Official G7 microphone help thread

[lightningbefore]

I'm having a tough time finding transformers (I'm in the US) can anyone help point me find them?
(110V Model)
1 pcs. Transformer 110:9V, ~5VA
1 pcs. Transformer 220:15V, ~3VA

 

[rock soderstrom]

I'm having a tough time finding transformers (I'm in the US) can anyone help point me find them?
(110V Model)
1 pcs. Transformer 110:9V, ~5VA
1 pcs. Transformer 220:15V, ~3VA

Wouldn't it make more sense to look for a suitable transformer right away, instead of the (2 transformer) back to back solution?

 

[lightningbefore]

I'm not sure - I hope so! But what would a suitable transformer be? I'm just following the components list on Gyraf's site (and I don't really know what I'm doing).

 

[rock soderstrom]

I'm not sure - I hope so! But what would a suitable transformer be? I'm just following the components list on Gyraf's site (and I don't really know what I'm doing).

I don't want to question the proven design of Jacobs G7 but the back to back solution (which definitely works) has some disadvantages and was probably due to the supply situation for such transformers at the time.

A dedicated tube transformer brings some advantages, the schematic says that you need 135VAC and 9VAC at least on the secondary side. The 135V rail must be able to supply one(!) EF86 with one or two mA, the DC heater voltage according to the data sheet for the EF86 must be able to supply 200mA.

You need such a transformer or similar (means with larger values), which you then make suitable for your purposes.



The schematic for the G7 microphone specifies well filtered 160V operating voltage and 80V (in cardoid position) for the polarization voltage and regulated 6.3V DC for the heater. Where they come from doesn't really matter, as long as the values and the quality are right.

Especially for beginners one should always point out that working with mains voltage and high tube voltages is dangerous for the environment (fire hazard) and life (electric shock).

Professional assistance and qualified testing and final acceptance by an experienced, certified technician are mandatory.

Under that circumstances, I also find the idea of converting an existing power supply to your needs not unattractive. This will save you some headaches and probably cannot be topped in terms of price.

Some examples...

the t.bone PSU Retro Tube II

the t.bone PSU Retro Tube II; Ersatznetzteil für Retro Tube II; Schalter für Umschaltung der Richtcharakteristik; 150 / 230V, 50 - 60 Hz; Trageriemen; Anschlüsse: 7-pin XLR Mikrofoneingang, 3-pin XLR Ausgang; Gewicht: 1.72 kg

www.thomann.de

the t.bone PSU SCT 2000

the t.bone PSU SCT 2000, Ersatznetzteil für SCT2000 Mikrofon

www.thomann.de

Just my 2€ cents, stay safe and have fun. Good luck!

 

[lightningbefore]

Thank you! Similar dummy question, how would I mod the t.bone PSU to fit the G7? Literally just take out the PCB in that and put in my G7 PCB? Or is it simpler or more intricate than that? I'm still very confused about trying to get any kind of transformer for the G7 PSU vs. doing something like you suggest.

 

[rock soderstrom]

Thank you! Similar dummy question, how would I mod the t.bone PSU to fit the G7? Literally just take out the PCB in that and put in my G7 PCB? Or is it simpler or more intricate than that? I'm still very confused about trying to get any kind of transformer for the G7 PSU vs. doing something like you suggest.

I just have power supply from a t.bone SCT700 on my workbench. This should be pretty similar and would be directly usable for the G7 with a small difference. B+ of 150V instead of 160V, would be ok or quickly adapt it by a swap of the Z diodes and one resistor.

Schematic:


If you want to go original G7 you can just swap the PCB as well, if it fit into the PSU.

Ahh, yes the Z diodes are drawn in wrong direction

 

[jonathan9473]

hello guys,so i have built the g7 microphone but it lacks of high frequency, i am not so sure what is happening, maybe because of the tube? but everything was fine, 6.3v heater, 1.3v cathode and 65v on plate.

I have tried to change the tube from wing c to rft ef86, it helps a little bit.

Then I try to put the feedback in the circuit, but oddly, once I put the feedback in the circuit, the high frequency sounds natural. Isn't the feedback feature will lower the high frequency? any possible problem? I have search many threads about this, but I can't find any information.


capsule:beesneez ck12 (65v)
tube:rft ef86
transformer:lundahl 1578xl

thankyou

 

[LinusGrane]

Hello, I have almost finished my G7 microphone.

I get sound out of the mic but it seems like only the back of the capsule works properly.
I only get a low and muddy sound out of the front, so if i use the figure 8 or omni the backside of the mic sounds good but if i try cardioid and use the front it sounds low and “muddy”.

When i first tested the mic i had 174.7v att pin 2, and now i have lowered the voltage to 128.5v by installing a 40k resistor in series with the 10k resistor in the psu.

 

[gyraf]

Capsule collapsing? Phase? (listening to your own voice in headphones)

 

[kingkorg]

Hello, I have almost finished my G7 microphone.

I get sound out of the mic but it seems like only the back of the capsule works properly.
I only get a low and muddy sound out of the front, so if i use the figure 8 or omni the backside of the mic sounds good but if i try cardioid and use the front it sounds low and “muddy”.

When i first tested the mic i had 174.7v att pin 2, and now i have lowered the voltage to 128.5v by installing a 40k resistor in series with the 10k resistor in the psu.View attachment 104290

Also you shouldn't have 51v at the voltage divider, might be something wrong somewhere. You should be getting 60v. Otherwise pattern will be off. Some of the edge terminated capsules i've tested (RK12 type) can't withstand 60v. I use them at about 50v. But then you have to adjust the pattern control to be 100/50/0V.

Not sure what you get by installing that 40k resistor, try lowering the b+ by using two 60v zeners in the psu. If we are talking about regular chinese psu.