Slewmaster - CFA vs. VFA "Rumble"

[still4given]

I can't see the type.
Are these true rms?
Are these specific for A.C MEASURMENTS 100khZ
Cheap digital voltmeters measure only sinusoidal and up to 400 hz
For square wave you need "true rms" ,these comes up to 1khz (usual).
If you want to measure high frequencies you need more expensive voltmetres.

This is the meter I use. How much difference does it make?

 

[ostripper]

O-stripper- Gentlmen Here's one for you, A little Leach, a little folded cascode and a little bit of me. An innovative mirror and a HawksFord VAS.

Tremendous PSSR and some serious distortion cancellation.

Add your favorite OPS VBE and...

Maybe Stripper should form the compensation to fit his EF-triple

That one went right to the desktop !

A "folded (miib) leach V1.0" it shall be.

OS

 

[5th element]

This is the meter I use. How much difference does it make?

A considerable difference, 100k @ 2v p-p should not smoke a zobel, unless your making the amp oscillate. If your meter's bandwidth is rubbish then it might show 1v when in fact it should be showing 10. If you then turn things up to get the output back where you think it should be, then the amp is in fact putting out significantly more than you think it is and poof, up goes the zobel.

For example the 10 ohm 3 watt resistor in the zobel should be able to handle being loaded directly with 100k 2v p-p all day. There's no way it should be smoking.

If you've got a scope simply use that to set the output level.

 

[5th element]

All, these different input stages lol. I like the idea of a mirrored input stage.

 

[still4given]

I also have a Leader LMV-185A but have never used it. I will try hooking it up and compare. The zobel that smoked was a 1w resistor.

 

[Kindhornman]

Terry,
If it is supposed to be a true rms dmm it will for sure say that on the front of the meter. I have a couple of them and they do cost more than a similar meter that is not supposed to be true rms.

 

[5th element]

2 volts DC into 10 ohms is only 0.4 of a watt. Whatever you're doing with the amp, even with that tiny zobel, if it's running properly, 2 volts peak to peak of anything put on the input should be entirely safe.

 

[Lazy Cat]

Ohhh, ... This is better at higher voltages and higher frequencies.

Nice one

 

[Lazy Cat]

2 volts DC into 10 ohms is only 0.4 of a watt. Whatever you're doing with the amp, even with that tiny zobel, if it's running properly, 2 volts peak to peak of anything put on the input should be entirely safe.

Super A is not properly compensated, phase margin fall well into positive gain bandwidth.

Properly designed power amplifier must withstand 20 kHz full power signal no matter the shape at all times, zobel must not smoke at 40 kHz/-3 dB full power output.

 

[still4given]

I was talking about 2Vac at 100K. I'm obviously doing something wrong. I should just be quiet at this point.

 

[Lazy Cat]

200 kHz/20 Vpp and no smoking zobel resistor, Terry something's not right with the amp smoking at 100 kHz/2 V, most probably oscillations occur there, releasing a lot of HF energy inside the amp. Don't worry you have plenty of other ones.

 

[5th element]

Don't worry you have plenty of other ones.

 

[still4given]

Laughing at me?

 

[5th element]

Laughing at me?

No! Hehe, just a small bit of humour based on the number of amplifiers you seem to have lying around

 

[Lazy Cat]

Laughing at me?

Terry, your participation to this forum is blessing, letting all those amps to variety of signals and whatever results are beneficial to all DIY-ers to avoid dangerously unstable designs. So please put the list back to your signature and continue with your precious work - lovely hobby.

 

[still4given]

I shorted the 10uf input cap and took some more scope shots. Looks like I need to try some different caps there.

 

[triplej]

So please put the list back to your signature.

I am quite impressed by the list of amps you have built still4given. Means when you say A sounds better than B your informed and unbiased. People (like me ) tend to have their pet projects and that colours their view.

 

[ostripper]

"FOLDED LEACH" ...

I'm still on Miib's first post ....

I DO like the "folded" deal !

(below) , the original spooky with Miib's folded hawksford and it rocks.

THD20 is now 2-3ppm (spooky is 10 ppm). TOTAL even order cancellation ,
NO h2/h4 .... just a little H3 , even beats the blameless (wolverine) now.

PSRR is 10db better.

I figured out what is happening ... an error- correcting hawksford.

OS

 

[ostripper]

I'm going to add the mirrors .... see what this "brings to
the table".

I did not see that second post (glitch ?).

OS

 

[TonyTecson]

Test repeated.
New measurements,the problem isn't input filter but generators out voltage which isn't stable when frequency changes.
-3db high .All these tested at 10VRMS/4R
NAD V1.2 / 445KHz
Spooky / 400KHz
Symasui / 400KHz
CFA-XV1.3 / 315KHz
CFA V1.2 / 322KHz
The rest of test later
PS THE BEST LOOKING SINUSOIDAL at 400 khz belongs to Spooky
Thimios.

good stuff.....thanks for posting....