SSL 9K Mic Pre

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Hmm, looks interesting! Nice find, bruno2000! Although I am concerned about this "no-name" brand. I'm passing audio through it (my whole mix, that is), plus I would not want it to break down after some (probably lots of) gain changes! I'm wondering whether it will fit on a 1U case without having to be laser-precise dead-centered. But it sure is an interesting option. Not sure if I need so many steps, though. Could probably do fine with 6 positions, and less effors (soldering) and less cost (resistors).

If it is a gain switch I wouldn't need 4 poles, could do with 2 switches with 2 poles each, as long as the resistances are identical, so will the gain be (for easy setting recall). The best solution would be some 2.2k / 2.5k quad-gang rev-log pot (I don't even think such thing exists), otherwise I will go for a pair of 2pole/6pos lorlins
 
you could use any switch you want. Don't get a 4 gang pot. It will work ok, but they generally are not well matched between gangs and your gain will not be identical. The chinese switch Bruno suggested will work fine if it is shorting. If not, you'll get pops every time you turn it. Quality-wise it should be OK. Many people have bought them for the PM670 and other projects.  You'd have to ask the seller if it is shorting. If it's not, you could get 2 of these:

http://www.banzaieffects.com/Rotary-Switch-2-level-2x1x12-pr-20274.html

Using two of these would give you the same exact stereo control (12 steps), you'd just have to turn two knobs instead of one. Use good 1% or 0.1% resistors and if you're super anal, hand-match them. Then, if you ever want to use these as mono pres, you have individual gain controls.

PS. I am.  Just got back from there 4 days ago.
 
Meh, it's going to be a dedicated summing mixer makeup gain. If I want a mono preamp I will build another one cause they're cheap as hell!!
I had an idea  :eek:

Can I use some 6position switches but have a minimum gain of 25dB and a max of 60dB? That way, I can still have 5dB steps (which is generally ok) but I don't need that many resistors. My summing mixer has 40dB loss anyway, so I won't need anything below 25dB or above 60dB. What do you think of that?
I'll need some time figuring out the resistor values, this whole 2-stage gain confuses me a bit..  ::)

PS: Nice, man! I live here. You chose the best time to return since it's pouring rain tha last few days or so, and the temp has gone down, like 8C. Anyway, nice knowing I'm not the only greek in this site!

Cheers! ;)
 
If you know the loss of your summing network (40dB from your previous post), forget the switch, build this preamp with just this amount of makeup gain and be done with it.  ;) YMMV.
This amp works in 2 stages with voltage gain setting network 1+((R73+R109)/(Ra+VR3a)) for the 1st.stage and 1+((R88+R115)/(Rb+VR3b)) for the 2nd.stage.
Making the 1st. stage +34dB (=voltage gain of 51.12), Ra will be a 42.72R (closest E96 value is 41 ohm) resistor and VR3a a wire link.
Making the 2nd. stage +6dB (=voltage gain of 2), Rb will be a 2K resistor and VR3b a wire link.
Good luck
-Harpo
 
Niiiceeee!!  ;D Extremely minimalistic! I like it as an idea, but I would like to have some kind of level control in case I ever mix without my GSSL (which would help with its makeup gain). It is a very nice thought and I might end with some 4-pole/3-position switch with minimal control like 30dB/40dB/50dB for both channels! What do you guys think of that?

Thanks for inspiring me Harpo!
BTW your gain switch resistor value calulator (excel file) rocks! You're the man!  ;D
 
OK, I think I may have come up with something:

I modified some values in Harpo's excel file.

Ra is now 127
Rb is now 127
VR3a is now 300
VR3b is now 300

That gives both stages 15dB minimum gain and 24,4dB maximum gain

I then set 3 step positions and the results were as follows

step gain a (dB) voltage gain Ra (total) "VR3a (var)single R" VR3a (var)adding series
0 15,092838 5,683840749 427,0         300,0                 198,6
1 19,786057 9,756697386 228,4         101,4                 101,4
2 24,479275 16,7480315         127,0           0,0                           0,0

gain b (dB) voltage gain                Rb (total) VR3b (var)single R VR3a (var)adding series     frontpanel dB
15,092838 5,683840749         427,0         300,0                         198,6                                   30,19
19,786057 9,756697386         228,4         101,4                         101,4                                   39,57
24,479275 16,7480315                 127,0         0,0                         0,0                                   48,96

Would that do the trick? Or am I missing something?
Of course, all this is good in theory but in practice I have no idea how to wire that thing.
Ra and Rb are on the board, right??
 
ummm,..., yes.
I'd do it a little different and calculate it backwards.
You want +40dB (really?) for makeup gain and optional +/- maybe 6dB, so steps are at 34dB, 40dB and 46dB.
The 2nd.stage has min.gain of +6dB for working stable, so 1st.stage could steady make up the most part of +28dB for less resistive noise and you vary the 2nd.stage for additional +6dB, +12dB or +18dB gain. Other advantage is, you only need a single pole switch.
+28dB is voltage gain of 25.119. The shunt arm resistor (sum of Ra+VR3a) is odd value 82.922644 ohm, so pick a 82R, giving a recalculated voltage gain of 25.39 or +28.09dB on paper.
2nd.stage shunt arm resistor (sum of Rb+VR3b) is 291.61R for +17.91dB. Pick a 294 ohm.
With an MBB switch the following series resistor for +11.91dB is 386.61R for shunt arm 680.61R. Pick a 383 ohm.
Last following series resistor with an MBB switch is 1376.52R for shunt arm 2053.52R. Pick a 1K37.
If you have a BBM switch instead, start with the largest value resistor and switch the needed value in parallel for the higher gain settings to prevent an open connection between steps while switching.

Ra and Rb are on the board, right??
Click to expand...
for usual - not.
The series resistor Ra+VR3a is wired in between the 2 holes marked "gain'A'" on pcb,
the series resistor Rb+VR3b is wired in between the 2 holes marked "gain'B'" on pcb.

From my previous blabla you have a 82 ohm resistor in between the 2 holes marked "gain'A'" on pcb.
The 2nd.stage switched shunt arm resistor is built by a 294R with one leg connected to the 1st.hole marked "gain'B'" on pcb, other side of this resistor goes to pin 3 of the MBB switch,
383R soldered between switch pin 2-3,
1K37 soldered between switch pin 1-2,
switch pole connects to the 2st.hole marked "gain'B'" on pcb.
Don't forget to place the end-stop washer at switch-pos.3 after turning your switch full ccw.
 
Harpo said:
ummm,..., yes.
I'd do it a little different and calculate it backwards.
You want +40dB (really?) for makeup gain and optional +/- maybe 6dB, so steps are at 34dB, 40dB and 46dB.
The 2nd.stage has min.gain of +6dB for working stable, so 1st.stage could steady make up the most part of +28dB for less resistive noise and you vary the 2nd.stage for additional +6dB, +12dB or +18dB gain. Other advantage is, you only need a single pole switch.
+28dB is voltage gain of 25.119. The shunt arm resistor (sum of Ra+VR3a) is odd value 82.922644 ohm, so pick a 82R, giving a recalculated voltage gain of 25.39 or +28.09dB on paper.
2nd.stage shunt arm resistor (sum of Rb+VR3b) is 291.61R for +17.91dB. Pick a 294 ohm.
With an MBB switch the following series resistor for +11.91dB is 386.61R for shunt arm 680.61R. Pick a 383 ohm.
Last following series resistor with an MBB switch is 1376.52R for shunt arm 2053.52R. Pick a 1K37.
If you have a BBM switch instead, start with the largest value resistor and switch the needed value in parallel for the higher gain settings to prevent an open connection between steps while switching.

Ra and Rb are on the board, right??
Click to expand...
for usual - not.
The series resistor Ra+VR3a is wired in between the 2 holes marked "gain'A'" on pcb,
the series resistor Rb+VR3b is wired in between the 2 holes marked "gain'B'" on pcb.

From my previous blabla you have a 82 ohm resistor in between the 2 holes marked "gain'A'" on pcb.
The 2nd.stage switched shunt arm resistor is built by a 294R with one leg connected to the 1st.hole marked "gain'B'" on pcb, other side of this resistor goes to pin 3 of the MBB switch,
383R soldered between switch pin 2-3,
1K37 soldered between switch pin 1-2,
switch pole connects to the 2st.hole marked "gain'B'" on pcb.
Don't forget to place the end-stop washer at switch-pos.3 after turning your switch full ccw.
Click to expand...

Perfect, easy to understand, real-world answer!
Way to go Harpo!
Well, while I'm at it, I might as well use a 2-pole 6-position switch (one pole for each channel!) and control both channels at the same time.
The three extra steps could come in handy for an extended range or smaller steps  ;)

Fool-proof explanation of the wiring, too...
Thanks a lot!
 
OK. Last questions before I buy the parts:

1) Is there any info on how can I add a meter on this thing? The obvious answer is "don't bother". OK, what about a clip indicator?? Can I implement something like this?

2) Should I connect a power LED to the 18V/15V rails? Would that cause any problems? (I read somewhere that it's not the best idea)
 
I added a signal/clip indicator to a pair of 500-format SSL9ks I built for a friend. I have to say it is quite nice to know if signal is coming in. The circuit I used is on the top left of the second page of this schematic: http://www.soundskulptor.com/pdf/mp12-schematic.pdf and I used a red/green LED with just two legs, which worked nicely. Connect the "VU in" to the unbalanced output of the ssl9k preamp card, in parallel to the balancing board.

A ten LED chain based on a LM3914/5/6 type circuit wouldn't cost much more in parts, but is a lot more hassle if you do your own case.
 
Thanks a lot for your answer!
Actually I decided not to implement any metering/clip indication, it seems a fair deal of hassle. In the end I think any clipping would be audible if nasty. Besides, I will be monitoring the levels from my sound interface's inputs.

Now, regarding that power led...  :-[ :-[

I can only find LEDs with Vf 2V max rating in the size and color I like (duh, orange OF COURSE!  :p :p)
How can I make this work? The circuit only has 18V/15V rails...  ??? ???
Could I use the spare PSU board to regulate it down to 2V?
Actually this is a lame thought, because if the PSU that powers the preamps dies, the LED will light up just fine (facepalm emoticons, please!)

How do these stuff work? (too unexperienced in DC voltage management, sorry)
Can anyone help? Some power indication really is necessary!
 
If I am not mistaken, most LEDs specify their internal resistance and or voltage drop. Put a resistor in series with said LED to create a voltage divider with the right voltage applied to the LED. Make sure you chose a resistor with the right power rating. If still in doubt, google "LED series resistor"  :D
 
Do you want to build an indicator for your supply voltages or a headlight?
Same question from you as in the gssl thread, just replace 12V by 18V for supply voltage. ;)
(18V - 2.4V) / 0.01A = 1560 ohm. A 1K5 resistor in series for 10mA LED forward current will be less blinding and 1/3W rating seems sufficient.
Harpo said:
ytsestef said:
I am unsure about (you're gonna laugh) the LED!!!
i mean, really. there are so many types and specifications. does it have to match the current and the voltage of the transformer output?
Click to expand...
Have a look at the schematic (in any case not the worst idea). The LED is not connected to the transformer but after rectifier and regulator, so it will see a predictibal DC voltage, +12V in this case, as it is connected between the output of a 12V regulator and 0V. The current flowing thru this LED is limited by a 1K resistor to not exceed the max. forward current If of this part. A red LED may have a If of 20mA or 30mA and a forward voltage Vf of typ. 2V. Brightness of this LED within limits is controlled by current and you probably don't want an eye blinding part on your frontpanel, so Jakob decided in his plan, a (12V - 2V)/1000 ohm = 0.01A = 10mA forward current for this LED could fit. If your plan shows a maybe blue LED, the value of this 1K resistor needs to be changed for this part, as blue LEDs come with maybe 3.5V forward voltage. Just pick a LED with colour and shape to match your plan and maybe tweak this 1K resistor to not exceed the parts limits. Ohms law will help.
Click to expand...
 
i am having a problem with radio interference with one of the ssl9k's i just built. it picks up a radio station at very high gains. the other channel doesn't seem to have this problem. any suggestions of what to look for?
 
outoftune said:
i am having a problem with radio interference with one of the ssl9k's i just built. it picks up a radio station at very high gains. the other channel doesn't seem to have this problem. any suggestions of what to look for?
Click to expand...
As you have 2 channels should'nt be to difficult to cross reference ?
check screens on gain pots.
 
thanks, i will have a look and compare with the other one.

should i be using shielded cable for the gain pots? right now i am just using single conductor wires
 
Hi All,

I have a little trouble finding where to connect the leads on the pcb from the gain pot.

I Know that B pot goes to R81 on the board, and Rb39 pot goes to R115 on the board.

The problem is that i don't see it clear for the A side.

Also i will use mono shielded wire and i don't know where to connect the shield and the signal.

I think B pot r81 is shield and Rb 39 is signal.

¿Can anyone help me?

Thank you very much.

JAY X
 

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