The official G9 help thread

[MeToo2]

When I initially fired up this unit stock, I lost all gain in the last two clicks of the gain switch.  I didn't have any oscillation problems at all.  I followed the instruction for the instrument in trace cut and this solved the problem completely.

Good to hear you've fixed your unit.

FYI The oscillation can be such high frequency that you can only see it using an oscilloscope (and not actually hear it at all) but it can still kill the AF signal gain on the highest gain switch settings. Anyway the fix is the same as you've done already: cut the PCB tracks and add shielding on the DI.

 

[keninverse]

@MeToo2

Thanks! This is exactly what I figured. The oscillation was too high for non-dog ears.  And thanks for keeping up with this thread.  I've read many of your posts trying to make sense of this pre.  A lot of knowledge gained from reading your stuff.  I appreciate all the stuff you've written.

 

[Maynard]

Hi All!

New in here and amazed after finding this cool group about the g9!

I just finished my G9 and so fa nothing exploted or burned down but I get such a small output So far I'm trying to check the unit using a XLR-jack cable. I know that passing from XLR to jack will reduce my signal amplitude but so much? I am pluggin the output to a guitar amp and I have to cranck up the volume in order to hear a little. I have to input a nice signal over 400mV to listen something. My gain is at max and also the output volume.
Tonight I wil try to trace signal with an oscilloscope and get a vocals amplifier with XLR hoping this improves.

Any hints? thak you for your help!

 

[bpucekov]

check your wiring from main to control board
clean thoroughly the pcb remains of garbage after soldering can cause some sort of short
at least that was the case with my g9

 

[Maynard]

Thanks bpucekov. Finally found out the problem tracing a tone, I got some mistake in the SRPP stage pcb already fixed. Now I'm working in the noise and hum. Got to clean the ckt since I put all together in a messy way and work in the start ground and a nice faraday case effect.
So far what I notice is that I get more sensitivity with the none phanton powered mic and less noise with the jack input  : gotta work that around. Big help with the noise in this post, I`ll keep reading.

 

[barthman.de]

I have a question about the official PCB (look http://www.barthman.de/bilder/g9_pcb.pdf).

In contrast to the input tube  the +12V heater connection was mount on the output tube on another (f) pin. 
Is there a particular reason to change +12V and 0V between input and output tube pins? I ask that because I want to build my own PCB's and want to connect all tubes strictly parallel to +12V and 0V.

I even wonder that the "f" pins at one of the input tubes are labeled with + / - 

I think, because it is principle possible to push the heater on AC it should be able to change the connections. Isn't it? Maybe this was made simple because of space reasons?

Sebastian

 

[gemini86]

The filament is bi-directional, there is no + or - pin. It's simply a matter of PCB layout and where it's convenient to place power.

 

[telefunk]

Hi there!

I'm building my second G9 and it's almost there BUT the Omron relays i had already bought got lost...

So, the only ones i seem to find from Paris right now are these:

http://shop.rabtron.co.za/catalog/relay-4052-12vdc-p-3379.html?osCsid=a71328ea0d3f18ee90b16d8779cbfffc

I dont know the "component scene" in Paris but place called "Cyclades Electronique" is just round the corner and they had those.

Are those as good as the Omrons for the job?

Thanks!

EDIT: I might add, that my first G9 had OEP in/out but this time i'm going for the Lundahl in and Edcor XSM2.4k/600 out. Anyway, i love G9. (Thanks, Jacob!)

 

[Edward]

This maby is a dumb idea, but could G9 be built as a one channel unit leaving out the balanced inputs and phantom power option using the PCB made by Gustav? Interested in building a "deluxe" DI for live audio use for bass/ac guitar.

The G9 really seems perfect in all ways but the size would be a problem for me.

Just a thought.


/E.

 

[gyraf]

Telefunk: no, that relay won't fit the pcb, I think

Edward: yes, you could, but you wouldn't save a whole lot of cost in doing so.

Jakob E.

 

[masoste]

I hope I haven't missed something in the help thread. I have been going through the help thread here for a few days trying to answer my own question, but can't seem to figure it out.

So, ...

1.) Before I go and build an external PSU for my G9 is it possible that I'm getting 60hz him (and it's harmonics) because my C14 and C15 capacitors are undersized?

I'm using 100uf 350V Caps such as these:
http://no.mouser.com/ProductDetail/Nichicon/UPW2V101MRD/?qs=64l3LOSZbCrVK%252bv2Dm%2fH%2fA%3d%3d

1,a.) Should I go to something like these while I'm at it?
http://www.tubedepot.com/cp-jj-100x2-500v.html

2.) Is there some way to tell if I'm getting 60hum from induction, from the 12v PSU, or from the 245V PSU?

I've hot a fluke meter which is telling me that the HT output is 257VDC with about 6mVAC @60 HZ, the 12v output at the panel light is showing 11.89VDC and about 6mVAC. I'm not sure if this much fluctuation is what is causing this hum.

I've done the instrument input mod direct to the PCB with shielded cable and cut the traces, I've tried moving my toroids around in my case and I've shielded them and the power switch from the PCBs, I've grounded the input Pin#1's to the chassis at the same point as the mains ground, and used shilded cable to run from the PCB to the XLR jacks. I'm using the Lundahl transformers.

3.) Where can I find a good description of how to build and hook up the spare PSU board? The layout looks fairly strait forward, but I don't know how to connect the HT caps to it or where to connect the output to the main PCB.

Attached is a screenshot of a scope of the output with nothing connected to the input. When I hook up a mic I get a signal that is amplified and relatively clear except for the 60Hz and its harmonics are overlaid which make it pretty fuzzy. The 60Hz and it's harmonics are present no matter which gain position I use or any other setting and increase (or decrease) along with the output signal as settings are adjusted.

Any help would be greatly appreciated.

 

[masoste]

I just realized that I'm using these 1000uF 25V Nichicon Caps for C16, C17, and C18:
http://ca.mouser.com/ProductDetail/Nichicon/UKZ1E102MHM/?qs=sGAEpiMZZMtZ1n0r9vR22e0BBN1kF1oiP9NzYB%252b2Kf8%3d
Rather than 35V capacitors. Could ripple from those capacitors be what I'm hearing/seeing?

thanks,
-Steve

 

[masoste]

Sorry to have so many questions as a new poster. I keep reading through this thread, but haven't figured out my problem yet.

I had another look at this tonight and think that the problem might still be in the HT supply. I say still be in because the first time I fired it up I had the polarity on C14 and C15 reversed. R34 got really hot right away so I powered it down right away. I turned C14 and C15 around, and replaced IC1 (the TL783), R33, and zeners D3, D4, and D5. I thought that I had everything fixes because HT output is 257VDC but maybe the 6mVAC @60 HZ that I'm also measuring on that is my problem. What else is there that I could have damaged which I should replace?

I can only think that either that's the problem or I've got a grounding problem but I've star grounded input ground pins and the incoming mains ground to the chassis. Am i missing something else. I've read here suggestions of something that sounds like I should run a wire from the ground on the PCB to the chassis as well, but the grounds of the inputs are already connected to the PCB ground. Grounding pin 1 of the outputs with a jumper doesn't seem to make a difference. Am I missing something?

Thanks,
Steve

 

[gyraf]

I turned C14 and C15 around

There is a VERY good chance that C14/15 were killed by the powering up with wrong polarity.

Jakob E.

 

[masoste]

Thanks Jacob. I suppose that they could have been killed, but I've just changed them for a pair of 150uf 450V caps (some cheap but new caps that I had hanging around) and I'm still getting about the same hum. It seems to be at the same level no matter what gain or output settings I use though.

With the new caps it seems like I might be getting a bit more hiss at higher output settings, but otherwise about the same results. Here are two images of the output, the first at the lowest gain and output and the second at full gain and output.

 

[masoste]

...and at maximum gain and output

 

[bernbrue]

Sometimes a closeup picture of your build helps a lot. Did you double check connections beetwen mainboard and switch board? When you did the DI mod, verify that the switchboard is still connected to ground.
regards
Bernd

 

[masoste]

Well I just put the whole project in a new enclosure because I had it in a re-used 3u box that was just too big. Unfortunately I've still got the hum, plus now I've got some new problems. I'm not sure if they are because of the fact that I may have shorted something on the rear of the front panel or if the problems existed before. Now I've got an intermittent 12vdc charge difference between the ground on the PCB and the chassis ground. I found this out when I turned it on and then plugged in the output connectors. When I did this the relays clicked and the pilot light went out.

Here are some close up photos.

or http://flic.kr/s/aHsjyGALPV (I'm still trying to figure out how to embed multiple images in a post)

I also tried disconnecting the power input transformers from the board one at a time and the 60hz hum would disappear when I pulled the high voltage supply.

As for the PCB ground having a charge I'm not sure if it's the front panel shorting out or something else. Any ideas?

Thanks for all the help.
-Steve

 

[gyraf]

12V on out ground COULD be one of the 9-pin main-to-front connectors reversed.

Try lifting connectors one at a time until problem goes away, then investigate how 12v gets into that connector.

Jakob E.

 

[braeden]

I'm trying to wire the following LED from the +/- 12v 50mA supply that typically would run to a jewel lamp.
http://au.element14.com/multicomp/mcl053ad/led-5mm-36-orange/dp/1581141?Ntt=1581141

I've tried a fairly large resistor (100k) or so in series with the LED but it just keeps blowing up.
I don't have that many LEDs left, can someone recommend a solution?

Thanks