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B1 Buffer Preamp
B1 Buffer Preamp
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Old 25th December 2010, 01:46 AM   #2851
Kinnja is offline Kinnja  United States
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Originally Posted by Kinnja View Post
In the article Mr. Pass recommends a regulated PS. I haven't had any complaints about the really cheap wall wart I've been using since I built mine a couple years ago.

I recently tried this one with some spare parts and some test leads, it sounds very nice. I got the idea from the ZCA here: DIY Class-A 2SK1058 MOSFET Amplifier Project
Originally Posted by AndrewT View Post
I hope you did not buy a 5A inductor.
The stereo B1 consumes ~20mA
No, they were all my parts box. What I've found so far says that the inductor should be rated for 20% more current than it is expected to draw. Does that sound reasonable?

It would be a lot cheaper than a 5 Amp one.
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Old 26th December 2010, 04:57 PM   #2852
Kinnja is offline Kinnja  United States
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Originally Posted by MechanicalAnimal View Post
Heey guys,

how important is the tolerance of the resistors. That digikey BOM shows metalfilm resistors with 1% tolerance.

Can is use 5% tolerance?

Or should i then switch to carbon resistors with 1% (or lower), with the "risc" of sounding a bit warmer then metalfilm, which might not be a big problem because the B1 will be connected to a neutral 400watt UcD amp.
I don't recall resistor tolerance being mentioned anywhere in the Pass B1 article, so I wouldn't expect 5% to be an issue.

Originally Posted by MechanicalAnimal View Post
.....and offcourse another question

Pass says:

"C3, C100 AND C200 are 1 uF metallized polypropylene film capacitors (Digikey BC2076-ND) C101 and C201 are 10 uF polyester film capacitors (I used Axon 10 uF metallized polypropylene from Orca Design). Feel free to use any comparable types."

Why does the Digikey-BOM show a different C100 and C200 then the above mentioned BC2076-ND?
I haven't seen that BOM, but maybe those part numbers were not in stock, or maybe they thought those other parts would sound better.

Can C3 be switched to the exact same 1 uF used in C100 and C200?

As long as it will fit the pcb, yes.

Can a 100Vdc be used instead of 63Vdc?
Yes. At least in this circuit, since C1 and C2 are rated at 25V, I think that shows us that any cap in the circuit should be rated at least 25V. Going higher doesn't hurt anything.

i have difficulties understanding why that digikey-BOM sometimes show other items of values then B1 manual. Example : all BOM-resistors are 0.5 watt instead of the specified 0.25watt. Quite confusing sometimes for those with less knowledge unfortunately.
Higher wattage resistors are also no problem.
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Old 27th December 2010, 09:11 AM   #2853
MechanicalAnimal is offline MechanicalAnimal  Netherlands
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Thank you very much Kinnja!
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Old 27th December 2010, 03:34 PM   #2854
abes99 is offline abes99  Mauritius
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i just a pair of IMF RSPM MK IV speakers, I`am usint it with HK citation 16 and carver preamp,the sound is very good,two days ago i decided to connect my B1 Buffer in,
the sound is very clean detail transparent,less bass than the carver,but i have to turn the volume full to have a good level and it`s not driving my amplifier to full power at full volume is just to fill the room.
any idea
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Old 27th December 2010, 06:47 PM   #2855
regiregi22 is offline regiregi22  Europe
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Abes, that means that you need voltage gain to drive your speakers. A buffer has no gain, so this would not be fitting your setup.

diyAudio, doing it as big as you can, JUST BECAUSE WE CAN!
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Old 28th December 2010, 04:33 AM   #2856
abes99 is offline abes99  Mauritius
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for the info,i seize this opportunity to wish all of you a happy new year ,happy listening and good diy
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Old 31st December 2010, 10:07 PM   #2857
intrator is offline intrator  United States
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Default differential B1 buffer preamp

I have some single ended signal sources (eg CD player) and some differential (eg phonostage) ones. I would like to drive the rest of the amplifier chain with differential signals (to take advantage of CMRR and its noise rejection) even though I dont start with differential.

Has anyone considered how to convert the single ended B1 buffer inputs into differential? I dont see how to make a phase splitter in the context of the B1 buffer common drain, source follower circuit topology. Therefore I am thinking of using a Jensen transformer, which needs to look into at least 20kOhm + 200pF load per differential leg, and have input driver with less than 600 Ohm source impedance:

Model # JT-11P-1
Impedance Ratio 10k:10k
Turns Ratio 1:1.00
Max 20Hz Input +20dBu
THD 20Hz 0.025%
THD 1kHz <0.001%
20Hz/20kHz -0.04dB/
re:1kHz -0.05dB
-3dB BW 100kHz
cost about $140/pair from Markertek

Another possibility is the Lundahl LL1592
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Old 1st January 2011, 10:09 AM   #2858
AndrewT is offline AndrewT  Scotland
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Originally Posted by intrator View Post
I have some single ended signal sources (eg CD player)
a pair of B1s could work as balanced line drivers.
You need an unbalanced to balanced stage.
Alternatively, look up Jensen app notes and convert all your unbalanced outputs to pseudo balanced. Each conversion uses 3 or 4 cheap passive components. The 4th is an optional film bypass around the electrolytic.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 3rd January 2011, 12:45 AM   #2859
Gordy is offline Gordy  United Kingdom
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Originally Posted by intrator View Post
Therefore I am thinking of using a Jensen transformer...
Another possibility is the Lundahl LL1592
Also consider Sowter transformers; they have a good range and will normally offer to wind you a custom job at small extra charge. (I've used their 9063 wired for 1:2 input, and it works wonderfully well).

You could do transformer input > volume control > B1 > transformer output. The input transformer would provide a break in the ground loop, gentle high frequency filtering, interference rejection and balanced to non-balanced conversion (and you could route your non-balanced input through it as well to maintain ground isolation, etc.).

On the output a transformer could do non-balanced to balanced conversion, however the output resistor of the B1 would best be reduced to something in the region of 100 Ohms.

Happy New Year to all,

: )
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Old 19th January 2011, 01:11 AM   #2860
6L6 is offline 6L6  United States
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B1 Buffer Preamp
My B1 is up and running!

PassDIY board and FETs, Peter Daniel PSU PCB, a neato series stepped attenuator, and a bunch of stuff from my project box and the local surplus store.

Pictures tomorrow.
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