Slewmaster - CFA vs. VFA "Rumble"

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#6,821
Board Bummer

Well that turned out to be quite the bummer.

Boards aren't being made and aren't available any longer.

Unless you are Terry and rolling your own.
All's I can say is Terry is one soldering fool!
And
I mean that in a good way. OS just finished the
design and Terry has a finished board already.

Terry, you must have at least one of everything
on there yes?

Horn man, how many of these do you have made?
 
#6,822
Kindhornman said:
Terry or OS,
If you do install the higher wattage resistors do you just leave them in when you are done testing or do you revert to the 1/4 watt resistors and if you do, why?

Terry I appreciate that you are actually comparing two input sections with the identical output section, that would be the only way to make a real comparison in an AB test. I really do believe that different people hear and tune into different aspects of sound, some may never notice something that someone else clues into immediately. But if you or anyone else is happy with what they have then that is all that is important. In the end it is about the music, isn't it!
Click to expand...

No , the CFA's need the larger resistors. In real life , 1/2W components
would do for music. 1W is safe for all day load testing.
That feedback network is "split in two" , but still will see 35ma at full
output with 70V rails.

If you ran this amp at "half throttle" , or with a low rail voltage .. 1/4w
might be safe.

OS
 
#6,824
Kindhornman said:
Terry or OS,
If you do install the higher wattage resistors do you just leave them in when you are done testing or do you revert to the 1/4 watt resistors and if you do, why?

Terry I appreciate that you are actually comparing two input sections with the identical output section, that would be the only way to make a real comparison in an AB test. I really do believe that different people hear and tune into different aspects of sound, some may never notice something that someone else clues into immediately. But if you or anyone else is happy with what they have then that is all that is important. In the end it is about the music, isn't it!
Click to expand...

I can't answer for them, but for me with what ever I test with is what
I'm going to use, otherwise why test with it? If you need the extra wattage
for noise reduction, stability, TC, etc., your ears will learn match what you test.

If you change parts after the test then nothing will match any longer.
You might end up wondering it tests so well or not but sounds like?
At least for me.

It kind of like playing piano. You usually get stuck playing some other
instrument that's different than the one you love. Guitarist, sax, horn player
drummer typically don't have that problem. Portable instruments are nice
for that reason.

I think you are right KHM people do hear differently.
And those that can hear it can make it work...just ask Nile Rogers.
 
#6,825
still4given said:
I will no longer be answering any more questions about the sound of an amp.
Click to expand...
So, Terry, where should we find an interest, reading-you ?
To know that you have build this or that ?
It is only with detailled listening reports from everybody, trying to see if we can extract some common feelings that we can begin to get an idea about this "CFA VFA rumble".
 
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#6,830
alcroner said:
Higher Quality are tantalfilm resistor perhaps for feedback network non magnetic inportant i think.
I use Beyslag 'german' resitor, very high Quality.
Click to expand...
Where you buy beyslag ?I have many of them, new old stock.
I can't find this time in Greece.
Small progress.
Many missing parts🙁
 

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#6,835
thimios said:
Where you buy beyslag ?I have many of them, new old stock.
I can't find this time in Greece.
Small progress.
Many missing parts🙁
Click to expand...

I see you have it set to try "A" and B" ??

The old "NAD" was "B" , no real issues (had a hawksford with + temp)
"A" -should be better ,
as the same Vceo for all 4 992/1845's will cancel thermally.
The super-pair VAS has close to 0 co-efficient.
The diamond resistive current source (mirrored by Q 5-8) just has
the ppm co-efficient of the resistors (TCR).

You looked over the layout ? - I'm still doing so. Still no error (I can see).
This IPS is "spooky" level in it's complexity.
Edit - when you "fire it up" , do so WITHOUT the servo ... at first.
(It will work without the servo) ....
You will see what level of Q1/2 matching you have. offset under 100mv
is good. Servo will counteract that with < +/- 2V to correct.
OS
 
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#6,836
ostripper said:
I see you have it set to try "A" and B" ??

The old "NAD" was "B" , no real issues (had a hawksford with + temp)
"A" -should be better ,
as the same Vceo for all 4 992/1845's will cancel thermally.
The super-pair VAS has close to 0 co-efficient.
The diamond resistive current source (mirrored by Q 5-8) just has
the ppm co-efficient of the resistors (TCR).

You looked over the layout - I'm still doing so. Still no error (I can see).
This IPS is "spooky" level in it's complexity.

OS
Click to expand...
Ok boss A:judge:
All 4 tranz.at the same stabilized supply.🙂
Don't worry, a little smoke is a must with Eastern 🙂
 
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