AR3a Guidance/Advice

[JKent]

On 3/25/2011 at 2:40 PM, ADVENTAGIOUS said:

Kent, do you want to do mine? Nice work!!!!! Did you build the Xover outside the box on a piece of plywood and then secure it inside? Are those the series resistors for the PP caps? Lots of questions eh?

Thanks.

Actually, I have built crossovers for others. Expecting some KLH Fives shortly.

But to answer your questions:

The AR3a xo I'm trying to build from scratch (remember, my speakers were originally AR3s) does have a 0.51 ohm resistor in the circuit. Please see the AR3a restoration manual. There is a xo schematic on page 10 showing a 0.51 ohm 20 watt resistor. This is discussed on page 11. Mike, maybe your speakers had the Nichrome resistor. What I used is two 1-ohm 10 watt resistors in parallel to make a 0.5 ohm 20 watt resistor. Adventagious--go back to post #11, your 4th photo shows the Nichrome resistor hiding behind the #1 inductor, just like the photo in the restoration guide.
Yes, I built the xo on a piece of 1/4" plywood (thinking outside the box ). But the big #9 inductor did not fit along with those big caps, so that's mounted on one of the braces inside the cabinet.
In the photo, the xo is not finished. Still need to install the terminal screws and finish wiring, but wanted to show the size of the Dayton caps: the 100 + 50 and the single 50. The 6uF tweeter cap was left over from the 1st crossover rebuild on these when I was keeping them as AR3s. Those used Clarity Caps PX series: one 25uF and one 6uF.

Regarding the use of resistors to simulate ESR, I didn't bother but that issue is covered on page 16 of the restoration guide (Really. READ the restoration guide! It answers all your questions and guides you along the path to AR3a nirvana!).

Kent

[Pete B]

No worries. Check page 16 of the restoration manual. NPEs are fine--that's what was used originally and they may sound better to some because the ESR is similar to the originals. OTOH if you want them to last forever, use film caps. Problem is, they're big! The Daytons are probably the most compact and lowest price but they are still big and expensive. And you'll have to parallel them. Here is a shot of my newly-constructed 3a xo being test fit in the cabinet. I used 100uF + 50uF Daytons but if you go that route three 50s, stacked in a pyramid may work better.

btw--I took your advice and drilled a 1" hole in the plastic pot enclosure. Hole faces downward and is covered with fiberglass screen.

Kent

That #9 is very close to the #1, I would move it as far to the right as possible.

Even the #1 and #4 are rather close - I usually try to start with inductors as

far into the corners of a new XO board as possible. Then work everything else

in around them.

ESR is really not critical for the mids and tweeters in a system like this

that employs pots where any difference can be made up for with the pot. It

probably does make sense to include a series resistance with the woofer cap

since nearly zero ESR will raise the Q of that LP filter. Try to duplicate the

ESR of whatever cap you replaced.

[Pete B]

I'll jump in here and answer for Kent. They are 1 ohm resistors he put in there to simulate the apparent ESR (equivalent series resistance) of the old caps. I think that might be a bit high. Pete Basel (Advent guru) recommends 0.23 to 0.3 ohm resistors be put in series with film caps replacing vintage caps. The purpose of adding the resistors is to minimize a possible dramatic apparent shift in the high freq. sound that might be objectionable.

I've recently measured an AR-6 10 uF paper/wax cap of the same type used on AR3a (6 uF). The ESR was about 0.33 ohms at 1.1 kHz (typical measurment freq.) and 0.283 ohms at 1460 hz around the crossover point where the cap takes over. The ESR drops from there to 0.143 ohms at 20 kHz.

Thanks for the credit Carl; I just wanted to add that it can be much higher

than .3 ohms. This is a quote from an old post of mine:

"I also see that people are quoting me on stating that a .33 ohm to .47 ohm resistor should be used with films in place of electrolytics. This is correct for what I measure of electrolytic caps that I estimate as having a dissipation factor of about 5% and for the smaller values used on tweeters and mids.

From what I've seen most of the early classic New England speakers, AR(not the early wax caps), Advent, Genesis, have used 5% dissipation factor capacitors. However, The later Jensen Advents used what I estimate are 10 % dissipation factor caps.

Another classic design, the Spica TC-50 also seems to use cheaper 10% DF caps. The TC-50 has several economy non-polar electrolytics with an ESR of over 1 ohm, and the .33 to .47 value would not be correct in that case. One of these caps is used in a tuned notch filter and it's ESR has a strong influence on the Q of that filter."

[JKent]

On 3/25/2011 at 10:50 PM, Pete B said:

That #9 is very close to the #1, I would move it as far to the right as possible.

Even the #1 and #4 are rather close - I usually try to start with inductors as

far into the corners of a new XO board as possible. Then work everything else

in around them.

Thanks for the tip Pete. When I put the #9 in there I thought it was too close to the #1. I'll move it.

I believe the 1 and 4 are OK. Looking at the photos of original AR3a crossovers, the 1 and 4 were only about 1/2" apart. Mine are farther apart than the originals.

But I agree about the #9. The crossover as shown is not complete--just put the parts in there to check the fit. Here's a shot with the #9 relocated (this is the other xo and the 6uF has not yet been installed).

Kent

[dynaco_dan]

Thanks for the tip Pete. When I put the #9 in there I thought it was too close to the #1. I'll move it.

I believe the 1 and 4 are OK. Looking at the photos of original AR3a crossovers, the 1 and 4 were only about 1/2" apart. Mine are farther apart than the originals.

But I agree about the #9. The crossover as shown is not complete--just put the parts in there to check the fit. Here's a shot with the #9 relocated (this is the other xo and the 6uF has not yet been installed).

Kent

Hi Kent and Pete

I just read both of your write-ups and I was trying to remember where I had read something recently regarding speaker coil placement.

AVA Audio by Van Alstyne (spel) I believe, wrote about a, KEF or B&O ? speaker, I believe.

He found and investigated an objectional sound issue, I believe.

The 70+/- back issues of his former newsletter, at AVA.COM, can be downloaded in their entirety, and at no charge.

Sorry if I am wrong but my getting to the point is, he found two coils should be an appropriate distance away from each other and

I believe he re-installed one perpendicular to the other as well.

The speaker factory apparently followed his advice later and changed the coil instalation locations in later production units.

He found by moving one coil away from the other and I believe re-installed it at right angles to the mounting board, the audible problem

either lessened or completely disappeared, there was an improvement at least.

I already downloaded all of the 70+ past newsletter issues but I don't remember which one I read this topic in.

Maybe I should do another interest and issues index, only this time, from the AVA Newsletter.

He published it from 1983 until around Y2K.

Some are monthly, some are every two months and there is a few months without an issue due to work load, etc.

This advice is not exclusively for use with AR speakers but any speaker system, with two or more speaker driver coils.

Just a thought for tonight.

[Carlspeak]

Here's a nice visual describing recommended ways to space inductor coils. I found it on the WWW and cannot vouch for it absolute accuracy or correctness.

[deek]

Some of the orientations on that illustration look like instructions on how to make a transformer!

-Deek

[ADVENTAGIOUS]

Thanks for that info on the coils. Does the magnet on the driver mess with the work that the coils do? I guess if I place the coils as close to original as possible it should be ok.

[Pete B]

That looks much better Kent, and I agree the 1 to 4 distance is good enough.

Re: Dynaco Dan it was the legendary B&W801 that AVA worked on and found

coupling. I think he drove the woofer section, probably for testing,

and heard output from the midrange section due to mutual coupling of

the inductors. You'd have to short the midrange input terminals or

hook up to an amp with no signal so that the mid section as a complete

circuit for current to flow in order to do a similar test.

[Pete B]

So Mexicomike, you think those little Bennics will do the job. Compared to the originals they look wimpy. Specwise, they should I guess. I did read something on another thread somewhere here that said not to worry too much about the woofer cap but definitley replace the mid and tweet.

That cap is a 5% DF cap as can be seen in the B05 code which

is good - the lower the better. AR used the very old wax caps,

and very low ESR computer grade style caps, and 3 - 50uF NPEs

in the AR-3a Limited or European don't remember exactly.

Three caps in parallel share the total current and heating due

to ESR losses and should therefore last longer.

The NPEs actually make sense for this cap, since you want some

resistive loss in this branch. You get the resistor and a cap

for a very low price. Film caps there have the advantage of

longer life but I would want to see an ESR resistor used with

them.

[ADVENTAGIOUS]

Kent, I'm going to solder all my connections. I notice that you've used a couple of crimps but I would recommend removing the insulation and soldering those joints. They've been the source of many electrical problems in cars and appliances. When we used to make/test harnesses for computers the crimps were the biggest source of problems at inspection even when they were machine/hand crimped with calibrated tools.

[Pete B]

Kent, I'm going to solder all my connections. I notice that you've used a couple of crimps but I would recommend removing the insulation and soldering those joints. They've been the source of many electrical problems in cars and appliances. When we used to make/test harnesses for computers the crimps were the biggest source of problems at inspection even when they were machine/hand crimped with calibrated tools.

Yes, it is well known in reliability analysis that non-gas

tight connections can be the dominant source of reliability

issues.

[Pete B]

Here are the Audio Basics Newsletter issues that cover the 801

crossover mod:

Available in .pdf online: http://www.avahifi.com/index.php?option=com_content&view=article&id=85&Itemid=181

1989/12 B&W 801 Crossover Design Goof four pages

We write to Stereophile documenting a design blunder in the B&W 801 Matrix crossover board layout. Two large inductors are positioned so that they interact magnetically and thus bass is dumped into the midrange speaker and midrange into the bass speaker. A minor do-it-yourself change to the crossover board greatly improves the sound quality of the speaker.

1990/01 B&W 801 Matrix Crossover modifications. 2 pages

We go into more engineering detail on the 801 crossover design and suggested upgrades, including graphs of the frequency response before and after the changes.

[ADVENTAGIOUS]

Has anyone tried to buy solder lug terminal strips lately??? Just like hens teeth. I needed some adhesive tie wrap holders too. I'm going to try this capstrap made out of plumbers strapping. I'll install some foam or soft velcro between the cap and the strap. The strapping is galvanized steel. Yay's or Nay's?

[dynaco_dan]

Has anyone tried to buy solder lug terminal strips lately??? Just like hens teeth. I needed some adhesive tie wrap holders too. I'm going to try this capstrap made out of plumbers strapping. I'll install some foam or soft velcro between the cap and the strap. The strapping is galvanized steel. Yay's or Nay's?

Hi there

Rather a creative idea, the use of All-Round steel gas pipe hanging iron.

This is also available in solid copper, nylon insulated and galvanized steel.

The steel or galvanized hanging iron is used for steel or equivalent gas piping support, etc..

It may also work, but, not necessarily approved though, for use with copper pipe, if an isolation insulating material is between

it and the pipe wall.

The solid copper strapping is used for copper pipe supports, lessen's the possiblity of corrosion from electrolysis, interaction of disimilar material.

If I might make a suggestion here.

If you make a loop from the strapping iron that is the same as the outside diameter of the item being clamped, plus add enough length

to add padding and also fold a flange outward about 1 or 2 holes larger that the item being clamped.

Then screw it against the cabinet wall with wood or sheet metal screws.

Place a padding between the cap and the strapping, so that the cap can breath or slip.

Using a 1/8" machine screw, nut and lock washer, or Nyloc nut and washer, through two of the flange holes, this will draw

the strapping tight against the padding and the item being clamped.

Capacitor maufacturers, such as Mallory, used to sell vertical and horizontal capacitor mounting clamps

for use with their round electrolytic caps.

At one time electrical wholesalers sold nylon straps molded with a screw hole flange.

Check at Home Depot, etc, for retail quantity, as I saw some recently here.

Businesses are always dropping poor selling items though.

Old solder and crimp connectors were usually tinned brass and are now mostly plated steel.

There were a few excellent brands such as Amp, more expensive, and Walden (spel) less expensive.

Radio Shack's solder terminals were found by a student of, W. Marshall Leach Jr, to be made of plated steel,

which were found to be un-solderable.

Same as the leads of some resistors and other parts today.

Perhaps we should carry a small magnet with us when shopping for these type items.

Just a thought for tonight.

[JKent]

On 3/28/2011 at 5:49 PM, ADVENTAGIOUS said:

Has anyone tried to buy solder lug terminal strips lately??? Just like hens teeth. I needed some adhesive tie wrap holders too. I'm going to try this capstrap made out of plumbers strapping. I'll install some foam or soft velcro between the cap and the strap. The strapping is galvanized steel. Yay's or Nay's?

Your cable tie tie-downs are clever and cheap. Don't see why they wouldn't work. I use the mounting blocks shown in the AR3a restoration manual (p 16). They have adhesive and screw holes. I usually use both. Also shown in Post #29 of this ever-lengthening thread. 

Terminal strips are tough. A lot of sellers have the "European style." Haven't used them but they look OK. I salvage strips from used equipment when I can, or check surplus parts suppliers like Nebraska Surplus Sales

http://www.surplussa...ermStrip-6.html

Ebay is another source. Try searching for bakelite, phenolic or vintage terminal strips.

Kent

[genek]

Has anyone tried to buy solder lug terminal strips lately??? Just like hens teeth. I needed some adhesive tie wrap holders too. I'm going to try this capstrap made out of plumbers strapping. I'll install some foam or soft velcro between the cap and the strap. The strapping is galvanized steel. Yay's or Nay's?

Today's electronics manufacturing is all SMT and plug-in cards. Hand-solder supplies are hard to find except online.

Last time I strapped caps down I just fired a couple of big staple gun staples into the wood and threaded my wire ties through them. Strips cut from old turntable mats make good cushioning.

[dynaco_dan]

Your cable tie tie-downs are clever and cheap. Don't see why they wouldn't work. I use the mounting blocks shown in the AR3a restoration manual (p 16). They have adhesive and screw holes. I usually use both.

Terminal strips are tough. A lot of sellers have the "European style." Haven't used them but they look OK. I salvage strips from used equipment when I can, or check surplus parts suppliers like Nebraska Surplus Sales

http://www.surplussa...ermStrip-6.html

Ebay is another source. Try searching for bakelite, phenolic or vintage terminal strips.

Kent

Hi Kent

Recently I see only steel connectors as shown at that site, plated for solderability.

At one time they were tinned brass or copper, now sellers rarely mention material type.

[ADVENTAGIOUS]

Thanks everyone for all your recomendations and suggestions.......a great source. My project is moving forward. Yesterday I drilled 3 x 7/8' holes in the pot cover boxes and installed the stainless mesh using a high temp gasket sealant. The mesh was used from from a new stainless steel coffee filter $10. I did a flame test on the one I found in the cupboard and even though it looked like metal it wasn't............poof! I plan to make a new cover plate for the pot box using aluminum flat stock with a couple of extensions on it to help dissipate the heat.......this might be overkill though. I am concerned about leaving the old 150/50uf cap in the cabinet and by adding new caps and the pot boxes will reduce the cabinet volume. I did a quick calculation on the new caps and the pot box and figured that they will diminish the cabinet volume by about 30 cubic inches. Now the pot boxes will be open as a result of the drilled holes so they don't completely dimiinish the volume by their size, only by the volume of the actual material that the box is made from. Would it be wise to remove the old 150/50uf cap to compensate for the reduced volume and make up the difference with more stuffing or something solid (piece of 2x4 glued to inside back of cabinet) or just leave the old cap in there, add the new ones and not worry about it. Thanks for your inputs.

[ADVENTAGIOUS]

Well I trashed the plastic box because I was nervous about the amount of heat and the possibility of fire. I DIY'd an aluminum one shown in the thumbnail and have moved forward with some wiring. Only 2 caps left to install and then the Pot box wiring and installation. I'm not going to close it up but rather leave it open for reference on the second one. I'll do both woofers together. There were no comments about my question concerning the loss of inside volume of the box (adding components and Pot box) so maybe it isn't a concern. I've attached a couple of thumbails for viewing. Comments are welcome.

[ADVENTAGIOUS]

Today I added the Solen 6uf (3uf +3uf) and 150uf. The Potbox has been fitted and will be installed/wired (harness on the left above the 150uf cap.) tonight.

[ADVENTAGIOUS]

First speaker wired!!!!! Moving on to second speaker now.

[JKent]

looks great! Very professional

Kent