FETZILLA - The Builders Place

[lineup]

Hi Lineup,

I like this general topology, the way you draw it makes it look very simple.

Reminds me of the JLH Class AB published in 1970, [http://sound.au.com/tcaas/jlhab2.htm]which of course was all BJT.


I do like the use of Laterals in the output for simplifying the thermal stability of the bias. I suppose this is the only output device that we can use without adding some temperature compensation ?

Bigun.
If you mean circuit in my first post,
this was the original Idea.
The idea that got AKSA Hugh started.
He suggested several changes including bootstrap.
If it wasnt for Hugh it wouldnt have been built.
Hugh is a man liked and trusted.

Yes, it isa nice circuit.
It is good to see that there are other ways to think and build good amplifiers.

Regards, LIneup

 

[lineup]

The FetZilla I've build is realy a special amp with nice mids good staging and detailed hights and very strong tight bass.If we need power it is only for the bass region.Is it possible to design a kind of a Fetzilla topology that goes to max 200Hz wouldn't this make things easier to design?

meanman
It is true what you say.
If we are to build only for BASS region .. upto say 200 Hz
then it simplifies the design very much.

Is it a BASS amplifier you are after?

 

[lineup]

meanman, how would you compare your FetZilla with your DX blame ?

Blame is a conventional and a bit boring amplifier.
Fetzilla has another topology and should be way faster.
I think a compare would be in favour of Fetzilla.
But lets hear what destroyer X has to say

 

[lineup]

meanman.
I had in mind 2x40 VAC transformer.
This would give like +/-55 VDC supply.
The max power would be like 150Watt into 8 Ohm and more into 4 Ohm.

 

[lineup]

Lineup, why have you posted a version of the circuit that has not been built and tested, and omits the lateral mosfets so pivotal in the original design?

Meanman,

I have built perhaps 9 versions of this amp topology with different device types (BJTs, etc) in the input, vas and output. I can tell you now that the JFET input, MOSFET vas, and lateral MOSFET output all play a key and synergistic role. Not only this, but the exact part used was decided on through extensive R&D. Substituting any one of them often causes problems. These problems can be solved but require circuit modifications. For more power we need higher voltage rails. Lets look at the problems this causes starting from the input.

1) The input jfet has a very limited dissipation capability. To run higher voltage rails means pushing it quite hard or switching to another input device. The other option is to run a cascode or buffer of some sort, both of which require additional circuitry and have their own sonic signature.

2) More power means more dissipation through the VAS due to the higher voltage rails and increased current required to run a larger output stage. The device selected by Hugh and I was chosen over numerous alternatives based on parameters like input capacitance, power dissipation and transconductance. It is already being run at about as much dissipation as we are comfortable with.

You can of course switch to a larger device such as the IRF610, or perhaps cascode the VAS. However, having tried both I can tell you that the sound quality suffers. Mikelm will also attest to just how much better the zetex mosfets sound in this amplifer. That said, the 610 might sound OK if you were to up the VAS current to 20mA or so.

Of course you can drop the current and run a buffer before the output devices, but that kills the elegance of the beautifully simple circuit.

3) The output. More power means we need either vertical mosfet outputs or a paralleled lateral mosfet output stage. Both of these options mean we need more current through the VAS or a buffer to drive the output devices. I can guarantee you that verticals sound terrible if simply dropped into the circuit as is. The increase in harshness is obvious. I don't know whether this is due to greater cross over distortion, poor drive capability of the vas, or the increased transconductance, but they really just don't sound as good IMO. Also, we need to consider thermal stability with verticals which means adding a Vgs multiplier or something.

All of the problems above are fairly easily solved but require a new circuit. Just this week I think I have come up with an alternative, though quite different to Fetzilla. I will post the results in coming weeks.

If you have built 9 versions of this amplifier, Greg
then you are a guy to listen to.

I hope you will assist meanman with his high power version he wants for his BASS loudspeaker.

Great to have the knowledge bank of someone who actually built this thing.

Regards, Lineup

 

[AKSA]

You could need three pairs of laterals for 150W, and I believe that increasing the VAS current around 30% and inserting a cascode on the input jfet you would be in business.

However, a complete rejig of the pcb would be needed, of course.

Cheers,

Hugh

 

[lineup]

Just what I have in mind, Hugh.
3 pairs of EXICON.
Have rather plenty bias for the VAS.
And a cascode for the 2SK170.

Rail voltage I suggest is +/-55 VDC from 2x40 VAC transformer.
This will give something like 150 Watt into 8 Ohm.
And more into the BASS if the impedance will go down towards 4 Ohm.

 

[GregH2]

If you have built 9 versions of this amplifier, Greg
then you are a guy to listen to.

I hope you will assist meanman with his high power version he wants for his BASS loudspeaker.

Great to have the knowledge bank of someone who actually built this thing.

Regards, Lineup

Thanks Lineup. The other person to talk to is Mikelm. He has his own very special direct coupled version...

One version I did like was a small signal mosfet for the front end and a BJT VAS. It sounded quite nice and if anyone is willing to experiment I think you might be pleasantly surprised.

 

[meanman1964]

meanman
It is true what you say.
If we are to build only for BASS region .. upto say 200 Hz
then it simplifies the design very much.

Is it a BASS amplifier you are after?

Well lineup,I was thinking the most power gets into the bass right?My first choice would be a fullrange amp like the FetZilla but with higher output power.
If it's possible you may design a fullrange amp.But don't forget I'm spoiled with the FetZilla it has to be as good.On the other hand my speakers that I've to build will be all active with two 20cm bass drivers each side and for this a real bass amp would be a great idea,what do you think?

 

[meanman1964]

meanman.
I had in mind 2x40 VAC transformer.
This would give like +/-55 VDC supply.
The max power would be like 150Watt into 8 Ohm and more into 4 Ohm.

That would be great

 

[GregH2]

meanman,

I think we could get a pretty decent sound for you by using an IRF9610 as the input, biased at 20mA and on the main heatsink. Then for a VAS I would use an IRF610 biased at 50mA and also on the main heatsink. For the VAS CCS I would use a single DN2540 mosfet without the bootstrap arrangement, also on the main sink. For the output 3x lateral mosfet pairs.

The only problem would be DC offset which would take a long time to stabilise as the heatsink heats up. However, this is less of an issue than some make out IMO. If it really bothers you we could devise a servo scheme.

Running the IR devices at high currents and voltages will make them sound better.

I made quite a few versions of fetzilla using a ZVP3310A/ZVN3310A mosfet as the input device and it sounded as good as the jfet IMO. A bit different, but equally good. More lively perhaps.

 

[meanman1964]

Greg,Just do what you think is best.What do you mean with a long time?

 

[destroyer X]

Because of Hugh i will not comment Bigun

Respecting a very good friend..but i have sent you direct message about.

About the Blame ST..... Super A have eated it.....so, if Zilla matches, then will have to face the Dx Super A.

there's a problem when we compare high end amplifiers..they are already touching the "roof"....how to be higher than the roof?

Maybe matched speakers can do that.... giving advantage to one or other, i cannot see other logical possibility.

regards,

Carlos

 

[Jay]

there's a problem when we compare high end amplifiers..they are already touching the "roof"....how to be higher than the roof?

Maybe matched speakers can do that.... giving advantage to one or other, i cannot see other logical possibility.

The level of knowledge in this forum is too high to be underestimated/bullied.

 

[Bigun]

Respecting a very good friend..but i have sent you direct message about.

About the Blame ST..... Super A have eated it.....so, if Zilla matches, then will have to face the Dx Super A.

there's a problem when we compare high end amplifiers..they are already touching the "roof"....how to be higher than the roof?

Maybe matched speakers can do that.... giving advantage to one or other, i cannot see other logical possibility.

regards,

Carlos

I don't think Hugh would be shy about any comments - he may in fact get rather too much fun out of the discussion !

Anyhow, not so much a question of which is better, that is a question that isn't useful - but rather a question of how they are different. Two reasons to ask, a) we can learn how different design choices can affect the sound, b) we can learn which designs might suit our own listening preferences, sources and speakers.

Now DX, you have made a Class A amplifier, this is very interesting for me because many years ago you did not have a good opinion of Class A that you had tried so now you must have something special...

 

[AKSA]

Carlos,

Bigun is right; I'm just fine with all these comments, I look at good circuits from thing every day, including your designs! I don't much contribute much, but I'm still very interested in DIYaudio and visit every day. I'm most grateful for the privilege of being a member here, in fact.

Cheers,

Hugh

 

[destroyer X]

It is all rigth to me Hugh...you know i have a lot of respect dedicated to you

You know much more than i know about amplifiers...i have learned a lot from you.

It is not a problem if your amplifier beat mine one...because mine one is not even mine..it is more Blameless than mine..the philosophy, the idea behing the circuit is from Self.

I am just so well impressed with this last model that i really do not believe someone can beat it...maybe match, a even result..but beat it is something i really do not believe.

But, as i do not earn any money with my amplifiers, i am not a professional, it is for fun, i would have no problems to say the one is better without any problems about.

I have not listened this Zilla..... but if one day i listen to it, and perceive it as better, will say to everybody...will scream to the whole world, will be advertising your amplifier and will send mine to junk and also will say my friends and builders to make yours..

I have a proposal...send me one...just one...then i gonna test it and compare and will be fair, will be 100 percent honest....and as i do not earn money i will do the following.

If your amplifier beat mine..then i will make a huge noise wide world, will ask my builders to build yours...will say mine was defeated and will be advertising yours, and for free.

But if happens the opposite..then i will be silent..no coments about i have beated yours..if this happens.

As people will never know if you sent me or not..then the silence will be to defend our old and strong friendship.

No one will know.... even bigun will not know..will say nothing..you say nothing.

So....only advantage to you.

I can kill my designs..no one have paid for them...so...i have just to point the one is better...and people cannot complain.

Carlos Eugênio Bezerra Mergulhão
Rua Dona Balbina Menelau 56 - 1601
Candeias - Jaboatão dos Guararapes
Pernambuco - Brasil - South America
54440-615

But i repeat...once and once again...no one can beat this one i have now a days...i do not believe this is possible!

Deal made?

Carlos

 

[AKSA]

Carlos,

I'm very sorry but I have no pcbs left over; in fact, I do not have a FetZilla either, it was sold. And this schematic was created by Lineout, then developed with Greg and Mike, not me, although I had some influence during laying out the pcb and documentation. There was significant input (the hybrid CCS) from a very clever engineer in Melbourne, Paul Bysouth.

There may be a #4 group buy, however. I am discussing it with a guy in Belgium and I am seeking permission from Greg and Mike, who did the hard yards and due respect.

I admit I was surprised that the FetZilla was so good. It's laughably simple, so integrating the power supply rails made it a very neat package, and I sold nearly 200 pcbs around the world. It presents almost a tube sound, which reflects low loop gain and lateral FETs in the output stage.


Ciao,

Hugh

 

[destroyer X]

I see Hugh....so, there's no problems of consciousness to myself

about it...good that it is not yours my dear friend.... i do not want to bother you..and my amplifier would eat this one easy.... it is extraordinary Hugh.

Do you know... i also do not have pcboards left from some designs.

So.... forget the whole stuff...the proposal was for you... and only for you. as it is not yours...proposal removed!

Receive a big hug my dear friend...God bless you and keep you healthy for more 15 years (minimum)

I am removing myself from this thead, to avoid comments about..to let the thread go ahead in perfect harmony.

regards,

Carlos

 

[Jozua]

Carlos esq

I am certain your amps are excellent.

What we should rather be testing is - if possible (?!!) is how much subjective enjoyment we have with our 'favourite' amps and how much money we have wasted in our search for audio nirvana?

Hugh- My Fetzilla is nearly done.... maybe by the end of 2012. I am curious to see how it compares with my other high maintenance "children".

Low cost and easy to repair circuits that sound good is now very much on my agenda.


Regards

Jozua