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Roll Call: Who's building, built, or thinking of building a beta22? - Page 63

post #931 of 2937
6/7/09 at 3:32am
Yeah well, I'd much rather have a working amp than an everlasting DIY project. I've been trying to get a working Beta for months.
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post #932 of 2937
6/7/09 at 3:18pm
Quick question. What is the voltage before the RLED's on both the Beta22 boards and the backplane board (wasn't clear in the voltage schematic)? I'll be using 30V configured Sigma22.
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post #933 of 2937
6/7/09 at 7:19pm
I am strongly considering building a 4 channel for use with both Headphones and Speakers. Interestingly, I haven't seen an implementation here with a sigma for each beta, which I seem AMB recommends on the site.

Considering two 350mm*151.5mm Conrads for this, and basically doing the same as the "Death Cube" as seen in this thread, and just FPExpressing the front and back. I figure I can get the 4 Sigmas and that gigantic 640VA Trafo that I saw in the other B22 thread in this case with a modder's mesh top panel and and *very* slow moving 120mm fan or two on the bottom to speed up heat dissipation.

The Beta boards would be in another, 350*100mm case to the right, with the option to have a Buffalo32 cased similarly on top.

FYI - Took me 3 days to read all of this thread. No stone unturned, I tell you.
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post #934 of 2937
6/8/09 at 7:59am
Quote:
Originally Posted by dbfreak View Post
Quick question. What is the voltage before the RLED's on both the Beta22 boards and the backplane board (wasn't clear in the voltage schematic)? I'll be using 30V configured Sigma22.
The LED resistors are run directly off the +/-30V rails.
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post #935 of 2937
6/8/09 at 8:02am
Quote:
Originally Posted by rshuck View Post
I am strongly considering building a 4 channel for use with both Headphones and Speakers. Interestingly, I haven't seen an implementation here with a sigma for each beta, which I seem AMB recommends on the site.
There is at least one (built by oj) shown in the β22 website gallery, but that one is for headphones only -- massive overkill!

Quote:
FYI - Took me 3 days to read all of this thread. No stone unturned, I tell you.
There is A LOT more at headwize, but unfortunately it's still down.
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post #936 of 2937
6/8/09 at 10:54am
I have noticed that the venerable internet has a distinct lack of easily accessible discussion about mounting multiple sources to one heatsink. The available models for heat dissipation seem quite heavy. The following format from amb's website seems to provide a good approximation with a small modification.

For single source per heatsink:

Tj = Ta + (Pd * (Rjc + Rcs + Rsa))

For multiple sources per heatsink:

Tj = Ta + (Pd * (Rjc + Rcs) + Pt * Rsa))

Where,
  • Tj = junction termperature
  • Ta = ambient temperature
  • Pd = power to be dissipated by device
  • Pt = total power to be dissipated by all mounted devices
  • Rjc = thermal resistance of junction to device case
  • Rcs = thermal resistance of device case to heatsink
  • Rsa = thermal resistance of heatsink to ambient

It looks like this is an easy way to dimension the heatsink. Just pick the hottest running MOSFET and have look that it runs in the safe zone with these figures, the rest of the MOSFETs should automatically be fine.

What is the consensus, will this work?
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post #937 of 2937
6/8/09 at 1:08pm
can anyone tell is there any difference between toroidal transformer and encapsulated one?
Will the sound be clear, and the noise becomes smaller?

I am struggling whether choose which one on my beta22,btw the sigma 22 and transformer are in separate case.
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post #938 of 2937
6/8/09 at 1:37pm
I don't think it would matter, and even less if your PS is in a seperate case.
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post #939 of 2937
6/8/09 at 1:45pm
If they're in separate cases, you probably don't need the encapsulated (shielded) one. It could matter quite a bit if you have your transformer in the same case. With my first beta, I tried to put it all together and even though I kept the toroid on the opposite end of the input and output wires, I still got humming until I moved it into it's own "enclosure." (This was for my cookie tin beta.)
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post #940 of 2937
6/9/09 at 1:46am
I need some fuse recommendations, since I'm not sure what the σ２２ needs (seems like 1.6A slow blow is enough?; the transformer is 80VA). I plan on getting this IEC and switch from Mouser:

- 103-R13-112A-02-EV (Mountain Switch)
- 693-6200.4315 (Schurter)

...*wonders what everyone is using for their IEC and switch*

Edit: 2A fuse it is!
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post #941 of 2937
6/9/09 at 2:26am
That switch would work, as will the IEC.

Personally, I REALLY like the anti-vandal switches, like the MP0045/1E2BL012.
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post #942 of 2937
6/10/09 at 11:51am
Still making my way through this entire thread but I have a question...

AMB or anyone else who may know for sure...

I did read what rshuck also read that if going fully balanced and you plan on using speakers you should use 1 S22 per B22. Does that still stand with high efficiency speakers? I'm thinking about building a balanced B22 to use on some 95db(24Wrms 32Wpeak) full range speakers. I was thinking 2 S22s for the 4 B22s would be sufficient seeing some cans like the K1000 are pretty inefficient and do fine on a 2S/4B setup.
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post #943 of 2937
6/10/09 at 11:54am
Quote:
Originally Posted by digger945 View Post
I don't think it would matter, and even less if your PS is in a seperate case.
spend the extra for a FULLY shielded trafo.

it does matter.

big-time.

in this amp more than any other I've ever seen.

believe it.
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post #944 of 2937
6/10/09 at 11:57am
I also thought I'd need 2 trafos and 2 s22's for my spkr driver.

I was wrong. it doesn't hurt to try and see how it works for you.

my sprkrs are tannoy pbm8 (pretty efficient, ported design) and I get enough bass and volume to fully fill a bedroom size room (12x12 or so).

what I'm going to do is to mount some heat sensors (lm34 or something) near the heatsinks in the b22 and see how the temp varies between phones and spkrs. at that point, I'll have DATA rather than "I think...".

but so far, nothing has blown up (lol) and I am continuing to use my 2ch b22 for spkr use, for music and movies.

honestly, I was not sure the b22 was cost effective for me. now that it does double duty, its a much better value
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post #945 of 2937
6/10/09 at 12:00pm
Quote:
Originally Posted by linuxworks View Post
spend the extra for a FULLY shielded trafo.

it does matter.

big-time.

in this amp more than any other I've ever seen.

believe it.
X2. In a single case solution I would say its almost a must.
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