SSL 9K Mic Pre

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Hi!,

Better news!. I discovered that my input path had reversed polarity. I corrected this, and noise figures improved a lot. :Fully ccw: -105dbfs, 1/4 turn : -100dbfs, 1/2 turn: -71,88 dbfs, 3/4 turn: -55,85 dbfs, fully cw: -36,76dbfs. With the c5 mic attached.
So, it was a phase problem... And in all mic preamps the last quarter turn is the noisiest, in this case, exacerbated by the high self noise of the akg c5. I hope to be in the right track...;)

Jay x
 
Hi!.
On page 35 of this thread, it is said that to avoid gain pot scratchiness, resistors R105/R69, must be matched, and also resistors R109/R73. Each two resistors of each gain stage. But it is not clear if both gain stages have to be the same exact value. So, 4 1002R resistors, or 2 1002R in the first stage, and say, 2 1004R, in the second stage...?

Jay x
 
Hi!,

I matched the four 1k resistors to the same value (1003R), and this helped a bit, but not much reducing scratchiness. The first half turn of the gain pot (up to 12 o'clock), is quite silent. From there to 3/4 turn it starts to become noisier till the end.
 
I had this problem on one of my builds, and couldn't find the problem. It's still in the project box if and when anyone does figure out what's causing this.

I know on some other types of builds scratchy pots is usually a sign of DC leakage. Tube guitar amps for example where a leaky cap is allowing some of the B+ through.
 
As the 9k gain pot is wired as a rheostat, I remember have seen a THAT 1512 schematic, where they placed an electrolytic cap in series with RG. ¿May this be a solution?
 
Hi!,

Is there a way to add a DI input, maybe changing the input impedance??. Because i would like to have the sound of the preamp for the instrument input. Otherwise, i know the only way to add a DI input is with a fet amplifier...🤔
 
Hi!,

Is there a way to add a DI input, maybe changing the input impedance??.🤔

I bulit a few of this mic pres in the past and read all the thread pages back them.
The only I've seen people adding a DI input to this project is using a JLM Go Between and then the JLM DI module, I have not seen it done any other way:

https://www.jlmaudio.com/shop/fet-di.html?display_tax_prices=1
The JLM has a FET input and that's actually to change the input impedance (much higher) and buffering the signal, then it goes from there straight into the mic input of the preamp so you will have the sound of the complete circuit.

So that's what I recommend
 
Hi!,

Is there a way to add a DI input, maybe changing the input impedance??. Because i would like to have the sound of the preamp for the instrument input. Otherwise, i know the only way to add a DI input is with a fet amplifier...🤔
I built a bunch of Bo Hansen DI's because it's always a good idea to have some DI boxes kicking around. They'll work with every mic preamp out there that has phantom.
 
Hi! Ok Thank you Whoops!


I have a question about the input impedance of the 9k5 preamp. It is all about the PAD circuit i think....

With the PAD switched OUT ¿What impedance see a Dynamic or condenser microphone? 10k8 at each side (+IN & -IN)??...
With the PAD switched IN, I understand that any mic will see the two 10k8 and one 2k2 resistor across +IN & -IN.. ¿Right?

To make a condenser or dynamic microphone see a suitable impedance (around 1000-1300R) should i activate the PAD always?

Thank you for your help!!

Jay x
 
You're asking in the wrong thread, this thread is for the first SSL 9K project, the pcb's were sold by Gustav and it was not for the 500 series

much later on there was a the SSL 9K5 project, for the 500 series, and there is a thread dedicated to that specific project, that's were you should post, I guess you will have much better luck there

this is the correct one:
https://groupdiy.com/threads/ssl-9k-4k-e-series-500-51x-new-boards-mic-pre-thread-2011.42552/
Have fun
 
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