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Texar audioprism peak diode CR9?

F

fugazi

Guest
Hi all,


I have a pair of audioprisms ( first version ) and i found out that on 3 out of 8 of the boards, diodes CR8 are fitted. On the other (5) boards these diodes are left out. These diodes are used in the peak input circuit. Does anyone have a clue why on some boards these diodes are left out?
I may assume this does something to the peak limiter, but what i have no clue.

Regards,

Evert
 
I take it you got these used from somewhere....

My guess is that someone didn't like the sound of the faster peak time constant, and did a mod to make the prism more of a multiband leveler. I vaguely remember some talk about that kind of a mod in certain circles...but that was so long ago....

-C
 
Hi Cornelius,

Thanks for answering. I already found out what it does.
CR9 and CR8 are used as rectifier diodes. CR8 does the positive half and CR9 the negative part.
When the audioprisms are fitted with a phase rotator unit, there seems to be no need to do full wave rectification. So, this seems why texar left diode cr9 out as i was told via the mail.

I was triggered since i see some abrupt reduction in gain ( fast, transient wise ) when the input level of my texars are beyond a certain thresshold and only on one unit ( which has the diode fitted on 2 bands ).
In these bands ( band 1 and 2 ) i see this transient suppressing behaviour. On the other bands i don't see it.
The other unit ( which is CR9 free ;-) ) doesn't have this behaviour.

Tommorow i will swap cards and let it know via the forum.

Taking out CR8 as well will probably make the texars more like an slow moving compressor (agc) as i may assume.

regards,

Evert

( ps. nice page you have by the way, are there some projects coming? i'm doing a project with the thats4301 audio engine chips )
 
Hmm...

Interesting. I'm always a fan of full wave rectification as there is always *something* that will get through the phase rotator, and cause too little (or too much) gain reduction, depending on whether or not the half of the wave form with the most energy is the same polarity as the rectifier.

Interesting. It's been eons since I looked at a Texar Prism schematic (and I have a pair in my collection), and I do recall something about the detector being half wave too...

( ps. nice page you have by the way, are there some projects coming? i'm doing a project with the thats4301 audio engine chips )
Click to expand...

Thanks! I usually do have a project going on! :) As Goran stated before, I've been working in the DSP world, and finally am getting a chance to do things that have been rattling around in my head for years, but was too crazy to attempt to do in analog!

A lot of people like to play with the THAT Corp engines. I've never played with them...I'm sure you'll let us know how it goes. ;) I've been a big fan of their VCA's.

Happy tinkering!

-Cornelius
 
Hi,

The advice for diode d9 was; " leave cr8 and put cr9 in all board OR leave cr9 out of all boards"
I think i am going to put them all in, but first swap some boards to see what happens.

Regards,

Evert
 
( ps. nice page you have by the way, are there some projects coming? i'm doing a project with the thats4301 audio engine chips )
Click to expand...

I have audio processors on the air still using those. None of the "cookbook" solutions were really designed for on-air use IMHO.
 
audiophile. said:
( ps. nice page you have by the way, are there some projects coming? i'm doing a project with the thats4301 audio engine chips )
Click to expand...

I have audio processors on the air still using those. None of the "cookbook" solutions were really designed for on-air use IMHO.
Click to expand...

Yeah...The "cookbook" stuff rarely does help with having a killer broadcasting audio processing applications. Most of the That Corp examples are geared more to recording studio stuff. There is a lot of great data on VCA's in general, though. Great site to learn about the particulars of those beasts! If only the Internet was around when I was starting out with building processors. That web site of theirs site has general info on VCA's that took me years to round up back in the day!

-C
 
Bob Moses of "AES" and "That Corp" fame lives here on Vashon Island. He helps out or Internet station and TIS setup. Trying to get him to make a cheap audio processor for the TIS with one or two of the VCA boards.

Look him up and email him if you have any questions about That Corp products. He is a really nice guy and very knowable. He also worked for Rane, designing some of their gear.
 
cgould said:
audiophile. said:
( ps. nice page you have by the way, are there some projects coming? i'm doing a project with the thats4301 audio engine chips )
Click to expand...

I have audio processors on the air still using those. None of the "cookbook" solutions were really designed for on-air use IMHO.
Click to expand...

Yeah...The "cookbook" stuff rarely does help with having a killer broadcasting audio processing applications. Most of the That Corp examples are geared more to recording studio stuff. There is a lot of great data on VCA's in general, though. Great site to learn about the particulars of those beasts! If only the Internet was around when I was starting out with building processors. That web site of theirs site has general info on VCA's that took me years to round up back in the day!

-C
Click to expand...

I was able to easily make a more suitable design for broadcast use with advanced time constants and "freeze" gating. Still works nice more than a decade later...
 
audiophile. said:
I was able to easily make a more suitable design for broadcast use with advanced time constants and "freeze" gating. Still works nice more than a decade later...
Click to expand...

I think I mentioned previously that the original Ariane analog units were built around the THAT 4301.

It's an amazing little chip! Pure genius to have the three opamps also onboard. The 4301's RMS detector is a real jewel.
And the VCA is no slouch either. The **unweighted** dynamic range of the output of the Ariane's seven bands of 4301 processing (4 L+R, 3 L-R) measured an amazing 107 dB, with about 0.01 % THD!!

Kind Regards,
David
 
That was the amazing thing to me about the THAT products. The noise floor on a complete processor was excellent!
 
audiophile. said:
That was the amazing thing to me about the THAT products. The noise floor on a complete processor was excellent!
Click to expand...

I'd agree! I couldn't believe how low the noise floor was / is on my four band analog processor. I used the 2180 VCA chips in that design. At the moment, I have the box on my TV audio to the stereo system - making all the levels nice and even, and uniform! ;D

-C
 
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