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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Fri Nov 29, 2013 7:43 pm Post subject:
Green Omeg pots |
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Has anybody else had problems with green plastic Omeg pots? I have had several fail recently and I am trying to find out why.
One of them is intermittent, it happens to be the coarse tuning on a VCO and the pitch jumps all over the place, especially if touch the knob or push it in slightly.
The other faults are generally only when I touch the knob, and again mainly noticeable if I slightly push it into the panel..
Is this a common issue?
Is it because I have been working on the panel face down and damaged the pots that are slightly higher that the others?
I have a new soldering iron that is temperature adjustable, do I have the temperature too high?
The one that completely failed had to be completely re-wired twice, could that have damaged it?
It looks fine and I can't see any obvious damage, so any suggestions would be welcome. _________________ Stephen
www.Rainsbury.Net |
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Skrog Productions
Joined: Jan 07, 2009 Posts: 1196 Location: Scottish Borders
Audio files: 155
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Posted: Sat Nov 30, 2013 3:34 am Post subject:
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Hi Stephen
When i built my Paia FatMan in 2001, i used these green omeg pots and had a few problems with them , the turn action of the pots slowly became stiffer, i think caused by a type of sillicon grease inside the pot body and also a few had intermitent carbon track glitches , since 2005, for my big modular system , i now just use the standard alpha 16mm pots , they are easy to change if one goes faulty , which ive not had to yet .
i did spray one of the green pots with servisol contact cleaner but 2 days later it was destined for the bin
Dave. |
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haima
Joined: Jul 25, 2008 Posts: 40 Location: Melbourne, Australia
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Posted: Sat Nov 30, 2013 4:16 am Post subject:
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I've had a few of these pots go bad too... They are probably 8-10 years old, but I have only just gotten around to using them.
I'd been saving them as I assumed they would be very high quality. But in reality I've found that the cheap alpha carbon pots have been more reliable...
I've had good luck with the blue bourns conductive plastic pots btw - if you want to go fancy. |
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magman
Joined: Feb 04, 2009 Posts: 363 Location: Liverpool, UK
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Posted: Sat Nov 30, 2013 4:21 am Post subject:
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I have also had problems with this type of Omeg pots and it is definately a known issue.
I was actually advised by Tony Algood of Oakley a few years ago that it was not a good idea to use these pots. Tony redesigned his PCB's several years ago to replace these pots, originally using Spectrol type pots but now using Alpha pots.
I still have a couple of modules that use this type of Omeg pots, I plan to replace them in the not too distant future.
Regards
Magman |
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analog_backlash
Joined: Sep 04, 2012 Posts: 393 Location: Aldershot, UK
Audio files: 21
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Posted: Sat Nov 30, 2013 5:58 am Post subject:
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Hi,
One problem I had with these is that I tried to fit one with a cheap push-on knob and I ended up breaking the thing apart . I would recommended using knobs with grub screw fixing with these...
Gary |
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Dave Kendall
Joined: May 26, 2007 Posts: 421 Location: England
Audio files: 3
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Posted: Sat Nov 30, 2013 8:28 am Post subject:
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I agree with all the above. I had some go bad quite quickly. Uing push-on knobs, or mechanical stress down the shaft into the pot seems to wreck them quite easily.
Alphas however, work fine and feel good, and are smaller than OMEG ECOs which often helps. As you're in the UK, Rapid electronics do alpha-type clones which are pretty good for the money. They've also got 10% off until midnight monday!
cheers,
Dave _________________ "Everything in moderation, including moderation" |
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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Sat Nov 30, 2013 4:19 pm Post subject:
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Thanks, that's the news I was dreading, but better now that half way through a gig.
I am 3/4 of the way through my new synthesizer panel, and this one is built to be small, so there isn't much room to work.
Some are soldered directly to fiber glass matrix board and held in place by solder on PCB brackets.
This is designed as alive performance instrument so I have tried to build it like a tank, all the wires are carefully laced with tiny cable ties, and all flying leads have rubber sleeving strain relief.
Although I laid it out so that any component could be replaced, it was never going to be an easy job. Those little suckers under the PCB will be a right pig to get out without removing the PCB.
The question is do I try to replace the pots piecemeal, or just start again _________________ Stephen
www.Rainsbury.Net Last edited by Zodiak on Sat Nov 30, 2013 5:34 pm; edited 1 time in total |
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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Sat Nov 30, 2013 4:49 pm Post subject:
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I am just going to bite the bullet and swap them all out now be fore I go any further
Where can I buy these alpha pots in the UK please? _________________ Stephen
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Dave Kendall
Joined: May 26, 2007 Posts: 421 Location: England
Audio files: 3
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Posted: Sat Nov 30, 2013 5:31 pm Post subject:
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Quote: | The question is do I try to replace the pots piecemeal, or just start again |
The panel cut-out holes for alphas, if using, are smaller than for OMEG ECOs, so they wouldn't be a drop-in replacement. You'd have to re-do the panel.
www.rapidonline.com/ do both Alpha 16mm clones, and another range of 24mm "commercial" potentiometers which would *probably* fit holes drilled for OMEG ECOs - check the datasheet to be sure.
I have only used a couple of the rapid 24mm pots, and preferred the 16mm alpha clones by a country mile - smaller, better feel, cheaper.
There are probably other pots with the same panel cut-out dimensions as the OMEGs, but I've never found any UK ones that could beat the rapid alpha clone for price/performance.
I also see plenty of other people use the rapid alpha clones without issues, which is reassuring. They and actual alphas are widely available, so easily replaceable.
Using alpha 16mms would mean a redesign/re-make of the panel, but if it were me, I d curse loads, then do it, cursing freely along the way.
But down the line, I'd be glad I did. . .
Just my 2 pence worth - Good luck with it all!
cheers,
Dave
cheers,
Dave _________________ "Everything in moderation, including moderation" |
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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Sat Nov 30, 2013 5:42 pm Post subject:
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Thanks Dave, I cut that panel down to fit with a guillotine at my last job and I don't have access to that anymore, which means I would have to pay somebody to make one for, which will put in yet another delay
I can't use 24mm ones the holes are too close together.
However I have been here before many years ago when I had to replace some pots with smaller ones. I cut very short lengths (3mm) of plastic fish tank air tube and forced them over the thread, it was just enough to hold the pot snugly in place.
I have a couple of these smaller pots upstairs and will try that in the morning. I can't go now, they are under our bed and that would wake 'er indoors. _________________ Stephen
www.Rainsbury.Net Last edited by Zodiak on Sat Nov 30, 2013 5:57 pm; edited 1 time in total |
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new voodoo
Joined: May 06, 2013 Posts: 94 Location: RVA USA
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Posted: Sat Nov 30, 2013 6:00 pm Post subject:
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for whatever its worth theres glue gun sticks that come in colors, ive had good luck using just a SMALL amt of glue in the color of the panel/wood/finish of whatever im wrking on in filling the gap and having it look good (you can always sand or dremel down the glue until it fits in or matches)..n it helps keep the pots in place too.
Maybe thats too lo-rent a solution but it wrks well for me. jsut a suggestion _________________ www.newvoodoodesign.com
-my creations, bends & bendable pieces
-vintage parts & tubes, IC's & audio chips
-oddities & weird
newvoodoo.blogspot.com
-bending DIY/projects
-crap |
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new voodoo
Joined: May 06, 2013 Posts: 94 Location: RVA USA
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Posted: Sat Nov 30, 2013 6:04 pm Post subject:
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ps I saw yr "stuff to share w kevin" link and that made me think what an incredibly good idea fr a few friends ive lost..a way to kind of think of them as still around in a way. very very cool. thank you for that. really. thank you. _________________ www.newvoodoodesign.com
-my creations, bends & bendable pieces
-vintage parts & tubes, IC's & audio chips
-oddities & weird
newvoodoo.blogspot.com
-bending DIY/projects
-crap |
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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Sun Dec 01, 2013 12:30 am Post subject:
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Thanks new voodoo, I had to do something similar for some of the 4mm sockets after I realized I had drilled some of the holes too big and yes they are solid but I spent ages trying to line them up as every slight imperfection in a symmetrical pattern like this seemed to be huge.
As it happens I have a couple of these pots, and I just tried them, yes they are loose, but if I use a shake proof washer the little raised bumps locate just nicely into the existing holes holding the pot pretty central. New pots don't seem to come with one of these so I will get back onto the web and see if I can track some down.
Thanks for the comments on the "Kevin page", having that certainly helped me deal with him dieing so unexpectedly. _________________ Stephen
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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Sun Dec 01, 2013 10:15 am Post subject:
Update |
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I have just bought a pack of 7mm internal diameter 2mm thickness o-rings, which means they will have an 11mm outside diameter, which is the size hole I drilled for the original pots.
In theory this should hold the new, smaller pots exactly in the right place, but I might have to get some 7mm flat washers just to keep the hole neat.
Hmm I could even spray them up to match the color of the socket they refer to... subtle
If that doesn't work I will strip it down, and stick a thin sheet of plastic laminate on the panel and drill new smaller holes in that. I will probably have to make a new labeling laminate, but that is only 30 minutes work, and I can use it to center the new holes. So all in all an evening's work before I start replacing the electronics. _________________ Stephen
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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Sun Dec 01, 2013 5:36 pm Post subject:
Aaaargghhh!!! |
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I have just found a length of plastic pipe that is EXACTLY right for holding these pots in place.
A 2mm long section JUST fits snugly in the panel hole and grips a pot firmly enough that it won't move, but can still be pulled out. Tightening the nut makes it absolutely solid.
So I didn't need to buy those o-rings
On an even more positive note, now I can use those funky little coloured rubbery knobs, from Rapid Electronics, which cost 15p, and they cover up the fitting nut completely.
Happier than this time yesterday.
Sweeeeet! _________________ Stephen
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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Wed Dec 04, 2013 4:43 am Post subject:
Subject description: Post mortem. |
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I think that I have discovered why these pots failed, the shaft was pushed into the body and damaged the wiper.
The two that have failed the most were slightly proud of the rest so when I was working on it they would have been pushed in.
It is a crowded panel so I have used small knobs but they didn't cover the retaining nut and I had to leave them slightly proud to avoid them rubbing, so there was no protection for the shaft.
In practice most of the rest are probably OK, but this will happen again so I am still going to swap them all out as the alpha pots have a step on their shaft which will stop this happening to them, plus the new knobs are slightly smaller, coloured and cover the retaining nut, so all in all a win.
I bought 50 log and 50 linear Omeg pots several years ago to get the lower price, so I still have 30+ of each left. These will still be useful for other projects where I can spread them out and fit a more protective knob, but that isn't going to be a eurorack project. _________________ Stephen
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Wed Dec 04, 2013 7:50 am Post subject:
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I blew out a Grayhill hex encoded switch trying to shove a knob onto it last week. Same kind of design I think. In my case I popped the back off the switch entirely. |
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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Wed Dec 04, 2013 8:04 am Post subject:
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The new pots have arrived, they feel much better and I can see that the way they are constructed will avoid that problem again.
I am however confused the linear ones are labeled B100K and the log ones A100K and I thought it was the other way round.
A quick google showed tow theories, one that they are different in the US and Europe and good old wikipedia has them down as having changed at some point in the recent past.
Hmm _________________ Stephen
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Wed Dec 04, 2013 8:31 am Post subject:
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In the two years I've been doing this, It's always been A for log, B for lin. I haven't researched the history because I haven't had occasion to work with older ones (I've worked on older synths, but didn't have to do any pot replacements). |
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analog_backlash
Joined: Sep 04, 2012 Posts: 393 Location: Aldershot, UK
Audio files: 21
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Posted: Wed Dec 04, 2013 9:25 am Post subject:
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Aaarrgh! It has raised its ugly head again - see the bottom of:
http://electro-music.com/forum/topic-37770-125.html
I always assumed that log = A and lin = B as well. I have Alpha pots from Tayda which are marked B100K and the bag says "B100K linear". I haven't made any measurements to prove that this is the case - perhaps I should.
Why do they mess around with these things?
Gary |
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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Wed Dec 04, 2013 9:31 am Post subject:
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Thanks I had missed that bit of the post.
I have been doing this for.. well a very long time, since RS were called Radio Spares in fact, I even remember the very first Maplin catalog (It was green with a picture of Concorde on the front) and I have only ever know A=LIN etc... so this was a bit of a shock. _________________ Stephen
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jukingeo
Joined: Oct 24, 2007 Posts: 166 Location: The dark side of the moon
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Posted: Sun Dec 08, 2013 9:30 am Post subject:
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Hello all
'scuse me for thread hi-jacking, but seeing that this discussion was fairly recent and I am looking to build a synth project myself in the coming new year the thought had popped in my head as to what pots and switches I should use. Being an electronics technician of past, I know very well what happens when companies use cheap Chinese parts and pots start to get scratchy and fail within a very short period of time. Naturally being aware of this, I wanted something that was good quality that wouldn't break the bank.
It seems like this company 'Alpha' has come up often here in the forum and there is a supplier that I would like to try out that is close by in NYC (I live on Long Island). So, hopefully, since they are so close, they will not kill me on the shipping. They are called Small Bear Electronics and from what I seen they have really good deals on parts AND they do bulk purchasing too. I can get the Alpha 24mm or the 16mm for .95 if I bulk buy lots of 25 and for .90 bulk buy in lots of 50. For under a buck each, I don't think that is a bad deal. They use a set screw type knob.
The question is should I go with the 24mm pots since they are larger, have a larger carbon area and should last longer? Yes?
Thank You,
Geo |
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Zodiak
Joined: May 20, 2007 Posts: 249 Location: Gillingham, Kent UK
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Posted: Sun Dec 08, 2013 10:06 am Post subject:
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I bought the Omeg ones on somebody a recommendation that being plastic track they lasted longer and were less noisy, but as I have found to my cost they are not very robust.
I have just started using Alpha pots so can't comment but as you say they are highly thought of here.
Previously I had used cheaper full sized pots and in practice have never had a real problems with them apart from a few mechanical failures. In practice if one starts to get a bit noisy or crackly then it is easy enough to get a squirt of switch cleaner in there. The only time I had to replace one was after it had received a hefty whack breaking it apart. _________________ Stephen
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jukingeo
Joined: Oct 24, 2007 Posts: 166 Location: The dark side of the moon
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Posted: Sun Dec 08, 2013 10:46 am Post subject:
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Zodiak wrote: | I bought the Omeg ones on somebody a recommendation that being plastic track they lasted longer and were less noisy, but as I have found to my cost they are not very robust. |
Yeah, I meant to say before, I AM sorry to hear you had such trouble. I just cringed when I saw all the hard work you put into that one module and then to think you had to do it all over. THAT is certainly something I would like to avoid.
I ran into a similar situation when sourcing out parts for guitar amplifiers Everyone said to try to get the enclosed controls so this way no dust can contaminate them. Well, as it turned out I paid MORE for those controls and I was getting amps back after two and three months use with complaints the controls were already scratchy. Now with no openings, the controls were near impossible to clean. So I rejected those new pots VERY fast.
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I have just started using Alpha pots so can't comment but as you say they are highly thought of here. |
Yes, I see they come up often and I have used them in the past. But materials do change over the years so I really just wanted to make sure they were still good. Back in the 80's it were the ALPS controls that were the best, but by the turn of the century, they started to become hit and miss.
Quote: |
Previously I had used cheaper full sized pots and in practice have never had a real problems with them apart from a few mechanical failures. In practice if one starts to get a bit noisy or crackly then it is easy enough to get a squirt of switch cleaner in there. The only time I had to replace one was after it had received a hefty whack breaking it apart. |
Yeah, I have always liked the larger format controls. On older receivers those older ALPS pots lasted for about 2 to 4 DECADES before needing a cleaning. While I am not expecting that with today's materials in construction, but if I could get a good 10 years without cleaning or replacing a pot, then I would say it is a decent quality control.
Geo |
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