View Full Version : tech question on my previous xo post

07-23-2006, 07:48 PM
When I look at the 1209 and 1201 Altec networks they are identical except the 1201 has a resistor value of 7.5 ohms and the same resistor in the 1209 is 8 ohms. The 1209 has a zobel circuit in the LF section. Other information that I can garner is that the hipass in the 1209 is a 12db slope while the 1201 is a a 18db slope. since that is in the hipass section and other values are ldentical I suspect that the inductor for that part of the circuit contributes that that. To make a long story short, are these small differences noticeable given that the zobel is there (I assume) for noise only????? :blah: :blah:

07-24-2006, 01:03 AM
Generally, the pupose of a Zobel is to level the impedance of the driver so that the filter operates predictably. Secondarily, it also serves to minimize impedance variations seen by the amplifier, thus providing a more uniform load. In some filters, it may used to shape the drive contour as well.

It's true that an R-C combination is conventionally used as a "noise" filter, but that's not the typical function in crossovers.

I cannot help you otherwise with these specific circuits unless you post the schematics or link to them, as I'm unfamiliar with most Altec....

07-25-2006, 03:43 PM
Thanks Zilch. Here is the 1201-8A schematic as posted by EalrK a while back.
I don't have the one for the 1209 or for the Model 19 but if we can get Earl to do his magic I am sure he can find them.

I am not absolutely sure if there is any difference between the 1201 and the 19 XOs but some say there was some EQ abilities added in the 19 XOs.

Sorry about the size, I can't get it larger. Here is the link to veiw in full size.http://home.earthlink.net/~jmarkwart/id7.html

07-25-2006, 04:20 PM
The 6 uF is bypassing everything above ~3.3 kHz around the attenuation, looks like. I'd have to model in Spice to see what's actually happening as the rheostats are adjusted.

That qualifies as compensation, I'd say.

No Zobel in the LF of this one....