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The BA-3 as preamp build guide
The BA-3 as preamp build guide
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Old 10th December 2015, 01:29 PM   #401
Dennis Hui is offline Dennis Hui  Canada
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The BA-3 as preamp build guide
If 20V is not available, I would personally go with 22V.

One thing to keep in mind is that it is recommended to have
input voltage at least 3 volts higher than your desired
regulated output:

http://www.ti.com/lit/ds/symlink/lm317.pdf

(see p.4, section 7.3: differential output voltage.)

Cheers,
Dennis
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Old 10th December 2015, 02:07 PM   #402
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by fwt1712 View Post
I am after some advice regarding the appropriate transformer for a ps-19 power supply (+/-24v). My issue is that 20v transformers are not readily available in Australia. I can get 18v or 22v easily - would one make sense than the other. Line voltage here is 240v so I am thinking that a 230v primary 18v secondary transformer should give me just over 24v, taking into account the extra line voltage (240/230), rectification (*1.4) and regulator losses (-1.5). Thanks Nigel.
That's pretty close to what you will get. But this should read "extra line voltage (240/230), rectification (*1.4) and diode losses (-1.4)".

Buy the 230:18+18Vac transformer. And measure the DC after you have connected it up.
Then add on the amplifier and remeasure. It will be down slightly from the unloaded.

Then bias up your ClassA output stage and the DC will drop a bit further.
This is the final one that your first 24Vdc target was aiming for.

The 24Vdc will allow ~16Vac of maximum output from the pre-amp.

If you want a series regulated supply (not a shunt style), then the transformer Vac should be around the final output Vdc.
i.e. for 24Vdc, use a 24+24Vac transformer.
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Old 15th December 2015, 05:28 AM   #403
watchal is offline watchal  Thailand
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Hi any one compare BA3 to p1.7
What the result
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Old 15th December 2015, 10:09 AM   #404
MASantos is offline MASantos  Portugal
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Is there any published schematic for a follower circuit that one could attach to the ba3fe output to drive headphones? Using the same toshiba mosfets and the psu power rails?

Or one could lift the signal just after the input jfets and send it to said follower circuit?
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Old 15th December 2015, 11:06 AM   #405
AndrewT is offline AndrewT  Scotland
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I thought the BA3 pre-amplifier had a low enough output impedance to drive headphones.
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Old 15th December 2015, 11:15 AM   #406
MASantos is offline MASantos  Portugal
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Quote:
Originally Posted by AndrewT View Post
I thought the BA3 pre-amplifier had a low enough output impedance to drive headphones.
It does, but not o much current capability since it is not a follower (buffer)
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Old 15th December 2015, 11:22 AM   #407
AndrewT is offline AndrewT  Scotland
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One needs a Buffer on the output when there is inadequate current capability from the Source to drive the cables and the load.

If the BA3 pre-amplifier has sufficient current capability to drive the cables and the load, then it does not need an extra Buffer stage.

I am sure I have posted a similar message many times on this Forum.
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Old 15th December 2015, 11:26 AM   #408
MASantos is offline MASantos  Portugal
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Not for preamp duties, but for headphones one does need more current to maintain class A operation.
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Old 15th December 2015, 11:39 AM   #409
AndrewT is offline AndrewT  Scotland
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Ask yourself:
What is the ClassA current capability of my BA3 Pre-amplifier?
What is the ClassAB current capability of my BA3 Pre-amplifier?
What is the maximum transient current demand of my headphone?
Does that use up all of the ClassA capability?
Does that use up any of the ClassAB capability?
Does that exceed the ClassAB capability?

Do any of those answers help me to decide whether my BA3 pre-amplifier can drive my headphones?

We cannot answer, you have to make informed decisions based on the information you used in your build.
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Old 15th December 2015, 01:25 PM   #410
MASantos is offline MASantos  Portugal
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I'll think about that! I'm not that well versed into the art of electronics so the math side of things is not easy!

Another question altogether: I'll be using regulated power supplies to power the BA3FE, +-32v. Are 35v capacitors enough to use in the C1/C2 positions or should I go with 50v ones just for that extra margin?
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