Slewmaster - CFA vs. VFA "Rumble"

[Bonsai]

That TO-220 resistor looks nice. I'll need to try that on my next amp.

[ostripper]

Originally Posted by Bonsai

"You have the array of resistors in parallel (the divider) near the OPS and
only run the divided Voltage back to the NFB point."

It looks like that but they are physically close to the summing junction. The boards are quite small. You have to watch out for capacitance from the feedback junction to ground or across the feedback resistors otherwise you can get gain peaking.

Could you show me an example of an existing layout ??
On a longer board , like mine ... would you run the full OPS signal right to the NFB/"2 resistor "summing junction" ??

PS - to-220 resistor is "gold", Costs $5-10usd.

OS

[Bonsai]

Yes. If you look at the nx-Amp that's how I did it. Your board is longer so you cannot avoid the long track but I don't think it will be an issue IMV. The important thing is to keep the feedback junction and diamond output transistors as compact as possible.

[ostripper]

I won't argue with success ...

Once I get the OPS/Vbe/Regulator section done ,
I will ask whether a modular unit is desired.

Below is the "madness". I did this on an EF2 ... and
actually listened to my schematic collection (20+ amps).

Once I make the OPS - I can cut and paste for both
dedicated full PCB's and modular daughtercards. Smaller card will solder on those
big square pads. OP signal will be right on that center pad (NFB)



OS

[ostripper]

Researched the Halcro , both the HK680/990 , and all the similar layouts
on this forum.

Refined the separation of "dirty" current pulse components and the clean
regulation of the IPS (clean).

Added these features :

1. Boosted rail capability.

2. dual pitch caps (3.5/5mm)

3. Rail augmentation - 14ga wire on top of PCB at the output rails.

4. Aluminum flashing for driver heatsink - no special sourcing. Any
parts will be "hardware store" simple.

5. Feedback return will "float" like a Halcro ! Air is the best insulator.

Standard features :

1. EF3 (triple) with output class driver stage (NJWxxxx).
Built ram tough .

2. 2 device HK680 bias spreader ... the MOST accurate thermal tracking
short of thermal-trak outputs. My 680 will stay within 1 mV ! , regardless
of ambient/amp use.

3. OPS .05% full power distortion in isolation.

4. Diode protected multipliers with large capacitance capability.
Hfe x 470uf @100v (max size C103/106) = 47K "fake" capacitance.
But , we lose 2-3 V on the rails ..... oh well.

5. Main rail caps can be 1000uF @ 80V max.

OPS (this board) numbers start at C/D/Q/R 101 and up and
IPS's (cfa -vfa "front ends") , start at 1 and up.

Below is High res. -both PCB and schematic. Dare you to find an
error ....

PS - many , many , many IPS's to use are soon to come !
(CFA-NX is first)

OS

[TonyTecson]

for diy'ers, having an output module wherein options for trying out several types of input sections is indeed nice....
i am sold to the idea of triple EF's, but i believe Technics came out with a quadie EF, have you seen that?
http://www.hifiengine.com/library/te.../se-a100.shtml

[ostripper]

Originally Posted by AJT

for diy'ers, having an output module wherein options for trying out several types of input sections is indeed nice....
i am sold to the idea of triple EF's, but i believe Technics came out with a quadie EF, have you seen that?
Technics SE-A100 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine

That's a beautiful amp !

This triple has worst case current gain of ...... 25,000.
Just 60uA VAS load will drive a 2R OP load with 10A.

The first in line is the "controversial feed back amplifier" -
I call it the "NX-hawksford" (below).
I also have the Hawksford VAS attached to the "VSSA/Peeceebee".

With the cap multipliers on this OPS board and zeners on the input stage
board , I'm getting much better PSRR/THD than the originals.

For voltage feedback amps , the "badger" does beautiful on this triple ,
doing 10ppm without fancy compensation (TMC). I also have
the luxman 120a and Sansui Z3900 for input stages.

All that needs to be done is to tweak the VAS for 3-6ma current
and plug er' in ....
All the input stage boards use just 12-15ma per rail ... no
heatsinking required ! You might want to thermally couple the VAS
like on the badger just to equalize devices - ALL runs super cool.

One could even SMD a input stage and run LTP's at 1ma with a 3mA
VAS - 30 X 75mm tiny boards.

PS - Bob cordell discussed on "trouble with triples" to have the fastest devices for the drivers - slow predrivers and
slow or equal speed (Ft)outputs. Decouple the driver/predrivers through a resistor (R112/113) ... and one hell
of a stable triple you shall have - I can "splice" anything on this OPS , not the slightest hint of instability!
OS

[Bonsai]

Looks good - I'm looking forward to seeing this sucker!

youve managed to get away with single sided boards - I usually give up after an hour and start laying topside tracks. I'll have to be more patient with my next effort.

[ostripper]

Originally Posted by Bonsai

Looks good - I'm looking forward to seeing this sucker!

youve managed to get away with single sided boards - I usually give up after an hour and start laying topside tracks. I'll have to be more patient with my next effort.

Thanks . The material on your site was like ESP's but a little "deeper".
Very helpful to get me thinking. I took a couple year break after making
the badger for DIYA and needed a "deep" project to clear out the cobwebs.

This is "round 2" ....and there is no reason a DIY project can not match
or exceed "high end". I know this simple single sided layout will really
kick butt. It IS the best of several high end layouts combined.

Absolutely assured that whatever IPS is "plugged in" will come startlingly
close to it's simulated expectations. (the "badger" did).

I did single sided as I did the badger for prototype purposes. It might even
be prudent to leave the NFB return and clean grounds in the atmosphere.

Ha , Ha ... even sheath them in UV reactive teflon with silver wire so
even DIY'ers can have a taste of "classe' "

On to the technical side , this EF3 is a wonderful candidate for
MJL21193/4 OP's or the insane Semitech MG9410/6330 BJT's.

IMAGINE 400-500 watts with just 3 pairs - this board was designed for it !

BTW - These are the IPS's that WILL be posted....
CFA-
1. NX - hawksford
2. VSSA -hawksford
VFA -
3. Sansui -hawksford (gla)
4. Blameless
Something for everyone ....the VFA's have been built and tested already,
they just have a better "home" now.
OS

[jkuetemann]

I really like this concept - Proven OPS and PSU coupled with 'swappable' IPS/VAS. Should make for some really interesting comparisons since you are only swapping the topology, all else remains truly equal. Quietly following with interest.