ARP 2600 Clone Build Diary

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dKRelease
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ARP 2600 Clone Build Diary

Post by dKRelease » Sat Jun 08, 2019 4:57 am

Hi everyone, my name's Dan, AKA 'dKRelease', and i've recently designed and built the '2600 Compact' which is an electronically identical clone of the legendary ARP 2600 (grey/white version, 4012 filter). It honestly sounds absolutely unreal.

Image

You can find more information and watch a couple of demo vids in this thread if you're interested

viewtopic.php?t=215178&highlight=

I really wanted an ARP for myself and given that an original is out of the question, I decided to build my own. It is in modular form and fits the Eurorack standard physically, although the 2600 uses +-15v so will need to run off an independent power supply.

I decided to go with a modular version for a number of reasons. Firstly, I think it is a much less intimidating build as it is 10 small projects as opposed to one huge one, and testing along the way can be carried out with ease. Secondly, it is a lot less cumbersome building this way, and flipping these small pcbs over to add components and then solder is obviously a lot less of a hassle than if the thing was all on one giant board. Thirdly, and probably most importantly, it offers the opportunity to customise. Ive seen repeated comments about the fact that the 2600 does not have enough dedicated LFO's for instance, as they are part of the VCO's. This means you can (generally) only use all 3 VCO's as sound sources if you aren't using any LFO's. With this modular version it is possible to have another row of oscillators for example, giving you a total of 6 VCO/LFO's to use as you wish. Imagine an ARP 2600 with 6 VCO's?!!

Like I said, this is electronically identical to the 2600 other the omitted speakers and power supply. In todays world it just didn't seem necessary to add the option of speakers, and i couldn't imagine in what context they would have been included. 1 module per speaker?? Nah, so i decided not to add it. The power supply was also excluded because i felt it is something which divides opinion too much, and i also think that todays offerings are probably better than what was going on in 1970, in terms of a power supply.

The unit in the picture and in the other thread is a prototype version. The front panels you see are the finished article and are the ones that i will be offering for sale, but the PCB's are mainly ones i have made myself to prove that everything works as it should. I have now ordered the professionally fabricated boards which i should receive at the end of the coming week, and i will use these boards to build and document a complete unit from scratch. This build diary will then hopefully serve as a resource for anyone who wishes to purchase a PCB and panel set to build their own. I'll also be offering as much advice as i can along the way with regards to sourcing components and things, and ill try and break down the costings as i go.

If anyone has any questions then please don't hesitate to ask.

Dan
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Enclosure

Post by dKRelease » Sat Jun 08, 2019 5:36 am

I explained the reasons why i wanted to build a modular version of this synth, and given that, it made sense to follow the Eurorack 'standard'. Some people will already have Euro enclosures and if not you can buy them from anywhere.

The case on my prototype is something i made in an afternoon out of wood and cost me basically nothing, then i wrapped it in a £20 piece of tolex that you normally use for guitar amps. I'd probably do the same again for the build diary unit, but i had to be 100% certain that i hadn't made a stupid mistake and that the modules where the right size. For that reason i bought this

Image

I was surprised at the price of the enclosures as theres nothing to them really, but all the expense is in the rails. This box is as basic as they come but it'll do the job fine. It is 312HP in total, so thats 3 rows of 104HP. My synth is 3 rows of 96HP the way that i have it configured. Given that its modular you could obviously arrange it however you see fit.

Someone was commenting that i shouldn't have designed it around a non-standard 96HP, but the ergonomics have always got to come before the box that it sits in. Due to the layout of the 2600 and more specifically, my modular version, each 'channel' has to be a multiple 1HP. 3HP would have been too narrow, 5HP would have been too wide, so i went with 4HP. Divide into 3 and you have rows of 96HP. I have these 4HP blanks to go at each end of each row which i can also sell to you if you are in a similar situation. Ill probably end up putting an on/off switch and a power LED in the bottom left one and them some kind of MIDI input bottom right possibly.

Image
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JohnLRice

Post by JohnLRice » Sat Jun 08, 2019 5:43 am

Looks and sounds great! :tu: :yay:

Once you are ready to start selling be careful about offering things for sale on the forum before you have gotten to 100 posts as that would violate forum rules. I'm just mentioning it in case you weren't aware. 8-)

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Post by dKRelease » Sat Jun 08, 2019 5:53 am

JohnLRice wrote:Looks and sounds great! :tu: :yay:

Once you are ready to start selling be careful about offering things for sale on the forum before you have gotten to 100 posts as that would violate forum rules. I'm just mentioning it in case you weren't aware. 8-)
Ok thanks for heads up. By the time the build thread is finished i should be well over that i'd imagine :eek:
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Post by dKRelease » Sat Jun 08, 2019 6:01 am

Just thought i'd mention, I had intended to work right through the original patch book to demonstrate a broad range of sounds but it is surprisingly time consuming when you don't have any normalled connections. The proto isn't normalled and so everything was connected with patch leads and it gets complicated pretty quick. This new unit will have normalled connections (via terminal connectors on the pcb and shielded coax) and so ill probably work through the whole book once the build is complete. I'll also record the calibration process and a demo of each module as we go along.

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Power supply

Post by dKRelease » Sat Jun 08, 2019 8:53 am

I won't be providing anything related to the power supply as everyone has their own ideas on whats best. However i'll tell you what i did and will be doing again for the next unit incase you wanted to do the same.

I basically put together a linear power supply using a 15v AC power adaptor (wall wart) as described on Ray Wilsons MFOS site. I got the adaptor from https://www.poweradaptorsuk.co.uk for about £14 delivered. It absolutely has to be AC/AC as if it outputs DC it won't work. The rest of the components aren't very expensive so somewhere between £20-£30 completed i'd imagine.

I'll be milling a pcb but i recognise that most people won't have the luxury so I've attached a silk screen and trace layout that you can print at 100% scale and glue to a piece of perf board. All the spacings are at 2.54mm so everything should line up. The traces have already been mirrored so stick the silk screen to the top (component side) and the traces to the bottom, or just use the trace print as a guide if you intend on actually soldering to the pads of the perf board. Id probably just try and use the legs of the components (as long as they are of reasonable thickness) to make the traces out of and add bits of wire where necessary.


*Changed BOM as I had some tantalum caps marked as electrolytics
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Post by dKRelease » Sat Jun 08, 2019 9:45 am

Just laid the panels in the box to get an idea how it's gonna look

Image

JohnLRice

Post by JohnLRice » Sat Jun 08, 2019 10:22 am

dKRelease wrote:
JohnLRice wrote:Looks and sounds great! :tu: :yay:

Once you are ready to start selling be careful about offering things for sale on the forum before you have gotten to 100 posts as that would violate forum rules. I'm just mentioning it in case you weren't aware. 8-)
Ok thanks for heads up. By the time the build thread is finished i should be well over that i'd imagine :eek:
No problem, check out this thread for details:
viewtopic.php?t=35996

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Post by Jaytee » Sat Jun 08, 2019 3:16 pm

This is a pretty rad project. Now I’m imagining how a rack of 2600 modules would complement my TTSH...

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Post by tobb » Sat Jun 08, 2019 5:28 pm

Awesome and great work :tu:

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Post by jonny_w » Sat Jun 08, 2019 5:57 pm

Sounds fantastic! Following :)

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Post by LED-man » Sat Jun 08, 2019 6:43 pm

It’s Eurorack Standard but 15V ?
Do you think Eurorack users want this modules and attach a second powersupply?
Eurorack modules are not 100% compatible with original Arp circuits.
where you see a market for this modules ? Or do you plan to sell a complete system ?

what’s the customer benefit compared to a TTSH ?
The sound, the price, the usability ?

Your device followed the original arp2600 schematics, which arp2600 Version ?
You wrote the normalization is with coax cables.. this means, it’s not compatible with Eurorack or you have to add on most modules addional CV and audio inputs/outputs.
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Post by LED-man » Sat Jun 08, 2019 6:52 pm

Why are the matches transistors pairs not thermal connected ?
Sorry for my stupid questions, but I don’t understand your business case and your development.
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Post by tobb » Sun Jun 09, 2019 4:53 am

LED-man wrote:
what’s the customer benefit compared to a TTSH ?
The sound, the price, the usability ?
-The panels are eurorack,so easy to find a case/rail system (Euro PSU not needed indeed if its 15V supply)
-Its modular so you can combine modules and make like described an ARP2600 with just more features..
-This bring us to more usability and price can be as cheap or as large depending of the modules you add.

This system is an all time winner

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Post by dKRelease » Sun Jun 09, 2019 4:53 am

LED-man wrote:It’s Eurorack Standard but 15V ?
It is Eurorack standard physically (i.e. size) but yes it runs off 15v.
Do you think Eurorack users want this modules and attach a second powersupply?


In an ideal world everything would be the same but the ARP is 15v and so a 15v power supply will be required. As I've explained, you can make your own for about £30 which will take about 2 hours to do.
Eurorack modules are not 100% compatible with original Arp circuits.
where you see a market for this modules ? Or do you plan to sell a complete system ?
Yes i plan to sell a complete kit, although individual modules will also be available. The main intention is that this is an expandable standalone setup, but given that the oscillator outputs are around 10v peak to peak and cv is 0-5v there shouldn't be any problem combining with Euro.

As a side note, and as Jaytee suggested, a set of oscillator modules would run seamlessly alongside a TTSH, were that required.
what’s the customer benefit compared to a TTSH ?
The sound, the price, the usability ?
It's natural that people will make comparisons but they are different entities. For some people only the original layout will suffice, and for others the space saving of this version is an advantage. Some absolutely have to have the LED faders, yet others who aren't as bothered may see the added complexity/work as something they could live without.

You'll have to judge for yourself in terms of sound. My feedback so far is that this sounds like an accurate representation, which by all accounts, so does the TTSH.

Price is likely to be £190+postage for 10 PCB's and 10 front panels.

Usability is user specific and so will have to be made by the prospective builder.
Your device followed the original arp2600 schematics, which arp2600 Version ?
4012 filter, 4027-1 oscillators. Ask away if you need anything more specific.
You wrote the normalization is with coax cables.. this means, it’s not compatible with Eurorack or you have to add on most modules addional CV and audio inputs/outputs.
Not sure i understand what you mean here. Connecting the modules together with coax at the rear is not going to have any effect on the possibility of interfacing with other modules outside of this setup.

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Post by dKRelease » Sun Jun 09, 2019 5:08 am

LED-man wrote:Why are the matches transistors pairs not thermal connected ?
Which transistors are you referring to?

Firstly, this is a prototype so i didn't bother.

If you're talking about the Oscillator pair, they have the tempo resistor between them which you may not be able to see. All the others including the ladder in the filter are located right next to each other and can be thermally connected if you wish. Both transistors are pointing in the same direction so would potentially need to be wrapped with thin wire or something similar to get more thermal contact. It was done this way as having the 2 flat faces together messes up the PCB layout which, if you look at the schematic you will see why. For what its worth, even with no thermal contact the tracking on this thing is rock solid through the whole cv range, so whether its necessary or not is up for debate.
Sorry for my stupid questions, but I don’t understand your business case and your development.
That's fine, thats what the thread is for. Im not expecting this to appeal to everyone and so if you don't see the benefits of it, it may not be for you.

Cheers

Dan

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Post by Jaytee » Sun Jun 09, 2019 7:23 am

Seems like at least a few of these modules should run fine on +/-12V without modification, and probably the rest could be coaxed into service on a 12V system with a few component changes.

What does the power header/connector look like?

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Post by av500 » Sun Jun 09, 2019 8:03 am

LED-man wrote: Sorry for my stupid questions, but I don’t understand your business case and your development.
why does there always need to be a business case? what happened to "just for fun"? ;)

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Post by nigel » Sun Jun 09, 2019 9:49 am

av500 wrote:
LED-man wrote: Sorry for my stupid questions, but I don’t understand your business case and your development.
why does there always need to be a business case? what happened to "just for fun"? ;)
This. A thousand times, this.

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Post by dKRelease » Sun Jun 09, 2019 11:10 am

Jaytee wrote:Seems like at least a few of these modules should run fine on +/-12V without modification, and probably the rest could be coaxed into service on a 12V system with a few component changes.

What does the power header/connector look like?
Its exactly the same as the euro connector but 15v, so 2 rows of 8 at 2.54mm pitch. Running left to right...


-15v, GND, GND, GND, +15v, SPARE, CV, GATE

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Post by LED-man » Sun Jun 09, 2019 1:04 pm

av500 wrote:
LED-man wrote: Sorry for my stupid questions, but I don’t understand your business case and your development.
why does there always need to be a business case? what happened to "just for fun"? ;)
Ahh, it’s open hardware or do we get the pcbs for 1€ each ?
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Post by Starspawn » Sun Jun 09, 2019 1:16 pm

LED-man wrote:
av500 wrote:
LED-man wrote: Sorry for my stupid questions, but I don’t understand your business case and your development.
why does there always need to be a business case? what happened to "just for fun"? ;)
Ahh, it’s open hardware or do we get the pcbs for 1€ each ?
The David and Enigma do look prettier, but it does not look good to badger a likely unintentional competitor.
Buyers are also interested and will ask the questions ;)

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Post by LED-man » Sun Jun 09, 2019 1:27 pm

I’m not a member of the LoganSoloman company !!
I’m not paid by LoganSoloman!

I was involved in few arp2600 projects and know the development costs.
The total price only for professional made panels Eurorack panels and pcbs are maybe the same price like a TTSH.
To include this modules with an Eurorack system you need normally a second case, or a quad powersupply.
And you need a solution for the Cv Bus.
I think it’s maybe better to develop modules like steffcorp made.
Or add optional stepup dc-dc circuits to use this modules in standard Eurorack environments, so better sales.
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Post by Starspawn » Sun Jun 09, 2019 1:40 pm

You do act in their interest on this forum, as they chose to leave it.
As such it will easily be viewed as partial bias when you comment in a perceived confrontational style on a similar project.
Just saying it doesnt look good is all, make of that what you will.

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Post by dKRelease » Sun Jun 09, 2019 1:41 pm

LED-man wrote:
av500 wrote:
LED-man wrote: Sorry for my stupid questions, but I don’t understand your business case and your development.
why does there always need to be a business case? what happened to "just for fun"? ;)
Ahh, it’s open hardware or do we get the pcbs for 1€ each ?
Not far off, about 20 Euros.

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