LAWO DW990 15khz roll off question - Help!

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brunoci

Member
Joined
Mar 24, 2010
Messages
7
Hi.
I've little  knowledge of electronics and I can't  find a way to solve the 15KHz roll off problem on a Lawo DW990  board ...
I read something here about DV975/3, but are different boards.
Can someone help me, please?
(attacched schematics ...  AudioKubarth is down these days ...)

Thanks in advance!
Bruno
 

Attachments

  • Lawo DW990 schematics.pdf
    959.3 KB · Views: 53
I'll take a frequency measurement soon and I'll it post here.
I'm working to mount this module in a mastering console I'm working on.
A relay/passive inserts one, with parallel compression and mid-side options.
Now I'm on the Cnc cutting/mechanical mount side of work and I can't take any measurement for some days.
I thought it was easier ...
Thanks!!!

 
There´s no lowpassfilter in your schematic. If there is a rolloff then there must be filtering action in the VCA subcards (=STV, Lawos homegrown discrete VCA).
 
Ah, Ok.
I've a schematic (from Kuberth Audio site) ) for  Lawo OpAmps used in DW990.
I post it here.
Maybe  hi/lo pass components are there ...
Thanks!!!
 

Attachments

  • Lawo Op-amps.pdf
    302.6 KB · Views: 30
That's the Ops, but not the parts STV1-STV2.

I would just live with it. If you can't well then you can always sell them.  3dB less at 15kHz will not turn a good recording bad :)
 
My German is not great, but looking at the data sheet it appears the rated response is 40Hz to 15kHz +/- 0.2dB  which is typical of German broadcast modules at the time.

Unless you have measured otherwise, I would doubt that they are even -3dB at 20kHz.
 
I'm still on rack mechanical mount of all parts (of the whole console: boards layout adaption, relais and switches placement, etc.).
Today I'll mount transformer/power supply on rack and then  I'll start to make audio connections.
After all this, I'll can take a frequency measurement ...
It's a slow work  ...
For now, thanks to all.
 
Hello there,
Sorry to dig this old topic but did anyone ended up doing some real Freq. response measurement of the Lawo cards ?
 
Hello,
I have some of the modules in use and they are ruler flat. 2 modules had extreme roll- off at about 7k( what i can remember). changing all the caps solved the problem.
cheers
 
Thanks
guess i'll just have to try if it's bothering me or not, and if so removing the highpass caps ;)

Another thing : i'm wondering where to put a fader for volume control ? as the 2 variable ones are only for going between +0dB and +30dB of total gain.
 

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