Burning Amplifier BA-1

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This is the place to discuss the latest Pass amplifier, the BA-1, which is documented in the article here:

http://www.diyaudio.com/forums/diyaudio-com-articles/154777-burning-amplifier-ba-1-a.html

As most of you are aware, Nelson "Papa" Pass distributed a bunch of almost complete amps at the second Burning Amp Festival, lacking only the gain stage. You can read all about it here:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=131663

The Burning Amps are modular in that you choose a Gain Stage and an Output stage to create the amp of your dreams.

The input "Gain Stage" section which increases the voltage can be used for any of the Burning Amps. The first gain stage is no longer in production, but the Second, confusingly called the BA-3 is available in the diyAudio Store.

So you can combine the gain stage with either one of two "Output Stages" which are also available in the Store

One output stage is single ended and the combination with a gain stage is the BA-1 Amp. The output stage consists of 2 small PCB's and two longer ones.

One output stage is complementary and the combination with a gain stage is the BA-2 Amp. The output stage also consists of 2 small PCB's and two longer ones. but they are all diff.erent than the ones for the BA-1 output stage.

Single-ended amps are quite inefficient, and only operate in pure Class A. The are the Audiophile Purist choice and probably have a small sound quality advantage, depending on your preference.

Complementary amps are more efficient, and transition smoothly from pure Class A operation to Class AB when more power is required

Nelson will be publishing a series of articles right here on diyAudio documenting designs for the various chassis that were distributed. They have different output stages so there will be at least an article for each of these configurations. That's good for us as we will have a multitude of great new designs! We will produce boards so that even people without the head start of the generous "gift of amps" will be able to make them. Nelson mentioned that these designs are to be a fundraiser for diyAudio, so the boards should only be available from here.
 
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Great article! Thanks Nelson! :D


Variac asked me to make a layout for the frontend and here it is. It is version 0.9, which suggests I'll pick up suggestions from you guys before diyAudio puts it into production. Any profit will go towards the forum upgrade.

The board is 3" x 3.5", and one of the primary design constraints is that it must be able to fit into the cabinets given out at the Burning Amp festival.
I have made one change in respect to the original schematics, which is the addition of footprints for 2sj74 as an alternative to the 2sj109.
 

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I haven't read the whole thing yet, but I would like to add my :2c: to the layout. Actually just the mounting of the front end board. I see a few good options.

First would be a relatively large board mounted on the psu caps. My chassis happens to have four of the big cans, but doing it this way would allow those with two cap chassis to conveniently add capacitance as suggested.

best regards,
psz.
 

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Second would be a large board mounted on the caps with psu parts hard mounted to it and swappable front end modules.

Another good option I see is to set the mounting holes on the front end boards to 1.5" by 4" so they can be mounted on standoffs and use the existing holes/hardware that hold the heatsink parts on.

best regards,
psz.
 

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diyAudio Editor
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Nelson warned us not to have the board close to the first pair of caps in the pi filter, so we won't be covering the top of the 4 caps. A pair the size we have is designed fit vertically beind the front panel... but any ideas will be of great interest... I personally have been tempted by separate front end modules because the front end will be the same for all the amps, its only the biasing components (which are onthese boards) that will vary... . But 2 different boards would be more expensive..



Mark
 
Variac said:
Nelson warned us not to have the board close to the first pair of caps in the pi filter, so we won't be covering the top of the 4 caps.


That's easy to solve. Just use the more remote caps as the first stage in the pi filter. That is how NP did it on the amp in my first attachment.

best regards,
psz.
 
cviller said:
I'll pick up suggestions from you guys before diyAudio puts it into production.

Hi Christian,

nice layout, a few first suggestions after quick look:
- Q203 should be heatsinked, so a bit space around it would be great. I would suggest putting it a little bit down, away from Q202 and the resistors right to it a bit to the right.
- C204 could also use some more space, e.g Wima FKP2 or Vishay KP1830 both have 4.5 mm width.
- C203 is very long but slim. Did you have any special capacitor in mind? Only 2 or 3 mm wider and a MKP10 would fit (20 mm)

Thanks to Nelson for sharing! :)

Greetings,
Chris
 
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I may be guilty of contributing this idea: The thought was that the cap could hang over the edge and be secured by a wire-tie around the outside of the board and through the hole in the board next to the cap.. This would pull the cap to the outside so maybe the MKP would fit? ....Comments?

I think that these would fit..

26x37mm Jantzen Z-Standard cap $7.16

http://www.parts-express.com/pe/pshowdetl.cfm?PartNumber=027-282&DID=7

Ultra premium caps are usually pretty fat, This one is
long and skinny, so fits well.. (and expensive) $44.15
36x107 Jantzen Z-superior
http://www.parts-express.com/pe/pshowdetl.cfm?PartNumber=027-497&DID=7
 
diyAudio Editor
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25 watts per channel seems low if the amps are dissipating 300 watts per stereo channel

Nelsons article says

The power transformer should be rated at 600 VA or more. Two channels of this amp will typically draw in excess of 300 watts, and we allow at least a 2 to 1 transformer margin.

So I think this means that each channel draws 150 watts for 300 total for 2 channels, then you apply the 2 to 1 transformer margin and get 600VA rating for the transformer. The transformer is for both channels

Mark
 
Variac said:
I may be guilty of contributing this idea: The thought was that the cap could hang over the edge and be secured by a wire-tie around the outside of the board and through the hole in the board next to the cap.. This would pull the cap to the outside so maybe the MKP would fit? ....Comments?

The idea is ok as long as the boards with capacitor still fit into the cabinets (cviller: "The board is 3" x 3.5", and one of the primary design constraints is that it must be able to fit into the cabinets"). I would expect that if the board with overlapping capacitors fit, it would also be possible to enlarge the board.

As the board is layouted now only axial caps would fit, if the board area is fixed maybe Christian can move the pads a few mm more to the edge so that radial caps would also fit (also hanging over the edge).

Chris