The official G9 help thread

Aha! I had messed up wiring the outputs to the XLR jacks and switched the output ground and the output hot pins. Now that I've corrected that wiring mistake at the XLR connector what could I have damaged? Could I have damaged my output transformers or part of the phase reversal circuit?

btw. I tried replacing the power transformers one at a time with no change in the hum that I'm getting, so it looks like they were fine in the first place.

If you just swapped ONE of the output leads with the ground lead, then you're going to be okay (just breath). That means you only wired the output single ended, unbalanced. So, is the hum gone, or not?

I had swapped the wires that go to pin 1 and pin 2 on both of the outputs (at the XLR jacks). That would be the ground and the positive outputs being reversed and the positive was grounded out to the chassis for a while. I've swapped them back but the hum is still there.

I had only had a test lead with alligator clips running from the ground (pin1) of the XLR to the chassis because I had fired it up a few time to test testing it, found the hum, and had experimented with removing that line because I figured it was a ground loop. I guess it was a major ground problem! Taking the positive to the ground could not have been good.

Without the ground pin (pin 1) of the XLR connector also connected to the chassis ground I get a lot of hum, with the ground pin (pin 1) of the XLR connector also connected to the chassis ground I get an annoying amount of hum, about the same amount as when I was incorrectly running the positive outputs to the ground.

I'm having some difficulties understanding which toroid transformers to get...

I have these two already:

http://www.musikding.de/product_info.php/info/p2883_Toroidal-transformer-230V----2x-15V-50W.html
http://www.musikding.de/product_info.php/info/p2885_Toroidal-transformer-230V----2x-12V-50W.html

What else do i need? And what about the 220v connection on the motherboard?
Also i see no 12v connection on the motherboard..
i'm a bit confused.

Someone care to share?

Those transformers should be okay, here is a wiring diagram for this project posted by Skylar.

http://www.groupdiy.com/index.php?topic=16168.0

Obviously the colours are not the same for every transformer so you'll have to figure out which wires go where but this should be a pretty good guide.

ok so i get the 2x 15v connections, but where does the 12v come in? and the 220v?

(thanks for the link btw)

... look at page 26 of this thread   

audiophreak said:

... look at page 26 of this thread 

Click to expand...

starting to make sense now... hopefully i'll understand it completely in the morning after some much deserved sleep

I think i got it:

T1 primary goes to the power inlet, one T1 secondary (15v) goes to 15v @ 220v location, other T1 secondary (15v) goes to the right of the PCB.
T2 primary goes to the 220v at PCB, than i combine, or parallel the two (12v) secondaries of T2 and join them together with the secondary 15v from T1 at the right of the PCB?

Can some one confirm?

Let me elaborate

This is how i understand it:



Correct?

Btw:

Does it matter/make a diiference how i position the two toroids?
Which one of the following is preferred? And do i have to shield them somehow?
Can i wrap a stroke of aluminum foil around the toroids, does that help? Like in picture 3...

Hey masoste - Re: your hum problems, this is what fixed it for me:

haima said:

Hey Chris - I believe you are describing is a textbook case of the same low level hum I and a few others have experienced with the G9... I fixed it by moving the HV power supply (rectifier, caps, regulator) off the main board - therefore feeding clean DC to the main board. If you read back over the last ten pages or so there should be a few references to this problem.

I think we need a FAQ....  ;D

I really suspect a LOT of G9 builds might have this hum problem - but it's low enough that it doesn't bother some people, or they just think it's what "tube diy" sounds like.... It doesn't have to be that way. I lived with the hum for 3 years (used it on a few released albums!) before i got a chance to try running the pres from an external power supply - now they are dead quiet.

Click to expand...

Yes, residual hum levels seems to vary quite a lot in different G9-builds, probably depending on amount of hum stray field from the actual transformer type used.

That said, I've always been able to reduce hum to below general noise floor by grounding right and orienting transformers (turning them for minimum hum).

Make sure to mu-shield if OEP's are used - these are much more sensitive to stray fields than Lundahls.

Jakob E.

any thoughts on my pictures above?

Pic two, stacked transformers mounted on bottom, is the most used way.

If you use screening, take care that the screening foil doesn't connect electrically to top and bottom holding hardware (would be one turn shorted on transformer)

Just to be clear - I had a low level hum in both my G9s. Re-orientating the transformers & different types of signal grounding, pin-1 use etc didn't fix my problem (Not to say it may not be a factor for others).

Moving the HV rectifier, caps and regulator off the main board and onto a small piece of veroboard/strip board fixed the problem 100%.

This was the same for both of my G9s.

Just putting it out there in case this helps anyone....

gyraf said:

Pic two, stacked transformers mounted on bottom, is the most used way.

If you use screening, take care that the screening foil doesn't connect electrically to top and bottom holding hardware (would be one turn shorted on transformer)

Click to expand...

and is my drawing of the power connections correct?

Hi haima,

Thanks so much for your suggestion. I'm going to move the HT supply to another board and see if that gets rid of the hum. I guess that I would be moving everything up to C15 off the board. I just noticed that I'm using a IN4007 in stead of an IN04004 for D2, although I doubt that that would make any difference as the IN4007 just has a higher voltage rating.


I suppose that it could be that I'm not grounding something properly. I've run ground lines back to the enclosure from each of the XLR jack ground (pin 1) terminals, and also have the mains ground run to the enclosure. But it seems like I've tried so many things that I don't know what else to try other than moving the HT supply and adding mu-shield to my power transformers.  I've tried moving my power transformers outside the enclosure with no change in this hum. I'm also using lundahl transformers. I'll let you know how moving the HT supply works out.

-Steve

Hum could also come from shorting the 78S12 heat sink tab to ground/chassis, making a ground loop. Make sure to use appropiate TO-220 isolation kit.

Jakob E.

Hi there - I have 2 x 240V - 12V toroids (95VA each). Apart from being overkill will they work OK for the G9?
Thanks!