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BA-3 As Preamp
BA-3 As Preamp
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Old 22nd November 2016, 11:06 PM   #1161
Hikari1 is offline Hikari1  United States
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I think an adjustment of P3 will have far more effect than the choice of mosfet in this preamp. Have you tried it?

I am not sure the mosfet choice will be as pronounced as on a power amp. current and bias levels are low, the mosfets are not doing much.

I have tried Fairchilds, IRF and Toshiba in the F5 power amp. My favorite are the Toshiba mosfets.
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Old 22nd November 2016, 11:49 PM   #1162
6L6 is offline 6L6  United States
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BA-3 As Preamp
I can't tell any sonic difference between Toshiba and Fairchild mosfets. Hikari1 is right- an adjustment of P3 will make much more difference.

Or this might be a great time to try different output coupling caps to "flavor to taste."
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Old 23rd November 2016, 12:08 AM   #1163
Hikari1 is offline Hikari1  United States
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Also, I would not consider the BA-3 as "bright" by any means. I feel if anything it might be a little rolled off on top.
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Old 23rd November 2016, 12:09 AM   #1164
madskaman is offline madskaman  United States
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Originally Posted by 6L6 View Post
I can't tell any sonic difference between Toshiba and Fairchild mosfets. Hikari1 is right- an adjustment of P3 will make much more difference.

Or this might be a great time to try different output coupling caps to "flavor to taste."
I'll try P3. Thank you for the input.

I've tried quite a few different output capacitors. More than I'd like to admit. I'm running it now without the output caps and the offset has been very stable.
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Old 23rd November 2016, 05:25 AM   #1165
Hikari1 is offline Hikari1  United States
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P3 effects DC offset. Just a warning since you have no output cap. And adjusting P3 has a pretty dramatic effect. I think adjusting for dominant 2nd harmonic will satisfy you.

Are you sure the offset is stable? That has not been my experience at all. I see 100mv fluctuations with temp.

Kind of off topic but I've communicated with someone who has changed the feedback arrangement on the BA-3 to one like the Vfet 2 front end. It's very interesting and it makes the offset stable (no need for a cap). All one needs is a few resistors to try it. I haven't tried it but it's worth a shot.
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Old 23rd November 2016, 09:30 AM   #1166
AndrewT is offline AndrewT  Scotland
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I am currently using the Fairchild Mosfets. I feel the sound it too bright. I tried them in my Aleph 3 and found it to make my system even more bright. That's why I'm considering using the 610/9610 in the BA-3 as well as going back to the 9610 in the Aleph 3.
I wonder if this "brightness" is down to a reduced phase margin of this "amplifier"?
Have you checked how well it copes with fast signals?
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Old 23rd November 2016, 02:28 PM   #1167
nashbap is offline nashbap  United States
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Kind of off topic but I've communicated with someone who has changed the feedback arrangement on the BA-3 to one like the Vfet 2 front end. It's very interesting and it makes the offset stable (no need for a cap). All one needs is a few resistors to try it. I haven't tried it but it's worth a shot.[/QUOTE]

You can find more on this in the BA3 balanced thread. Generg has experimented with it and has also posted some simulations. I wonder how it changes the sound?
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Old 23rd November 2016, 02:30 PM   #1168
nashbap is offline nashbap  United States
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I am currently using the Fairchild Mosfets. I feel the sound it too bright. I tried them in my Aleph 3 and found it to make my system even more bright. That's why I'm considering using the 610/9610 in the BA-3 as well as going back to the 9610 in the Aleph 3.
What is your source and how are you attenuating the signal?
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Old 23rd November 2016, 02:50 PM   #1169
6L6 is offline 6L6  United States
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Nasbap - so they are adding feedback. That's a great idea, totally worth trying.

I'd still keep the cap if using this as a preamp, however.
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Old 23rd November 2016, 03:59 PM   #1170
madskaman is offline madskaman  United States
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I'll recheck the DC offset again tonight, but it has been pretty stable. I was previously using the B1 buffer with this setup and I found it to not be on the bright side at all. I just needed more gain. I am using the preamp for 2 turntables, CD player and Burson DAC. I am using a Blue ALPS 20k pot shunted with a 47k resistor. I've also use a 50k before and had the same results. I'm sorry for the scattered responses to the questions.

One thing I did change from the norm is R13. I decreased it's value to 150 and 170 because there was too much gain there is a channel imbalance.
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