Just got in a new (to me...) acoustic musician amplifier by Behringer. The reason why I bought it is due to its separate channels for Instrument and Mic, along with separate digital effect systems on both channels. Plugging in for the first time, with volume set low, on the Microphone channel I notice whenever I connect the mic cable to the microphone the amp goes POW!. Whenever I switch the mic on/off slide switch - that one on the mic - POW! Different make model mic - same. I thought this is ridiculous...No other XLR input on anything I've ever owned has done this. I searched for the 48V phantom enable switch - no dice. Then I searched for a schematic - found something on my amps bigger brother.
Why did they think it was a good idea to pull both balanced mic lines high only on the XLR input? To +15, never mind 48 - a little something better than nothing? I dont mind going in and hogging out R7 and R5, but before I open the box, I'd like to know Why?
Uh, people dont use dynamic mics anymore? People dont mind a big "KaPoW!" coming from their amp when they switch their mic on and off? Some juice for the case when someone plugs in a condenser is better than none? Mics these days all have built in preamps, which need at least 9V phantom power - those old Shure SM57s arent the design target anymore?
Anyway, I can see what's the work to be done ahead of me. Feels strange to be this out of touch with modern, yet 15 year old mic input designs.
Why did they think it was a good idea to pull both balanced mic lines high only on the XLR input? To +15, never mind 48 - a little something better than nothing? I dont mind going in and hogging out R7 and R5, but before I open the box, I'd like to know Why?
Uh, people dont use dynamic mics anymore? People dont mind a big "KaPoW!" coming from their amp when they switch their mic on and off? Some juice for the case when someone plugs in a condenser is better than none? Mics these days all have built in preamps, which need at least 9V phantom power - those old Shure SM57s arent the design target anymore?
Anyway, I can see what's the work to be done ahead of me. Feels strange to be this out of touch with modern, yet 15 year old mic input designs.
That design is very common.
48volts is not essential, 10volts is fine, 15volts is more than enough for any decent powered microphone; Beta57/58 etc. 48volts is required for active DI boxes in some cases.
Most sound engineers mute the signal path when connecting equipment.
Switching a Beta 57/58 on and off does not affect the phantom power to it, all it does is connect pins 2 & 3 together on the XLR.
If your mic 'thumps' when switching on and off, on the mic, it is either faulty or a cheap mic.
Shure SM57 is still industry standard for instruments back line!
48volts is not essential, 10volts is fine, 15volts is more than enough for any decent powered microphone; Beta57/58 etc. 48volts is required for active DI boxes in some cases.
Most sound engineers mute the signal path when connecting equipment.
Switching a Beta 57/58 on and off does not affect the phantom power to it, all it does is connect pins 2 & 3 together on the XLR.
If your mic 'thumps' when switching on and off, on the mic, it is either faulty or a cheap mic.
Shure SM57 is still industry standard for instruments back line!
Attachments
That phantom power circuit is fairly standard.
Most mics will create a pop, thump when plugged into a active phantom powered mic input.
What model is the mic and have to checked the wiring on the XLR mic cable.
Actually on off switched mics short pins two and three together to turn off the mic, if phantom is on that mic input
there is no voltage potential between pin two and three.
If your never going to use a condenser mic then you could cut out R7 & R5.
Most mics will create a pop, thump when plugged into a active phantom powered mic input.
What model is the mic and have to checked the wiring on the XLR mic cable.
Actually on off switched mics short pins two and three together to turn off the mic, if phantom is on that mic input
there is no voltage potential between pin two and three.
If your never going to use a condenser mic then you could cut out R7 & R5.
I see...thanks for the replies! Looks like I'll be making up an XLR to TRS cable, which is the path of least resistance. Ar-ar.
1) a very common Phantom circuit, +48V only really required on OLD style Neumaanns and such, but modern SS electronics, using those fancy newfangled Fets or Op Amps can and do quite well with less.
15V being popular because they usually are ¨*already there.
In any case, MANY plain vanilla modern mics just use an Electret, so.....
The electret itself is designed to be happy with +1.5V, go figure.
2) terribly wired microphone (yours), no specific fault of the amp.
3) that said, I WOULD add a small Phantom switch to the amp.
Not permanently remove resistors because of, you know, Murphy´s Law.
The very next day you remove them you´ll have an important gig where the ONLY mic available will be a Phantom powered one, or you´ll need a phantom powered direct box or interface or active guitar or .... you know the drill 🙁
15V being popular because they usually are ¨*already there.
In any case, MANY plain vanilla modern mics just use an Electret, so.....
The electret itself is designed to be happy with +1.5V, go figure.
2) terribly wired microphone (yours), no specific fault of the amp.
3) that said, I WOULD add a small Phantom switch to the amp.
Not permanently remove resistors because of, you know, Murphy´s Law.
The very next day you remove them you´ll have an important gig where the ONLY mic available will be a Phantom powered one, or you´ll need a phantom powered direct box or interface or active guitar or .... you know the drill 🙁
You beat me to it!
Not going to get much from the plugging your mic into a line level input.
Some mics do sound better with a higher phantom voltage or at least have less noise
floor as well as active DI boxes.
On the mic you have turn the switch off and measure between pins 2 and 3 on the mic it should show a short also check between 2 and 3 to pin 1 that should show open.
Eyeya, I didnt see that.
It looks like I'm going to have to open it up afterall... Gives me a chance to lay down a little deoxit, as the controls arent perfect.
That's doable!
I have a MicPre kit that is meant for musicians.
If you like to try it out, I'll be happy to send you a free sample.
https://ampslab.com/MICpreLIVE.htm
If you like to try it out, I'll be happy to send you a free sample.
https://ampslab.com/MICpreLIVE.htm
Wow, Michael, that's very kind of you. However I'm pretty sure I wouldnt be able to pay back any useful information to you in a timely way. I'm swamped!
If you look up "cheap" in the dictionary, 1. Behringer
Well, it only took me two years, but I finally knocked out the stupid bias supply for the microphone XLR input on my Behringer "ultracoustic" amp. Good thing I saved the schematic from the 1000 model; mine's a 450 and they share the same suspected candidate 10 Ohm padding resistor for connection to +15 (+12V measured on my amp). Noticed you cant find that schematic on line anymore... C'mon intellectual property rights; all I wanted to do was remove this one little thing about it.
I knocked that SMD off the PCB and gone is the 12V bias with it's attendant "Kapow" - sounding just like an outdoor gunshot through the #3 reverb setting - whenever I use the mic on/off switch on the mics that I have and use. Also gone is some hum/noise that I suppose came with the bias. Hooo_effin_rayy!
I knocked that SMD off the PCB and gone is the 12V bias with it's attendant "Kapow" - sounding just like an outdoor gunshot through the #3 reverb setting - whenever I use the mic on/off switch on the mics that I have and use. Also gone is some hum/noise that I suppose came with the bias. Hooo_effin_rayy!
I've just noticed R198 and R199 in that schematic - noise creation resistors! They should be more like 50 ohms than 2k... But its an inverting opamp circuit so you can't just do that...
Perhaps reduce R202, R240 to 2k, and R198/R199 to 200 ohms?
The whole circuit is dubious...
Perhaps reduce R202, R240 to 2k, and R198/R199 to 200 ohms?
The whole circuit is dubious...
It'd be some work to pull off the preamp PCB from the chassis, as those resistors are leaded and on the front side of it. Lucky the 10 was on the backside with a lot of the SMD stuff. I only use this for singing into a mic practice, as the guy at the open mike doesnt like my headset mic for some reason. Okay, I'll learn to use one on a stand...like everybody else.
As is, with the mic switched off, I can hear shot noise with the volume between 8-10 - with my ear right in front of the speaker. At 6, I dont hear anything and that's plenty of mic gain for what I do. Thanks for the improvement suggestions anyway!