Burning Amp BA-3

[Backbones]

Originally Posted by buzzforb

NS,
.

buzzforb,

Can you use the FQA19N20C / etc matched mosfet set in the BA-2 power boards as shown in Nelson's circuit diagram or do you neeed to change the components?

[buzzforb]

I think that was what the original BA2 output stage used. Either way, You can use any fets in the output, you just might have to make some adjustments to bias circuit. With either Fairchild or IRF, you are OK. I have use laterals and needed to make some changes.

[Backbones]

Thanks. I'm thinking of building another amp. The BA-2 I am very happy with but as I had another chassis I thought why not a BA-3 as well that I can play around with. Just wondering whether Nelson isn't planning something.

Could I get away with a 300VA transformer for two channels (one output board each) set at about 400mV bias? Presently I am using a 300VA transformer for each channel but maybe I could reduce the weight.

[buzzforb]

Should be OK, assumingit is not getting pushed hard very often. I think you might be surprised how much you like BA3. Make sure you fiddle wth P3.

[nkdk]

@buzzforb
Hi, what is the best way to fiddle with p3, hook up at functions gen. and scope, ore are there other ways to do it ??

nkdk

[Backbones]

Originally Posted by nkdk

@buzzforb
Hi, what is the best way to fiddle with p3, hook up at functions gen. and scope, ore are there other ways to do it ??

nkdk

You may have problems finding the point of minimum distortion without the right equipment but it's what you can hear and whether it sounds good to you that really matters. So set it up so you can adjust P3 and then have a listen and then try another position for P3. Worked for me.
I found you didn't have to keep adjusting P1 and P2 or worry about dc offset each time you moved P3. Obviously once you have a sound you like then balance-off the rest of the circuit.

[Alettagla]

Dear everyone,

Which versions of the 2sj74 and 2sk170 should I use.
Should I use the GR BL or V version? There is considerable difference in price.

BTW do they need matching?

Your advise is very much appreciated

[tinitus]

Originally Posted by noSmoking

found this wish I found it earlier,lol

he, thats mine
sure hope its correct

[Backbones]

Originally Posted by Alettagla

Dear everyone,

Which versions of the 2sj74 and 2sk170 should I use.
Should I use the GR BL or V version? There is considerable difference in price.

BTW do they need matching?

Your advise is very much appreciated

Idss currents of the GR are less than the BL, which in my experience are difficult to find, which might explain the cost. Nelson used the BL I believe with an Idss of about 10mA. Mine come in at 8mA. If you use the GR you will have to have P1 and P2 as 1K not 500R. I don't know about the V.
They don't need matching but I did anyway.

[Backbones]

The first time I built the BA-2 power boards I used ER74, 3W 1R wirewound resistors and everything sounded good but going over the BOM now I see these resistors are specified as metal oxide. Any reason other than possible inductance issues with the wirewound?

Also in the BOM there is only note of four of these resistors rather than six.