Burning Amp BA-3

[bcmbob]

Thanks Evan. Need any aluminum dust ??

[giuliodido]

Originally Posted by giuliodido

Thank you Jim!

Regarding JFETs matching: sorry for my poor English. I'm able to measure Idss (actually I use a regulated 10V psu), but in my stock I can't find matching 2SJ74 and 2SK170.
What I might find (I don't have them at hand right now) are 2SK170 and 2SJ74 with different Idss that are suitable for "EUVL's degeneration trick" ( http://www.diyaudio.rs/index.php?app...ttach_id=13749 ), obviously using Idss (2SJ74) = Id * (1 + Rs*Yfs). I was wondering if this approach could be used here too. In this way I will be able to use every piece of my stock.
I hope it's clearer now

The Singapore temperature thing: if I measure Idss of my JFETs with the same condition in which Spencer measures his (room temperature and 10Vdc), and then I order from him JFET with matching values, maybe I can hope to come up with actually matched pairs. I hope this is clearer too, sorry again for my English (and for my ideas :P)

Ok, I managed to find matching 2SK170 and 2SJ74 below 0.7% at 10Vdc. The first couple is at 11mA, the other one around 9mA. I don't think there will be problems in having different front end channels.

[bcmbob]

This build has been running without a C9 cap (ghosted blue). Instead of just asking where to place it (them), I drew out the circuit so any additional suggestion could be added. The CL-60s run very hot which I believe is normal, but not sure they are in the best location.

So how many C9s and where?

[Zen Mod]

NTC needs to be hot , to drop resistance

greenhorn alert !: pull off mains cord!! , then touch NTC !

that way you'll burn just finger , not brain

[AndrewT]

Fitting bypass relay contacts will get the temperatures down.
And prepare the NTCs for the next occasion they are required.

[bcmbob]

My fingers are just fine - thank you! As for the brain part, remember I lived through the "60s" so I'm working mostly with cinders there.

My thought was the CL-60s should cool somewhat after the resistance falls, but they stay right up there. I won't fret about it.

Andrew - your idea sounds slick, but I believe would require an additional power source - correct?

No mention of the C9 filtering. Does that imply it may be considered optional and required on noisy mains only? I see there are two in the BA-1 PS schematic:


"Capacitors C1 and C2 are line-rated types only, as they will be filtering AC line voltages."

[Andersonix]

Originally Posted by bcmbob

Andrew - your idea sounds slick, but I believe would require an additional power source - correct?

Not if you use an AC relay. Look at the attached soft-start circuits.

[Zen Mod]

same talk - last few posts :

http://www.diyaudio.com/forums/pass-...ml#post3879616

[bcmbob]

Some clever ideas. I'll take a shot at incorporating something similar in the upcoming complementary (& hopefully balanced) build.

Thanks

[mstomaso]

How about a BA-3 3-deep Turbo? With 32V rails and 1A bias per device what would we get for output power? Would the big chassis heat sinks be big enough? Would I need a fire extinguisher? What would it take to get to 50 watts?