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Old 18th August 2008, 01:29 PM   #461
BFNY is offline BFNY  United States
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I've noticed sometimes DC on the wiper of a pot makes it noisy when you adjust the volume. So if you skip the input cap and you hear scratchy noise on volume adjustments, you'll know what it is. A discrete resistor based attenuator may work better in that scenario.
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Old 18th August 2008, 03:11 PM   #462
udailey is offline udailey  United States
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Instead of using a 15,000uf cap is there any downside to using 12,000uf? I was going to start building today and well, 12kuf is what I have.
Nevermind, took my own advice and reread the article. Down to 1000uf if I want.

Uriah
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Old 18th August 2008, 05:35 PM   #463
avr300 is offline avr300  Denmark
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Quote:
Originally posted by jleaman
Hey nelson, Do you think that the B1 Buffer would be good with the Mini A ? I'm currently running the mini a with a passive pot, but a little more gain would be nice :P
The B1 is unity gain, no amplification or gain if you want.
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Old 19th August 2008, 11:56 AM   #464
Salas is offline Salas  Greece
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Default Ready & cool

Here it is. The dual supply no coupling capacitors version of B1.
The offset is no problem. We can null it down to zero by adjusting one PSU side out of opposite balance. The channels keep almost totally together for offset. I used 2x6.9mA and 2x7.1mA Idss 2SK170BL as matched pairs. Because one channel grew a little (1.5mV) for offset when the other was totally null, I adjusted for +/- 0.3mV matched between channels. Had to make the PSUs +16/-15V for that. Watched it for 2 hours. No offset wandering. Then I fed 10kHz & 100kHz 6V peak to peak square waves through it, one channel after another. Could not see any difference from feeding the generator directly to the scope. I fed 6V p-p sine waves too. No deformation or compression. That is 2.1VRMS and the same as the CD output standard. I made it totally point to point and used a 50k Bourns dual Log that I had. Its paralleled with Dale resistors from wiper to ground. There is also a 7sec delay output relay circuit.
Listening tests I will do probably tomorrow, hopefully with the aid of a friend. There is a sequence of tell tale pictures concluding my construction report.
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Old 19th August 2008, 11:57 AM   #465
Salas is offline Salas  Greece
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Old 19th August 2008, 12:01 PM   #466
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..
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Old 19th August 2008, 12:02 PM   #467
Salas is offline Salas  Greece
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...100kHz
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Old 19th August 2008, 12:03 PM   #468
Salas is offline Salas  Greece
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....100kHz close up.
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Old 19th August 2008, 12:05 PM   #469
Salas is offline Salas  Greece
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.....Steady @ 0.3mV offset for both channels.
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Old 19th August 2008, 12:30 PM   #470
Tolu is offline Tolu  Germany
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Impressive

It would be interesting to compare the no-caps-dual-PS-version against the original NP-B1!
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