Official G7 microphone help thread

[Alexandru marian]

I doubt AC is called for anywhere.  250V is a more conservative rating. If you have the part and it fits, use it. 

 

[gyraf]

And yes, it's simply inconsistency between the layout and schematic. 160V types works well.

Jakob E.

 

[Alexandru marian]

Jakob, what do you think about that little schematic I posted on the previous page?  Thanks!

Also, do you think the mic would draw enough to kick-start a TL783?  I bought several for the G9 and could set one for 160. 

 

[Alexandru marian]

Is this OK for testing without a capsule?

 

[gyraf]

Yes, that's the right way to do it.

 

[CurtZHP]

Apologies in advance for cross-posting...

Just finished building the power supply for my second G7 mic.  After chasing down a problem with a stray solder bridge, all is well.  Except.....

On my first power supply, I read the following voltages (these are all WITHOUT the mic connected):

Pin 2 = 172VDC
Pin 5-Figure 8 = 172VDC
Pin 5-Omni = 0VDC
Pin 5-Cardioid = 83VDC
Pin 6 = 6.3VDC

On the second power supply, I read the following:

Pin 2 = 236VDC
Pin 5-Figure 8 = 236VDC
Pin 5-Omni = 0VDC
Pin 5-Cardioid = 114VDC
Pin 6 = 6.2VDC

All components between the two are identical except for the second transformer, the one wired "backwards."

On the first supply, that transformer is an Amveco 62013 15V 3.2VA.  On the second supply, it's an Amveco 62042 12V 10VA.  (I got it cheap from a surplus supply company.)

Is that the short answer for the discrepancy?  Is there any harm/advantage to keeping it?

 

[gyraf]

Yes, it's because of the difference in transformers.

With mic connected and heated (ca. 30sec.), find a series resistor that gives you 115-120V HT at the supply.

Jakob E.

 

[CurtZHP]

Thanks, Jakob.

Or I might just spring for the correct transformer and do it right, like I should have done in the first place.

I'll throw this one in the parts pile for a future project.

 

[CurtZHP]

Any chance I could use that 2x12V 10VA transformer for the GSSL? 

 

[gyraf]

You NEED to measure the supply voltages with mic attached and heated up.

2x12V is too little for the GSSL

 

[CurtZHP]

2x12V is too little for the GSSL

Ah, nuts!  Oh, well.  I'm sure it'll come in handy eventually.

 

[MetalD]

EDIT: Just noticed I made a dumb mistake. Carry on.

 

[Potato Cakes]

Hello.

I'm starting to build my G7 and I'm trying to use as many parts I currently have left over from other projects. What affects would there be if I used a 1.5K resistor in place of the 1.6K that is listed on the BOM? Would this be far enough off to create to adversely affect the sound?

Thanks!

Paul

 

[Murdock]

Hey Jakob,

I'm searching a suitable power transformer for my G7. I asked someone, and he said the PRR176 Transformer would work (https://www.don-audio.com/prr-176-power-trafo-sec-18v-18v-120v_1).
He said the LM317 could handle the 18v.
Can you confirm that this transformer will work with the G7?

 

[ln76d]

Hey Jakob,

I'm searching a suitable power transformer for my G7. I asked someone, and he said the PRR176 Transformer would work (https://www.don-audio.com/prr-176-power-trafo-sec-18v-18v-120v_1).
He said the LM317 could handle the 18v.
Can you confirm that this transformer will work with the G7?

You can connect both 18V in anti seriall and get 9V.

Also you can order custom toroid, in my opinion, better made and probably cheaper:
http://sklep.toroidy.pl/en_US/index
Am using it in my last G7.

 

[gyraf]

You can connect both 18V in anti seriall and get 9V.

Note that you can only do this if it's a 18V center-tapped trafo (i.e. 2x9V)!

Jakob E.

 

[ln76d]

Note that you can only do this if it's a 18V center-tapped trafo (i.e. 2x9V)!

Jakob E.

Sorry, my mistake! With two different voltages there will be a drop.

 

[Dumbascii]

Had an old (though unused) MXL V69 with a popcorn-ridden tube. Research showed it wasn't worth fixing, especially due to the soldered in submini tube. I used the Gyraff G7 schematic to hand build a new head amp and make some simple mods to the existing PS-69 power supply. Even with the giant V69 body it was a challenge to cram everything in there. I was shocked to find that it worked on the first try! Super quiet and sounds quite nice. The only major deviation from the G7 drawing is the transformer, where I used a cheaper Hammond 560C wired as 600 and 24 ohm.  I did have to bend the stock frame a bit to fit the huge transformer.

Thank you so much Gyraf and GroupDIY!

Here's too many photos.

-frank

 

[knight84]

Had an old (though unused) MXL V69 with a popcorn-ridden tube. Research showed it wasn't worth fixing, especially due to the soldered in submini tube. I used the Gyraff G7 schematic to hand build a new head amp and make some simple mods to the existing PS-69 power supply. Even with the giant V69 body it was a challenge to cram everything in there. I was shocked to find that it worked on the first try!

-frank

Hi,

I wonder If the G7 pcb can fit into this microphone. I am looking for a donor body but looking in the forum, couldn't find any body given as decently enough for G7.

 

[hitchhiker]

I suspect that body is not long enough. The G7 pcb is quite long.