I'd like to have some sort of balanced output with my BA2018, and mostly considered using a Hammond BMCF-like transformer to do the work. But since this would be after the preamp stage am I asking for trouble? Considering the stock BA2018 has 3.7 dB gain, am I still safe if I pump that voltage to the transformer?
(Edit: Maybe it would be better by just building a second BA2018 board set, but could I still get a true balanced output without having a balanced input? I'll dig through this thread to find that answer...)
And yes, these things do keep me up at night!
(Edit: Maybe it would be better by just building a second BA2018 board set, but could I still get a true balanced output without having a balanced input? I'll dig through this thread to find that answer...)
And yes, these things do keep me up at night!
Obviously I am thinking of reducing the R19 value. I wonder how this will affect the sound, but I don't know how safe it is and what value of R19 is acceptable
Today was the day for me to button up my WBA2018. I have 2 Meanwell +/-15VDC SMPS units in a Korg B1 chassis for full dual mono after the AC mains in. I added a switch on the front, drilled holes for/secured the PCBs, and added a grommet for the mains cable. Tight fit, but success!
Edit: it sounds fantastic with my ACAMini.
Edit: it sounds fantastic with my ACAMini.
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Thank you.
By the way Since I did not receive an answer to the question from several posts earlier I will ask again.
Is it safe to lower the value of R19 (from 27Ohm to, say, 2 Ohms)? I am using the line stage as a headphone amplifier with headphones with an impedance of 25 Ohms.
You will probably gain little in doing that. If doing it, I would not lower to less than 10R. This ls has very low output impedance in any case. You could consider increasing Iq too or instead, just remember dissipation.
Iq is quiescent current, meaning bias. You can trim this changing two resistors per side. But what is you goal in reducing the output resistor? To reduce output impedance? This linestage has so low output impedance and drive capability that the 27R output resistor is almost irrelevant.
To rephrase my question: is the line stage having problems driving your headphones?
To rephrase my question: is the line stage having problems driving your headphones?
R19 is not in parallel with the load, so it’s not going to make much of a difference at all on the output. I’d keep it there so the circuit always has something to look into as things power up/down, and when sources are changed, or headphone plugged in/out. (Which is it’s reason for being in the schematic.)
I agree with @andynor, I’d not reduce to less than 10ohm, and personally would just leave it be.
I agree with @andynor, I’d not reduce to less than 10ohm, and personally would just leave it be.
No.
only it seems to me that the output impedance at the level of the impedance of the headphones (27 Ohm vs 25 Ohm) is not right. I wonder if lowering R19 will affect the sound.
Not finding anything for hammond BMCF transformer.
You could absolutely add a transformer to the output, it would work beautifully. Something like a quadfilar line transformer, CineMag CMOQ-4 or Jensen jt123flpch. Also a 600:600 Edcor would work very nicely indeed.
I have learned to always listen to 6L6. Plus this one is made by Wayne, nuff said 
If you want sound difference, there are more effective ways of doing that. Volume pots, or bias, and importantly also output transistor choice, may have far greater effect than touching R19. There are Toshiba output BJTs out there that fit the bill perfectly, and I know several here use them. You can even pull all your transistors and match up new ones very tightly. Will it be worth it? I don’t know. Thing is, this linestage is very good as is.
Regarding R19 there is a safety aspect. I have removed the output resistor on my B1R2, but I am told there is a risk. But I never listen to warnings until the magic smoke teaches me a lesson. Why not try 10R and see what happens?
Halfing the voltage swing? I’ll pass on that one leaving it to cleverer people to answer.
If you want sound difference, there are more effective ways of doing that. Volume pots, or bias, and importantly also output transistor choice, may have far greater effect than touching R19. There are Toshiba output BJTs out there that fit the bill perfectly, and I know several here use them. You can even pull all your transistors and match up new ones very tightly. Will it be worth it? I don’t know. Thing is, this linestage is very good as is.
Regarding R19 there is a safety aspect. I have removed the output resistor on my B1R2, but I am told there is a risk. But I never listen to warnings until the magic smoke teaches me a lesson. Why not try 10R and see what happens?
Halfing the voltage swing? I’ll pass on that one leaving it to cleverer people to answer.