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 Forum index » DIY Hardware and Software
Pots Inquiry - Alpha Quality and also MOTM Quality Pots
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Abby Normal



Joined: Feb 20, 2010
Posts: 66
Location: USA
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PostPosted: Sat Feb 20, 2010 11:28 am    Post subject: Pots Inquiry - Alpha Quality and also MOTM Quality Pots Reply with quote  Mark this post and the followings unread

Hello all,
I ordered some Alpha pots to replace some failing Omeg pots in my Oakley modules.

The Alpha part # is RV24AF-10-150B50K
Mouser's part # is 31VA405-F

After installing the pots, I found that they make a very noticeable scraping noise when they are turned. It's very annoying! Electronically, these pots seem fine. The noise is coming from the pots themselves (it's not an audio issue).

I haven't noticed this with any other Alpha pots that I have. Synth.com uses Alpha pots, and while I can hear the scraping sound, it is nowhere near as noticeable or distracting as these new pots.

Is there a different series of Alpha pot that is quieter, or of a slightly higher quality and price? Or have Alpha pots' quality gone down a notch or two recently?

The second part of my thread here is related to the above. I'm wanting to replace pots on my Oakley VCO and filter (and some others with failing Omeg pots). For the VCO and filter, I'd like to have a nicer quality pot that the Alphas. I found the Bourn's 91 series at Allied for a little under $5 a pot, but I noticed that the MOTM 300 VCO uses the Spectrol 149 series. I can't afford those, so I was wondering if the Spectrol 249 or 248 series would be the next best bet (even though I can't find any so far!), or would the Bourns 91 series pot be an acceptable substitute?

Are there any other similar quality pots (I'm in the US) that you would recommend for the VCO and Filter? How about for use in Mixer and other modules that might not need the very best quality pot?

Finally, I have an Oakley Multiladder that requires a 47K reverse log taper pot. Does anyone know where I can buy one of these? I haven't found a source yet.

Thanks for any help.
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e-grad



Joined: Sep 12, 2008
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Location: Berlin

PostPosted: Sun Feb 21, 2010 4:36 am    Post subject: Reply with quote  Mark this post and the followings unread

I have Alpha, Bourns, Omeg and Spectrol pots among other brands in my system. None of them introduces scratchy sounds into the audio path.

Once I had a scratchy pot this was due to a bad solder joint. Could a bad joint be the culprit or possibly some lemons among your Alphas pots?
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Abby Normal



Joined: Feb 20, 2010
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Location: USA
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PostPosted: Sun Feb 21, 2010 8:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello e-grad, thanks for the reply. I don't think it's my soldering. I have many years of experience, and I'm NASA certified in hand soldering techniques. I'm also trained in soldering surface mount components.

I have a relavtively large modular, and the only modules that are having problems are the ones with Omeg pots. I built most of my Oakley modules 8-10 years ago, so I believe it's a quality vs age issue (of the pots, not me of course! Wink).


I really don't know what to do about the Alpha pot mechanical noise issue. I'd hate to buy and install Alpha pots and have them exhibit the same level of mechanical noise. There are 38 Omeg pots remaining in my modular that I still have to replace. I want to be sure to pick a nice balance of price and quality. After reading more in the last day though, it seems that my choices are limited.
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bugbrand



Joined: Nov 27, 2005
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PostPosted: Sun Feb 21, 2010 11:40 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Abby Normal

I'm surprised you're finding problems with the Alphas - though I've rarely used the 24mm versions (I use 16mm) I find them to be an extremely good brand, certainly given the price.

If I understand right your pots are making an audible mechanical noise and perhaps feel scratchy when you turn them?
Did you perhaps have to cut down the shafts before fitting the knobs - 'cos this could have damaged the resistive element or even material could have got inside the pot?
I have actually had this sort of thing happen before but never had such problems when using pots with the correct shaft length.

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Abby Normal



Joined: Feb 20, 2010
Posts: 66
Location: USA
Audio files: 2

PostPosted: Sun Feb 21, 2010 1:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hello bugbrand. These pots were of the correct size, so no cutting was necessary. Good call, though!

Really the sound isn't that loud in the sense that others would notice (non-techy types, that is), but they are much more noticeable than the dotcom pots. IMO, it gives the impression of a cheap pot, and I don't want my modular to give off that vibe. Esp. since this hobby is anything buy cheap. Smile

Maybe I'll see if I can record the sound later tonight. Heh...I can see myself at work tomorrow -

Them: So what did ya do over weekend?
Me: Oh, I recorded the sound of my pots! Very Happy
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magman



Joined: Feb 04, 2009
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Location: Liverpool, UK

PostPosted: Sun Feb 21, 2010 4:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you can find a supplier with them in stock, a good compromise between quality, feel and costs are the BI/TT Electronics P260 Series pots, like these:

http://www.rapidonline.com/Electronic-Components/Resistors-Potentiometer/Control-Potentiometers/0.5W-12.7mm-Rotary-potentiometers/82067

They are conductive plastic, so have the smoothness of the Bourns and Vishay plastic pots, but at a significant difference in cost. I've decided to standardise on them for all of my projects for now (including a few Oakley modules), so I have over 100 of these and counting. The Omeg pots I originally bought will serve as breadboard parts only.

I've found one value of this series at Newark, here:

http://www.newark.com/bi-technologies-tt-electronics/p260t-s1af3cb100k/potentiometer/dp/14N5364

These were the pots that Oakley moved to when the Bourns and Vishay pots got too expensive (I also heard that they had found the Omeg pots to not have the best long term stability and they are nearly impossible to maintain). Oakley have now decided to use Alps 16mm pots for all of their future modules though.

Just a few thoughts, hope this helps.

Regards

Magman
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Abby Normal



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PostPosted: Sun Feb 21, 2010 5:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the info, Magman. I checked out the datasheet for the BI pots, and those at Newark are 1/4" bushings. I don't think they'll fit in my panels, since they're drilled a size larger than 3/8" for the Omegs.

I wish those BI pots were commonly available in the US. The datasheet states a rotational life of 1,000,000 turns! That's compared to 25,000 for the Alphas. I wonder if those specs are accurate? I think the Bourns had a 50,000 turns rating.
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Abby Normal



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PostPosted: Sun Feb 21, 2010 6:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just checked out your link for the the BI Pots at Rapid Electronics. For the price they're selling them (1.65GBP), I'm thinking of ordering from them. Has anyone in the USA ordered from them before? I'm wondering what a ballpark shipping fee would be. With the current exchange rate, these pots would come out to less $$$ than the Bourns pots. The only drawback is that Rapid has the 50K Lin BI pots on backorder (1-2 months lead time).

Is anyone using the BI Technology Pots?
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peng



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PostPosted: Sun Feb 21, 2010 9:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Check the MOTM site. he may be selling the BI pots.
Mouser is a supplier of BI pots but , last I checked, they barely carry any in stock. They could probably get them for you but there might be minimums .

p.
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Abby Normal



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PostPosted: Sun Feb 21, 2010 9:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks peng. I just checked the MOTM site, and it shows that Paul has the BI pots (100K Lin), but I think I can get them at Rapid for less money. Plus, I don't want to zero out Paul's stock.... I just completed a spreadsheet for all of the pots in my Oakley modules. I need to buy 59 pots! Shocked
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Abby Normal



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PostPosted: Sun Feb 21, 2010 11:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Okay, well just to show everybody how boring I am, I recorded the sound of the new Alpha pot and compared it with an old Alpha pot from a Dotcom module. I tried to turn them both about the same speed and travel. The microphone distance is roughly the same.

One thing that I noticed is that if you turn the volume up to listen to the MP3, the differences in volume between the two pots is not as distinct. Try keeping the volume kind of low to simulate a normal in-room listening level. It's very apparent then.


New vs Old Alpha Pots.mp3
 Description:
This is an MP3 of me turning a new Alpha pot, and then an old Alpha pot. The same mic distance was used for each pot.

Download
 Filename:  New vs Old Alpha Pots.mp3
 Filesize:  158.45 KB
 Downloaded:  468 Time(s)

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Abby Normal



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PostPosted: Mon Feb 22, 2010 8:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

It looks like I'll be passing on the BI/TT pots. Rapid Electronics has a minimum order $ amount for overseas customers. I also found out that the the BI/TT pots do not work in the final 10% of the pot's CW and CCW settings.

It looks like I'll probably do a mix of Alpha and Bourn 91 series pots. I might try ordering some Alpha pots from different vendor to see if the noise problem is better. I read that there are differences in the pots, depending on the supplier.
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sduck



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PostPosted: Mon Feb 22, 2010 9:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's really weird. I just installed a bunch (12) of those same 24mm alpha pots - mixed bag of values, 50K, 100K, 1M's - that I just got from mouser 2 or 3 weeks ago, in a fairly large module I'm building, and they're all fine. Noiseless.

Are the ones you got covered in that machine grease that they're always covered with? I think that's one of the key parts in how these work - it's what makes them turn with the right feel, and keeps the mechanical noise down. Over the years I've gotten one or 2 that didn't have this grease on them - maybe you just got a batch that had a problem?

Have you tried calling mouser about this? I doubt that they'd replace your already installed pots, but they might give you a discount on replacements. Anyway, I wouldn't write off mouser just because of these few bad pots - obviously they still have good ones in their system.

I'm sure you've probably isolated and eliminated this possibility, but the recording sounds like the knob scraping on something. Do these pots still make the noise without the knobs? Do they make it when removed from the panel?

edit - rereading your original post - yes, mouser also carries the spectrol 249's, which are great replacements, but they're really pricey. I still like to use them in high tolerance locations, like frequency controls on vco's.
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Abby Normal



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PostPosted: Mon Feb 22, 2010 10:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't recall seeing any oil or grease on the Alphas. Maybe this is just a bad batch? Thanks for the tip about calling Mouser about it. I hadn't considered that. I'm about ready for sleep now, but I'll try turning the unused Alphas (I bought extras for another project) to see if they are noisy right out of the bag. I'm thinking they will be...
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