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Old 15th October 2012, 02:35 PM   #3621
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Thank you Tinitus.
I´ll use the B1 with 300B monobloc, JE labs schematic. The speakers have 97 db/wm and have a little hum with my dact pasive preamp. Perhaps the problem be in the ground or wire. Without pream, bridge rca don´t have hum. Independently of noise, I hope the sound will be better with the buffer.

Whats transformer do you use with B1? I´m thinking purchase 2x12 30VA
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Old 5th November 2012, 07:44 PM   #3622
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Default Is this what is happening?

I am in the process of building a B1 Buffer and want to understand what is going on with the JFETs as the CCS is forcing the upper JFET to work at Vgs=0

I got some curves from the generic 2sk170 in LTSPICE and drew what I think is the load line.

Can someone confirm if indeed this is the case?

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Old 6th November 2012, 08:56 AM   #3623
AndrewT is online now AndrewT  Scotland
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Yes, the lower jFET (the CCS sink) has G connected to S and that sets it up to pass ~Idss when the voltage of Vds is ~10V
This current is pulled through the upper jFET (the amplifier).
When the upper device is selected to have the same Idss as the lower, then when Id is = Idss then Vgs must be zero. That is what you have measured.
Because your input is between Gate and Audio Ground and the output is between Source and Audio Ground, then the output offset is the difference between Gate voltage and Source voltage. If you measure between the DC blocking capacitors you will see that near zero Vgs.
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Old 6th November 2012, 12:41 PM   #3624
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Great, thanks.
So even though that the Vin swing for a single ended 2SK170 is approx .5Vpp, the nature of the operating line of the buffer will allow passing an input signal close to 18vpp (not that we are using sources that high). Is this correct?
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Old 6th November 2012, 01:07 PM   #3625
AndrewT is online now AndrewT  Scotland
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The supply sets the limit for the maximum output swing.
If the supply is 18Vdc then expect output swing to be <16Vpp.
If you increase the supply to 24Vdc then expect output swing to be <22Vpp.

This is exactly the same as for power amplifiers and for opamps and everything in between.

If you have a buffer that has a gain of ~1, then the max input swing will be <Rail to Rail voltage less a bit.

BUT !
The second harmonic starts becoming enormous as the output approaches the rails.
That's where the voltage overhead gives a big benefit to music reproduction.
I try to get near 20dB of overhead from max signal to max not clipping voltage, in stages preceding the power amplifier. I would suggest a minimum of overhead of 10dB.
i.e. if you use Sources that can output a 0dBfs signal of 2.3Vac, then the Buffer should be able to handle ~7Vdc unclipped and that requires ~21Vdc for ~19Vpp. The DCB1 uses +-10Vdc allowing +9.2dB above 2.2Vac
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Last edited by AndrewT; 6th November 2012 at 01:17 PM.
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Old 6th November 2012, 02:02 PM   #3626
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Thanks Andrew.

I will be using a dual regulated supply that I found at my local surplus. It is +-15V. That should give me then approx +13db on the 2.2Vac. Initially I was planning to modify the supply voltages to +-9 cause from what I have read on the threads most people prefer the sound of it. I should probably listen to the +-15 before modifying it.
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Old 6th November 2012, 04:39 PM   #3627
AndrewT is online now AndrewT  Scotland
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watch device temperatures at higher voltages.
What is the standard voltage of the PASS B1? 18V?
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Old 6th November 2012, 04:46 PM   #3628
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Yes, 18V.
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Old 2nd February 2013, 09:47 AM   #3629
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Hi guys!

Did someone compare the B1 vs the Burson one? What difference in sound impression?

Thanks have a good day
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Old 3rd February 2013, 04:07 PM   #3630
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Hi,

I bought a chinese copy of the B1 buffer on the bay:

What could you recommand me to improve its quality?

I think I'll supress the 10 uf capacitor because this cap is only there to protect the input of the amplifier... since my amplifier has already a 2.2uf cap on its input there's no problem to avoid the 10uf and as you know less is more...

For pot I've already a 10k RK40 alps black beauty pot; the best of this type I've heard

So there's only the 1uf to change for a better one: which one could you recommand me?

And what about the serie resistors? is there a better brand you can purpose me?

Have a good week!
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