SSL 9K Mic Pre

[chefducuisine]

darkcharly,

from your description i am assuming you are using the LM394 in a 6 Pin metal case.
Please keep in mind that the SSL9k is a differential amp (check Google for the Cohen design).

As a first step please check if a signal appears on pin 6 of IC 29 and IC 22 together with the gain set to the mid position of the switch and a 1kHz sine applied at the input. In a second step try moving the gain switch around to see if the amplification changes.
If you want to exclude your gain switch from the equation simply replace the switch by adding a resistor instead of the switch - something in the 1kilohm region should be enough. You will need two resistors to replace both decks of one switch.

If this works apply the same procedure on pin 6 of IC 30 and IC 23.

It is always a good idea to check the solder joints. Visually and by using an Ohm-Meter.

 

[chefducuisine]

Emptymusicbox1

there is no better - the MAT-02 has been used in the original 9K pre. The MAT-12 is the sucessor.
Both can be used and will produce good results. Why not build two???
The last four digits indicate the year and calender week of manufacturing.

 

[darkcharly]

Hello!
Following the advice of chefducuisine, I tried the circuit 9k inserting an audio signal, and testing the circuit with an audio probe (listening to the audio signal through the circuit). The signal stops at pins 1 and 6 of the LM394 (Collector of each transistor). The LM394 is malfunctioning?
Thank you!

Is the voltage for the IC right? Checked soldering?

G-Sun
I check and re-check for bad solder. Check also my voltage rails and become +18 and-18V to 5534, and +15 and -15 to TL052.

 

[darkcharly]

darkcharly,

from your description i am assuming you are using the LM394 in a 6 Pin metal case.
Please keep in mind that the SSL9k is a differential amp (check Google for the Cohen design).

As a first step please check if a signal appears on pin 6 of IC 29 and IC 22 together with the gain set to the mid position of the switch and a 1kHz sine applied at the input. In a second step try moving the gain switch around to see if the amplification changes.
If you want to exclude your gain switch from the equation simply replace the switch by adding a resistor instead of the switch - something in the 1kilohm region should be enough. You will need two resistors to replace both decks of one switch.

If this works apply the same procedure on pin 6 of IC 30 and IC 23.

It is always a good idea to check the solder joints. Visually and by using an Ohm-Meter.

Chefducuisine:
Yes, I'm using the LM394H (Metal Can). I'll check voltage on pins you have indicated me. First the switch and secondly, I will replace the switch for shorts (giving me highest gain with Ra and Rb placed. It right?) and also will check signal.
Then I'll post the results.
Thanks for the support.
Cheers

 

[darkcharly]

Well, here reporting back !
First I test the voltage to the ICs mentioned above. Here are the results :
IC22 : pin 4 pin 7 = -16.50 v = 17.70 v
IC29 : pin 4 pin 7 = -16.50 v = 17.70 v
IC23 : pin 4 pin 7 = -18.14 v = 18.15 v
IC30 : pin 4 pin 7 = -18.14 v = 18.15 v
With the switch connected to the circuit (6 positions total , now in the third position ) put a 1khz signal and check with my audio probe .
Testing the pin 6 of IC22 and IC29 , only hear very low signal .
Testing on pin 6 of IC23 and IC30 , the signal sounds ok!
With the switch in sixth position , IC22 and IC29 are unchanged ( very low signal) . In contrast, the IC23 and IC30 , increased the volume of the signal.

Now I pulled the switch. I placed the Ra , Rb resistors in place of the switch.
I sent the signal and checked the following ( always testing the pin 6 of ICs) :
The ICs 22 and 29 the signal is very low. The ICs 23 and 30 the signal sounds good.
What is wrong? Should I try to exchange the 5534s ?
I'm a little lost ... :-[

 

[chefducuisine]

Good - this means you are getting signal through the first two stages of the pre.

Now I pulled the switch. I placed the Ra , Rb resistors in place of the switch.

By doing this you have set the pre to it's maximum gain (highest amplification). Leave it at this setting for now.
Do not change the 5534 yet!

Next step is checking the ouptut stage and the servos:
- IC24 is the output stage, the output is - you guessed it - on pin 6. Check for signal.
- IC31a/U32b is a TL052 according to the shematic. You already measured the voltages around it (+/-15 V). Good.

Please check all connections around the TL052 - the pre behaves very 'funny' when there is an error around the servos.
Also check that you installed all capacitors that are needed for stability: C46, C47, C74 (3,3pF ceramic) and C48 10 pF.
This ensures that none of the OpAmps starts to oscillate.

Did you add the balancer board (DRV134)???
Did you twist the In/Out wires?

 

[darkcharly]

Good - this means you are getting signal through the first two stages of the pre.

Now I pulled the switch. I placed the Ra , Rb resistors in place of the switch.

By doing this you have set the pre to it's maximum gain (highest amplification). Leave it at this setting for now.
Do not change the 5534 yet!

Next step is checking the ouptut stage and the servos:
- IC24 is the output stage, the output is - you guessed it - on pin 6. Check for signal.
- IC31a/U32b is a TL052 according to the shematic. You already measured the voltages around it (+/-15 V). Good.

Please check all connections around the TL052 - the pre behaves very 'funny' when there is an error around the servos.
Also check that you installed all capacitors that are needed for stability: C46, C47, C74 (3,3pF ceramic) and C48 10 pF.
This ensures that none of the OpAmps starts to oscillate.

Did you add the balancer board (DRV134)???
Did you twist the In/Out wires?

Hey Chef!
As you said, I check the ouptut stage and the servos. The pin 6 of IC24 has good signal.
The solders around the TL052 are ok. Ceramic capacitors are also right.
I placed the balanced board (ssm2142) and check signal. Yeeees! I got the signal!
Now, I'll try the other channel of balanced board, and the gain switch.
Do you think you should now test my circuit with a dynamic microphone?
Thanks for the support!

 

[chefducuisine]

Congrats!!!

I see no problem in testing the circuit now with a dynamic mic.
Is the balancer board working? Or don't you need it?

 

[darkcharly]

Congrats!!!

I see no problem in testing the circuit now with a dynamic mic.
Is the balancer board working? Or don't you need it?

Hey!!!
The balanced board, works fine but...
There's something weird / wrong. When I put the test signal in the circuit, I hear perfectly on output. The gain switch also does his work properly. But when I plug in a dynamic mic (SM58) no sound. I checked the mic, cable and XLR connections (Pin1 = Grd, Pin 2 = positive, Pin 3 = negative) but no sound. I understand that the sound goes through the preamp. But why not the microphone signal?
Apologies! I must be doing something wrong ... but I do not know that ... :'(

 

[chefducuisine]

What was the voltage you sent to the pre before connecting the microphone?
The output of an SM58 is fairly low. But the Pramp should hanlde this.
Please check that the signal you inject is in a similar range.

At the moment I think you are shortening the input in some way when connecting the mic.

 

[darkcharly]

What was the voltage you sent to the pre before connecting the microphone?
The output of an SM58 is fairly low. But the Pramp should hanlde this.
Please check that the signal you inject is in a similar range.

At the moment I think you are shortening the input in some way when connecting the mic.

I checked for shorts, but everything is fine.  ???
I used a 1kHz tone at 0db (Sound Forge) through my sound card. I measure the voltage at the output. What is the range of a microphone as the sm58?
At this time, I hear my voice through the sm58 very low, with interference. When I touch the switch contacts, the garbage down a little. Any suggestions on how to connect the ground?
Again, thank you very much!

 

[chefducuisine]

0 dB in Soundforge doesn't tell anything as this is the digital level (0dBFS).
It depends on your hardware (soundcard) to what this 0dBFS is related in the analog domain.
However, this is way to much - difinitely more than the output of a dynamic mic.

The output of the Beta 58A is specified as:
Open Circuit Voltage: -51.5 dBV/Pa* (2.6 mV) *1 Pa = 94 dB SPL
e.g. in the lower mV Range, depending on the sound pressure level

In a previous reply you said there are changes when moving the gain switch. Is this still true?

Your question on how to connect the groud confuses me.
Can you please dicribe how ground is connected on your Pre. The circuit (COM) should be connected to ground when operated.
Can you please provide some pictures of the circuit as it is difficult to help with just a desciption.

 

[darkcharly]

0 dB in Soundforge doesn't tell anything as this is the digital level (0dBFS).
It depends on your hardware (soundcard) to what this 0dBFS is related in the analog domain.
However, this is way to much - difinitely more than the output of a dynamic mic.

The output of the Beta 58A is specified as:
Open Circuit Voltage: -51.5 dBV/Pa* (2.6 mV) *1 Pa = 94 dB SPL
e.g. in the lower mV Range, depending on the sound pressure level

In a previous reply you said there are changes when moving the gain switch. Is this still true?

Your question on how to connect the groud confuses me.
Can you please dicribe how ground is connected on your Pre. The circuit (COM) should be connected to ground when operated.
Can you please provide some pictures of the circuit as it is difficult to help with just a desciption.

Hey Chef!
I took a few days to rest. Back to SSL, I decided to check the second board. Moved the ICs, gain switch, and the inputs and outputs. I used the same PSU.
I connected everything, I checked voltage and ... voila! It works perfectly!
So now I have a channel that works, I'll use it as a reference to fix the other.
My question about the connection of land meant that found post, in which say connecting all to the mains ground and others suggesting separate audio ground of mains ground.
I will keep working to find the error in my channel. When I find out, I'll post here.
Probably my next project is to design your own SSL
Thank you very much for your support!
Cheers!

 

[critterkllr]

Could somebody help me figure out how to change the input impedance on the 9K pre? I've attached the original schematics for the 9k preamp. The original has a Hi-Z switch. It is located on the lower left corner of the schematic and is SW47.

I'm not quite understanding it. It looks like in one position the switch puts a 2k28 (R102) resistor in between the positive and negative inputs and sends TRZ to ground.

The other switch position removes the 2k28 resistor and sends +5V through a 4K7 (RP16) resistor to TRZ.

What is TRZ?

How would I figure out how to make the DIY SSL 9K have a 10k ohm input impedance? Whether its switchable, variable or just modifying the existing circuit.

 

[chefducuisine]

I am not shure what you are trying to accopmlish.
The HiZ Switch is for allowing the Mic input of the console to accept line levels.
If this is what you need then the 2k28 resistor between + and - does the trick.
The second deck of the switch is for switching the LED on (5V via an 4k7 Resistor). TRZ is the connection for the corresponding LED. Check the numbering on the switch. When the 2k28 resistor is switched in, the LED connected to TRZ will light up (HiZ 'On').

The same is true for TRP - this is the indicator LED for when the -20db Pad (SW48) is pressed.

Please remember that this is a symmetrical input (Cohen type) pre. Google 'symmetrical pad' to get a hint... 

 

[critterkllr]

Wouldn't that be the line pad (SW48) that you're referring to? The Hi-Z switch can be used regardless of if it's mic or line level correct?

So, TRZ is just an LED. That helps! Basically, the Hi-Z switch just adds a 2k28 resistor in between the positive and negative inputs then? I'm wondering how to calculate how much resistance would be needed to find a specific input impedance.

This preamp will mostly be used with a ribbon mic. I'd like to hear what the difference in input impedance would be for the microphone. I've used other pres with input impedance switches and the higher the impedance, the better the mic sounds to me.

 

[chefducuisine]

Check the manual here:
http://students.expression.edu/files/2009/10/SSL9kJ_Console_Manual_Pt_1.pdf

The HiZ switch of the SSL is not what you are expecting.
Typically the input impedance should be variable in the 200 Ohms to 1kOhms range to do this.

I have never been an fan of a variable impedance on solid state pres as to me this is just another feature for the marketing department.
Basically you a creating a 'resistance dominated' mismatch between mic out and pre input which will add just a nuance of an effect on the highs by applying a slight damping.

To me the concept is only interesting for mic pres with trafo-coupled inputs ideally with coils that are  switched in and out to change the impedance and this has an effect on more parameters of the pre than just resistance...Ymmv...

 

[tomas1808]

I am having doubts about the pot shielding thingy.  Can somebody help me out? I made a bunch of questions in another thread:

http://groupdiy.com/index.php?topic=61367.msg777201#msg777201

Thankss

 

[EmptyMusicBox1]

hello SSL9K DIYers !!!

I have a question about to add a Input transfo on my SSL9K preamp !

i have bought a NTM1 Professional studio transformer 1:1 (Mic input) : 
http://www.neutrik.com/en/accessories/transformers/ntm1

But i don't know how i can integrate it on my project... because when i use a LINE level on the Input i think the transfo make distortion no ?

I have a JLM go between for a phase/48v and PAD maybe i can add the transfo after the 20db PAD when i use a LINE input ?
it's correct ?
How i can wire the ground pin ?

If i want to add an tranfo on the input i need to add an other on the Line OUT of the SSL9K for a perfect ground isolation !
i have bought the NTL1 :
http://www.neutrik.com/en/accessories/transformers/ntl1

I think i can add it directly after the Output for have a Balance OUTPUT but how i can wire it for do that correctly ?

thanks for your help

 

[G-Sun]

Personally I'd not use a transformer.
But, if you're determined on that route, I guess either pre or post the gobetween.
But I'm no expert.
Edit: It will block phantom if pre, so I guess post is right.