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Sun Audio 2A3 Modifications

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#41
andyjevans said:
This has been an interesting thread. Where are you now with the 2a3 amp if you still have it?
Click to expand...
I actually have the SunAudio 300b, but the preamp section is the same as the 2a3, so I considered the above design. With two stages in series there is too much gain and noise and hum. By eliminating the first stage, everything improves. By connecting the two states in parallel, as described by the project above, it improves even more, less hum, more controlled bass ... so I wanted to take the final components to finish the modification.
 
#42
FORNO22 said:
I actually have the SunAudio 300b, but the preamp section is the same as the 2a3, so I considered the above design. With two stages in series there is too much gain and noise and hum. By eliminating the first stage, everything improves. By connecting the two states in parallel, as described by the project above, it improves even more, less hum, more controlled bass ... so I wanted to take the final components to finish the modification.
Click to expand...
You might find StepheK's experience with the Sun Audio design useful. She's posted about it on here and on AK and on her YouTube channel.

https://www.audiokarma.org/forums/i...fier-build-series.962798/page-3#post-14965944
 
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#43
I used to follow the Sun Audio, JE Labs, and Audio Note design with 6SN7 direct coupled to 6SN7 driving the 2A3 and 300B. A year ago, I decided to separate the two 6SN7 stages with coupling capacitor. This allows me to fine tune the distortion for the 1st stage. The 2nd stage will be tuned to cancel out the 300B distortion at the speaker output.
My buddies prefer direct couple from the driver to power stage but it is too complicated for fine tuning minimizing the distortion.
 
#45
Having great success with this schematic, Just changed the frontend to 6sl7's, the sound is very in your face, open and airy.. so easy to listen to.
 

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#46
andyjevans said:
A 6SN7 has a mu of 20. That might be rather borderline unless there's some gain in the preamp if one is used. When I use an EL33 to drive a 300b output, I could do with more amplification into 89db sensitive speakers coming from a DAC with the usual 2v stated output. EL33 is also mu of 20. That's why I'm thinking a driver with a mu of 30 or more.
Click to expand...

andyjevans said:
A 6SN7 has a mu of 20. That might be rather borderline unless there's some gain in the preamp if one is used. When I use an EL33 to drive a 300b output, I could do with more amplification into 89db sensitive speakers coming from a DAC with the usual 2v stated output. EL33 is also mu of 20. That's why I'm thinking a driver with a mu of 30 or more.
Click to expand...
Rough approximation time

2x20x2.83 =113.2 (as you indicate borderline to not enough gain for a 300B that may be biased at least 60V)

113V of pk to pk swing should, on the other hand, be sufficient to drive a 2A3 that is biased in the circa 45V range, ie 90V pk to pk.

But with resister loaded 6SN7, you need may not get mu of 20 either, so possibly to probably not viable for a 2A3. Would not take much effort to find out.

But, yeah, higher than a nominal mu of 20 is probably helpful for a two stage 2A3.

6C45P, 417, 437 resistor loaded, 12AY7 CCS loaded with mu output driving the tube etc etc might all be options.

My 2cents, ymmv etc, etc
 
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