[Phrazemaster]

Hi All, Proudly Presenting the Cinemag BV11 Transformer Many thanks To Dave at Cinemag to take the challenge.
for all  DIY Microphone Requiring a BV11 Style Transformer 

For All information about this transformer and ordering
http://cinemag.biz/contactus/contact_us.php

The Cinemag CM-6511 ( BV11 Mic output X-Transformer)


Connection


For All information about this transformer and ordering
http://cinemag.biz/contactus/contact_us.php

Tried getting info about this. Contacted Cinemag but haven't heard back. There are no specs or details that I can find on the Cinemag website.

Dany, do you have more information about this? How authentic is this to an original BV11? Do they still offer this?

I am also thinking of going with Haufe. I tried contacting AMI/Tab but so far no response from them either on their BV11, and there is no link for that transformer. I know I can use a T49 but I'd rather a recreation of the original.

Thanks for any thoughts,

Mike

[poctop]

Give Dave a Call and let me know how it goes ,
Best,
DAn, <

[Phrazemaster]

Thx Dan; I've been talking to AMI so at this point I'm probably going to get one of their x-formers. I appreciate your support.

How are you man!!! My M49b "poctop" is still going strong; I just used it yesterday and it sounds warm, full, rich, and awesome! Thanks for helping me troubleshoot it; remember it was the mic with "gremlins" you said!

Best,

Mike

[muffy1975]

Hi there,

Is there a problem using 100m ohm resistors in place of the 150m ohm resistors in this circuit?

Thanks in advance for any insight with regards to this matter.


Michael

[ln76d]

No, unless it's 100M (mega) not 100m (mili)

[rmburrow]

You're better off with the 150 meg ohm (or higher value) resistors in that capsule circuit.  Go too low on the capsule resistors, the time constant of the capsule and resistors "loading" it falls in the audio range.  If you have a number of the 1/4 watt or smaller 100 meg resistors, try two of them in series in place of the 150 meg resistor.  The original tube in the M49 (the venerable and expensive AC701) liked to be loaded with 150 meg.  There is not a lot of published data about how the 5840, 6072, 5703, 7586, etc. behave when used with high grid impedance.  Those tubes I listed have been used in condenser microphones over the years.

[ln76d]

Bla, bla, bla - theory - bla, bla, bla
100M will work very nicely - no problems i guarantee that - most tubes works much worse with too high value resistors like 1G - FET  is  different pair of shoes.

[muffy1975]

Thanks guys. Archut used to use a lot of 1g resistors in his designs. I'll try both ideas. Those 1/4 watt resistors are quite cheap. Hopefully they are no noisier than the 1/2 watt ones in this position in the circuit?

What do you think?

Gonna build a p2p m49 with a bunch of old mica caps and pio 10n caps. Also a massive Ampohm  1 uf 630v oil filled cap and  beezneez  M7 . I have  a long acrylic tube for the body. Gonna shield where appropriate.



I know 1/2 watt resistors are quieter in UA designs etc.

[ln76d]

That's why i wasn't fan of Oliver mods ideas and some circuits implementations - still - missing the guy around us...
Test two values - even direct comparison via switch (100M + 1G in parallel) and you will see - do you hear difference or not - there's no better option
Probably not noisier, much more be carefull with soldering (don't overheat) and clean soldering points after work.

[rmburrow]

Bla, bla, bla - theory - bla, bla, bla
100M will work very nicely - no problems i guarantee that - most tubes works much worse with too high value resistors like 1G - FET  is  different pair of shoes.

The late Dr. Karl Schoeps used 180 meg ohm resistors in the M221 with the 20 pF capsules...Agree the 100 meg will work but experimentation will find what's best...

[justinheronmusic]

Just getting into my M49b build. Can someone please explain to me the floating pins? My pins don't seem to fit my PCB, and from looking at the PCB ground plane, are they absolutely necessary or are they optional?  I am not totally clear as to whether or not I am soldering these in place.

 Also, can anyone post a photo of the front and back of their finished M49b Mini Driver PCB?

[stelin]

I’m trying to get my head around what the feedback resistor R3 (5M) does in the M49c circuit.
I understand the basics of RC-filters, but there are too many components involved… 
Is it negative feedback? Is it only affecting the bass? Adding or subtracting?
I’ve tested the AC701 “Electronic tube” from Phaedrus. That “tube” oscillates in an M49c circuit and the fix is to remove the R3 resistor. But how does that affect the rest of the circuit?

[stelin]

Never mind, guys.
I've found a good answer here: http://www.neumann.com/forums/view.php?bn=neumann_archive&key=990963033&v=f
The R3 is part of a bass roll off filter.
I suspect that the problem with the AC701 “Electronic tube” is the very hefty phase shift staring at 10 Hz (yes, I've measured it). That turns a negative feedback into a positive feedback at very low frequencies (around 4 Hz).
The size of the R3 determines the amount of bass roll off. If removed, there will be no roll off at all.

[ln76d]

Never mind, guys.
I've found a good answer here: http://www.neumann.com/forums/view.php?bn=neumann_archive&key=990963033&v=f
The R3 is part of a bass roll off filter.
I suspect that the problem with the AC701 “Electronic tube” is the very hefty phase shift staring at 10 Hz (yes, I've measured it). That turns a negative feedback into a positive feedback at very low frequencies (around 4 Hz).
The size of the R3 determines the amount of bass roll off. If removed, there will be no roll off at all.

What did you found is not an answer but crap.
Neither R3 or R5 doesn't make "bass roll off".
R3 is feedback resistor, so if you want to get same level and other "artifacts" then don't mess with it.
If you want to increase low end then change C3 for higher value - that's it.

[Delta Sigma]

I’m trying to get my head around what the feedback resistor R3 (5M) does in the M49c circuit.
I understand the basics of RC-filters, but there are too many components involved… 
Is it negative feedback? Is it only affecting the bass? Adding or subtracting?
I’ve tested the AC701 “Electronic tube” from Phaedrus. That “tube” oscillates in an M49c circuit and the fix is to remove the R3 resistor. But how does that affect the rest of the circuit?

It is a feedback resistor. I assume your goal is to eliminate the oscillations and not to change the circuit. Why not increase the value of R3 until it stops oscillating? Try 8M or 10M.

The negative feedback depends on the feedback path and the amplifying device. You've changed the tube to what I understand is a semiconductor of some sort. Don't think that should mean you have to eliminate the feedback, just change it.

M49 is a great circuit to modify and learn from; R3 is just as good a place as any to start. There's nothing wrong with the denial and error technique as long as you end up with the mic you love.

[stelin]

I don’t want to start a discussion about what is “crap” and what is not, so I’m not going to comment on this any further.

[ln76d]

I don’t want to start a discussion about what is “crap” and what is not, so I’m not going to comment on this any further.

No one expects it from you - your microphone - your problem

[Rlucas41]

Could I get some clarification on calabration please?

I measure the B+ and H+ On the PSU Pads/point to calibrate each respectively using the trim resistor and 250k pot... correct?

And then measure at which points in the mic itself to adjust R7 to ?

I am building a b and c version...

I just need a clarification of steps for proper calibration and exact point to measure please

Kindest Regards,
Robert

[e.oelberg]

Initially I didn't put a low pass filter (600pF to ground) into my freshly built m49oid mic. But I'm too close to a GSM tower and I heard low level radio signal, so I installed  a 560pF capacitor with the result of no radio in the signal anymore: success !
Nevertheless, I don't like the sound as much as before, of course this is a better compromise, I guess phase shift contributes to the change of sound.  Nevertheless: Did anybody experiment with that ? How high can I I move the low pass ans still get rid of the GSM signal ?

[Ericbazaar]

Initially I didn't put a low pass filter (600pF to ground) into my freshly built m49oid mic. But I'm too close to a GSM tower and I heard low level radio signal, so I installed  a 560pF capacitor with the result of no radio in the signal anymore: success !
Nevertheless, I don't like the sound as much as before, of course this is a better compromise, I guess phase shift contributes to the change of sound.  Nevertheless: Did anybody experiment with that ? How high can I I move the low pass ans still get rid of the GSM signal ?

Wich output transformer did you use? Is the Microphone cable shielded correct? Maybe test a shorter one, 5 meters. Is the Transformer Lamination intern connected to the chassi? This is why i use only transformers with static shielding! Important because of the many Wlan Router(wich are sending with 300mW ore more), Mobile Internet ect.
Best

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