Arp 2600 / upgrades?

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Arp 2600 / upgrades?

Postby Ohm's Law » Fri Feb 10, 2012 10:13 am

Hi all.

Curious how everyone feels about "upgrades" to old synths / the Arp 2600.

Found a few threads online talking about replacing the LM301 opamps with something like a LF-411. Thoughts?

A few places offer upgrades for 2600s. Guessing it's something similar. ?

:?:
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Re: Arp 2600 / upgrades?

Postby Synthacon » Fri Feb 10, 2012 8:20 pm

I have had a few 2600's, the last one of which got the full CMS upgrade to the signal path. Changing out op amps etc can be fine, along with re capping as well. The 2600 can have numerous mods done to it to make it better. It is down to you if you decide they enhance the synth or detract from it. In some collectors eyes only an untouched unit is worth good money, so the choice is yours.

I am getting a new toy next month that has some mods and in my eyes it has enhanced the original ;)
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Re: Arp 2600 / upgrades?

Postby Don T » Sun Feb 12, 2012 7:19 am

.....
Last edited by Don T on Sun Feb 03, 2013 12:56 am, edited 1 time in total.
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Re: Arp 2600 / upgrades?

Postby Explorer » Mon Feb 13, 2012 12:55 pm

http://www.discretesynthesizers.com/arp ... rp2600.htm

Website from Phil Cirocco.
Nice overview on the mods and prices.
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Re: Arp 2600 / upgrades?

Postby pflosi » Mon Feb 13, 2012 4:34 pm

Don T wrote:That said, I've done some heavy-duty audio path upgrades in a Yamaha SK-15, and a Korg Polysix. In the Polysix, the change was quite noticeable, giving the sound a bit more "life" (better response from the filters, and a less constricted sound from the oscillators).


Interesting, what did you do exactly? Replace all op-amps and recapping? Anything else?

Thanks!
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Re: Arp 2600 / upgrades?

Postby shaft9000 » Mon Feb 13, 2012 11:15 pm

a nice mod is to replace the hardwired Noise input to a PWM amount slider for osc 1 and osc 3. if your tech is savvy he can do it pretty easily, and with no drilling or changes to the panel. my tech also replaced the tuning offset on the old keyboard to an LFO control w/ jacks out. this opens up osc two for other uses as it is no longer the sole symmetrical LFO on the 2600.

my tech was Kurt's Keyboard Repair in Prescott AZ
in addition to the above mods i got a new PSU, a filter rebuild, input/preamp repair, key bushing replacement, keyboard resistor replacement, exponential/linear portamento mod to get response as fast as a mini, a new fitted keyboard cable, and full recap for a little over a grand. i transported the 2600 myself.
i didn't go to CMS because of expense, the wait queue and his 'no compromise' approach to the audio path that I don't necessarily agree makes it sound any better. i LIKE the dirty cheap op-amps; it's part of it's character!

it's a crazy-powerful machine now - all design shortcomings have been resolved, with minimal to no perceivable cosmetic alteration - it's the jewel of the studio!
2600.solus.modcan a.eurorack.cs60.JP8.Juno6.A6.sunsyn.volcakeys.jd990.tb303.x0xb0x.revolution.
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Re: Arp 2600 / upgrades?

Postby schmidtc » Tue Feb 14, 2012 12:29 am

shaft9000 wrote: my tech also replaced the tuning offset on the old keyboard to an LFO control w/ jacks out.


Cool. What sort of control. . . speed / waveshape? Did it's range expand at all?
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Re: Arp 2600 / upgrades?

Postby Don T » Tue Feb 14, 2012 5:44 am

.....
Last edited by Don T on Sun Feb 03, 2013 12:56 am, edited 1 time in total.
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Re: Arp 2600 / upgrades?

Postby pflosi » Tue Feb 14, 2012 7:01 am

Cool, thanks. Keep us updated ;)
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Re: Arp 2600 / upgrades?

Postby Sir Ruff » Tue Feb 14, 2012 3:22 pm

Don T wrote:For me, it depends on the synth, and which parts of the synth you choose to upgrade. I usually won't mess with something that is actually generating sound, but I experiment sometimes with audio path upgrades.

I keep thinking my xpander would really benefit from this, but the jury seems kind of out on how much of an improvement can be made.
Do you even post on vse bro?
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Re: Arp 2600 / upgrades?

Postby Don T » Wed Feb 15, 2012 5:16 am

.....
Last edited by Don T on Sun Feb 03, 2013 12:57 am, edited 1 time in total.
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Re: Arp 2600 / upgrades?

Postby madtheory » Wed Feb 15, 2012 11:42 am

You can already cut holes in walls with the XPander, so I would think there is not much room for "improvement"!
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Re: Arp 2600 / upgrades?

Postby atkbg » Wed Feb 15, 2012 4:28 pm

Don T wrote: In my opinion, the 4558 is possibly the worst opamp for any audio path job.


Would you mind telling which opamp you replaced it with? And, do you do this with most 1458/4558s in the audio path?
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Re: Arp 2600 / upgrades?

Postby madtheory » Wed Feb 15, 2012 5:42 pm

If it was a 741 that's easy, there are pin for pin compatible replacements that are improved in areas that do not affect over all circuit design. But with a more complex device like the 4558 it's impossible to answer that question without considering the circuit involved.

I think he was saying that he simply bypassed it in the Yamaha. I have a hard time believing that Yamaha didn't think of that, there's likely a very good reason that it's in there. Without the buffer there is loading which will mess with bandwidth and create new distortion. The question is- is the cure worse than the cause? The answer is probably subjective.

Hard/expensive to beat the old 5532 but it's not trivial to swop opamps. You really need to know very well the design of the circuit you're modifying. It could well be that the 4558 was the best choice at the time and the whole circuit is built around its characteristics. Get it wrong and you could easily have more noise, and spurious oscillation.
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Re: Arp 2600 / upgrades?

Postby Sir Ruff » Wed Feb 15, 2012 6:07 pm

madtheory wrote:You can already cut holes in walls with the XPander, so I would think there is not much room for "improvement"!

No, there definitely is... It suffers from a grungy quality that makes low-end stuff sound muddy, and high end stuff sort of muffled. Sounds quality is just not quite there. Part of that could simply be aging caps, so I've often wondered if recapping the lot would help. A colleague did that to his, and the results were palpable (though it was hard to make an objective judgment since I couldn't compare his to mine).
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