Burning Amp BA-3

[wengtech]

Hi Biju,
For me, if I want a pushpull amp, I will considered to build F5T.
Because to my newbie ear, common drain complementary output much better.
But other people may have a different taste.

 

[Russellc]

Russell: Are you running the BA output stage and the ba3 preamp together? Do you have enough gain without a preamp in front of the ba3 front end?

Iam considering swapping my f5 for a ba complementary os. I love the f5 but it might be time to switch to something with more current for low z loads.

I am using both the BA-3 preamp AND a complete BA-3 Power amp. Plenty of gain!

Russellc

 

[stormfrontier]

What are people using for the N and P MOSFET outputs on the FE boards? I'm having a hard time finding either the right part or the alternate parts on the BOM.

P: 2SJ313 or FQP3P20
N: 2SK2013 or FQP3N30

 

[6L6]

Mouser has thousands of the Fairchilds -

FQP3P20 Fairchild Semiconductor | Mouser

FQP3N30 Fairchild Semiconductor | Mouser

 

[stormfrontier]

That's bizarre. I did a Google search on them earlier and the Mouser result never came up. If I don't have the means to match these myself, who on here sells them?

EDIT: I PM'd Buzzforb. Let's see what he has.

 

[6L6]

There's no need to match them.

 

[stormfrontier]

There's no need to match them.

I'm such a new guy. So what needs matching then? The JFETs and the MOSFETS (IRFP240's) on the output boards?

 

[6L6]

Yes. Get those from Buzz.

 

[AndrewT]

the BA3 has no paralleled active devices.
Therefore

There's no need to match them.

as stated by 6L6 applies.

Only where paralleled active devices are used, does it become necessary to do some selection/matching.
Pass has a webpage describing how they recommend that you do this, if needed.

 

[zz1969]

Hi 6L6,
I 'd like to build 2 x BA-3 Balanced mono blocks. Will you point me to the right direction please ( thread?)? I suppose I don't need complimentary boards.

Zz

 

[stormfrontier]

the BA3 has no paralleled active devices.
Therefore as stated by 6L6 applies.

Only where paralleled active devices are used, does it become necessary to do some selection/matching.
Pass has a webpage describing how they recommend that you do this, if needed.

So this leads me to believe the only matched pieces on my whole SE BA-3 are the IRFP240's? Can I forgo matching the input JFET's as well?

 

[AndrewT]

Is there a single Nchannel jFET and a single Pchannel jFET?
Then no matching.

 

[stormfrontier]

Is there a single Nchannel jFET and a single Pchannel jFET?
Then no matching.

There's two of each, but on separate channels, so I'd assume I'm good to go.

 

[6L6]

Zz -- http://www.diyaudio.com/forums/pass-labs/201281-burning-amp-ba-3b-balanced.html

Cheers!

 

[stormfrontier]

Zz -- http://www.diyaudio.com/forums/pass-labs/201281-burning-amp-ba-3b-balanced.html

Cheers!

That's enough to make my head spin.

 

[stormfrontier]

So, I haven't heard from buzzy yet. Would it be safe if I just went and bought the output mosfets from Mouser w/o matching, and then sourced the matched JFETS online or whatever?

I'm confused on why the JFETs would need to be matched, but not the output MOSFETS. Doesn't the signal run through both of them?

 

[AndrewT]

So, I haven't heard from buzzy yet. Would it be safe if I just went and bought the output mosfets from Mouser w/o matching, and then sourced the matched JFETS online or whatever?

I'm confused on why the JFETs would need to be matched, but not the output MOSFETS. Doesn't the signal run through both of them?

Is there a single Nchannel jFET and a single Pchannel jFET?
Then no matching.

No matching because there are no paralleled semiconductors.

 

[6L6]

If the Jfets are in the same general area of Idss, say within 10-15%, then they have fairly equal self-bias, letting the bias pots (P1, P2) have enough adjustment for the mosfet to get in balance and keep the DC offset (before the output cap) in good trim.

 

[AndrewT]

The two jFETs are in series. The upper NjFET passes the same current as the lower PjFET.

The difference between the actual Id and the Idss determines the Vgs of each device. This can be estimated from the graph in the jFET datasheet.

 

[stormfrontier]

Thanks guys. I have 12 matched IRFP240's coming, and am compiling some last remaining items. Then all I need is the transformer and chassis.

I'm putting some effort into the front panel too. I'll be turning some giant aluminum knobs myself and then I'm going to make a bird's eye maple front panel with blue backlit knobs. Stay tuned.