The official G9 help thread

[tony dB]

[quote author="laiben"]
...
Also look at the guts of those Hi-end audiophile equipment their transformer are always ridiculously big!

laiben[/quote]

those Hi-end audiophile equipment is usually ridiculously expensive :green: , if you get big cash selling it, why not spend a little of it on expensive looking components?

IMHO you would have less heat buildup

 

[nielsk]

on my second G9 now, 1st one works perfectly, 2nd built identically, & has a hum I can't find the cure to. They both have outboard supplies, using 1 tranny for B+ and heaters & (rated 263V@100ma / 15.3v @ 1 a) and one 15v for the phantom. Other than that built strictly to the scematic, the bridges and res caps are in the remote supply w/ a 100K 2w bleeder resistor to ground on the post cap side of the B+ and 48V.
The B+ measures 356v DC & around 1v AC before the reg, and 258DC / .1v AC after.
(I am seeing 1.5v AC on my scope, a very distinct triangle waveform, when I measure on the fluke, it reads around 20 volts to begin with, and rapidly drops to stabilize around .5v...is this normal?)
I see the same "ripple" on all voltages.
I have rotated & moved everything every which way, not inductive as far as I can tell.
I have replaced all caps, bridges, regulators, no change.
I have tried every ground scheme I can think of, no improvement (I can make things worse!)
When the AC mains is removed & it runs off the caps, it is as clean as can be. Would this rule out a bad tube?
I did the DI bypass, works great (I am waiting on parts to try a relay switch DI mod, using a 113 style 1/4 jack to switch the 12v to a relay at the input tranny when the jack is inserted)

I am using an EMI filter AC input.....
maybe a choke?

any ideas?????

 

[gyraf]

I am using an EMI filter AC input.....

That is probably the problem. These are fine for digital/switchmode stuff, but often problematic in linear. Try with a standard ac input without filter.

Jakob E.

 

[Greg]

Don't those AC inlets with filters dump a bunch of hash into ground?

 

[gyraf]

yes - that is the problem with'em..

 

[nielsk]

with much anticipation for my salvation, I removed the EMI AC inlet, & tried it wired direct......
No change

Is the "sawtooth" shaped waveform what I should expect to see out of the bridges?

any other ideas?

 

[INDI03]

G9 newbie question - where is the 0V connected to the Chasis ? thx IA

 

[gyraf]

[quote author="INDI03"]G9 newbie question - where is the 0V connected to the Chasis ? thx IA[/quote]

As always - at the input XLR, and only there. Connect XLRpin1 to XLR ground tab. In case of more than one input XLR, then the first one.

Jakob E.

 

[INDI03]

thx for quick reply

 

[INDI03]

another question on cases - yesterday I got an aluminum case from a friend - is this ok or does it have to be an ordinary steel case to have optimal shielding ? and 2nd I wanted to know how the airslots on the case effect the shielding ? no slots will probably heat up the case too much ?! - thx IA

 

[INDI03]

one more thing - can I use JJ ECC802S tubes for the G9 ?

 

[dissonantstring]

hi indi03,
check here for some chassis discussion:
chassis discussion
i simply did a search and came up with this, so please make sure you do the same. i know sometimes i like to have answers quickly, but doing a search will often give you the same answer quickly.
as to your tube question, the ECC802S is listed as a premium 12AU7/ECC82.
i'm not expert so double check the data sheets for specs and pinout config.
hope this helps.
-grant

 

[INDI03]

thx for reply - its not the way that I didnt use the search function but on most things I get 20 threads with 100 posts - it would take 10 days to find an answere for 1 question - well on some I found easy

 

[nielsk]

I just solved the hum problem, I was able to look at the 1st one I built and found I ran the secondary B+ cap ground to the HV in ground point and the input Ground to the secondary cap ground point (I used single 100/350 caps mounted off board instead of a multicap, WAY cheaper). switching this on the second unit made it totaly clean...kind of odd, the ground path connects all the way through. The remote supply is great, extremely clean. I used high voltage cable and AMP circular plastic connectors, female pins on the cable end. I placed the bridges and primary caps in the supply, & jumpered out these parts on the main board. All B- and grounds tied to power ground in the supply, and a seperate chassis and p/s ground run from there to the unit. The trick is to connect the p/s ground to the secondary B+ cap ground point.
I also tried using a P&B shielded 12v relay for the DI input, switched by the 1/4 jack (Switchcraft #113). I was able to fit the relays right next to the input transformers, it works fabulously. This would make a good revision to the board.

 

[Wolferl]

About six months after finishing my G9 I found the time to reanimate my "old" problem with this preamp:

http://www.groupdiy.com/index.php?topic=15513&highlight=

In a few weeks I have a recording session and I want to use the G9 for Vocals because it sounds sweet. But I have still some hum at the outputs - stable without any gain - left. It is a bit 50Hz hum and a lot of 100Hz, both good audible on both channels (right channel has got more 50Hz hum). I changed / adapted / increased /measured capacitors, regulator, diodes, resistors, ... I even used a additional 10H Choke for B+.

No improvement.

I checked ground lines for loops, earth, shielded all cables, ....

No improvement.

I turn the power-transfomers outside the housing - no improvement.

In the next step, I will change the HV-power-transformer

Any ideas left? I invested so much time in this project and hope to find finally the solution for a clean output signal... :? :roll: :roll:

Thanks a lot!

 

[Wolferl]

yesterday I changed as a last action the HV-tranny. No improvement. So I close this chapter of DIY and try to be satisfied with about -90dB@100Hz noise. It's not really bad but I expected a bit less hum.

 

[laiben]

[quote author="Wolferl"]yesterday I changed as a last action the HV-tranny. No improvement. So I close this chapter of DIY and try to be satisfied with about -90dB@100Hz noise. It's not really bad but I expected a bit less hum.[/quote]

Hi,

I am going to make a G9.. hopefully all the parts will be here by March.

Just some thought, what is the filter cap value you are using? if you are using 100uF as suggested in the schematic, you may try to use 220uf?

 

[nielsk]

BTW, I also added a Line + 48V position just by making the switch 4 position and jumpering the 48V to that pos, actually very useful. It just so happens that I mostly need the pad on phantom powered mics......
you should try changing the ground point for the off board caps to cure your ground noise, it worked for me, any line freq noise is so far under the hiss that it is not a problem.

 

[radiance]

I'm using my G9 on the insert of a group/bus of my mixing console and I'm noticing a low end roll off starting at 60Hz. It seems like the G9 is lacking bottom end. Could this be because of an impedance mismatch?
(inserts are fully balanced with separate xlr's for send and return and they're spitting out line level)
When I connect my G9 between the in and outputs of my RME Adi 8 pro soundcard there's still a lack of low end.

I've checked my G9 very thorough and could not find any fault. It's working like it should, low cut works fine. I realy don't know where to look further....
Also, if I use the instrument input there's still a low end roll of so I guess I don't have to look for faults at the input tranny. I build my G9 with Oep's.
I even replaced the output Oep for a Lundahl but that did not solve the lack of low end.
The G9 should deliver a solid bottom right?

Could it be the JJ tubes I've used?

 

[waldorfcave]

Hi Radiance,

i will also build a G9. For my synths and mostly line signals, going into my
rme fireface audiointerface.

The your lost of the low end, worries me :?

I hope you will find out why.
g. Lars