Seventh Circle Audio

Soundwise, I am very happy with my two J 99 preamps.
However, using a Brauner Phantom C ,even with Gain set to 1 and trim on minimum,
I easily overdrive the soundcard ( RME 9632 , set to low input gain).
The mike doesnt have a -20 db pad.
Is this normal ?
I wanna be able to record a variety of signal including guitar amps and percussion....

That seems a bit crazy...... There shouldn't be very much gain at all when you turn the knobs all the way counter clockwise. How are you running the cables? Are you running a XLR to TRS cable out of the J99 and into the RME? Change your input ref level to +4 dBu. This should be correct for running balanced signals and it will probably fix your problem.

Look at the directions again and make sure you have he preamp jumpered for a 1/2.5 ratio aqnd not a 1/5 ratio. I think this could make the output too hot like you are experiencing.

Also, I second the above recommendation. Make sure you sound card is set to +4 and not -10 input level.

Shane

Ok, it took me couple of days to be able to look at it.
It is not the jumpers.
I have soldered both J1 jumpers into the board but only one has got a black cap (closed)
Thats at least how I understand it.
Should the jumper be closed without the cap (In that case I can see two separate pins ) then there would be a problem.
I have read somewere that the new powersupply Ps3 adjust to different voltages. ( I am here in Germany with 230 V ) If the powersupply is mismatched there would be smoke coming from the pres, I guess .

I followed the instructions in" initial power up and testing " and everything seems right.

What about putting down the trim potis R 28 and R32?
The soundcard is on low gain still.
That means my levels are too hot

From the J99 instructions

"J1 and J2 - These headers are used to select input impedance. Shorting both J1 and J2 selects a 1:5 step-up ratio, and a 250 ohm input impedance. Use this setting for very low output, low impedance microphones, such as ribbon mics. Shorting across J1 and J2 with a single jumper selects a 1:2.5 step-up ratio, and a 1000 ohm input impedance. Use this setting for most microphones. "

This is from the RME site

"* The HDSP 9632 ships in a basic version including two RCA/phono breakout cables (headphone: TRS jack). Therefore all analog I/Os and the SPDIF I/O are unbalanced. XLR breakout cables are available as an option (headphone: Neutrik TRS locking jack), turning analog and AES/EBU into balanced mode."

Did you get the extra balanced cables? ...or are you tring to interface some other way. Are you using external converters? If so, what is the input level on THOSE set to?

The J99s are hot, but not significantly hotter than most other preamps at minimum gain. With the dial all the way down you should get like 15db of gain. Unless you are double preamping, or recording a Jet engine up close I can't see why this would overload.

Have you tried recording to anything other than the DAW to narrow down the trouble?

Shane

I guess I have to contact Tim. The levels with I get when changing to all different 12 levels of the gain pot are simply far too funny....

It sounds like there are some resistor placement errors in the attenuator switching array. Check the values against the schematic to be sure some of them aren't in the wrong places.

I'm not sure what you mean "the soundcard is on low gain still." Can't you change that setting manually? I think you want to switch it to +4dBu. your soundcard is probably expecting a low gain signal, so it is boosting what you are sending it.

Or maybe you have some resistors or something in the wrong place.

@Reggie: My RME has three possible settings . Low gain means it gets the least amount of amplification before digital conversion. I can con firm that by switching between the three settings. But that is not the real problem.
I have written to Tim waiting for an answer.
here is what I wrote:
"Today , I checked again that all the resistors are with the right value in the right place.
Also, I did some test with recording a constant sound from a synth while I switched through all the 12 steps one channell after the other.
The results were really weird. I will give you the reading of the RME soundcard in db for all the 12 steps, starting from gain 1 through 12 :
channell 1: over means overload)
-37,-33,-28,-23,-18,-13,-8,over,over,-52,-47,-42
Now this looks like step number 10 is actually step 1 ( it has the lowest value)
channell2:
-16,-12,-7,over,over,over,-100,-100,-30,-26,-22
I repeated both measurements and ended up with same results.
A suspicion I had was that the stop pin of switch 2 is in the wrong place.
But both channells are also very different in their results.
I really hope you can help me to get this fixed!"

These result do not make me happy.
When I do not clip my soundcard , I get a very good soundquality.
So basically, the amp works but just these step poti is playing some tricks on me...

I've got questions:
- did you build these from kits?
- are you using a 7th Circle chassis and knobs? If you are, you can confirm that the stop pin is in the correct location visually.

It still looks like you may have the transformers jumpered differently, and/or you've got some problems in the resistor network on the switches. I'd examine it very carefully for the correct values on the resistors, and for any shorted pins on the switch.

Sounds to me like the most likely issue is a misplaced stop pin. Position one is only position 1 relative to the position of the stop pin.

Shane

Cat 5 - I agree, though I also notice a significant difference in levels on those two channels. If the input signal level was unchanged, it suggests something else might be different. The stop pin is an easy visual check with the 7th Circle front panel installed.

@teleplayer: Yes , I got 2x the full kit J99. Everything is SCA including the chassis.
@Category 5: Thats what I guessed myself.
last message from tele player: I didnt quite get how to check out if Cat 5 s guess is right or not.
tele_player said: The stop pin is an easy visual check with the 7th Circle front panel installed.
Could you explain more clearly?

I put a gold foil after inserting the stop pin. And I also thougt , if it will be possible at all to get the stop pin out , or I am better off to replace the switch alltogether.
Thanks so far for replying!

The visual check: when the stop pin is in the correct position, using the knob supplied with the kit, full counterclockwise should point to '1', and full clockwise should point to '12'. It's that simple.

Yes, you can get the stop pin out. The way I have used is to get some heavy duty 3m double sticky foam tape (used for permanent mounting - available at Wal Mart/Walgreens, etc.). remove the gold foil from over the pin, and press the foam tape over the hole and pull it off. You may have to do it a couple of times until it grabs the pin.

If the pin fits in too tight, you can remove the nuts from the back of the switch just enough to pull the layers aprt in the front and slide the pin out. I have done this as well. After you re-tighten the nuts on the switch back, it is a good idea to get some loc-tite thread-lock at a hardware store and secure the threads so the switch doesn't loosen up eventually.


To compare stop pin positions, turn both the properly working module and the messed up one fully to either extreme. Then, compare the knob positions. You may have to remove the plastic knobs depending on whether you properly aligned the lock screw with the flat part of the pole (unless the latest grayhills have no flat side - I have a couple of single deck grayhills from another project that don't).

Shane