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Old 4th August 2013, 01:20 AM   #3821
evanc is offline evanc  United States
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Post 53 of this thread juma has a great simple pre that I have been using for some time. I have it at one input of my dcb1 to help my iPad out.
Preamp ideas for F5
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Old 4th August 2013, 02:25 PM   #3822
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A computer sound card is not exactly TOP-END Hi-Fi so if you do need a bit of amplification a reasonable op-amp would do the trick. (The computer's sound card will be using them anyway).
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Old 5th August 2013, 01:05 PM   #3823
WalterW is offline WalterW  Netherlands
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Thanks everybody! I know my soundcard isn't the best. Next project will be to build a reasonable USB-DAC. Maybe I can select a DAC with a higher output voltage, and not needing a preamp anyway.
Now still busy finishing my loudspeakers
Pass F5, F5Tv3, ACA, Aleph J, DDDAC1794, DCB1, BA3-preamp, VFET CSX1, Pass F6
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Old 9th August 2013, 12:15 PM   #3824
Rixsta is offline Rixsta  United Kingdom
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Originally Posted by AndrewT View Post
This seems broken.
Most properly built B1 have zero Output offset. The DC blocking cap and the leakage to signal ground resistor ensure the output offset is zero.

0.01Vdc = 10mVdc is wrong.
0.34Vdc = 340mVdc is broken.
So Im thinking that the B1 I got was from china, possibly dodgy fake transistors causing the problems. SO before i give up on B1 am going to order some 2SK170 from germany, no wonder the sound didn't sound good before!
Will check the resistors before ordering the new Fets.
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Old 10th August 2013, 09:25 AM   #3825
AndrewT is offline AndrewT  Scotland
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The B1 is available from Pass.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 13th August 2013, 09:17 PM   #3826
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Originally Posted by 6L6 View Post
There is another solution - if you don't want to have an active preamp to get the signal to full output, make the amplifier more sensitive so your 1.5V can drive the amp to full output.

It's very simple - make the feedback resistors (R7, R8, R9, R10) 220ohm. This will increase the amps gain at the expense of a little feedback and you can now clip it with a CD player or computer.
Regarding this suggestion on increasing the amp's gain, by doubling the values for the feedback resistors.

I assume the only penalties are an increase in harmonic distortion (which is aleady quite low) and an increase in output impedance. Has any one actually done this and measured it. Or is there a calculation that will give me a ballpark estimate.

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Old 13th August 2013, 11:01 PM   #3827
6L6 is offline 6L6  United States
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I did it with 150ohm and it worked wonderfully. Quite a few others have used 220 ohm and reported back nothing but good.
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Old 21st August 2013, 10:25 PM   #3828
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Default B1 Surpassed

Hi Folks,

This maybe the wrong thread for this post, so apologies in advance, but further to my previous post, 23/06/13, about the B1... After many hours of critical listening, I have the concluded that the B1 just does not sound right with my A40 monoblocks. So I built the JLLH buffer with ripple eater PSU's and the sound is mind blowing. This thing just ROCKS!!
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Old 21st August 2013, 11:00 PM   #3829
6L6 is offline 6L6  United States
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Interesting ! Do you have any links or information on it and the PSU ?
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Old 22nd August 2013, 12:30 AM   #3830
flg is offline flg  United States
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Originally Posted by Earthloop View Post
Hi Folks,,,
... So I built the JLLH buffer...
Is that a small typo there?
"It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.
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