Hey all,
Just a quick question. I've had a project floating around in my head for a while, and figure I'll give it a crack while I have a few free weeks.
I'm looking to make a very simple, portable amplifier that will amplify a signal from microphone level to headphone level. It needs to be battery powered and provide 48v phantom, with a volume pot. It only needs to be in mono, but I might make a stereo version later if it works out.
I have a very limited knowledge of gain staging, so my question is. Is there a way of doing this with one circuit, or would I be better off piggybacking two chips - one to amplify to line level and another to headphone level? I realise that would be pretty easy, but to make it small is another thing entirely.
Any thoughts you could give would be much appreciated.
Thanks,
BlindMelon7
Just a quick question. I've had a project floating around in my head for a while, and figure I'll give it a crack while I have a few free weeks.
I'm looking to make a very simple, portable amplifier that will amplify a signal from microphone level to headphone level. It needs to be battery powered and provide 48v phantom, with a volume pot. It only needs to be in mono, but I might make a stereo version later if it works out.
I have a very limited knowledge of gain staging, so my question is. Is there a way of doing this with one circuit, or would I be better off piggybacking two chips - one to amplify to line level and another to headphone level? I realise that would be pretty easy, but to make it small is another thing entirely.
Any thoughts you could give would be much appreciated.
Thanks,
BlindMelon7
The 48V phantom supply is the hard part, will you need that regularly?
If not, it would best be in a separate box.
http://www.ebay.com/itm/DC-DC-Boost...le-/191992009687?_trksid=p2385738.m2548.l4275
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Just buy this and be done with it. 9v battery powered headphone out XLR in with 48v phantom. Small and portable.
IK Multimedia iRig Microphone Preamp/interface | Staples
You can't diy it for less
IK Multimedia iRig Microphone Preamp/interface | Staples
You can't diy it for less
Good shout! That's ridiculously cheap. I would need it quite regularly, but I'm sure I could squeeze that chip in with the rest of the amp.
Looks like the iRig above is the way to go, a finished product for only $40.
Just buy this and be done with it. 9v battery powered headphone out XLR in with 48v phantom. Small and portable.
IK Multimedia iRig Microphone Preamp/interface | Staples
You can't diy it for less
You have no idea how long I've been looking for something like this. Your googling skills are on another level sir!
However, I cant work out if this monitors directly to the headphone output or if you have to use an app to monitor? In which case, would it be using the preamp on the phone to add gain?
"The irig mic pre features a 3.5mm headphone out that allows you to monitor the processed sound... however you sound."
"The irig mic pre features a 3.5mm headphone out that allows you to monitor the processed sound... however you sound."
From a bit of googling, it seems the iRig is just a mic pre with a return from the phone's headphone amp, so it wouldn't work as a direct monitor in standalone. I'd rather have something that I can just throw in my pocket without having to use any other devices.
Just get a basic headphone amp like a Fiio A1 or similar.
https://www.amazon.com/gp/aw/d/B01LYYKP29/
My guess is that the signal from the unit if connected to your headphone would probably sound ok if you had high impedance phones (250ohm). But even a cheap $25 portable headphone can boost that to work with any headphone.
https://www.amazon.com/gp/aw/d/B01LYYKP29/
My guess is that the signal from the unit if connected to your headphone would probably sound ok if you had high impedance phones (250ohm). But even a cheap $25 portable headphone can boost that to work with any headphone.
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This might work but not sure if has to be connected to USB to work? It says can operate with 9v battery and has headphone jack. You get 2 channels and an ADC to boot.
ART USB-DUAL-PRE-PS USB Microphone Preamp
ART USB-DUAL-PRE-PS USB Microphone Preamp
True, but I'd still rather build something - I've been looking for a project to brush up on my soldering skills.
So would you say I'd still need two discrete gain stages or is there a way of skipping the line level and going straight to a headphone level?
Yes 2 stages. 1st is high gain mic preamp. Second is headphone power amp. 4 transisotrs total.
Use Rod Elliot's preamp:
http://sound.whsites.net/project13.htm
Then you could use my simple headphone amp which sounds superb.
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb.html
Looks like this:
Since you are mono you could use only half that space and put mic preamp in other half.
Then use a small DC to DC step up to get 48v phantom.
There's probably a way to make the preamp with just two BF862 JFETs.
Use Rod Elliot's preamp:
http://sound.whsites.net/project13.htm
An externally hosted image should be here but it was not working when we last tested it.
Then you could use my simple headphone amp which sounds superb.
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb.html
Looks like this:
Since you are mono you could use only half that space and put mic preamp in other half.
Then use a small DC to DC step up to get 48v phantom.
There's probably a way to make the preamp with just two BF862 JFETs.
Learn gain-staging. IMHO it is the audio-person's MAIN skill.
Yes, the 48V may be tougher than the rest.
The iRig is probably not a complete solution. (Another model only goes TO a mini microphone IN; this may be only USB out plus a loopback?)
A clever designer "could" do the gain-range in a "single stage". Should charge more than the project is worth; certainly more than an added chip.
Voltage rails is another concern. You want a 48. But headphones can blow your brains out with 10V; any more is waste heat. On the third hand a "microphone preamp" may cover such a wide range that 15V to 30V may be nice. Now your smallest load is your highest voltage, an awkward power-stack to manage.
"Phantom" implies "balanced" (differential) input. The single-ended preamps don't work this way.
Most "good" mike preamps don't go below unity gain. Most power amps (even headphone power) have a narrow range of stable gain. 0dB in pre and 26dB in power amp may be too much gain for loud voice in sensitive cans.
There is a reason almost all compact mixers have two knobs in the path: an input gain knob and a channel mix knob. (And usually a third knob for headphone gain, though if there is no other output this might be skimped-out.)
I'm thinking 9V wall-wart, a '555-based voltage multiplier to get several higher rails, the "$10 mike preamp chip" for a -good- mike input, and even a LM386 (better a LM380) power stage. But the '555 buzz-booster begs for audio trouble. Voltage boosters are cheap from Asian suppliers, but I do not know quality.
Yes, the 48V may be tougher than the rest.
The iRig is probably not a complete solution. (Another model only goes TO a mini microphone IN; this may be only USB out plus a loopback?)
A clever designer "could" do the gain-range in a "single stage". Should charge more than the project is worth; certainly more than an added chip.
Voltage rails is another concern. You want a 48. But headphones can blow your brains out with 10V; any more is waste heat. On the third hand a "microphone preamp" may cover such a wide range that 15V to 30V may be nice. Now your smallest load is your highest voltage, an awkward power-stack to manage.
"Phantom" implies "balanced" (differential) input. The single-ended preamps don't work this way.
Most "good" mike preamps don't go below unity gain. Most power amps (even headphone power) have a narrow range of stable gain. 0dB in pre and 26dB in power amp may be too much gain for loud voice in sensitive cans.
There is a reason almost all compact mixers have two knobs in the path: an input gain knob and a channel mix knob. (And usually a third knob for headphone gain, though if there is no other output this might be skimped-out.)
I'm thinking 9V wall-wart, a '555-based voltage multiplier to get several higher rails, the "$10 mike preamp chip" for a -good- mike input, and even a LM386 (better a LM380) power stage. But the '555 buzz-booster begs for audio trouble. Voltage boosters are cheap from Asian suppliers, but I do not know quality.
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