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Recapping my old AR 10pi


menchs
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Hi all,

After reading some threads in this forum, I have finally gathered the courage to open up my 40 years AR 10pi old speakers to replace the old caps. My AR's serials are advanced (10233 & 10245) so I guess they are late productions of the 2nd version. I attach a photo of the cabinet below which shows very neat and tidy arrangement of the crossover, with two Callins caps (2500uF and 100uF) and other caps that I could not identify (are they film and foil?). All capacitors lay in a POOL of glue (hot glue?). I have already arranged and prepared new caps (thanks to DavidR for advice), and I would appreciate some guidance on the following questions (I have no knowlege in electronics).

1. How do I take out the old caps and the glue around them?

2. Is it a bad idea to leave the old caps as is (just disconnect them) and preapre a board with the new capacitors attached and glued to the board (some are quite big and some also require to connect them in parralel) and then fix the board on one of the side walls of the cabinet and use electrical wires to connect and solder instead of the old contacts?

3. If 2 above is acceptable (can't help it being a CPA), few more questions : a. can I use hot glue to attach the new caps to the board? (I will also tie them up as the old ones)  b. does it matter what kind of electric wires I use ?(I have some simple loudspeakes cables that i thought could be useful for that)

Any other Do's and Don't tips?

Thanks   

crossover AR.jpeg

WhatsApp Image 2021-08-13 at 08.44.43.jpeg

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The old hot melt glue can be softened with isopropyl alcohol (rubbing alcohol). Dribble some over the glue and let it sit for about 5 mins. Use a small flat screwdriver or similar tool to carefully pry at the edges and slowly lift it up. Just take your time. It is normal for a small layer of the masonite board comes off with the glue.

There's not a whole lot of room in there. I recommend removing them. I think I have a thread on my 10Pi xovers. If I can find it I'll post a link.

I think yours might be version 1. Are the badges brass?

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On 8/13/2021 at 1:53 AM, menchs said:

a. can I use hot glue to attach the new caps to the board? (I will also tie them up as the old ones)  b. does it matter what kind of electric wires I use ?(I have some simple loudspeakes cables that i thought could be useful for that)

Hot glue may damage new caps. Either use something like E6000 or screw cable tie anchors to the cabinet.

Marine grade (tinned) 18AWG is good. Most of us try to keep the color coding. I never recapped a 10-Pi but you may not need to add any wire.

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You shouldn't have to add any wire. I left the old cap leads as long as possible as it is very tight in there when working. Makes it easier to tie on the new caps.

I did add some wire from the transformer to the 2500uF cap but I used AR wire from a AR94 crossover board.

Kent has a good point about hot melt effects on a cap. I used Goop and not a lot. Very similar to E6000. Not sure what's available down under.

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3 hours ago, DavidR said:

The old hot melt glue can be softened with isopropyl alcohol (rubbing alcohol). Dribble some over the glue and let it sit for about 5 mins. Use a small flat screwdriver or similar tool to carefully pry at the edges and slowly lift it up. Just take your time. It is normal for a small layer of the masonite board comes off with the glue.

There's not a whole lot of room in there. I recommend removing them. I think I have a thread on my 10Pi xovers. If I can find it I'll post a link.

I think yours might be version 1. Are the badges brass?

Thanks for that. I suppose I can deal with replacing the Callins caps, but as for the rest of them (the 10uF, 20uF and 40uF) this is a different strory, as they are much much bigger and I also have 2 X 20uF caps to connect in parralel to replace the 40uF cap. This is why I brought up the idea of arranging them on a separate mazonite board on the side wall and reconnect them.

As to the version, the badges are gone a long time ago (that's how I bought them when they were 10 YO). Maybe the attached picture can help...

 

20210814_213431.jpg

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I really think the iso-OH will separate the glue from the plastic. Can't hurt to apply some and carefully pry a thin blade between the 2. Better yet, just put a thin blade between the old cap and the glue after dribbling some iso-OH on it.. I bet it will pop off. I use one of the very small flat screwdrivers.

Based on the stuffing material I can see it looks like version 1 that used fiberglass and not polyfill.

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  • 2 weeks later...

Almost done. following your advise, I managed to take out the big Callins caps and one of the small caps, however two of the black caps did't want to depart from their glue (after softenning the glue with the iso alchohol). As I was concerned not to break the coil's plastic, I disconnected them and left them inside.

One of the speakers didn't have a rubber gasket between the speaker and the wood - any suggestions for replacement? 

Also, I noticed that some people in the forums use a small value cap (0.01 uF) to bypass the big value caps, what is the purpose of this ?

Another question - how can I check electronically if the 3 switchs on the front work properly? how can I get to them physically?

Thanks 

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  1. This works very well. Use it to replace both woofer gaskets since the one that's still there is probably flattened: https://www.parts-express.com/Speaker-Gasketing-Tape-1-8-x-1-2-x-50-ft.-Roll-260-542
  2. "Bypass caps" are controversial. Some say it improves the sound, some say it's snake oil. Small value caps are cheap so if you want to try it couldn't hurt but I think most of us here are skeptical. You can Google "Bypass capacitors in crossover" or "bypass capacitors in speakers" if you want to learn about them. Here's a good explanation: https://speakermakersjourney.blogspot.com/2016/01/advanced-speaker-crossover-mods.html
  3. Dunno about the switches.
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You can use ordinary window foam gasket (comes in rolls) for the drivers. Its a little softer than the Parts Express foam and makes a better seal IMO.

As for bypassing there is a guy named George E. Short III who was an audio engineer and worked for AR for a period of time. He went on to form North Creek Audio and made speakers and some great audio capacitors. He made a living on his bypassing and cascading techniques. I will try to attach a 'white paper' word document. I used some small (0.01uF) bypass caps on my 10Pi series caps (10 and 40) as I had used NPE and wanted a bit more detail than they are known to provide. There several current day audio engineers who incorporate bypassing in some of there designs. One is Paul McGown of PS Audio and Dan Richie of GR Research.  If you add them and feel it is giving you a negative effect then its very simple to snip the leads.

The switches might be more than you want to deal with. Each of the three switches has a hex nut threaded to the main shaft of the switch body. They all need to be removed and the pcb is pulled out from the inside.

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Short BYPASS white paper.docx

 

George E. Short III BYPASSING

 

 

 

North Creek Music

The Art of Bypassing

 

Bypassing capacitors is a little like blending watercolors. With watercolors, the dominant pigment can be brightened, softened, darkened or lightened with small additions of other hues, and it takes a delicate touch to make the perfect shade.

With capacitors, the signature of the base cap can be brightened, softened, darkened or lightened with the addition of the appropriate choice of bypass capacitor. The "perfect" tonal balance can only be determined by ear.

And, like watercolors, the whole is often greater than the sum of its parts.

The bypass capacitors we have developed have very specific subjective characteristics that can be applied to improve the performance of most loudspeaker crossover capacitors significantly:

 

Cascade Bypassing

 

Classically, bypassing a capacitor means paralleling a very small cap (0.5% to 1% of the base cap) to improve the effective high frequency performance of the base cap. While this works to a point, the problem with simple bypassing it that it tends to sound a little discontinuous, with the large cap dominating the signature at the low end while the bypass cap dominates the upper extreme.

Cascade Bypassing (or simply "Cascading") is a bypassing method that yields the best and most homogeneous sounding combination of capacitance. Cascading is essentially paralleling smaller and smaller capacitors of increasing voltage to reach the target value. We usually suggest a cascade of 5% to 25% steps, with each smaller cap having a higher voltage rating.

Examples of Cascade Bypassing are:

100.0µF = 100µF 100V + 4.7µF 225V +1.0µF 625V (=106µF, within 10% of 100µF)

6.8µF = 4.7µF 200V + 1.0µF 600V + 0.10µF 800V

4.0µF = 4.0µF 200V + 1.00µF 600V + 0.10µF 800V

Cascading sounds better than simple bypassing because it yields an overall homogeneity to the sound of the equivalent capacitor.

 

Bypassing with North Creek Capacitors

 

Harmony Capacitors were designed specifically to bypass other metallized capacitors. Their signature is lightweight with a wealth of detail, and the top end has a nice sparkle without being bright or forward. They are also much quieter than most capacitors, particularly those that wound with very high tension. We best describe the Harmony caps as "cleaning up the sound" of other capacitors.

Crescendo Bypass Capacitors were designed to correct the harmonic imbalance we found in most of the film capacitors coming out of California; that is, a weak lower midrange, forward upper midrange and over-emphasized treble.. Many listeners equate this tonal imbalance with a "wealth of detail", although we find it unnatural and unsatisfying for long term listening. The Crescendo bypass cap, with the thick 600 Volt and 800 Volt film and heavy conductor, is very rich through the midrange and much softer in the top end than most of the premium capacitors coming from California. In designs where both the tweeter and the electronics tend to be bright, but a "wealth of detail" is a primary design goal, the combination of a "West Coast" capacitor with a Crescendo bypass capacitor usually yields the best of both worlds.

 

Unusual Qualities of the Crescendo Capacitor

 

We have noticed some of the strangest things can occur when one bypasses with a 1.0µF crescendo capacitor.

Perhaps the most unusual is the way this cap can "quiet down" a woofer when used in the capacitor stack going from the output of the low pass input coil, to ground. This is true of both Zobel circuits and shunt legs of second or higher order low pass filters. Frankly, we can not pin down why this effect is so dramatic in a parallel application, but it is. Try it - you'll like it. It may even blow you away.

We have heard of several customers using five 1.0µF 600V Crescendo caps bypassed with a single 0.10µF 800V crescendo to drive a Focal T120 tweeter. This is a driver with excellent information retrieval but when used with the wrong caps tends to get a little brittle. The stack of Crescendo caps is said to yield the ultimate combination.

For those using the Scan Speak Revelator tweeter, one should cascade Crescendo caps throughout. The Revelator has a broad peak in the 8kHz to 20 kHz region that will be emphasized considerably by any of the brighter film and foil caps available. Make no mistake - this may be the best tweeter in history, but it needs proper care and feeding to sound its best. See our Rhythm-Revelator project for more information.

 

 

Danny Richie of GR Research, concerning bypass capacitors: Danny felt that it wasn't just about the bypass cap being superior to the base cap. It was also the fact that you were adding a small value capacitor to a larger capacitor. Danny felt that the resulting paralleled pair of capacitors offered a better discharge rate than the single larger capacitor. Danny seemed to feel the faster discharge rate was audible, and improved the quality of the sound. He stated that it helped with the perceived 'speed' of the transient response of the circuit.

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  • 8 months later...

End of story:

After experimenting with recapping the crossover of the 10pi, I finished with the following capacitors:

Jantzen Superior Z-CAP for the 10uF

JB capacitors (JFX 220) 2X 20uF (=40uF)

Mundorf MCap MKP Classic for the 100uF

Bennic NPE 2X1000uF + 1x500uF (=2500uF)

I did not use bypass, but because there was no equivalent to the 2,500 uF I ended up cascading them as above.

As you can see, part of these are high-end expensive caps.

After burning inn period, I found the result better than the original speaker. Highs became more present and sweet, but there was also a considerable improvement to mids and bass. I love the result.

Thanks for all those who helped and guided me in this jurney. 

Menachem

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