NEW: Professional balanced Mic-PreAmp, DIY project

TravelRec. · Jul 29, 2005, 08:34 AM

Hello!

www.electricstart.de , electronics section is updated with a professional preamp module for professional balanced dynamic and condenser microphones. It has a S/N-ratio below -75 db (mic dependent) and a linear frequency curve up to 80kHz. The performance of the INA217 chip, that is used for the module, is really great and specially matched for this task. I use a similar module (10 of them) in my studio mic setup for years and I think you can benefit from my experience. Have fun!

TravelRec.

2ndhannes · Jul 29, 2005, 08:59 AM

Hey, now that's something for my taste!

Unfortunately, I managed to fetch a symmetric pro preamp card when the WDR (large german TV/Radio) threw out their old studios

I just never manage to build a good 24V + 48V power supply so I can use it...

Bye,
Hannes

TravelRec. · Jul 29, 2005, 09:34 AM

Whow, cool - the WDR I know very well

, but only from the TV, not in the real life... To build a good phantom power supply you first have to get a little transformer of 30V AC, connect a graetz rectifier and a big electrolyte condenser (2200µ/50V), connect this over a resistor with a second condenser of say 100µF / 50V, connect a zener diode with ground so that the phantom voltage cannot excced 48V and then connect your XLS-Socket over the 6.8k reistors, like you can see in the schematics. Alternatively you can build a step-up coverter (my way) to transform 15V into >30V. BTW, the most available mics accept phantom voltages above +12V on both signal wires as sufficient.

Doug W · Jul 29, 2005, 05:08 PM

Very nice TravelRec.

Would it be possible for you to put a 2nd schematic up there showing the 48V Phantom power supply option? Even without the PCB board layout, it would be nice to have.

If you don't have time to do it I understand-I can just sit here and look down at the ground with little tears spilling down my cheeks.

TravelRec. · Jul 30, 2005, 11:00 AM

Okay, don´t be sad, I´ll see what I can do - my solution was very non-orthodox, but is working. I used a transistor and a selfmade coil to transform the voltage up, but that´s not that good for rebuilding. Better you try to get a small transformer with 30V AC output or a small DC/DC step-up converter. I will make a schematics for both versions.... Finally you can check whether your mic works with only 12V phantom power... But don´t burn your mic!

Schematics updated with first solution...

Doug W · Jul 30, 2005, 07:19 PM

Thanks TravelRec

I feel better now. I need to make a tranportable mic preamp with phantom power.

2ndhannes · Jul 31, 2005, 03:25 AM

Hi Doug,

you could always connect five 9v batteries in series, that would be an easy + mobile way to get 45v, and that's close enough (most mics work with even less).

If you want to get 48V from one battery, then it gets more difficult, as you must either convert the voltage to AC, use a voltage multiplying circuit and convert to DC again or use a dc-dc stepup converter. I just tried googling but did not find anything fancy on the first pages

Bye,
Hannes

Doug W · Jul 31, 2005, 04:03 AM

Quote:

you could always connect five 9v batteries in series, that would be an easy

Or I could connect 4 car batteries in series....maybe your idea is more practical though. With the amount of free time I have these days, maybe just 9volt batteries would be the easiest.

Thanks for the idea,
Doug

**dj_stick** · Jul 31, 2005, 09:42 AM

8 torch batteries would work too - but it gets a bit heavy

TravelRec. · Jul 31, 2005, 10:08 AM

What´s about solar cells? No just a joke..., if I find a good solution with a step-up converter thing that is working great for this purpose, then I will post schematics too. I think I can order a DC->DC converter module next time and then I will try...

max13 · Aug 1, 2005, 10:34 PM

Hi travelrec

Maybe i can help you how to get better snr

first of all
pin 1 ofl xlr should be tied to groung as close as possible to voltage source
no other component should use GND path of pin1. Found out from your PCB that pin1 share same ground with all components that is really not a good idea.

second try to use standard (non SMD) resistors. Some of them use resistive path like a coil. 1% Metaloxide resistors are probably best to use. 1 advantage of non smd resistor is higher heat dissipation area so they resistance are more stable. Also noise generated in resistor is lower.

Add low pass filter before INA 217 cutoff frequency shoud be +-60-100khz this filter WILL change phase characteristics of signal but it is not too dramatical.
LPF will help ina217 with input bandwidth. ina will be more stable and not stressed too much by inducted voltage.also higher harmonics sould make problems to ina217 so LPF is probably VERY good idea.

If you can you can get ina163 it has little bit better parameters.
in +-3-4 weeks i will introduce diferential input/output mic preamp based on ina163. It will be DIY so it will be complement to yours preamp.

Maddogg6 · Aug 2, 2005, 02:40 AM

this IS EXACTLY what Ive been hankering for - kudos.. I must place some parts orders soon.

Thanks TravelRec - you are THE man!

TravelRec. · Aug 2, 2005, 09:50 AM

Quote:

Originally Posted by max13

Hi travelrec

Maybe i can help you how to get better snr

first of all
pin 1 ofl xlr should be tied to groung as close as possible to voltage source
no other component should use GND path of pin1. Found out from your PCB that pin1 share same ground with all components that is really not a good idea.

second try to use standard (non SMD) resistors. Some of them use resistive path like a coil. 1% Metaloxide resistors are probably best to use. 1 advantage of non smd resistor is higher heat dissipation area so they resistance are more stable. Also noise generated in resistor is lower.

Add low pass filter before INA 217 cutoff frequency shoud be +-60-100khz this filter WILL change phase characteristics of signal but it is not too dramatical.
LPF will help ina217 with input bandwidth. ina will be more stable and not stressed too much by inducted voltage.also higher harmonics sould make problems to ina217 so LPF is probably VERY good idea.

If you can you can get ina163 it has little bit better parameters.
in +-3-4 weeks i will introduce diferential input/output mic preamp based on ina163. It will be DIY so it will be complement to yours preamp.

Hi max13,

nice to have one more electronics specialist here. Thank you for your tips, but I thought, that the performance I get is quite cool. So nice to know that there are some possible ways to increase it a bit. I was very impressed about the quality I got with the 10 modules I have running for years, and they are set up like I posted. I love SMD parts and never realized a problem so far, the big groundplane all around the module gives a good noise immunity. Since I get better results in sound compared with my ZECK FMS mixing console, I´m pretty satisfied. But thank you for your input - comments and suggestions are welcome.

**dj_stick** · Aug 2, 2005, 10:36 AM

this design looks promising

might give me something to do when i finish school next year

igor_levicki · Aug 2, 2005, 10:56 PM

@travelrec:

I have very similar schematics built with 4 OP-Amps it might come in handy for those who can't find INA217:
http://i2.photobucket.com/albums/y12...ak/mic_amp.gif

TravelRec. · Aug 3, 2005, 08:47 AM

Quote:

Originally Posted by igor_levicki

@travelrec:

I have very similar schematics built with 4 OP-Amps it might come in handy for those who can't find INA217:
http://i2.photobucket.com/albums/y12...ak/mic_amp.gif

Thank you for your input Igor, this way you can substitute the INA, but you will not get the same results, I fear. The INA is specially laser-trimmed for this purpose, do discrete OpAmps and components have some tolerances that may affect the performance. If you place a socket on the pcb, you can check the circuit with different instrumentation amps on the market (with the same pin-out and function)- it´s not absolute necessary to apply the INA217, there are different INA´s and some older SSM.....chips that may work. Check your local distributor for low noise instrumentation amps with DIL8 package.

igor_levicki · Aug 3, 2005, 06:10 PM

Thans for a tip Travelrec, this schematic I posted was originaly designed around OPA27GP. Theoretical SNR is I believe around -82 dB.

TravelRec. · Aug 4, 2005, 08:48 AM

With nothing than a virtual load of 600 ohm that is connected to the inputs, the INA217 produces noise below my measuring border which is around -90db, with a mic connected it rises to around -72 .. -75, so background noise and cable noise and the noise of the impedance matching FET inside the Mic is higher than the amp´s noise. All values are given for a gain of 50db.

igor_levicki · Aug 5, 2005, 12:08 AM

Hehe, check this schematic out -- this one is the direct replacement for your circuit and is meant for those who can't obtain INA217.

http://sound.westhost.com/project66.htm

EDIT: for 48V stabilised low noise and ripple phantom power check this:

http://sound.westhost.com/project96.htm

TravelRec. · Aug 5, 2005, 05:38 PM

Yes, cool design and well documented. It´s on the user to deceide. Thank you for the information!

igor_levicki · Aug 6, 2005, 02:00 AM

You are welcome!

Doug W · Aug 9, 2005, 05:48 AM

TravelRec,

I was just at your site and noticed the 48V power supply schematic. You are a gentleman and a scholar.

Thanks,
Doug W

TravelRec. · Aug 9, 2005, 06:14 AM

Hi Doug W!

You are late...

, but it dosen´t matter, post your results if you have some - as a reference take also a look to igor´s suggestions.
Greetings!

Doug W · Aug 9, 2005, 07:53 PM

I know I overslept for work today but what else am I late for?

TravelRec. · Aug 10, 2005, 01:48 PM

Quote:

Originally Posted by Doug W

I know I overslept for work today but what else am I late for?

Update was done on july 29th, your last posting in this thread before yesterday was on july 31st. - but no problem

I´m not your boss

...

Jul 29, 2005, 08:34 AM	#1
TravelRec. Alternative Audioproductions Join Date: Sep 2003 Location: Germany / Sachsen-Anhalt Posts: 1,710 Rep Power: 0	NEW: Professional balanced Mic-PreAmp, DIY project Hello! www.electricstart.de , electronics section is updated with a professional preamp module for professional balanced dynamic and condenser microphones. It has a S/N-ratio below -75 db (mic dependent) and a linear frequency curve up to 80kHz. The performance of the INA217 chip, that is used for the module, is really great and specially matched for this task. I use a similar module (10 of them) in my studio mic setup for years and I think you can benefit from my experience. Have fun! TravelRec. __________________ Always take a look behind.

Jul 29, 2005, 09:34 AM	Thread Starter #3
TravelRec. Alternative Audioproductions Join Date: Sep 2003 Location: Germany / Sachsen-Anhalt Posts: 1,710 Rep Power: 0	Whow, cool - the WDR I know very well , but only from the TV, not in the real life... To build a good phantom power supply you first have to get a little transformer of 30V AC, connect a graetz rectifier and a big electrolyte condenser (2200µ/50V), connect this over a resistor with a second condenser of say 100µF / 50V, connect a zener diode with ground so that the phantom voltage cannot excced 48V and then connect your XLS-Socket over the 6.8k reistors, like you can see in the schematics. Alternatively you can build a step-up coverter (my way) to transform 15V into >30V. BTW, the most available mics accept phantom voltages above +12V on both signal wires as sufficient. __________________ Always take a look behind.

Jul 30, 2005, 11:00 AM	Thread Starter #5
TravelRec. Alternative Audioproductions Join Date: Sep 2003 Location: Germany / Sachsen-Anhalt Posts: 1,710 Rep Power: 0	Okay, don´t be sad, I´ll see what I can do - my solution was very non-orthodox, but is working. I used a transistor and a selfmade coil to transform the voltage up, but that´s not that good for rebuilding. Better you try to get a small transformer with 30V AC output or a small DC/DC step-up converter. I will make a schematics for both versions.... Finally you can check whether your mic works with only 12V phantom power... But don´t burn your mic! Schematics updated with first solution... __________________ Always take a look behind. Last edited by TravelRec.; Jul 30, 2005 at 12:30 PM.

Jul 31, 2005, 10:08 AM	Thread Starter #10
TravelRec. Alternative Audioproductions Join Date: Sep 2003 Location: Germany / Sachsen-Anhalt Posts: 1,710 Rep Power: 0	What´s about solar cells? No just a joke..., if I find a good solution with a step-up converter thing that is working great for this purpose, then I will post schematics too. I think I can order a DC->DC converter module next time and then I will try... __________________ Always take a look behind.

Aug 1, 2005, 10:34 PM	#11
max13 DriverHeaven Newbie Join Date: Jun 2004 Posts: 1 Rep Power: 0	Ina217 as mic pre Hi travelrec Maybe i can help you how to get better snr first of all pin 1 ofl xlr should be tied to groung as close as possible to voltage source no other component should use GND path of pin1. Found out from your PCB that pin1 share same ground with all components that is really not a good idea. second try to use standard (non SMD) resistors. Some of them use resistive path like a coil. 1% Metaloxide resistors are probably best to use. 1 advantage of non smd resistor is higher heat dissipation area so they resistance are more stable. Also noise generated in resistor is lower. Add low pass filter before INA 217 cutoff frequency shoud be +-60-100khz this filter WILL change phase characteristics of signal but it is not too dramatical. LPF will help ina217 with input bandwidth. ina will be more stable and not stressed too much by inducted voltage.also higher harmonics sould make problems to ina217 so LPF is probably VERY good idea. If you can you can get ina163 it has little bit better parameters. in +-3-4 weeks i will introduce diferential input/output mic preamp based on ina163. It will be DIY so it will be complement to yours preamp.

Jul 29, 2005, 08:59 AM	#2
2ndhannes DriverHeaven Junior Member Join Date: Jan 2005 Posts: 37 Rep Power: 0	Hey, now that's something for my taste! Unfortunately, I managed to fetch a symmetric pro preamp card when the WDR (large german TV/Radio) threw out their old studios I just never manage to build a good 24V + 48V power supply so I can use it... Bye, Hannes

Jul 29, 2005, 05:08 PM	#4
Doug W HardwareHeaven Senior Member Join Date: Mar 2003 Location: Montevideo, MN USA Posts: 973 Rep Power: 0	Very nice TravelRec. Would it be possible for you to put a 2nd schematic up there showing the 48V Phantom power supply option? Even without the PCB board layout, it would be nice to have. If you don't have time to do it I understand-I can just sit here and look down at the ground with little tears spilling down my cheeks.

Jul 30, 2005, 07:19 PM	#6
Doug W HardwareHeaven Senior Member Join Date: Mar 2003 Location: Montevideo, MN USA Posts: 973 Rep Power: 0	Thanks TravelRec I feel better now. I need to make a tranportable mic preamp with phantom power.

Jul 31, 2005, 03:25 AM	#7
2ndhannes DriverHeaven Junior Member Join Date: Jan 2005 Posts: 37 Rep Power: 0	Hi Doug, you could always connect five 9v batteries in series, that would be an easy + mobile way to get 45v, and that's close enough (most mics work with even less). If you want to get 48V from one battery, then it gets more difficult, as you must either convert the voltage to AC, use a voltage multiplying circuit and convert to DC again or use a dc-dc stepup converter. I just tried googling but did not find anything fancy on the first pages Bye, Hannes

Aug 2, 2005, 02:40 AM	#12
Maddogg6 Tail Razer Join Date: Jun 2005 Location: Bernyurass, AZ - USA Posts: 4,027 Rep Power: 0	this IS EXACTLY what Ive been hankering for - kudos.. I must place some parts orders soon. Thanks TravelRec - you are THE man!

Aug 2, 2005, 10:56 PM	#15
igor_levicki Intel Black Belt Join Date: Dec 2003 Location: Belgrade, Serbia Posts: 128 Rep Power: 0 System Specs	@travelrec: I have very similar schematics built with 4 OP-Amps it might come in handy for those who can't find INA217: http://i2.photobucket.com/albums/y12...ak/mic_amp.gif __________________ Regards, Igor Levicki -- Creative Audigy 2 ZS Retail (SB0350) kX 3538h

Aug 3, 2005, 06:10 PM	#17
igor_levicki Intel Black Belt Join Date: Dec 2003 Location: Belgrade, Serbia Posts: 128 Rep Power: 0 System Specs	Thans for a tip Travelrec, this schematic I posted was originaly designed around OPA27GP. Theoretical SNR is I believe around -82 dB. __________________ Regards, Igor Levicki -- Creative Audigy 2 ZS Retail (SB0350) kX 3538h

Aug 4, 2005, 08:48 AM	Thread Starter #18
TravelRec. Alternative Audioproductions Join Date: Sep 2003 Location: Germany / Sachsen-Anhalt Posts: 1,710 Rep Power: 0	With nothing than a virtual load of 600 ohm that is connected to the inputs, the INA217 produces noise below my measuring border which is around -90db, with a mic connected it rises to around -72 .. -75, so background noise and cable noise and the noise of the impedance matching FET inside the Mic is higher than the amp´s noise. All values are given for a gain of 50db. __________________ Always take a look behind.

Aug 5, 2005, 12:08 AM	#19
igor_levicki Intel Black Belt Join Date: Dec 2003 Location: Belgrade, Serbia Posts: 128 Rep Power: 0 System Specs	Hehe, check this schematic out -- this one is the direct replacement for your circuit and is meant for those who can't obtain INA217. http://sound.westhost.com/project66.htm EDIT: for 48V stabilised low noise and ripple phantom power check this: http://sound.westhost.com/project96.htm __________________ Regards, Igor Levicki -- Creative Audigy 2 ZS Retail (SB0350) kX 3538h Last edited by igor_levicki; Aug 5, 2005 at 01:17 AM.

Aug 5, 2005, 05:38 PM	Thread Starter #20
TravelRec. Alternative Audioproductions Join Date: Sep 2003 Location: Germany / Sachsen-Anhalt Posts: 1,710 Rep Power: 0	Yes, cool design and well documented. It´s on the user to deceide. Thank you for the information! __________________ Always take a look behind.

Aug 6, 2005, 02:00 AM	#21
igor_levicki Intel Black Belt Join Date: Dec 2003 Location: Belgrade, Serbia Posts: 128 Rep Power: 0 System Specs	You are welcome! __________________ Regards, Igor Levicki -- Creative Audigy 2 ZS Retail (SB0350) kX 3538h

Aug 9, 2005, 05:48 AM	#22
Doug W HardwareHeaven Senior Member Join Date: Mar 2003 Location: Montevideo, MN USA Posts: 973 Rep Power: 0	TravelRec, I was just at your site and noticed the 48V power supply schematic. You are a gentleman and a scholar. Thanks, Doug W Last edited by Doug W; Aug 9, 2005 at 06:02 AM.

Aug 9, 2005, 06:14 AM	Thread Starter #23
TravelRec. Alternative Audioproductions Join Date: Sep 2003 Location: Germany / Sachsen-Anhalt Posts: 1,710 Rep Power: 0	Hi Doug W! You are late... , but it dosen´t matter, post your results if you have some - as a reference take also a look to igor´s suggestions. Greetings! __________________ Always take a look behind.

Aug 9, 2005, 07:53 PM	#24
Doug W HardwareHeaven Senior Member Join Date: Mar 2003 Location: Montevideo, MN USA Posts: 973 Rep Power: 0	I know I overslept for work today but what else am I late for?