Roll Call: Who's building, built, or thinking of building a beta22?

[RedLeader]

I'm extremely curious about how to do this build, but to do it cheaply. If you could do this with 2 boards, a regulated wallwart and some cheap pre-fab cases, or a simple wooden build, I wonder what it would end up costing. I noticed the kits for a single board are around $100, has anyone managed to do it cheaper by buying pieces from mouser or elsewhere? About how much was the cost per board?

Seems like you could likely make a hell of an amp for under $300

 

[m1abrams]

I would not skimp on the psu on a build like this. If need to go that cheap better to build a different design.

 

[Anonanimal]

RedLeader, I'm fairly certain that someone did a low-cost build and posted it in this very thread. Search around a bit and you'll probably find it.

 

[RedLeader]

Quote:

Originally Posted by m1abrams /img/forum/go_quote.gif I would not skimp on the psu on a build like this. If need to go that cheap better to build a different design.

Don't need to, just curious how well it would work, compared to other DIY amps at the same parts cost.

 

[tintin47]

I think that cfcubed did a budget beta 22 for around $350. I could not tell the difference between it and a 3ch b22 o22 during a meet, whatever that says.

That said, I don't really understand the idea of skimping on this amp. If you need a great cheap amp, build a CK2III. If you want no holds barred amping insanity, go with a beta. If you want NHBAI, you don't skimp on parts, IMO

 

[RedLeader]

Quote:

Originally Posted by tintin47 /img/forum/go_quote.gif That said, I don't really understand the idea of skimping on this amp. If you need a great cheap amp, build a CK2III. If you want no holds barred amping insanity, go with a beta. If you want NHBAI, you don't skimp on parts, IMO

Fair enough, but one of the things I love about DIY is that you're free to scale projects up and down as you see fit. You can trick out a CMOY or scale back a beta22, IMO it depends not on your budget (though of course that's a consideration) but more on what you can do with a design. I'm of the mind to start simple and scale up from there. I know most people would decide on exactly what they want, build it and be done with it. I'd likely start off with a skeleton build and add on to it if I felt I liked the way it worked/sounded. And if I don't, I sell the amp as a cheap design and move on to something else. I suppose it's the curse of the endless tinkerer.

 

[oneplustwo]

I did my first beta as a three channel in a cookie tin (see my sig). Sounded great. To answer your question, I think the glassjar audio kits are going to be about the same as building your own kit via Mouser. Unless you plan on building a bunch of them, the kits are the way to go. Especially since you don't need to source from amb AND mouser AND digikey AND whoever else.

The other thing to consider is that you need to be concerned about trafo hum with this amp. Not to say you couldn't do it cheaply, but it is something to consider when thinking about your enclosure. Shielded trafos are another option if you want a single enclosure.

I'm in the process of building a 2 channel in a wooden enclosure with a shielded trafo. This is probably about as cheap and simple as I would go personally. It will cost me about $400 in parts (2 betas, 1 sigma, shielded trafo, ancillaries) and nothing in the enclosure since I'll basically be using scrap wood from other projects. I expect the result to be a great "bang for the buck" contender.

 

[linuxworks]

Quote:

Originally Posted by RedLeader /img/forum/go_quote.gif I'm extremely curious about how to do this build, but to do it cheaply.

omit an expensive case and re-work a throw away case. I never 'finished' this case but got it up to the point where it held things reliably and safely, it kept wiring away from sensitive parts and when the top was off (which was always, lol) it gave all the cooling I needed. not everyone's style but it was dead silent, with the PSU being a 'floor box' of some other nondescript kind (just a trafo running 30/30 ac down its longish wire to this box)

the trafo box is super simple:

that thing sits on the floor and is remotely switched on/off so, in fact, it can go behind some shelf or book case or something and disappear. disappear sonically, too, as any physical hum from the windings (there is some) also goes away when you 'floor box it'

style wise, its ugly; the 2 box thing. its extra parts and extra hassle but it also does have some advantages. remoting the trafo does solve a lot of problems very cost effectively. and you can re-use some metal chassis for the b22, keep it to 2ch and save a lot. b22 in 2ch mode is still a very 'worthy' amp and building it on the cheap is not a bad idea at all.

 

[cfcubed]

Quote:

Originally Posted by tintin47 /img/forum/go_quote.gif I think that cfcubed did a budget beta 22 for around $350. I could not tell the difference between it and a 3ch b22 o22 during a meet, whatever that says.

Others that tried it felt the same... I think it says that it'd take critical listening in a quiet environment w/good equipment to try to detect a difference vs full/real 3-ch builds. Of course it could be that y'all were being nice saying such things

My 2c about it:

1. I'd not do one-case build w/o nice shielded transfo & lots of room to sep it+o22 from amp proper, so "real/full" build would likely = 2-case build for me. And that costs. Using wallwarts yielded most of the advantages of a 2-case build.
2. that said, I'd use a bit bigger case next time to get some sep between PS & amp boards. Also consider the lower-noise fixed regs talked about in another thread here (like MC7924CTG / MC7824CTG?). Perhaps build off simplistic tracking +/- design from datasheets (e.g w/TIP42A, etc).
3. BUT think considering nice M³ build instead of all this business could be great way to go if nice <= $350 USD SS amp is desired.

Quote:

Originally Posted by tintin47 /img/forum/go_quote.gif That said, I don't really understand the idea of skimping on this amp.

It's to save $$$ of course

Best bang-for-the-buck & all that. (Edit: Perhaps linuxworks said this better)
In my mind, if you go o22 then you should go good toroidal transfo & 2-case build & that adds cost & complication.
We all pick our points on the cost/perceived-benefit curve.

Edit: Note also that I had two spare 24VAC WWs around that I'd gotten cheaply & they wanted something to do.
Also, the simple +/- 24VDC PS in my budget build generates little heat. Stock ventillation in HB-350 case top, w/some bottom/back holes, is quite enough.

 

[RedLeader]

Quote:

Originally Posted by cfcubed /img/forum/go_quote.gif [*]BUT think considering nice M³ build instead of all this business could be great way to go if nice <= $350 USD SS amp is desired.

Very valid point, and one I am considering as well, as that design looks like an interesting one. I'm not sure its quite as flexible and "tinker-friendly" but you could do some fun stuff with it.

Part of this is prompted by my desire to get another set of K340 as I have some more ideas about what to do to them this time. And as I have found out, they are probably the most difficult cans to drive properly that I have ever come across. The only amp that I've heard that did justice to them was a $3000 custom monstrosity by McAllister audio, and for several very good reasons that's not an avenue I can attack. Given the stupid level of difficulty in driving those cans, I don't want to too heavily invest in time/money going one way when I won't be completely happy with it.

 

[luvdunhill]

Quote:

Originally Posted by RedLeader /img/forum/go_quote.gif I'm not sure its quite as flexible and "tinker-friendly" but you could do some fun stuff with it

A M3 is much more "tinker-friendly" than a beta22. Note how many warnings amb issues on "don't change these parts, don't change these values, don't allow long wires to this, or keep leads as short a possible on that" on a beta22 compared to the M3 design.

 

[tintin47]

So how hot is too hot for the inside of the cases in terms of temp? I don't have a thermo couple right now but I'd like to know a ballpark temp that is too high for when I do.

My amp gets quite toasty, but it has plenty of ventilation directly over the heat sinks as well as on the sides, and it looks like more ventilation in terms of surface area than most other betas.

 

[luvdunhill]

Quote:

Originally Posted by tintin47 /img/forum/go_quote.gif So how hot is too hot for the inside of the cases in terms of temp? I don't have a thermo couple right now but I'd like to know a ballpark temp that is too high for when I do

One generally accepted value is that the heat sinks shouldn't exceed 60C. A good way to check this is to put your hand on the heat sinks, and if you have to pull it away in three seconds, you're right about on target. In other words, shut the lid, wait 1 hour, open the lid and stick your hand on the heat sink and start counting.

 

[johnwmclean]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif One generally accepted value is that the heat sinks shouldn't exceed 60C. A good way to check this is to put your hand on the heat sinks, and if you have to pull it away in three seconds, you're right about on target. In other words, shut the lid, wait 1 hour, open the lid and stick your hand on the heat sink and start counting.

Pain threshold accountability?

 

[cfcubed]

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