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B1 Buffer Preamp
B1 Buffer Preamp
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Old 25th September 2018, 06:21 AM   #4461
thegoldenear is offline thegoldenear  Australia
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Quote:
Originally Posted by Zen Mod View Post
I believe/hope you used B1 feeding AVC , not the other way?


i use the aVC in place of the volume pot on the B1 board. Am i doing it wrong?
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Old 25th September 2018, 06:31 AM   #4462
Zen Mod is online now Zen Mod  Serbia
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B1 Buffer Preamp
yes

B1 , then AVC

read Iron Pre thread
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Old 25th September 2018, 08:41 AM   #4463
helitim is offline helitim  Canada
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Originally Posted by mpmarino View Post

It's not in common with anything......There is a kook here that says ground is a state of mind. We're not talking about EARTH here!
Understood . Thanks for taking the time!

Are there many instances in amplifiers where the PE, and the audio ground don't share the chassis in common? I've seen lifted audio grounds, etc. But they always end up at the chassis...?

Most of the circuits(systems) I work with are referenced to a common ground( Airframe). At my current employer, I don't get to work inside the boxes though. That's all outsourced to bench shops...
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Old 26th September 2018, 03:16 AM   #4464
Mihan is offline Mihan  New Zealand
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Having built a B1 in 2009 with the original circuit and PCB I have just noticed the revised 2014 R2 schematic. Would someone please explain or point me to a discussion about this revise. Thanks.
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Last edited by Mihan; 26th September 2018 at 03:40 AM.
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Old 26th September 2018, 08:09 AM   #4465
helitim is offline helitim  Canada
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Disclosure: I am probably the least qualified person on this forum to answer your question. In the spirit of SNL, I'm going to "chime-in" anyways! and hope someone corrects me (maybe I can learn something from the experience too ) .

1) I believe that C X01 & R X04 in Ver. 1 were deleted to allow for a DC offset adjustment that didn't put a capacitor in the audio path.

2) RX02 had the described purpose of preventing parasitic oscillation. Seeing that it is removed, I'm guessing it was an "extra" safety net, for a "just in case" situation. It was potentially removed to simplify the signal path from the most likely low voltage source.

3) C X00 I don't fully understand the purpose. My best guess is that they were blocking the audio signal from the "1/2 source" bias voltage from the PSU section to the base of the transistors. *Sorry, Gate. I think that the voltage divider at R X03/X04 probably accomplishes this now.

I'll start with that and see where I stand. Others, please feel free to critique and point out my errors. Hopefully I am in the ballpark, or at least playing the right sport

Last edited by helitim; 26th September 2018 at 08:17 AM. Reason: Typo
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Old 26th September 2018, 11:11 AM   #4466
Mihan is offline Mihan  New Zealand
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Thanks Helitim. What is the procedure for adjusting DC offset with P102?

Last edited by Mihan; 26th September 2018 at 11:21 AM.
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Old 26th September 2018, 11:20 AM   #4467
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B1 Buffer Preamp
simple as DVM black probe to output GND , red probe to output

wait some time to parts reach temperature equilibrium , then slowly (in half steps) fiddle with trimpot , to set as close to 0mV , you can
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Old 26th September 2018, 11:25 AM   #4468
Mihan is offline Mihan  New Zealand
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Great, thanks for the quick reply Zen Mod
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Old 27th September 2018, 06:25 AM   #4469
Hikari1 is offline Hikari1  United States
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Quote:
Originally Posted by Mihan View Post
Having built a B1 in 2009 with the original circuit and PCB I have just noticed the revised 2014 R2 schematic. Would someone please explain or point me to a discussion about this revise. Thanks.
Original b1 is single ended, b1 rev2 is push pull using a complimentary and much harder to get pair of jfets. Also it has dual polarity psu which lets you get rid of the coupling caps in rev1.

I have built both although rev2 had a much bigger and better psu and better pot. They sound totally different. Rev1 sounded like what I expected. Very tame and nice. Rev2 is totally ruthless and revealing in both good and bad ways.

I donít use buffers...it was just an test so neither stayed in my system. But with the F5 amp I felt like the rev2 version was just too revealing and hard although it was amazing at what it did and initially I had a big smile on my face.

I loaned both to a friend with big emotiva amps and he felt the same way.

With a different amp/speaker combo your results might be different.
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Old 27th September 2018, 08:00 AM   #4470
helitim is offline helitim  Canada
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I don't know a whole lot about JFETs, aside from the fact that I've seen them talked about in the Burning Amp Videos.

Are the PNP (P-Channel?) hard to get for most JFETS, or specifically the 2SJ74?
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