[steaxauce]

For my first project I decided to jump in more or less head first, with a 3-channel beta22. I decided on the 3-channel because I couldn't see balanced operation making much of an improvement with my ~30 ohm Ultrasones. I ordered parts from Glass Jar Audio and they came in on Wednesday, and I got to work right away. The kit included 3 B22 boards, one S22 board, and an E12 muting delay/DC offset protection circuit board. I had ordered an E22 groundplane board, but he didn't include that because of a misunderstanding. I should receive that soon. I had ordered a 100VA transformer, but he upgraded it to a 120VA, I guess because that's what he had on hand. It saved me a ton of time to be able to order everything as a package from one place. I highly recommend it.

I started this thread because I want to stay connected to the community throughout this project, to make sure I get it done and that I don't make any huge mistakes. I also thought that following a beginner's acquaintance with DIY through building a beta22 would make for an interesting read.

Hopefully this will be the first of many projects.

On Wednesday the kit arrived and I pulled everything out and got to work. I started with the E12, since it was the smallest. I worked by finding parts on the parts list and then soldering them into their respective locations on the board. I had to google several parts to find out about their polarity. I would place several parts of the same type on the board and then flip the board over, cut their leads and solder them into place. It was going very slowly at first, but as I got used to soldering it started going faster, and I finished it that night. I didn't read its schematic until the next day. I'm pretty sure it was the first complete schematic I'd ever read. Clever, simple circuit. I noted that if one of the channels has a DC offset of more than 70mV, but |V[size=xx-small]L[/size] + V[size=xx-small]R[/size] + V[size=xx-small]G[/size]| < 70mV (say, the DC offset is positive on one channel and negative on another), the headphones wouldn't be disconnected. That situation's not very probable and I guess AMB determined that the simplicity of the circuit was more important.

I put the E12 away and the next day I got started on the S22. I would've finished it before I went to bed that night, and I was about 9/10ths of the way through with populating the board, but I ran out of solder! I had ordered some on Wednesday, and it just arrived as I was typing this, so I'll finish it up soon (but I need to get some homework done first).

As of now I have no idea what I'm going to do for an enclosure. I have no tools for building one, but I can probably borrow some from someone. I have a few friends who can weld, too.

I'll post some pics as soon as I can get them hosted. I'll be posting pics and updating this thread (and asking questions) throughout the building process.

Thanks guys!

 

[nikongod]

casework is at least half of the effort for most amp projects.

good luck.

 

[n_maher]

With this amp in particular case work is going to be more than half the battle. Be very careful if you decide to put the trafo in the same enclosure with the amp boards. You'll likely end up with some EMI hum that will be very difficult to deal with.

 

[steaxauce]

Thanks for pointing that out, guys. I'll start looking into casework. N_maher, I do plan on building the power supply in a separate enclosure, so that shouldn't be a problem.

So far, I've completed the e12, and the s22 all except for the mosfets, because I need to purchase mounting kits for the heatsinks. I also need to purchase RCA and headphone jacks. For now I'm building the amp without a volume control, but after I finish everything else I'm going to build a stepped attenuator.

As I said in the first post, for now I'm building the amp in 3-channel configuration, but I may end up purchasing two b22 boards and some more s22 boards to make it a balanced amp. I would use the single active ground board to drive two sets of unbalanced headphones. Since the amp inverts polarity for one of the unbalanced headphones, the net current for the combined grounds should be the difference between the current levels of the two headphones, rather than their sum, which is why I figure I'd only need one ground board.

I'd try to set it up so that I can use a single volume control for the balanced headphones, or two separate volume controls for the two unbalanced headphones. I would also replace the heatsinks with larger ones so that I could use the amp to drive speakers as well, but for now I'm just building a 3-channel headphone amp.

I'm a bit behind in school at the moment though, so I probably won't be getting a ton of time to work on the amp over the next few weeks. I'll keep y'all updated, and I'll probably post the first pics tomorrow.

A few quick questions though: I had never bought solder before, so I did a few hours of research before making my first purchase. I ended up getting Kester 63/37 with "44" activated rosin core, .031" diameter. Was that the right choice? Kester claims that the flux is non-corrosive if not cleaned, but would it still be better if I cleaned it, and if so, what should I use to clean it? Amb's website says that I can clean it with alcohol, but another source said that this is far from ideal; that it would be far better for the board if I used something made specifically for cleaning circuit boards.

My second question is about what tips I should buy for my soldering iron. I have a Hakko 936, and I've been using the stock tip, but I'm afraid that it's too large for the beta22. My grandfather bought me a few tips, but I haven't seen them in a while and I'm afraid they're lost. I couldn't tell you what tips they were. I just need to know which tips I should have in my inventory. I'm also interested in tips about caring for my tips.

Thanks again!

 

[amb]

Hakko 936 is excellent. Just get a smaller tip for fine PCB work. The Kester 44 solder is also just fine. Personally I use .025" diameter solder for my PCB work, but for β22 .031" is ok.

 

[steaxauce]

Hey guys,
I've been utterly swamped with homework for the past few weeks, so I haven't had any time at all to work on the beta22 since the last time I posted in this thread. I have pictures taken and I'll post them as soon as I have time. I expect that I'll be able to get some work done on the project after my Calc 3 test on Tuesday.

I need to finish it fairly soon because my Headroom Maxed desktop is about to be sold. I just bought a Bel Canto DAC3, so I'm probably going to order more boards and build this amp in balanced configuration to take advantage of the DAC's balanced outs. I should've known ths was going to happen. Nearly all of the DACs I was considering had balanced outs.

At the moment I have the E12 muting/delay board completed and the S22 is completed except for the mosfets, because I still need to purchase heatsinc mounting kits.

A few more questions:

Amb, thanks for confirming my choice of solder. I chose the size pretty arbitrarily (from a range), but I thoroughly researched the different flux types and alloys, and did a lot of searching to find out if there was anything to those expensive "audiophile" solders (there wasn't) or if they were just more nonsense (they were). Apparently silver and gold containing solder were originally intended by legitimate companies like Kester for soldering silver and gold (or silver/gold plated) components, respectively; not for a perfectly negligible decrease in resistance or any kind of audiophile voodoo. I went with the cheaper, slighly better handling Pb/Sn eutectic solder and I'll buy some silver or gold containing solder if I ever need to solder silver or gold contacts. I haven't been able to find any info about cleaning the joints, however. Can anyone recommend any good cleaning solutions?

I also need to order RCA and 1/4" stereo jacks soon. Are there any high quality 1/4" jacks that have a switch built into them? As I said this amp will eventually be balanced, and it will also have an active ground board for driving unbalanced headphones. I want to be able to control volume of the two pairs of headphones with separate stepped attenuators and the balanced headphones with a single, 4-channel stepped attenuator. I want to design a circuit that would drive the balanced headphones in unbalanced configuration when I plug a pair of headphones into one of the 1/4" jacks and disable the XLR outputs entirely when two pairs of unbalanced headphones are plugged in, and that would be simpler if I had switches in the 1/4" jacks that would open or close when I plugged a pair of headphones in. But these are signal path switches, so they need to be high quality.

I'm also very open to any suggestions about casework, and I need info on how to care for my soldering iron's tips.

I've been having problems with solder sticking to my iron's tip when I solder a joint. What about soldering technique? And do you guys clip your leads before or after you solder a joint? I've been doing it before.

 

[poo]

Sorry to dig up am old thread... but it would be great to hear how things have/haven't progressed with your amp...

 

[peanutbutterjam]

Hey I'm considering building this with a friend, can someone kindly PM me the approximate total cost? I think its a very promising project, but I want to know the kind of cost I'm looking at first. Want something to feed the K701...

Thanks!

 

[cobaltmute]

The cost of a beta22 will be determined be how much effort you put into things like the case and things like your volume control.

the going comment seems to be that only about 50% of your cost will be the boards and stuffing them.

 

[krmathis]

Quote:

Originally Posted by peanutbutterjam /img/forum/go_quote.gif Hey I'm considering building this with a friend, can someone kindly PM me the approximate total cost? I think its a very promising project, but I want to know the kind of cost I'm looking at first. Want something to feed the K701... Thanks!

It all depends on several factors.
* The number of β22 boards (2, 3, 4 or 6).
* The number of σ22 boards (1 or 2).
* The attenuator, jacks, speaker bindings, ... you use.
* How far you stretch the chassis design and build quality.

Anywhere from $400-2,500 I would guess.

 

[TimmyMac]

It's tough to build a case with internal heatsinks, because you need to drill a ton of vent holes, and it's hard to get them in straight rows or anything that looks decent.

$5 for 4' of mahogany
$10 for steel plates cut by a welder
$40 for extruded external heatsinks
$35 for hardware and taps
= $90 shipped for 2 chassis for PSU and amp, and you don't have to buy heatsinks or standoffs to mount your boards with.

drill and tap holes in the sinks, screw them down to the bottom plate, add front and back panels of wood and screw a steel plate on top same as you did the bottom. Easy, and now you don't need any special tooling to make the front and back panels look nice.