BA-3 Amplifier illustrated build guide

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#42
I may need a +0dB, +6dB, +12dB pre-amp that is reputed to sound good.
It could also double up as a line driver and/or as a headphone driver.

Much is being said about how good the BA3 is.
So I thought "I want some of that".
But I need something other than a guessed at gain from 8.5times to 60times.
 
#43
I think you can trust the people like Botte (or me…🙂 and other guys that had 8-10 x gain.

and changing the load resistor at the output gives the values you need,

but not the 0dB….. 🙂

and you must endure not to have a math for perfect calculation……. 🙂

It is also possible to use the BA-3 with some feedback resistors going F5 like to the sources of the J-Fets, omitting the load resistor at the output.

But I did only Spice some time ago…..
 
#44
NFB in a two stage amp should not end up with excessive phase and thus should not see any instability on the output with fast transients.

But I would check anyway.
Converting to a low gain stage with NFB, to mimic either the F5, or Juma seems a worthwhile set of experiments.
 
#45
if you pull the 332R resistor that is currently loading the output and attach it to the top of the 100R resistor on the Jfet source pins, you have low gain stage. You can still load the output, if you wish to influence the gain of the output stage. I would imagine that playing with these values is where most of you the trial and error will occur.
 
#46
AndrewT said:
....................
NFB would make this all so easy. Gain depends on resistor ratios until the open loop gain becomes too low.
Click to expand...

buzzforb said:
if you pull the 332R resistor that is currently loading the output and attach it to the top of the 100R resistor on the Jfet source pins, you have low gain stage. You can still load the output, if you wish to influence the gain of the output stage. I would imagine that playing with these values is where most of you the trial and error will occur.
Click to expand...
 
#48
buzzforb said:
if you pull the 332R resistor that is currently loading the output and attach it to the top of the 100R resistor on the Jfet source pins, you have low gain stage. You can still load the output, if you wish to influence the gain of the output stage...
Click to expand...

Loading the output in this configuration will reduce open loop gain. And so, also reduce feedbak. 😉
 
#58
So, I'm about to start setting two BBA-3 monoblocks, with 3 pairs per channel and front end and output section of each channel in the same enclosure (I used the "crippled" version for the output section, and omitted the coupling capacitor in the front end).

Let's assume that for each additional section connected I will test it before with the bulb test.

For each monoblock I will connect parts and check them in the following order:

- PSU (mains, +transformer, +rectifiers, +capacitors)

- output section: bias and offset of each of the two halves with DETACHED front end. This will set the temperature inside the case to almost equilibrium. Let cook and check again.

- front end: bias and offset for each of two halves, with output section ON from before and still DETACHED. Let cook and check again.

- Connect front end to output section: check everything, let cook, check again

- Connect the two halves in balanced mode. Check, let cook, check again.


Do you think it is a reasonable procedure?

Thanks,
Giulio
 
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