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Old 9th May 2009, 06:50 PM   #1621
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Default Two Boards from One Wall Wart

I am building a four channel B1 buffer using two stereo boards. I am using a single wall wart which has 18 volt and 1.1 amp (HP power adapter for a printer).

Each board will be attached to the same wall wart. Each board will be fully populated. Meaning each board will have its own set of power supply caps and resistors (C1, C2, C3, R1, R2, R3 etc). Ultimately all the grounds will be tied together (IOW, the grounds on each board are linked)

As recommended I will be using 15,000 uF caps for C1 & C2. My naive thought is that since the grounds are all tied together, am I actually gaining more capacitance in the power supply filtering? Would the value of R1 need to be changed (currently it is 1 ohm 3 watt).

Is there something I am forgetting by hooking two boards up to a single power adapter?

What is obvious to some is not obvious to me.

Thanks
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Old 13th May 2009, 03:51 PM   #1622
crt is offline crt  Indonesia
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i have finished B-1 buffer Salas version. (picture will follow)

- i have DC output (no load) 3.0mV and 1,2mV. is that fine ?
- is there any way to reduce the DC output ?

Thank's
La Ode
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Old 13th May 2009, 04:13 PM   #1623
Salas is offline Salas  Greece
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Yes, if you have read my presentation back then, you may remember that by adjusting one polarity side of PSUs voltage slightly different to the other when measuring output offset, you can get it down to even zero.
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Old 13th May 2009, 04:18 PM   #1624
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Default Re: Two Boards from One Wall Wart

Quote:
Originally posted by WithTarragon
I am building a four channel B1 buffer using two stereo boards. I am using a single wall wart which has 18 volt and 1.1 amp (HP power adapter for a printer).

Each board will be attached to the same wall wart. Each board will be fully populated. Meaning each board will have its own set of power supply caps and resistors (C1, C2, C3, R1, R2, R3 etc). Ultimately all the grounds will be tied together (IOW, the grounds on each board are linked)

As recommended I will be using 15,000 uF caps for C1 & C2. My naive thought is that since the grounds are all tied together, am I actually gaining more capacitance in the power supply filtering? Would the value of R1 need to be changed (currently it is 1 ohm 3 watt).

Is there something I am forgetting by hooking two boards up to a single power adapter?

What is obvious to some is not obvious to me.

Thanks
Perhaps the lack of input is due to my misarticulation of the question. Let me try another approach. I am using two stereo boards (4 channels).
My first thought was to parallel each board off a single wall wart and each board would be fully populated (both buffer sections and the power supply filtering).

My second thought was that each power supply section currently drives two buffers (left and right channels). So why not use the power supply section on a single board to drive the 2 channels on the first board AND the two additional channels on the second board. IOW, don't populate the power supply section on the second board. Rather, take a wire from the power supply side of R203 (or R103) and connect it to the equivalent Resistors (R103 and R203) on the second board.

I assume there would not be a problem since each channel is drawing fairly little current.

Thoughts or concerns? Am I missing something. I checked the previous threads and I don't think anyone has done something comparable.

Thanks
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Old 13th May 2009, 04:24 PM   #1625
crt is offline crt  Indonesia
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i have try to adjust the positive supply a little higher 0,2V, but the DC output just a little.
it will fine if the difference about 1V (negatif to positif rail) ?
now i use +/- 10V.


and with the DC output (3.0 and 1,2mV) if i put to my amp, will make any trouble ?

Thank's
La Ode
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Old 13th May 2009, 06:03 PM   #1626
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Check if your amp has an input cap. If it has one I would not worry. Those are very good values !

If you have a DC coupled amp ( = without input cap ) the DC could be a minor problem as the amp would amplify the DC component. That is bad for woofers. That is why I told you to include a possibility for an output cap on the PCB.

Most amps have the input cap and most preamps have output caps. So in the real world in much cases you will find that 2 caps are in series when you couple such devices. I have never understood why the industry did not find a standard way of doing things like "always input caps and no output caps" or vice versa. Just one cap really is enough !
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Old 13th May 2009, 06:17 PM   #1627
Salas is offline Salas  Greece
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Quote:
Originally posted by crt
i have try to adjust the positive supply a little higher 0,2V, but the DC output just a little.
it will fine if the difference about 1V (negatif to positif rail) ?
now i use +/- 10V.


and with the DC output (3.0 and 1,2mV) if i put to my amp, will make any trouble ?

Thank's
La Ode
Yes it will be fine to offset the supplies enough. True symmetry is manifesting in DC offset. You just offset the Jfets differences by doing that. Anyway your offset is negligible even with no trimming. Waiting to see your pictures, and know if you can hear differences over the capacitor coupled B1.
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Old 15th May 2009, 10:02 PM   #1628
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Default Re: Re: Two Boards from One Wall Wart

Quote:
Originally posted by WithTarragon


Perhaps the lack of input is due to my misarticulation of the question. Let me try another approach. I am using two stereo boards (4 channels).
My first thought was to parallel each board off a single wall wart and each board would be fully populated (both buffer sections and the power supply filtering).

My second thought was that each power supply section currently drives two buffers (left and right channels). So why not use the power supply section on a single board to drive the 2 channels on the first board AND the two additional channels on the second board. IOW, don't populate the power supply section on the second board. Rather, take a wire from the power supply side of R203 (or R103) and connect it to the equivalent Resistors (R103 and R203) on the second board.

I assume there would not be a problem since each channel is drawing fairly little current.

Thoughts or concerns? Am I missing something. I checked the previous threads and I don't think anyone has done something comparable.

Thanks
BUMP ......

Thoughts and comments.
Am I on the right track or am I completely missing something?
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Old 15th May 2009, 10:20 PM   #1629
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Originally posted by Salas
Yes you can use 25k, only make the wiper to ground resistor 270k-330k. Don't omit that resistor! Strong DC will show up at output when switching the step attenuator if without that shunt resistor.

6VRMS input it can handle if with +/- 10VDC PSUs.

Good luck, I hope you will like it. Report your news.
-------------------------------------
Can I run the B1 without this resistor???
Wiper to ground mean what?
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Old 15th May 2009, 10:23 PM   #1630
Salas is offline Salas  Greece
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In capacitor less B1, no, you must use it for safety. Wiper to ground means from that arrow on a potentiometer symbol, to ground. Pot out to ground in other words.
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