Will this work as audio amplifier?

[MikeB]

Originally posted by lumanauw

OK, so there is no need for CFP in VAS

Really? So CFP works in opposite ways if put in final stage than in differential?

Yes, I read this in DougSelf book. He didnt mentioned about the fit for class A, class B, class AB. But is it really bad for Class B or AB? Randy Slone usually using CFP output stage for class AB amp. He's using K1058 as the final pairs.

I haven't seen any design with CFP in VAS, seems not to be good.

The CFP in outputstage helps with increasing dampingfactor,
reduce thermal drift and so on. It does not sound bad.
I have built one with mosfets, and it had some very interesting
sound. It sounded like having 10times the power, crying for
pumping up the volume. But i had audible crossover. Sadly i
detected later (when reusing the parts) that the mosfets were
completely mismatched (vgs: 3.2v to 4.8v,irf540n irf9540n)
I would say, if mosfet in output, then with CFP.
I will try again, as the sound was really fascinating.

Originally posted by thanh
lumanauw! Have you ever built a symmetry amp?

I did, i like the symetrical ones for their stability and reliability.
They have perfect switchon/off behaviour, eliminating the need
for relays. My latest simus resulted in a symetrical again, it showed
up the best results. (lowest 3rd harmonic at 20khz, best stability)
I will build this one these days. (I must be crazy, 12 bjts for input
only, will be much work matching these)

Mike

[lumanauw]

I will build this one these days. (I must be crazy, 12 bjts for input only, will be much work matching these)

What? 12 device for input only? You built full complementary differential with CFP or you parrarel those? What's the design look like?

Thanh!
Yes, I've built full complementary audio power amp. Infact, quite many of them.

Perfect design and preferable actual listening design maybe quite different. If you design with SIM or electronic theory, you will end with very complicated design, full complementary design. Many buffer stages, many cascodes, etc.

If you design with your speaker as your benchmark, you will find "the minimum component/minimum stages" stream is prefereable. You will end up with designs like Aleph.

After building several kind of design, I began to search for "perfect" design. I tried "Optimum" power amp by Randy Slone. If you read this chapter on his book, you will feel that this is the one. But after I finished it (with modif in the current mirrors), it feels no great difference with other design. (Maybe not so, a master said Detail is everything, I never explore/experimenting with this design more deeply)

So, I continue to search for this "perfect" amp. At first I was inspired by numbers, like minimum THD, 1000 damping factor, etc (you can read this in pro-audio amps, like MC2, stunning numbers) Trying to get close to these numbers.
(you should read DestroyerX thread on "Blameless" amp. This amp gives perfect measurement, but he complained about the sound)

BUT,

then, I found out that simple design or classic designs (that people overlooked) tends to sound better. Then I post the thread "single or dual differential" for knowing why is that. This thread never finish with exact conclusion. Different masters gives different opinion, each with strong argument. Like Mr.John Curl insisted on full complementary design, because the VAS will be perfect push-pull. He's right about this.

For now, I concluded (for me) that single differential tends to sound better. It will not as clean as full complementary design (yes, you can hear it gives not so clean reproduction compared to full complementary designs), but this non-symmetrical design have distortions that makes the amp sound better (to me).

I dig up this fact and look at some master's design, and try to find out why they make cct like that. Like Mr.Pass Aleph, AKSA (never find out the real thing, just the approximation by DestroyerX thread). Then I make experimental amps, and somehow I feel that the more "imbalance" design, it will give preferable sound (again, to me). Maybe this is why JLH or NAD3020 is so strange if you look at the schematic.

This is the conclusion for small power (like 100W or less). I still feel that if you built big rating amp, (250W upwards) you will need full complementary design. You cannot power up the speakes in the stadium with 20.000 watt with not so clean sound. Almost all of pro-audio amp cct uses full complementary, while smaller ratings you called "hi-end" at home audio took different path.

Read about the man who changes career from audio designer to aircraft intrumentation designer after he hears the Single Ended Triode sound. Whats so symmetrical in SET? What's so perfect about SET measurement results? But why it sounds good?

[MikeB]

Originally posted by lumanauw

What? 12 device for input only? You built full complementary differential with CFP or you parrarel those? What's the design look like?

Hi !

It sounds more than it is. Yes, it is full complementary diffamp with CFPs.
That makes already 8. The other 4 are the 2 ccs to the diffamp.
Then 2 for VAS, and 6 for output.
I think it's still "simple". It shows great measurements in the sims,
now i want to know how important it is, to have "ultimate" low THD
at high frequencies and extreme bandwidth. Somehow i was not
really satisfied with my previous amp, i had the feeling that something
is not as it should be. The version with the currentmirror was some flop,
it was very hard to stop it from oscillating. I would never trust this one.
If i am not fully satisfied with this one, i will try completely different
topologys, as simple as possible. (except the CFP-mosfet one)

Mike

[lumanauw]

Hi, Mike,
What kind of CFP mosfet output stage are you using? Bipolar as driver and mosfet as final stage?
Actually I'm thinking about making discrete CFP-IGBT, that is mosfet as driver (but L mosfet like K1058) and rugged bipolar (C2922) as final stage.
Which is better?

[lumanauw]

FAB,
I just read article of Lavardin power amp with its "Heat Memory" effect. You have built one. What does it sounds like?
Where can I see Lavardin schematic?

[fab]

Originally posted by lumanauw
FAB,
I just read article of Lavardin power amp with its "Heat Memory" effect. You have built one. What does it sounds like?
Where can I see Lavardin schematic?

lumanauw

I have not built a Lavardin amp but used the concept described in the patent (for my personal use of course) on reduding the memory effect caused by thermal variation in transistor.
I Have incorporated the concept in an old DH-200 amp and the result was quite noticeable (before and after comparison). There was more details which I could not notice before the mods. Almost all the peoples I who did not know about the mod told me that my sound system sounded "better" than before after noticing that the sound seemed more "real".

I do not have a Lavardin schematics but if you have a look at the US patent 5,635,874 it says everything you need to know. However, on my side I did not use the DC servo connected at the VAS. The low memory concept is also used in Halcro amp patents.

Fab

[lumanauw]

It is really interesting topic. I learn about "Heat Transfer" when I was a student in university. It is true, that in small dissipating area (like TO-92case), small heat will stack. But this is a slow process (compared to electric speed). Heat are moving very slowly, like having big dampers. There is "Thermal Inertia" that you cannot add or substract instantly (like heatsink cooling down, you cannot force it cool or to heat it up naturally in 1 second).

From the solutions offered, I saw it more as solutions to minimize transistor distortions.
From what I learn, transistor distortions coming from 2 point, the fluctuation of current and fluctuation of voltage.

Output stage suffer from both alot. VAS have big bias current, so the voltage fluctuation is dominant here.

The remedy of voltage induced distortions is to put cascode. The remedy of current induced distortions is to make the bias stands bigger than the fluctuating signal current.

I see all the "Thermal Inertia" theory remedy is the same as "Transistor distortion-elimination" theory.

If you can make both Voltage and Current steady in a transistor, you will get steady dissipation (P=VxI), would't you?

Lavardin theory call it steady dissipation, but I also can see it as steady voltage+steady current=minimum transistor distortion. No thermal consideration needed here.

[thanh]

Oh! My input stage includes 20 bjt!
I am building it but I have not succeeded in it yet
Larvadin? do google with the word "peufeu"

[MikeB]

Originally posted by lumanauw
Hi, Mike,
What kind of CFP mosfet output stage are you using? Bipolar as driver and mosfet as final stage?
Actually I'm thinking about making discrete CFP-IGBT, that is mosfet as driver (but L mosfet like K1058) and rugged bipolar (C2922) as final stage.
Which is better?

Yes, i use bipolar as driver and mosfet as final stage. This way
you should have best of both "worlds".
Hmm, it seems a strange idea to me to exchange this, but often
strange ideas are good...

Mike

[fab]

Originally posted by lumanauw
It is really interesting topic. I learn about "Heat Transfer" when I was a student in university. It is true, that in small dissipating area (like TO-92case), small heat will stack. But this is a slow process (compared to electric speed). Heat are moving very slowly, like having big dampers. There is "Thermal Inertia" that you cannot add or substract instantly (like heatsink cooling down, you cannot force it cool or to heat it up naturally in 1 second).

From the solutions offered, I saw it more as solutions to minimize transistor distortions.
From what I learn, transistor distortions coming from 2 point, the fluctuation of current and fluctuation of voltage.

Output stage suffer from both alot. VAS have big bias current, so the voltage fluctuation is dominant here.

The remedy of voltage induced distortions is to put cascode. The remedy of current induced distortions is to make the bias stands bigger than the fluctuating signal current.

I see all the "Thermal Inertia" theory remedy is the same as "Transistor distortion-elimination" theory.

If you can make both Voltage and Current steady in a transistor, you will get steady dissipation (P=VxI), would't you?

Lavardin theory call it steady dissipation, but I also can see it as steady voltage+steady current=minimum transistor distortion. No thermal consideration needed here.

lumanauw

This is only my understanding and interpretation of the Lavardin patent:
All in all you are saying about the same thing as Lavardin finally. Lavardin says that in order to avoid thermal variation you need to keep the power constant in a device (thus both voltage and current as constant as possible). The thermal variation makes the operating point of the transistor to change a bit. This bad effect is amplified by the subsequent stage(s) with their gain. After all, you have also a higher DC offset variation at amp output that the overall feedback send to the diff input stage that will try to correct it. Of course, the higher the DC offset variation the "harder" it will be to correct it.
The temp. inertia of a small device is not comparable with a big dissipator. The thermal variation is named "memory" by Lavardin because of the thermal inertia since when the large signal has ended the device does not come back quickly enough to its "previous" temperature.

Fab