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SvenMZ8

The MIG-15

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Nearly a year ago, on the month of July 2009, iitoo, joshua, eawtan and me were chatting and talking about audio, eventually the discussion led to inspire me to build a consumer grade portable amplifier. With the support and testing by iitoo, joshua as well as eawtan giving me technical backup, the result of these past 10 months of research and development is the MIG-15.

 

Lets go over the development stages, i know u guys like to see this kind of stuff.=)

 

August 29th: 1st prototype

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First of all, the amp has to be sufficiently small to be portable. I drew a few ideas from other currently available amps and i settled on the hammond casing, used by the mini3. Ideally i had joshua's mini3 which i was fixing at the time, so i followed the dimensions of the mini3 circuit and there i knew how much space i could work with.

 

Secondly it has to have a good circuit topology. Having a cmoy doesn't quite have the sound I'm looking for. I chose a 3-channel topology that guarantees a better sounding system. It also has to have a decent battery life. Therefore battery capacity and current draw have to be noted.

 

Lastly it has to have all the best components possible without blowing the budget. u can see that theres wima decoupling caps already.

 

Dec 7th: Hammond Casing

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I ordered Hammond black anodized aluminium casing from mouser usa. Parts came in just 3 days, shockingly fast. There i managed to cut a prefboard to fit in nicely. However my amp couldn't fit in length wise. Some parts have to be changed, so i decided the fat 9v battery has to go. Clearly 9v was too much for a portable amp, and having 4 AAA batteries like my pimeta leaves very little space for power supply capacitors. Having two AAA batteries seems to be the only viable option. However 3 volts is insufficient and hence i decided to go with either buck-boost convertor or a invertor that doubles the voltage. I discussed with eawtan many possible ways of doing this, considering efficiency, battery life, regulation and working voltage for opamps. With this i bought a couple of chips to experiment and to accomplish this feat.

 

Dec 19th: Portable rigs meet

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I managed to find the right circuit for the voltage booster, with the 2 AAA batteries and the booster circuit and the right voltage regulator. i managed to fit the circuit into the casing. Just in time for the jabenite portable rigs meet. Many people tried the new prototype and the general response was good. I apologize that i lost the photos of the circuit board, its somewhere in my harddisk and its a mess. But the board already had some audiophile components such as vishay dale military spec resistors, blackgates power supply capacitors, switchcraft female 3.5mm jacks and an Japan alps volume control.

 

Jan 30th: More features added

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The amp had a new miniture switch for gain setting of low and high gain. A new aluminium silver knob as well as a painstakingly hand milled acrylic faceplate that fits the hammond casing. U can see that the circuit board is pretty dense now, with a stacked mini board for the power switch and gain switch.

 

Feb 22th: New knob

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I found the old knob too big and it stuck out of the amp, which was quite unsightly. i managed to source a matching colour aluminium knob, and it had a clearer volume indicator. The amp is actually card size.

 

March 10th: Laser Etching

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the amp needed labels and its name on the amp. I designed the logo and the labels on the faceplate and lining them up by vernier calipers and guides on the photoshop software. I had no idea what would come out when anodized aluminium is etched by laser. Turns out great! The labels lined up as they supposed to be.

 

May 3th: Tweaking

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I drilled a new hole for the blue led, and yes its blue not UV purple in the photos, i think its the camera, any white balance setting came out purple. The circuit board has been through lots of desoldering and soldering of components and wiring changes but more or less the layout is nearly finalized.

 

 

May 6th: More tweaking + battery charging testing

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Well technically on the day of posting this, i was exploring different ways of charging the 2 AAA batteries. One was a chip which enabled fast charging of the batteries in just 3hours. but as tempting it may be, it was in smd, or rather in TSSOP package, a real challenge and was too expensive for the amp. The worst came while bending the pins of the chip into submission, i broke off one of the important pins>.<. i knew its not viable so i tried trickle charging which is much safer for the batteries and a proven and popular technique in charging batteries.

So far the charging is good via 5 volt dc adaptor. I would see an option for a usb port to charge via computers but testing has to be done to confirm that charging from usb is safe for the computer.

 

Also u can see that there actually a special feature that is unique to this amp. The jumpers u see here are for implementing a modular component.

Here is an example is the use of blackgates as input capacitors inside the amp, instead of usually in the d-o-c-ks of imod LODs, a good feature for imod users i must say, since they will not be limited by their current imod lod and are now free to try other considerably cost effective non-imod lod without the worry of capacitors. A crossfeed module is also planned for this amp.

 

Heres a short summary of the features.

 

Power Supply

2 x AAA 1000mah batteries - 20hours battery life, tested

Trickle charger

High efficiency voltage booster circuit

Low Dropout voltage regulator

2 x Blackgates power capacitors

1 x Panasonic FM low ESR capacitor

4 x WIMA decoupling capacitors

 

Amp section

3-channel topology

Vishay Dale Military Spec Resistors, hand matched

Alps volume control

Gain Switch settings, gain of 3 for iem or 6 for headphones

 

Casing

Black anodized hammond casing

Matching black anodized volume control knob

Hand milled acrylic faceplate

Laser Etched logos and labels

 

Disclaimer: This is only a research. It is to find out how much can a portable amplifier design be pushed. Through the course, i have learnt a lot about circuit design and has benefit me in the course of my studies in NUS. No large sales on this amplifier will be made due to high cost and man-hours. Only three will be built which includes this one and all will be sold cost price, only to recover costs made during the research, no profits made. All information,circuit design, logos are intellectual property of mine. Do not use information from here without prior permission from me.

 

The MIG-15 is nearing its final stages, and hopefully be completed soon. I hope you guys enjoyed reading this as much as i enjoyed building this.=)

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Great stuff. Wow, I am deeply impressed. 2 AAA batteries with DC-DC conversion. Outstanding.

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Guest jacj6049

impressed! Might to organise a mini meet for us to try them out?

 

 

i'm second this,i also jus completed a icute,really wanna try tat great amp too

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thanks all for the nice comments

 

blackmouth0, jacj6049 - Just give me a pm if you like to come listen to it.

 

freddie - i cut my acrylic at the void deck outside my home, got them etched from some guy in hardwarezone

 

The MIG-15 is already completed. one has already been booked so there is two left.

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May 11th: Charger and FacePlate

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finished the charger board yesterday. i realised i didn't need the extra voltage regulator since the amp already has one, one less to worry about too.

charged the amp with a 5v dc adaptor overnight and its fully charged, the 2 NiMH AAA reads about 3volts after about 8hours of charging. its trickle charger, so theres no need to worry about overcharging. two more faceplates have been made, tried my best to keep the holes neat.

whats left is the hole for the dc socket at the back.

 

hopefully i could finish building the other two amps by this sunday.

 

may 13th: Second board

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heres the second amp. its half built, making one of these amps proved to be really time consuming, so i guess the 3rd one would have to wait till next week.

 

May 16th: 2nd amp board completed, 1st amp ready for sale

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charging port at the back of the amp. serial numbers #01 #02 #03. going to shorten the volume pot today.

LED brightness turned down. too bright.

the MIG-15 can power iems and efficient portable headphones, it will not power high impedance headphones, use a desktop amp for that.

 

the amp is available testing at pioneer mrt. pm for details.

 

 

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maybe it could release the BOM and pcb, i would be interested to build it and try.

 

support local designer

 

BOM is quite long, and some are smd parts.

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