B1 Buffer Preamp

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#1,821
Thanks for the info. I guess it is the σ11 V1.b. No audio is better than its psu and you did well to pay special attention there. Enjoy your extra careful and expensive build. One suggestion: Try at a point thin coaxial of any quality you may fancy on just one of your inputs instead of the twisted Mundorf and HGC, and compare.
 
#1,822
Hi All,

I was wondering if there is a complete list of all the parts required to build the B1? I've been going through all the thread pages and its hard to find.

Here is the one of the lists I've found on the net, but not sure if its complete or correct.

2SK370 N channel JFET Transistor 4x (GR or BL grades)
1N914 Diode
Generic LED
15000 uF 2x Electrolytic 25v
10 uF 2x Film
1 uF 3x Film
1 ohm 3w
1k ohm 4x .25w
10k ohm 2x .25w
15k ohm .25w
25k ohm 2x .25w
221k ohm 2x .25w
1M ohm 6x .25w
2 way switch
RCA jack 6x
Linear Taper Pots 25k 2x


Thanks.

The B1 looks like a great unit. The only mod I would like to do is have a bypass switch so I can integrate it into my home theatre.

I almost purchased a Meridian G02 PRE @ $7000AUD, but then I came to my senses.
 
#1,823
Re: Re: Using B1 with an amp requiring balanced inputs

Diomedian said:


To use the B1 in a balanced application, you'd need four "channels" of B1 - two each for the left and right balanced channels. To do this you'd probably want to use matched quads of jfets. If that's not what you've built, you may as well use it in your unbalanced setup.

-j
Click to expand...


Nelson Pass said:
Quad match is nice, but really not essential at all. If you don't have
matched devices, don't let that deter you, just use the lower Idss part
as the current source.

😎
Click to expand...


Might be a stupid question, what if you only need 1 input from the B1, can you use both channels to create a balanced setup? i.e. only have a CD player connected to the PRE.
 
#1,824
the B1 that Pass has designed runs the amplifying FET at very close to Idss.
The lower FET is a CCS to keep the upper FET at or just below Idss.
The two FETs are doing different jobs.
They do not need to be matched. They need to be selected for similar or equal Idss.
As Nelson says use the lower Idss as the lower device (CCS). One does not want the signal modulation to take the amp FET current too far above the Idss current.

In balanced mode again the FETs do not need to be matched. Just choose similar Idss. Use the lower pair of Idss as the CCS and the higher pair as the amps. Keep the ratio of Idss of each buffer pair ~equal.
eg.
9, 9.1, 9.2, 9.3mA Idss for 4 devices.
use 9(CCS) and 9.2(amp) for first buffer, use 9.1(CCS) and 9.3(amp) for second buffer.
 
#1,826
soundengine355 said:
C1 and C2 are 15,000uF 25V capacitors. I was hoping to use some Nichicon Muse KG's, they are 15,000uF 50V, will this be OK?

Are C1 and C2 to do with the power supply?
Click to expand...

Electrically those caps are fine, but if you're using them on the PassDIY board, they won't fit through-hole because they've got solder lugs (rather than leads). And yes, those caps are in the power supply. You don't need to use such large ones - 2200uF or more should do. I'm using 4700uF and a voltage regulator, and I believe even this is some major overkill. I can't argue with the sound though. 🙂

-j
 
#1,828
Yes, it can compare up to anything. After the ''where is the gain false oomph?'' initial reaction it will come across as natural and full of unforced detail and stage. The noise floor lowers without gain. It does not have pushed spectrum parts. Its like it is not there apart from its caps and a bit of grayer tone than best of tube on wind instruments, voice and piano. You will need a 28-32dB gain amp after it for circa 90dB speakers or higher for a CD source in order to compare fare.
 
#1,829
Volume Pot Tricks

With my B1-F5-100db speaks,
using a 25K log pot, I am still not getting a lot of room before it cranks!
I dont need a lot of gain here. My assumption is the linear pot makes things worse here, (will jump up quicker).

I dont know if running a resistor across 1-3 and lowering it to a 5-10k pot will give me some more range on the pot here.

I am not sure of best way to do this without negatively impacting the circuit.😕
 
#1,831
If you are referring to the resistor from wiper to ground, it is a good
trick, but keep in mind that a resistor value that does the job will
dramatically lower the input impedance of the pot when turned up,
so you will want to think about scaling the pot value upward.

😎
 
#1,832
Thanks Nelson. Hadnt considered that. But it makes sense. The wiper to ground resistor and the wiper to ground part of the pot are now parallel, therefore if the resistor were X and the wiper to ground were Y the their total resistance would now be (X+Y)/2 and when volume goes up the top part of the pot goes down in resistance so overall input impedance is really effected.
I guess then you would only do this if you STARTED with a way over resistance pot or if you preferred the curve it creates.
Uriah
 
#1,835
Samuel Jayaraj said:
Tea-Bag, try a resistor between input and wiper (1 & 2), value between 8.2K and 10K. You should be able to overcome the sudden jump in volume that you are experiencing now.
Click to expand...


Thanks guys.

is it possible for supply voltage to affect this?
I am running it at 24v. I can lower it to 18 or 24v

My cdp runs hot, at 2.4v output.
 
#1,836
Salas said:
Yes, it can compare up to anything. After the ''where is the gain false oomph?'' initial reaction it will come across as natural and full of unforced detail and stage. The noise floor lowers without gain. It does not have pushed spectrum parts. Its like it is not there apart from its caps and a bit of grayer tone than best of tube on wind instruments, voice and piano. You will need a 28-32dB gain amp after it for circa 90dB speakers or higher for a CD source in order to compare fare.
Click to expand...


What do you mean by a 28-32db gain amp?
 
#1,837
+28dB of voltage gain = 25.1 times voltage gain.
+32dB = 39.8 times voltage gain.

eg.
dB gain = 20 * log (Vout / Vin)
Voltage gain = inv log (dBgain / 20)

The amplifier requires some voltage gain to send the source signal to the speakers.
Salas is recommending 25 times to 40 times amplifier gain for 90dB/W/m speakers in a domestic listening situation.
 
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