AR Potentiometer Replacement

[dynaco_dan]

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....

Hi there;

It appears that an issue has shown up now regarding already past posted information.

It appears that we need a to-do or re-do-box.

Or rather a forum or folder for the ocassional article update or human error.

Perhaps Mark can look into this issue at a future date when he has the time or has a helper.

A helper might be more inline with our needs and Marks personal life and work load.

This website has become an amazing example of finest quality information.

Vern

[Zilch]

Hi there;

It appears that an issue has shown up now regarding already past posted information.

Hi, Vern.

Well, we're not SURE yet; just sorting it out so far....

[RoyC]

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

OK...Let's see if we can sort this out before it gets too "grumbly" :-). I think I have.

First of all, I did not post a schematic for any AR model in my post in 2007. I simply was sharing an idea that seemed to hold promise for an easy way to emulate the original pots near their typical settings. I never posted it in another forum, preached its use, or for that matter, have I ever had ANY feedback from anyone who has tried it. I doubt it is much of an issue for anyone but a few geeks like us. I did try it a few times on various AR models, and, imo, it worked for the intended purpose. Modified l-pad equipped 3as and originals were virtually identical sounding when A/B-ing at 1 to 4 ohms in series with the tweeters and mids. A schematic can be found in the "Restoring The AR-3a" document pinned in this section of the forum (Section 3.8, Figs 3.14 and 3.15). BTW, Jerry's graph is not consistent with the meter measurements I have made. Up to just shy of 5 ohms in series, all series and parallel measurements add up to 15 to 16 ohms. Is it "linear"...no, but it works well enough within the target range to sound like the original pots.

As for the basic wiring of l-pads in AR speakers....A couple of months ago a CSP member privately told me that my 2007 post (forget about the 25 ohm resistor for a moment) contradicted Vintage AR's l-pad wiring instructions. When I checked it out, he appeared to be right, as I noticed I had not wired a 2ax (the model in question) that way in recent memory. When it was brought up in this discussion, I didn't want any possible error with that post to confuse the issue...yet it did, because it actually is NOT in error for the 4x! Sooo, just to be sure I just opened, a 4x I had wired with an l-pad (and parallel resistor) last year, and found it was consistent with Zilch's schematic. I apologize Zilch, your schematic is fine. (Of course, you knew that, as you really journeyed here looking for a debate regarding the 24/25 ohm resistor mod, not l-pad wiring).

So why my l-pad wiring confusion?

...The 3a, 2ax, and the 5 have their series caps connected on the negative leg of the circuit. That negative lead, which originally connects to the #1 pot terminal must be connected to the #3 l-pad terminal. which traditionally connects to the positive side of the circuit. For those non-4x models, my pot terminal to l-pad terminal description in the 2007 post is wrong...but it IS correct for the 4x, which has the tweeter cap on the + side of the circuit. I really didn't take a look at the details until tonight. It also explains the inconsistency with VR's instructions, which were for the 2ax, not the 4x. I'll go back and clarify that post in accordance with the results of this discussion.

BTW, Zilch, I see a bunch of 4x cabinets in your photo, but I'm not sure any of them are 4xs. It would seem "restoration" is not your main interest in AR speakers...but hey the cabinets are nice:-)!

Anyway, I just found, and attached, a couple of AR-3a crossover schematics showing the l-pad circuit vs the original circuit for that model. Fire away...

Roy

[Zilch]

OK...Let's see if we can sort this out before it gets too "grumbly" :-). I think I have.

Thank you, Roy, for taking a fresh look at this. I struggled with the same issues in attempting to present a "universal" AR approach with my switched attenuator. Finally, it occured to me that it didn't matter; the switch has no rotation, and an L-pad only has but one if the input and driver are connected in the standard manner which you and I have both described above. What matters is that the driver polarity remains the same as original.

While you and others have worked through development of your L-pad substitution from the perspective of the series and parallel resistances, I see it as a conventional L-Pad with a fixed resistor across the driver altering the load impedance. How well that works as emulation of the original potentiometer, I don't know, but certainly selection of the optimum resistance is somewhat a function of the actual driver impedance, as another member pointed out in the earlier discussion. At least now your design intent is clear, and I'm in a better position to verify the actual performance via measurements, and the sim guys can do it with their driver models, if desired.

As you suggest, in practical terms, all of this may be of little consequence, and Jerry and I have gone 'round and 'round about that on AK with respect to his bypass vs. remove the pot arguments. As you correctly observe, I'm an upgrader, not a restorer, but I also recognize and respect the desire of restorers to achieve an optimum result. There are ascertainable facts associated with the relative "correctness" of each of these approaches in terms of how well they replicate the original design performance; certainly there is value in understanding them and having the associated facts at hand....

[genek]

...The 3a, 2ax, and the 5 have their series caps connected on the negative leg of the circuit. That negative lead, which originally connects to the #1 pot terminal must be connected to the #3 l-pad terminal. which traditionally connects to the positive side of the circuit. For those non-4x models, my pot terminal to l-pad terminal description in the 2007 post is wrong...but it IS correct for the 4x, which has the tweeter cap on the + side of the circuit. I really didn't take a look at the details until tonight. It also explains the inconsistency with VR's instructions, which were for the 2ax, not the 4x. I'll go back and clarify that post in accordance with the results of this discussion.

Any idea which side of this my 6's fall on? I've never seen an AR-6 schematic anywhere.

[RoyC]

Zilch, I agree with all your points...wish you were here when we were first discussing this.

As you know most of the members and visitors here are looking for in-kind repairs and restoration tips, and my interest has primarily revolved around easy to implement solutions. The truth is that the resistor trick or building a switch is probably beyond the capabilities and/or interests of many visitors to this forum, which is why Larry sells so many ordinary l-pads with "simple" installation instructions :-). Further, tired old AR-3a, 2ax and 5 tweeters are deteriorating, and probably benefit from the added output and extension provided by an ordinary l-pad (which is why I drew a dotted line for the 25 ohm resistor in the 3a schematic). Most folks set the controls and forget about them anyway...so the need for precision is often questionable.

Its a hobby.

Thanks for your patience...hope you stick around. For starters the mods and tweaks section could certainly benefit from your 4x adventures.

Roy

[RoyC]

Any idea which side of this my 6's fall on? I've never seen an AR-6 schematic anywhere.

Klaus posted some AR-6 schematics awhile back, as their are a number of versions of that crossover. According to some notes I have, I believe it is on the negative side.

Roy

[Rlowe]

Klaus posted some AR-6 schematics awhile back, as their are a number of versions of that crossover. According to some notes I have, I believe it is on the negative side.

Roy

Here's a couple, hopefully the quality is OK!

1-Alnico Woofer/RoyC's,

(I've been told the NiCr in the cct also limits the 10uF & Coil "resonance")

2- European Ceramic ,

3- Klaus's/Ceramic.,

[genek]

Here's a couple, hopefully the quality is OK!

1-Alnico Woofer/RoyC's,

(I've been told the NiCr in the cct also limits the 10uF & Coil "resonance")

2- European Ceramic ,

3- Klaus's/Ceramic.,

Thanks. Looks like I have the "A" model.

[genek]

This one's so bad it's funny. Just pulled it down off "that" auction site. Apparently, the "retired engineer" owner's crossover pots went south and he installed a pair of L-pads from Radio Shack.

[RoyC]

Here's a couple, hopefully the quality is OK!

1-Alnico Woofer/RoyC's,

(I've been told the NiCr in the cct also limits the 10uF & Coil "resonance")

2- European Ceramic ,

3- Klaus's/Ceramic.,

Wow, Richard...Forgot you had those schematics. Nice!

Thanks,

Roy

[JKent]

This one's so bad it's funny. Just pulled it down off "that" auction site. Apparently, the "retired engineer" owner's crossover pots went south and he installed a pair of L-pads from Radio Shack.

Let's hope the engineer was a guy who drove a train

Sad thing is the cabinets are shown in the other auctions and they look pretty good, but the seller decided to part them out (after "cranking" the woofers with deteriorated surrounds--wonder how much damage THAT caused!). Then again, the surrounds in the photo appear to be new. I think there is more here than meets the eye.

Kent

[genek]

Sad thing is the cabinets are shown in the other auctions and they look pretty good, but the seller decided to part them out (after "cranking" the woofers with deteriorated surrounds--wonder how much damage THAT caused!). Then again, the surrounds in the photo appear to be new. I think there is more here than meets the eye.

I'll know in about 10 days. I contacted the seller and he hadn't taken them apart yet. I just bought the speakers.

The seller sent me some additional pics. Turns out the surrounds look intact from the front, but started to separate along the mounting flanges at the sides when they were played.

It's new project time!

[JKent]

I'll know in about 10 days. I contacted the seller and he hadn't taken them apart yet. I just bought the speakers.

The seller sent me some additional pics. Turns out the surrounds look intact from the front, but started to separate along the mounting flanges at the sides when they were played.

It's new project time!

GOOD FOR YOU GENE!

So glad to see these have been rescued from being parted out!

And as a bonus you get those really cool Rat Shack L-Pads

Seriously--Good luck with them

Kent

[Zilch]

Yet another approach....

http://www.humanspeakers.com/o/ar/3a.htm

[genek]

Yet another approach....

http://www.humanspeakers.com/o/ar/3a.htm

If I was going to do anything other than restore, I think it would probably be the switch and resistor scheme.

[Zilch]

I apologize Zilch, your schematic is fine. (Of course, you knew that, as you really journeyed here looking for a debate regarding the 24/25 ohm resistor mod, not l-pad wiring).

Anyway, I just found, and attached, a couple of AR-3a crossover schematics showing the l-pad circuit vs the original circuit for that model. Fire away....

http://www.audiokarma.org/forums/showthrea...858#post2561858

And I apologize for the delay....