LAWO 325 DOA schematic

The output opamp from a LAWO DW990V Pegelsteller module :thumb: Does this look right?

;Matthias


EDIT: A nicer PDF including parts layout is on the way to Kubi...

I compared the original to your schematic for about 30 minutes and could not find any faults.... but jeeez, what are these things small. Did you desolder some stuff from it to get a better look? What made you decide to draw a schematic of this opamp? Are they any good and did you ever try them out? I have a few DV990v cards laying around and so far I have not found any use for them except ripping off the transformers....but your schematic might change this :thumb:

[quote author="radiance"]but jeeez, what are these things small. Did you desolder some stuff from it to get a better look?[/quote]
The layout/parts density is truly insane :shock: . Just a bright LED flashlight and some careful bending :wink:

[quote author="radiance"]
What made you decide to draw a schematic of this opamp? Are they any good and did you ever try them out?[/quote]
Just curiousity if they used special circuit tricks (like the crazy 'optocoupler with feedback'-VCA thing) (which they didn't :? ) and if EAGLE works for reverse engineering (it does).
They pass sinewaves when used in the DW990V (that's all i found out so far), but kubi seems to think they are OK for some things.

A transformer lifts the o/p signal to max. +22dBu, that's what they need a low Z output for.

Click to expand...

They usually used 1:1,75 torroidal outputiron, Haufe or Pikatron

My collegue at work used to work a lot on Lawo boards. He told me that they had several Lawo and SSL studios over there and all the tonemeisters prefered to work on the Lawo boards because they were cleaner and didn´t add any sound to the signals. I guess that´s what the Lawo DOA does: straight wire with some gain.

Does this look right?

Click to expand...

The topology looks correct, I think that C1 is a bit high in value though for the low current of the input stage and the high value of R7 (you seem to be unsure of this considering the question marks on the schematic). I'd assume something in the order of 22 pF.

I compared the original to your schematic for about 30 minutes and could not find any faults...

Click to expand...

So they give 150 pF for C1 on the original schematic?

Samuel

[quote author="kubi"]3. seems to be the best of them all: [...]
+/-18V (or 0/36V) was the highest voltage I could drive them with before they died [/quote]

Thanks, that's good to know :grin: The BC413/415 are 30/35V parts :twisted:

[quote author="Samuel Groner"]C1 is a bit high in value [...] I'd assume something in the order of 22 pF.[/quote]

You are right, after closer inspection it looks more like 15pF

[quote author="Samuel Groner"]

I compared the original to your schematic for about 30 minutes and could not find any faults...

Click to expand...

So they give 150 pF for C1 on the original schematic?

Samuel[/quote]

Sorry, I should have been more specific.I don't have the original schematic. All I did was look at the real opamp. I only looked at the traces and if they where connecting to the right components. I did not look at cap or resistor value's at all.

Kubi has hosted the original schematic IIRC. It might be in the files of the DW990, W995 or another Lawo card
If not I have it somewhere around here.

[quote author="jensenmann"]Kubi has hosted the original schematic IIRC. It might be in the files of the DW990, W995 or another Lawo card
If not I have it somewhere around here.[/quote]

Could not find it @ Kubi's place...would be nice to compare it to EZ81's version.

:evil:
I can´t find it. I was really sure that I´ve sent it to you, Darius. It was part of the W995 EQ schematics. Anyway, maybe I´m wrong, I don´t know
Sorry for the fuzz. Maybe I should try to reanimate my contacts to Lawo
:wink:

Finishing this thing was my holydays project (with BC550/560 instead of the unobtainable BC41...):

bigger pic



Zip with Eagle board+schematic files

Untested except a short test on a solderless breadboard, but it is easy and cheap enough to try. Parts cost (without PCB + pins) was ~ 1EUR. The layout should work for DIY etching (hole diameters might be wrong). I used the toner transfer method.

Maybe someone has a use for this.

;Matthias

Cool! So you've build one....Does it work OK? How does it sound? Did you compare it to other DOA's such as the 990 or the 2520?

[quote author="EZ81"]
Zip with Eagle board+schematic files
[/quote]

Hi Mr. Rectifier-Tube,

I get an error here when I open the file ('not a valid file'), I'm on version 5.6.0.
Does it open OK at your side ?

Enjoy that DOA :thumb:

Thanks/regards,

Peter

@radiance: With my recording skills i don't dare commenting on the sound, i don't even have any gear to plug it into yet. Maybe someone else with better ears wants to check it out and share the results
Plugged into the bread board the DOA seemed to work OK with test signals (some ringing on squarewaves, but that might have been caused by the wire mess).

@Peter: The files from the zip open OK with Eagle 4.11 light here, no idea what might have gone wrong.

[quote author="EZ81"]@Peter: The files from the zip open OK with Eagle 4.11 light here, no idea what might have gone wrong.[/quote]
Hi EZ81,
Oops I goofed, over here the files are opened by ExpressPCB, need to fix that :wink:

I was happy to pick one of these up recently (thanks to the seller :thumb: ) using the smt doa version in the v975/4



Built like a proverbial tank. I can only imagine what an entire
console made from components such as this would feel like to use.

Pretty damn good, I guess. :shock:

Anyway - the circuit is single railed with +Vcc (not sure what voltage yet)
from the 24V supply regulator? And is that little block of metal fastener
at the bottom of the doa just a fastener?

Soon to put this finely manufactured piece to work in it's new humble duty
of summing amp in the middle of a whole bunch of diy and another mixer.

Real thanks to all those who that have made it possible by for me to even have the opportunity to try this build. :sam:

[/i]

Its a fastener but also connected to ground IIRC. Don´t mess with the SMD-DOA cards - don´t even think of trying to touch them. They are VERY sensitive. I sadly expierienced this with several cards :evil:

Feed it with 24V and replace the red Roe electrolytics, they are shite. The onboard regulator supplies the amps with 21V

Thanks Jens - will do!

Anybody has a spare 325/4? 
We have a broken one in a LAWO DV975....

andow said:

Anybody has a spare 325/4? 
We have a broken one in a LAWO DV975....

Click to expand...

Bump!!
Actually, if I understand the schematics correctly, a 325/1 would work here, too... But we would need two, then - to keep the channels matched...