Burning Amp BA-3

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#221
Backbones said:
Can we say that once the 1V across R10 and R11 have been achieved via P1 and P2 then we can adjust and listen to the variations using P3 without going back to adjust P1 and P2 each time?
Chris
Click to expand...

Difficult, already 60mV offset change, changes the distortion spectrum clearly

Indeed using a cap in front of the small j-FETs, isolating the pot dc wise from them, makes the offset more stable, when turning on the volume.

And forget the wish to cancel k2 completely, you can do it only for one position.
Or let us say you can minimize it for a region....of volume.

And I had at the moment no possibility to hear at the same time over the speakers music when changing P3.

I ended up with a constellation, low volume more k2 than k3 and at higher levels more k3 than k2.

I treated my output stage, (F4 like, with one pair and bias network with an higher impedance) by paralleling source resistors from 3-7 Ohm and finding the right side I could reduce k2 considerably.

Nelson did it with his F5, in the pictures of 6moons you can see a paralleled 2 ohm resistor.

All very interesting.....😀
 
#223
generg said:
I treated my output stage, (F4 like, with one pair and bias network with an higher impedance) by paralleling source resistors from 3-7 Ohm and finding the right side I could reduce k2 considerably.

Nelson did it with his F5, in the pictures of 6moons you can see a paralleled 2 ohm resistor.

All very interesting.....😀
Click to expand...

That’s easy to do with one pair and it’s a little more challenging with 12 pr.

See http://www.diyaudio.com/forums/pass-labs/166784-pictures-your-diy-pass-amplifier-88.html#post2733726 😉
 
#230
I have now finished the first complete round of the distortion pleasure....😀😀😀

- I treated the BA-3 and the F4 (without J-fets and one pair only) seperately......

- on both gears in one channel it was easier to cancel the k2 than in the other.....

- I can only speculate the reasons...... bigger mismatch of Semis.....?

At any case the reduction was clearly possible!

I heard Cassandra Wilson afterwards, not an easy task for amps and speakers, heavy bass and crazy rythms.........

I found outlines and the picture being better....

and I think driving Lowthers with these NFB gears is a good idea, they were never before so tame.........

happy generg 🙂
 
#233
I'm planing to mount following chain of elements: BA-3 preamp + passive crossovers + and four chanels of F4 for bi-ampling, like on attached Fig from F4 manual. Is it better to have F4 regular chanels with Jefs in front or without them like BA-2 push pull output stages.
 

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#234
I am afraid you need the j-FETs to drive the F4s!

As far as I remember the three pairs have 5kOhm input and a couple of hundreds of pF.....I suppose your crossover cannot drive this.......or can it?
 
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#237
Just for another confirmation. On the BOM list of BA-3 front end I found:
Q1 N-Channel JFET Input 2SK170
Q2 P-Channel JFET Input 2SJ74
Q3 N-Channel MOSFET Output 2SK2013
Q4 N-Channel MOSFET Output 2SJ313
so I'm little bit confused. First 2SJ313 is P chanel type. Second are the Q3 and Q4 in correct position ? In other words according to schematic
Q3 should be 2SJ313 and Q4 = SK2013 ? Am I right ? There is always possibility to make an error when chosing between the two.
 
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