002r - line in 5-8 different than 1-4?

[chris h]

I just got an 002 rack, and I'm in the process of integrating it with my other equipment. The other equipment includes a 24 channel Soundtracs Topaz console and a Neutrik TT patchbay brought out to an ADC punch down panel.

I'm hooking up the tape outs of channels 1-8 of the Topaz to the line in of channels 1-8 on the 002 rack, via the patchbay. I'm making my own cables using Mogami 3080 cable and Neutrik connectors.

The console has unbalanced tape outputs, set up to run at +4, so I'm using TS connectors on that side, and TRS connectors on the 002 side. I'm wiring the cables according to the Topaz manual (and according to what I've used for "pseudo-balanced" cables): hot is connected to the tip on both ends, cold and screen are connected to the sleeve on the TS connector (Topaz), cold is connected to the ring on the TRS (002) connector, and the screen is lifted on the TRS connector.

When I plug a mic into the Topaz channel, the TS connector into the tape out of the Topaz channel and the TRS connector into inputs 5-8 of the 002 rack and set up an audio channel in Pro Tools to record, I get a great signal with very very low noise.

When I do the above, except plug the TRS into channels 1-4 of the 002 rack, I get a tremendous amount of noise that puts the meter on the channel in Pro Tools into the upper yellow, almost at red. The noise does not change by changing the input gain on the Topaz channel, however, the noise does change when changing the input gain of the 002 rack. The noise actually gets quieter as the knob moves from fully off to 12 o'clock, and then increases as the knob goes from 12 o'clock to fully on.

I've tried various troubleshooting techniques such as lifting the shield on the TS side and connecting the shield on both sides. The only thing that worked for me was to connect an unbalanced cable (single screened cable with TS connectors on both ends) from the Topaz to the 002. I could just wire it up this way, but I already bought a bunch of TRS connectors and was hoping to be able to use them.

What I'm really trying to figure out is why it works perfectly for inputs 5-8, and why it is so noisy for inputs 1-4. Its almost like 1-4 is set up for -10 instead of +4 (the manual states that 1-4 are set up internally for +4). If anyone has heard about any kind of problem like this or has any insight into this, I'd like to hear about it.

Sorry my first post is so long, but this is really starting to bother me!

Chris

[Obsidian Dragon]

Just to check, are inputs 5-8 set at +4 or -10? I have an 002 (not R) and there are switches for inputs 5-8.

[gerax]

I spotted something different than I do in you wiring scheme for the TS-TRS cables: usually (at least it's what I've been doing for years and never had any troubles) the hookup goes with hot on tip (both ends) cold and sleeve connected together on the TS end (going to the sleeve pin), cold on ring and sleeve connected on the TRS end; I think this is the right way to make an unbalanced/balanced cable; I've been doing my own cables this way and though you have a slight signal loss due to the unbalancing, I've never had any noise problem whatsoever, and I have my 002R hooked up to my patchbay just like that; I tested the connections and though there's some minor level difference from the I/O 1-4 to 5-8 (probably due to the fact that 1-4 have a preamp stage in them) everything is working OK; you may just give it a try, after all it's only a soldering hit away .

Hope this helps

L.G.

[JamesV]

I believe you will not bypass the preamps using line in on 1-4.

[Chris Cavell]

you bypass a gain stage of the pre

[chris h]

Thanks for the suggestions.

Obsidian Dragon - Yeah, the switches for 5-8 are set for +4, which matches the +4 output of the Topaz board. I get a nice low noise signal on those channels, but get a great deal of noise on 1-4, which leads me to believe that 1-4 are being totally overloaded for some reason.

gerax - I tried that configuration already, and still got the noise. There are actually many ways to wire up unbalanced to balanced cables, and lifting the shield is common to help reduce noise from ground loops. Some great info is included here: Rane website and here: Rane website #2.

JamesV - As Chris said, you do bypass a gain stage of the pre. Mic levels and line levels are at different voltages.

I'm wondering if maybe my 002 rack was somehow internally setup to have inputs 1-4 be at -10. I might have to take the 002 apart and see if I can spot any noticeable differences on the circuit boards between 1-4 and 5-8. I could also have a ground loop between the 002 rack and the Topaz board, but in theory that should cause noise on all channels.

I'm open to any and all suggestions to getting this fixed. If no one else has had or seen this problem, it might be time to call Digidesign and get the 002 rack looked at.

[Sacred Spirit]

If you look in the DigiOO2 'getting started' guide, appenix f, it shows the Line/Instrument as a TRS parallel to the Mic In XLR connector. These both go into the PreAmp Gain from there.

[Chris Cavell]

If you look in the DigiOO2 'getting started' guide, appenix f, it shows the Line/Instrument as a TRS parallel to the Mic In XLR connector. These both go into the PreAmp Gain from there.

My appendix F deals with OMS setup...but anyway, My appendix G seems to correspond to your appendix F. Keep in mind that this is a block diagram, not a technical schematic. They are completely isolated from each other by the line/mic switch. Phantom power is applied to the xlr input after the switch, so phantom cannot leak into the line input (it would if they were a true parallel). In addition to this, the switch also serves to bypass one of the preamp gainstages (there is more than one) when set to line/inst mode.

With this gain stage bypassed, the TRS line inputs on channels 1 through 4 should behave in very similar fashion to the line inputs on channels 5 through 8 if the gain trims are turned all the way down.

Chris H,

Did you purchase this patchbay used? Is it sharing any commons (busses, mults, or rails...or even a shared ground wire) across multiple connections on the inside? Is it wired internally so that it's half normalled, fully normalled, straight through, or no normal at all? Is it wired identically for each channel inside the patchbay?

If it works perfectly fine by using a quarter inch TS to TS cable directly b/w the mixer and 002, then the problem lies in the patchbay wiring. (a quarter inch TS to TS is the same as tying the ring to ground on a TRS to TS cable with this particular connection and the balancing circuit used in the 002)

Basically, I need more info on the patchbay, how it's wired internally, and how it's wired to the pushdown panel.

Cheers,
Chris

[ZiggY!!]

If you look at the spec's, inputs 5 through 8 have marginly better figures than inputs 1 through 4... it could be adding to what you are experiencing...

[chris h]

Chris,

The patchbay was purchased used. There is a jumper on each of the PCB's (the terminals that the wires are connected into in the back of the patchbay are spring loaded push terminals, and are soldered to a PCB. There is one PCB for the top row of terminals and one PCB for the bottom row.) The jumper is labeled chassis common ground (or something to that effect, I don't have the patch bay in front of me right now.) Neutrik's website does not have the manuals on it for their patch bays, so I don't know yet what the different jumper settings do. I'll have to take the patchbay apart more and follow the traces on the PCB.

The patchbay's front connectors come out and you can change the normalling there via a jumper. I have only hooked up channel 1 so far for testing and it is fully normalled. As far as I can tell from reading on Neutriks website, the first 2 channels have a green border around the TT cable inserts on the front, which corresponds to full normal, and the rest of the channels have no border, which corresponds to half normal. To be sure though, I'll have to pull each channel out seperately and see how they are set up.

The patchbay is wired the same internally for each channel. Each channel has a tip, ring and sleeve connector on the back push terminal, and they are wired to tip, ring and sleeve on the ADC push down panel. I wired my cables to the push down panel, connecting tip, ring and sleeve to the corresponding tip, ring and sleeve, and then terminated my cables according to my post above.

I see what your saying about the TS to TS cable, I was going under the impression that if channels 5-8 were fine through the patchbay, then channels 1-4 should also be fine through the patchbay (which logically makes sense.) Obviously, this assumption is NOT correct, and I need to do more testing. Tonight I'm gonna make a TS to TRS cable (using the same terminations as my above post) that will go from the mixer to the 002. If that causes me troubles also, then I can eliminate the patchbay as the source of the problem. If not, then I'll try another channel on the patchbay. I also need to talk to Soundtracs because I took my mixer apart to see if it had internally been jumpered for +4 operation (which it was), but I noticed that someone soldered a 100 kohm resister into the tape output circuit (the resistor is connected to the positive input of the op amp and the ground of the TS connector.) I think they were trying to make the output balanced, but it seems to me that more components are needed then just the single resistor. Hopefully the guy at Soundtracs can shed more light on this.

Thanks for your help and I'll let you know if bypassing the patchbay causes the noise or not.