Studer 169 Mic Input Channel Issue

[Shakusky]

Hi,

I've got a problem with one Studer 169 mic input channel. The sound that comes out sounds weak, thin and noisy. I've fully recapped the channel,  changed electrolitics and and tantalum caps, replaced IC1 and also replaced transistors from Q1 to Q7. Don't  know what else  could It be. If anyone could help me I'll really appreciate it! thanks!

 

[zamproject]

Hi

I don't think changing IC and transistor without understanding what happen is a shoot in the dark...
Did the module already have this issue before your work on it ?
Having the issue at mic input only as you state is a possible help to locate trouble, have a check at the four way rotary selector (mic/line) as the phase switches...

Clean all switches, clean insert jack, check all jumpers that set up the signal path, clean connector at the frame. This is the usual to do anyway, after that if issue still there, trace the signal in the path until it goes out of spec.

Best
Zam

 

[Bo Deadly]

You need to do an AC sweep and measure the output of each stage (preferably DC coupled so points with no DC bias) to verify it's working properly. In the simplest case this could be done with a sound card and some software that does an FFT or bode plot. Spectrum analysis is a critically important tool. I would never just blindly replace components. Many components are almost certainly just fine.

 

[Shakusky]

Hi

I don't think changing IC and transistor without understanding what happen is a shoot in the dark...
Did the module already have this issue before your work on it ?
Having the issue at mic input only as you state is a possible help to locate trouble, have a check at the four way rotary selector (mic/line) as the phase switches...

Clean all switches, clean insert jack, check all jumpers that set up the signal path, clean connector at the frame. This is the usual to do anyway, after that if issue still there, trace the signal in the path until it goes out of spec.

Best
Zam

Thanks for your reply Zam!

I live in a place where theres no tech to fix so I'm trying to do it by myself. I know that swapping components without understanding exactly whats going on its not the best solution. I'm newbie in this matter, my knowledge is very limited,  so I'm doing  what worked well with the rest of the channels. I'm starting to understand how desk works but I'm still far to fully understand it.  Replacing electrolytic and tantalum caps and some switches  fixed 95% of the issues of the mixer. 

The module had this issue before I worked on it. I thought it was something related to bad caps because I fixed a similar issue (it doesn't sound full, lacks of bass, lower level and a lot of noise compared to the rest of input channels) on other  channel just doing a  recap. But in this channel  after the recap  the issue persist. I've checked channel schematic and replaced components that I thought that could get wrong on the input and output amplifier (caps and transistors) of the circuit, because all the switches were cleaned, replaced the bad ones  and work now properly. 

Yesterday I modded an JLM 500 module extender card that works with the studer, but I'm no sure how to trace the path correctly or wich values are supposed to be the expected in every place.  I've got the skills to replace any component its needed but I lack the knowledge. I know that this is time consuming, but If anybody could help me and show me how to proceed or knows about someone that could,  please send me a pm (no free of course, we can come to an agreement).

thanks for you attention.

All best!

Joan.

 

[Shakusky]

You need to do an AC sweep and measure the output of each stage (preferably DC coupled so points with no DC bias) to verify it's working properly. In the simplest case this could be done with a sound card and some software that does an FFT or bode plot. Spectrum analysis is a critically important tool. I would never just blindly replace components. Many components are almost certainly just fine.

Thanks for your real squarewave!  I'll check how to proceed to do an AC sweep, its the first time i've heard about this. As I said before, I'm interested in learning how to deal with this mixer issues but I'm far to fully understand it. Tips like Zam or you have given me help me to improve my knowledge and fortunately get closer  to fix the issue. Thank you so much!

All the best!

Joan

 

[guy_4]

Hello,

If the problem is only on the Mic input, I would suspect a bad input transformer.
Along the years I have replaced several Mic and Line transformers  on these consoles.
The wire is very thin, and it breaks on the terminals, it is sometimes possible to fix it by resoldering.

Best,
Guy

 

[zamproject]

Hello

If the problem is only on the Mic input, I would suspect a bad input transformer.

Yes, I confirm that !
Fortunately easy to source.

Best
Zam

 

[Shakusky]

Thanks for your answer guys! I've checked and it looks like we've found the troublemaker! So I guess that I'll have to pick a neutrik ntm4.  I'll try to fix it first. Maybe i'll ask the dumbest question of the forum, doe anyone know how  to easy remove the transformer plate in order to access  the wires? Thank you  again for you answers, really appreciate it!

All best!

 

[zamproject]

I'll try to fix it first. Maybe i'll ask the dumbest question of the forum, doe anyone know how  to easy remove the transformer plate in order to access  the wires?

It don't come easy, I usually use a cutter blade to dissociate the upper part of the mu metal can, it's a mechanical tight fitting with glue addition (not always), you turn around gently, and at some point you'r able too pull off the part.
There is a thin spring blade that will probably go too, this is a connection from case to a pin don't loose it.
Then use magnifying glass to see which wire is broken (also check resistance with multimeter) and try to resolder it to the pin.
the plastic support melt over easy, be carefull !
Check again with multimeter to be sure the connection is here again.
If you succeed at this point, be careful when resoldering the trafo to the PCB, as the pin and plastic holder have been stressed
with the heat it's easy to unsolder what you just do... fast soldering requested here

From my experience (about 10 trafo replacement/repair) the ratio to resurrect them is around 1/3 or 1/4...
so good luck !!

best
Zam

 

[Whoops]

You can swap a transformer from a good channel to that one and see it that does the trick

If not build yourself an signal audio probe,
inject signal at the input (I like to use music) and follow/probe the schematic to listen when it becomes bad

Having a good channel next to it makes it pretty easy as you can inject the same sound in both channels inputs and probe it side by side, that way you can compare the behaviour of the bad one to the good one

 

[Shakusky]

It don't come easy, I usually use a cutter blade to dissociate the upper part of the mu metal can, it's a mechanical tight fitting with glue addition (not always), you turn around gently, and at some point you'r able too pull off the part.
There is a thin spring blade that will probably go too, this is a connection from case to a pin don't loose it.
Then use magnifying glass to see which wire is broken (also check resistance with multimeter) and try to resolder it to the pin.
the plastic support melt over easy, be carefull !
Check again with multimeter to be sure the connection is here again.
If you succeed at this point, be careful when resoldering the trafo to the PCB, as the pin and plastic holder have been stressed
with the heat it's easy to unsolder what you just do... fast soldering requested here

From my experience (about 10 trafo replacement/repair) the ratio to resurrect them is around 1/3 or 1/4...
so good luck !!

best
Zam

Thanks for the info Zam! I'll try to do the repair today today. Let's keep our fingers crossed. 

 

[Shakusky]

You can swap a transformer from a good channel to that one and see it that does the trick

If not build yourself an signal audio probe,
inject signal at the input (I like to use music) and follow/probe the schematic to listen when it becomes bad

Having a good channel next to it makes it pretty easy as you can inject the same sound in both channels inputs and probe it side by side, that way you can compare the behaviour of the bad one to the good one

Thanks Whoops! I'll follow your advice.

 

[zamproject]

Hello

You can swap a transformer from a good channel to that one and see it that does the trick

I would not recommand that, unsoldering and resoldering this neutrik trafo is an easy way for OP to kill a second one  :-\

Best
Zam

 

[Whoops]

Hello

I would not recommand that, unsoldering and resoldering this neutrik trafo is an easy way for OP to kill a second one  :-\

Best
Zam

Well,
I did that so many times and never damaged any transformer.
You  just need to de-solder it carefully, use a solder sucker pump

 

[Shakusky]

I think I'll play safe. I don't want to take the risk and break another input trafo becasue of my  clumsy hands.  I've seen how delicate this transformers can be trying to fix one  and  you need to be very precise. Maybe  in a couple of years I'll be more confident to do it.