The official G9 help thread

[Deepdark]

Yup, it helps to cancel as much as possible electro magnetical noise emited by AC power (hope that I'm explaining correctly)

 

[BeeHaniwro]

Hello everybody,

My G9 is finally finished and works perfectly. I fixed the buzz issues on channel 2 in a specific (and maybe over complex :) way but I now have a silent unit .

What an emotion to plug a mic for the first time in it and realize that this really sounds good. It's colored, rich, funny to use. You feel the warm of tube and it's really joyful. For that, i really want to thank you Jacob, for your design, your spirit, and your products (that i hope to be able to buy one day). Thanks also to those who helped me.  The definitive frontpanel (from schaeffer) will come later.

Some informations about my buzz fix and why there is a battery in my G9 ​

As a reminder, I do to mini modification on this preamp : I add a "standby" switch and wanted to put switch and lamp on the middle of front panel (FP). The problem was that the alternative current running to and in the FP's switches was generating buzz in the sensitive part of FP's controls and connector (instrument input and four first stage of gain).

The twisted pair solution wasn't enough to kill the buzz, neither was a shielded wire :-\. I tried to change the position of the channel 2 intrument input ( you see it on pics on the left on top of the channel 1 one) but there still was buzz.

So my solution was to do not  run AC current to the FP. With some imperatives : I want switches on FP (racked gear so no rear panel everyday switch), I want that the unit to do not consume a single mA when it was powered off (no sleep mode). I found a solution based on two power relays. A 9V battery is here to power the first relay that fire the first Tranny (9v is a lot, but I did that with the relays I had at home). When it's "on" the 12V run in the circuit and it's used to replace the battery to power relays.

This is an interesting solution that allow to keep all emitting wire in one place in the enclosure (you can seal this place with a Faraday cage to make it complete). But my problem is still that I have a battery to change someday. If one day my battery is dead and we are on a sunday and i can't buy one and I have a session to run, an emergency switch is on the back panel to shortcut the first relay and power up T1.

Thank you again, this build was really interesting to me. I think about building more, but I want to try a LA-2A first
Sorry for my english. Bee.

SOME PICS​

Click here to see full resolution and full album​

 

[gyraf]

*like* 

 

[RO4350]

Hey Guys,
yesterday I put my G9 together. Unfortunately it doesn't work. At the moment it is more like an attenuator than a preamplifier : .
I think the problem has something to do with the HT Voltage. It is round about 275 Volt, 12 Volt and 48 Volt are fine. Measured with the Tubes in the circuit.

If I play with a Bass or Guitar through the Instrument Jack, I get a very very weak Signal. Actually it is only audible by setting Gain and Output to maximum and also turning up the Gain of my Audiointerface as high as possible. But than I get a clear and nice Signal except the hum and noise floor of course which is caused by the audiointerface Gain settings.
Furthermore, the Signal follows the G9s Gain. So it gets quieter by turning the poti anticlockwise.
In my opinion it means, that the first gainstage is working and I guess the mistake is somewhere after the low-cut? Since the HT Voltage is not regulated by the TL783 the current through it seems to be to small? I guess the tubes also should be able to work with HT of 275V only the working curve should be different. Which indicates a problem with the second tube Stage not with the regulator.
So I checked all resistors around the TL783 and also all connections to the anodes and connections from cathodes to ground. For me everything seems to be right. Hope you guys can help me.

Best regard

 

[gyraf]

Maybe the switching jack is wired in reverse? Check...

Jakob

 

[RO4350]

Hi Jakob,
thanks for your answere.
Checked the wiring, it is correct.
Any other idea ? :/

Edit:
I got it. I had swapped two of the cables going from the poti Pcb to the main Pcb. Made the same mistake on both channels.
But still the HT Voltage is not regulated and is about 275 V. Could something get damaged by this ? The curious thing is, that the TL783 gets about 50 degrees warm. So it seems to drop some Voltage there. Furthermore I am not able to measure the Voltage right behind the rectifier, the Scale of my Multimeter just jumps around. The rectifier is fed by 306 V from the toroid.

 

[PitchFork38]

Hello !

Something weird happen on my G9, everything worked well until a loud high noise sometimes appear  on Channel 1 and If I tap gently on the frontpanel, the noise disappear.
Do you know what this could be ?

I already cut traces on both channels to avoid  oscillation .

Pierre

 

[dthodoris]

Hi, I just received PCB's and can't wait for the parts to arrive in order to start building this fantastic project! Thumbs up to Jacob!

I have two questions:

1)My PCBs are rev#1.Are there any modifications i need to do to my PCBs in order to work correctly? (appart from the DI mod which i am aware of)

2) On the PCB i see several places where i should connect wire links.However, two of these links are connecting pads that are already connected to ground via separate traces.Wouldn't this create a ground loop? Am i missing something here?

Thanks!
Thodoris

 

[gyraf]

There only ever was one version G9, so nothing has changed - you still want to do the mentioned trace cuts for the instrument inputs.

Mounting the ground link in your pic never caused a problem - but omitting it was problematic on at least one occasion (at very-thin copper layer).

Jakob E.

 

[jezburns]

I had similar problems to RO4350 with a low output on the instrument inputs - turned out as Jakob suggested that the switching jacks were wired the wrong way (to jack / from jack the wrong way round = quiet output, screen on the wrong terminal = no output).  At first I thought it was wiring between the main and control board PCBs - I built the G9 a couple of years ago and noticed when trying to fix the low instrument output that the trafo+ and - and Output + and - were labelled in a different order on the control PCB to the main PCB.  I knew at the time but must have forgotten that these four connections are mislabelled on the PCB I have (from Audiokitchen), and that the pins between the two run in the same order (as if attached with a ribbon cable) with the leftmost being marked with a *.  Thought I'd post this in case anyone else runs into the same confusion.

I love my G9 and only recently made a beautiful recording of a Steinway piano with it paired with a couple of ribbon mics.  Just wanted to pass on my thanks to Jakob Erland for making this amazing design public and sparking my interest in DIY audio! 

 

[jeroberts]

Hi All -- I'm having issues with my G9.  Some of which seem to be intermittent, but I was wondering if you could help me out.

-- Weird noise on gain settings 9 and 10 on the right channel. This happened when using dynamic mics and condensers.  I used the "Mic" setting for the dynamics and the "+48" setting with condensers. Later when I tested the pre out, I got a clean signal with plenty of gain when using a dynamic mic on setting 9.  Gain setting 10 still had a strange noise with a dynamic mic though. Both settings 9 and 10 were still messed up when using a condenser.

-- Weird noise on the left channel in gain setting 10 when using a condenser. Also, gain setting 9 provides way more gain than 10 on this channel when using a condenser mic.

There have been other problems, but I want to tackle one thing at a time.  Has anyone else had this issue or know what's going on?

 

[gyraf]

..weird noise at high gains is often caused by oscillation. Did you cut traces and connect the front-panel jack directly as recommended?

Will moving around the cable to front-jack change the noise?

Jakob E.

 

[jeroberts]

Thanks Jakob...I didn't cut them.  Thanks for the tip -- I will cut the traces and see if that helps.

 

[nada.kiran]

Hi guys,
Built a couple of G9s for my studio. One works like a charm. The second one has a problem with the output gain.  IF I disconnect the the 3rd pin of the output pot, I get enough gain. If I solder it back, inspite of output knob at full, I get a very low gain. Please  guid.
I will upload the pictures soon.

 

[Ashayar]

Hey there

Sorry to bother you guys, but I am working on a project using a part of the G9, and I have a little question.

I do not know how to design a SRPP yet, so I plan on using the same that is inside the G9, but in differential mode. I mean, their will be two SRPP, wired in differential.

The question I have is quite simple: how much current is drawn by the SRPP, in the V2 tube on the schematic please?

With that I will be able to start the design of my power supply

Have a nice day!


François

 

[gyraf]

The magazine "Glass audio" had a big article on srpp design, I'm sure it's available online somewhere.

But I dont get why you would want to run it differentially?

 

[Ashayar]

Hello Gyraf,

And thanks for the answer, I'll search for this article
I am sorry because my English is really poor, so maybe I didn't say the right things about the design I'm working on (and hoping I'll finish it one day ).
As I don't want to put some off-topic stuff here, here is the link leading to the post where everything is explained.
https://groupdiy.com/index.php?topic=63258.msg801255#msg801255
They are not exactly the last schematics I made, but it's really close

Have a nice day!


François

 

[Dokdude]

Hello everyone. I read this thread since 2011, when i started to build a G9. After just 6 years i finally managed to complete the project.  Of course in the meantime i got married, got a baby, a new house and a new job.
I built the G9 in just a month, long time ago, but i had a major problem that i wasn't able to solve. So i put it in a box. Until a week ago, when i decided to rebuild it with new boards.

My G9 was noisy. I followed all your suggestions, from trace cuts to GND tips. But there was no way to make it sound clear. It was like a random white or grey noise, but also variable like an old untuned radio. I thought it was something like a cracked copper track or some dirt shortcircuiting tracks.
So I cleaned the parts (also ECC82 tubes and their sockets) and installed the G9 in my rack just to see what it sounded like, what the problem really was. I was shocked when i found out that the unit was silent, clear and powerful. So what was going on?
No matter, it works. I just prepared the rack and installed the G9 in the final configuration.
Few hours later i got a bad hum noise caused by a bad soldering on the instrument jack. So i had to reopen and solder again the instrument wires under the mainboard. To do this i had to remove tubes and wires. Mounted again, turned on and ... hell! again that old grey noise.
I accurately cleaned all the tracks, the points, the sockets, all the contacts, all, all. Tried again: noisy.

Long story short: I swapped some tubes. Turned on: silent and clear.
It took forever to solve my problem because the only things i was sure about were trafos and tubes.
(N.B. i verified the sockets, the soldered pins  and tried to gently move tubes while the unit was turned on = no problem here).

Now the question is: should i replace the tubes? Since i don't know why and what (or if) tube is defective, can it lead to some minor/inaudible problems?

Thank you all guys, this thread is a treasure. And finally, thak you Gyraf. Your contribution to the diy audio world is amazing.  I can't be happier of my G9 and GSSL.
Have a nice WE!

Donatello.

 

[Mbira]

I'm sure this has been asked here a few hundred times...

I'm finally wanting to finish up my second G9.  This time I'd like a nice pretty case for it.  I'm in the US.  Is anyone making them these days, or can anyone point me to  Frontpanel express file?  I have an old Par metal case here, but I'd like to make something nicer than my typical chassis with sharpie written all over it!

 

[gyraf]

Now the question is: should i replace the tubes? Since i don't know why and what (or if) tube is defective, can it lead to some minor/inaudible problems?

You most likely have a broken solder joint, or a PCB pad that's almost separated from a track.

If it works, don't worry about changing tubes. It's very rare for a tube to be intermittent-err'ed, and even if it happens, it would show clearly and not camouflage as a half-hidden sonic catastrophe..


Jakob E.