BA-3 Amplifier illustrated build guide

[SoaDMTGguy]

Ozorfis, did you buy the matched kits from diyA, or individual transistors from elsewhere?

 

[andynor]

He bought individual, much cheaper DIY!

 

[SoaDMTGguy]

Ahh fantastic. The diyA store states that they are selling the "Harris" FETs instead of the "International Rectifier" version. Then on Mouser all I see are the Vishay Semiconductor IRFP****PBF. Is there any meaningful quality difference here? I assume not.

 

[ozorfis]

Yes I bought 100 devices each. From the German shop Reichelt they are quite cheap (but comparable from Mouser or Digikey in large quantities)

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I used a 24 Volts lab supply and a 33 Ohms resistor screwed to the heatsink in the foto and the schematic according to Papas article. Slight variances in Vgs and hence current were adjusted by adjusting the supply voltage to give constant voltage drop across the 33 Ohms resistor. Also I used a fan and measured all in one go to have the same conditions. Attached you can find the results I got.

 

[ozorfis]

The Harris are better - you can read at the end of the BA2 article (attached) why.

Didn´t know the shop was selling the Harris now. If you are not going to build a balanced system, you might then be better off with the parts from the shop.

 

[ozorfis]

Just realised the excel file was an invalid file. So attached are the IRFP240 results for orientation.

 

[Zen Mod]

if shop is selling Harris, that's from Papastash

 

[andynor]

If your first build, and since store is selling Harrises, get ‘em. Papa matched them personally. Plus, if you only need 6 per side, buying in the hundreds will cost you.

That’s bot to say Papa does not make mistakes with matching, but can you do any better?

Those are matched close enough for 0R47 source resistors.

If you plan on macing bias, consider higher source resistance or jig them.

Or trust Papa the man

 

[SoaDMTGguy]

Cool, I'll get the Harris' Papa breathed on

I suppose it would make sense then to get a few different values of source resisters, so that I can go to a lower resistance depending on the quality of the match? Not like resistors are expensive...

 

[SoaDMTGguy]

if shop is selling Harris, that's from Papastash

Papa's stash stash?

 

[andynor]

I would just use standard Pass 5% Panasonics @ 0R47, as specced. If you run into matching issues, post here and you will be helped. Also, depending a bit on speakers you use, 1R is perfectly fine. RusselC uses that on his sensitive speakers, and is very happy with that. 6L6 did too on the amp in the guide. 1R is the ubersafe choice, 0R47 is the specified for 3 deep config (6 transistors per side).

Regards,
Andy

 

[SoaDMTGguy]

I didn't know Panasonic was the standard Pass resistor. That's a good reference point! Any other Pass-standard parts?

 

[Zen Mod]

care to ask some question demanding less than full page of text, to be replied properly?

 

[SoaDMTGguy]

I just mean preferred brands, lines, tolerances. General sort of stuff, not product-specific.

 

[andynor]

Maybe that came out a bit wrong. The blue-grey Panasonics are widely used in Papas designs, is probably a more correct statement

This one, I think: Blocked

Cheap and cheerful, like Dennis Hui always says

I am not the one to ask about «standard» Papa parts. I think he uses what fits the purpose and is good enough. He is more about active components, and there the J74/K170 JFETs are PL standard, as you prolly know allready

Edit:

MZM! Not nescessarily requring a full page, for a GH like me, a few key takeaways that never go out of fashion:

IRFP240
2SJ74
2SK170
Nichicon Audio Grade caps
Elna Silmic 2 caps
Claritycaps «For Pass».
Plitron transformers

No more, will be a page then…

 

[SoaDMTGguy]

Ok cool, thanks! As a newbi, I'm looking for any guidance when picking between half a dozen identical parts for every spec slot.

 

[Zen Mod]

Ok cool, thanks! As a newbi, I'm looking for any guidance when picking between half a dozen identical parts for every spec slot.

FIRST WATT

 

[andynor]

Read, read and read, and if you don’t before asking about something, bpt read read and read some mo’

 

[SoaDMTGguy]

Oh, I have been! He doesn't often talk parts, though. I'm still working my way through. Are there any in particular that are Must Reads so I can move them to the top of the stack?

 

[andynor]

This:

https://www.firstwatt.com/pdf/prod_f5_man.pdf

https://www.diyaudio.com/forums/att...08d1618428012-beyond-fringe-beyond-fringe-pdf

Also the «distortion and feedback», F5 Turbo, BA-1/2/3 and «leaving class A» are good reads.

List is not extensive, prolly many more are important…

Also, on the Passlabs website, the article about parts selection, he talks about «squeezing the lemon» of the IRFP9240s midrange irregularity/distortion in a non-feedback circuit, and there you have it: the F4 and BA-2 OS. No lemon on the Harrises though, so be prepared to get your sugar from elsewhere using those. P3 is the solution if a little H2 is your kinda thing