D-EF47 Tribute To Oliver Archut U47 Build Thread.

[iturnknobs]

DMP-

I'm having similar questions/issues. My back capsule is not heating up when switched to omni.  Your drawing appears to make sense and I have come up with a similar idea.  How/where do you propose connecting "crd" and "com" together? Maybe here at the switch? My switch appears to have a common center lug and selects either position 1 or 2.  I believe my drawing matches your schematic of the switch connection. This should satisfy the ground for the relay when in cardioid and energizes the relay to make contact for backplate voltage in the omni position.

-Brian

 

[iturnknobs]

DMP-

Your drawing/this wiring works for pattern switching. I have tested it. My only complaint would be the "pop" when switching between patterns. Anyone know if a(and what value) capacitor might reduce this problem. I'm guessing it would go in between the "CRD" and "COM"(tied together) and switch lug. Any ideas?

-Brian

 

[dmp]

DMP-

I'm having similar questions/issues. My back capsule is not heating up when switched to omni.  Your drawing appears to make sense and I have come up with a similar idea.  How/where do you propose connecting "crd" and "com" together? Maybe here at the switch? My switch appears to have a common center lug and selects either position 1 or 2.  I believe my drawing matches your schematic of the switch connection. This should satisfy the ground for the relay when in cardioid and energizes the relay to make contact for backplate voltage in the omni position.

-Brian

I was going to connect them right on the power supply PCB and run a single wire to the switch.  They are forming the voltage divider to create the relay voltage so it would not make sense to run two wires. 
Your drawing looks fine.

DMP-

Your drawing/this wiring works for pattern switching. I have tested it. My only complaint would be the "pop" when switching between patterns. Anyone know if a(and what value) capacitor might reduce this problem. I'm guessing it would go in between the "CRD" and "COM"(tied together) and switch lug. Any ideas?

-Brian

Good to know. I wired it up but have not tested yet.

Unfortunately, I don't think you'll be able to get rid of the pop. The relay is switching the connection of the back to the front.  Adding a capacitor to the power supply to the relay won't make this gradual. And having a capacitor between the front and the back of the capsule will allow signal to go across, messing up the cardiod setting.
Best to just get in the habit of muting the mic while changing patterns.
Any mic that uses a switch or relay to change patterns will pop. Using a pot to switch patterns by adjusting the back polarization voltage is quiet, but is a different design than this. 

 

[iturnknobs]

So...

I have assembled a mic which seems to work correctly in cardioid and omni and appears to have a low noise floor. The problem I am encountering is with the B+ voltage.  Turning the potentiometer/trimmer resistor in the psu, I can only get a maximum of 101.8 vdc.  Unloaded, the PSU shows 138vdc.  I'm guessing that swapping resistors R1 and R3 in the psu for a lower value might be the trick(any suggestions?)

Also, I have spoken with Dennis over at AMI/Tab Funkenwerk about a similar point to point build and he has told me that the B+ 105V should have always been 120vdc (not 105). Can anyone comment or clarify?

-Brian

 

[Bonnie1]

Also, I have spoken with Dennis over at AMI/Tab Funkenwerk about a similar point to point build and he has told me that the B+ 105V should have always been 120vdc (not 105). Can anyone comment or clarify?

-Brian
[/quote]

Hello Brian,
To clarify, 60v on the backplate and 120v on rear diaphram for Fig. 8.  If your psu B+ is 105v the resistor divider setup 2M/3M, however if your psu B+ is 120v then equal value resistors.
Cheers-

 

[Nollman]

I am building a modified 3-pattern switching version of this circuit and would prefer 120v B+ but currently I am working with 105v in my schematic. The difference in voltage will affect the resistors supplying the bias voltage for the EF800 as well. I am having difficulty finding the mathematical solution to this as all formulas I have come across require the amperage of the circuit which is unknown to me. I am very curious find your resolution to this issue. I am attaching my schematic as it is now (105V).

 

[dougch]

Nolman, in the thread "DIY AMI U47" which is back a page, there is some discussion that may help. They talk about the Lucas CS-4 mic. The Schematic I have seen for the CS-4 shows that 120v is used. In place of the 30K resistor is a 47K. On the cathode is a 110 ohm resistor instead of the 100 ohm. The voltage divider uses two 1M instead of the 3M in the U48. The tube is not specified but is either an EF800 or EF802 I think. Funny, in photos of the CS-4 mic, there are Lucas labels on the tube hiding the tube number. Really? The schematic was a Tab-funkenwerk drawing.

 

[Nollman]

Dougch,  I can't open the link to the Lucas CS-4 schematic. Can you post it here? Thanks for the help!

 

[dougch]

Let's see if this works. I hope it is okay to post this. It was public when I downloaded it.

 

[Nollman]

Thanks Dougch! That is the schematic with the values I needed. Could someone more learned than myself explain why resistors R1, R5 and R10 are 1G and how lower values would affect the behavior of the mic. It was recommended to me to use 100M in these positions.

 

[dougch]

Nollman. I have been reading about this for the last couple of days and I have found some info in other forums. I just googled "1G resistors on mic capsule." I found there was science, experience and opinion involved. The trend has been toward higher values over the years. Oliver sure used 1G on his circuits. In short, there are some differences in frequency response and distortion figures, but it's up to you. The U48 had 150M on the rear capsule. See also Miktek CV4:
https://groupdiy.com/index.php?topic=61684.20

 

[la-2a]

Hi Folks, i was wondering if it is possible to replace the two A408 Tubes. I have some 5654 Telefunkens  here.  In my opinion it should work......any Suggestion..
Thanks in advance....

 

[Colorblind]

Hi Folks, i was wondering if it is possible to replace the two A408 Tubes. I have some 5654 Telefunkens  here.  In my opinion it should work......any Suggestion..
Thanks in advance....

Perhaps you're thinking of a different U47 style mic?  This one is a single tube design (EF800, etc.).

 

[la-2a]

I dont think so. There are 2 Versions. Single Tube and dual Tube . ...

 

[Mjwever]

Hey guys, mouser don’t have the 1/2w 14k ohm metal film resistor for the PSU,  until next year & im finding it difficult to source one elsewhere. Any suggestions?

 

[59flame]

finished the psu all voltages are correct with load.  How is the pattern switch to be  wired  that comes with danys  pcb kit?
seems i have it wired wrong. Anyone help with correct wiring of the pins on the switch?

 

[Colorblind]

finished the psu all voltages are correct with load.  How is the pattern switch to be  wired  that comes with danys  pcb kit?
seems i have it wired wrong. Anyone help with correct wiring of the pins on the switch?

I can't recall the pin numbers, but I found this pic of my PSU.  The multicoloured goes to CRD, red goes to COM, and grey goes to OM.  Hope that helps!

 

[59flame]

Need to wire mic transformer it is a Moby bv08. Anyone know how this is wired to poctop pcb. I am sure I am overthinking this. But I for the life of me cannot be for sure I have this correct by  the schematic. Would like to just make sure from one of you experts. Thanks for any help you can offer

 

[59flame]

finally finished this mic. sounds great with mobys  bv8 and danys capsule!

 

[Larsson]

Hey guys, mouser don’t have the 1/2w 14k ohm metal film resistor for the PSU,  until next year & im finding it difficult to source one elsewhere. Any suggestions?

Maybe this one could work?

https://uk.farnell.com/vishay/mrs25000c1402fct00/res-14k-1-600mw-axial-metal-film/dp/9464565

BR,
Mats