Refreshing AAs

[PrestonTom]

I wanted to share my thoughts & experiences on refreshing the AA crossovers on my Klipschorns. These are my experiences and some of my observations will certainly be a function of the idiosyncracies of my my setup, listening habits and priorities. As such, none of my comments should be interpretted as criticisms or attacks toward anyone else.

There is a cottage industry out there that makes some fine & innovative products. However, there has been some confusion about the impact resulting from the various modifications available. My intent was to bring the crossovers up to spec. The assumption being that old caps may provide a series resistance with the driver and decrease its sensitivity. Since I use solid state, I am not terribly concerned about the possible advantage of a redesign that presents a more uniform impedance (tube users may want to be concerned about this however). I am intrigued about a steep crossover design. However, without the further step of time re-alignment between the drivers, I am unwilling to spend the money (in the future I will attempt both via DSP prior to amplification ... but that is in the future).

Of course there are a number of steps in between simply refreshing the caps vs a full blown re-design. If you follow the various threads, there is something that has confused me and it probably a result how we use words to describe our percepts and how our expectations influence what we perceive & report. This is nothing new, and it has plagued the pursuit ..... but such is life. For instance, many folks note an improvement in the bass response. This is confusing since the bass is controlled by a single pole filter (which is typically not altered). In truth, much of the roll off of the woofer is dictated by the driver. PWK is said to have used his cabinets with out the inductor. The confusion is heightened since many of the re-designs mostly involve filtering up at the mid to high crossover regions. So some healthy skepticism is called for. Again this the nature of things

This is another reason to go a bit slow on some of these mods, but I did want to share my experience since there are probably a number of others who are on the fence about what to do with our older Heritage equipment.

What I did was to buy some Solen caps from Parts Express (nice folks to work with). Each cabinet will require a pair of 2 uF caps (high pass on the tweeter) and a 13 uF for a high pass on the midrange. Parts Express does not carry the the 13uF (they are available in Canada but there may be some extra charges). So I substituted a 6.2 + 6.8 for the 13 uF. There may actually be some benefit with the 2 caps in parallel, but I suspect with a single pole design, the possible difference is probably inconsequential.

All totalled, the parts cost less than $20 plus shipping. These are Solens: metal poly propylene caps. The ESR is decent as is the tolerance. You can spend much more on caps with comparable specs and design. Or you can spend an even greater amount of money and go to a film & foil design. If you have not then spent enough money, go ahead and supplement this with bypass caps. My perspective is that if you remain with the same crossover topology, the biggest improvement occurs from refreshing the the caps (assuming there was deterioration resulting from age). In my case the caps were from 1982, but I did not have the equipment to measure the resistance. So there is an assumption about any deterioration, however others have been able to measure this and have reported that it is not uncommon.The other part of my perspective is that aside from the deficits produced by added resistance in the old caps, any difference between caps (poly vs film/foil) are probably very small if the same crossover topology is maintained. Seriously the difference in price can be easily 10 fold or more. With that kind of extreme expense, the improvements would need to be comparable. So I remain skeptical, but this is something the user needs to decide.

The point of my post is that you should not remain frozen and not do any sort of upgrade because of the possible expense, I am suggesting that you spend $20 & test the waters.

In the first version, I added a wire and a pair of connectors. This was to allow a simple way to bypass the diode circuit. The diodes are probably fairly linear prior to their shunting, but I was more concerned about distortion and less concerned about tweeter protection (I do have a fuse on the speaker line, although that is probably a false sense of security for a tweeter). This is also a good time to clean all the contacts of any corrosion. This in fact could account for some of the improvement

In the second version, I eliminated the diodes entireley. After I had re-installed the cross over I noticed some faint, high fequency buzzing in the tweeter. I elimated some possible culprits, and inadvertantly found that the "dangling leads" (with the diodes unattached via the wire/conectors) was functioning as an antenna. With careful jiggling I was able to modulated the amplitude of the buzz and actually get radio reception. This only occurred in one speaker. I am still confused why this happened since that usually occurs with high impedance signals and not 8 ohm line level. Who knows... The fix was simple. I snipped the leads & removed the diodes. That is what you will see in version 2.

What does it sound like. Initially, I auditioned these with symphonic music. This was my first mistake. There is not much energy at the very high frequencies with this sort of music& recording. So I then went to things like Tracy Chapman & Paul Simon. These are very much studio recordings with close-mic'ing, compression, exaggerated highs etc. It was more revaling but I used a span of music. The cabinets are now much brighter. In my opinion, it is a more faithful to the recording. I can see why folks use wordds like "crisp" & "sparkle" (percussives, cymbals, lip smacking & vocal mechanics, attack on the strings). The upper mids seemed more pronouced. Some of the reverberation from the recording hall was more easily discerned an the vocal & brass were more pronounced. These are not "laid back". Although they were not very laid before either.

However these are comments about the qualtities that were changed. So let me describe the degree of change. Yes, it is an improvement. Is it dramatic? At best it is mildly dramatic. Things are improved, but I did not fall out of my chair. There is a caveat, recordings that are compressed (most pop , IMO) or have tape hiss now sound worse. The K-Horns have now become even more ruthless, BTW, I never got a chance to A/B with & without the diodes.

It was $20 and 2 hours that were well-spent. Those who have been on the fence about updates & mods, by all means go ahead and do it. It is easy to order the parts and remove the diodes. The soldering is trivial since there is plenty of room.

How to apply this perceived change on a relative scale? Well ....

Compared to placing the cabinets along the long wall: This upgrade was comparable (although a different consequence)

Compared to putting the cabinets snug into the corners with pipe foam & building a half-false corner: This was not comparable (less impact with the new caps)

Compared to locating the listening chair on-axis with the cabinets: This upgrade was not comparable (less impact with the new caps).

Good Luck,

-Tom

[Guest " "]

20 bucks total is pretty good.

Are you still evaluating or have you noticed specific changes to the sound of your speakers?

[PrestonTom]

Here is the original crossover (circa 1982)

[PrestonTom]

This is the first version. I attached a second lead & some connectors so I could plug & unplug the diode protection. For some reason (even though this not high impedance) the dangling leads acted like an antenna. Simple fix: These leads got snipped & the diodes removed.

[Guest " "]

I think you have the makings here for an intresting DIY offering to sell via e-bay.

A kit to modernize your AA's.

20 bucks, well done.

[PrestonTom]

This is the second version. The diodes are now gone.

For the DIY crowd, notice there is plenty of room to work in. Some solder lugs are helpful. Now is good time to clean any oxidation & make sure the contacts are clean & snug

[PrestonTom]

Here is the beast installed.

Notice a couple of things.

First, for those who are unaware of this tidbit, adding pipe foam along the horizontals (and on the tail piece) will ensure a snug fit. There is an audible improvement (it is simple, quick & cheap).

Second, adding a fuse on the speaker wire is a good idea. It is not fool proof protection, so use some common sense also. It does not degrade the sound.

[soundbound]

A great job, pictures, and write up! Thank you.

[Daddy Dee]

Thanks for walking through that process with the post and pics.

Looks very good.

I think you have got a good point that more ambitious crossover upgrades are meaningful only after one knows the base line sound of factory spec.

With vintage Heritage speakers, one will not know this sound without restoring crossovers to factory spec first.

[Al Klappenberger]

Guys,

There is one problem with all this. No matter how good the parts are in an AA network, it's still and AA. It is a poor design and will always present a bad load to your amp, waste half the power that your tweeter should get and give you a rough high frequency response! Now that you know the best the AA can be, build my original "ALK" universal network from the plans on my web site and compare! You will be glad you did. Of course, report those experineces here too!

AL K.

[Erik Mandaville]

Tom:

Excellent job with this! My findings are very similar to your own, and I have appreciated both the cost and performance of the less expensive Solens for some time. Their high frequency performance is outstanding, IMO, and I have done the same as you in terms of paralleled values for desired capacitance.

I have also used Hovlands, Kimbercaps, Jensens, and some others, and for crossover networks have been very satisfied with the HF performance of even less expensive mylar types from a nearby electronics stores.

I couldn't agree more that it's possible to bring an old network back to very good level of performance and service for a reasonable cost.

Same goes, I think, concerning the deep dark mystery and secrets of soldering. If someone can tie his or her shoe, which actually requires a greater amount of fine motor control, the same person can easily learn to solder. It's very often made out to be a complex and very involved pursuit (hmmm, I wonder why?) and that is just not the case.

Thanks for taking the time to post the pictures, as well.

Erik

[colterphoto1]

Thank you Tom,

As I get closer and closer to buying the stock of parts needed to bring my many heritage cabinets up to 'par' (whatever that is), your post is one of the few I have read here that gives a simple, well thought out, economical solution to those of us with aging crossovers.

Your post was well worded and gives good explanation for the cost/benefits of refurbishment versus redesign or replacement. Now I wonder about the simple question of purchasing stock motor start caps versus the Solen types. How did you resolve this quandry?

I also appreciate Dee's comment about having a listening baseline of the original cabinet and network and would follow up with a caveat that each of us can perform our own before/after listening test if we but pause at the 50% mark of changing our networks and listen directly to the old next to the new. No guesswork, no time lag, just A/B the updated speaker with the stock in your own listening environment.

This gives me hope.

And I do know which end of the soldering iron to hold.

Michael

[Guest " "]

Guys,

There is one problem with all this. No matter how good the parts are in an AA network, it's still and AA. It is a poor design and will always present a bad load to your amp, waste half the power that your tweeter should get and give you a rough high frequency response! Now that you know the best the AA can be, build my original "ALK" universal network from the plans on my web site and compare! You will be glad you did. Of course, report those experineces here too!

AL K.

 

AL

I'm getting that your universal AA upgrade provides a constent load to the amp using stock drivers, what load does the amp see? I am guessing it would have to be the lower k-33 load.

I have been looking into amp loads, and came across the below product concept. Its an autoformer that claims frequency response of 2hz - 2 mhz. It's a multi tapped autofomer that allows you to select the load you want your amp to see.

http://www.enjoythemusic.com/magazine/equipment/0603/midmonth/zeroautoformer.htm

[Erik Mandaville]

I've used both the AA and A with new capacitors, and there is not an enormous difference between the two. I heard slightly higher HF output from the tweeter, and that's about all, really.

What I don't care for (sorry, but it's the truth), is the swamping resistor on the autoformer. I've rebuilt these networks with and without it several times, and always end up removing it -- despite what I know about its function. I even included it in this last network I made where I used the lacing technique on the leads. That resistor is now gone. Again, I understand the reason for it, which makes perfect sense.

It's just my personal preference to leave it out. Some also proclaim to hear a difference between the autoformer and more common variable L-pad. The only difference I hear in terms of sound between the two has to do with the finer control afforded by the variable pad.

Erik

[Guest " "]

I've used both the AA and A with new capacitors, and there is not an enormous difference between the two.  I heard slightly higher HF output from the tweeter, and that's about all, really.

What I don't care for (sorry, but it's the truth), is the swamping resistor on the autoformer. I've rebuilt these networks with and without it several times, and always end up removing it -- despite what I know about its function.  I even included it in this last network I made where I used the lacing technique on the leads.  That resistor is now gone.  Again, I understand the reason for it, which makes perfect sense. 

It's just my personal preference to leave it out.  Some also proclaim to hear a difference between the autoformer and more common variable L-pad.  The only difference I hear in terms of sound between the two has to do with the finer control afforded by the variable pad.

Erik

Have you ever used the selectable autoformer that used a rotary dial tied to multiple tap configurations? It's kinda click stop with 10 or 12 settings.

There is also resistor loaded versions of the multiple selectable rotary dial.

[Deang]

What I don't care for...is the swamping resistor...I've rebuilt these networks with and without it several times, and always end up removing it -- despite what I know about its function...Again, I understand the reason for it...

What cap value are using at the primary position when you have the resistor in place?

[PrestonTom]

Guys,

There is one problem with all this. No matter how good the parts are in an AA network, it's still and AA. It is a poor design and will always present a bad load to your amp, waste half the power that your tweeter should get and give you a rough high frequency response! Now that you know the best the AA can be, build my original "ALK" universal network from the plans on my web site and compare! You will be glad you did. Of course, report those experineces here too!

AL K.

Al,

I appreciate that you have spent a great deal of time designing & refining your product. I am very appreciative of the fact that you are willing to share the schematics with the rest of us. You are to be commended.

But let's take a different perspective for a moment. A casual reader of the forum, or one who is not very experienced with electronics etc, will be confused by the various threads and discussions. The solutions being proposed by you and others can be costly. Trying to figure out ahead of time what the benefits might be is quite complicated.

I am simply tyring to say that for a small amount of money ($21.12) and some rudimentary soldering, one can get a benefit. This is a no brainer, and everyone should at least do this (or have some else do it). However, if what you are saying is that a $500 redesign ($300 if it you DIY) is better than the $21 refurbishing. Yes, I agree. You have probably achieved a better design than the original. And yes, spending over a $1000 on the steep slope design will be even better.

But let's be fair in our comparison. Many consumers out there will be confused by what is the actual degree of improvement. This is a tough one since, the proof is in the pudding and you really need to listen for yourself and judge whether the the extra money is worth it. It is difficult to read about (rather than experience) the effects. First, I was very careful to mention that the original AA is not providing a constant impedance. But in my case, with SS equipment, this is not an issue (I did give your design credit for those who might use tubes). Second, I did acknowledge that your premium design with the steep slopes has some very good features (although I have not yet had the pleasure of hearing them, I agree with your logic and will accept it on faith). However it is impossible to say ahead of time how much improvment will actually be perceived the the user.

My perspective is that much of the design work by you and others has concentrated on improvements at the very high frequencies. The truth is that there is not always much energy up in these regions (this is a relative statement & I am not going to debate it, the user must decide). Additionally, many of the comments that have been made in the past suggest huge gains in performance (for all types of re-designed or re-furbished crossovers). I was simply trying to temper the expectations, when one performs a simple refurbishment. Again, evaluating a subjective effect is tricky at best. So what does a listener do. In my case I was confused by how much of an improvement might be actualized with the different levels of design, re-design, or messing around with "botique" parts. As such, I (and I assume others) simply froze and did nothing. In retrospect this was a mistake.

However for $21 and a couple of hours, you can acheive an improvement. I tried to quantify the degree of improvement in the most realistic & communicative way that I could. We are always plaugued by the law of diminshing returns. More money will mean more improvement. Will a great deal more money mean a great deal more improvement? I will let others decide for themselves.

My simple advice is to spend the $21 today. If you want something even better the next day, then by all means go ahead.

Good Luck,

-Tom

[PrestonTom]

I think you have the makings here for an intresting DIY offering to sell via e-bay. A kit to modernize your AA's. 20 bucks, well done.

Thank you for your encouragement and comments.

My intention was simply encourage folks to do something about their old crossovers, rather than getting caught up in "thinking" about the various options (and doing nothing).

No kit needed. Simply go to PartsExpress.com

You will need the following Solen capacitors

4 @ 2.0 uF caps (027-534)

2 @ 6.2 uF caps (027-558)

2 @ 6.8 uFcaps (027-560)

this totals $ 21.12 in parts

Some cable ties, silicone adhesive or caulking, and solder lugs are helpful. The 6.2 & 6.8 caps are paralleled to replace the original 13 uF cap. It is also a good time to clean up any oxidized contacts and attach some pipe foam for a snug fit into the corners.

The investment is small. There will be some improvement and you can always do something more ambitious in the future. But at least do this.

Good Luck,

-Tom

[BEC]

Tom,

The improvement going to new caps you saw when you rebuilt your late model type AA crossovers is probably less than most see when when rebuilding older crossovers. The little black caps you replaced usually read around 0.25 ohms each for ESR. There are exceptions to that with some of them reading close to an ohm ESR. Most of the older metal can caps in the AAs test at around 1 ohm ESR. With that reading, the difference is much greater after replacing the caps.

New good caps will have an ESR of around 0.02 ohms.

One more point on the Type AA rebuild is to make sure that Klipsch used the right type screw in the 245 uH inductor. Lots of times you will find a steel screw in it and it should be brass. If it has a steel screw, the value of that inductor will be increased a lot. I have not been able to find the correct brass screws, but they are readily available in stainless and that is what I use. You can just check the screw with a magnet. If it is attracted by the magnet, you should replace it.

Bob Crites

[PrestonTom]

Thank you Tom,

As I get closer and closer to buying the stock of parts needed to bring my many heritage cabinets up to 'par' (whatever that is), your post is one of the few I have read here that gives a simple, well thought out, economical solution to those of us with aging crossovers.

Your post was well worded and gives good explanation for the cost/benefits of refurbishment versus redesign or replacement. Now I wonder about the simple question of purchasing stock motor start caps versus the Solen types. How did you resolve this quandry?

I also appreciate Dee's comment about having a listening baseline of the original cabinet and network and would follow up with a caveat that each of us can perform our own before/after listening test if we but pause at the 50% mark of changing our networks and listen directly to the old next to the new. No guesswork, no time lag, just A/B the updated speaker with the stock in your own listening environment.

This gives me hope.

And I do know which end of the soldering iron to hold.

Michael

Michael,

I am not to be held liable if you grab the wrong end of the soldering iron.

The Solens were an easy choice. The ESR and tolerances were respectable. The price was reasonable and engineers that I know recommend them for audio.

Actually, I was thinking of you and others when I wrote up my "guide". With all those cabinets you have, updating/re-furbishing them would cost you a small fortune. I hope this provides some perspective.

Good Luck,

-Tom