G7 finished!!!!!!

After long, long, time (over one year) G7 works :grin: .
I have problem with right voltage. I must exchange second transformer with 220V-15V (I cant get higher than 140V).
Now I use 220V-12V (in wrong way) and I had 180V and with zener and poly in parallel now I have 160V.
Voltages:
After 10K- 156V
On plate- 70V
Cathode- 1,39V
Capsule- 75V
Pattern works very good. When I assembled mike and push on I measure all voltage and I got sound but I
had only omni :shock:. What happened: I cant find new styroflex 10n and I used old one who was bad. I find another old one and problem was solved. Also I cant find 2,2uF for stabilize voltage and I use two 1uF. I have one 2,2uF but I cant put in chassis.
On first listening it sounds very good. Other mikes doesnt sounds better but different
Like on other two mikes I have hum (who is decrease to zero when I touch mike near capsule or when I put another one mesh over this. Now I used mesh about 16x16 on Ela M and 18x18 on C800D and G7.
Mesh is nickel steel. Soon pics.
Thanks to Ward, Thomas, Jonathan, Moby for parts and to my friend Vasco who help me with works on lathe. All other works is handmade.

Congrats Duka,
:thumb:

At the moment I'm putting together the PSU for the G7, and I was wondering :

The 220:9 - 15:220 gives somewhat 135 VAC.

If I understand correct you used 220:9 - 12:220,
which gives theoretically +- 165 VAC.
Please correct me if I'm wrong.

We need 160V regulated,
I don't understand how that could be done with only 135 VAC.
It seems more logical to start from 165 VAC before regulating.

Somebody knows for sure ?

With tube microphones you can use a voltage doubler and 3 to 5 stages of passive filtering. The current is often under 3ma for the plate supply and pattern control parts. I used a 125Vac transformer into a X2 for the 800 type microphone and got about 290VDC with no load.

Hi Ward,

135V AC gives 135*1.41 V DC = 190V DC unloaded.

You'll find that under load the supply will drop somewhat lower under load. I ended up with 144V under load, and the mic works quite happily like this. I don't think exactly 160V is critical forJakob's design.

http://www.omnipressor.com/Other/G7mics/Comments.html

Zebra,

You're right. I experimented with anything from 120 to 160V and there seems to be very little difference in the resulting sound...

Jakob E.

Any suggestion about hum & mesh?
Underheating EF86?
Duka

I used an old HT & heaters transformer.

It had 2 heater windings so I put them in serries to get enough voltage for the LM317 to regulate.

The HT was about 210V so I just adjusted the 10K resistor between the 2 high voltage caps & now have exactly 160v under load. It was strange because I wound up with a resistor that was about 4 times my calculated value !!

Great Duka!

thanks for the inspiring message :razz:

Congrats :thumb:

Tony

Duka

It sounds like you might have a problem with the wiring ground in the building. I do not know how Kotor, Montenegro power wired. Do you have a friend that can check the wiring in the building?

Thanks guys,

Can I ask some more questions ?
I'm sorry if it has been asked before.
What should I do with the grounding ?
In the microphone, and in the psu?
This is all new to me.

[quote author="Gus"]Duka

It sounds like you might have a problem with the wiring ground in the building. I do not know how Kotor, Montenegro power wired. Do you have a friend that can check the wiring in the building?[/quote]

Hi Gus
I will check it but I wrote : when I touch mike near capsule it decrease hum to zero and when I put another one wire mesh around mike too.
Also when I push low cut its gone.
Duka

Duka,

I think the wire mesh you use is too open. Try with one more layer or two to see if that gets rid of the hum..

Jakob E.

New pics!!!!!!

[quote author="ward"]Thanks guys,

Can I ask some more questions ?
I'm sorry if it has been asked before.
What should I do with the grounding ?
In the microphone, and in the psu?
This is all new to me.[/quote]


Ward,

Read the Microphone Meta, especially the G7 bits. There are lots of comments about grounding. Look at the schematic and the circuit board layouts too.

0V should tie to the PSU chassis at one point - preferably at, or close to,
the XLR.

IIRC, in Jakobs layout the heater -ve is tied to the 0V inside the mic in just one place. In my mics I often make this connection in the PSU instead and that has worked too so there is not just one answer to this problem.

z50

I like how you did your mount. I had the hardest time with mine. The mike is so heavy I had to come up with a locking pin to keep it in place when I put it on the mike stand. Yours looks more professional than my design, simpler too.

[quote author="gyraf"]Duka,

I think the wire mesh you use is too open. Try with one more layer or two to see if that gets rid of the hum..

Jakob E.[/quote]

Hi Jakob
Yes, when I put another one hum gone. I cant find thin mesh here.
Duka

Parts:

XLR:

[quote author="zebra50"]
0V should tie to the PSU chassis at one point - preferably at, or close to,
the XLR.
z50[/quote]

Hi Stewart.
What with mains ground?. Does it goes to XLR or near Euro conector?

Thanks Zebra,

I read (and reread) the posts in the meta about the G7.
But some things are still unclear to me, because I'm bad at english, and even worse in technical english, I'm sorry.

If I understand correct there should be only one point where everything goes to ground ?
Jakob wrote : "... the heater 0V, chassis ground, HT 0V, audio ground has to be connected. Preferably in the mic."
What is HT ??
Where do I connect the earth from the power inlet ? I let it unconnected for the moment.

My supply is finished,
it doesn't smoke or blow up. Jippie !!!

I measure, without any load.
6.20 Vdc between pin 6 and 7. (which is ok I guess)
+-160 Vdc between pin 1 and 2.
BUT if I measure it AC then I read 360 Vac (which is a little scary)