B1 Buffer Preamp

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#1,482
The B1 is not there to help improve the performance of the amp that follows.

The purpose of the buffer is to help the drive ability of the preceding stage/source cope with the load presented by the interconnect cables and the Zin of the next stage/receiver.

The B1 should be located at the outlet of the source, not at the inlet of the receiver.
 
#1,487
I think that what Andrew is getting at is that the B1 is more buffer than preamp. The pots are the preamp and the circuitry is a buffer, so if your MyRef will perform well with just the pots then there is no need for the buffer and you can still cut out all the interconnects and integrate them into the same chassis. When I got my B1 I was psyched and built it right away. Then the MyRef board arrived and I built that quickly as well. Put a 10k pot on it and 'voila' it worked. Which depressed me cuz I wanted a reason to use my B1. So right now the B1 sits on the shop table waiting for a source that needs help driving a poorly matched amp through some particularly capacitative interconnects and in your case you probably do not need to help the source drive the MyRef. The 10k pot will probably do the trick fine. However, nothing is hurt by trying the B1 with the MyRef. It shouldnt change the sound and this is good but it might be unnecessary to use it in this setup.
Uriah
 
#1,488
Re: Re: Re: Re: Integrated?

marc brown said:


Ummm . . . an integrated amplifier?



One less set of interconnects, one less chassis. My source control, buffer, volume control and amplifier in one box.

:clown:
Click to expand...

The Myref has like a 100K input impedence. It doesn't need a buffer. It has a ton of gain too so I can't imagine you would ever need a preamp.
 
#1,489
merlin2069er said:
I was in the process of hooking up my 2nd b1 buffer, and was expecting the LED to light up when hooking up the power.

It didn't, I checked the power coming into the b1 and it was ~ 35 vdc ( I have a walwart that's rated for 24v dc).

Anyways, I've unplugged the transformer and started checking the circuit. I retested the transformer and get ~2 volts out of it now. 🙁

I'm not sure if it was a bad walwart or faulty hookup.

Any suggestions? What would cause such odd results.
Click to expand...

1) As you said, a bad wallwart to start.

2) A short to ground somewhere on the 18V power rail circuit would likely take out the protection built into the wallwart. Usually there is some sort of fuse in there, sometimes embedded in the transformer windings. Test the resistance of the 18 volt rail to gnd at the where the wallwart input hooks up. It could also maybe be a bad power cap, or a cap in backwards.
 
#1,490
Re: Re: Re: Re: Re: Integrated?

labjr said:


The Myref has like a 100K input impedence. It doesn't need a buffer.
Click to expand...

Yeah, I know the MyRef doesn't need it -- even moreso now that I'm building a DIY.Lightspeed.VCCS. But, after I joined the MyRef group buy I needed to get some sort of line control stage. I've always loved Pass gear and building the B1 is the only way I could afford to get even a small piece of something designed by Nelson Pass. Eventually I may build an amplifier that needs a buffer stage so I can put the B1 in front of it.
 
#1,494
b1-the trail goes on forever

Marc
thats how mine is being used-
sources into a selector (R-2R) into a volume control(same R-2R)
into the B1 then on to a dynaco st70 and its great- quite a bit more detail and immediacy than a very good discreet SS preamp from the 70's-its vvvvvvvvvery good indeed. Looking forward to building the F5 soon.
Question for those of you who are still looking at the schematic of the B1-
I'm thinking that the "rail ground scheme" might be improved with a "star ground scheme";
Looking at the First Watt "Fig 1 B1 Buffer Preamp" schematic I would suggest cutting the "rail just after Q101/Q201 and run a wire directlly to the single ground point beneath C1. Lift R105 and R205 from the ground rail and wire them directly to the same ground point beneath C1.
Any opinions? Andrew, care to yell at me for this idea?(just kidding)
rob
 
#1,495
Re: b1-the trail goes on forever

rob lenk said:
Marc
thats how mine is being used-
sources into a selector (R-2R) into a volume control(same R-2R)
into the B1 then on to a dynaco st70 and its great- quite a bit more detail and immediacy than a very good discreet SS preamp from the 70's-its vvvvvvvvvery good indeed. Looking forward to building the F5 soon.
Question for those of you who are still looking at the schematic of the B1-
I'm thinking that the "rail ground scheme" might be improved with a "star ground scheme";
Looking at the First Watt "Fig 1 B1 Buffer Preamp" schematic I would suggest cutting the "rail just after Q101/Q201 and run a wire directlly to the single ground point beneath C1. Lift R105 and R205 from the ground rail and wire them directly to the same ground point beneath C1.
Any opinions? Andrew, care to yell at me for this idea?(just kidding)
rob
Click to expand...

Yeah, how does it sound without the B1 ?
 
#1,497
Re: b1-the trail goes on forever

rob lenk said:

...

Looking at the First Watt "Fig 1 B1 Buffer Preamp" schematic I would suggest cutting the "rail just after Q101/Q201 and run a wire directlly to the single ground point beneath C1. Lift R105 and R205 from the ground rail and wire them directly to the same ground point beneath C1.
Any opinions?
Click to expand...


I did so ""successfully"" :smash:


>🙂<
 
#1,499
Re: b1-ground revision

rob lenk said:


did you do a before and after listen or measure?
did you revise exactly as I saw it or did you do it differently?
Click to expand...


Hi Rob,

I did it from the beginning based on my principle of ground loop arrangement, before or after doing anything else. I always try to send the input signal and the output signal electrons through clean path, avoiding dirty path possibly polluted.

Cheers,

>🙂<
 
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