Official G7 microphone help thread

[Gachet]

Hello

How do you guys wire the CT12?
The two pins on the side of the capsule goes to center?

 

[gyraf]

yes, the two on the side are backplates (connect those together and to the +50-60V), the membrane-retaining-ring-connections are front/back

Jakob E.

 

[Gachet]

Thank you Jacob

So my capsule is wired correctly.
I've tested the connections between the capsule and the tube.
I've measured the styroflex to make sure they are ok.
I reversed the capsule front and back...

But I'm still having the same problem:

When I switch directivities I have:

Figure 8: Lots of lo end , a bit woofy
Cardio: A great sound pretty well balanced
Omni: No lo end at all, like a 500Hz Hi pass...

I recorded it so it's not  the phase issue beetween  headphone and mouth.

Any suggestion?

 

[rcphillips]

[posting to the official help thread now]
I'm finally getting around to building a G7 (majority of parts have been purchased and sitting in a box for a decade or so), and after reading the META and META-META, I still have some questions, maybe some of you all could help me?

[project details]
PCBs: Gustav's
Body: Chunger's Alctron MK47
Capsule: BeesNeez M7
Tube: PF86
PSU Case: Dan's PSU case
Transformers: Lundahl LL1538
Appropriate mods: in the PSU pattern switching section 100k+100k resistor becomes 40k + 50k+50k; in the mic itself, the second 470k resistor becomes 282k (maybe higher, depending on actual measurements) to lower the polarization voltage of the capsule - I think the combination of changes should result in the heater voltage being around 4-4.5v for the PF86 (I think that's what I've read, and calculated)

[mic pcb questions]
- For connecting the tube socket pcb to the main pcb, should I just use a bunch of thick resistor leads bent at a close-to-90-degree angle? [Jakob says "yes", thank you!]

[PSU and PSU case questions]
- Should I just use wire nuts (twist-on wire connectors, like: https://en.wikipedia.org/wiki/Twist-on_wire_connector ) for connecting things like the two toroids? Seems like it would be fine.

- I'd like to add a power indicator lamp; it looks like I could get a panel mount one like:
https://www.mouser.com/ProductDetail/VCC/2152A6?qs=I7nE1oQSFs9skzm1Siom9g%3D%3D 
https://www.mouser.com/ProductDetail/VCC/2120A3?qs=rHu0DOexXLC4pEbHTBL8Fg%3D%3D   

and wire it to the power switch. Does that make sense to do, or would you recommend something different?

- Any preferred pattern select switches? I have some Lorlin rotary 2pole/6position, but I'd have to spend some time widening the hole in the case (the rotary shaft is maybe 1/32-1/16" too  large to fit).

- Any preferred standoffs + bottom screws for mounting the PSU board to the case?

- For the panel mount XLR (Neutrik D series) and IEC outlet (Schurter 6200.2100), are some flat 4-40 machine screws appropriate, or is there a better choice?
-----------------

Thank you in advance for any and all help you can give.

Cheers,
-Robert

 

[Joekkel]

hi there

i've just finished building two g7 with changeable caspules/heads  8) everything sounding good so far.

i have two minor issues, where i could need your help/opinion:

first: i have a small hum from the transformers in the psu, the hum disappears the moment i turn off the power on my psu, the clean signal stays for some seconds. my trafos are not toroids, in hindsight, that would have avoided the hum, i guess. should i replace my transformers with toroids or can i shield my two signal cables by using a microphone cable inside the psu? and if so, should i use the shield of the cable as the signal ground or just connect it to ground and leave the xlr7pin1-xlr3pin1 connection with a single cable?


second issue: i modded the psu for 120v for k67/c12 capsules, they work fine. the 60v polarisation is however too strong for my k47 capsule which needs around 45v. so i thought about building a voltagedivider inside the headbasket. to get 45v out of 60v i need a divider ratio of 1 to 3. now.. how high have the values to be? would e.g. a 1k and a 4.5k resistor be ok or can i forget about suitable resistors after the 1g resistor? is there another way to get the voltage after the 1g resistor down to 45v (inside the headbasket).

best regards
joachim

 

[shabtek]

Position of transformer can make difference in mains frequency hum magnetic coupling.

grounding and shielding really matters too.

Bias voltage divider should be higher value in megaohm range

 

[Joekkel]

thank you! will try shielding the two signal cables. and build a voltage divider with megaohm resistors!

 

[JerryPbury]

Anyone know where I can get any of these transformers?
I did a search and nothing is in stock. I have the Triad equivalent but they are 3” in diameter and it’s pretty crowded in the PSU chassis.

Avel Lindberg: Y236201 & Y236203
Amveco: 62011P2S02 & 62023P2S02
Talema: 62081 & 62083

Any others in low profile or smaller than the Triads?

Thanks,

Jerry

 

[JerryPbury]

Tight fit but it works!

 

[gyraf]

..one of the benefits of having played tetris too much..

 

[earlfsmith]

It would be nice to find some audio examples of the G7 mic

 

[gyraf]

..honestly, audio examples tells you absolutely nothing when it comes to microphones - UNLESS you set it up yourself, so you know exactly how the room/position/performance was..

..yes, I know there are companies claiming otherwise, but it seems massively unconvincing to me..

/Jakob E.

 

[earlfsmith]

..honestly, audio examples tells you absolutely nothing when it comes to microphones - UNLESS you set it up yourself, so you know exactly how the room/position/performance was..

..yes, I know there are companies claiming otherwise, but it seems massively unconvincing to me..

/Jakob E.

Yes i agree but examples will at least get a ball park character to have somewhat an idea of usage.

 

[Joekkel]

Hi there

I recently finished two Gryaf G7 mics with interchangeable headbaskets/capsules. For bodyparts/headbasket i used 4x this mic: https://www.musicstore.com/de_CH/CHF/Fame-Audio-Studio-CM1/art-REC0004714-000

Had to cut the pcb to fit the diameter of the body (stainless steel tube bought on ebay). A XLR conector is mounted to the interchangeable headbaskets, i even didn't need to drill new holes, as the holes in the metallplate of the headbasket fitted the XLR connector almost perfect The capsules are hot-swappable (loud popps happening of course).

I made 4 capsules; 2x OPR CK12, 1x generic chinese K67 and 1x chinese K47 bought from Bessneez Microphones. I always wanted to have a stereopair CK12.

If you're interested in the sound of these mics, you can have a listen to my first test recording in comparison to a genuine Neumann U87AI. I hope you don't mind bad pitch, i'm not a singer at all, i'm a tech..but singing for me is a very good way to hear, how a mic sounds in general:

https://www.dropbox.com/sh/5xo44ch128eo6kg/AAA1JzUfSc6Qux63mKmQPZFja?dl=0

There are 5 comparisons with me singing in both mics simultaneously. 4x singing a swiss folkore (i have no idea why i chose this song..), 1x speech. With the CK12 capsule i did an omni and cardioid comparison, with the other capsules only in cadioid.

I'm surprised, how close the U87 and Gyraf with K67 sound. Of course the Gyraf has more highs, as it features no de-emphasis unlike the U87. And i'm really surprised about the proximity effect and overall bass on the CK12. It' almost too much, which makes me wonder, if the CK12 in a Gyraf would benefit from a higher value output capacitor for a lighter bass. Is it normal for a CK12 capsule to have that much more bass in comparison to the K67? And i don't really care for the sound of the K47, at least on my voice.

Would be interesting to hear some feedback!

 

[lampas]

Hi there

I recently finished two Gryaf G7 mics with interchangeable headbaskets/capsules. For bodyparts/headbasket i used 4x this mic: https://www.musicstore.com/de_CH/CHF/Fame-Audio-Studio-CM1/art-REC0004714-000

Had to cut the pcb to fit the diameter of the body (stainless steel tube bought on ebay). A XLR conector is mounted to the interchangeable headbaskets, i even didn't need to drill new holes, as the holes in the m

What the great idea to make interchangeable capsules !!!! Need to listen samples too !!!

 

[Joekkel]

What the great idea to make interchangeable capsules !!!! Need to listen samples too !!!

thanks! yeah, i couldnt let go of the idea, once i had it in mind

 

[LevinGuitar]

Hi! just modded my TB1 into cardioid "G7" with Rode K2/NT2a capsule (with damaged rear diaphragm), Telefunkn EF86 and AmiT14.
Never biased a EF86 before, I used a 1k7 resistor directly to ground that gives me 0.95v on cathode and 65v on plate. 5.9v on heater and 120v on B+ (60v on capsule). Is all ok? Should I use the 220R resistor (not easy with this pcb) or just go for a higher biasing voltage?

It have big gain an very low noise, any reason to change the T14 for a lower ratio?

Also the Rode capsule is a bit bright, could I use a small cap from plate to ground to tame the highs as is used with triodes?

Thanks!

 

[gyraf]

Congrats with your build!

No reason to change anything if you have plenty of signal/noise

Adjusting high end with feedback equalization really never ends well imo - you can try and see if your taste is different though. The thing is that hard- and bright-sounding capsules are most often about resonances that can't be countered with simple first-order filters anyway..

/Jakob E.

 

[LevinGuitar]

Thank you!
I tried 2k14 and have 1.28v and 59v, now the capsule does not seem that bright, will leave it that way.

 

[LevinGuitar]

I tried T13 Transformer and K103 capsule. Sounds really good, better than with royermod circuit, but I guess I have too much gain and I wonder if it would be better to reduce sensitivity a bit.

Edit: tried a 3pf from anode to grid and quite happy with the result, have less gain but sounds better overall, more focused and less sibilant.