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Old 2nd June 2009, 08:46 PM   #1
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Default Building a symmetrical psu B1 buffer

Although I did mail the mods to separate the info on a symmetrical B1 from the standard B1 thread this wasn't done. Info on the symmetrical B1 confused some people so I opened a new thread. Making the B1 with symmetrical ( +/-) supplies makes it possible to go capless or DC-coupled with the B1. Since 99% of standard equipment has out- or input caps this will be beneficial as long as you know what you are doing. So it is not exactly without risks. You've been warned. These are some points as quoted by Salas:


1. By trimming the supplies a bit non symmetric, the output offset falls to either zero or under half mV, steady. It counteracts naturally non perfectly alike JFET pairs.

2. If the applications situation can be non safe (general tests use with possibility of unknown non DC offset checked sources?), an input capacitor only can be used. It will be small value and can be even Teflon and rather affordable. That will obviously guard against most of the danger scenarios and will still be cheaper and more transparent than having an additional big output quality cap. The DC coupled output will not deviate to non safe, unless one psu ceases when in service, or the input resistor to ground is not used and a pot becomes dodgy. Always use that resistor, does good to the pot's transparency too. Hence, a non issue.

3. Each one to his own risks. Situation is well reviewed.

4. Benefits are: Much cheaper, audibly more neutral, more compact.

5. Risks are: If you are not careful and there is no input capacitor in your power amplifier, or DC output sensor and relay, you can burn woofers, if you connect a source device with much DC offset, or one symmetric B1 supply fails during service. Be warned.



I hope something nice will be created with the schematic Salas designed. Crt ( La Ode ) did a design on the PCB which is not 100 % finished but it is useable.
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Old 2nd June 2009, 09:00 PM   #2
Salas is offline Salas  Greece
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I was to split it, but I was waiting for the full works from La Ode. He sent me the last stuff just today evening.

The idea started very early in the B1 thread by a ZenMod suggestion. Link.
Then I took it a bit further.
Link.
And I actually made it in P2P.
Link.
This year, interest came back and La Ode made it on a nice PCB.
He is planning a full monoblock version with delay relays and four supplies.

*Actually because the symmetric stuff is scattered in a very long thread in a year long span, maybe the initiative of a new thread is better since a late split would make the original thread incoherent around those posts.
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Old 2nd June 2009, 09:18 PM   #3
Salas is offline Salas  Greece
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The first he has made was without delay relays, its the simplest to make. Has common supplies between channels. Actually 220R gate stoppers and output resistive buffers worked just fine.

Click the image to open in full size.

Click the image to open in full size.
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Old 2nd June 2009, 09:25 PM   #4
Salas is offline Salas  Greece
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There are Eagle files too, but I would ask LaOde to give us the dimensions in mm so for those who will use print and transfer to know the scale. I prefer not to post the Eagle files so not to give ready made food to commercial rippers, since this is good work for DIY use ONLY.

Click the image to open in full size.
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Old 4th June 2009, 06:18 PM   #5
crt is offline crt  Indonesia
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forgot:

the dimension of PCB is 122,0 mm x 53,5 mm

i still working with new layout of symetric b-1 buffer with shunt. reg (by salas too).

@salas
Check your e-mail.

regards
La Ode
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Old 13th June 2009, 04:25 PM   #6
crt is offline crt  Indonesia
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wohooooo

the new symetric B-1 Buffer with Shunt Regulator PCB is done
maybe tomorrow i can finished the job

Click the image to open in full size.

Thank's Salas
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Old 13th June 2009, 09:31 PM   #7
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Hi Salas,

Great project but
..............think shunt! I built this with a small shunt regulators with great results all it took was a small current source and a zener.

Jam
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Old 13th June 2009, 09:52 PM   #8
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Did you really read his post ? He made the latest version with shunt supplies.
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Old 13th June 2009, 10:22 PM   #9
jam is offline jam  United States
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Oops...............my bad.
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Old 14th June 2009, 12:53 PM   #10
Salas is offline Salas  Greece
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Crt says he could hear the difference in moving up from series regs to shunt regs right away.

He wrote enthusiastically about the subjective performance in an email to me, but I will let him listen more and tell it by himself.

Here is the design in detail.
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