B1 Buffer Preamp

[wdecho]

If I am not mistaken all he has left is G grade.

 

[AndrewT]

great for LTP pairs that are biased from 1mA upto 4mA.

 

[Dennis Hui]

Another trustworthy seller is Spencer:

Contact FET Audio | Hi-End Audio Projects

 

[riksu]

If I am not mistaken all he has left is G grade.

4x Toshiba Original 2SK170BL (2 Matched pairs) | eBay

 

[wdecho]

4x Toshiba Original 2SK170BL (2 Matched pairs) | eBay

I actually have bought some of the K170's from him but he is not selling the J74 BL anymore to make a set. I since have found a source for original K170's in the USA.

 

[riksu]

I actually have bought some of the K170's from him but he is not selling the J74 BL anymore to make a set. I since have found a source for original K170's in the USA.

What? More than 10 available / 176 sold

 

[AndrewT]

I miss-read his information as well. I thought he meant that only GR grade of 2sk170 were available.
But his update clarifies where he states

he is not selling the J74 BL anymore to make a set

Why he said G grade? I have no idea.

 

[Spe@kerBox]

I am inexperienced with electronics, busy with my B1 Build. I have two regulated PSU units, one supplying 15V and the other 24V. The buffer works well with both. I know 15V is below the recommended 18V spec and the 24V is at the high end of the spec. My caps are rated to 35V.

Which PSU will be best to use, 15V or 24V?
I am not sure how, if at all, voltage affects the sound?

Mine is running at 24V for the last year or so. Sounds great and no issues.

 

[wdecho]

Short for GR, sorry. One could always parallel a set but that would increase price. I suggest buying LSK from store as a matched pair. Work great where I have used them.

 

[twocents]

B1 running on 24V, but with BF862's?

Mine is running at 24V for the last year or so. Sounds great and no issues.

Thanks - good to know that the B1 can run on 24V. Anyone know if you can run the B1 or ACA amp on 24V with BF862's? The BF862's are rated 20V only.

 

[kpsthakur]

Last I understood from Andrew we need to reduce voltage less than 18V while using BF862's....somewhere in the region of 16V


Sent from my iPhone using Tapatalk Pro

 

[ElFishi]

Thanks - good to know that the B1 can run on 24V. Anyone know if you can run the B1 or ACA amp on 24V with BF862's? The BF862's are rated 20V only.

I have a B1-turbo buffer - similar to this - with BF862 running on 24V.

Top and bottom jfet ideally equally share the supply voltage so each sees 12V.

 

[Curlycat]

Mine is running at 24V for the last year or so. Sounds great and no issues.

Thanks Cwmartin. I could not hear any difference between 15V or 24V on mine either. I have been running at 15V for months and 24V for about one week. I am still going to regulate to 18V - that will make the OCD part of me happy

 

[AndrewT]

Last I understood from Andrew we need to reduce voltage less than 18V while using BF862's....somewhere in the region of 16V..............

Agreed.

The bf862 is variously specified at 225mW to 300mW.
It's Idss range is 10mA to 25mA.

If you run a bf862 at half supply rail voltage of 24Vdc
then you will find that a 10mA Idss device is dissipating 120mW (53% of Pmax) when no signal is present and Ta<=25°C
if you have a 25mA device then Pq = 300mW (133% of Pmax)

I consider 53% of Pmax right up at the top limit for the quiescent state.
Even a PSU @ 20Vdc is too much in my opinion.
16Vdc seems much more sensible. 14 or 15Vdc would also work for signals upto 2Vac.
A 15mA Idss running at half of 16Vdc dissipates 120mW. This leaves a small margin for signal and mains variation.

 

[ElFishi]

or use a source resistor

 

[AndrewT]

or use a source resistor

Then it's not a B1.
Look up D.Feucht to see how to do it properly.

 

[twocents]

24V

Ok, thanks for all the inputs - that settles it for me - there is therefore no real benefit from running the B1 on 24V then.

 

[xrk971]

B1 in stereo on 4cm x 6cm P2P veroboard. Sounds fantastic and is dead quiet.

10uF cap provided by MLCC on bottom side and bypassed with 1uF 230v film cap (same one used on inputs). This and 2.2mF power rail caps helps keeps the size small.

 

[AndrewT]

What voltage/signal is applied to the 10uF MLCC ceramic?

 

[xrk971]

As it is at output of FETs in single ended operation from single rail, I suppose at most 7.5v since I am running 15v supply? But nominally I would imagine a few volts in normal operation.