Slewmaster - CFA vs. VFA "Rumble"

Kindhornman · 2014-03-10 3:41 am

OS,
The only thing my kids messed up was my stylus on my turntable. They saw me using it and decided that they could put a cd on it and play that! It was a long time before I replaced that.

ostripper · 2014-03-10 3:42 am

Analogy....

Zero D said:
Triac soft start to the mains power transformer has been used on Pro Amps for years, & is very successful Another way it's been done, is a with a circa 50W 0.5R resistor in series with the Tranny, which gets shorted out with a power relay after a delay.

That upc1237 looks the ticket though

Bonsai's solid state output protection "appears" to be very well worth exploring.

Also a mosfet, or bipolar, DC supply cutoff seems like a good idea too !

Seems to me ....
Disconnecting the rails is like "pulling the plug" (on the whole amp)
in a microsecond. Minus the main caps , of course.

Disconnecting the speakers is like "cutting the cord" (while the room
fills with magic smoke).
Both are valid techniques , I need to "dream on it" ...

OS

thimios · 2014-03-10 3:12 pm

First test .
Amplifier is singing!
+/-44V
idle current =20mA
Offset= -1mV
One pair c5200 a 1943
Resistors R9,R11 changed from 5k6 to 3k3 because with 5k6 Vzener =5.3v only.

Krisfr · 2014-03-10 3:20 pm

thimios said:
First test .
Amplifier is singing!
+/-44V
idle current =20mA
Offset= -1mV
One pair c5200 a 1943

SWEET Congratulations ENJOY

thimios · 2014-03-10 3:29 pm

Krisfr said:
SWEET Congratulations ENJOY

Thanks Krisfr .
I come back with first measurements later.

ostripper · 2014-03-10 5:05 pm

thimios said:
First test .
Amplifier is singing!
+/-44V
idle current =20mA
Offset= -1mV
One pair c5200 a 1943
Resistors R9,R11 changed from 5k6 to 3k3 because with 5k6 Vzener =5.3v only.

This was predicted ... (zener "tweaking")
I will add this to the IPS schemas ..

3K3 for "baby" OPS 40-50V
4K7-5K6 for master - 60-70V
6k8 for 70-85V (monster).

This effect also reflects servo IC choice (2-4ma) , red LED current
and CCS current (all using the 12V supplies).

You do it just like I do ... start with 1 pair OP for 1st test

.
Smart !
OS

thimios · 2014-03-10 8:06 pm

First measurements.1kHz,10KHz,20KHz,30KHz,40KHz.FULL POWER, PEAK TO PEAK 70V!
No:6 Nice symmetrical clip at 24V RMS
No:7 Hard clip.
1V RMS inp. 24V RMS out. just before clipping,72W RMS /8R/+-44V SUPPLY.

31697B · 2014-03-10 8:45 pm

When you have two channels... even before putting it in a chassis.... can you listen to it also and tell us how it compares to other?

THx-RNMarsh

thimios · 2014-03-10 8:58 pm

RNMarsh said:
When you have two channels... even before putting it in a chassis.... can you listen to it also and tell us how it compares to other?

THx-RNMarsh

Yes of course but now i haven't many parts for this second channel.
I will try to find parts soon.
Thimios.

ostripper · 2014-03-10 9:57 pm

3 ways to reduce "overshoot" on your SW tests.

-39/43/47p C9.

-Inductor on the board ??

-fine tune the VAS Re/I
150Re - 1.2V =@ 7.5ma current.

This also might be the long wires or other
unknown/non-ideal conditions.
It's not bad at all - but could be a little better.

Clip behavior is supurb ...

OS

maouna · 2014-03-10 10:54 pm

some people also use a capacitance of about 1uF in parallel with dummy load to view potential oscillation with difficult loads such as electrostatic speakers..you can use a small square wave input of about 10mv or 100mv at 10khz ancheck the response..

ostripper · 2014-03-11 2:24 am

Another one ..

Some one..

found my "gla-survivor" thread ..

To do that endeavor justice .... the best "symasym" type IPS
I could muster is about to be unleashed.... drum roll ...

(below 2 ) is the schema ...

(below 1) is the output ...

(attached) is the .asc ... it is cool !
A mix of the Sansui /symasym /and the HK680 IPS ...

A cascoded/ differential /wilson current mirror "mutt"? of a VAS ..
Any "symasym" fans - it totally "smokes" the original ...
AND is kind of simple !!

OS

meanman1964 · 2014-03-11 5:14 am

Pete,you're keeping yourself very busy

Vostro · 2014-03-11 5:50 am

@ thimios
What does clipping look like at 20kHz sine wave?

Be careful when testing with sqaure waves at 40kHz and up at high power, zobel and outputs will have to work very hard.

Thanks

naf · 2014-03-11 7:04 am

Uncle OS, post #504, the "monster"
C102/C103 have wrong polarity "Silk Screen"
just incase somebody non experienced build it

Thimios's 5P Monster has has correct polarity.

thimios · 2014-03-11 7:14 am

ostripper said:
3 ways to reduce "overshoot" on your SW tests.

-39/43/47p C9.

-Inductor on the board ??

-fine tune the VAS Re/I
150Re - 1.2V =@ 7.5ma current.

This also might be the long wires or other
unknown/non-ideal conditions.
It's not bad at all - but could be a little better.

Clip behavior is supurb ...

OS

My VAS seems to run in double current.
Please Ostripper have a look at measurments on the attached.

thimios · 2014-03-11 7:28 am

Vostro said:
@ thimios
What does clipping look like at 20kHz sine wave?

Be careful when testing with sqaure waves at 40kHz and up at high power, zobel and outputs will have to work very hard.

Thanks

I will look for this(20khz clipping) soon
Yes agree testing in such conditions is a hard stress very hard!
It is danger,and only for a little time.
Thimios.

maouna · 2014-03-11 11:51 am

You mean You are going to add the hawksford to cfa-x?

bimo · 2014-03-11 6:30 pm

thimios said:
My VAS seems to run in double current.
Please Ostripper have a look at measurments on the attached.

You can change R5 and R8 to 750 Ohm. May be you put super bright red led on D3 and D4 which have higher forward voltage than standard red led.

still4given · 2014-03-11 7:25 pm

SymaSym, my first favorite amp build. Watching with interest.

Slewmaster - CFA vs. VFA "Rumble"

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