B1 Buffer Preamp

[EUVL]

"physical xerox copy"

So Lundahl is a xerox copy of Jensen ?

"of someone else's product ..."

Quote, "It stayed at prototype level."
https://www.diyaudio.com/community/threads/b1-w-jensens.359388/post-6354778

So a prototype is a product ?
Can't find it on the FirstWatt website.


Cheers,
Patrick

 

[Zen Mod]

whatever

 

[Skylar88]

I recently built an M2 from Teabag's boards. Then I tried 3 preamps with the M2: a B1 buffer, AKSA Lender pre and H2 (V2) set for minimal distortion. The verdict is that the H2 sounds better as a preamp in my system. I just thought that members might want to know this.

 

[ranshdow]

Idk why anyone wanting to build a B1 buffer wouldn't just buy the board and JFETs from Pass Labs directly for $51.60 and be done with it.

 

[Halauhula]

Idk why anyone wanting to build a B1 buffer wouldn't just buy the board and JFETs from Pass Labs directly for $51.60 and be done with it.

I happened to have bought a B1 buffer board directly from PassDIY earlier this year. I think the issue for me was whether I could find a buffer board without the input switching and pot as I am going to be using separate input switch and a Glassworks Attenuator. Could not find it, so I am using the PassDIY board and connecting directly to the active circuitry. A simple buffer board would also be handy to drive the Glassworks tilt control. As it is, for a different application I am trying to figure out the best staging of pot, preamp (possibly BOZ - I still have an unused PCB from Audio Amateur), tilt control, and H2 Generator in a manner that ensures I do not drive the H2 to more than a volt.

 

[Skylar88]

I need some advice, please. I want to remove the pots from the B1 V0 circuit since I don't use or need attenuation. Can it be done like shown in the modified schematic below? Do need to install a 25K resistor in the place of the pot? IOW, does the circuit need the 25K resistance?

I'm currently using cheap "Alpha" pots, one for each channel. Will I gain anything by removing the pots?

 

[Zen Mod]

replace pot with simple resistor, anything between 100K and 470K

input cap needs to have path for bleeding down, to avoid nasty surprises while re/connecting signal cables

 

[Skylar88]

Thank you ZM, that makes sense - even for me. 👌

 

[IanA]

Finally finished my B1.

Board and Fets from Auburn, case Modushop, Chi-Fi RCA sockets, other bits from Mouser)

Sounds lovely

 

[Maurizio]

Good Morning everybody.

I'm testing the B1 in a balanced configuration using a signal transformer to covert unbalanced input to balanced.

It works pretty good and i'm quite satisfied .

Do you know guys the output impedance of the B1 ? Am i wrong or is close to 50 ohm?

The Class D amplifier i'm using is having a 10k input impedance.

Many thanks in advance..!!

Maurizio

 

[Zen Mod]

Rout:

for complementary buffer : (xconductance of upper plus its source resistance) in paralel with (xconductance of lower plus its source resistance)

for "same sex" buffer : xconductance of upper plus its source resistance

so, you're in bracket with said 50R

in any case, more than good to drive 10K

 

[Maurizio]

Hi thanks for your reply.

But is it the B1 output impedace close to 50R?

Thanks.

Maurizio

 

[Zen Mod]

didn't I actually replied to your question, covering both B1 iterations?

of course, shorting 1K output resistor (present in first B1 iteration with same sex buffer) is a must

download datasheet of 2SK170 and 2SJ74, read and you'll understand explanation

 

[zintolo]

Ciao Maurizio,

"be in the bracket with" is equivalent to"be in the same range as".
It means Zen Mod replied to your question saying that Zout approximately is 50 Ohm, so low enough to properly drive your 10k input class D amp.

Have fun with that buffer!

 

[Maurizio]

Hi. Thanks to clarify.

Thanks @ Zen mod for the explanation. I'm sorry i did't get the mean be in te bracket with.

I'm vey happy about the results.

Actually i'm using one hammond 108 series xfrm to convert unbal to bal before the pot.

 

[Zen Mod]

 

[A Jedi]

Guys, can someone sanity check me please? I'll be ordering this PS for a vanilla B1. Just want to make sure I'm not doing something stupid.

https://www.digikey.com/en/products/detail/mean-well-usa-inc/GSM90B19-P1M/7703588

 

[ranshdow]

Guys, can someone sanity check me please? I'll be ordering this PS for a vanilla B1. Just want to make sure I'm not doing something stupid.

https://www.digikey.com/en/products/detail/mean-well-usa-inc/GSM90B19-P1M/7703588

Uh, why so big? A B1 "typically draws fewer than 0.02A", the one you linked to is a 4.5A laptop monster. I use the same wall wart that came with my B1 Korg NuTube kit from the store. It's a Triad WS2U240-0500, rated for 24V 0.5A, and it's probably overkill.

 

[A Jedi]

I'm not familiar with the Triads and went with the same line of Meanwell that Nelson adds to recent project BOMs. No other reason.

 

[A Jedi]

Oh and also I wanted stay close to 18v since higher voltage does nothing but put more heat into the components.