The official G9 help thread

Normally I'd say you'll need a 15V transformer for the DC heaters to work, but since they're so big, you may see that they output closer to 15VAC which will work fine. I say, try it. If it doesn't work, get new ones!

Hello, I am realizing my G9 and I have a doubt around the power supply transformers.
Considering that the first one must be 220v:15+15v (30ma) I am not sure for the second one.
Is it better a 220v:12+12v or a 220v:15+15v?
I am sure that this is not a new question, but I have not found a reply (using the search function)

How about looking at the schematic.

Fablab said:

Hello, I am realizing my G9 and I have a doubt around the power supply transformers.
Considering that the first one must be 220v:15+15v (30ma) I am not sure for the second one.
Is it better a 220v:12+12v or a 220v:15+15v?
I am sure that this is not a new question, but I have not found a reply (using the search function)

Click to expand...

220:12 is better for the second.

Thank you!

Building a G9 for first time. It's seems like it's highly suggested that the HT Supply
be moved off board to stop any hum. Could someone post pictures or drawings of this mod?
showing;
The main board without the moved componets,
The breadboard onboard wiring
The wiring of the breadboard to main board.
Any help is appreciated.

It's seems like it's highly suggested that the HT Supply be moved off board to stop any hum.

Click to expand...

Not really. Imo, it is a rare problem, just one that is often tried solved by asking in this thread.

I have built quite a few G9's in the diy version - and helped tune/setup many also, and have never yet had to move the psu off-board to get it quiet.

On the other hand, the circuit will be MUCH more forgiving about small circuit and wiring errors if the psu is somewhere else - so it's an easy solution if you have a persisting hum problem in your build.

Jakob E.

So i just finished my unit, which looks gorgeous in my opinion.
Le moment supreme, powering it up didn't go so well...
I heard a sound which can probably be best described as rattling, coming from my psu.
Then i heard a tiny tiny explosion coming from my 78s12. After some inspection it turned out be Diode D13 1N4007 as you can see in the picture.

Haven't replaced the diode just yet (i'm 100% sure it was positioned correctly!) Any thoughts? besides replacing the diode? I'm wondering what might have caused this...

Oh and is my heatsink for the 78s12 sufficient??

same thing again, replaced d13, powered up, burned within seconds...

so searching thru the forum i may have incorrectly connected my psu.

please bare with me:

T1 primary connected to the power inlet.
T1 secondaries (got two blue wires and two yellow wires, one yellow and one blue have a green sleeve)  i connected the blue/yellow with the sleeves to the 15v input at the 78s12 location. the yellow/blue without the green sleeve is connted to the 15v at the right side of the pcb.

T2 primary goes to the 220v input at 78s12
T2 secondaries (got two black wires and two green wires, one black and one green have a yellow sleeve)
i connected the two blacks (one with sleeve other without) together (with the yellow (without sleeve) from T1 sec) at the right pin of the 15v rightside of the pcb
i connected the two greens (one with sleeve other without) together (with the blue (without sleeve) from T1 sec) at the left pin of the 15v rightside of the pcb

Hope you still understand?

Did i misunderstand the parallel part of the T2 secondaries?

synnys said:

i connected the blue/yellow with the sleeves to the 15v input at the 78s12 location. the yellow/blue without the green sleeve is conneted to the 15v at the right side of the pcb.

Click to expand...

Mistake 1

synnys said:

i connected the two blacks (one with sleeve other without) together (with the yellow (without sleeve) from T1 sec) at the right pin of the 15v rightside of the pcb
i connected the two greens (one with sleeve other without) together (with the blue (without sleeve) from T1 sec) at the left pin of the 15v rightside of the pcb

Click to expand...

Mistake 2.

Unit working fine now after burning a load of D13's

60Hz Hum Problem Solved!

Thanks (Especially to Haima) for the suggestions. I just moved the high voltage psu to off the main board. I actually used the little extra PSU board that came with the other boards. I wish that I could have figgured out what the problem was without requiring the additional board. But it was easy to move and the hum is 99.9% gone. And I can live with the last .1%.

Thanks again to Gyraf for the design.

Here is a (kind of fuzzy) photo:

well, the instrument inputs sound fine and are working topnotch. guitar sounds great thru it.

Mic input not so good, the last three steps of the gain switch cause an eerbleedingly loud high pitched sound (around 3kHz) each of these three steps has it's own characteristic distorted sound.. will try to sample it after the weekend. i used an 12 step endless rotary switch, like this: (advantage of being very rugged, disadvantage that you can't lock any position like the plastic lorlin type switches.



I do hear some sound coming from the mic input, although it is very soft and especially very thin and hollow...

About the 78S12, i checked the datasheet and it's operating temperature is between 0 and 150 degrees celsius. The heatsink is getting quite hot, I can't touch for longer than a couple of seconds without hurting myself. I had the unit on for a couple of hours this afternoon when recording some guitar riffs, but it seems it can manage the high temp. Will a bigger heatsink extend the life of the 78S12 perse, or is just  got a picture of the heatsink at the top of the page...

any suggestions?

btw on which pins of the xlr plug can i measure how much volt the phantom power gives me?

Here is a pic of my G9 ;D

synnys said:

btw on which pins of the xlr plug can i measure how much volt the phantom power gives me?

Click to expand...

i think phantom power stays on pin 2 and 3. Pin 1 is gnd.

no matter in which direction i turn the little trimpot on the pcb, when i select 48v (and mic and hi-z too) on the frontpaneli measure absolute 0 volt on the XLR's...

how is this possible?

synnys said:

no matter in which direction i turn the little trimpot on the pcb, when i select 48v (and mic and hi-z too) on the frontpaneli measure absolute 0 volt on the XLR's...

how is this possible?

Click to expand...

You have to set the Pot on the frontpanel to [48] and then turn the trimpot clockwise. The voltage should rise slowly.
Do you have the 15V from the Transformer?

Phantom Power should just run by setting the Forntpanel pot to 48.
The hi z jack intermids the singnalpath after the input transformers.
You could also measure the 48V voltage on the front panel connector look for P48 on the PCB before and after the switch.
So you can check out if the switch is working correct.
If there is no voltage you could follow the path with the circuit diagram to check for bad components.

yeah but it doesn't 0 volt