B1 Buffer Preamp

There are normally four wires to an attenuator.

The Input signal Flow and Return.
The Output signal Flow and Return.

The input pair are twisted to help reject interference.
The output pair are twisted to help reject interference.
Thanks for the good advice Andrew. In fact that is exactly what I have done in previous preamp builds, but this time I elected to follow what Nelson Pass and others have done with their B1 builds. Apart from the problem outlined above there is no background noise at all.
 
Hello to everyone.

I was wondering, if there will be improvement in sound quality by attaching B1 to a F5, if I was directly driving F5 fron DEQX DSP xover. No potentiometer in path, volume control digitally in DSP. I have 3 way active system, DEQX as active xover with some DSP correction, then 3 x F5 amplifiers. Please advise, I luck a little of withdness in sondstage.
 
I'd look at the digital resolution, noise floor and output impedance of your DEQX. The usual arguments regarding analog vs digital volume control will apply.

If the output impedance is low enough to drive the F5 nicely, you can adjust volume within the range you need without eating up the digital resolution of the audio to a noticeable degree, and the noise floor of the DEQX output is low enough that it isn't audible from your listening position, then it's unlikely that the B1 will improve the quality of your playback (unless the B1 distortion spectrum sounds good to your ears).

If on the other hand the DEQX doesn't pass all of these criteria, adding the B1 may well improve your system.
 
Did something dumb

For reasons that are not clear right now, when I built my B1 this summer I committed a double error, intending to shift r102/104/202/204 to 330 ohm resistors, but I mistakenly bought 330k ohm.

I then compounded the mistake by putting them in r101/103/201/203 instead of the 1M resistors that should have been there.

The unit sounds mighty good to be honest, but I am wondering if I screwed up so badly that I need to rip them out and replace them with the proper values.

Any thoughts (besides that I should read a schematic more carefully)?
 
For reasons that are not clear right now, when I built my B1 this summer I committed a double error, intending to shift r102/104/202/204 to 330 ohm resistors, but I mistakenly bought 330k ohm.

I then compounded the mistake by putting them in r101/103/201/203 instead of the 1M resistors that should have been there.

The unit sounds mighty good to be honest, but I am wondering if I screwed up so badly that I need to rip them out and replace them with the proper values.

Any thoughts (besides that I should read a schematic more carefully)?
Changing R101/201 from 1M0 to 330k changes the DC input impedance of in2 to 330k. Not much effect. You can leave this with the 330k. It may reduce very slightly the noise when you remove in2 interconnect.
Changing r103/203 from 1M0 to 330k changes the AC input impedance to 330k. Not much effect. You can leave this with 330k

The combined effect is that the input impedance becomes 165k from the 500k that it would otherwise have been.
 
Changing R101/201 from 1M0 to 330k changes the DC input impedance of in2 to 330k. Not much effect. You can leave this with the 330k. It may reduce very slightly the noise when you remove in2 interconnect.
Changing r103/203 from 1M0 to 330k changes the AC input impedance to 330k. Not much effect. You can leave this with 330k

The combined effect is that the input impedance becomes 165k from the 500k that it would otherwise have been.

Andrew, thank you for your quick response!

Would there be any sonic impact from these changes?
 

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A B1 Story

I was debating, since this past Saturday, whether or not to post on my findings. Might come off as rude, pretentious or crazy by some or simply unnecessary. But, it is rather cool in my opinion.

A friend of mine had a ASL Flora preamp go dead. It now has to go to the factory. My friend can't live without his music. He gets pissed if he goes too long without listening. Knowing this, I volunteered my B1. I said, "...give it a chance". I wasn't using it at the moment.

My B1 contained a Blue Alps pot, generic 1% metal film (MF) resistors, Jentzen Cross Caps, Dayton audio 1% bypass caps and some other generic film caps. The wiring is Radio Shack 4-color rainbow wire used for telecomm purposes, I think. It's solid core.

Not thinking he'd like it much at all, my friend said he really liked it. He was surprised it could "drive" his system, which include, tube mono-blocks and 7 ft tall ASL panel speakers. He said there was a bit of an edge to vocals and needed a bit more body.

He decided he wanted one as a "backup" to his Flora, but wanted more exotic parts. In lieu of buying his own chassis, he wanted to try it first in my chassis with the switching power supply. If the changes were not good, he'd just scrap the idea.

After about 6.5 hours, I had his version ready, which included new boards and jfets from Pass Labs site, Jupiter copper foil caps, "Obbligato Gold Premium+ caps, "naked" Vishay resistors in the signal path only, a ladder attenuator with 1% MF resistors. All costs added up, not terrible more than my B1 build.

I ran a burn-in track over night and listened on Sunday morning. Using basic 8ft AudioQuest ICs and AQ speaker cables, Linux music server, Voigt Pipe 6" speakers and F6 amp. Other than the F6, not an extraordinary setup.
My BOZ-J was always tiny bit better to my ears over my original B1. The results were stunning with the new, more exotic parts. In comparison, my BOZ-J makes me feel like I'm listening with cotton in my ears. The results were stunning. :eek: :beady: If my original B1 was transparent, the new version is even more transparent.

It's a little sad this whole thing. It's the burden of knowing. :sad:
Some will say it's just new solder or an expectation or psychological effect. I don't think so. No way.

I don't think a passive, discrete pot only setup would give the same results. Need that B1 circuit in there doing its thing. The supporting parts count. Unfortunately, these exotic parts are huge.

I never heard the DCB1, but I imaging the results are similar, but of course I really can't say. I would choose no cap over caps in the path, but here's a real argument for using the B1 board as is.

The end result is that my friend really loves the B1, a preamp that he probably never would have considered on his own. I was happy to push him in this direction. ;)
 

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Hi Vince

Could you add some details about your Volume control - what switch, resistors and, if handy, the values too - quite interested

I think your heatsinks are possibly a bit oversized (as per photos in your gallery) and the fets won't get at all past warm

Also, what are the leds near the power fets - are they the +/- power supply voltage indicators (rails)?