skrasms

Some T4B info I came across today
« on: June 23, 2004, 11:24:31 PM »
Hey everyone. I came across this group right when it was moving to this server and you guys are GREAT. I think I can learn a lot here. I'm really new to all this stuff, but everyone seems really helpful. I'm a EE student, but I'm just going into my second year so I don't really know how to design anything yet. Anyway, I was going to attempt to offer something to the board. I was tracking down a T4B and found a couple places. The first is JBL (since I heard they own Urei). They sell the T4B for $209 direct from them (I was told you can get it cheaper if you have a local JBL dealer who can order it for you, but wasn't given a price for that). They told me on the phone you can just send an e-mail to their sales department to set up an order. I also called Universal Audio to see if they had T4B's (since they do the LA2A re-issue and all), and they said no, that they only make and use the T4 (no B). They DO sell the T4, however, for $149 when they have stock around. They said the only differences between the T4B and the T4 are the physical size and "maybe something about the attack time." Can anyone verify that? I also tried calling Anthony Demaria Labs a few times, but I just got a message saying their phone line was being checked for problems. I found this store though, that carries the ADL T4B for $209. I hope some of that information is useful!


Scenaria

Some T4B info I came across today
« Reply #1 on: June 23, 2004, 11:50:36 PM »
we make our own now days  :green:

http://www.vacuumbrain.com/docs/t5.html

enjoy!

PRR

Some T4B info I came across today
« Reply #2 on: June 24, 2004, 12:49:52 AM »
The T4 modules are $10 of parts and $100 of testing and selection. Then they list-price it at double the cost so the dealer can pick his profit (full list price for annoying one-off orders, deep discount for favorite customers). The factory won't under-cut the dealer price; they need those guys to push the product. The dealer probably isn't real interested in a $200 special parts order, when in the same time he could sell a $20,000 system. UREI's price is probably low; they probably don't sell enough loose modules to really care about the price.

The exact selection criteria are unclear. Unlike a resistor or transistor, that can be fairly completely specified, the response of the LDR (photo-resistor) is very erratic, especially against time. You can approximate its response as time-constants, but it isn't that simple. Each test condition (light level, duration of light before darkness, resistance level) gives different values for the "time constant": the constant is far from constant.

Scenaria and others have done a lot of study of genny T4s and have criteria they like. Because the original test method and criteria were never published (I suspect it is an art that only a few guys know), we don't know how close the clone is (except by long-term listening on real music, as several LS2 cloners have done: if it works the same on music, that's maybe more important than test-rig criteria).

If you are just beginning to build stuff: don't spend $209 for your first try. Get an assortment-pak of photoresistors and one of those green-screen plug-in nightlights. That's all a T4 is, except there are dozens of "recipes" for photoresistor stuff (it isn't a simple chemical) and you may not find one of the right "blend". Even so, almost any photoresistor in the LS2 circuit will compress: just maybe not the "right" amount or speed to be an LA2.

ECG sold the photoresistor racket to someone else. If you can find the new outfit, they have datasheets on all their stock photoresistors. You can squint at the resistance/time plots and try to pick a suitable cell. Then try to find one that is in-stock at some distributor who will sell you just a dozen. You may have to rig a test setup (pulsed light source and slow oscilloscope) and select a few from the dozen with a long smooth tail on the release (dark) characteristic.

Oh: don't these modules have two photoresistors? One just to work the GR meter? Then you really want two matched photoresistors. You can trim-out a reasonable difference in nominal resistance, but the time characteristics should be closely matched for accurate GR metering. (Then again, if you trim a limiter by ear, maybe you don't need such matching.)

gyraf

Some T4B info I came across today
« Reply #3 on: June 24, 2004, 08:31:22 AM »
Look here for a nice pic..:

http://img56.photobucket.com/albums/v172/gyraf/T4b_05.jpg

 :razz:

Jakob E.
..note to self: don't let Harman run your company..


 

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