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Old 25th June 2009, 12:14 PM   #21
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Quote:
Originally posted by juma
NowI'm under impression that you would like to have some of these PCBs.
If so, PM me.

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Question...separate regulators for each channel??
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Old 25th June 2009, 02:03 PM   #22
juma is offline juma  Germany
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Quote:
Originally posted by sandyhooker
Question...separate regulators for each channel??

No, one set of regulators is used for both channels.

YGM
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Old 30th September 2009, 05:42 PM   #23
juma is offline juma  Germany
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In the meantime I added shunt regs (fellow member Salas published this reg) to the preamp, so final schematic now looks like this:
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Last edited by juma; 30th September 2009 at 05:45 PM.
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Old 30th September 2009, 05:57 PM   #24
juma is offline juma  Germany
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PCB looks like this (picture shows bottom view, dimensions are 16cm x 4cm):
Note: This PCB does not contain prereg (7915) in negative shunt reg as well as pi filter after 7915. I used that prereg just because my transformer had too high voltage (15V AC). 9V AC is OK.
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Last edited by juma; 30th September 2009 at 06:04 PM.
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Old 30th September 2009, 10:38 PM   #25
mlloyd1 is offline mlloyd1  United States
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juma:

nice job - looks impressive!

i am curious to know if you ever thought about using an emitter follower buffered reference to supply the negative voltage for the first bf862 and parallel a couple of nice, large value film caps instead of series electrolytics for the output.

to me, that's a lot of negative regulator for the purpose it's serving ...

again, not complaining, just curious ...

mlloyd1
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Old 1st October 2009, 12:11 AM   #26
jleaman is offline jleaman  Belgium
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I was just shown this thread, is any one selling boards ?
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Old 1st October 2009, 05:44 PM   #27
juma is offline juma  Germany
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Quote:
Originally Posted by mlloyd1 View Post
juma:

nice job - looks impressive!

i am curious to know if you ever thought about using an emitter follower buffered reference to supply the negative voltage for the first bf862 and parallel a couple of nice, large value film caps instead of series electrolytics for the output.

to me, that's a lot of negative regulator for the purpose it's serving ...

again, not complaining, just curious ...

mlloyd1
Thanks mlloyd!
- output coupling can be solved in many different ways (film caps, dc servo...). The solution shown is my preference (anti-serial elkos with negative polarization in the middle, bypassed with stacked foil cap) because it sounds most neutral to me (those elkos are nice rubycon caps)

- negative rail is actually crucial because just the first JFET is preamplifier (the other two are variation of Nelson's B1) and it has almost no PSRR. Anything bad from negative rail will not be just present in output signal but also amplified. Positive shunt I added just for good measure

Now I see that I made a big MISTAKE in the last schematic drawing - R17 (in the Source of Q2) should be 10-15R, not 1k
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Old 23rd October 2009, 08:59 AM   #28
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Compliments Juma this is a great schematic ....... i go to build it to drive an F5 amp.
Well, then this should be the circuit in accordance with the PCB?
Click the image to open in full size.

The potentiometer is put breferibile at the input.... or output?
What Pot value is good to drive an F5?

Regards
Giuseppe.
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Old 23rd October 2009, 09:31 AM   #29
AndrewT is online now AndrewT  Scotland
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the buffer/amplifier is inserted immediately after the volume pot.
The output through the 33r drives the cable feeding the F5

The F5 Rin and the pot value are completely independant of each other.
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Old 23rd October 2009, 09:44 AM   #30
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Quote:
Originally Posted by AndrewT View Post
The F5 Rin and the pot value are completely independant of each other.
Ok ..... if the pot is at the input

Thanks AndrewT.
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