11R ! woow .... 
This attests to the major "slop" that this particular CFA topology
can withstand without "magic smoke".
I did the same with a early "Badger" (10R Re's by mistake) ...
leaving me with too much gain + insufficient margin.
Blew the zoble , nearly fried the OP's - burned other devices.
Glad we have it now , Terry. Good job.
As far as Guru's go ... I don't want to be one . They can write
the books , I'll just stick to producing good projects.
Bob Cordell was VERY helpful in getting the OPS correct - he's
a real gentlemen.
PS - I was the instrumentation "guru" at GE selkirk ... this greatly
prepared me to design/build/ test ... I had to do all 3. This
wonderful hobby is "custom made" to take advantage of this (training ?).
Edit - 2.7K /68R /33pF = 1.2mhz UG , 78 degree PM , 27db gain ...
OS
This attests to the major "slop" that this particular CFA topology
can withstand without "magic smoke".
I did the same with a early "Badger" (10R Re's by mistake) ...
leaving me with too much gain + insufficient margin.
Blew the zoble , nearly fried the OP's - burned other devices.
Glad we have it now , Terry. Good job.
As far as Guru's go ...
I don't want to be one . They can writethe books , I'll just stick to producing good projects.
Bob Cordell was VERY helpful in getting the OPS correct - he's
a real gentlemen.
PS - I was the instrumentation "guru" at GE selkirk ... this greatly
prepared me to design/build/ test ... I had to do all 3. This
wonderful hobby is "custom made" to take advantage of this (training ?).
Edit - 2.7K /68R /33pF = 1.2mhz UG , 78 degree PM , 27db gain ...
OS
Playin' around ....
BV's "cheat" (increasing decoupling on driver/pre) , got me "playin' ".
Increasing the existing R/C on the OPS board to (10R/47u , 15R/47u , and
22R/47u) will increase global PSRR by 3-10db with NO performance
degradation.
The 15R/47u combo seems to be best (according to LT spice) .
OS
BV's "cheat" (increasing decoupling on driver/pre) , got me "playin' ".
Increasing the existing R/C on the OPS board to (10R/47u , 15R/47u , and
22R/47u) will increase global PSRR by 3-10db with NO performance
degradation.
The 15R/47u combo seems to be best (according to LT spice)
.OS
Just a little lower UG (1mhz) - same margin. (below)
<30db gain, 964khz UG , 77 PM. (nice and stable)
Edit - at this config .... >200 V/us slew (plenty).
OS
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I suppose that it will be nothing audible, nothing visible at osciloscope screen, but for sure it will be measurable as cleaner background at spectra measurements. "Everything" should be always at least 110dB-120 bellow signal (maybe except some signal harmonic). It will improve the "black background" in music..Brightness , detail, resolution.
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Ι haven't made any modification yet.
Instead of this ι decided to repeat listening tests.The same music track was repeated again and again.
Now i have clear image.
Spooky is so clear as Vssa but very-very powerful .
Two pairs musical ears have the same opinion about this.
Test at 28VRMS out Att 1:28
I'm glad you like the "spook" ,Thimios. All the others are hung up on the
CFA's , LC thinks I'm a "spook" because I'm too poor to build now
.I did this all before ... built every IPS on the forum (except for the spook)
on my "Supersym thread".
I want to experience this IPS . Not to discount these CFA's , the spook
topology is often used for pro audio - it is TOUGH !
I have a V2 (TMC
) spook that goes sub PPM ... w/ 220v slew.Let them build the CFA ... I really will "drop the VFA bomb" (with a
super refined layout) when I come back in july.
Super work ,Thimios ... (made in Greece) rules
!!! Edit - spook ... better bass , better psrr , durable - same fast slew - "whups " the VSSA
I DO think the BV modded CFA-XH is nearly an equal (nearly - but not quite).
OS
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Hi BV,
It's weird because the generator by itself show very good square waves all the way to 150kHz. I have to believe that the wave shape shown at the input is coming from the input on the amp. No matter really, it is good enough for what I do.
I have made a drawing of the modifications needed to make the latest circuit that you shared. Look over the board and see if you find something wrong. I may try building it just for fun.
I'm not hung up on CFA. That is just the only boards I have to play with right now. Remember just last week I was playing around with the Symasym IPS. Juan Vargas is making some gerbers for the wolverine so I guess that will be my next adventure, though I already have a Honey Badger.
I will have an HP Laser Jet Monday so I may tackle one of the ones that aren't scheduled for gerbers.
Blessings, Terry
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At this point I don't see how there can be a significant difference between the two topologies. The CFA and VFA seem to be merging in specifications. Both have similar slew, distortion numbers and now even PSRR with the BV mods. Now the question becomes have the people who have been saying that the CFA's sound more musical hold true or have we made both so similar you would be hard pressed to tell them apart?
Terry , you were the inspiration for the "wolverine". From the point of
the badgers bad clipping behavior (remember) ... I fixed that , the
next step was a HD version.
Wolverine tames the CCS saturation and has both options for the active
end of the VAS. On the EF3 , the blameless must be SUPER crystal clear ...
It should sound "badgerish" but with more tolerance of different loads.
Of course , critics will label it as "clinical" ... as it should be (at 3 ppm) .
PS - the non ground referenced cascode (I was told) , makes for a
totally new level in sound quality (as compared to the "old" way).
OS
the badgers bad clipping behavior (remember) ... I fixed that , the
next step was a HD version.
Wolverine tames the CCS saturation and has both options for the active
end of the VAS. On the EF3 , the blameless must be SUPER crystal clear ...
It should sound "badgerish" but with more tolerance of different loads.
Of course , critics will label it as "clinical" ... as it should be (at 3 ppm)
.PS - the non ground referenced cascode (I was told) , makes for a
totally new level in sound quality (as compared to the "old" way).
OS
I would bet .... that the spook and CFA-XH would be nearly indistinguishable
A/B 'ed.
If I make the spook .5ppm , who would know ? Just "bragging" rights ,
at this level.
The only other metric is durability , the spook is the best "clipper".
OS
Some trouble
Tried to fire up the CFA-x"h" that OS released long time ago.
OPS is the baby.
However when I connected the combo to my PS both 150r resistors on the ips cascode smoked.
I do not have a proper bench supply to slowly rise the operating voltage so I am not properly able to measure the voltages over these resistors.
Could someone give me a hint where to start the troubleshooting?
J
Tried to fire up the CFA-x"h" that OS released long time ago.
OPS is the baby.
However when I connected the combo to my PS both 150r resistors on the ips cascode smoked.
I do not have a proper bench supply to slowly rise the operating voltage so I am not properly able to measure the voltages over these resistors.
Could someone give me a hint where to start the troubleshooting?
J
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Nothing is weird , Terry. Look at attached picture, Rg is generator internal impedance, I suppose it is 600ohm. Omit C1, and You got ideal square wave signal.
If You will make new PCB, make ground traces as wide as possible, or as poured copper ground plane.
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