The official G9 help thread

If you go to the preamp page on my website (www.zerrohouseproductions.com) you can see the pictures of my G9 build.  There are a couple pictures showing how the power transformers are connected.  I used Amveco toroidials.

Basically, I took the secondary of the mains transformer (115V Pri -15V Sec) and attached the wires to two solder lugs located OFF the PCB.  At those solder lugs, I also attached wires to each of the points on the PCB that call for 15VAC.  Finally, I attached the 15V secondary of the tube plate transformer (15V - 220V).  If you don't have any solder lugs handy, you could just attach all the wires off board with wire nuts.

Basically, you're just taking the 15V secondary of the mains transformer and splitting it off to three different places:  the two points on the PCB, and the secondary of the plate transformer.

Note: If you use solder lugs, make sure they are COMPLETELY isolated from the chassis.  In my initial build, I made the mistake of using one that wasn't, resulting in the mains secondary being connected directly to ground.  An Amateur Hour mistake that fortunately only cost me a fuse.  Better yet, just use wire nuts. 

  Thanks so much CurtZHP,

    But I am still confused, I'll explain....  If both transformers were still 15vac secondaries, I would not be confused and everything makes seance. But Gyraf changed transformers to one 15vac and one 12vac, and in the graphic I posted the 15vac that the black arrow indicates is now 12vac - Thats whats confusing me , do I use the other 15vac from T1 to backfeed T2 12vac  for 220 on T2? will I get 12vac from the other secondary on T2 to feed the 12vac indicated by the Black arrow?

anyone?

actually your black arrow is pointing to the left side. Draw this arrow pointing to the right side to see in what direction your T2 is fed.
The paralleled secondaries of your T2 connect to the feeding 15VAC secondary of T1 and get a 1:18.33 step up transformation as this transformer is connected backwards. This is not 12VAC in this spot, but a 12VAC:220VAC has a higher ratio than a 15VAC:220VAC transformer to get the increased target voltage.

  Thanks so much Harpo,

    I think I have it now..  after reading you post and looking closer at the schematic. I think what was throwing me off ( besides the Newbeeness ) is that the PCB is printed 12vac at the black arrow so I thought that I needed to "Feed" 12vac TO there.

  So let me see if I have this right:

    One 15vac secondary from T1 FEEDS 15vac TO PCB near the 220vac on PCB
    The other 15vac secondary from T1 FEEDS the other 15vac at the Black arrow in the Graphic AND is Tapped to FEED the paralleled secondaries of T2 and the Primary of  T2 FEEDS the 220vac on the PCB.

  This makes sence to me.... is this correct?

    ;D

yes 

  YIPPEEEE  !!!!!    ;D ;D ;D ;D

    Thanks Harpo and CurtZHP for taking the time.

      My G9 is done except for this and a nice face plate,  so tomorrow I will wire this up and flip the switch 

  Thanks again,
                      Chip  ;D

 

  Well.... I hooked it up.. I used a terminal strip and parralleled the secondaries of T1 to the terminal strip the branched out to both 15vac inputs on PCB and input to secondary of T2.
    flipped the switch and blew the fuse    , replaced fuse with correct value, flipped the switch, smoked D15 and blew the fuse 

  checked the schematic and saw that D15 is traced directly to the power input for channel two supply from the 15vac on PCB, so I replaced D15 and the fuse and disconnected that 15vac to the PCB, flipped the switch..... no smoke .... did some checking and got:

  119.2 incoming AC
  16.8vac from T1 secondaries
  270.8vac from T2
  12.29 from indicator light feed
  240.8vdc from C14
  309.8vdc from C15

  I think these reading are all within spec. so I think my problem is isolated to channel two power supply

  ... any ideas/thoughts/suggestions ?

 

audiophreak said:

.. and parralleled the secondaries of T1 to the terminal strip the branched out to both 15vac inputs on PCB ..

Click to expand...

there is a reason for dual secondaries. Why don't you wire this transformer as already described in your previous post?

One 15vac secondary from T1 FEEDS 15vac TO PCB near the 220vac on PCB
The other 15vac secondary from T1 FEEDS the other 15vac at the Black arrow in the Graphic

Click to expand...

I will do that tomorrow --  Thanks  ;D

  O.K. ...... I think I fell out of the Newbie tree and hit every branch on the way down ...  ;D

  I finely got the power transformers hooked up correctly and all voltages look good, set the 48v with trimmer, no audio  :'(  forgot what color leads I used for the input and output jacks on the starquad shielded cable, fixed that,

  Channel two up and running, no occiation , no noise, all switches work correctly and sounds great !  ;D

  No audio on channel one   

  I think it maybe the input or output cables, I soldered them directly to the PCB, makes troubleshooting a pain, so I'm gonna order the Mollex connectors to make that neater and better for removing the PCB.

  I'm sure I will have more questions and I will try to be more thorrow before asking, so thanks for putting up with me.

 

 

Check and make sure you've soldered all the pins on the rotary switches, paying particular attention to the center pins.  When I first fired mine up, I had no audio on one channel and discovered that one of the center pins of the phase switch was never soldered.  Oops!

Relax.  If the thing worked perfectly on the first try, it would just make you paranoid.

  Ha Ha Ha... Thanks CurtZHP, 

  I think I did solder them all but i will defiantly check.

    Thanks

audiophreak...i recently had a similar problem that left me puzzled for hour/days....i'm a newbie here too...and it turned out that my DI jack wasn't making contact on the shorting tongues...i clamped them together and bingo! just replaced the jack....just a thought...easy to try it...cheers, alex

 
Hi junkmaster ,

  Thanks for the tip, I didn't get a chance to check the DI inputs yesterday, so I did today and BOTH channels work ! 

  so I guess my problem with Channel 1 is on the XLR input side, need a break for a few days anyway

Question, I did the trace cut fix for oscillation and noise, so I just want to verify that with the trace cut fix, it doesn't matter what position the input selector switch is in because the " switching jack" takes care of that - correct?

  - also I read earlier in this thread about the relays making a clicking sound  when 1/4" jack inserted, mine do not, is that also a result of the trace cutting?

    all other switches work correctly, that 78s12 IC does get very HOT, I have a good large heat sink on it but the case top above the heat sink gets VERY warm, the case is vented top and bottom though.


  Thanks so much,
                        Chip

p.s.  - CurtZHP  - that was " I'll Definitely check on that " - my spelling sucks 

O.K. ... you didn't think I could keep my OCD ass away from this for a couple of days ... did ya?

  after finding out the instrument jack worked on Ch.1, I knew it had to be on the input cable to PCB. I found that the insulation on the + lead had melted and shorted to ground, as well as, I broke the 0v trace to the relays trying to make sure there was no solder bridge between the XLR pads. 

  So I scrapped off some trace mask and made a little jumper, then soldered the Input cable directly on the ground trace-0v,(+)-R3,(-)-R2-R4.

  It Lives!!    and all works, Inst. w/relays, Mic, Mic +48,  Phase, Low Cut, Both Channels  !!! ;D ;D ;D


  I havent had a chance to put it through ALL the paces and let it burn in, but I did notice that with no input plugged in and the output to a crown D-75 to some old Marantz 3ways, there in a Humm with the Gain in any position, and the Output pot full Counter Clockwise, as I move the Output pot it gets quieter up to the Twelve O'clock position, then gets louder to Full Clockwise and as it passes from 12 O'clock to full Clockwise it changes to a Buzz instead of a hum ...

  Any Ideas ? 


  Thanks in Advance ,  I gotta get some sleep now




 

audiophreak that's great ....seems we had similar problems w/ jacks and cable connections...i had to rewire my molex connectors a couple of times before i got the hang f it....in my very limited experience it seems to be mechanical faults that cause the most problems....i'll wait for someone better informed to offer you advice on the switches and the hum...good luck! alex

  I havent had a chance to put it through ALL the paces and let it burn in, but I did notice that with no input plugged in and the output to a crown D-75 to some old Marantz 3ways, there in a Humm with the Gain in any position, and the Output pot full Counter Clockwise, as I move the Output pot it gets quieter up to the Twelve O'clock position, then gets louder to Full Clockwise and as it passes from 12 O'clock to full Clockwise it changes to a Buzz instead of a hum ...

  Any Ideas ? 

Click to expand...

Don't test with no input connected - at least plug in a shorted 1/4" jack to the front.

For noise/hum tests, also make sure that you de-balance correctly when going into unbalanced equipment.

Last - you need to know and relate to the levels you are working at: you can always have a lot of noise if you use high enough gain. The real test is if it's usable in your studio setup - and how it behaves there.

Jakob E.

Hi Jakob,

    Thanks for the insight !  and Thanks for making such a great piece of gear available to the community. I've only done a few Royer Tube Mods prior, although I have read that the G9 would not be a good first large project, I think I did pretty well, I had a ton of fun over the last few months and learned a LOT. also learned I have a lot to learn.  ;D
  Thanks to all that helped and all that post with their own experiences with their builds, it helped tremendously with avoiding some of the more common pitfalls.
 
          Photos to follow...


      Thanks again to all,
                                Chip

Hi,

Would it be easy to make just one channel out of this? I still need all the tubes, or is the "B"-tubes channel 2 in a way? I don't understand how the signal from each channel don't get mixed The tubes seems common for both channels, but everything else is separated?

Hope anyone can fill me in, or anyone knows about a DIY 1 channel tube preamp. Thanks

Best Regards,
Vegard

Hi All,
   
      My new G9 is AWESOME !!!!!!!!!

    I haven't recorded with it yet,..so I can not comment on this low frequency roll off stuff,but strait to an amp and speakers, this thing shakes the walls, plenty of smooth low end. I have a modest collection of Vintage tube and Diy'ed tube microphones and just the mics, through G9 to crown D-75 to old Marantz three-ways, the G9 ROCKs !

  Very very quiet, and the adjustability between the gain and output is very cool , you can " Dial In " some pretty cool tone, or Very Clean, or in between. The case gets VERY warm from the 78S12 heat sink - is it supposed to get this warm ?  I have let it Burn In over the last 36 hours or so, so no thermal shut down, but it does get very warm.

the only thing I need now is the nice face plate.

  Here is a link to pics of my build, my first large project.

    https://goo.gl/photos/dpxSrUpnvGHRzyhH9

comments/questions welcome

    Thanks Jacob/Gyraf  Audio, Harpo ,CurtZHP,junkmaster, and everyone for helping me complete this very cool project.
                                                                                                                                                                        ;D ;D