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Old 18th April 2016, 09:07 AM   #7141
erik777 is offline erik777  United States
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Here is just an idea shunt circuit to add to the FX8. Its not too big, nothing expensive. Can design something more robust by adding a partner the TL431, but max is 100ma. But I left off the TL431.

It could make sense to give up a small fraction of real estate on the PCB to make way to do a much needed shunt circuit. With the goal to improve the PSRR = Improved SQ.

10uF
445-14933-1-ND
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File Type: jpg FX8 shunt concept.jpg (563.3 KB, 1178 views)

Last edited by erik777; 18th April 2016 at 09:28 AM.
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Old 18th April 2016, 10:43 AM   #7142
mrmax063 is offline mrmax063  Serbia
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Quote:
Originally Posted by erik777 View Post
Here is just an idea shunt circuit to add to the FX8. Its not too big, nothing expensive. Can design something more robust by adding a partner the TL431, but max is 100ma. But I left off the TL431.

It could make sense to give up a small fraction of real estate on the PCB to make way to do a much needed shunt circuit. With the goal to improve the PSRR = Improved SQ.
That's not a shunt regulator. In your circuit you're using standard adjustable 3-pin series regulator.

If you want to increase the PSRR of FX8, the simplest way is to add capacitance multiplier.
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Old 18th April 2016, 11:22 AM   #7143
erik777 is offline erik777  United States
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Keeping the fx8 pcb miniature is important. Adding a Cs can create a problem if there is a large bank of caps. What is needed is an inductor, in the 1st stage. An LC filter is a great idea to really improve PSRR, which would sit between the psu and the amp.

Last edited by erik777; 18th April 2016 at 11:26 AM.
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Old 18th April 2016, 02:12 PM   #7144
minek123 is offline minek123  United States
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[QUOTE=xrk971;4686033]Does the PX6 preamp operate in class A or AB?[QUOTE]

What are recommended substitutions for BC639/640 ?
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Old 18th April 2016, 03:56 PM   #7145
mrmax063 is offline mrmax063  Serbia
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Quote:
Originally Posted by erik777 View Post
Keeping the fx8 pcb miniature is important. Adding a Cs can create a problem if there is a large bank of caps. What is needed is an inductor, in the 1st stage. An LC filter is a great idea to really improve PSRR, which would sit between the psu and the amp.
A simple amplifier like FX8 requires simple solutions. If you want to improve PSRR, a simple capacitance multiplier on the power supply rails before the VAS transistors will not take very much PCB real estate. Otherwise, if you want to to have fully regulated supplies, you can use APEX regulated PSU.
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Old 18th April 2016, 03:58 PM   #7146
prasi is offline prasi  India
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Here are the files for DIY for anyone, for the FX-8 mod by Bimo.
Here are the layout considerations,
1. 470u/220u caps have 13mm dia x 5mm pitch.
2. 1uF caps have 5mm or 7.5mm pitch.
3. On board inductor of ~13-14mm dia
4. holes for optional 10mm pitch silver mica caps
5. 3296W MT trimmer.
6. 0.5 w res have min pitch of 10mm, 1w has 15mm, 2w has 18mm
reg
Prasi
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File Type: png fx-8-bimo.png (90.2 KB, 1135 views)
Attached Files
File Type: zip fx-8-bimo-mod.zip (205.1 KB, 516 views)

Last edited by prasi; 18th April 2016 at 04:01 PM. Reason: scrn shot attached
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Old 18th April 2016, 04:25 PM   #7147
xrk971 is offline xrk971  United States
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Prasi,
Very nice. Could you also please post the associated Gerber files?
Thank you.

Last edited by xrk971; 18th April 2016 at 04:29 PM.
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Old 18th April 2016, 05:21 PM   #7148
erik777 is offline erik777  United States
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Since your volunteering to help. Would like to see a schematic showing your simple Cm with a range of 100-110db PSRR improvement.

Quote:
Originally Posted by mrmax063 View Post
A simple amplifier like FX8 requires simple solutions. If you want to improve PSRR, a simple capacitance multiplier on the power supply rails before the VAS transistors will not take very much PCB real estate. Otherwise, if you want to to have fully regulated supplies, you can use APEX regulated PSU.

Last edited by erik777; 18th April 2016 at 05:27 PM.
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Old 18th April 2016, 06:03 PM   #7149
mrmax063 is offline mrmax063  Serbia
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Quote:
Originally Posted by erik777 View Post
Since your volunteering to help. Would like to see a schematic showing your simple Cm with a range of 100-110db PSRR improvement.
I have no interest in FX8 amplifier. However, mr. Mile did publish a version with added simple capacitance multiplier, but it went unnoticed (it was called AX13). You can see the circuit in post #2126: 100W Ultimate Fidelity Amplifier
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Old 18th April 2016, 06:12 PM   #7150
prasi is offline prasi  India
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Quote:
Originally Posted by xrk971 View Post
Prasi,
Very nice. Could you also please post the associated Gerber files?
Thank you.
here you go.
prasi
Attached Images
File Type: png gerb scrn shot.png (130.7 KB, 1068 views)
Attached Files
File Type: zip gerbers.zip (184.0 KB, 361 views)
File Type: zip fx-8-bimo-mod1.zip (199.7 KB, 500 views)
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