New A7's

[Analogluvr]

Hi guys,
I have been lurking on here for a while and reading some of the knowledge that is accumulated in this board. I have just gotten myself a pair of A7 voice of the theatres. They have 416s on the bottom N 501-8 crossovers 511 horn's and 909 drivers. I just noticed that the one 909 driver seems to have a little bit of static distortion around some of the high-frequency notes. Any ideas as to how I can fix this? also how do I reinforced the midbass horn flare? And I have an Ashley active crossover Will that be an upgrade over the 501 passive? also does anybody have a schematic for a better version of a passive? Or if I'm sticking to the passive route should I just replace the components with newer versions of the same values? Thanks in advance for any help, I apologize for all the questions.

[Elitopus1]

Hi welcome to the hostboard.

Somewhere there is a big thread about how to add bracing to the 825/828 cab. You can probably find it by searching but you might also find some useful info by just browsing through the threads. I know I learned a lot by reading old threads here. Maybe someone will link the one in question.

For the driver I would start by taking the diaphragm out of the bad one. Check to make sure it isn't coming apart. Check the VC gap for debris. Also make sure the gap is still evenly spaced. You can always swap in the good phragm to make sure the HF driver is good.

When I first got my A7's I used an active xover. It let me see what xover point I like best. For me thats 800hz. If you decide you like 500hz you could just rebuild your passive Altec xover.

[Analogluvr]

Yes I guess I'll have to do some more digging for the thread. Did you find a radical difference sound quality wise between running them passively or actively?

[LowOhms]

Hi welcome to the hostboard.

Somewhere there is a big thread about how to add bracing to the 825/828 cab. You can probably find it by searching but you might also find some useful info by just browsing through the threads. I know I learned a lot by reading old threads here. Maybe someone will link the one in question.

For the driver I would start by taking the diaphragm out of the bad one. Check to make sure it isn't coming apart. Check the VC gap for debris. Also make sure the gap is still evenly spaced. You can always swap in the good phragm to make sure the HF driver is good.

When I first got my A7's I used an active xover. It let me see what xover point I like best. For me thats 800hz. If you decide you like 500hz you could just rebuild your passive Altec xover.

Hi,

Before disassembling a suspect driver, he should measure the DCRs of both the voice coils, with drivers mounted on the horns. If there is a difference, that will tell us all something. He could report DCRs to us.

Then, assuming there is little or no difference in DCRs, he should swap high frequency drivers, and see if the bad treble switched sides , in which case its most likely a driver problem,. If it does not switch sides, it is a crossover, wiring, amplifier problem,


Low Ohms .... Jeff

[Elitopus1]

Hi,

Before disassembling a suspect driver, he should measure the DCRs of both the voice coils, with drivers mounted on the horns. If there is a difference, that will tell us all something. He could report DCRs to us.

Then, assuming there is little or no difference in DCRs, he should swap high frequency drivers, and see if the bad treble switched sides , in which case its most likely a driver problem,. If it does not switch sides, it is a crossover, wiring, amplifier problem,


Low Ohms .... Jeff

Just depends on how comfortable he is taking the diaphragm out. I take apart EVERY HF driver I get and inspect the diaphragm/VC gap. I also like to know if my diaphragms match.

But yes, it could be a xover problem too. He could check that also

[LowOhms]

Hi guys,
I have been lurking on here for a while and reading some of the knowledge that is accumulated in this board. I have just gotten myself a pair of A7 voice of the theatres. They have 416s on the bottom N 501-8 crossovers 511 horn's and 909 drivers. I just noticed that the one 909 driver seems to have a little bit of static distortion around some of the high-frequency notes. Any ideas as to how I can fix this? also how do I reinforced the midbass horn flare? And I have an Ashley active crossover Will that be an upgrade over the 501 passive? also does anybody have a schematic for a better version of a passive? Or if I'm sticking to the passive route should I just replace the components with newer versions of the same values? Thanks in advance for any help, I apologize for all the questions.

Hello,

I commented on another post in this thread, on trouble shooting / finding the treble distortion.

There are pros and cons, active and passive.

I will discuss crossovers from "my" perspective, which is " theoretically " to obtain the highest possible fidelity. So friends, this is written only IMHO :

(1) Avoid active. It adds an un-necessary line stage to the audio electronics. It, like a passive, also uses caps, etc to get the roll off in that line stage. Why add an un needed stage??? KISS rules.

A second problem is that when biamping IDEALLY, one should use two amps of exactly the same design, on the top and bottom, hopefully a zero feedback design to keep the music intact. MOST all active biampers I see do not do this and there is an audible discontinuity between differing amps IF the system is executed at the highest level. .

(2) Optimize the passive crossover. Optimize every aspect of feeding a signal to the A7, from the amp to crossover, system wiring, the crossover itself, pick a frequency, and use GOOD parts, and optimize it.

Then use a single highest-possible-quality no-negative feed back mono amplifier on each channel, to run the whole shebang.

- - - - - - - - - - - - - - - - - - - -

This is ONLY my opinion, but optimized passive is how I would suggest one do it for the best possible " ultra fi" result.

BTW, a very conservative alternative to internal bracing is mass loading, its very inexpensive, its totally reversible - which keeps the enclosure original, and has benefits bracing alone does not provide. YMMV, yada yada.

Have fun. There are lots of people who will want to assist you, and opinions differ.

Low Ohms.....Jeff Medwin ( A7-800 VOTTs, 515B, 802D )

[Earl K]

One needs to keep in mind that if the plastic phase plug has become unglued ( an excellent source of distortion ), then a simple dcr test won't illuminate that as a problem.

These plastic phase plugs ( in the 900 series drivers ) do let go from time to time .

Gently shaking the driver ( off the horn ) & listening for rattles will give an indication of a loose phase plug ( as will removing the diaphragm for a visual inspection ).

[LowOhms]

One needs to keep in mind that if the plastic phase plug has become unglued ( an excellent source of distortion ), then a simple dcr test won't illuminate that as a problem.

These plastic phase plugs ( in the 900 series drivers ) do let go from time to time .

Gently shaking the driver ( off the horn ) & listening for rattles will give an indication of a loose phase plug ( as will removing the diaphragm for a visual inspection ).

Good point Earl ! Liked that post.

You know, from the " human " aspect, many brand-new owners will be afraid, or not confident, to touch it, let alone open - up a high frequency driver.

[Elitopus1]

Everyone has to start somewhere. Take the plunge!

[mah]

Analoglvr, here's how: http://www.greatplainsaudio.com/SmDrvrDiaRpl.pdf Note the caution message.


Should you remove the 909 from the horn would you please measure the throat exit diameter. There is some uncertainty as to whether it is 1 inch as shown, here: http://alteclansingunofficial.nlenet...909-8AData.pdf , or 7/8 inch as in all other 90x models.