[bismack]

Hi guys,
I found a beta 22 for sale (FS: Three Channel Beta22 - Head-Fi: Covering Headphones, Earphones and Portable Audio), but I am not sure if the unit is well built. Please help me evaluate the amp. Thanks!

 

[luvdunhill]

I'd recommend using the search function and seeing what sort of questions or problems the builder in question posts and see if you feel that he or she has a good idea of what they're doing.

Here's one thread, but looks like there are many more:

http://www.head-fi.org/forums/f6/b22...estion-472390/

 

[jh4db536]

ask to check or see the DC offset of all the boards at operating temperature - should be zero otherwise it might need some work. this may reveal a blotched build. this test should go for Any amp, new, used and commercial, portable, etc.


http://www.amb.org/audio/beta22/setup.html

 

[LeMat]

Quote:

Originally Posted by jh4db536 /img/forum/go_quote.gif ask to check or see the DC offset of all the boards at operating temperature - should be zero otherwise it might need some work. this may reveal a blotched build. this test should go for Any amp, new, used and commercial, portable, etc.

i guess it should be helpful to specify a tolerance in the DC offset. Basically, you can't really achieve a perfect steady 0 offset right ? It's always drifting by a little margin.

 

[pistolsnipe]

wrong thread... my bad

 

[jh4db536]

you're right _+ 5mV as specified in amb site. based on my own experience i would say that +_1mV isnt unreasonable. It CAN be adjusted after all.

i meant as long as it is within the adjustable limit and it does drift a little which is why i mentioned operating temp - my own shows stability after it warms up. i seen mine run from 55celcius +-10 depending on the output bias setting.

 

[askforwhy]

IMHO, It is a decent bulid.

 

[Mr.Duck]

Quote:

Originally Posted by bismack /img/forum/go_quote.gif Hi guys, I found a beta 22 for sale (FS: Three Channel Beta22 - Head-Fi: Covering Headphones, Earphones and Portable Audio), but I am not sure if the unit is well built. Please help me evaluate the amp. Thanks!

Build quality is probably fine and it probably sounds great. But from what I can see I have a few issues with the safety...

1) It looks like the earth wire is only fixed with a spade (it could come off, it should be soldered)

2) If the cases are anodized (I'm not sure but I think they are), then the safety earth is useless unless the anodized finish has been scraped off so the safety earth can make contact with the bare metal. I can't see if this is done or not.

3) No fuse. If there is one built into the mains plug then that is ok. Depending on the country though, I'm not sure which ones can do that.

4) Worst of all, none of the electronics is earthed. If there is a fault with the transformer for example, you could end up with an amplifier that is outputting lethal mains level voltages instead of music.

 

[ford2]

Quote:

Originally Posted by Mr.Duck /img/forum/go_quote.gif Build quality is probably fine and it probably sounds great. But from what I can see I have a few issues with the safety... 1) It looks like the earth wire is only fixed with a spade (it could come off, it should be soldered) 2) If the cases are anodized (I'm not sure but I think they are), then the safety earth is useless unless the anodized finish has been scraped off so the safety earth can make contact with the bare metal. I can't see if this is done or not. 3) No fuse. If there is one built into the mains plug then that is ok. Depending on the country though, I'm not sure which ones can do that. 4) Worst of all, none of the electronics is earthed. If there is a fault with the transformer for example, you could end up with an amplifier that is outputting lethal mains level voltages instead of music.

A very fair assessment,many worry about quality and sound but ignore safety issues.Any electrical gear with no/bad earth is a time bomb.

 

[Pars]

Quote:

Originally Posted by Mr.Duck /img/forum/go_quote.gif Build quality is probably fine and it probably sounds great. But from what I can see I have a few issues with the safety... 1) It looks like the earth wire is only fixed with a spade (it could come off, it should be soldered) 2) If the cases are anodized (I'm not sure but I think they are), then the safety earth is useless unless the anodized finish has been scraped off so the safety earth can make contact with the bare metal. I can't see if this is done or not. 3) No fuse. If there is one built into the mains plug then that is ok. Depending on the country though, I'm not sure which ones can do that.

That looks like a fused IEC, but good to check.
Quote:

Originally Posted by Mr.Duck /img/forum/go_quote.gif 4) Worst of all, none of the electronics is earthed. If there is a fault with the transformer for example, you could end up with an amplifier that is outputting lethal mains level voltages instead of music.

The only place you could run across mains voltage is in the PSU case, and it is earthed. I don't see ground to case connections in the amp chassis, but not sure it matters at all as the umbilical is DC only and I can't think of a way that it could come across live AC. I would guess the crimped spade would be fine for the earth connection provided it is crimped well. The bolt running thru the hole drilled for it should make good enough contact, but not a bad idea to scrape the anodizing off at that point as well.

 

[oneplustwo]

The IEC is fused and I did scrape off the anodizing. I'm not sure what you mean by earthing the electronics though. Can you help me understand that? Last thing I would want is to kill someone!

 

[Pars]

I believe he means tying the board grounds -> chassis. Chassis is then tied to IEC ground i.e., earthed. As long as it is wired up like the diagrams (The β22 Stereo Amplifier), you're fine.

 

[luvdunhill]

one thing that I see very little around here is scraping off the anodizing on all panels so that every panel is electrically connected to one another.

 

[Pars]

I would think the screws would take care of that, but perhaps not. Easy enough to verify with a meter, but I would bet most people don't do that as well.

 

[johnwmclean]

Par Metal cases as far as I've had experience with, form a good ground shield, the screws form the connection, I've confirmed this with a DMM.

As to the build in question, the psu needs the ground connection only. Whether the connection is sound rests entirely with the builder.

The Beta22 should be a last build for a large majority of DIYer's, a statement amp, the quality should be profound, no corners cut. Even those on tight budgets should at least be able to route cable neatly, ensure there's a washer on each nut, solder in a neat fashion where capacitors are not tilted, clean and de-flux all boards etc.

Anything less is unexeptable. IMHO.