Burning Amplifier BA-1

[Rush]

BA-1 Single Ended

I have collected the transformers and associated parts to build this and other amps. Now that I am retired, I have some choices to make.

My intention is to build a single ended 3 pairs per channel IRFP040 (12 total both channels) stereo amp.

I have 4 ohm speakers and need some advise which voltage 1000 VA transformer I should use to maximize output power at 4 ohms.

I am using current inventory, not buying anything new, if I can help it.
Antek 1000VA:
So a 0-18, 0-18, 0-18, 0-18 VAC (23 VDC 1 amp per device)
Or a 0-25, 0-25, 0-25, 0-25 VAC (32 VDC .75 amp per device)

Which transformer would be best to use?

My heatsinks will handle over 150 watts per side.

Rush

 

[Zen Mod]

18Vac

 

[Zen Mod]

I am not in any way gifted in electronics. I have been trying to assemble the BA-1 and do not understand how to interface the front end and output stage.
It seems to revolve around D and S but it is unclear to me

Any advice would be appreciated

see pic

I have collected the transformers.....

more than 3 pairs per channel could be wise 🙂

 

[Rush]

ZM,

Well, I only have 12 matched devices. I don't think you can buy them anymore.

Rush

 

[Zen Mod]

in that case , just crank 'em 🙂

 

[Dennis Hui]

Wow...IRFP040? I seem to recall those were pretty rare even back in the original Zen days.

 

[Rush]

Wow...IRFP040? I seem to recall those were pretty rare even back in the original Zen days.

Dennis,

I think so.
Someone said they sounded better than currently available Mosfets, but that is probably because you can't get them, even back then. If they are unobtainium, then of course they sound better!🙂

Rush

 

[indra1]

On alternative mosfets for Zen amp :

... the best choice for the N channel device in my experience is the IRFP040, which is no longer made.

The 040 is doped a little differently than the 140 or 240 and the lower withstand voltage comes with higher transconductance, which accounts for the better performance...

On IRFP040 vs. IRFP044 :

The real difference is that you can get the 044's. I just scored a thousand of them.

Thus The Wizard hath spoken. 🙂

 

[cobar53]

Thank you for the help. It is clear now

see pic



more than 3 pairs per channel could be wise 🙂

 

[Rush]

Building the amp in an old Threshold 4000 chassis

In the process of laying out the power supply and caps and I wanted to use a smoothing choke instead of resistors in a CLC configuration.
Well, I am running out of room. Can't stack the 2 chokes (too tall) can place them side to side (too wide). Could place the front to back, but crowding the rear plate and I might need to place the BA3 input board there and the choke will be awfully close.
So I started to think. I remembered in the Tube days, you could place the choke in the ground instead of the high voltage side of the power supply.

So tell me if this configuration has merit, see attached.

Rush

 

[Rush]

Ops, I think this looks better, see attached.


Rush

 

[Zen Mod]

in tube days , choke in GND was in "return" route (there was not negative rail) ...... here is not - on amp's side practically everything is happening between two rails ...... gnd being practically bored

I had same brilliant idea several years ago , then someone did told me the same thing ; when I learned to sim a little , I checked and it is that way

in case that you're using "split" choke , one winding in positive and second in negative (appropriately phased) , that will be other thing ......

 

[Rush]

in tube days , choke in GND was in "return" route (there was not negative rail) ...... here is not - on amp's side practically everything is happening between two rails ...... gnd being practically bored

I had same brilliant idea several years ago , then someone did told me the same thing ; when I learned to sim a little , I checked and it is that way

in case that you're using "split" choke , one winding in positive and second in negative (appropriately phased) , that will be other thing ......

OK, then I will do it this way.

Rush

See you at BAF this year

 

[Zen Mod]

🙂

these two chokes are separate ones ?

funny me ...... I never remember proper phasing of "differential" or how it is called anyway - choke , but luckily there is NEM AI-50 thread on forum , with properly drawn choke

find it enclosed , to save you of search ......

 

[Rush]

🙂

these two chokes are separate ones ?
......

Yes, separate ones.

Rush

 

[Rush]

BA1 Power Supply

Here is a picture so far. Test fitting front and back panels and right heatsink.
Made a new back panel, haven't completed all the holes yet. I'll paint it after the work is done.
I'll rotate the transformer to shorten the secondary leads.
I was hoping to make the amp lighter than the original 200 watt Threshold Class A.
The old transformer was 27 pounds, the new one is 17 pounds. The 10 pound difference was eaten up by the 13 pounds of chokes. Probably going to weigh the same 83 pounds. (Which is too much for my bad back.)

Rush

 

[cobar53]

Q201

Hi BA1'ers


I have seem cpmponents use fro Q201 of the BA1 Front End that are one unit construction instead of the J109s


Could anyboday explain to me this part so that I might consider using it?


Cheers


Wayne

 

[Zen Mod]

2SJ109BL is factory packed pair of single JFet , marked 2SJ74BL

so , we can use nicely matched pair of these instead , and they will fit in same pinout for 2SJ109BL , just looking in opposite direction

sticky thread in forum is giving you some info where to obtain them - easiest to visit Forum Store and look for current Linear Systems production - see LSJ74B type

 

[cobar53]

J109 positions

I have tried to use SJ109s and something is wrong. I would appreciate comments on the attached photo. I have the J109s facing in different directions but I may have misinterpreted the schematic.
Assistance would be appreciated
Cheers, Wayne

 

[Zen Mod]

will find that little sketch tonight