Alpha Nirvana 39w 8ohm Class A Amp

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#643
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#645
I bought a cheap desolder with the heat and suction built in awhile back and that little bugger is the cats rear. I hit those dudes with it and they damn near fell out of the board and the holes where perfectly clean. I spun them around and soldered them back in. It took longer for the desolder tool to warm than it did to complete the op.



Thanks again for pointing me to the correct pinout, I'm going to get Mouser on the horn, so someone else doesn't get hosed by the incorrect data sheet.


JT
 
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#649
Sorry to be such a pain X, but I want to make sure on a couple things here.

Looking at the bottom of the board C171 C133 C134 have no option on top and therefore must be SMB on the bottom. Cool I get that, but then we have C126/O which is C125 from the top of the board. In your built as schematic you used 11pF I think. I get that, we don't want one of both sides of the board, or we would double the value. Cool, so use a 10-11pF on the top and leave the bottom empty. Same with C121 and C122.

Now we move on to C114 C115 which is where I get lost, there is no /O designation, on either top C114 nor bottom C115. It's the same point top to bottom and putting in another 15p would give us 30p. I do not believe that's what you want, nor did I mount one there. Was it just a type-o in the lack of the /O or did I miss something.

Thanks for all your help X.

JT
 

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#650
Hi ThompsonTech,
The layout by JPS64 has a lot of options for folks who like to use SMT NP0/C0G caps vs TH silver mica caps where the smaller critical audio compensation caps are placed. You can tell it is critical when the schematic shows NP0/C0G or Silver Mica. Do not use both, use what you like. Personally, I like NP0/C0G. But, I have been told sonics of silver mica is better. I use whatever I have on hand and I happen to have the silver mica's. If there is a SMT pad on same spot as through hole and designation is same first few digits but either incremented by 1 (C114/115) or an extra zero is added, it is alternate configuration. In some rare cases where you need say 30pF but all you have is 15pF silver mica and 15pF NP0/C0G SMT, then use both TH and SMT pads!

799467d1575397209-alpha-nirvana-39w-8ohm-class-amp-proto-schematic-built-dec-3-2019-jpg


General rule is go with what the schematic shows, and if you see that I only mark red designation once for a place that shows two caps, pick the one.

Hope that helps.
 
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#654
Francois G said:
....
I wondered if for my situation (explained below) a 22v transformer would be acceptable, if not preferable. Hugh’s design called for +/- 27 vdc. Based on X’s build and use of SLB PSU I believe he gets 28.5 vdc in practice.

Question 1: X, for the record, what is your wall power AC voltage? Mine is consistently 125-128 VAC. So, if X’s utility provides around 125Vac, I estimate that I should get about +/- 26 vdc from a 22 vac transformer also using a SLB PSU.

Question 2: Is a supply of +/- 26 vdc acceptable for the AN, or is +/- 28.5 vdc preferable? I do not mind loosing a few watts output power, and will appreciate reducing the heatsink load a bit.

Question 3: Will a 500VA transformer be sufficient for my two channel build? Unfortunately Antek does not offer a 22 VAC transformer in VA rating >500 (AN-5222). Or should I just get the AN-6424 even though I might end up with a supply of +/-29 or so?

Your discussion and input shall be appreciated.
Click to expand...

I got a reply from X on his wall voltage (thanks much), but nothing else.
I shall appreciate more help with my specific questions. I can imagine these questions are relevant to many builders regarding their power supplies. Any comments?
 
#656
Francois G said:
I got a reply from X on his wall voltage (thanks much), but nothing else.
I shall appreciate more help with my specific questions. I can imagine these questions are relevant to many builders regarding their power supplies. Any comments?
Click to expand...

+/-26.5v is fine if you don’t mind losing peak power. Any lower then you need to adjust resistor that sets bias current in LTP to keep at near 2.6mA.

For Antek in Class A, because of voltage sag at high currents, I would always “buy up” to next size. 29v rails are ok as long as your heat sink can take it. Size VA rating at 3x nominal power to ensure minimal voltage sag. Get the 6424.
 
#657
xrk971 said:
+/-26.5v is fine if you don’t mind losing peak power. Any lower then you need to adjust resistor that sets bias current in LTP to keep at near 2.6mA.

For Antek in Class A, because of voltage sag at high currents, I would always “buy up” to next size. 29v rails are ok as long as your heat sink can take it. Size VA rating at 3x nominal power to ensure minimal voltage sag. Get the 6424.
Click to expand...

Thanks! I would rather have a few watts less output than many more watts heat, so I will aim for the design optimal +/- 27 Vdc supply and look into adjusting, if necessary, the LTP bias current. Which resistors would that involve?
 
#659
thompsontechs,

Nice work with the PCBs - looks like you will be finishing the project soon (hopefully)!

What chassis are you going for?

Also, you mentioned that you got a desoldering pump with heat and suction - can you please share the make/model?
 
#660
xrk971 said:
I think R112 but will let Hugh answer that. You might try looking at the schematic for the 4R version as it has lower voltage rails and see where difference is. At 27v I wouldn’t worry. But 24v or lower then need to adjust.
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I thought the “standard AN 39 watt” design specially called for +/-27 Vdc, and your practical +/-28.5 Vdc was a compromise. No?
 
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