[JMPGuitars]

I finally have my M49C back to try and fix the output. It's still not loud enough, even with preamps cranked really high.

I want to test my AMI T49 in circuit. I don't know know what the transformer resistance values should be in circuit. Currently I'm getting 15.7Ω between A and B, and 703.5Ω between C and D.



These are my voltages when last tested a while ago:
Mic Connected, 5840W heater set to 6.3:

B+:
O 123
C 120
8 119

Polarization (Pin 6 on mic PCB):
O 0
C 58
8 119

Cathode:
O 1.6
C 1.93
8 1.93

Anode:
O 52.4
C 34.7
8 33


Thanks,
Josh

[Purplenoise]

Ok time for testing and calibration.
Phaedrus ac701, hydra MP coupling cap, nos wima tfm 0.01uf caps, wet tantalum 22uf cap, Moby BV11 and Neumann k49fet.

[Purplenoise]

Calibrated and sounding great and quiet...with the phaedrus ac701 it sounds much closer to the originals. 5840 is pretty good but it doesn’t have the size and smooth presence of the ac701. With the ac701 it sounds “aged” with a nice “grain”. The 5840 sounds more “glassy” and modern. Also a nice nos MP coupling cap helps too.
Dany thank you again for all your hard work on these kits.

[Rlucas41]

Calibrated and sounding great and quiet...with the phaedrus ac701 it sounds much closer to the originals. 5840 is pretty good but it doesn’t have the size and smooth presence of the ac701. With the ac701 it sounds “aged” with a nice “grain”. The 5840 sounds more “glassy” and modern. Also a nice nos MP coupling cap helps too.
Dany thank you again for all your hard work on these kits.

Hi Purplenoise, I just ordered my Phaedrus AC701 yesterday... got any advice for the installation you would care to impart

[Purplenoise]

Hi Purplenoise, I just ordered my Phaedrus AC701 yesterday... got any advice for the installation you would care to impart

Hey Rlucas41. As far as the connections they are:
K to k
a to A
h- to HG
h+ to H
g to fgrid ( s2b)
The phaedrus is self biasing so leave the trimmer resistor in the middle. My measurements when calibrating were 0v for K,  29,9V for A ( which is a little low but fine). At the suggested B+ 115v the plate current after the 100k resistor is 0.85mA. According to phaedrus that is on the high side but totally fine.
I had this discussion with a very respected and knowledgeable member today about this today actually. He suggested changing the 100k resistor to 56k to bring the plate current closer to 0.73mA as per the Neumann schematic. If you do that then the B+ will go up so it would be maybe necessary to change the two 6k 0.25w resistors in the psu to 10/15k. Also make sure your H+ is between 3.8 and 4V.
Also IF you have any low frequency oscillation just remove the 5M feedback resistor. I soldered just one end to experiment. I hope I am not forgetting anything.

    ——-UPDATE——

No need to change the 100k resistor. Those measurements are correct for the phaedrus. Since it is self biasing it will always go back to 0.85mA.

[Rlucas41]

Hey Rlucas41. As far as the connections they are:
K to k
a to A
h- to HG
h+ to H
g to fgrid ( s2b)
The phaedrus is self biasing so leave the trimmer resistor in the middle. My measurements when calibrating were 0v for K,  29,9V for A ( which is a little low but fine). At the suggested B+ 115v the plate current after the 100k resistor is 0.85mA. According to phaedrus that is on the high side but totally fine.
I had this discussion with a very respected and knowledgeable member today about this today actually. He suggested changing the 100k resistor to 56k to bring the plate current closer to 0.73mA as per the Neumann schematic. If you do that then the B+ will go up so it would be maybe necessary to change the two 6k 0.25w resistors in the psu to 10/15k. Also make sure your H+ is between 3.8 and 4V.
Also IF you have any low frequency oscillation just remove the 5M feedback resistor. I soldered just one end to experiment. I hope I am not forgetting anything.

    ——-UPDATE——

No need to change the 100k resistor. Those measurements are correct for the phaedrus. Since it is self biasing it will always go back to 0.85mA.

Thanks Purplenoise! Hopefully my AC701 will be here in a few days! I will post my results too!

[Spencerleehorton]

im not hearing any pattern difference when changing the stepped pot, whats a good way to test if its working correctly?

[Purplenoise]

im not hearing any pattern difference when changing the stepped pot, whats a good way to test if its working correctly?

When set to cardioid or figure 8 you don’t hear a difference when you talk and slowly rotate the mic?

[Spencerleehorton]

No I dont, no difference

[Delta Sigma]

Measure what's coming ou on the pattern pin (6, I think) in the power supply. If it's 0-116 as you sweep the pot, measure inside the mic on either side of R11. The Hi-Z side of R11 will be loaded by your DVM so it will read lower than what it actually is.

[Spencerleehorton]

ah ok, R11, i've measure at stepped pot and all voltages seems fine but not on mic yet, will rig up tomorrow and check, thank you.

[Purplenoise]

Had the first session today recording male vocals...wow. This mic sounds gorgeous...smooth but with great definition...present without sibilance with a wonderful weight and proximity effect. Sounds big...definitely what I would expect from an m49.
After a lot of tweaking here is what I ended up with:

Neumann k49fet capsule ( cardioid only)
Moby bv11
Phaedrus ac701
Super pup ( MP )1uf 200v coupling cap.
Wima tff 0.01uf 400v caps
Elna silmic 22uf cap

In the beginning it sounded a little “peaky” and “direct” but after burning it in for 3 or 4 days the sound mellowed out and the response became very balanced and even. I have found that it takes some time for the electronics to “settle”.
Thanks again Dany for this wonderful project...super excited

    ———UPDATE——-

Ok...a little update. Since I got a Neumann k47 for the u47 clone I decided to try the 3u audio m7 on the 49. I think I prefer the response of the m7 on this build. Although this m7 doesn’t have the depth and detail of the Neumann capsule it does have a presence and creaminess that is very nice, even and forgiving in various sources. I also put back the hydra coupling cap and it sounds awesome. I like both versions a lot but I believe now it “agrees” more with my ears.

[JMPGuitars]

It turns out there was an issue with the T49 transformer I was using, and I'm going to try something else.

Has anybody tried the BeesNeez B-BV-11? I think that's what I'm going to try out instead. I'm also switching to the M49b because the board was there, and I was bored.

EDIT: I'm still curious about the BeesNeez BV-11, but I'm going to try a T47 in the M49b circuit. It's supposedly good in there with the 5840 tube.

Thanks,
Josh

[Delta Sigma]

I sure like their capsules but no experience with a Beesneez transformer.

If you want the best, Moby is the way to go. His BV.11 is built to the original specs including the laminations.

Be careful with grounding in your power supply for the M49b. It's easy to have problems with hum. I had success with only grounding the power supply PCB to the chassis at the 7 pin connector (same ground point as cable shield) and grounding the earth ground to the chassis at the IEC power connector.

[Purplenoise]

As Delta Sigma said the Moby bv11 is awesome and you can order it with either a 10:1 or 6:1 ratio. I believe the t47 you are thinking of has 6:1 ratio

[Moby]

As Delta Sigma said the Moby bv11 is awesome and you can order it with either a 10:1 or 6:1 ratio. I believe the t47 you are thinking of has 6:1 ratio

Hey guys, thanks for your kind words
Just to correct the info.about  Bv.11's  They are 10:1 or 7:1 ratio and much more revisions in the past but I produce this two.

[Purplenoise]

Hey guys, thanks for your kind words
Just to correct the info.about  Bv.11's  They are 10:1 or 7:1 ratio and much more revisions in the past but I produce this two.

Oups...I should have known better since...mine is the 7:1 haha. Thanks man.

[JMPGuitars]

Hey guys, thanks for your kind words
Just to correct the info.about  Bv.11's  They are 10:1 or 7:1 ratio and much more revisions in the past but I produce this two.

I wound up exchanging my defective T49 for a T47.

I emailed you about the BV8 (for my next project, D-EF47).

Thanks,
Josh

[JMPGuitars]

I've got the M49b circuit built now (no capsule connected yet).

M49b voltages (5840W tube):
H 6.3V
K (measured across R6) 1.6V
B+ 116V
A 55V

Voltage across R10: 63V



Voltages are staying consistent (with and without a dummy load for the capsule).

My rear diaphragm voltages are weird. I assume they're supposed to also be OV Omni, Half B+ Cardioid, and full B+ Fig8. However, I'm getting 0V, 2V, and 4V respectively.

The circuit is standard per M49b schematic, except I omitted C6, R3, and C4.

Thanks,
Josh

[Delta Sigma]

Are you measuring in the power supply or in the mic?

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