LA-2a T4b Comparison

[Kingston]

I think you may have got the capacitors in the t4b's wrong. They should all be 4700pF which is 4.7n. (not 47nF)

Also, I really think you should somehow try to get your hands on the slow (ie. vintage time constant) drip t4b to test. The fast version does not really belong to this shootout at all.

Other than that, thanks for taking the time to do this.

 

[igs]

I just looked under the microscope and you're right. The capacitor is 0.0047, so it is 4n7/100V. It really doesnt matter for a wave form.
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[Brolik]

why are you responding to all comments except those about how you should be testing with the slow drip t4B? do you intend to include this in your tests?

 

[igs]

I didn't include the slow Drip in my tests simply because I don't have it. I used of the best photocells I could get a hold of.
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[j.frad]

So has anyone ever tried the IGS T4Bs?

 

[kepeb]

i thought these things were tuned specifically to ignore the lower frequencies in some cases. was reading about diy ones a little while back.
I cant see how to get much from the chart there...
is this a standard way of noting t4b responses?

 

[Kingston]

You can certainly tune the low freq output of the photo resistive element. Just stick a cap in series with it. Some T4B's have these included internally (4700pF going to pin 3 inside the box). But they are actually useless.

LA2A has a separate controllable sidechain high pass filter already, so that extra tuning cap only limits your options. Just use the 1meg trimmer that's already there to tune the low freq response.

 

[kepeb]

ya,
just curious about the 1k sig used to test in the first post.
was thinking about variable LF cut but with a t4f anyone diy these besides joe yet?

 

[dandeurloo]

So has anyone ever tried the IGS opto's yet?  What is the word on T4B's currently?

 

[Uhl]

I'm currently building a D-LA2A using the IGS Cells. Unfortunately I have no other cell here for comparison. When I'm finished I'll let you know. 

 

[ilfungo]

I've Build 3 x LA2A point to point and I've tried Drip Slow cell and Kenetek cell.
Kenetek is for me the best!!!
Great responce and natural sound....

 

[Che_Guitarra]

Has anybody experimented with the newly revised Drip Electronics slow T4B yet?  I'm about to put money down on the Opto 4 PCB, and could potentially kill two birds with one stone by buying their in-house T4B.  But, it's all about the results - if a UA or Urei T4B is undoubtably better i'll go that route.

 

[Biasrocks]

I'm about to put money down on the Opto 4 PCB, and could potentially kill two birds with one stone by buying their in-house T4B.  But, it's all about the results - if a UA or Urei T4B is undoubtably better i'll go that route.

Check out Bill's Kenentek T4B's, got a pair here and they are spot on. The drip is in the ball park, but this one nails it.

http://www.kenetek.com/T4AT4BUnits/KenetekT4BModules/tabid/300/Default.aspx

Regards,
Mark

 

[Whoops]

Can you please change the first post picture and be Clear that the Drip T4 that you used is the Fast one so it's a different thing than the Urei or UA and it's expected to clearly see the different attack characteristics that are represented.
Not being clear about that you are misleading people into false judgement and its not really fair.

Comparison of T4B photocells by various producers.

Recently I had an opportunity to gather together a few T4B photocells used in the legendary TELETRONIX LA2A. Basing on the IGS 2LA replica I compared the T4B opto-cuplers. The T4B photocell is the single most important element responsible for the compressor’s sound. Every T4B circuit is composed of an electroluminescent panel (EL panel) and 2 photoresistors. One of them reduces gain and the other influences the meter. The setting for the compressor are: GAIN 60, PEAK REDUCTION 100.

Read more:

http://www.igsaudio.pl/index.php?option=com_content&task=view&id=51&lang=english

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www.igsaudio.com