SSL 9K & 4K (E Series) 500 / 51X NEW BOARDS Mic Pre Thread 2011

[TillM]

Some folks that are building these have asked about the HPF setup, so here goes.  It's the same for the 9K and 4K boards.
R226 adjusts the "knee" of the HPF.  Start with R226 fully counter clockwise, the frequency control fully clockwise, and the HPF engaged.  Then send a swept tone through the unit from 20 Hz to 5k Hz, and observe a significant "bump" in response just before it takes a dive at around 400 Hz.  Adjust R226 to eliminate this "bump" so that the frequency response is flat until the HPF takes over.
R3 adjusts the overall gain of the HPF section.  Send a 5k Hz tone through the unit.  Adjust R3 so that the output signal level is the same with the HPF in or out.
Enjoy!
Bruno2000

This it how it works.

 

[Ricardus]

This it how it works.

That explains the calibration of the HPF when it's working correctly, yes? Which I was aware of.

But in my case, when you engage the filter it just starts generating a waveform at maximum output gain.

You're telling me that's how it's supposed to work??

 

[TillM]

Yes and this happens, because you don’t have calibrate the filter section.
If you don’t calibrate the filter section, then it starts to oscillate.

 

[Majestic12]

That explains the calibration of the HPF when it's working correctly, yes? Which I was aware of.

But in my case, when you engage the filter it just starts generating a waveform at maximum output gain.

You're telling me that's how it's supposed to work??

The HPF has a resonance bump that can be very high and go into self-oscillation. Just turn down the adjustment trimmer and the oscillation should go away. You still need some sort of analyzer or similar to adjust it correctly though.

 

[Ricardus]

The HPF has a resonance bump that can be very high and go into self-oscillation. Just turn down the adjustment trimmer and the oscillation should go away. You still need some sort of analyzer or similar to adjust it correctly though.

Right. I see that now. I didn't see it anywhere else in the thread. I mighta missed it.

 

[Ricardus]

So instead of the two 1/3rd watt 10 ohm fusing resistors, would it be possible to use two of something like these in their place?

No idea what value, though.

https://www.mouser.com/ProductDetail/650-RXEF075

 

[TillM]

Absolutely !
Take some 1/4w or 0,6w or whatever you want.

 

[Ricardus]

I looked up the typical current draw per slot on 500 series stuff, and most makers supply about 250 mA per slot. Some modules more draw a little more, some a little less. So I would think  a 300 mA fuse would be fine. It will hold 300 mA all day, but trip at 600 mA.

 

[TillM]

I mean, that you can just use a normal resistor. You don’t have to take a fuse.

 

[Ricardus]

I mean, that you can just use a normal resistor. You don’t have to take a fuse.

If you use those fuses you won't have to be replacing those fusing resistors when something happens though. The DIY Recording CP5s I just built use them on the power rails so it seems like a good option.

 

[Ricardus]

First SSL 9K is finally done.

 

[Piotr]

Hi !
I built two a while ago and I remember there was an issue with the default polarity of the output signal being inverted. Check it. If I'm not mistaken , the pol switch should be in active (led on) position so that pol in is pol out.
Good job ! Good sounding press, Schaeffer frontpanel ?
Regards !

 

[Ricardus]

Hi !
I built two a while ago and I remember there was an issue with the default polarity of the output signal being inverted. Check it. If I'm not mistaken , the pol switch should be in active (led on) position so that pol in is pol out.
Good job ! Good sounding press, Schaeffer frontpanel ?
Regards !

The panel is from Frank Rollen.

I thought they fixed the polarity issue in the latest revs of the board. At least I hope they did.

 

[Ricardus]

Hi !
I built two a while ago and I remember there was an issue with the default polarity of the output signal being inverted. Check it.
Regards !

I just checked it. Pin 8 of the That preamp chip goes to pin 2 of the edge connector, which is correct.

 

[Ricardus]

I brought some of my 500 series stuff to a live sound gig tonight and used this 9K preamp on lead vocals. Really good woman singer. Sounded gigantic. Really happy with this thing. Can't wait to build more!

 

[Ricardus]

Just ordered more of these boards. Woot!

 

[Whoops]

The panel is from Frank Rollen.

Who is Frank Rollen?
Can you provide a link?

thanks

 

[Ricardus]

Who is Frank Rollen?
Can you provide a link?

I know he's on here, but I don't recall if he uses that name or another. This is his site:

https://www.frontpanels.de/

 

[Ricardus]

Just an FYI. CAPI is now stocking AS194s. He just got them in. They'll be on his site soon.

AS194's (as I understand it) are equivalents for LM194s, which are mil-spec versions of the LM394s.

I wish he had these a few months ago when I started this journey! I ended up finding LM394s at surplus houses, and AS394s elsewhere.

 

[Ricardus]

Finished my 2nd one of these. I did something fekkin stupid and ended up frying the 1646 on it, and had to replace that. But just calibrated it a couple hours ago. Sounds as great as the first one. Got more boards on order to make more!