Alec Crossover?

[WntrMute2]

I have just picked up a pair of Heath Kit AS-21 cabinets with two 414-16 ohm LF drivers and one 806 CD/horn.-16 ohm I believe. The LF are wired in parallel I believe.
The crossover is reportedly a N-800-F. I'd like to rebuild or replace the crossovers. Any suggestions? Not looking for some experimental design really; I'd like to freshen up the existing crossover. Experiments to come later.
Thanks

 

[gdmoore28]

I have just picked up a pair of Heath Kit AS-21 cabinets with two 414-16 ohm LF drivers and one 806 CD/horn.-16 ohm I believe. The LF are wired in parallel I believe.
The crossover is reportedly a N-800-F. I'd like to rebuild or replace the crossovers. Any suggestions? Not looking for some experimental design really; I'd like to freshen up the existing crossover. Experiments to come later.
Thanks

Man oh man - there are so many good choices to make with this configuration. But, you will need to clear something up for us. You say, "I'd like to rebuild or replace the crossovers." Then, "I'd like to freshen up the existing crossover." If it's the latter - freshening the existing network - then your task is rather simple: replace the capacitors in your current xovers, clean the L-pads, and you are done.

But, (and at this point I will sound like a broken record since I and several other Altectistas regularly recommend this ) there is a major - and cheap and easy - addition that you can make that will transform your AS-21s into a super hifi assemblage. To wit: insert the Altec 30923 horn attenuator/eq between your N800F and the horn drivers. This simple circuit (one capacitor and three resistors!) dramatically dials back the highly accentuated midrange frequencies - the very frequencies that give rise to complaints about horns that are "too forward," or "in your face," or simply sounding "horny." I would be hard pressed to think of any other single addition to your speakers that will result in so much change for the good.

Note that if your horn drivers are, indeed, 16ohm versions, you will need to change the component values. All of that is spelled out here, including the appropriate values for use with 16ohm variants:

http://audiokarma.org/forums/index.php?threads/using-altec-30904-atteuator-with-511-416.155640/

Now, if you really want to "replace" your current networks, that will open up even more possibilities, and we can discuss those, as well. Just let us know which direction you want to go.

GeeDeeEmm

 

[WntrMute2]

Thanks GDM, Your help is appreciated. I am thinking of doing both. Replacing the network as one step and once that is done, refreshing the originals so as to have both to play with. I just found that one of the HF level controls is frozen so that will be my first order of business.

 

[gdmoore28]

Thanks GDM, Your help is appreciated. I am thinking of doing both. Replacing the network as one step and once that is done, refreshing the originals so as to have both to play with. I just found that one of the HF level controls is frozen so that will be my first order of business.

If you want to build new ones exactly like your factory xovers, just find the schematic (readily available) and duplicate it. And then add the 30923 network between the xovers and the horn drivers.

If you want to go full tilt boogie, start your reading here:

http://www.audioheritage.org/vbulle...s-Altec-846Bs-w-EV-Tweeters!&highlight=babies

This thread is the genesis of the Zilch Z19 network with lots of cool features - and incorporating the 30923 network for horn eq!

GeeDeeEmm

 

[twiiii]

Call the guys at Great Plains Audio, they still build new Altec, crossovers, drivers, woofers and Coaxial speakers. They can make great recommendations on restoring your speakers. From crossovers to re-coning, etc etc.

 

[WntrMute2]

Call the guys at Great Plains Audio, they still build new Altec, crossovers, drivers, woofers and Coaxial speakers. They can make great recommendations on restoring your speakers. From crossovers to re-coning, etc etc.

No luck there. They don't sell a replacement for that specific network nor do they work on them. They were my first stop. Great service and reasonable prices. I had some work done there recently and they were a joy to deal with.

 

[BillWojo]

There is another board similar to the 30923 unit that has a zobel network built into it. I believe that was made for your combination, just not sure if it was built in 8 or 16 ohm. Somebody with more Altec smarts will chime in I'm sure.

BillWojo

 

[bowtie427ss]

30904, 8 ohms, Zobel configured for a single 411-8A woofer which uses a very different motor from 414/416.

If i were going to use the cookie cutter approach, i'd probably pop for the GPA N-1200 and a new pair of 8 ohm diaphragms(for a couple hundred more replace the entire driver with GPA 902 for superior HF extension) and be done.

The dual 414's are capable of a much higher crossover point while at the same time the 811 does a fairly poor job of maintaining an acoustic load on the driver all the way down to 800hz.

The last well engineered speaker from Altec to use the 811 horn also used the N-1200 in conjunction with it. The N-1200 incorporates better EQ than a 30904, or 30923 slapped in circuit with one of Altecs ancient networks. If i had to say something good about the N-800-F network, it would be "good bye".

 

[WntrMute2]

Is there a way a novice like me can determine whether the diaphragms in my existing compression drivers are 8 or 16 ohm? I do have a decent multimeter. I just had GPA change those diaphragms in my 902s from 8 to 16 ohms for a different project dammit!

Also, the pots for HF attenuation are shot. For starters, I'd like to change those out. Parts recommendations?

Thanks for all the help!

 

[jeb98]

Is there a way a novice like me can determine whether the diaphragms in my existing compression drivers are 8 or 16 ohm? I do have a decent multimeter. I just had GPA change those diaphragms in my 902s from 8 to 16 ohms for a different project dammit!

Also, the pots for HF attenuation are shot. For starters, I'd like to change those out. Parts recommendations?

Thanks for all the help!

You can connect the multimeter to the corresponding positive and negative terminals on the compression driver, and then it will give you a read out in ohms. 16 ohm drivers should read around 11 ohms or so, while the 8 ohms will read between 6 and 7 ohms.

 

[WntrMute2]

Does anyone know the specs for the HF pot? I'd like to get the parts on the way tomorrow if possible. Is it a simple potentiometer of an L-pad?

 

[Steve O]

Does anyone know the specs for the HF pot? I'd like to get the parts on the way tomorrow if possible. Is it a simple potentiometer of an L-pad?

If truly an N-800F, the HF attenuator is a 25 ohm 5W wirewound pot. If an Altec mfgd x-over, the 3/8” threaded bushing on the pot is extra long and may be difficult to source.

Heath sometimes used the OEM’s actual OEM x-over and sometimes they copied the OEM’s x-over circuit and had the builder construct the x-over from supplied parts, frequently of higher quality than OEM parts.

Note that there were two versions of the Altec N-800F one had 10.5uF caps for both LP and HP sections. A later, poorly documented version used 10.5uF in LP and 4uF in HP. Not sure what you have but the later version sounds better IMO...somewhat less “prominent” mids and maybe a little more pleasant overall.

 

[WntrMute2]

Thanks to all for the help.

 

[Dr. Beaker]

I generally agree with Bowtie’s recommendation, but another option is to let the 414’s run full range and use a first order hi pass on your 16 ohm 902’s. A series cap calculated to give a crossover somewhere from 6000 to 8000 and a 16 ohm lpad is all you need. May need to try several cap values to see what you like.

 

[WntrMute2]

I guess at this point I'd like to build a n-800-f clone and move to something like the 1200 crossover in the future. I can sort of read the schematic but does anyone have pictures or sketches of a completed n-800-f that might help me layout the project?

 

[gdmoore28]

I generally agree with Bowtie’s recommendation, but another option is to let the 414’s run full range and use a first order hi pass on your 16 ohm 902’s. A series cap calculated to give a crossover somewhere from 6000 to 8000 and a 16 ohm lpad is all you need. May need to try several cap values to see what you like.

Hi Doc,

Unless I'm misunderstanding you, I think you may be giving the 414 credit for considerably more mid/hi frequency extension than it's able to provide. The following is a fr graph posted by CLIPX Audio (Japanese) as a result of testing a pair of gorgeous 414s.

Clearly, the tested 414s were shouting "sayonara" by the time they reached their secondary peak at 2kHz. A little more searching online turned up graphs showing that this curve is more common than not with similar-condition speakers.

A number of 414 owners on this forum and others report that they run their 414s full range, but horn implementation has to take place much closer to to 2kHz in order to avoid the -20 odd decibel trough that would otherwise bury the 2-8kHz upper mid range frequencies.

Using only a capacitor to properly throttle the 902 driver would require insertion at closer to 3kHz, I'm guesstimating.

Your thoughts?

GeeDeeEmm

 

[Dr. Beaker]

Interesting plot GDM. There are a variety of 414 versions and likely don't all measure the same. I have GPA 414 8B and cross at 6500. Couldn't be happier. I have seen posts by Joe Roberts saying 8000 works well for 414A's and 414C's. First order provides a pretty gentle slope and gives a fair amount of output much lower than the crossover point. Might still work well with the plot above.

Not implying that this is the best solution for all. For me it sounds great and it is easy to implement. The midrange on the 414 is awesome, IMO.​

 

[Dr. Beaker]

Here's a 414-8B I found on the www.

 

[bowtie427ss]

Using only a capacitor to properly throttle the 902 driver would require insertion at closer to 3kHz, I'm guesstimating.

Your thoughts?

GeeDeeEmm

When using a 1st order filter you have to consider that whatever knee point you choose, the HF will only be attenuated 12db 2 octaves below that, 1 octave is an approximate halving of frequency. At Dr Beaker's 6500 XO, he's still getting significant output from his horn at 3k, and from the sound of his report this provides a nice overlap for his system, room, preference, etc..

 

[WntrMute2]

I just replaced the 25 ohm pots on my stock N-800-F crossovers because the originals were non-functional. Unfortunately, I replaced the called for 25 ohm pots with 25K ohm pots. Needles to say, they are also non-functional. I have a couple of 16 ohm L-pads but I am unsure how to wire them up in place of the stock pots+20 ohm resistors. Any help appreciated.