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Old 13th August 2010, 06:05 PM   #281
juma is offline juma  Germany
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Quote:
Originally Posted by kp93300 View Post
...Can i substitute all these for 47 uF ?

...Can i substitute BC 548c with BC 548B and BC 560 C with Bc 560 B.?
Yes - to both questions.
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Old 18th August 2010, 03:27 PM   #282
kp93300 is offline kp93300  Malaysia
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Default Power supply specifications

Hi Juma,
i assembled the negative rail and has a voltage of -4.75 V dc at the output. Is this acceptable?


I like the power supply very much and made another one for my dac that requires 18V dc. The dc after rectification is only 22V and after the salas shunt i have a 18.8 V . There is only 3.2 V difference .
Can this shunt work well ?Sorry, I do not have a scope to tell.
Thank you in advance .

kp93300
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Old 12th August 2011, 07:14 PM   #283
juma is offline juma  Germany
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I received a request for version of this preamp that uses 2sk170BL (Idss about 9mA). Right now k170 is easy to get and BF862 is a SMD component (not convenient for old hands and eyes ), so here is the schematic.
The gain is a bit higher (9 dB) and the PSU is a bit different (be exact with input DC voltages +28V and -8V).
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Old 12th August 2011, 09:23 PM   #284
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Now we have BF862 preamp without BF862.
This reminded me of my late grandmother. She didn't like coconut, so she has been making coconut flour rolls without coconut flour.
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Old 12th August 2011, 11:35 PM   #285
juma is offline juma  Germany
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Quote:
Originally Posted by dobrivoje View Post
... coconut flour rolls without coconut flour.
So, what did she use instead of coconut flour ?
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Old 13th August 2011, 12:33 PM   #286
juma is offline juma  Germany
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Those who have already built B1 and just need some additional gain, can add just the gain stage (and the PSU) in the existing box. Coupling cap (C3) is not needed if your B1 already has one at the input.
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Last edited by juma; 13th August 2011 at 12:36 PM.
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Old 13th August 2011, 01:33 PM   #287
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Quote:
Originally Posted by juma View Post
So, what did she use instead of coconut flour ?
Wheat flour. The taste was something between sweet bread and bicycle tire.
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Old 13th August 2011, 03:54 PM   #288
juma is offline juma  Germany
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Quote:
Originally Posted by dobrivoje View Post
Wheat flour. ...
Wheat flour is a basic part of the recipe anyway and spicy coconut flour was left out unsubstituted.
It looks like we don't have an analogy with this preamp ...
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Old 13th August 2011, 06:58 PM   #289
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Quote:
Originally Posted by juma View Post
Those who have already built B1 and just need some additional gain, can add just the gain stage (and the PSU) in the existing box. Coupling cap (C3) is not needed if your B1 already has one at the input.
Wow, thanks I think I will try this. Do the sk170 jfets need to be matched?

Are you saying this needs its own power supply, or is it fed off the existing one?

Russellc
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Old 13th August 2011, 07:20 PM   #290
juma is offline juma  Germany
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Quote:
Originally Posted by Russellc View Post
Wow, thanks I think I will try this. Do the sk170 jfets need to be matched?
If you are talking about gain stage from post #286 it's just one JFET per channel, but both channels should be same.

Quote:
Originally Posted by Russellc View Post
Are you saying this needs its own power supply, or is it fed off the existing one?
It needs -3.3V and +24V (both very, very clean, the neg. rail especially).

Gain stage is designed to use 2sk170BL with Idss about 9mA (8-10mA). Voltage of neg. PSU is chosen for amount of gain we aim for and Idss of JFET at hand. That determines the Rs and Rd too. I always aim for Id between 70% and 90% of Idss.

Last edited by juma; 13th August 2011 at 07:23 PM.
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