100W Ultimate Fidelity Amplifier

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prasi

prasi

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Joined 2014
sites.google.com/site/analogdesign1234/
Paid Member
xrk971 said:
Here is a blast form the past. This was my FX8 Bimo Mod by Prasi that I built maybe 5 years ago. Wow, time flies. I set it up on a plank (as usual for verification builds) and ran as Class AB, although bias is pretty high so it runs quite warm. A few years went by, and I later installed it in a DIYA 4U Dissipante case and ran it at +/-24v and 1.25A bias current in full Class A. It worked well and sounded great. It is a lateral FET amp, so pushing bias into Class A is fine without fear of thermal runaway. Very nice layout by Prasi - awesome amp. Highly recommended.
Click to expand...

Hi x,
Yes, I saw those photos and your class -A build when I was browsing through for info for my build...

Very nicely done. I always kept promising myself that I will build this amp, but never really did. Better late than never.

Take care.

regards
prasi
 
M

manniraj

Member
Joined 2012
prasi said:
Chinese boardhouses are accepting orders but shipping is on hold for India.
Indian ones are all closed..:eek:
here are gerbers and sch... you could use a small aluminium plate as heatsink ( shown as hatched lines ) for the rectifiers (insulate rectifiers if using such single heatsink).
Click to expand...

Thanks Prasi, yes I see that Chinese board houses are not accepting any orders if shipping to India. Nice idea of having the big wattage resistors underneath the board as well as the bleeder resistors, then we need to install slightly big spacers for the board.
If using onboard bridge rectifiers B1/B2 which needs to be isolated if using a single aluminium plate as heat sink. Then in that case I can skip the 4 diodes (marked CS,CS',CX, CX') and a pair of resistors (marked RS,RS') directly connect the transformer secondaries to the 3 hole marked 4 pins.
If I use offboard bridge rectifiers then I can connect the +/- from the bridge rectifiers directly to the +/- near the either side of the 2 bridge rectifiers. What is the purpose of RB and RB' which I can see underneath? I thought of using 1 of 0.22 or 0.33R 5W cement type resistors on each side (R7 and R1' so that I can install them on top of the board rather than underneath) with 4 capacitors of 10000uf 63v as my usage is going to be not more than 30v@5A AC transformer.
 
prasi

prasi

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Joined 2014
sites.google.com/site/analogdesign1234/
Paid Member
No, please study the schematic carefully...
1. using on-board rectifiers b1 /b2:
cs/cx , cx', cs' and rs , rs' are the quasimodo snubber components (optional).
2. off board rectifiers:
connect the off-board first bridge rectifier's +ve WIRE to the B1+ terminal towards the top AND rectifier's - wire to the B1's - terminal.

connect the off-board second bridge rectifier's + wire to the B2's + terminal and then rectifier's - wire to the B2's - terminal.

RB and RB' are the bleeder resistors...

R1 to R7 on positive and R1'-R7' on the negative side are in parallel...
So you would be better off using 1 ohm , 1W to 2W resistors.

I will make a 3D on how to mount components...


edit: 3-d pics attached
 

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manniraj

Member
Joined 2012
Thanks Prasi, I think I understood the schematic correctly but maybe did not put the markings correctly for the offboard rectifiers if I am using. I will better use onboard rectifiers looking at the small form factor of the board :)

Regarding the R1-7 and R1'-R7' you are suggesting to use either 1R of 1W/2W resistors as they are parallel rather than using one of 0.1R 5W resistor like this 10pcs BPR56 5W 0.1 0.15 0.22 0.25 0.33 0.5 ohm Non inductive Ceramic Cement Resistor 0.1R 0.15R 0.22R 0.25R 0.33R 0.5R|Resistors| | - AliExpress as 1R of 8 in parallel makes it to 0.12R. As I was thinking of using the cement resistor on top of the board and for better heat dissipation.

Thanks again
 
M

manniraj

Member
Joined 2012
Also a bridge rectifier like this - 5PCS 25A 1000V diode bridge rectifier KBU2510|Rectifiers| | - AliExpress should be sufficient looking at the 3D image should easily fit and with the mounting hole we can put a small aluminium plate with some kind of insulation if both the rectifiers are mounted on the same plate. I am not sure if I have to use the aluminium plate as I will not be using more than 5A secondary trafo with this board for now in my class AB builds. What do you think?

thanks
 
prasi

prasi

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Joined 2014
sites.google.com/site/analogdesign1234/
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manniraj

Member
Joined 2012
prasi said:
Those legs seem to be equispaced, i had in mind some thing like this. https://www.mouser.in/datasheet/2/427/pb3506-1767492.pdf

for aliexpress, MCIGICM 5PCS 35A 1000V diode bridge rectifier gbj3510|bridge rectifier|diode bridge rectifier|diode bridge - AliExpress

For normal listening, you can get away without using heatsink...
Click to expand...

Thanks Prasi, I found similar one as well like the PB3510 :)
5PCS GBJ35M KBJ3510 PB3510 integrated circuit|integrated circuit|circuit integre| - AliExpress

I think sinking them with an aluminium strip seems to be tricky with the other componens and AC wiring being very close to the rectifiers. Maybe we can lift the rectifiers up a little bit and use the aluminium strips and the plastic isolation To-220 should fit with couple of silicon thermal strips in between with some grease.

Otherwise your boards look perfect and awesome for anyone to build and use, hats off :cheers:
 
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I

ivanlukic

Member
Joined 2010
prasi said:
Meanwhile I am well on the way to building Apex FX-8 Bimo Mod amp. see attached pic from yesterday.
Today I fitted output transistors (2SK and 2SJ) and tested for bias and offset.
All ok...

I am also building a case with upc1237 protect , CRC PSU and VU meter and ESP P88 preamp with volume control. All the pcbs are designed by me.:)

Because of the lock down in India, I am finally able to complete some of the long pending projects.

PCBs for the Bimo amp are kindly donated by Ivanlukic... Thanks Evan...

regards
prasi
Click to expand...

Very nice build, prasi!
 
S

Sunny22g

Member
Joined 2016
Apex fx 100 psu

Hello guys I made fx 100.every components I checked before set on pcb after soldier.but psu protection not working .like short circuit.and dc also .plz suggest me .how i sold first I give 35-0-35 also on 50 0 50 ac volt
 

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xrk971

xrk971

Founder of XSA-Labs
Joined 2012
etsy.com/shop/XRKAudio
Paid Member
prasi said:
No, please study the schematic carefully...
1. using on-board rectifiers b1 /b2:
cs/cx , cx', cs' and rs , rs' are the quasimodo snubber components (optional).
2. off board rectifiers:
connect the off-board first bridge rectifier's +ve WIRE to the B1+ terminal towards the top AND rectifier's - wire to the B1's - terminal.

connect the off-board second bridge rectifier's + wire to the B2's + terminal and then rectifier's - wire to the B2's - terminal.

RB and RB' are the bleeder resistors...

R1 to R7 on positive and R1'-R7' on the negative side are in parallel...
So you would be better off using 1 ohm , 1W to 2W resistors.

I will make a 3D on how to mount components...


edit: 3-d pics attached
Click to expand...

Nice compact layout, Prasi! We could use the active bridge boards for the rectifiers. Even for Class AB, I have found that an LT4320 reduces the diode switching noise, and really, eliminates the need for the snubber. This is all possible because the switching is at zero-crossing vs 0.6v (Si diode switching), hence no noise generated. This results in a cleaner or "blacker blacks" noise background. Your GBJ format active bridge boards are perfect for this. The only issue is added expense of a $7 LT4320 chip x 2, plus nominal cost of the active bridge board.

Just pointing this out as I have noticed a substantial improvement in sound quality, even with non Class A amps whne LT4320 is part of the PSU.
 
A

alain98

Member
Joined 2006
M

manniraj

Member
Joined 2012
xrk971 said:
Nice compact layout, Prasi! We could use the active bridge boards for the rectifiers. Even for Class AB, I have found that an LT4320 reduces the diode switching noise, and really, eliminates the need for the snubber. This is all possible because the switching is at zero-crossing vs 0.6v (Si diode switching), hence no noise generated. This results in a cleaner or "blacker blacks" noise background. Your GBJ format active bridge boards are perfect for this. The only issue is added expense of a $7 LT4320 chip x 2, plus nominal cost of the active bridge board.

Just pointing this out as I have noticed a substantial improvement in sound quality, even with non Class A amps whne LT4320 is part of the PSU.
Click to expand...

Where can we find the LT4320 at $7? Can you please provide the link?
Edit: Ok I found the SMD one for $7.13 on mouser but the through hole is around $8

thanks
 
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P

priyank

Member
Joined 2020
apexaudio said:
+/-24V DC is the lowest operating voltage, if you have +/-32V DC you can use this amp but power will be about 40W on 8R load.
Regards
Click to expand...

Dear Sir apex..I am very new here and join this just to make your amplifier ax14 I ha e found all your posted circuit diagram regarding ax14 ..My question is that what transformer should I purchase to drive this amp stereo version because I am gonna make a teri version
 
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