The official G9 help thread

[Phil]

I did that - the problem is, that the trimmer is turned all the way up and the max i get is 5 volts

 

[audiophreak]

...  are you getting the 15vac on the power input for that section ?  check orientation of the trimmer ,  check value of the trimmer and other components in that section , check 10 pin header going to and from switch PCBs and also switch positions , (  the position setting washer if using the Lorlin type switches )

 

[Harpo]

I did that - the problem is, that the trimmer is turned all the way up and the max i get is 5 volts

You double checked, the zener D6 is a 56V part (or a series string of lower value zeners that add up to about 56V), not a 5.6V part ?
What is your DC voltage reading between collector of TIP121 (center pin) and 0V ?

 

[Phil]

I did that - the problem is, that the trimmer is turned all the way up and the max i get is 5 volts

You double checked, the zener D6 is a 56V part (or a series string of lower value zeners that add up to about 56V), not a 5.6V part ?
What is your DC voltage reading between collector of TIP121 (center pin) and 0V ?

aaaaahh - thx very much. The zeners were 5.6 & 3.6 .. ;-)
Now it works! yaaay

Both channels sound great & most important they sound the same ;-) I think i fell in love with the overall sound, sweeet!

I still have one problem left to solve though. It's very strange but i have a 100 hz hum once i plug in the output to my soundcard (no mic inserted).
There's no 50 hz hum tho, just 100 - shouldn't there be both?!
I'm thinking that i might have to try to plug it into some other plug than the one my PC is in - maybe that could help.. but actually ..  i don't think so ..

 

[pachi2007]

Hi there. I´ve just powered the G9 and everything seemed ok: 11.9V , 239V, +48V. The thing is it burned the 12V part of the tubes (239V ok and all tubes get hot, though both at channel2 run a bit hotter) . I didn´t notice they burned at first but I tried with another tube I had and I saw it light for a couple of sec. and then die fast.

I´ve used the spare power pcb and connected 239V DC at the main pcb (CAP2+,OV), the 12V at (F+,F- to light)

Any help? Does anybody has a NOS Telefunken to send me so I can try if it burns too?

Thx a lot guys

 

[pachi2007]

A picture of the power supply

 

[gyraf]

If you have 12V heater voltage, it can't damage the tube heaters. Make sure that you have the right voltages.

Maybe you have a short between heater pins, giving 12V across ½a heater?

What are the supercaps for in the psu image?

Jakob E.

 

[Phil]

hmm .. i've tried disconnecting the ground as a test but no luck, i still have this 100hz hum on the output. it's not very loud but it's there and annoying .. any ideas?

 

[bernbrue]

Hi,
most hum and noise issues in the G9 are caused by incorrect grounding. I learned it the hard way and struggled for about 2 month with my G9. I was almost ready to sell this ungrateful beast until I finally found out that the main board had no ground connection via the input molex connector. This connection is the only one that connects the main board to ground. Double check this. There are also ground bridges on the main board. Verify that you bridged these connections as well. See picture attached. I´m really glad that I finally fixed it and didn´t sell the G9.  We are best friends now.
regards
Bernd

 

[pachi2007]

Hi Jakob.

I checked again at the base of all the tube sockets (F,F+) and it reads 11.9V DC.  I´ll try to check better this weekend.
Why supercaps? I´m building the g9 with a friend and it was only a joke. A golden "uk made" instead of cheap asian unbranded I always buy. I bought a 5 lot for a fair price, didn´t know they were supers

Thx a lot

Pachi

 

[Phil]

Hi,
most hum and noise issues in the G9 are caused by incorrect grounding. I learned it the hard way and struggled for about 2 month with my G9. I was almost ready to sell this ungrateful beast until I finally found out that the main board had no ground connection via the input molex connector. This connection is the only one that connects the main board to ground. Double check this. There are also ground bridges on the main board. Verify that you bridged these connections as well. See picture attached. I´m really glad that I finally fixed it and didn´t sell the G9.  We are best friends now.
regards
Bernd

Hey Bernd,

thx for the answer - I double checked everything and it's grounded and bridged .. so this is not the problem.
I also noticed, that when speaking a "test 1, 2" that right after the transients of my words there is some sort of very short feedback exactly in that 100hz hum frequency as if it was amplified ..

 

[gyraf]

Ah - I misread the picture - thanks for clearing that up.

But again, 11.9V can not damage a 12.6V tube, unless it's either set up for 6.3V or has one half-heater shorted (pin9 of the tube connected either to +12V or 0V/gnd - pin9 is NOT a shield like in ECC88).

I have never ever had one single tube dying on me like that.

Jakob E.

Hi Jakob.

I checked again at the base of all the tube sockets (F,F+) and it reads 11.9V DC.  I´ll try to check better this weekend.
Why supercaps? I´m building the g9 with a friend and it was only a joke. A golden "uk made" instead of cheap asian unbranded I always buy. I bought a 5 lot for a fair price, didn´t know they were supers

Thx a lot

Pachi

 

[gemini86]

Are you sure your regulator isn;t just going into thermal shutdown after a few seconds? Then popping in a new tube gives it enough time to reset?

I've had that happen on a build before. Just one little clip on heatsink was all it needed (only powering one tube for a tube mic at 300mA, thought I could get away without a sink.)

 

[gyraf]

Aah yes, thanks, that would be a classic scenario: I excluded this explanation because I'd expect it to be checked already (has been brought up several times in this thread already)..

Jakob E.

 

[qwerty8787]

Hi all!
I'm new here!

I recently finished building my G9. Sounds nice but has an annoing hum problem  :-\
When I have the gain and output knobs ALL way down, I get a good amount of noise. the fundamental might be 50 or 100hz, then I have all the harmonics (200, 300 and so on...).
I tried to make and unmake connection from pin 1 to chassis of one of the inputs: no results.
I tried to move around the trafos (2 toroidal ones): the hum only increases, when I get them very close to the pcb top. Also outside of the chassis there are no good results.
I tried to put one trafo upside down on the other one, no result.
I tried to unmake connection from earth IEC pin and chassis (ground lift): no results.

I checked out that the output pots chassis are electrically connected to ground by chassis
I checked out if the OEP shields are connected to ground, and only 3 are.
The tubes are JJ's, and i've mounted them on shielded sockets!!! 
I used shielded cables for I/O and also for the front jack, but I haven't tryed the DI mod (I think it's not fault to this because noise is gathering with outputs at 0!!)
Trafos are from RS:  1x220V 2x15V 50VA (code 671-8965) and 2x110V 2x12 50VA (code 671-9090)
The 78s12 has mica and heat sink is mounted directly on it, so is not touching chassis.


I'm getting very frustrated, I can't find the problem.....anyone has ideas?

Thank you in advance

 

[nashkato]

  I didn´t notice they burned at first but I tried with another tube I had and I saw it light for a couple of sec. and then die fast.

maybe quite a stupid question , but are you sure the tubes are burned ?
older tubes sometimes do have the effect of lightning up a few seconds until the resistance of the heaters is stable.
quite usual and not really something to worry about. (at least to my experience , though it looks like this :

damn !!

after that the heaters aren´t necessarily visible on a quick look in a bright environment.

please measure the DC heater resistance of the "burned" tubes and compare them to the "still working" ones .
(tubes only of course , not plugged in obviously

 

[tmuikku]

Hi all!
I'm new here!

I recently finished building my G9. Sounds nice but has an annoing hum problem  :-\
...
I'm getting very frustrated, I can't find the problem.....anyone has ideas?

Thank you in advance

Yello! Check with FFT software if the fundamental is 50Hz or what. 50Hz would be from mains xformer induced hum. From 100Hz up is propably coming from poor PCB layout, build the B+ powersupply on veroboard and see if the problem still exists. Here is a thread about it http://www.groupdiy.com/index.php?topic=32559.0 and some results also found from this thread. (Tip: click the Print -link so you can use your browser "Find" function to quickly scan the thread).

Be sure you've followed general guidelines of good grounding scheme. Some of it here http://www.groupdiy.com/index.php?topic=17980.msg527591#msg527591

 

[MeToo2]

I checked out if the OEP shields are connected to ground, and only 3 are.

I'm getting very frustrated, I can't find the problem.....anyone has ideas?

Thank you in advance

You need to make sure those screening cans are properly installed for a start.

I posted earlier in the thread about a bunch of things I did to reduce hum, including a picture of how to install the OEP cans properly.
In the end my G9s were whisper quiet, even at full gain and full output level, so the problem is build or layout, and not circuit design related.

see http://www.groupdiy.com/index.php?topic=17980.msg468609#msg468609

The tip on trying off-board HT supply worked for me too if you are using a PCB based build.

see http://www.groupdiy.com/index.php?topic=17980.msg497043#msg497043

You can get a good idea of the source by trying simple things.

Is the hum actually in your test set up, outside of your G9? [test with other sources, and a direct bypass of your source to test kit via another pre]
Is the hum equal on both channels? [if it is it points to a common cause like HT supply or heater supply]
Is the hum independent of gain? [if it is it points later in the circuit or output transformer]
Is the hum independent of source impedance? [check with a 200 ohm mic attached]
Is the hum channel related? [swap input and output conenctions and check if hum switches channel]
Is the hum louder on the channel closer to the power transformers [right worse than left => possibly points to HT noise leaking into 2nd stage]

 

[keninverse]

Maybe I can gain some insight to my problem here.

I built up my G9 had some issues with no output on the last two gain settings so I did the gain fix mod. Took care of that.  I noticed some serious noise on the output and looking at the spectrum coming into logic shows a noticeable hump around 100-150hz.  After some reading I built the HT supply offboard using the external power supply but it seems I'm still having this issue.  I didn't build up the heater supply just the B+ and it's being injected to a wire jumper that's labeled HT on the PCB itself.  I'm at a loss here.  Should I build the B+ supply on vero? Is there some other issue I should be looking at after the rectifier.  By the way I'm using fairly large 330uF caps for the psu filter.  I haven't measured for ripple yet but can anyone please suggest something.

Please!!!!

 

[keninverse]

[FIXED]

Intermittent connection on the front panel caused from cold solder joint.  No 100-150hz bump and this thing is extremely quiet.  I'd like to just point out that moving the B+ off the board using the extra psu supplied with my board worked very well to fix this issue.  I also ended up using 330uF caps for filtering. 

I'd like to also point out here for anyone else having this problem.  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.

Quite impressed with this beast.  Extremely smooth on vocals and I'll give it a try on my jumbo guitar tonight.

One more thing....Thanks Jakob for putting these projects out there as well as helping countless others with projects that you aren't compensated for monetarily.  I think it's freaking awesome that you do this and shows you're a stand up dude.