The official G9 help thread

[ramshackles]

Hmm...I was testing it by plugging into wall strip, which has other things plugged in. Perhaps this can be a problem? I'll find a direct socket and go in there.

All Pin 1's together. Does this mean that pin 1 on the input XLR's should not be connected to the input ground pad on the PCB? Or that it should ALSO be connected to pin 1 on the output XLR's?

 

[ramshackles]

I get about 40V AC between the chassis and the XLR cable, but only when the XLR cable is plugged in at the other end (to the audio interface)....could this be like the problem you have mentioned about ungrounded computer?

 

[bruce0]

It bears mentioning that the G9 when operating correctly has voltages inside that can EASILY kill you (both B+ and Phantom).

One troubleshooting approach, at your own risk would be:

You could plug in both interface and G9, but not connect them.
Then:

Measure DC and AC voltage between the two different cases.
Measure DC and AC voltage between each case and the mains ground (safety ground)

All of these values should be near 0V.


I sounds to me like you have a grounding problem in the new case because the Shock on pulling an xlr means that either the case of the XLR or the case of the G9 is not at ground potential  (because I assume if you had shocking values in your interface you would have noticed it at some time before.

We have not seen pictures of the unit and it's guts, is it possible that the well painted unit (I have seen a well painted screw hole become an insulator between panels) has poor ground between it's different panels (for instance, that the star ground is not bolted to the same panel that the XLR's are, and that you are depending upon the panel attachement screws for grounding?).

 

[ramshackles]

The chassis is not painted, apart from engravings. Just raw aluminium 3U case from schroff.

chassis connection has it's own dedicated bolt through the back panel. This is connected to IEC connector ground (power) and pin 1 of the xlrs.
The problem of a live XLR cable went away when I used a different power socket for G9.
It is now plugged into the same  rackmounted power strip as the audio interface and there is no problem.

Plugging it into a different power strip meant there was a voltage between the G9 chassis and the xlr cable connected to the audio interface...??

So that problem is...half resolved?

I discovered 2 other problems
1. The level of the instrument input is very low
2. From gain positions 9-11 there is just a very loud hum/buzz/oscillation type noise. I've read about problems with oscillation in the OEP transformers, although mine are in screening cans. I'll check through the thread to try and get further knowledge.
There isn't much scope for moving the power transformers around in the box as it is not very deep, but maybe some kid of screening around them would improve things? Wire mesh or mu-metal or something?

I'll try to get some pics.

 

[gemini86]

The oscillation is not caused by the transformers so much as the unshielded, high impedance pcb traces that the signal goes through to route to and from the DI Jack. Search for DI mod to remedy this.

 

[MeToo2]

The chassis is not painted, apart from engravings. Just raw aluminium 3U case from schroff.

chassis connection has it's own dedicated bolt through the back panel. This is connected to IEC connector ground (power) and pin 1 of the xlrs.
The problem of a live XLR cable went away when I used a different power socket for G9.
It is now plugged into the same  rackmounted power strip as the audio interface and there is no problem.

Plugging it into a different power strip meant there was a voltage between the G9 chassis and the xlr cable connected to the audio interface...??

So that problem is...half resolved?

I discovered 2 other problems
1. The level of the instrument input is very low
2. From gain positions 9-11 there is just a very loud hum/buzz/oscillation type noise. I've read about problems with oscillation in the OEP transformers, although mine are in screening cans. I'll check through the thread to try and get further knowledge.
There isn't much scope for moving the power transformers around in the box as it is not very deep, but maybe some kid of screening around them would improve things? Wire mesh or mu-metal or something?

I'll try to get some pics.

re Oscillation: Oscillation is different from hum. Hum is generally 50Hz and related to stray magnetic fields and currents.
Oscillation is generally of the MHz range (although it can have audio artifacts at much lower frequencies in the audio band)

Have you done the track cutting mod on wiring the DI input? Mine oscillated too at high gains before doing the mod (OEP in screening cans)
See http://www.gyraf.dk/gy_pd/g9/G9-EDIT.GIF

Otherwise look for parasitic capacitances in your cabling that could be feeding signal back into the grid, which is very high impedance.

Re Shock: Have you also connected chassis ground to "GND/0V" of your power supply (at one point only)?

Are you on a 3 phase mains supply? If so, you may have equipment connected on different phases, that you are then connecting together via the audio path.  And the differences between phases in the UK is 415V differential voltage, not 240V, which may be another source of problems, although that would be unusual. Be careful. A shock that you can feel is certainly not normal.

 

[Jamie1234]

Hello everyone. This is my first post here.

I'm just about to make a start on my g9 and I've realised the pcb I got from pcbgrinder is rev#1 from 2002.

I see on the gyraf site that the PCB is now up to rev#5. Am I ok to use rev#1? Has anything changed since then that I should know about before soldering everything to the board (component changes etc)?

I plan to make the shielded wire mod from the start as it will be easier to cut the traces etc before I populate the board.

I'm fairly new to this stuff so sorry in advance for the string of stupid questions I'll probably be asking in the next few weeks! (I'm doing a g9, a gssl and 2 g116s - one with the transformer input..) Quite possibly biting off more than I can chew.

thanks

 

[gemini86]

Thats quite the workload you're taking on.

I don't know about the various rev #'s the G9 went through. I don't think there were any large changes.

Patience is key here, so stay strong, friend.

 

[gyraf]

..the pcbgrinder version is the current one..

(and actually I don't remember any revisions - look at the bottom of the gyraf-g9-diy-page for revision history)

Jakob E.

 

[Jamie1234]

Thanks, I'd somehow confused myself there..

Got all my metalwork done this morning so I'm sure I'll be back soon when it comes to wiring it all up!

 

[pearldrum944]

Does anyone know who is still selling G9 front panels/racks?

Don Audio seems crazy expensive, $210usd just for a front panel.

I emailed NRG but they are closed until the 22nd.

Thanks!

 

[gareth33]

www.diy-racked.com

Just got my G9 in, looks great, good price and quick delivery.

 

[pearldrum944]

www.diy-racked.com

Just got my G9 in, looks great, good price and quick delivery.

Not a bad price for the rack, shipping to the US hurts though.  Thanks for the link, this is the head-runner currently.

 

[gemini86]

hmmm... still have a sore spot when it comes to Tat Parusha.

 

[pearldrum944]

hmmm... still have a sore spot when it comes to Tat Parusha.

Sore spot...  Details?  (feel free to PM if needed)

 

[gemini86]

I don't want to dig up the hatchet... so I'll PM you.

 

[gareth33]

Hi everyone

I am in the final phase of wiring up and mounting the G9 in it's case. I have a question related to the instrument jack which I am not so sure about. I bought this jack

Farnell part no: 4169232 Neutrik: NMJ6HC-S

It has 6 terminals in all, or 3 pairs that are connected. Could anyone please advise on how to wire this up and whether this is a switching jack. I have cut the traces for the DI mod, so I am looking for the pinout for 'from jack' 'to jack' and  'shield/0V' according to the mod data.

Thanks in advance

Gareth

 

[gemini86]

Yes, it is a switching TRS jack. One side will contact the plug when it is inserted, the other side will become disconnected when a plug is inserted. Insert a plug into it and it's easy to see which side is which. The tip contact (furthest from the mounting nut) will be wired to V1's grid via C2. The other side of the tip contact (the one that becomes disconnected when a plug is inserted) will be wired to the input transformer's secondary winding. Then the sleeve contact (closest to the mounting nut) is wired to ground.

this arrangement allows the signal to flow: input transformer>jack>C2>V1 grid

When you insert a plug into the jack, the input transformer is disconnected and signal flows: instrument cable>C2>V1 Grid.

Hope that makes sense.

 

[gareth33]

Thanks very much, yes, that is very clear, I didn't notice the contacts break as I plugged in the jack :

I thought I would have this all wired up and ready to test tonight, but with countersinking holes and the DI mod there are still odd bits and wiring up to do, but tomorrow life to the G9!

Nice one...

Gareth

 

[gareth33]

Hi all

I'm back with another question, I've read through most this thread and searched but the information seems to allude me when I need it.

I've done the DI mod, I understand that the DI jack is wired now directly to the main PCB via the shielded cable, so the 5 pin molex connector next to the 10 pin on main PCB is now redundant? Or should I connect the two remaining pins to the control PCB?

Many thanks, any advice is greatly appreciated..

Gareth