The official G9 help thread

gyraf said:

black is live and brown is neutral (blk/brn can off course be swapped).

Click to expand...

Just for my understanding, is it possible that you meant "blue is live and brown is neutral"?

For your info - these are the markings on the transformer:

Yes, you're right - marked like this, you input mains to blue and brown, connecting together white and violet.

i.e. the order of the colors mentioned on the label matters for describing phase

Jakob E.

Hi Guys.. had posted the same problem couple of years back.. my G9 is running the same problem.
I dont have enough gain on the output when the ground is connected to the output pot. If i disconnect the ground in my pot, I have enough gain.
Have checked all the values. Seems good.
This is my second G9 build. First one went smooth.
Please help.

Is the output level pot the correct value (47K/Log)? Or maybe shorted/shorted to chassis?

Check from top to bottom of pot with an ohmmeter. And from either to chassis/housing/metal.

Jakob E.

Hey Jakob
At first, thanks for the beautiful design.. it's been my go to pre from 2 years..
I hooked up the pre today after checking for dry solders and pots.. it is miraculously working like a charm..
Had one more issue... we dont get 78s12 here in india.. had to use 7812cv which is readly available.. I hooked a bigger heat sink with enough compound.. I observed better performance as well.. hav put it in observation... will let know.. 

Thanks for reporting back - and yes, I think that a 7812 will be able to do the job when it's heatsinked properly.

I myself lived in India as a kid, and depending on where you are, you may need a very efficient heatsink

Jakob E.

And I hav attached a photo of the build.. took the liberty of getting those tubes on front panel.. its easy to swap tubes acording to the recording material... have tried RCA, Telefunken, BEL.. different texture..
Power trans are housed in a different box..  no hum or any kind of noise... ;D

Finished my second Unit.
For this build I use a red frontpanel and OEP transformer IN and OUT.
Could not make a comparison with the Lundahls but the bass DI sounds a bit different in my opinion.
Now I’ll take a build break

Hi , I'm fairly new to diy with just a couple of projects under my belt,
I have ordered the g9 pcb's and I'm proceeding with the bom purchase,
could anyone tell me what wattage the zener diodes need to be?
I'm going by the bom on the gyraf site as links to newer bom's all seem to be dead on this thread,
if anyone could hook me up with a recent bom that would be great,
cheers ,
nick

I used 1,3w.

Hey TillM,
Many thanks,
I'll get some on order.....

Where do you live ?
I’ve a bom on my pc.

I am in the UK....
if you could email a copy that would be great,
I'm getting there, but it would be really useful...

Hey guys,

I just finished building my G9. Everything looked fine when I turned it on but after a few minutes the tube filaments went dark and the relays deactivated at about the same time. When that happened the indicator light started to fade out slowly. Every time I try again, the behavior is the same as described.

If anyone has an idea how to fix this problem, help is deeply appreciated!

Actually, I'm pretty sure that we have had this at least a couple of times earlier in this thread (please read closely in order not to repeat someone else's  mistakes).

12V shutting down is a sign of the 78S12 getting too hot and going into thermal shutdown mode. Make sure that you have enough cooling capacity on it, ant that it is secured (but isolated from chassis) with good thermal transfer

/Jakob E.

I really like the feel of the stepped input.
So I’m interested in using a step attenuator at the output instead of the potentiometer.
The only way for 21-step attenuator is a Elma Switch.
I found a calculator, but these one is only for 75db. Also the calculator used 22,3k in series as input resistor.
I know that the G9 has less output.
Can someone give me a advice for a 47k log step attenuator switch?
Thanks for your help in advance.

EDIT:
Yesterday I used to do a 21-Step log resistor table in excel. Maybe someone with more experience can confirm it.

This may just be a general question or a problem. I built a G9 some time ago (detailed here: https://lensprojects.wordpress.com/2015/07/11/gyraf-gix-tube-preamplifier-build/)

When changing tubes and doing a checkup, I noticed that the output voltages (relative to ground) on each side of the balanced output were different on channel 1 and 2 (with settings and input the same). For example, on channel 2, the two  XLR output pins would read about the same (say 4Vpp), but on channel 1, one XLR pin reads 2Vpp and the other reads 6Vpp. When looking differentially, the output is the same on both channels.  Looking at the schematic, I now see that the output is a completely floating transformer secondary.

Should I expect the same voltage on both sides of the balanced output when looking with a scope relative to ground?  Does anyone add something like MegOhm resistors to ground on each side to keep them from floating around? Or does this not matter at all?

for transformer balanced outputs, it does not make sense to measure single-ended to ground. They are not connected, which is why it's called "floating" balanced..

Jakob E.

Hi everyone,

I'm about to start building a G9.It will be my first Tube DIY project. I already purchased almost all PCB components except the  22.1kohm resistors (ref : CMF6022K100FHEK) that is out of stock everywhere, even in USA. They will be Available again on November 2020. I wondered if they can be replaced by this reference : CCF6022K1FKE36. The only difference between the two of them is the PPM. 50 PPM for the one out of stock and 100 PPM for the one available almost everywhere.

Thanks for your advises.

It doesn’t matter.
Take it.
You also don’t have to use these super expensive Vishay resistors.
You can also take cheaper ones from mouser.