The official G9 help thread

[redmojosteve]

MeToo2
I must admit that it wasn't the first solution that sprang to mind but I followed your suggestion and replaced the trafos with  exactly the transformers you have used and guess what, it works just fine and the transformers are as cool as cool things. Clearly the previous transformers weren't the right type for some reason. They will always come in handy for power supplies anyway. Thank you very much for your help and patience.  I'll now move on to G9 number 2.
Good luck with yours Sono

Cheers

Steve

 

[MeToo2]

MeToo2
I must admit that it wasn't the first solution that sprang to mind but I followed your suggestion and replaced the trafos with  exactly the transformers you have used and guess what, it works just fine and the transformers are as cool as cool things. Clearly the previous transformers weren't the right type for some reason. They will always come in handy for power supplies anyway. Thank you very much for your help and patience.  I'll now move on to G9 number 2.
Good luck with yours Sono

Cheers

Steve

I'm genuinely happy for you that you've got your build working properly. I've had a lousy day in the office today and this made me smile. Glad I could help

 

[sonolink]

Happy to hear that, Steve and thanks for your encouraging words. I have to find some spare time now for my G9 troubleshooting. We just got a little puppy and my daughter was born a few days ago
I'll be back very soon. Promised...
Cheers
Sono

 

[rmaier]

Congratulations! The birth of a child is by far the most intensely rewarding DIY project we're lucky enough to get. All the best to you and family.

 

[psychedelnick]

First power up tonight, tubes all glow nicely but oh no! A little bit of smoke, a burnt out resistor! R 40. I listened to both channels on PT and it's a sad and shitty loud buzzing humming everything. Identical on both at least and signal is passing. Everything else seems cool. I'll check voltages tomorrow. Any thoughts? Thanks

 

[MeToo2]

First power up tonight, tubes all glow nicely but oh no! A little bit of smoke, a burnt out resistor! R 40. I listened to both channels on PT and it's a sad and sh*tty loud buzzing humming everything. Identical on both at least and signal is passing. Everything else seems cool. I'll check voltages tomorrow. Any thoughts? Thanks

D6 installed the wrong way around? It's a zener. If it's reverse biassed then the voltage across the zener is 56V and the current through R40 is max 3mA. If D6 is forward biassed then the voltage drop is ±.6V and the current through R40 = ±27mA = 1.6W or enough to burn out R40.

 

[bigswole]

Will 2 115+115 : 15+15 power transformers work?

 

[psychedelnick]

Thanks MeToo2 I will check tonight!  8)

 

[gyraf]

Will 2 115+115 : 15+15 power transformers work?

Yes, they should.

Jakob E.

 

[psychedelnick]

You were right MeToo2. The diodes I used were 5.6 V! So hopefully once I swap that out with the right one it should be good! Thanks a million! ;D

 

[psychedelnick]

Okay, installed the 56V Zener and no smoke! Tubes glow evenly.... bad sound, no signal, a bit of RF, that's it! Voltages all within reason except! the terminal next to C 29 is getting nothing, zero. But the one just next to it, literally next to it, is getting 15V on the nose. Is this normal? Could I have a bad toroid? My real problem may exist elsewhere but this is all I got for now. The group of wires in question are at the bottom of the 15 V terminal to the very right in the attached image, Black Orange and Yellow. Thanks

 

[MeToo2]

Okay, installed the 56V Zener and no smoke! Tubes glow evenly.... bad sound, no signal, a bit of RF, that's it! Voltages all within reason except! the terminal next to C 29 is getting nothing, zero. But the one just next to it, literally next to it, is getting 15V on the nose. Is this normal? Could I have a bad toroid? My real problem may exist elsewhere but this is all I got for now. The group of wires in question are at the bottom of the 15 V terminal to the very right in the attached image, Black Orange and Yellow. Thanks

errm that's ~15V AC on those PCB terminal blocks: not DC. One terminal connects directly to signal ground, so it should measure 0v. Measure the voltage on C23 (to check your 48V phantom) doubt this is the issue, but it's a start (and will check if D6 was the only problem with the phantom supply).

 

[tobi.pl]

So I nearly got my G9 finished and have to sort out some Problems that appeared.
First of all I got some really annoying hum with 100Hz@-69dB (Gain and Output closed) and 100Hz@-52dB if Gain and Output are cranked up and a SM57 Mic is connected.
Beeing audible hum, theres no way leaving it there. As I only have 100µ on C14 and C15 it would be my first guess to change them to 220µ. The AC Voltage measured at C14 and C15 is about 0.9V (I guess that might be why it is audible  8)), but  I do not really trust my measurement equipment. HT Voltage is about 205V as I accidentally bought 2x 230V/15V transformers, so the second thing would be to change one of them into 230V/12V to get a decent HT Voltage.
My second problem is a 50Hz@-67dB  if Gain and Output are turned fully clockwise. If I turn down the output Volume, the 50Hz hum disappears, if the Gain is down and the Volume turned up it is still there. The Hum is all the same at both Channels,
The Box is properly grounded (I think) with the Input XLR's Pin 1 being connected to the Case and this point itself to the AC inlet ground.
I'm using shielded Wires for the output Connection. Anyone got some Ideas how to fix this? I read about 40 pages of this thread and all Metas about this topic and I'm pretty fed up with this thing keeping me from recording 

 

[MeToo2]

So I nearly got my G9 finished and have to sort out some Problems that appeared.
First of all I got some really annoying hum with 100Hz@-69dB (Gain and Output closed) and 100Hz@-52dB if Gain and Output are cranked up and a SM57 Mic is connected.
Beeing audible hum, theres no way leaving it there. As I only have 100µ on C14 and C15 it would be my first guess to change them to 220µ. The AC Voltage measured at C14 and C15 is about 0.9V (I guess that might be why it is audible  8)), but  I do not really trust my measurement equipment. HT Voltage is about 205V as I accidentally bought 2x 230V/15V transformers, so the second thing would be to change one of them into 230V/12V to get a decent HT Voltage.
My second problem is a 50Hz@-67dB  if Gain and Output are turned fully clockwise. If I turn down the output Volume, the 50Hz hum disappears, if the Gain is down and the Volume turned up it is still there. The Hum is all the same at both Channels,
The Box is properly grounded (I think) with the Input XLR's Pin 1 being connected to the Case and this point itself to the AC inlet ground.
I'm using shielded Wires for the output Connection. Anyone got some Ideas how to fix this? I read about 40 pages of this thread and all Metas about this topic and I'm pretty fed up with this thing keeping me from recording 

205V HT is way too low. The TL783 won't be regulating at all: It needs about 5-10V drop out voltage which means at least ±250V on the input after the smoothing caps. So the PSU will be passing through 100% of the ripple from C14/C15 straight onto the anodes of your tubes (which explains all of your 50 and 100Hz problems). You need that replacement 12V step up transformer as your first modification. Replacing the 100uF caps with 220uF caps might help eventually on the margin to improve some residual low level hum, but they are certainly not the primary problem.

 

[tobi.pl]

Well, this new transformer made all my problems vanish into thin air =) thanks a lot. Now it doesn't make any noise at all. Just pure Signal =)
I just have two more little questions. As one of my Output Pots was doa i ordered new ones, but oversaw that their power rating is just 0,05W instead of 0,1W. Can i use them as well or do i have to get some, that stand a little more Power. Second. As I built the whole unit in my prototyping case I need to get a decent Box for this one. Where did you all get these nice cases and Front Panels that I saw in the finished G9 threats.

 

[gyraf]

0.05W post should be fine in G9.

 

[Luax]

Hi Guys,

First the good news:
I'm typing this message with a smile on my face. The project was on break for a while after I had some humm issues on my second channel, that led to a lot of insecurities, depressions and what not…
This week I found strength again to rebuild some weak spots and now I have superb clean audio signal from both my mic channels! After I tested it with a matched pair of mics!

The bad news:
In my rebuilding I also changed the instrument cable for 3 seperate shielded cables. (maybe i overdid it in my enthusiasm) The problem I have now, is that there is a big ground humm in both instr. channels.
Could it be that using three separate wires don't ground well?

Any insights on the problem are more than welcome. (Before I screw anything up or make things worse)
Can't wait to have a pristine working G9!

Cheers!

 

[gyraf]

The instrument input "mod" only takes two screened cables: One from input-transformer to the switch (that closes to tip terminal when no jack is inserted) - and one from tip terminal back to input capacitor. Shield on both from audio gnd (at input-transformer 0V) to jack ground (and ring if you have stereo input jack)

Jakob E.

 

[Luax]

Thanks Jakob,

I already concluded that the schematic uses a stereo input were I was using mono.
Things are getting clear now. I'll change it after the weekend.
And hopefully bring another finished working G9 to this world.
I'll let everybody know in case of succes

All the best!

 

[tobi.pl]

And here we are again. Got my new case, put everything in place, took some measurements and listened closely a last time. And again... hum. It's 100hz@-75dB, but constantly. No matter how much gain and output. I have a 12V to 230V step-up transformer now (which improved it about 10dB), the voltage at the caps before the regulator is 320V after it it's 242V. If I turn power off the hum vanishes and the tubes still amplify for some time, so it should be from the power section. I already changed the TL783, the Diodes, 2W Resistors and C14 and 15 to 220µ 500V VishayBC (before 50 + 50 JJ) in the HT Circuit and still no improvements. What makes me wonder is the ripples, before the regulator it's about 1,5V and after it 1,05V but my multimeter is not the best one, so it could be less. Grounding Scheme is the pin 1 of the input xlr's at chassis bolt and this to power inlet ground, the output xlr's use shielded wires. I've also cut the traces of the DI inputs and wired it directly to the pcb. Any Ideas what else could be done? I want to do some orchestra and vocal recordings with it, so it should be as quiet as possible...