The official G9 help thread

[Alexandru marian]

I've looked (quickly) at the JLM page.  They didn't like the 1528 as much but that one has a different ratio. I guess they wired it 1:2.5 but maybe that is not optimal for the Neve?  Anyway I guess you can simply try the Marinair for output, I imagine nothing will explode because of it but keep in mind the pin layout is probably different.  You'll have to improvise a bit, either glue it to a wood base and lift it off the PCB so you can run jumper wires in the holes.  Or mount it somewhere else.  A bit too much hassle if you have the Lundahls already. 

 

[APL]

I didnt think it would work for  input.
I will probably just use the Lundahls for output  (certainly until I know everyelse works) maybe try in future.  The Marinairs were a bonus  as I was pleased to get the Lundahls I needed.

 

[milosh]

I am confused with the toroid transformer markings.
I bought Toroids that was marked  in the shop:

Transformer 1
30VA; 230VAC; 15V; 15V; 1A; 1A

Transformer 2
30VA; 230VAC; 12V; 12V; 1,25A; 1,25A

But on the labels on the transformers there is no 30VA marking but:

Transformer 1
"SEC:
0V-15V/15VA
0V-15V/15VA"

Transformer 2
"SEC:
0V-12V/15VA
0V-12V/15VA"

So each secondary winding is 15VA and the sum of two secondary windings powers is 30 VA.
Is it as it supposed to be? Or each secondary winding should have 30VA of power an I bought wrong toroids :-\?

cheers

 

[Alexandru marian]

I've had the same problem a couple pages back   Jakob's reply seems to suggest you'd need 30+30VA.  I've seen people using 25+25 without apparent problems but less than this, trafos will probably heat up .

 

[milosh]

Thanks Alexandru

Hopefully I can return the toroids to change them with more powerful.
They have 40 + 40VA or 25+25VA toroids in the shop (They don't have 30 + 30VA)
Which to choose ?

 

[spase]

40va toroids

 

[milosh]

Thank you spase..
What a fast reply 

 

[Alexandru marian]

I'm using 2x40VA too

Making some progress on my build:

-pre modules at 50% (still have some caps and the tubes in the mail)

-12V module done and working:  12.2V DC out

-250V module done and working:  383 V out, can't wait to hook a pre module and see  how it settles. 

Strange though, when testing the 12V all is fine.  Then I hooked the second trafo to check 250 and it buzzes/makes a continous noise...

 

[Alexandru marian]

Finished the tripler, I get 125V rather than 60.  I'll recheck everything.  Edit:  everything seems fine. Finished the module, 51V, a few turns on the trimmer, magic, 48.2V.  Starting to love this electronics thing

12V trafo still making noise, the 15 is dead quiet. 

Edit 2:  unwired the 12V and tested it in the normal way.  Makes no noise, output is 13V on both secs. 

 

[xazrules]

hi everyone, just finished my g9 but no signal pass through.
but if i add plenty of gain in my DAW with the unit turned on i can hear a little bit of hum and white noise and if i turn off the unit the hum go away. checked every wiring connection and seems all fine.
the tubes lights, but very little.
the first time i've turned on d15 smoked because i wired wrong one winding of the trafo, then i've corrected it and change d15 with a new one, maybe the 78s12 is gone?
can you suggest what to check first?

thank you very much for your time 

 

[Alexandru marian]

You need to check the voltages first, hopefully you have a multimeter.  You can easily pick both filament and HT on the PCB left and right of C103 and C105. 

 

[xazrules]

Thank you alexandru i'll check the voltages and post the results maybe it could be useful for anyone interested, even if in the all 87 pages someone had already covered this problem, maybe is easier for new diyer like me!

 

[xazrules]

i'm back  so, the results are:
now channel 2 pass audio but with a lot of hum and buzz and if i touch any of  the pots the hum change and sometimes it almost disappear and if i change the gain knob it change the gain of the input and of the hum, mic line and 48v both, low cut works fine.
two tubes of one channel are brighter than the other.
if i plug my guitar in hi-z gain at 11 squeals.
last but not least at the 220 vac input i read only 198 vac and at tip 121 i read only 18/19v with the trimmer at full.
i've tried to read the voltages in other point but my multimeter read 0.00
what are the issues? step up trafo?

 

[Alexandru marian]

Hmm if it was my build I'd unplug everything, take out the board and with a print of Jakob's pdf verify everything.  Drain the big caps first.  It is common to put a diode or cap the other way around, or have cold solder points, or wrong value zener or resistor...Check everything with great care. Give a gentle wiggle for each component and see if the lead tips move on the other side. 

 

[Alexandru marian]

OK I fired it up yesterday and it works just sweet!  With just 1 channel HT is 255 V.    Thanks Jakob!

BUT, I have a little bit of noise that should be investigated. It is not enough to completely ruin a recording but I can hear it on quiet passages.  I think it is AC/PSU related not from the pre. 

Here is a recording.  I am attaching the G9 to my RME Babyface interface.    I set G9 gain to zero and RME gain to +20db so the noise gets amplified and easily heard.  This is the first 7 seconds of the recording.  Then I turn down the RME gain to zero.  You can now hear to real level of the noise.  Then I turn on phantom, set the G9 gain to the max and place the microphone near the transformer so you can hear the mechanical noise of the 12V transformer up-close. 

https://soundcloud.com/chitare-marian/noise3

 

[Graph]

Hi, sorry for bothering again

I wanted to ask, i got voltages like this:

From Transformer:265v AC
From Capacitors, 330v DC.

Are these normal values? Because tube arent having a long life(1-2 years), tranys are making some noise, and i got some noise(i can live with it). And... a Resistor from the HV i remember it was white coloured(the one in 1n400x side), not its something like Green/Gray.

Thanks

 

[Alexandru marian]

You are likely measuring the first capacitor which gets unregulated voltage.  Mine read 380V and 255VDC, with 265 AC input voltage. 

As for the transformer noise, probably you get the same saturation noise as I do (and a few other builders I found).  Listen to my soundfile above.  It is simply the 12V winding not liking being fed 15V. 

I've found a step-up transformer at the link below. Seems to be made for G9. I am going to buy one soon and replace the 12V with it.    http://www.ampmaker.com/store/20W-toroid-power-transformer-PT06.html

 

[Alexandru marian]

Finished!  I love the sound, and the microphone bass is fine without any hard roll off.    Just -0.8db at 30Hz and -0.4db at 50 Hz (maybe a bit more on some gain settings). 

The second channel is virtually hum free, I might guess a trace of the 50Hz hum only if I crank the interface gain to +40 db.  The middle channel hum is audible though, but only if I have rested ears or press the headphone hard on the ear.  It was worse before but I thought about trying to rotate the first transformer a bit. A 3cm or so turn and voila, hum is halved.  But still there.  Fortunately i can't say it has any impact on a real world recording. 

Voltages are 240.2, 11.95 and 48. 

I'm amazed at how much heat the 12V regulator puts out. I used a large copper heatsink and I'm very glad I did so.  Jakob wrote something like 5W of heat but really it feels more like 50   I'm actually thinking about adding an ultra quiet computer fan over it because the caps under it must be cooking. 

Total weight: 10 kilos. 

The only problems I have now are: 
-finding some cool knobs. 
-improving transformers.

Something is definitely not right.  Both are getting hot.  Not burning hot but after 2 hours of testing, they are as hot as a room radiator in winter.    Edit:  just took them out of the box, it is the 12V one generating the heat.  The 15 only gets warm.  I am thinking about ordering a  single custom made toroid with 265, 15, 15 secondaries. 

I thought 265 because that is what i am getting in terms of AC under load at the PSU entry.  Or maybe go for 275 and get slightly higher HT (i currently have 240 not 245)  What I definitely don't want it to have to change any of the PSU parts. 

 

[andow]

First post, so hello everybody!  8)
Really great forum with lots of valuable info!

I'm about to source parts for my first G9 build and I can't get C4 which is 1,5µF. Is it ok to use 1µF or 2,2µ here?

 

[bruce0]

First post, so hello everybody!  8)
Really great forum with lots of valuable info!

I'm about to source parts for my first G9 build and I can't get C4 which is 1,5µF. Is it ok to use 1µF or 2,2µ here?

C4 is a signal coupling cap, so making it smaller will effect lower frequencies.  So 2.2uF would be fine but 1uF I am not sure if the effect would be audible ( as I don't know the impedance of the circuit at that point). 

General rule, don't make signal coupling caps smaller. 

As C4 is part of a feedback circuit I am not sure if a smaller cap would increase or decrease low frequencies, but using a larger cap won't effect them.