B1 Buffer Preamp

I looked and saw that on the XP30 Wayne loaded the output of the volume
control with 1 Megohm.

Is it that the current from the wiper pin of the digital volume controller needs to be kept at very minimum for low distortion? Is that the reason , it is being recommended to follow it up with a very high input impedance stage?

So if we would like to use this chip to replace regular potentiometers in filter or tone control circuits like (baxandall tone control ckt), do we need to use a combination of this chip and a buffer to replace a potentiometer?
ie. replace regular potentiometer with "this chip + buffer" ?

Or do we need to directly replace potentiometer with this chip and change the resisters in the tone control circuits so as to keep the wiper current less?
 
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Original B1 with autoformer

Just watching Nelson's talk at BAF2017 with special attention to the B1-XFMR
and just have to ask:

Can a autoformer be added to the original B1? I have a pair of Jensens wired as in the attached figure. If so where would be it best be placed?

B1 original is here
http://www.firstwatt.com/pdf/art_b1_man.pdf

Thanks

Bob

Of course I would love to see B1-Korg or B1-XFMR in DIY store:D
 

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Official Court Jester
Joined 2003
Paid Member
speaking of (complementary JFet pair) B1 ?

cascoding done , strictly as saving them of excessive voltage (rails)

trimpot (say 10-20R) already done , as way of nulling DC offset at output ....... and it can work partially as THD shaper , if you connect output through cap (so no DC to worry about) and proceed fiddling with pot chasing THD change

but , that change isn't so big , considering that in B1 output is taken at sources , not at drains , as in F5 , BA3 etc.
 
I do not see a need for cascoding in an amplifier/Buffer that is handling signals that never exceed 3Vpk (2Vac). The B1 operates from supply rails at least twice the voltage of the peak signal - 3Vpk = 6Vpp in a supply at 18Vdc, i.e. it uses only 33% of the available rail voltage.

For ultra low distortion in a gain amplifier, there is a small advantage in using a distortion reducing cascode.
 
I hope this a good place to ask this question.

It has been discussed before but not much was said and I would like to hear what others who know more I think.

I am using a pair of the complimentary buffers instead of the BUF03 in the TRUTH line stage/volume control. I think these sound much better than the BUFs and I thank ZM for pushing towards trying this. They were installed about a month ago and I know I will not return.

Now to get to the question - in this device there was no input load for the BUF03s. My guess is that this would not be the ideal situation for lowest noise. But I can see the possibility this could be good for the second buffer following the photocell.

I read that one should only remove input cables with the power off. Can't remember if this the case with the output cables. It is not as if I am changing components often so this would be a small inconvenience to me.

Would someone be so kind as to explain what this resistor does? Is it simply there to set the input impedance or in this very simple circuit does it have a bigger role. Most importantly is there anything to be gained if one wants to present the highest possible input impedance to the preceding "device"?

All counsel is appreciated.
 
Official Court Jester
Joined 2003
Paid Member
gates of JFets need to be referenced to somewhere , in most cases to GND ;

resistor shunting gates to GND is doing exactly that - referencing them (gates) to gnd , so gadget is functioning as it should ....... having properly established input modulating .......

and , it is .........conveniently , defining input impedance too , simply because JFets are having pretty biggish input impedance per se