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Ar3a Improved crossover


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Hi,

I'm going to recap the crossover in my pair of Ar3a Improved speakers, and have some questions I hope can be answered here. I'm not trying to recreate the original sound of these speakers - my aim is to have them sounding as good as is reasonably possible, using modern components of high quality.

Is it worth considering a conversion to the AR3a crossover? My reasoning is that this would give more tonal control via the pots, rather than the switch of the AR3a improved crossover.

What is the best way to remove the crossover from the cabinet? It seems to be glued and I'd hate to break anything trying to get the board out...

What are some recommended replacements for the caps? In other gear I've built (Pultec style EQs, LA2A compressor) I've used V-Cap and Mundorf, but the price of an exotic 150uf Cap is $$$...

Thanks in advance,

Stephen

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4 hours ago, Stephen M said:

I'm not trying to recreate the original sound of these speakers - my aim is to have them sounding as good as is reasonably possible, using modern components of high quality

Are you swapping the original drivers for new components?

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Hi Stephen

I recently completed a pair of AR-11 crossovers (very similar to your Improveds) and only after completion did I learn that our friend johnio (John O'Hanlon, editor of the AR-3a restoration booklet) prefers the AR-3a LIMITED crossovers, mainly because of the improved tonal control via L-pads, as you mentioned. If I were doing another pair of 11s I think I would build 3a Limited crossovers. johnieo's xo schematic is attached below.

As far as caps, we've avoided going down that rabbit hole. I use inexpensive film caps from Erse, Dayton or Carli. Ken Kantor believes in replacing NPEs with NPEs. SOme members here like the Mundorf E-cap NPEs ($3.60 each for 150uF). Your choice of caps is totally up to you but take a look at the Limited xo. It not only has L-pads, it's also bi-ampable.

Kent

AR3a Limited crossover.jpg

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The 150uF is a shunt to ground.  A NPE would be fine for that.  The 40 and 4 uF are series caps, and I tend to use poly for those.  I've tried Audyn, ClarityCap, Dayton, and Mundorf for those, and like Mundorf best.  But, a combination of ClarityCap CSA's and Mundorf EVO Oils would sound very good in parallel together, for the mid dome.  Warm and open.  A Dayton or Clarity CSA's would work fine for the tweeters.   All IMHO.  :D

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8 hours ago, Aadams said:

Are you swapping the original drivers for new components?

I'm going to use HiVi Q1R tweeters. The rest are original.

I'm aware of the need to use an inductor coil with these tweeters. Is this the only mod necessary?

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15w. Many of us use the 3/8" shaft but I think Roy said he likes the 1"

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That AR-3a Improved crossover is nearly the same as the AR-11 with the noted use of

Lpads except for the tweeter cap going from 10 uF in the AR-11 to 4 uF.  I would probably

experiment with 6 to 8 uF when using the AR-11 tweeter.  I measured some peaking in the

stock AR-11 tweeter crossover section with the 10 uF and the level full up.  I'd have to check

my notes on the measured crossover frequency.

I would not go larger that 4 uF with the older non-ferrofluid tweeter in the 3a.

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15 hours ago, JKent said:

15w. Many of us use the 3/8" shaft but I think Roy said he likes the 1"

They both work well. I've been combining orders with Larry Lagace/"Vintage AR" who orders the 1" version in large quantities. When properly installed it is sometimes more convenient to route certain crossover wires under the L-pad body.

Roy

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On 2/27/2020 at 11:24 PM, Pete B said:

That AR-3a Improved crossover is nearly the same as the AR-11 with the noted use of

Lpads except for the tweeter cap going from 10 uF in the AR-11 to 4 uF. 

Hi Pete,

The schematic Kent posted above is for the AR-3a Limited (circa 1990), not the 3a Improved of the mid 70's. The 3a Improved's tweeter cap and coil is 10uf and .11mh, just like the AR-11...but paired with the old 3a tweeter. The 3a Limited used an AR-11 tweeter along with a 4uf cap/.16mh parallel coil combo vs the AR-11's 10uf cap/.11mh. The 3a Improved was a bit of an aberration. I still believe the Improved was really not much of an improvement. Perhaps it was a way to unload a surplus of Euro cabinets before the introduction of the AR-11/10pi models. ?

Out of curiosity I had acquired a pair of original 3a Limited boards in the early 90's when Parts Express was selling "original AR-3a crossover boards" as "buyouts". Since these printed circuit boards were set up with the same configuration as the original 3a crossover, and not knowing what they were originally used for, I used them for much experimentation for over 10 years years until sending the remnants of one to John O'Hanlon. (Minh Luong, another of our 3a restoration guide brethren, had identified the curious 3a board's original use by that time.) Using the original board as a guide, John produced 4 very nice AR-3a Limited printed circuit boards and sent two to me. My new O'Hanlon/3a Limited crossovers were placed in Euro/3a Improved cabinets and John's were used in original US 3a cabinets, both with Tonegen AR-11 replacement tweeters. Imo, the AR-3a Limited is the best of the bunch.

Roy

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