefer the longer envelope of the Steel Drum on the Pro Soloist. The DGX also has a healthier output signal (on XLR) so is less prone to noise and hum.

The metal chassis on the early dgx looks similar to the Pro Soloist but is much more sturdy and the base board has metal edges. The DGX also has two tilt supports that unscrew from the bottom, which is perhaps better than the Pro Soloist's tilt stand (if you can find one).

Wonderful sounding instruments with the same highly-responsive aftertouch. Anyone used to aftertouch on a JX10 would have a shock. I have to say that tweaking one knob at a time on my minimoog feels rather limiting after modulating up to 6 destinations at once with aftertouch on the Pro Soloist/DGX. And you still have a hand free to play another board!

[schmidtc]

I don't remember offhand, but I'm pretty sure you can swap 4075's 4035's and 4023's with no or at least very minimal modifications. They talk about it in either the Odyssey service manual or one of the field change notes. It's probably a good idea to replace the caps while you have it out.

[CZ Rider]

Does anyone know if I can just swap the filter boards of my Omni and DGX????????????? I have no idea if the filter is even its own separate board. I havent looked yet. Any ideas

I swapped out a 4075 for a 4035 in my MK3 Odyssey. The 4035 was made by CAE Sound. Was easy to remove, and you would have to remove the 4075 to do the filter fix anyway. Here is a photo of the removed 4075 top right and the CAE 4035 on the top left, above the Oddy circuit board.


From what I understand the 4075 and 4035 have the same pinout, but not the 4023 2-pole filter found in the whiteface Oddy.
Infos for all the various Arp sub modules are still at the Arp Tech site found here.
Arp Tech site with list of Arp Submodules

The Arp tech site has a DIY filter schematic for a custom filter module called the 40235, that is a drop in replacement for the 4075. It is switchable between the 4035 4-pole ladder and 4023 2-pole via a switch. If you were going to make your own DIY filter, that would probably be the best choice. Info here:
Arp Tech 40235 filter page


The CAE 4035 I used, is still listed on their site for $150.00, and is a drop in replacement for the 4075. Not sure if they still make them, found mine on Ebay.
CAE Sound web page with ARP 4035 filter sub-module

The 4035 was a big difference sound wise on the Oddy. I liked the nasal tone of the 4075, it had a unique ARP tone to it. But the 4035 gave the MK 3 Oddy a ton of balls. The bass just came alive with that upgrade. I don't think the 4075 was that bad sounding, just different. But both the 4023 and 4035 ARP filters were awesome sounding. That Arp Tech 40235 would get both 2-pole and 4-pole ladder(Moogish). If your Arp model has a 4075 in it, these are easy solder in replacements.

[gearfixer]

I have a DGX and a Avatar I wonder if a filter change would make them sound better. I find the DGX sounds a lot better that the Avatar which sounds very thin. I have not done the resistor mod to the Avatar filter maybe I should try that first. How can you tell which filter is in the DGX if it is not incapsulated?