First off my apologies for any grammar and or spelling errors, it's 5AM and I'm more than a little bit tired. I have been pretty busy with school, work, and my 3D printer, so I haven't had much time to work on other projects. But after a failed attempt to improve my printer, I found myself needing to unwind and not stress over it [it's been quite a challenge]. So I spent a few days working on a present for a friend of mine. It is a small custom audio amp that was a complete scratch build. Custom electronics, custom enclosure, I even went so far as to turn and knurl the gain knob on my lathe. I made up the design as I went along, so I must say that I am rather pleased with how it turned out. I will post more pictures tomorrow today after I get some sleep. Until then here is a teaser shot. As always, questions and comments are welcome.
Hey, you can't tease people with modding goodness and then just leave them hanging like that! That's just wrong!
That picture was totally taken with my camera at my desk It's been a fun process watching you make it.
After a long rest it's time for me to update this thread with the pictures I promised. To begin, I started out by making a prototype on protoboard. It was a rather tiny circuit and the main chips for the amplifier weren't much larger than a penny. After ironing out some of the kinks and testing out the circuit it was time to make a permanent board. Since there weren't any surface mount parts, I decided to go with the toner transfer method. Here is a picture of the board after it was etched. Then I cleaned off the excess toner with some acetone and drilled out the board. Soldering together the final circuit was much easier than hobbling it together using protoboard Then it was back to testing the circuit. Even though I do point to point checks with my multi-meter before powering a circuit on, I always worry that I might see the magic smoke. Though these chips are tough as nails and can survive shorts between most any pins. Oh yeah I forgot to mention, this amp was specifically designed to be used with a certain type of audio output... Surface Exciters: The easiest way to describe a surface exciter is to picture a speaker that doesn't have a cone. Literally it is just the voice coil/driver. You attach these devices to other materials and they then use that medium as their "cone" of sorts. They are really neat little devices and can be used with a wide variety of materials with varying degrees of fidelity and clarity. So far cardboard boxes and foam core (a thin sheet of foam with 2 layers of card stock laminated to it) are the community favorites. The audio is surprisingly clear and crisp. Depending on the size of the exciter and the size and density of your medium, you can create a first rate audio system. The camera really doesn't do it justice, the audio was very clear. When you hear distortion and scratching it is because the surface exciter was breaking free from the surface (pizza box) as it was only held down by double sided tape. To think I was just using double stick tape and a pizza box from that nights meal. That's all I'm going to leave you with tonight. I need to catch up on sleep so I will post the rest of the pictures later.
Whew, glad that is over with... While I waited for some new parts for my printer, I decided to use that amp circuit to teach a class at the local hackerspace. I made up ~20 kits that included all the parts to build an amp and also included some surface exciters with the necessary cabling to get it running. Along the way there were a few accidents, and I came to appreciate just how sturdy this circuit was. We had some hook up the power with a reverse polarity, and some accidentally supplied the circuit with an AC signal (at 16v). Some even put the chips in backwards! After hooking up the proper power supply and getting chips flipped around proper, the amps fired up just fine. There were a few minor issues of bridged traces as well and one reversed cap, but at the end of the night everyone left with a working amp! I decided to leave the enclosure up to the participants but it sounds like they left with some good ideas for what they wanted to do. Now that I am all done with that, I can take the time to post the rest of that picture set from when I made the first amp. Here is the leftover stock after cutting out the halves of the amp case. Also, this stuff smells awesome! The bamboo is caramelized and has the scent of brown sugar. It can also give you some nasty splinters. The parts were cut on a small CNC router that we had built at the hackerspace. Not bad considering it was the first time I had ever attempted to use a CNC router. Then there was the little detail that it was the first time that router had been used. The router isn't even done yet as we have yet to complete the dust shroud. I didn't want to permanently seal the case together, so I drilled some holes and threaded some M3 bolts right into the bamboo. They are a very tight fit and show no signs of stripping out. I was worried about chipping, so I beveled the edges and then sanded the case to flush up the halves. Alas I did cause a little chipping along the way, but managed to avoid any serious damage. Once that was taken care of, I cut out some holes for the electronics and mounted the circuit in place. The circuit was press-fit into place. It is snug enough that it won't nudge about, but can still be removed if the circuit should ever need to be repaired/replaced. Though in hind sight I should have moved the power jack more towards the rear of the amp. I lathed the knob on my old metal lathe and then used a knurling tool to press that pattern into the knob before I parted it from the stock. I test fitted the knob to make sure there was enough clearance. I would later go about taping out the knob and then threaded it over heatshrink on the potentiometer. This gave it a solid grip on the potentiometer but still allowed the knob to slip if forced beyond the min/max. After a few coats of a clear varnish I was done! And a few photos of the completed amp: I accidentally chipped the back near the end of the project, but luckily it's an area that won't be seen very often. And of course, the money shot:
Looks wonderful, you mentioned that it was for a 'certain type of audio output' do you feel like elaborating on that a bit? It seems really small and compact, what kind of input/output power do you get?
I'd love to hear the specs too. I have an unnecessarily large amp sitting on my computer, and this looks perfect to replace it if it has enough power. Your case for it is definitely gorgeous.
I'd be happy to elaborate on what little I know. What specifically would you like to know about it? There is a brief description of the surface exciters at the bottom of that post, along with a small video demonstrating them. I don't have the tools to properly measure the circuit (just a cheap multi-meter), but I do know that circuit is drawing ~5 watts peak output. The amplifier is technically capable of pushing 8 (2 x 4 watts), but given the source voltage and the load it really is only pushing 3-4 peak through the outputs. Thanks I still need to send it off to my friend, hopefully they like it too. As far as specs go, HERE is the data sheet for the chips used in the circuit. From looking at the graphs and based off what I know of the design I made, I would have to guess that each channel is ~1-1.5 watt RMS and THD is somewhere around .05-.1% The panels put out a decent amount of sound and are more than enough to keep me happy in my apartment. I don't have a nice calibrated meter, but I can get an approximation with a cheap one. I'll edit this post when I have a rough figure. If there is enough interest I can supply the design, though I don't really have anywhere to upload it.
That's a damn fine job. I'm currently in the process of building a CMoy headphone amp; I have built one in the past, but that was more of a proof-of-concept to prove to myself that: a) it worked; and b) I didn't make a complete hash of it. I plan to use a pre-made aluminium case for my new CMoy; sadly my local hackspace doesn't have a CNC mill (though we do have a lathe, reprap and a pretty meaty pillar drill...)
Thanks, and double thanks for linking me to your headphone amp, it was a fun read. Now I have an itch to build one, too bad I don't have a good set of headphones that are worthy of their own amp. Thanks, for the compliment. And thanks to the others who also commented and asked questions. It's always nice to hear from people and get feedback.
The CMoy is such a simple and cheap design - I think I built my first version for less than £15 and the main expense was an enclosure. Usually the op-amps are the most expensive part, but you can get free samples of the OPA2132P & OPA2132PA from Texas Instruments; the last batch I ordered got from Maryland (US) to Cardiff (UK) within 3/4 days - impressive for something that cost me utterly nothing. The only difference between the P and PA versions is in their DC performance, which is completely irrelevant when being used in an audio amplifier. To be honest, I thought exactly the same thing regarding headphones. At the time I built the first CMoy I was only using a set of cheap Sony MDR-V150 headphones and I was dubious about any improvement in sound quality, given that my headphones weren't exactly "audiophile" quality. Compared to just using the PC's headphone/speaker jack however, I was pleasantly surprised to find that the CMoy did actually make a big difference. I only really built the amp as an entry point into DIY audio gear, but it has turned out to be a practical endeavour. The "finished" article in the thread I linked to was actually given to my brother; I'd always planned to build a more compact unit, but never got round to finishing it. I've since purchased a pair of Grado SR60i headphones, which are a massive improvement (despite the varying opinions on Grado headphones) and certainly worthy of their own amp. Although they are only three weeks old and the left headphone has already died, which does not bode well for a £90 pair of headphones... My over-arching plan is to integrate my USB DAC (the Behringer UCA202, which doubles as a 2-in/2-out recording device) into the headphone amp and connect the RCA output jacks of the DAC to the input of the CMoy. It would be useful if I could use the RCA input jacks on the DAC without it being connected to the PC because then it could be used with any audio source, not just USB. Whether or not the DAC can be powered up and used without the data lines of the USB connector actually being connected to a PC is a matter that I have yet to investigate... I think I need a decent benchtop power supply before I get that far though - baby steps, etc... Anyway, apologies for the slight tangent!
Great jobs mate ... I'll take some time to read the headphone amp thread too. I've started designing an headphone amp to drive my AKG K701 since these cans are really hungry and doesn't allow any sub-decent amp. I'm going for tubes, since I really like how tubes sounds and here is the schematics I'm going for : EDIT : As BLC mentioned, TI can provide you with samples. I'm still burning to build a DAC using a pair of PCM1704 ... om nom nom. TI / BurrBrown makes a lot of nice chips, and they are all well documented on their sites. http://www.ti.com/lsds/ti/analog/audio/audio_overview.page
