Large Advent crossover replacement.

[Guest westend]

I started posting in a different thread about production years and construction differences and later found that one of my crossovers was not functioning. What I'm concerned about is the best manner of duplicating the original crossover network and if there are any tweaks to enhance the sound of my Large Advents. It seems as I have both the older style Large Advent with an inductor on the speaker back and a newer Advent with all components on the switch board. Both speakers have the masonite ringed woofers and the orange "fried egg" tweeters. I would suppose I will have to build two crossovers to achieve a perfect balance or should I try to duplicate the older, working crossover. As some have posted, keeping to the original component values would be the best way to go. Does anyone have some input on crossover construction, parts availability, sources, etc.? Thanks for all and any advice. Doug, thanks for your input on the other thread. BTW, the tweeter connected to the bad crossover checks out OK.

[Guest One-Shot Scot]

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It sounds like you have two variations of The Advent Loudspeaker, which preceded The New Advent Loudspeaker. The original Advent crossover network was much more complicated than the one used in the New Advent system.

In order to adequately identify and test the various crossover components, you will need a good multi-meter. Most inexpensive meters have the ability to measure resistance and capacitance, however, while the less expensive meters may adequately measure resistance, they can fall short of delivering accurate capacitance readings. Unfortunately, only more-expensive meters are able to measure the value of the crossover inductors.

Parts Express has two meters which measure inductance:

http://www.partsexpress.com/pe/pshowdetl.c...FTOKEN=86467477

http://www.partsexpress.com/pe/pshowdetl.c...FTOKEN=86467477

I chose the $94.65 (390-513), because the $54.11 (390-570) does not have the ability to measure resistance. The meter arrived last Thursday and I was finally able to obtain the inductance value as well as the DC winding resistance of my New Advent crossover inductors. The values of the resistors and capacitors are printed on the parts, but the values of the inductors are not.

Parts Express is an excellent source for all crossover components, except for the crossover board. I want to build a New Advent crossover network from scratch (without the 3-position switch) and I am still debating what material to use for the board. It seems that one good choice would be to use the same 1/8" thick Masonite as was used in the original. Another good choice might be plastic sheeting. I am going to try the plastic sheeting, because removing a Masonite board from the cabinet for replacement or repairs would damage the board, whereas, the plastic board would probably remain intact.

The biggest challenge presented by either board material will be dealing with the binding posts, which seem to be made for installation in much thicker material. One of the Parts Express technicians measured a Dayton Heavy Duty Binding Post and found that the minimum thickness of the material in which the posts can be mounted is 3/8". (For some reason, the maximum thickness is stated at 1", but the minimum thickness is not stated.)

http://www.partsexpress.com/pe/pshowdetl.c...FTOKEN=86467477

On the other hand, I'm thinking that maybe the plastic crossover board should be thin enough to flex slightly (say 1/8" or 3/16" thick) when using a spatula to pry it out of the cabinet for replacement or repairs. With this flex-factor in mind, I am thinking that I could glue a 3" x 3/4" x 1/4"-thick plastic strip on the back of the crossover board to accommodate the binding posts. Or maybe some spacers on the binding posts would do the job.

Anyway, I'm going to order the crossover parts on Monday and decide on the crossover board during the next few days.

[Guest westend]

Thanks for the reply. I have a Fluke true RMS meter so no problem with reading the values. As to the mounting board; I see them on Ebay with the sealant still attached and the components glued onto the board. If you use a heat gun judiciously that shouldn't be a problem. Regarding the posts; the original binding posts were lacking and a replacement wouldn't be out of order. You could use a washer or two to achieve the needed dimension.

What I'm wondering about are the capacitor values and if I should build two networks to the 16/16 configuration or 16/8 as some have used. Also, are there any suppliers who sell a kit for this crossover or do I shop the distributors for parts? I see there are some posts here about removing the switch and it's circuitry and I would be all over that as I see no need for it. What I would like to avoid is any "harshness" increase due to the wrong parts. These tweeters are plenty strong on the high end and don't need any boost, IMO. Some have said that use of Solen caps produce just such an ill effect. Good luck with your crossover build and post back with your impressions.

[Guest One-Shot Scot]

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You are not alone in your observation that Advent tweeters have a strong high end. Presently, I am doing listening observations involving the use of my 4 rebuilt New Advent crossovers, which contain Solen capacitors. My benchmark recordings are the two CDs of the incomparable Lavay Smith & Her Red Hot Skillet Lickers. The Extended tweeter position (total bypass) is especially shrill. The Normal position (with a 1 ohm resistor) seems a bit harsh and brassy. However, the Decrease position (with a total of 2.5 ohms of resistance) seems to provide the most pleasant listening position of the three. As a result of these listening tests, I realize that it is unrealistic to expect that making an extreme modification to the stock Advent capacitors will not require making an additional modification to the original resistance values.

In my first two crossover rebuilding project, I replaced Advent's stock electrolytic capacitors with polypropylene capacitors of the same value. I also replaced the original resistors with nearly-identical sand-cast models of the same values and then replaced all of the original speaker connectors with 18 gauge copper wire. Next, I put the stereo pair of speakers with the rebuilt crossovers on the A speaker output opposite the pair of speakers with the original crossovers on the B speaker output. Then, I sat between the two sets of speakers and switched between them while playing familiar music. The speakers with the rebuilt crossovers sounded dramatically smoother and more plush than the speakers with the original crossovers. After this, I rebuilt the crossovers in the other two speakers, once again using the original capacitor and resistor values.

What I didn't appreciate before making the comparison, was that the tweeters in the speakers with the original crossovers always had a somewhat-harsh and indistinct sound in the midrange. The reason that I now know this is because the speaker pair with the rebuilt crossovers greatly minimized this harshness, while at the same time adding clarity and an increased brightness in the high end. Now, I am thinking that a slight increase in resistance between the capacitor and tweeter might be in order when I build my new crossovers. Choosing a Mills capacitor with a value of 1.5, or maybe even 2 ohms might give better results than using the original "Normal" value of 1 ohm.

I think that you are going to need to shop a supplier for parts, because I have never seen an Advent crossover refurbishing kit. I have had excellent experiences with Parts Express.

It appears that you are attempting to rebuild a 1st, 2nd or even 3rd generation original Advent crossover. I looked at some recent crossover posts, including one entitled:

Large Advent - Original Capacitors Compared to Axon Poly

"Response #8 from Jerry says, "So far, I have found three different crossovers for the original Advents, not two as usually reported. The first was 16/16 uF with a 4 ohm series R for the tweeter used on very early models before 1971; second was 16/16 uF with a 3 ohm used until mid 1975; and the third was 16/8 with 3 ohms used from mid 1975 to the end of production in 1977. The resistance of the parallel inductor on the tweeter also changed between version 2 and 3, dropping from around 2.2 ohms to around 0.5. The higher resistance is not needed for damping on the third version with 8 uF and the corner on the tweeter at rolloff is sharper with the lower DCR value."

Not being an electrical engineer, I find that I am far more comfortable dealing with the simplicity of the New Advent crossover, whose component specifications apparently never changed. Right now, my main dilemma is whether to go with a copper foil inductor or an air core inductor.

[dynaco_dan]

Hi there;

Interesting reading, thank you.

[Carlspeak]

>I started posting in a different thread about production

>years and construction differences and later found that one of

>my crossovers was not functioning. What I'm concerned about is

>the best manner of duplicating the original crossover network

>and if there are any tweaks to enhance the sound of my Large

>Advents. It seems as I have both the older style Large Advent

>with an inductor on the speaker back

This is not normal. Someone may have added it. Is that the speaker with the non-functioning xover?

After your rebuild, both speakers should have an internally mounted inductor. It's there to roll off the woofer so interference between the woofer and tweeter outputs doesn't get excessive. Visit my website and you'll see some examples of large advent xover upgrades.

http://www.classicloudspeakerservices.com

Contact me privately if you want and I'll send you a schematic I drew following the rebuild shown in the photos. Keep in mind there are 3 different xover versions of this speaker. My experience was with a 3 ohm resistor. The differences appear to be in the capacitor values however, not the resistors.

and a newer Advent with

>all components on the switch board. Both speakers have the

>masonite ringed woofers and the orange "fried egg"

>tweeters. I would suppose I will have to build two crossovers

>to achieve a perfect balance or should I try to duplicate the

>older, working crossover. As some have posted, keeping to the

>original component values would be the best way to go. Does

>anyone have some input on crossover construction, parts

>availability, sources, etc.? Thanks for all and any advice.

>Doug, thanks for your input on the other thread. BTW, the

>tweeter connected to the bad crossover checks out OK.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[Doug G.]

Didn't Advent build some of the early ones with the large woofer inductor mounted on the back board instead of on the crossover board? I thought I had seen or heard of this before.

If I were to rebuild the crossover, I would use modern equivalent components. Namely, non-polorized caps, iron core inductors, and wirewound resistors. This would assure you of having them sound like Advent would have originally voiced them.

Not that I'm a real big believer in significant sound differences with different types though. I am aware that others claim to hear these differences, however.

Doug

[Guest westend]

Thanks, Doug and Carl for your extensive replies to my post. That was just the kind of information I'm after. Since I will be using fairly inexpensive components it will leave me some leeway to experiment, I realized. For an additional $ or two I can change out a resistor or capacitor and not feel any twinges, lol. I won't be buying any Mundorf high $ caps for these as I would think it adds little, sonically. Carl, I will take you up on your kind offer of a schematic and will contact you through your website. Again, guys, thanks to all that posted.

[Guest westend]

I feel like I entered the "Stephen King" repair school. I acquired a Sansui reciever which had the left channel playing intermttently. I have had my Large Advent with the burnt resistor on that channel. I was able to restore the receiver to a good operating condition. At the same time the tweeter in the speaker with the bad resistor began playing. Perhaps I misdiagnosed my crossover problem but the resistor is black and the foam around it in the enclosure is melted and black from the heat. At the time these electronics were healing themselves I was ordering the crossover parts from PE. I will plan on replacing the crossovers but does anyone know what the heck could have happened to restore the crossover? Can a resistor melt to the point that it is a direct connection?

[Doug G.]

Actually, instead of melting to the point of a direct connection, any intermitant component has two surfaces which are making contact at some times and not others. This can be affected by temperature and physical movement.

In the case of your resistor, it is probably a wirewound and there is a broken connection in there and it has decided to make contact between the two ends of the break again. It will undoubtedly fail again, however - sometime.

Replacement is a good idea.

Doug

[Guest westend]

Doug, that was my take on the part, also. I have the crossover parts in hand and am going to build Carl's "switchless" design. Thanks Carl for your help with that. Right now, I'm enjoying the sound of these speaks driven by a Leak 3400 receiver (English built). Great matchup for the Advents, IMO. Since the Advents don't take anymore than 60w. or so, it does'nt seem to make any sense to drive them with a big-power amnp. Sooner or later I'll get a tube amp audition for them.