For weeks I have  been searching for  a wiring diagram so that I could build a circuit powered from the phantom power from my mixer but none of the 48 volts gets to the dynamic or ribbon mic.  I have come up with the perfect 4-transistor circuit.  The low level from my Shure SM7 is boosted by more than 20db which is enough so that there is no need to increase the gain control of my mixer and therefore not increase the noise level.  It uses 4 fet transistors and 3 resistors and 2 caps.  Really easy to build.
« Last Edit: January 12, 2020, 02:54:45 PM by computerlen »


Ricardus

Re: Low output ribbon/ dynamic microphone phantom-powered circuit
« Reply #1 on: December 24, 2019, 12:09:45 PM »
I've actually been looking for a DIY Cloudlifter type thing, myself, but haven't found what I'm looking for. This doesn't sound like it has enough gain, though.
Audio mastering for hire..

Re: Low output ribbon/ dynamic microphone phantom-powered circuit
« Reply #2 on: January 10, 2020, 12:15:58 PM »
If 20db boost is OK then this is for you.

If you build this circuit I would really appreciate it if you would let all of us know the results that you get. I have built two and they work perfectly. You must use the fet transistors specified for the lowest noise. I have read that the gain is from 20-25db.  Len.
« Last Edit: January 11, 2020, 03:14:19 PM by computerlen »

Ricardus

Re: Low output ribbon/ dynamic microphone phantom-powered circuit
« Reply #3 on: January 10, 2020, 03:18:41 PM »
Oh. 20 is perfect for me
Audio mastering for hire..

Ricardus

Oh, I just noticed you posted the schematic. Thanks!

A nice feature to add to this would be a switch to select 10 or 20 dB boost, and maybe an LED indicator somewhere so we know phantom is activated.
Audio mastering for hire..

Lennie

Oh, I just noticed you posted the schematic. Thanks!

A nice feature to add to this would be a switch to select 10 or 20 dB boost, and maybe an LED indicator somewhere so we know phantom is activated.


That is exactly what I am working on now.  A switch for more gain and I will be adding an LED.  Len.
« Last Edit: January 13, 2020, 08:25:02 AM by Lennie »

Ricardus

A tech friend said 2n5458 will work for this too, but they seem harder to find than 2sk170s.
Audio mastering for hire..

ruffrecords

Unless you have a very poor mic pre, do not be surprised if this kind of device makes no improvement to the noise level.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Ricardus


That is exactly what I am working on now.  A switch for more gain and I will be adding an LED.  Len.

Do you think it really needs more gain? From what I have seen most of these boxes top out at 20 or 25, and have attenuator switches for less.
Audio mastering for hire..

Lennie

I just tried it and found that my ribbon mic could use a gain boost. I will complete  the wiring up of the circuit and I will let you know the result. By the way, the 2SK170 fet transistors are super quiet I have read. Plus that is what one manufacturer uses in their preamps.


Ricardus

I think what Ian suggested was probably true. A circuit like this is great for boost, but if you have weak noisy preamps to begin with you might want to upgrade those.

Where are you getting your 2SK170s? I happened to have about 20 laying around, but they are getting hard to find. I know there is a good re-issue out there also. LSK170s.

I'm curious to see where this goes. A friend and I have actually whipped up a quick PCB layout for this.
Audio mastering for hire..

Ricardus

My friend suggested even using supermatched LSK389s, which is like dual 2SK170, for the matched pairs. The board should be able to support both options.
Audio mastering for hire..

Whoops

I posted the schematic for the Fethead a similar device in another thread, you can find it here:

https://groupdiy.com/index.php?topic=5743.300

Ricardus

I posted the schematic for the Fethead a similar device in another thread, you can find it here:

https://groupdiy.com/index.php?topic=5743.300

Similar circuit.

Haven't heard from Computerlen in a few days. He said he was adding some more features.

A friend and I started whipping up a board for this one.
Audio mastering for hire..

Lennie

Re: Low output ribbon/ dynamic microphone phantom-powered circuit
« Reply #14 on: January 18, 2020, 07:41:35 PM »
If 20db boost is OK then this is for you.

If you build this circuit I would really appreciate it if you would let all of us know the results that you get. I have built two and they work perfectly. You must use the fet transistors specified for the lowest noise. I have read that the gain is from 20-25db.  Len.

I have another question about a dynamic mic preamp.  I have built a few mic preamps in the past and the same thing happens with this 4-FET mic preamp that we are writing about. As I have just written, I added a blue LED. No problem. But I have also added  a DPDT switch that reverses the phase of the microphone at the female XLR socket. Can anyone tell me why I hear a difference in sound coming from any mic I hook up when I reverse its phase? I am not using or comparing any other mic to it when I do this. I cannot easily describe to you what the mics sound like when I switch back and forth. One position seems to have more bass frequencies to it. The output level is just as high. It's just that the quality[?] of the mic changes. Chances are no one else has wired a dynamic or ribbon mic this way. I figured that there should be no difference in sound by simply reversing the wires to its coil. Len.

Lennie

My friend suggested even using supermatched LSK389s, which is like dual 2SK170, for the matched pairs. The board should be able to support both options.

He is absolutely right.  That is very close to what the Cloudl Lifter people have done.
I have a question for everyone. In my latest preamp [which is almost identical to a Cloud Lifter] I have included a blue LED to show that the phantom power is turned on. Now the LED must be a blue coloured LED for this to work because I have two 1 meg resistors in series with the LED.  Any other LED colour will not work. One resistor is connected to pin 2 and the other to pin 3. The anode is connected to the junction of the two 1 meg resistors and the cathode of the LED goes to ground. [pin 1 of either  XLR connector]
« Last Edit: January 19, 2020, 09:50:32 AM by Lennie »

Whoops

Re: Low output ribbon/ dynamic microphone phantom-powered circuit
« Reply #16 on: January 18, 2020, 09:40:11 PM »
reverses the phase of the microphone at the female XLR socket.

reverse its phase

What you mean is "Reverse Polarity" as reversing phase does not exist.

And yes reversing the polarity by swapping Pin 2 and 3 of the XLR connector should not impact the sound.

I'm pretty sure you are doing something wrong, like for example  swapping Pin 1 and 2 (instead of Pin2 and 3)

Lennie

Re: Low output ribbon/ dynamic microphone phantom-powered circuit
« Reply #17 on: January 18, 2020, 10:20:36 PM »
What you mean is "Reverse Polarity" as reversing phase does not exist.

And yes reversing the polarity by swapping Pin 2 and 3 of the XLR connector should not impact the sound.

I'm pretty sure you are doing something wrong, like for example  swapping Pin 1 and 2 (instead of Pin2 and 3)

Why I put the phase switch in the circuit is because the mic might somehow be reverse-phased as compared to a second mic used at  the same time. I am not mistakenly reversing pin 1 with either pin 2 or 3. I am simply reversing the two wires of the capsule-pins 2 and 3. I have made a few preamps where I add a phase-reversal switch and the sound does change. Not a lot but it does change. It's just a coil and reversing the two wires should not change the sound but there is a subtle change in sound. Not a hum sound but, using headphones, I hear a slightly lowering in bass frequencies or even an out of phase sound. Don't doubt me. I have been doing this for years-decades actually and I hear a slight difference using only one microphone  and switching its two leads.
« Last Edit: January 19, 2020, 09:52:37 AM by Lennie »

Whoops

Re: Low output ribbon/ dynamic microphone phantom-powered circuit
« Reply #18 on: January 18, 2020, 11:53:48 PM »
somehow be reverse-phased as compared to a second mic used at  the same time.

 phase-reversal switch and the sound does change.

As I already told you in the previous post what you mean is "Polarity Reverse" , "reverse-phased" is something that doesn't exist



EmRR

Yes, you can generally hear the difference of polarity.  Not always, but many times.  Plenty of literature out there concerning that.    Many sources do not make symmetrical waveforms, and it's audible.

Agree with Ian. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde


 

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