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Green Omeg pots
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Zodiak



Joined: May 20, 2007
Posts: 242
Location: Gillingham, Kent UK

PostPosted: Fri Nov 29, 2013 7:43 pm    Post subject: Green Omeg pots Reply with quote  Mark this post and the followings unread

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.

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Skrog Productions



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PostPosted: Sat Nov 30, 2013 3:34 am    Post subject: Reply with quote  Mark this post and the followings unread

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 Smile .

i did spray one of the green pots with servisol contact cleaner but 2 days later it was destined for the bin Very Happy

Dave.

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haima



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PostPosted: Sat Nov 30, 2013 4:16 am    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sat Nov 30, 2013 4:21 am    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sat Nov 30, 2013 5:58 am    Post subject: Reply with quote  Mark this post and the followings unread

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 Embarassed . I would recommended using knobs with grub screw fixing with these...

Gary
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Dave Kendall



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PostPosted: Sat Nov 30, 2013 8:28 am    Post subject: Reply with quote  Mark this post and the followings unread

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

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Zodiak



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PostPosted: Sat Nov 30, 2013 4:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
The question is do I try to replace the pots piecemeal, or just start again Sad

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Last edited by Zodiak on Sat Nov 30, 2013 5:34 pm; edited 1 time in total
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Zodiak



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PostPosted: Sat Nov 30, 2013 4:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

I am just going to bite the bullet and swap them all out now be fore I go any further Crying or Very sad
Where can I buy these alpha pots in the UK please?

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Dave Kendall



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PostPosted: Sat Nov 30, 2013 5:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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Zodiak



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PostPosted: Sat Nov 30, 2013 5:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

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 Sad
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.

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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
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PostPosted: Sat Nov 30, 2013 6:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

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

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new voodoo



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PostPosted: Sat Nov 30, 2013 6:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.
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Zodiak



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PostPosted: Sun Dec 01, 2013 12:30 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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Zodiak



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PostPosted: Sun Dec 01, 2013 10:15 am    Post subject: Update Reply with quote  Mark this post and the followings unread

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 Wink

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.

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Zodiak



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PostPosted: Sun Dec 01, 2013 5:36 pm    Post subject: Aaaargghhh!!! Reply with quote  Mark this post and the followings unread

I have just found a length of plastic pipe that is EXACTLY right for holding these pots in place.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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 Confused
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! Very Happy

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Zodiak



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PostPosted: 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. Crying or Very sad

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elmegil



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PostPosted: Wed Dec 04, 2013 7:50 am    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Wed Dec 04, 2013 8:04 am    Post subject: Reply with quote  Mark this post and the followings unread

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 Confused

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elmegil



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PostPosted: Wed Dec 04, 2013 8:31 am    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Wed Dec 04, 2013 9:25 am    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Wed Dec 04, 2013 9:31 am    Post subject: Reply with quote  Mark this post and the followings unread

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. Shocked

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jukingeo



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PostPosted: Sun Dec 08, 2013 9:30 am    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sun Dec 08, 2013 10:06 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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jukingeo



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PostPosted: Sun Dec 08, 2013 10:46 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

Quote:

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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