AR Potentiometer Replacement

[Zilch]

See Attachment.

S1 is a three-way (on-on-on) miniature toggle switch with sealed terminals and silver-plated contacts, C&K 7211SYZSQE or Alco MTA206PA04, available from Newark, DigiKey, others. Use a sealed rotary selector switch for more settings and/or finer resolution, if desired. The toggle switch and resistors cost about the same as quality L-Pads, substantially less than replacement wirewound pots.

As shown in the schematic, fixed resistors comprise a stack providing three levels of attenuation, the values specified giving ~4 dB per step, i.e., 0, -4 dB, and -8 dB. Resistor values must total ~15 - 16 Ohms to match the original circuit impedance and performance.

Measurements of AR4x attenuation with several different resistances shown here:

http://audiokarma.org/forums/showthread.ph...693#post1369693

Want attenuation adjustability about some intermediate level? See second attachment below. Choose R values for any desired range and resolution.

[genek]

I'm experiencing a philosophical conflict between my natural desire to keep my classic AR's all-original and the reality of corroding pots and the fact that the pots on all of my speakers have been at pretty much the same positions for over 30 years.

[Zilch]

I'm experiencing a philosophical conflict....

It's in your head, of course.

Actually, you're in a good position to make a precise determination of what R-values to use, by measuring the setting of the pots once you remove them.

The little toggle fits in the same hole the pot comes out of, and nothing says you can't save them funky pots for posterity in an illuminated display case on your mantel.

Change the flowers weekly and burn incense on the solstices and equinoxes.

"Ohmmmm...."

[genek]

It's in your head, of course.

Naturally, but then again so is the sound.

I have toyed with the idea of doing something like what you've drawn when/if the pots do go out on me (since I never change the settings there's not much point in opening them up otherwise). 1p3t rotary switches would even let me keep the original knobs. I haven't ever had any MF or HF drivers go quiet on me, though, and I have a sneaking suspicion the wipers on the pots have just fused in position.

[Zilch]

Naturally, but then again so is the sound.

I ain't goin' THERE, nope, nope.

1p3t rotary switches would even let me keep the original knobs.

Spec a suitable sealed 1P3T rotary switch, and let's work past the bypass/rehab/L-pad madness here, then.

The 10W non-inductive Rs are $1.25 apiece at Parts Express, so, worst case, we're talking $5 for those....

[Carlspeak]

I feel replacing the pots with a switch (ala-Advent) qualifies this post as a mod/tweak, etc. and thus should be moved to that catagory within CSP.

[Mexicomike]

Why not just disassemble/clean the oem pots, coat them internally with a generous slathering of di-electric grease, put them back together and forget about them.

[RoyC]

Why not just disassemble/clean the oem pots, coat them internally with a generous slathering of di-electric grease, put them back together and forget about them.

Agreed...or, if the pots are too far gone, wire a 25 ohm resistor across the parallel leg of a brand new $4 (8 ohm) l-pad. It easily approximates the typically preferred pot settings in the first 1/3 of the rotation.

I also agree with Carl. This should go to the mods section of the forum.

Roy

[Zilch]

Agreed...or, if the pots are too far gone, wire a 25 ohm resistor across the parallel leg of a brand new $4 (8 ohm) l-pad. It easily approximates the typically preferred pot settings in the first 1/3 of the rotation.

As shown below for AR4x? If so, let's discuss it.

Help me, now, the "Normal" setting for the mid pot in the three-ways is in the top 1/3 of rotation?

[genek]

Help me, now, the "Normal" setting for the mid pot in the three-ways is in the top 1/3 of rotation?

I think he's referring to where the stock limits would fall on a new L-pad with resistor. On all of my ARs with original pots, the "Normal" (white dot) setting is more or less at the midpoint of all the pot rotations.

[Zilch]

On all of my ARs with original pots, the "Normal" (white dot) setting is more or less at the midpoint of all the pot rotations.

I do recall reading that the white dot is not at the midpoint in some models, the pot being rotated somewhat when originally installed.

In any case, we are already indefinite in this respect, "Normal" not being the same as "Preferred," apparently.

Where have YOUR pots been set for the last 30 years?

Here's Roy's exposition:

http://www.classicspeakerpages.net/IP.Boar...amp;#entry62294

[genek]

I do recall reading that the white dot is not at the midpoint in some models, the pot being rotated somewhat when originally installed.

In any case, we are already indefinite in this respect, "Normal" not being the same as "Preferred," apparently.

Where have YOUR pots been set for the last 30 years?

On my 2ax's, both mid and hi pots are about halfway between the dot and full increase, and on my 6's about a third of the way up.

For each of these speakers, when I bought the speakers I played one or two records whose sound is typical of most of my listening and tweaked the speaker pots to give me the sound I liked best with the tone settings at neutral, then adjusted the amps as needed for others (unlike some "audiophile" listeners, I buy amps and receivers with tone controls, and am not above using them from time to time).

I've never done any frequency response "tests" on either my systems or my listening spaces, but except for one apartment I lived in for a couple of years, all of my listening rooms have been what is generally called "bright" (wood or tile floors, wood or other cottage-cheese-free ceilings, no drapes or curtains.

[RoyC]

Before we get too far into the discussion, it should be noted that only a couple of AR models with the knobs on the shafts (ie AR-3a and 5) were fine tuned at the factory to compensate for variations in pot tolerances. The pots typically vary from 15 ohms to over 16 ohms. All pot tabs were placed in indentations on the crossover board to position them for the increase/white dot/decrease markings on the back of the cabinet. The white dot was a decidedly subjective setting AR determined to be optimum for most listening environments.

Your assumption is correct, Zilch, once we get into l-pads, modified or otherwise, the white dot becomes even less meaningful than it probably already was after 35+ years. The modified l-pad provides a range (the typically preferred, near maximum/full "increase" pot setting values) in its first 1/3rd rotation..actually very close to 1/2 rotation. Incidentally, only two AR models use the 1/2 way point of the pots for the white dot settings. They are the midrange pots of the AR-2ax and the AR-5. The rest, including ALL tweeters, are within 1/4 to 1/3 turn of the pot shaft from full increase. One of the most common errors made after reinstalling the pots is failure to insert the pot tab into the corresponding indentation on the crossover board. (Additionally, if the tab is not seated properly, it will contribute to cabinet leakage.)

I've attached some pics of pots at full increase on the AR-3a, AR-2ax and the AR-4x. Note, in the second photo, that only the 2ax midrange shows a pot whose white dot is halfway through the shaft's rotation (8+/- ohms series/8+/- ohms parallel), where full increase and full decrease are equidistant from the white dot. The values associated with that setting would be just past the limit of the modified l-pad's efficacy...but it would still work well enough, imo.

Zilch, your 4x schematic would work but you need to reverse the wires attached to l-pad terminals #1 and #3 to make the l-pad act in the same direction as the old pots. What was attached to #1 pot terminal goes to #3 l-pad terminal and what was attached to #2 pot terminal goes to #1 l-pad terminal. The driver wire, "B" pot terminal becomes #2 l-pad terminal. (I posted this incorrectly here awhile back). R1 can be 24 or 25 ohms

BTW, the 4x white dot is at 1/4 turn of the pot shaft (4 ohm series and 11.5+/- ohms parallel).

I'm really not opposed to any approach that comes close to the original electrical characteristics, including switches. The original pots are only needed for those desiring "authentic" restorations. In fact, it is very easy to measure any single optimal pot setting, and simply insert the appropriate series and parallel resistors, as long as they add up to 16+/- ohms...Zilch's switch expands on that concept to provide more settings.

Most pots I have seen show the most corrosion where the pot was positioned 35+/- years ago, and was probably never touched again.

Roy

[genek]

Before we get too far into the discussion, it should be noted that only a couple of AR models with the knobs on the shafts (ie AR-3a and 5) were fine tuned at the factory to compensate for variations in pot tolerances. The pots typically vary from 15 ohms to over 16 ohms. All pot tabs were placed in indentations on the crossover board to position them for the increase/white dot/decrease markings on the back of the cabinet. The white dot was a decidedly subjective setting AR determined to be optimum for most listening environments.

I've never ascribed any significance to the dot, except as a measuring point for where my actual settings ended up (halfway between dot and full, 1/3 between, etc.). Sometimes I even use letters in "increase" and "decrease."

My 2ax's have pretty smooth pot operation, mostly because I exercise them once or twice a year. They do make a bit of static when being turned, but have no dead spots. My 6's, on the other hand, each had a dead spot on their pots when I got them, and every time I've turned the pots they start out really stiff and it takes a fair amount of work to loosen them up, so they haven't been touched for quite a while (hence my speculation about them fusing in place over time). I imagine that sooner or later one or both of them will simply stop emitting highs, at which point it'll be time to open them up and either try to clean the pots or think about one of the L-pad or switch schemes described here.

BTW, my 6's were made with the 3-lug terminal block. Why, I don't know. Who would go to the trouble of biamping a 2-way bookshelf speaker with an 8" woofer?

[Zilch]

Zilch, your 4x schematic would work but you need to reverse the wires attached to l-pad terminals #1 and #3 to make the l-pad act in the same direction as the old pots. What was attached to #1 pot terminal goes to #3 l-pad terminal and what was attached to #2 pot terminal goes to #1 l-pad terminal. The driver wire, "B" pot terminal becomes #2 l-pad terminal. (I posted this incorrectly here awhile back). R1 can be 24 or 25 ohms.

You posted it incorrectly here?

http://www.classicspeakerpages.net/IP.Boar...ost&p=62288

It's your instructions there I reconciled with Onplane's AR4x schematic, attached below, ignoring the red mods. Is that schematic correct? Where's the reference "official" AR4x schematic? Not in the CSP Library, that I can find.

In any case, I would argue that the L-Pad doesn't care; it attenuates in the counterclockwise direction of rotation, so long as its input is between terminals #1 and #3, and the driver is connected between terminals #2 and #1. Flip the polarity, and the operation is not altered. I opted for this connection scheme to maintain continuity with the INPUT terminals and consistency of wire colors, and also as a model for the more generally applicable switched attenuation I present in post #1 of this thread.

Note also that there is another AR4x version with a two-pole low-pass and inverted tweeter polarity, which I have documented in the link to AudioKarma, above, having the green tweeter wire connected to the pot's "B" terminal. CSP has encountered this previously, but erroneously concluded it to be a user mod.

[RoyC]

>You posted it incorrectly here?

http://www.classicspeakerpages.net/IP.Boar...ost&p=62288

Yes...At the time I thought the same thing as you regarding the l-pad not "caring", but it was reported to me that the attenuation reversed direction when wired that way. I quickly tried it in a 2ax, and it seems that person was correct. One of the primary purveyors of replacement l-pads ("Vintage AR") recommends that l-pads be connected as I described above in this thread. No sense debating it unless you try it first...but I agree that the overall sound should not be affected.

>It's your instructions there I reconciled with Onplane's AR4x schematic, attached below, ignoring the red mods. Is that schematic correct? Where's the reference "official" AR4x schematic? Not in the CSP Library, that I can find.

Yes that schematic is typical of most of the 4x's I have seen, and was originally posted by CSP member, John O'Hanlon. There is no "official" 4x schematic. It should be noted that AR played around with wire color, polarity, and inductors. All models have more than one configuration. Nothing should be taken for granted. For example, the yellow dot on the 4x tweeter designates the + side, and the yellow dot on the 2ax midrange designates the - side of that driver.

Roy

[Zilch]

At the time I thought the same thing as you regarding the l-pad not "caring", but it was reported to me that the attenuation reversed direction when wired that way. I quickly tried it in a 2ax, and it seems that person was correct. One of the primary purveyors of replacement l-pads ("Vintage AR") recommends that l-pads be connected as I described above in this thread. No sense debating it unless you try it first...but I agree that the overall sound should not be affected.

L-Pad will work "backwards" (and incorrectly) if the driver (load) is connected between terminals #3 and #2 instead of #2 and #1.

That's NOT what you intended, I trust....

[RoyC]

L-Pad will work "backwards" (and incorrectly) if the driver (load) is connected between terminals #3 and #2 instead of #2 and #1.

That's NOT what you intended, I trust....

So which is it, Zilch, "incorrectly" or the "l-pad does not care"? It really does not matter.

I am well aware that #1 is typically the negative l-pad connection, #2 is the output to the driver and #3 is the + input. We have proven, however, that when attached in the manner described above, the l-pad can be made to act similarly to the old pot, with the series resistance between #3 and #2, and parallel resistance (with the driver) between #2 and #1...and #2 remaining as the output to the driver. Add a 24 or 25 ohm resistor between #1 and #2 and it electrically acts like the original 16 ohm pot over a range most often used with the original pot. It works. Try it.

Roy

[onplane]

... Add a 24 or 25 ohm resistor between #1 and #2 and it electrically acts like the original 16 ohm pot over a range most often used with the original pot. It works. Try it.

Roy

I have to agree with my friend Roy here. His solution is elegant, cheap and NOT prone to further corrosion problems.

Attached is a plot of the impedance of both the pot and L-pad.

In the range of interest, they are close enough.

Now many of you know, I'm not a big fan of controls, but I can appreciate the desirability for a control on a two way like the AR-4x. Further, I really like Roy's solution. In the "full on" position only 24 vs 16 ohms is draining current away from the tweeter, so ... you do get just a tad more control than with a pot.

Regards,

Jerry

[Zilch]

So which is it, Zilch, "incorrectly" or the "l-pad does not care"? It really does not matter.

L-pad DOES care if the output load is erroneously connected across terminals #3 and #2; not only will it operate "backwards" with respect to rotation, but also, the attenuation will not be linear, and the impedance will not be constant.

I'm perfectly willing to "Try it," as you suggest, but unclear what "It" is. Post a schematic of your recommended mod for AR4x, please, so that it will be possible to compare....

[Zilch]

I have to agree with my friend Roy here. His solution is elegant, cheap and NOT prone to further corrosion problems.

Attached is a plot of the impedance of both the pot and L-pad.

In the range of interest, they are close enough.

And this you offer up as proof?

May we see impedance in combination with the driver vs. attenuation (dB) of both so as to make an assessment of how "close" they actually are in meaningful terms such as how the filter frequency is affected, please?

"NOT prone to further corrosion problems" is somewhat of a stretch, as well, without further intervention....

[RoyC]

Zilch, your 4x schematic would work but you need to reverse the wires attached to l-pad terminals #1 and #3 to make the l-pad act in the same direction as the old pots.

Zilch, so what part of the above sentence did you not understand? (Oh, I forgot, the l-pad won't care anyway.) BTW, the original pots, when installed in the circuit with the driver, did not maintain a "constant" impedance either. At least not in the same way an "l-pad" is theoretically meant to.

I contacted Larry (Vintage AR), and he confirmed the pot to l-pad conversion wiring as I described above. He has included those directions with literally hundreds of ordinary 8 ohm l-pads sold to AR customers over the years. He has had no complaints or malfunctions.

If assembling switches floats your boat, I'm fine with that. Most folks visiting this site are looking for easy fixes to old AR issues. The solutions we have discussed in this thread (including your switches) will work fine for all practical purposes, whether you choose to believe it or not. I just took a peak at the Audiokarma website, and see that you have been playing around with one pair of 4xs for some time now. I'm guessing you really don't have much in the way of AR speakers to "try" anything with.

Roy

[Zilch]

Zilch, so what part of the above sentence did you not understand? (Oh, I forgot, the l-pad won't care anyway.)

Here's my difficulty with this. Your "Solution" to the AR pot problem is frequently cited on other forums, with a suggestion that users come to CSP for the details. I did that, with the intent of trying it. I documented my best interpretation of how that might be done in Ar4x. Now, you inform us all that your previous instructions are wrong, and won't work. Fine, show us what WILL work, so that we might compare the results. I'd certainly prefer that YOU do it, rather than me, since you've already decided that I've got it wrong. It's YOUR solution; show us how to do it correctly, please.

BTW, the original pots, when installed in the circuit with the driver, did not maintain a "constant" impedance either. At least not in the same way an "l-pad" is theoretically meant to.

Yes, and I studied that in depth and documented it on AudioKarma. It's part of the voicing of the speaker, and a primary reason I concluded that a simple L-pad substitution was not an optimum approach if the desire is to maintain the original sonic signature in detail.

I contacted Larry (Vintage AR), and he confirmed the pot to l-pad conversion wiring as I described above. He has included those directions with literally hundreds of ordinary 8 ohm l-pads sold to AR customers over the years. He has had no complaints or malfunctions.

Fine. Post it.

If assembling switches floats your boat, I'm fine with that. Most folks visiting this site are looking for easy fixes to old AR issues. The solutions we have discussed in this thread (including your switches) will work fine for all practical purposes, whether you choose to believe it or not.

Link us to where the correct instructions for your "easy fix" pot replacement approach may be found, please.

I just took a peak at the Audiokarma website, and see that you have been playing around with one pair of 4xs for some time now. I'm guessing you really don't have much in the way of AR speakers to "try" anything with.

You've certainly guessed wrong. It'll take more than a "peak" [sic] to know:

[genek]

what part of the above sentence did you not understand?

Roy, this grumbly yet mildly entertaining exchance aside, some of us here are sufficiantly schematic-challenged that leaving an incorrect diagram online and uncorrected and just saying, "oops, the original diagram was wrong, just reverse X" in a subsequent post leaves us up a creek with no paddle.

[Zilch]

Roy, this grumbly yet mildly entertaining exchance aside, some of us here are sufficiantly schematic-challenged that leaving an incorrect diagram online and uncorrected and just saying, "oops, the original diagram was wrong, just reverse X" in a subsequent post leaves us up a creek with no paddle.

Continuing on with the grumbly part, where is the notification that the earlier description is wrong, as posted?

http://www.classicspeakerpages.net/IP.Boar...amp;#entry62294

Ironically, I'm arguing that the earlier description is NOT wrong, and neither is my schematic, at least insofar as I understand the intent.

Further, "Just reverse X" is itself ambiguous, and there's plenty about it not to understand.

I'm just trying to get at what the proposed solution actually IS, so that we can discuss it here....