LAWO DW990 15khz roll off question - Help!

[brunoci]

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

 

[RuudNL]

Difficult to tell without knowing what is going on inside STV 1 and STV 2...

 

[[silent:arts]]

What is a 15KHz roll of problem?
Do you hear it?
Can you show us your measurement?

 

[brunoci]

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!!!

 

[jensenmann]

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).

 

[brunoci]

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!!!

 

[synthiaks]

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

 

[[silent:arts]]

We still don't know if there is any 15khz roll off at all ...

 

[mjrippe]

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.

 

[brunoci]

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.

 

[dasnevestheo]

Hello there,
Sorry to dig this old topic but did anyone ended up doing some real Freq. response measurement of the Lawo cards ?

 

[versa]

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

 

[dasnevestheo]

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.

 

[Whoops]

What is a LAWO DW990 ?

thanks

 

[[silent:arts]]

What is a LAWO DW990 ?

It is a remote VCA Fader (dual VCA card)

 

[Whoops]

It is a remote VCA Fader (dual VCA card)

thanks