The official G9 help thread

[Majestic12]

Hi there,
I am collecting parts for my G9. Is that Toroidal Transformers are must for G9? or can i use normal PSU transformers?
Regards
Dinesh

You can use normal transformers but the chances that you will get hum problems are much higher than with toroids

 

[tobi.pl]

Hi there,
I am collecting parts for my G9. Is that Toroidal Transformers are must for G9? or can i use normal PSU transformers?
Regards
Dinesh

You can use normal transformers but the chances that you will get hum problems are much higher than with toroids

I'm already using toroids, so this can't be the issue. As it's level is all the same, regardless how much gain or output level i'm using, it isn't induced by the transformers (at least that's what i'm thinking).

 

[sonolink]

Sorry if these are silly questions but I'm trying to do my homework with the schematic and fully understanding it.
-V1a and V1b are the same tube right? A and B are each half of V1 (same for V2). Please confirm.

-what does "ff" stand for in "Heater 12V (ff)". It also appears at the V2 tube filament.

- what do the small circles with a dash mean. Does the angle of the dash mean anything? (seems like some are angled differently than others.

-Some switches are marked "cw". Is that "clockwise"?

Thanks a lot for your time and help
Cheers
Sono

 

[psychedelnick]

OK! I've got my G9 in the ballpark of good sounding. However....Noise! 2 kinds! Ch 1 is white noise, and 2 is a loud hum. Before I star grounded everything it was waaaayyy worse. How much difference does the MU shield make? More importantly Ch 1 is quieter than Ch 2. A LOT quieter. Checked all resistors (are 32 and 132 supposed to be 22R? I ask cause the value is 10K on parts list) but all others, diodes, caps, tubes. Good. All the right shit is heat sinked. Worried it could be a bad tranny? Is this common? Right out of the gate? Gonna test for continuity tonight but if anyone has a different idea, i'd love to hear it. Thanks!

 

[gyraf]

Very common problem - have you looked through this thread for possible fixes?

Did you do the recommended mod with cable-mounting the front panel jack?

Have you tried rotating/moving power transformers?

Jakob E.

 

[sonolink]

Well thanks a lot for answering, J

 

[psychedelnick]

Hi Jakob, yes, I did the line mod.  I have been reading the thread all morning and have a few new ideas to try. On the upside, this thing sounds great! Thank you so very much for turning me on to the very addicting world of DIY! I also now have a clean quiet GSSL thanks to you and everyone on this forum.  8)

 

[MeToo2]

Sorry if these are silly questions but I'm trying to do my homework with the schematic and fully understanding it.

-V1a and V1b are the same tube right? A and B are each half of V1 (same for V2). Please confirm.

confirmed

-what does "ff" stand for in "Heater 12V (ff)". It also appears at the V2 tube filament.

heater filament. ff is traditionally 12v6. On tube pin out diagrams, the two pins of the end of the heater filament were each marked 'f' whilst the pin at the centre of the filament was marked 'c' (for 6V3 heaters) thus 'ff' = the two halves of the heater in series =12v6 heaters

- what do the small circles with a dash mean. Does the angle of the dash mean anything? (seems like some are angled differently than others.

generally these are just connections from a wire to a PCB track. AFAIK the angle has no significance

-Some switches are marked "cw". Is that "clockwise"?

confirmed

Thanks a lot for your time and help
Cheers
Sono

You're welcome.

Well thanks a lot for answering, J

Patience will be rewarded.

 

[sonolink]

Thanks a lot for your fast and kind reply MeToo2

 

[psychedelnick]

Okay seems like a no brainer but, my switched line in on both channels stays on in mic, 48V and line. Does this mean I wired it wrong? Haha. Seriously though....

 

[gyraf]

If you mean the front panel jack - that is NOT line, but Hi-Z input.

Line is through the xlr at back - only looking into ~10k in stead of 600R (that is, when "line" is selected).

Xlr inputs are disabled/switched out when front panel connector is used.

Jakob E.

 

[psychedelnick]

AH! Thanks!

 

[Nick-ES]

Hi,
I'am building a G9 at the moment and have some question
concerning C3, C103 Cap.

In the shematic there the value of C3 and C103 is 470 nf
On the PCB and component layout it is  220nf

whats the right value ? if both are possible witch one is better ?

regards
Nick

 

[haima]

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...

This sounds like the problem I had with my two G9s. The fix for me was to move the high voltage aka "B+" PS off the main board. Move the B+ rectifier, caps & regulator off the main board and building them on a small piece of vero/strip board. Run clean B+ to the main audio board.

The constant low level hum has completely gone from both my units once I did this - hum levels are now below the background hiss, which is VERY low.

I have scope photos & audio samples from before and after and it's very noticeable - I'll try and find them and post them some time.

Before I did the off board PS fix I noticed that if you unplug the mains and listen to the preamp the hum will go away for a few seconds - before the HT caps completely die. I then tried running the preamp with an external B+ and the hum was gone. So I built the B+ supply off board - hum gone.

I think I've mentioned the fix in a bit more detail in some previous posts in this thread if you have a search.

Good luck!

 

[Nick-ES]

just a bump to all that that allready built the G9

Hi,
I'am building a G9 at the moment and have some question
concerning C3, C103 Cap.

In the shematic there the value of C3 and C103 is 470 nf
On the PCB and component layout it is  220nf

whats the right value ? if both are possible witch one is better ?

regards
Nick

 

[psychedelnick]

My finished G9. Thanks Jakob and everybody else! What should I make now?  :

 

[gyraf]

In the shematic there the value of C3 and C103 is 470 nf
On the PCB and component layout it is  220nf
whats the right value ? if both are possible witch one is better ?

Does not matter really (that's why I didn't change it). Put in whatever you have that fits the space.

Jakob E.

 

[sonolink]

Hi all,
I noticed this difference between the schem and the board. I don't know if it matters but just thought I'd point it out. Also, in case I'd go for a point to point which should I follow? I guess the rev.8 schematic, right?
Cheers
Sono

http://img31.imageshack.us/img31/5165/c7network.jpg

 

[gyraf]

Both should work very-very close to the same. If in doubt, follow the pcb, as this is known working.

Jakob E.

 

[sonolink]

Ok. Thanks J