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This makes no significant difference in this application IMHO.
Take what you can get.
Official G7 microphone help thread
- Thread starter gyraf
- Start date
Help Support GroupDIY Audio Forum:
Take what you can get.
chrispbass
Well-known member
brndvnrdn
Active member
Hi everyone,
I'm building a G7 mic and it's working but I'm getting a bit of a strange frequency response. I felt I was getting too little low end from the sound after which I started to do some testing.
It turns out it's coming from the tube. When inserting a sweep at grid 1 (control grid) of the EF86 I'm getting the frequency response as pictured. This doesn't seem correct, right ?
With the test signal after the tube the frequency response is perfectly flat.
Does anyone have any insight into this frequency response and how it can be mitigated? Or am I overthinking things and is it simply a part of the circuit?
I'm using a PSU that outputs 120V instead of the original 160V.
Many thanks !!
I'm building a G7 mic and it's working but I'm getting a bit of a strange frequency response. I felt I was getting too little low end from the sound after which I started to do some testing.
It turns out it's coming from the tube. When inserting a sweep at grid 1 (control grid) of the EF86 I'm getting the frequency response as pictured. This doesn't seem correct, right ?
With the test signal after the tube the frequency response is perfectly flat.
Does anyone have any insight into this frequency response and how it can be mitigated? Or am I overthinking things and is it simply a part of the circuit?
I'm using a PSU that outputs 120V instead of the original 160V.
Many thanks !!
Attachments
I see a -3dB point of ca. 40Hz ref 1000Hz?
brndvnrdn
Active member
Is it normal/ to be expected ? Maybe it's just the capsule I was using and I'm looking for problems that don't exist
I haven't measured the original this way, but I don't think it's far enough out to suspect anything wrong..?
/Jakob E.
/Jakob E.
chrispbass
Well-known member
Another G7 has entered the world!
A nice story in that the pcb’s were given to me over a decade ago when there used to be the annual give away at Xmas.
They were part populated and I just had to add a resistor and trimmer to the psu and the high value resistors and film caps to the mic pcb.
Bit of a delay, but finally got around to it!
I’ve used a NOS PF86, Sowter 3678 tx, AliExpress ‘ck12’ and U47 body. I have also got a mic grade PF86 to try but on and for initial testing I’ve just used the NOS. I’ll take it to my friends studio to do some proper comparisons and testing soon but all seems to be well.
I think there maybe 2 types of U47 body. One that has proper guide rails and one that has three long pcb standoffs (perhaps someone can confirm if that’s the case?)Anyway I have the latter.
I cut some ‘rings’ of 22mm copper water pipe, and flattened it to create some copper strips. I fashioned these into ‘P type’ clips to mount the pcb the the rails and also made a bracket to mount the Sowter. These are bolted to the pcb with nylon bolts.
Gives it a bit of a steampunk look!
I did forget to ground the heater supply, so hum on initial test, but 5 mins on the bench solved that. It’s now exceptionally quiet and sounds good.
I’m obviously pleased it’s working, but I’m sure there will be further tweaks and possibly a change of capsule (Arienne K47?) in the future.
As I’m using a PF86 (4.5V heater) I used a 6V 5VA and 9V 3.2VA back to back in the PSU. Both of these came to about ten English pounds (good value) and mounted them on some Veroboard.
You can pop a 20 turn trimmer on the pcb and solder a jumper on the underside of the pcb to make it easy to dial in the heater voltage. I used a 56k in place of the 10k dropper resistor and got a B+ supply of about 113V, so I’ve left it at that for now.
.
I had a large piece of brass in the drawer which I’m not sure where it came from. To continue the steampunk theme, I drilled and tapped it to use as a heat sink for the LM317.
The case is recycled with lots of cutouts. I added a cutout for an IEC socket and mains switch from the parts drawer. There were 2 holes already drilled (labelled fuse) and DC and so they have become fuse and the top will be an indicator.
Front is rough 
Will make a nice face plate (I have a cunning plan) and paint it up soon when I case up my CJ DI’s. Just wanted it up and running.
Big thank you to Jakob and all the trail blazers on this project
Have a great Sunday all
A nice story in that the pcb’s were given to me over a decade ago when there used to be the annual give away at Xmas.
They were part populated and I just had to add a resistor and trimmer to the psu and the high value resistors and film caps to the mic pcb.
Bit of a delay, but finally got around to it!
I’ve used a NOS PF86, Sowter 3678 tx, AliExpress ‘ck12’ and U47 body. I have also got a mic grade PF86 to try but on and for initial testing I’ve just used the NOS. I’ll take it to my friends studio to do some proper comparisons and testing soon but all seems to be well.
I think there maybe 2 types of U47 body. One that has proper guide rails and one that has three long pcb standoffs (perhaps someone can confirm if that’s the case?)Anyway I have the latter.
I cut some ‘rings’ of 22mm copper water pipe, and flattened it to create some copper strips. I fashioned these into ‘P type’ clips to mount the pcb the the rails and also made a bracket to mount the Sowter. These are bolted to the pcb with nylon bolts.
Gives it a bit of a steampunk look!
I did forget to ground the heater supply, so hum on initial test, but 5 mins on the bench solved that. It’s now exceptionally quiet and sounds good.
I’m obviously pleased it’s working, but I’m sure there will be further tweaks and possibly a change of capsule (Arienne K47?) in the future.
As I’m using a PF86 (4.5V heater) I used a 6V 5VA and 9V 3.2VA back to back in the PSU. Both of these came to about ten English pounds (good value) and mounted them on some Veroboard.
You can pop a 20 turn trimmer on the pcb and solder a jumper on the underside of the pcb to make it easy to dial in the heater voltage. I used a 56k in place of the 10k dropper resistor and got a B+ supply of about 113V, so I’ve left it at that for now.
.
I had a large piece of brass in the drawer which I’m not sure where it came from. To continue the steampunk theme, I drilled and tapped it to use as a heat sink for the LM317.
The case is recycled with lots of cutouts. I added a cutout for an IEC socket and mains switch from the parts drawer. There were 2 holes already drilled (labelled fuse) and DC and so they have become fuse and the top will be an indicator.
Front is rough
Will make a nice face plate (I have a cunning plan) and paint it up soon when I case up my CJ DI’s. Just wanted it up and running.
Big thank you to Jakob and all the trail blazers on this project
Have a great Sunday all
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