[doqmemory]

I hope that works for you.  I plan to do the same with my D-M49 when I get around to ordering the rest of the parts.

[Spencerleehorton]

Yeah should be fine, need to look at both my m49 psu as I noticed the pot didnt change anything and having a stepped pot is much more precise.
Think I've missed a connection on the psu that's why it doesnt work!!

[Spencerleehorton]

Getting 116v and lower when testing B+ with adjustable 100k pot for pattern selection but not hearing any difference between them when plugged in?
I have the link from c1 over to the other connection.
Have set H+ to 3.9v.

Am I missing something here?

I'm adjusting from the psu btw.

[doqmemory]

Is the polarization voltage (XLR pin 6 in schematic) changing when switching positions?  You want 0v with 0 resistors, 60v with 4 resistors, and 120v with all 8 resistors.
Have you wired the switch to OM, COM (wiper), and F8?

[Spencerleehorton]

I've got just a normal 100k potentiometer in there at the moment, lorlins not arrived.
Yes I've wired them to 0M, com and f8, just need to check they are correct.
When testing wiper and 0M CCW I get 0v and CW I get 116v.
On the schematic it says 116v, but you said 120v?

[doqmemory]

Sorry, I was looking at the M269c schematic, which is 120v.  Have you implemented switch S2?  If not, it should be closed to get the back diaphragm signal to the gate.

[Spencerleehorton]

I've got a link from c1 to the isolated pin where C4/Gate/R5/back capsule, will have to check this is all correct.

also I have a small trimmer in for the H+ adjustment, trying to find the value of it on the schematic and it doesnt say? on the BOM i can see a 250ohm wirewound.

is it a wirewound 250ohm?

[Spencerleehorton]

On my psu I have 100R wire wound potentiometers in there for heater bias.
Have put in lorlins now, just need to re jig one psu bits and drill then I can test them all.

[adrian]

just a little update to let you know I tried to inverse the capsules between the 2 new mics:
 the frequency response follows this change. so this difference comes from the capsules...

I would really like to understand why there is so much difference in figure of 8 directivity... maybe a big difference between rear and back diaphragm?
any idea?

[Spencerleehorton]

Have changed my H+ trim pot as it was totally shot as I'd only put in a trimmer!!
Put in a 100R same as my other psu and I can only get 4.7v as lowest!!
On my other psu it has the same but I can get 3.9v to 4.2v with the 100R pot?
What should I change, the pot or the resistors?

[rmburrow]

What tube are you using?  The AC701 heater voltage is critical...4.7 volts is way too high....you may try a 150 ohm pot or wire a 50 ohm 1 w resistor in series with the pot input....you can try loading the heater supply with 40 ohms 1 watt resistor (to simulate a AC701 heater) and measure the voltage across it....determine what works before connecting a real AC701....

[Spencerleehorton]

Ah ok, 40ohm 1w resistor is the load resistor will try that, thank you.

[Spencerleehorton]

im not hearing any pattern change when i adjust the stepped pot, whats the best way to check, as when i test the pot im getting the different voltages just doesnt seem to be changing the diaphragm?
i've got the link in from c1 to grid/C4, back capsule and R5.

[Purplenoise]

After finishing a round version I am starting a square version mostly for instrument recording. I want to deviate a little from the original design by leaving out the feedback resistor (5M) and c4 capacitor ( 8pf). I have a 3u audio m7 capsule but I wanted to ask if anyone has tried a ck12 capsule with this circuit. I am thinking of the maiku ck12 which is a little darker. Also if anyone has experience with the Luke  audio la-9 capsule and would like to chime in it would be greatly appreciated. Thanks.

[Purplenoise]

So just finished a version of the square m49. I wanted it mostly for instrument recording...more accurate sound and it came out really great. Low and high filters removed. Also the mica 8pf was not installed. I used a Luke audio LA9 capsule ( cardioid only), Ami bv11r, super pup MP coupling cap, silmic 22uf cap.
Recorded some acoustic guitar and it sounds awesome...great reach too from a distance. “Pleasantly real”

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