Studer 089 line amp problem 7.091.36

[Aref]

Hi everybody,
I'm struggling to fix my 089 mixer for many years now. Recently asked a tech expert to take a look at line amp boards.( I have one working on a mixer and few spares which are not working) Surprisingly, he believes the amp design is so bad which makes it so unstable and unreliable. He offered me to design a different amp in the same size format with the studer dla transformers.
I asked him to explain a bit to get some advice from experts.
He says that stablizing the middle point of the op amp with potentiometer is problematic in design. In his test, this middle point of the op amp (-11v) is changing when the board gets hot or when the gain is changing.


Please let me know if you have a solution for that.
Thanks

 

[Aref]

More info from studer manual

 

[zamproject]

Hi

he believes the amp design is so bad which makes it so unstable and unreliable

As I already say in other forum PM... change your tech

Cheers
Zam

(edit/ps: the correct ref is 1.091.036)

 

[Aref]

It's very disappointing to hear that Zam...
He's an expert in repairing Studer gears. This is a better claim from himself;
"although the regulated -22 volt supplies the unit, during operation and heating and also changing the gain, the center point of supply ( -11 volts) varies considerably.
For more, I also changed all the parts of the unit totally ( except the mounted transformer), but this failure happened again."
Any idea?

 

[moamps]

I serviced some older Studer consoles and racked some 089 modules, and in fact the biggest problem was the mechanical damage of few switches in the EQ section, but never that there was any instability. Can you describe in detail how the failure of that module manifests itself?
P.S. When you changed parts, did you change the LM301 or did you keep it?

 

[gyraf]

Maybe if you tell us what problem you have? What "instability"?

 

[Bo Deadly]

Using a separate network to bias the amp as opposed to using a proper signal 0V is not ideal. Also this circuit is of an era where op amps were just starting to become usable. I don't see any obvious reason to immediately reject your tech's claims. It's very possible that the tech's conclusions are incorrect but the path of least resistance might be to just use the offered alternative. I doubt it can have a negative impact on performance since, again, the circuit is not ideal for various aforementioned reasons.

 

[abbey road d enfer]

It's very disappointing to hear that Zam...
He's an expert in repairing Studer gears. This is a better claim from himself;
"although the regulated -22 volt supplies the unit, during operation and heating and also changing the gain, the center point of supply ( -11 volts) varies considerably.

That maybe what he observes, but it shouldn't be so.
His failure is not being able to find what causes the drift.
I've never seen anything designed by Studer to fail operationally. It may not be the best sounding, but reliability is the proverbial Swiss.

For more, I also changed all the parts of the unit totally

Really, down to the last resistor and capacitor?
I would check the electrolytics first.

 

[zamproject]

Hi Aref

It's very disappointing to hear that Zam...
He's an expert in repairing Studer gears.

Sorry to have been harsh and probably over concise without explanations in PM as in public here.

I just can't get how expert can have such claim about Studer engineering without contextualisation.
If such design is not his cup oft tea I'm fine with it, it's almost 50 years old and some expect different things/sound today but "unstable and unreliable" is just a lie.
Now if his agenda is to charge you with premium modern design as replacement it's up to you.

I'm not an expert audio electronic at all, it's more a side passion (and a way to keep my "daily job" tools alive), I lack lot of knowledge regarding electronic, especially related to audio design. But I restore/rebuilt about four x89 series, including 2 large 289 (and services few other more), one of them (289) being in service for 12 years 7/24 until 1990 ! at the final room for french national classical music radio.
THIS specific line amp probably daily wave hundred million ears in eastern europe in the 70' an 80'...so for sure it work.

the center point of supply ( -11 volts) varies considerably.

We need a value here, +/- 1mV or 5V ??? and from what ref ???

About heat instability, depending on past life of your console (use, storage, humidity), some carbon comp resistors can be tired...

I would check the electrolytics first.

That's for sure !!!
Those gold Frako caps are now in the 100% fail rate after such time.
Also everything up to 47u (and sometime 100u) in those consoles are tantalum, they should be cheeked too (and replaced when needed)

Cheers
Zam

 

[Pan_work]

Hello I see there is some 89 experts hère. I have a board fully functionnal except for few things. One aux (reverb1) seems dead. I try to find wich cards provide signal for AUX. Is someone knows something about it ?

 

[zamproject]

We need more info about configuration, do you have REV module in the desk or the 4 REV send at the vertical plug unit?
The REV sum amp may have different location depending of that.
For the REV line out it should be labelled on the card rails.
Here again we need more info, card position and function depend of desk option/configuration...

 

[Pan_work]

Thanks for answer Zam (tu es français ? ) ,
Here IS my Desk mk1 Setup , its a 2 aux setup, under thé desk there is few cards , Peak meter, 2 Line amp and 2 Big card on the right

 

[zamproject]

Ok it's a MKI... don't know that well the signal path for this version.
My guess, as master main line out circuit is at master module for this version (and not on a line out card), your aux out is probably at ch2 of first (from left) line out (if stereo card), or second line out card.
Yep, Froggy here.

 

[Pan_work]

salut les froggs, ok merci pour la réponse oui c'est chiant car pas de manuel précis pour la mk1 en pdf, on a les schémas dans le Book MK2 mais pas le routing précis... J'ai trouvé une étiquette écrit rev2 sur le second Line amp, ce qui laisse supposer que le rev1 serait plutôt sur celle de gauche, a moins que les deux soient sur la même. Pas de signal rev1 aux aiguilles et évidemment ni a la sortie directe....

sinon par ailleurs j'ai une voix line qui n'arrête pas de sauter (fusible du module qui claque a répétition/) et dernier truc que j'aimerai faire si possible ce serait modifier le board de manière a interchanger le master mono contre un module stéréo HL input ce qui me permettrait d'avoir 14 entrées Line (le bus mono n'étant pas très utile) ça semble possible ?

 

[Pan_work]

Il y a des petits trucs que j'ai pas cherché à investir sur la 089 , c'est le sélecteur a droite du bandeau (enceintes?) qui semble rincé. Il y a aussi le selecteur d'entrée line qui propose SM1 et SM2 , techniquement je pensai que c'était un renvoi de routing des masters vers entrée Line même si j'en vois pas l'utilité. Il reste aussi C1 ...a C4 qui ne semble pas très utile non plus (entrée pour le monitoring?) ?

Sinon je trouve la sortie monitor carrément sonore, il y a des transfos d'entrée sur les étages de cette sortie j'hésite a passer par la pour récupérer de la couleur , a voir

 

[zamproject]

désolé je ne répondrais pas en francais ce qui excurait bon nombre de menbre du forum de l'échanges...

sorry I won't reply in french which will exclude lot of members around...
also please rewrite in english so the whole Q/A flow stay coherent for all

 

[Pan_work]

You right ! And .... Scuse my french, I will reformulate everything - as the purpose Of a Forum IS to Share Knowledge - its obviously a matter of truth to choose english for this purpose and help each others !

 

[Pan_work]

I Can start to Share about a strange 089 Expérience. Mine was totally renewed in 2013 by a master French Tech (o.Bolling the owner of AL.SO). He propose to create an external power supply - who work great At All ... But he told me there is sometimes irregular - a POP in the master section - this 1 sec Pop happens randomnly (sometimes 1 per hour, sometimes 3 per minute)... looks like a capa or something - but he tried to detect but too much hours. So we check by dropping off All modules except master, and the Pop continue. He tried with lab power supply : same same ...

So I consider working with this désagrément but Time has Come to dig it .. I dont know how to start to investigate this intermittent failure !! Some ideas ?

 

[Pan_work]

Préviously I talking about finding one the second Line amp a stickers with writing REV2. But not Shure if the REV1 is one the Other Or in the same one. As the Mk1 Book isn't alvailable on PDF, I have to retrofit things by looking on the part.

Also make a clean board is something important to me, because a 089 desserves it. Very nice round beautiful Sound. I owned a 902, two 169's, one 269, a 961... and a Acousta DCA100 (very différent because modern stuff but Broadcast)... I owned a lot Of separate module , 33114 Neve etc... And I choose to keep the 89 by taste. Like the flavour. This mixer have character. So its a form of respect to solve problems on it..
I will start by solving the master intermittent pop noise, thé dead Aux and thé dead Line module (one have fuse failure looks like a shorten component Somewhere).

Is someone expérienced problems with the 1:3 Eingangstrafo ?

 

[zamproject]

As the Mk1 Book isn't alvailable on PDF

Not all but lot of MKI modules and cards are in the -MKII- labelled service manual pdf

a POP in the master section

All master modules or just one modules?

I dont know how to start to investigate this intermittent failure !! Some ideas ?

Touching the pcb for bad joint ?
Hair dryer, for temp dependant failure ?
Simultaneously prob audio at various section of the circuit, and record via multitrack DAW enough time to see which section get the issue ?
My first guess will be bad transistor, as DOA if there is some involved in the suspected section, the older A101 potted version (black epoxy can) have an important failure rate after 50+ years (blue potted verssion are not that better but I don't think you'll find some in MKI ?)
I speculate the desk is recapped if -renewed- in 2013, but if not, that's mandatory in the todo list...

But not Shure if the REV1 is one the Other Or in the same one

What is the line out card ref ?

Is someone expérienced problems with the 1:3 Eingangstrafo ?

What kind of problem ? what is the function and location of this trafo ? there is trafo everywhere in this desk...