I m too not sure about my pass b1 - diyAudio
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Old 25th January 2013, 11:30 PM   #1
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Default I m too not sure about my pass b1

hi everyone
I have build a pass b1 and I'm not totally convinced. I have however used good quality caps but I have used regular resistors.
The pre amp really take away inner details, resolution, clarity. the bass is less defined, the highs more strident. It is not a night and day difference. lets say, it goes from a 10/10 to a 8.5/10
What can I do. would changing the resistors could really bring back everything, or the design simply hold me back?
What are the most important resistors in the pass b1? if anyone can point me to the most critical resistors, that would be great, I use a noble pot, good interconnects.

My chain is quite ordinary for now: buffalo-- ckIIII-- ath m50

any help would be great!

Last edited by murphythecat8; 26th January 2013 at 12:11 AM.
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Old 25th January 2013, 11:55 PM   #2
biju55 is offline biju55  India
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both jfets are genuine ? did you do mach those before mount it on pcb .
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Old 26th January 2013, 12:10 AM   #3
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yes, the jfets were bought from the distributor in montreal
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Old 26th January 2013, 10:44 AM   #4
AndrewT is offline AndrewT  Scotland
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Measure the Vgs of all 4 jFETs.
They should be very close to zero millivolts dc.
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Old 27th January 2013, 02:47 PM   #5
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ok I will.
Also, can anyone tell me if im not mistaken. I would put the best resistors (probably vishay VAR series) at R104 and R102, or is it only R104 that is the most critical? Or is R105 also super critical, but its not in the signal path right?

since they are 15$ each, please someone confirm with me that both resistors are critical and that im not throwing money down the toilet!

thanks!
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Old 27th January 2013, 03:03 PM   #6
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The resistors won't make a massive difference. If it sounds WRONG then you have other issues.

Once it's working well you can then consider playing with expensive components.

Most guys will find it hard to hear any difference between 1% metal oxide resistors from normal sources to Snake Oil resistors.

I'm not saying that you can't make improvements but I think you have another problem.
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Old 27th January 2013, 03:10 PM   #7
billyk is offline billyk  United States
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My b1 sounds swell. I used prp resistors at $0.40 ea. I did get the FETs with the board from PassDIY YMMV...
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Old 27th January 2013, 03:12 PM   #8
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hey guys, it sounds good for sure, but not 100%. I do hear degradation when the sound oes thru the preamp versus going straight to my headphone amp...

can anyone tell em which are the most important resistors, its worth a try...
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Old 27th January 2013, 04:25 PM   #9
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I take it that you did not measure the Idss of the Jfets before putting them in?

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Old 27th January 2013, 05:20 PM   #10
Telstar is offline Telstar  Italy
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Well, your signal is passing through several more components, it's obvious that a slight degradation will occur. In your case is quite more than that, so probably something is not right in your B1.

But, did you need a buffer in the first place? Maybe redoing the output stage of the Buffalo would have been a better option (along the lines of the D1 perhaps)?
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