The official G9 help thread

[Sergio]

That's true
I can't help you without any useful answer 

 

[synnys]

I'll measure some more points tomorrow night... just gonna follow the trail...

 

[haima]

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..

This sounds like you need to do the the "DI mod" - involving cutting the PCB traces that run to the DI and wiring shielded cable in it's place. This is well documented earlier in the thread...

 

[Sergio]

Here is a pic of my G9 ;D

Any idea??????
To locate the crackeling source?

 

[Majestic12]

Another question concerning the phantom power. I adjusted it to exactly 48V with no mic hooked up.

When connecting a condensor mic to the input, the voltage drops down to 33V.

Should I check the TIP121 or is this just normal behaviour ?

 

[synnys]

Another question concerning the phantom power. I adjusted it to exactly 48V with no mic hooked up.

When connecting a condensor mic to the input, the voltage drops down to 33V.

Should I check the TIP121 or is this just normal behaviour ?

very normal behaviour

 

[Sergio]

Another question concerning the phantom power. I adjusted it to exactly 48V with no mic hooked up.

When connecting a condensor mic to the input, the voltage drops down to 33V.

Should I check the TIP121 or is this just normal behaviour ?

For most condensor mic s this is no problem. I dont know if this is normal because i've never looked for it. Most not all condensor mics run between 9-52V

 

[synnys]

Wow, DI Mod totally solved my problem! still no 48v at xlr though, gonna follow some trails next..

below is a picture of the output noise/hum with gain and output at absolute maximum. starts at -76dB not bad at all! (using OEP btw)

 

[synnys]

I measure 39,3 Volts of phantom power, but it's on "ground and +" or "ground and -" if i meausre between "- and +" there's nothing! Also i can't get higher than 39,3 volt,  i have the little trimpot completely turned to the left.. if i turn it to thr right the voltage drops.

how is that possible? I connected xlr correct by looking at the schematics, am i missing something?

 

[synnys]

also i measure two different voltages on the two 100uf 350 caps.

one gives me 239 volt the other gives me 312 volt. 73 volt difference between the two... is that ok?

 

[masoste]

Looks like I'm back to the work bench...One channel is super quiet and I don't know why.

Moving the high voltage power supply off the main board did get rid of the hum and now I've got a channel that is perfectly clear with great gain. But he other channel is now super quiet. Plus, when I flip the phase switch for that channel it gets even quieter. I've changes the tubes with no help. I'm just searching through here to see if anyone else has had a similar problem.  Does this sound familiar?

Thanks,
-Steve

 

[Majestic12]

I measure 39,3 Volts of phantom power, but it's on "ground and +" or "ground and -" if i meausre between "- and +" there's nothing!

It's supposed to be this way. Phantom power is fed to hot and cold. When you measure between + and -  you will always read 0V...

 

[synnys]

I measure 39,3 Volts of phantom power, but it's on "ground and +" or "ground and -" if i meausre between "- and +" there's nothing!

It's supposed to be this way. Phantom power is fed to hot and cold. When you measure between + and -  you will always read 0V...

ok thanks for confirming! i now read exactly 48v so that's nice, gonna hook it up now and do some testing.

 

[synnys]

ok so left channel is working fine now, mic incl. 48v also confirmed. Right channel is still a bit messy, got about 25dB more noise and hum!
pictures below we're taken with no mic or instr. attached with gain and output at maximum:

LEFT CHANNEL

RIGHT CHANNEL

 

[synnys]

whenever i put a jack cable into ch.2 the hum and noise, immediately drops about 20/25dB.

any ideas why the second channel could be messed up?

 

[synnys]

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]

My hum is loudest on the rigth channel, closest to the PSU (almost 30dB louder!). I Swapped channels and that didn't help. It is most certainly NOT independant of gain. i got all audio connections shielded thoroughly. haven't tried moving to the HT board yet. will be my last resort...

 

[Sergio]

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]

My hum is loudest on the rigth channel, closest to the PSU (almost 30dB louder!). I Swapped channels and that didn't help. It is most certainly NOT independant of gain. i got all audio connections shielded thoroughly. haven't tried moving to the HT board yet. will be my last resort...

WOW -76db. I think thats great!
I had the same problem with the other channel and solved that with an external psu. Have used my old phonopre supply.

 

[synnys]

you think it would change much if would mount the PSU's on the outside of the case? i currently have them on the inside (on the right) next to eachother..

i'll try tomorrow.

 

[Sergio]

Hi sunny,

NO... NOT OUTSIDE  > JUST AWAY FROM THE MAINBOARD <
I think there are many individual problems with the G9. You can hopefully clarify your problem by moving your PSU away from the preamp.
But i wonder that there are people who build this "diva" together without any problem. I dont know if there are some really "no compromise" units out there....Don't misunderstand my statement....I love that unit

Let's be grateful for Jakobs work.

Cheers!

Sergio 

 

[masoste]

Any suggestions on why I've got one channel on my G9 that isn't working?

Here are the symptoms:

-Output from the first channel does not have any gain.
      -With the Gain and Output settings at maximum I get about unity gain output. In other words I get an output that is the same level as the output from a mic that I feed in to it.
      -When I flip the phase (polarity) switch for the first channel I get no output. Nothing at all.

-The second channel is great. I guess that this isn't really a symptom, but I have no problems with the second channel which is producing nice clean signal with lots of gain, no hum, and very little noise.

Here are things I've tested or tried:

-I tried plugging the front panel controls from the second (good) channel in to the first (bad) channel. But I got the same results. So I guess that rules out a problem with the front panel.

-I've tried swapping the output transformers, but didn't get any change. (There was a post by someone with a similar problem a while back and it had turned out to be a bad output transformer for them.) Looks like both my output transformers are fine though.

-I appear to be getting the same voltage in the V1 tube sockets for both channels. I'm not really sure what I'm looking for here though.

Thanks again for any help offered here. I'd be lost without this help thread.