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Variac 10th April 2009 03:16 AM

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

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:

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.

cviller 20th April 2009 06:27 AM

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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.

Zen Mod 20th April 2009 10:57 AM

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as always .......

BA1 front :

Zen Mod 20th April 2009 10:58 AM

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BA1 output

Zen Mod 20th April 2009 10:59 AM

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PSz. 20th April 2009 05:58 PM

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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. 20th April 2009 06:07 PM

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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,

Variac 20th April 2009 06:18 PM

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..


PSz. 20th April 2009 06:43 PM


Originally posted by Variac
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,

Nelson Pass 20th April 2009 06:44 PM

Always a pleasure when not all the mistakes are mine.

Prepare for BA#2, which uses the complementary output stages.


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