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Replaceing Pots/L-pads in Ar-3a


Guest loudsubz
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Guest loudsubz

I tested out my set of ar-3a tonight and the pots are beyond fixable. I remember my uncle tried to fix them a few years back and ended up just putting a dab of solder in the controls so it only works on a certain setting but the mid is way to strong for my liking in that spot, and the other ones are very crackily even after repeated workings with contact cleaner.

So my question is: What are they? L-pads or Potentiometers. And what values are they?

Sorry if this has been mentioned before but i did a search but didn't see any solid evidence on what they were exactly.

If they are pots, what value are they etc, same with l-pads.

thanks.

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They are pots. If you were to measure them in action you would find:

1)Between terminals "1" and "B" is the series resistance

2)Between terminals "B" and "2" is the parallel resistance

3)The sum of 1) and 2) is 15 ohms

4)Between terminals "1" and "2" is always 15 ohms.

If you were to put an ohm in series with the tweeter and 14 ohms in parallel and

you were to put 3.25 ohms in series with the mid and 11.75 in parallel, you would be close to what many folks consider to be the "optimum" pot settings. This would be equivalent to the "dot" midrange pot setting, and the "increase" tweeter pot setting...

By-passing or using l-pads could change the impedance which would affect the crossover points (usually lower) and therefore the sound. It may also endanger the tweeter which only has a 6mfd cap between it and oblivion.

With all that said its best to try to replace the pots with originals. I believe dogmeninreno has refurbs for sale on this board.

Roy

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Guest loudsubz

thanks Roy

on the Layne audio page it has the "OEM level controls" under the AR section. They also have aftermarket ones for half price that they suggest over the OEM ones, saying "unless you want a museaum showroom piece get the aftermarket ones"

Any advice on that. They say the aftermarket ones are better and wont corrode.

thanks.

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I took apart the old pots on my AR3a's , cleaned them up and re-intalled them but the speakers just kept cutting out. After 500 times of getting up out of my chair to jiggle the pots (and lots of cursing after a while), I bought the replacemnt pots for about $9.00 each and have been happily sitting and listening ever since. The bottom line is that you could store the old pots in an old mayonaise jar in case you sell the speakers to some anal buyer or the local museum calls you up and asks you to donate them.

I also ditched the carcinogenic stuffing and installed some "acousta-stuf".

And finally, I replaced all the old caps with new ones from Madisound.

I know my changes work beacuse I have another pair that I left in original condition. The re-furbished ones definitely sound better. And the re-worked pair still has that distinctive AR3a sound.

Someone may respond to this post by saying I don't have AR3a's any more but I really don't care - I like them. And thats what counts.

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Guest loudsubz

yes, thats exactly what counts, if they sound good to you thats all that matters. I have no intentions of ever selling these speakers. They have been with us since brand new when my father was a teenager, and now when I am one.

I just want them sounding good again so pots and cap upgrade are in order for sure.

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I'm not sure they make 'em anymore. If you can get restorable pots and use automotive dielectric grease (battery cable, spark plug cable stuff) to coat the innards after a thorough cleaning, the restoration will last a long while. I have a 35 year old pair that have been working flawlessly with no dead spots for 2 years after restoration. They were a mess when I got them and failed the first attempt at fixing them. I got better at it. Modern l-pads get scratchy too...they are simply disposable, cheap and easy to replace.

Another thing to remember is that you will need to get small replacements if you intend to use the same holes for the shafts.

Some folks on this board are having trouble getting Layne to respond. I believe he was selling simple L-pads...don't know the impedance. There is a guy on EBAY by the name of Vintage AR (I think his name is Larry) who may be worth talking to. He also sells AR replacements but discloses that they are l-pads...again no mention of impedance. Keep us posted on the outcome of your inquiries.

Roy

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Guest loudsubz

this is what I found

RHE-15.jpg

15 Ohm, 15 Watt ceramic rheostat. Body is 1.2" diameter x 1." 6mm x 0.5" long split, knurled shaft. 9mm diameter threaded mounting bushing. Includes hardware. Large quantity available.

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Be careful ordering 15 or 16 ohm pots from electronic suppliers. I've tried to get some from Parts Express and MCM Electronics and both had oversize bodies the would not allow two to be installed side by side at the current center distance which, if I remember is about 2.25 inches. As far as lame, I mean Layne Audio is concerned, the web site looks inviting but....customer service is terrible. There is no on-line ordering system and the phone is hardly never answered, nor are voice mails ever responded to.

I just finished refurbishing 2 sets of AR3a's and ended up cleaning up the old pots and re-installing them.

Carl, The speakerdoctor

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They look promising! The original pots are 1 3/8" in diameter..They should fit. It certainly doesn't look like the typical "l-pad" sold by Parts Express, etc. (which we really don't want even if they do fit). How much $ and how do we get a hold of these to conduct a little research?

Roy

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Guest loudsubz

thanks for all the help guys. This board is great, full of so much info, I look forward to finally getting these ar3a's going for the xmas holidays.

I am too experiencing problems with layne. They said they respond 2-3 days for emails, but that was over a week ago and no response back so I pretty much gave up on them.

the site I saw those reostats was on allelectronics

thanks.

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Hello there

Ya know when I say a picture is worth a thousand words I mean it.

What a great technology we have today.

You could have written quite an article on describing that pot.

That one picture is very well done thank you.

>this is what I found

>

>RHE-15.jpg

>

> 15 Ohm, 15 Watt ceramic rheostat. Body is 1.2" diameter x 1."

>6mm x 0.5" long split, knurled shaft. 9mm diameter threaded

>mounting bushing. Includes hardware. Large quantity available.

>

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>Be careful ordering 15 or 16 ohm pots from electronic

>suppliers. I've tried to get some from Parts Express and MCM

>Electronics and both had oversize bodies the would not allow

>two to be installed side by side at the current center

>distance which, if I remember is about 2.25 inches.

Are we confusing potentiometers with L-pads? I have never seen 15 Ohm potentiometers in Parts Express. P-E does sell 16-Ohm L-pads, which are well over two-inches in diameter. In any event, one would not purchase these for use an AR-3a.

MCM is one distributor of Ohmite rheostats. For example, see Ohmite part number RHS15R, a 25-Watt, 15-Ohm potentiometer with an outer diameter of 1-5/8 inches and a body depth of 1-3/8 inches. These dimensions are identical to those of the AR-3a originals. The Ohmite units are dear--low volume--but considering their expected lifetime, they likely represent a better long-term investment than commercial restoration.

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You're right John, Parts Express, Layne (assuming they are still in business) and most others, offer l-pads, not potentiometers or rheostats (which seem to overlap in definition). The original AR3a potentiometers measure 1 and 5/16" in diameter which may make the MCM offering at 1 5/8" too wide. I just measured a couple of them to make sure...not sure how you got your measurements.

The one pictured above is smaller and only $1.50 and therefore worth a try. I've ordered some to take a look at. The 15 watt rating should not be a problem as the "AR3a Limited" crossover discussed at length here recently uses 15 watt 8 ohm l-pads (yes, l-pads, not pots). I've used that crossover for almost 7 years with no problems other than some minor dead spots developing in one of the four.

John, have you tried the resistor substitution you posted awhile back for fixed levels? I believe you had the right solution.

Roy

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Roy, my apology for misreading my scribbled notes. 1-5/16 it is. However, from the outside I measure a pot spacing of 1-3/4 inch. The Ohmites would fit with an eighth to spare! Ohmite also makes a 12.5 Watt unit (REE15R) that is the size of the pot shown above.

We considered resistors and a switch, but realize that switch contacts also wear. What about replacing the mid-pot with fixed resistors and outside taps in the manner of an AR-1 incantation? One could choose mid-driver values yielding (-3/0/+3) dB. For the hi-driver- a single 15-Ohm resistor with no pot. Alternatively, 14+1 and taps, if really fussy.

We have not tried resistors yet. My pots are good--recently reworked by a perfectionist. However, one day ...

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They all sound like worthy possibilities for those who are willing to try and don't mind altering the original arrangement. The main thing for me is that our discussion is taking into account what it takes to maintain the original character of the sound. I have a "project" pair of 3a's with the pots hanging out the back as we speak. Maybe thats the solution, easily accessible, "hanging" pots!

I just checked out the MCM pots....$25 to $30 each ($100+ for the required 4)!! Youch! That certainly would be at the bottom of my list of solutions.

Roy

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  • 14 years later...

This is an interesting LPad retrospective considering where CSP stands today on LPAD use in the classic ARs.  For the record I am a late but fervent advocate of LPads.   I posted this so anyone searching for advice will know to move on to recent discussions JIC they are trying to make a decision now, almost 16 years later.

Aadams

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On 12/7/2004 at 1:57 AM, RoyC said:

There is a guy on EBAY by the name of Vintage AR (I think his name is Larry) who may be worth talking to.

Hey Adams

Thanks for a walk down memory lane. Interesting to see how opinions/expertise evolve. One of the great things about this forum.

I was amused to read Roy's comment about Vintage AR from 2004. Apparently Larry WAS worth talking to. Roy now does restoration work and provides expert guidance for Larry.

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8 hours ago, JKent said:

Hey Adams

Thanks for a walk down memory lane. Interesting to see how opinions/expertise evolve. One of the great things about this forum.

I was amused to read Roy's comment about Vintage AR from 2004. Apparently Larry WAS worth talking to. Roy now does restoration work and provides expert guidance for Larry.

Wow, memory lane, indeed! We were just getting to know each other. John later purchased level controls from AB Tech (based on a misleading website description) and ended up with overpriced 15 watt L-pads. This in turn lead to my playing around with resistors to compensate for the L-pad's higher parallel resistance, and the eventual use of a parallel 25 ohm resistor for this purpose. I really didn't know Larry at all at that time. When we later became acquainted we had some interesting debates on this issue.

About the time of this thread John and I began spending many email hours comparing notes, and discussing other AR repair/restoration topics. Tom Tyson joined in early on, which ultimately resulted in the idea to put together the 3a restoration guide.

Roy

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