A8's Now in the Fold

BillWojo

Junior Member
The welded magnetic pots are earlier ones, they changed to cast steel later in production.
At one time I took one of each to a customer while doing a service call and had them zap the pots with a XRF spectrometer to do a chemical analysis.
At first the readings showed lots of cadium on the welded pot and lots of zinc on the cast pot. Hmmmm, maybe I need to clean off more than just the paint. Used a hand held belt sander to get past the plating and retested.
I knew that the welded pots were steel pipe and plates but was very surprised that the cast pots were cast of steel. Steel castings cost a bit more than iron castings. Altec did not skimp out on these.
The analysis showed that the welded pot contained just a fraction more iron than the cast pot but they were both about 98% iron or better.
I prefer the cast pots myself, I think the magnetic flux lines would flow better in an uninterrupted material and there is a small radius in the inside corner of the cast pot while the welded pot has a sharp inside corner.
I have not run this through any kind of FEM simulator but it makes intuitive sense to me. But than again....

BillWojo
 
The welded magnetic pots are earlier ones, they changed to cast steel later in production.
At one time I took one of each to a customer while doing a service call and had them zap the pots with a XRF spectrometer to do a chemical analysis.
At first the readings showed lots of cadium on the welded pot and lots of zinc on the cast pot. Hmmmm, maybe I need to clean off more than just the paint. Used a hand held belt sander to get past the plating and retested.
I knew that the welded pots were steel pipe and plates but was very surprised that the cast pots were cast of steel. Steel castings cost a bit more than iron castings. Altec did not skimp out on these.
The analysis showed that the welded pot contained just a fraction more iron than the cast pot but they were both about 98% iron or better.
I prefer the cast pots myself, I think the magnetic flux lines would flow better in an uninterrupted material and there is a small radius in the inside corner of the cast pot while the welded pot has a sharp inside corner.
I have not run this through any kind of FEM simulator but it makes intuitive sense to me. But than again....

BillWojo
And that's the one that came in the one A8.
 
While I am dodging the cold weather for the next steps in the woodshop, I need to start gameplanning on what to do about the crossover. Of course I have the original N800-F. Should I build a new crossover per this schematic, or should I consider a different route?
 
While I am dodging the cold weather for the next steps in the woodshop, I need to start gameplanning on what to do about the crossover. Of course I have the original N800-F. Should I build a new crossover per this schematic, or should I consider a different route?
Is it potted with tar? If so I'd build from scratch for sure (though I'd probably do that anyway) or consider biamping with an active crossover

I wouldn't risk roasting original diaphragms with an old crossover unless running super low wattage amps
 
Is it potted with tar? If so I'd build from scratch for sure (though I'd probably do that anyway) or consider biamping with an active crossover

I wouldn't risk roasting original diaphragms with an old crossover unless running super low wattage amps
Yep, potted. They worked fine before the de-construction so I know they can be used if even temporarily or for the heck of it.
The way I am building the rear panels includes a door section for access that all the penetrations and connections will be in. That way once I settle on what the final version of all that is (attenuator or no etc) I can re-do that door panel or not as needed.
I agree on the active biamp thing although in the end I think I will want to keep it simple.
 
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Did you say you had 802's?... I'm confused. Anyway, if you have those then use em. This horn was designed for these. Others might work but it would be an experiment... which I love to encourage others to do cause it saves me time and money.

With the 802's, you should start with Salectrics xover which is a modified JELabs xover. Remember that Joseph (and JoeR I should ad) uses 12"ers full range and that Sal uses 15"ers and the 800 is 8ohms which crosses over around 1200. I can pass you my schematic which are Sal's converted to 16ohms.

These have a high end boost to help the 800 on the very top (Sals actually have a few more tricks) and are easily flexible with the exchange of Resisters (and cap values). I didn't have much luck with L-Pads but others think they're great. Changing a few Resisters does the same thing and sound much better... in my humble opinion. More info later on actual "parts" recommendations.

My next step is to take some REW measurements and modify accordingly. I really struggle with this software, so its slow going for me at this stage. I'm also wrestling with high pass and subwoofer integration schemes. The good news is, the xover 'as is' sounds marvelous.... which makes me lazy and a happy listener instead of a frustrated speaker designer.
 
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Did you say you had 802's?... I'm confused. Anyway, if you have those then use em. This horn was designed for these. Others might work but it would be an experiment... which I love to encourage others to do cause it saves me time and money.

With the 802's, you should start with Salectrics xover which is a modified JELabs xover. Remember that Joseph (and JoeR I should ad) uses 12"ers full range and that Sal uses 15"ers and the 800 is 8ohms which crosses over around 1200. I can pass you my schematic which are Sal's converted to 16ohms.

These have a high end boost to help the 800 on the very top (Sals actually have a few more tricks) and are easily flexible with the exchange of Resisters (and cap values). I didn't have much luck with L-Pads but others think they're great. Changing a few Resisters does the same thing and sound much better... in my humble opinion. More info later on actual "parts" recommendations.

My next step is to take some REW measurements and modify accordingly. I really struggle with this software, so its slow going for me at this stage. I'm also wrestling with high pass and subwoofer integration schemes. The good news is, the xover 'as is' sounds marvelous.... which makes me lazy and a happy listener instead of a frustrated speaker designer.
Yes I have 802D 16ohm. Also have 808, and 806 plus some new Radian Diaphragms I can use.
1205190741a.jpg

Great Idea with the Salectrics crossover.
 
Have you put a multi-meter on these? Should measure around 9ohms.

When (not if) I buy another pair of these, they will go straight to GPA for a check up. My experience was that even with good measurements and good sound, mine were a bit of a mess which was remedied and came back from GPA much better. Unfortunately, their prices have gone up... but I heard there might be "local" discounts to be had.
 

je2a3

Junior Member
Have you put a multi-meter on these? Should measure around 9ohms.
When (not if) I buy another pair of these, they will go straight to GPA for a check up. My experience was that even with good measurements and good sound, mine were a bit of a mess which was remedied and came back from GPA much better. Unfortunately, their prices have gone up... but I heard there might be "local" discounts to be had.
FWIW, if you value the original 20275 diaphragms like I do, I'll take them out and safely store at home before sending the drivers to GPA.

Just my 2 cents...

JE
 
Have you put a multi-meter on these? Should measure around 9ohms.

When (not if) I buy another pair of these, they will go straight to GPA for a check up. My experience was that even with good measurements and good sound, mine were a bit of a mess which was remedied and came back from GPA much better. Unfortunately, their prices have gone up... but I heard there might be "local" discounts to be had.
9.4 on one, 9.7 on the other.
Because of that pricing I have only done stuff when truly needed. Unfortunately hard to tell though. And most of this stuff is at the age that it should be recharged etc.
 
FWIW, if you value the original 20275 diaphragms like I do, I'll take them out and safely store at home before sending the drivers to GPA.

Just my 2 cents...

JE
I read that in a thread or two elsewhere. Good advice I guess. But how do we know the old 20275 are okay? Do they either work or not work?
 

je2a3

Junior Member
I read that in a thread or two elsewhere. Good advice I guess. But how do we know the old 20275 are okay? Do they either work or not work?
Yes! Plus the DCR test: the aluminum VC of the 20275 will read on the low side for a 16 ohm 'fram usually 7.5-9 ohms, while the later copper VC 34852 reads in the 11 ohm range.

I never sent a driver for re-charging. But then most of my 802s don't look like they've been banged up.
 
Yes! Plus the DCR test: the aluminum VC of the 20275 will read on the low side for a 16 ohm 'fram usually 7.5-9 ohms, while the later copper VC 34852 reads in the 11 ohm range.

I never sent a driver for re-charging. But then most of my 802s don't look like they've been banged up.
An Altec alnico driver shouldn´t need remagging unless it´s been ”banged up”. This is the message in the remagging article on the GPA website. If you want a second opinion, this is what Howard Tremaine has to say on the subject (Audio Cyclopedia, 2nd ed., 1969, question 20.23): "Permanent magnets lose about 1 percent of their charge when they are first energized. After that they lose about 0.2 percent, for a total of approximately 1.2 percent within the first year. From then on, the loss is in the order of 1 percent in the next several thousand years, asuming that the magnet is not abused”. Very good news for us Europeans!
 

Audionut

Next Round Is On Me
An Altec alnico driver shouldn´t need remagging unless it´s been ”banged up”. This is the message in the remagging article on the GPA website. If you want a second opinion, this is what Howard Tremaine has to say on the subject (Audio Cyclopedia, 2nd ed., 1969, question 20.23): "Permanent magnets lose about 1 percent of their charge when they are first energized. After that they lose about 0.2 percent, for a total of approximately 1.2 percent within the first year. From then on, the loss is in the order of 1 percent in the next several thousand years, asuming that the magnet is not abused”. Very good news for us Europeans!
Best news ever! Looks like I’m saving me a GPA magnet recharge fee on my 802D’s.
 
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