ARP Odyssey 2800 No Audio

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tdlunsfo
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ARP Odyssey 2800 No Audio

Post by tdlunsfo » Thu May 02, 2019 3:18 am

I have an ARP 2800 white face on the bench, 1973 model. It turns on but barely makes a sound. I have my +/-15v and electrolytics check good on capacitance and ESR. I also see a lot of the waveforms mentioned in the service manual but I am not getting anything out of the VCF pin 10. Almost identical to the problem here: viewtopic.php?f=5&t=77584.
My Issue is I really don't know much about synths and how to set this thing up to ensure my 4023 is toast. According the post above, it appears I should get something out of pin 10 on the VCF regardless. It appears someone is selling an aftermarket replacement on reverb/ebay but hate to shell out the $ without verifying its is in fact the issue. Thoughts, suggestions?
Last edited by tdlunsfo on Thu May 30, 2019 3:20 am, edited 1 time in total.

tdlunsfo
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Re: ARP Odyssey 2800 No Audio

Post by tdlunsfo » Fri May 03, 2019 3:38 am

I was able to jumper the VCF and had sound. Customer agreed to attempt a repair.. if it doesn't work out well go with the reproduction. Are the opamps the most common 4023 VCF failure?

synthchaser
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Re: ARP Odyssey 2800 No Audio

Post by synthchaser » Sun May 05, 2019 3:16 am

Check out my video:



LM301 is the most common failure in them. I'm working on 4 Odysseys in parallel now, two have the 4023 and both of them are bad and need to be excavated and repaired. You won't need to buy a replacement clone.

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Re: ARP Odyssey 2800 No Audio

Post by synthchaser » Sun May 05, 2019 11:12 pm


tdlunsfo
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Re: ARP Odyssey 2800 No Audio

Post by tdlunsfo » Mon May 06, 2019 1:08 am

I have actually already excavated mine using the video. Found 2 bad 301's confirmed utilizing a opamp test circuit. Unfortunately I didn't have any replacements so had to order some from ebay. In the meantime I tried some TL081's. It either didn't like those or I also have some bad CA3080's. Plan of attack is to get the 301's in there and see if I end up needing some 3080's. The VCA 3080 is the to5 package in a circular pattern, those on the VCF are to5 but look like I can replace those with DIP8 versions. Anyone ever try TL081/71's in a 4023 VCF?

tdlunsfo
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Re: ARP Odyssey 2800 No Audio

Post by tdlunsfo » Wed May 08, 2019 2:10 am

Well.. seems I am supposed to remove the caps between pins 1 and 8 if I am going to install tl082's. I think I will just wait for my 301's to get here and see. Hoping I don't have CA3080 issues especially in the VCA. More to come I'm sure.

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Re: ARP Odyssey 2800 No Audio

Post by tdlunsfo » Fri May 10, 2019 3:21 am

301's installed. Still no output. Now I can tell the VCA slider affects the gain by the noise levels. So sounds like the VCA amp works. Progress albeit small. Looks like I will need to go down the ca3080 route on the VCF now.

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Re: ARP Odyssey 2800 No Audio

Post by synthchaser » Fri May 10, 2019 5:48 am

Assuming you can't scope out the filter in a test circuit, you might consider testing the JFETs out of circuit before you try replacing the OTAs.

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Re: ARP Odyssey 2800 No Audio

Post by tdlunsfo » Sun May 12, 2019 3:26 am

I did pull the 3080's. One of them is dead the other okay, found a test circuit to breadboard and verify. I went ahead and ordered a few stateside and popped in a few IC sockets. I may have the equipment to test this out of circuit. I have an audio gen, dual power supply, and an o-scope. Is there a diagram somewhere on how to hook it up?

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Re: ARP Odyssey 2800 No Audio

Post by tdlunsfo » Sun May 19, 2019 10:55 pm

3080s were replaced. The fets were swapped out for j113's. It sounds like it is oscillating at a very high pitch (or not at all?). When messing with the VCF frequency fader the audio cuts out past three quarters. I cleaned both the VCF frequency and resonance faders. The faders on this synth are in pretty good shape has it has been stored in a crate for most of its life. Struggling where to go next. Any thoughts? Bad 3080's?
Update: the 3080's are at least one of the issues. I reinstalled one of the old ones that I presumed was good and it sounds a world difference. Guess I need to rebuy a 3080 and try this again.

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Re: ARP Odyssey 2800 No Audio

Post by synthchaser » Tue May 21, 2019 10:44 pm

Don't buy the 3080s or any parts for that matter on eBay. See if Jameco or some reputable seller still has any. If all else fails, I have a high quality replacement submodule on my site...

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Re: ARP Odyssey 2800 No Audio

Post by tdlunsfo » Fri May 24, 2019 1:39 am

I have one coming from small bear. I thought I found a reputable source on Ebay as it was located stateside. When I went to get my money back the seller was obviously not from the USA. Lesson learned. I luckily got my money back but lost about 2 weeks messing with ebay. Honestly the chips worked well as opamps just not OTAs. Probably rebranded 741's. I should have the chip from small bear tomorrow. More to come.

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Re: ARP Odyssey 2800 No Audio

Post by tdlunsfo » Thu May 30, 2019 3:20 am

Finally got the last 3080 in and she is up and running. Looking back, if I had better access to the parts this wouldn't had been a bad repair. All these parts being obsolete definitely took some time to work through. Alas, it works again.

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