F5 Cascoded - an alternative for my interest in the Balanced F5

[NYCOne]

I was a big proponent of the Balanced F5 effort (Balanced F5 question see post #1). Being new to DIY Audio, I was interested in various permutations of possibilities around the F5. My neophyte status worked against me, I didn't know what was feasible vs. foolish.

As the Balanced F5 effort started, I was hopeful there would be a wealth of information from the experts on the trade offs of different building strategies. Unfortunately, that thread has become a private club effort, with little information for those of us just trying to build the amp.

Moving right along - I decided to try a cascoded F5. I have VGS matched IRFP and Toshiba outputs. I hope to try both. As a start, I:

1. Got out some PCB
2. Etched a cascoded circuit (based on NPs comments on how to set up a cascoded F5)
3. Stuffed the boards (Mosfets, caps and trimmers to be added shortly)

Now I'm trying to decide on rail voltage. I have a 22v transformer I'll try for testing (~30V rails), but that doesn't get me any real change from the stock F5. What are the limits for rail voltage folks have encountered in the cascoded F5? I was hoping to use 2 outputs on each side of PP circuit and bias a bit higher than the stock F5.

Thanks

[tinitus]

Originally Posted by NYCOne

I have a 22v transformer I'll try for testing (~30V rails), but that doesn't get me any real change from the stock F5.

ah, but the trick is that it doesnt change anything or should I say, doesnt ruin it

I think 22V is a good choise, with the cascode
and thats what I am going to use
It gives you 30V rais, and I know for a fact that 30V makes a surpricingly powerful amp
monos ofcourse, and with good heatsinks
I will try to do this with one output pair, and cross my fingers

my point is, I can run a single output pair into 2ohm speaker with 30V rails, in classAB
but its dissipating similar power into lowest impedance
but no guarantees
and I will use only cheap and easily available non matches outputs

well, maybe 25V trafos would work to
but I wouldnt go higher than that
everything just gets bigger and harder to handle, with little gain

anyway, who says it needs to be full classA all the way
maybe it will be fine having 40watt with "just" 20watt in classA

[Nelson Pass]

The trick in cascoding the F5 would be to use some nice
bipolar devices and see to it that their Bases see a low
impedance at high frequencies. Nice big caps to ground
would do it.

[flg]

Originally Posted by NYCOne

I was a big proponent of the Balanced F5 effort...

Hey, sounds like you still are...

Originally Posted by NYCOne

Being new to DIY Audio, I was interested in various permutations of possibilities around the F5. My neophyte status worked against me, I didn't know what was feasible vs. foolish.

As the Balanced F5 effort started, I was hopeful there would be a wealth of information from the experts on the trade offs of different building strategies. Unfortunately, that thread has become a private club effort, with little information for those of us just trying to build the amp.

Wowa, why do you say it worked against you? This is a forum with all the typical give and take, social, technical, high level, low level, etc. etc... You admit your new and I sense some desire to learn or you would not still be here. No one person is in control of anything here, not even N.P. himself. Starting a thread does not mean you will get what you want, or the thread will even continue on the tract you intended. It just means you are part of the group and contributing. Even by only asking questions. Do you realize how many people could have had the same questions but couldn't, wouldn't, or didn't ask? Now we ar all getting the benifit of you starting this thread.
There is a wealth of information here about F5. Both in the Balanced question and the original thread. I realize you can spend weeks reading the 1000 odd posts in the original but it's worth it.
As far as the private club Yes it does appear that Patrick and the "developement team" have taken over. But, that was a direction other participants thought was interesting and I don't think that is so bad or even OT. Patrick is a very intelegent, highly educated individual who works in the very high tech world along with being a decerning audiophile and participant like you and me. And I believe, one of those experts. Trouble is, he dosent want to become the center of attention, answering questions and helping the hundreds of poeple who see the value in what he has done but can't quite do it themselves. He has generously offerd to organize, develope, design etc. etc. a system that will undoubtedly be a most worthwhile project that everyone can likely achieve success with. He seems to be running it like a project at work but, that's Patrick I guess. It's not the most comfortable but, I see the value in what he's doing. There has been much discussion about some parts of the project and the why's and how's already. There is much more to come when it is ready to publish as he would say. It's not a private club, it's a developement period focused on a permutation of the F5 for the forum to enjoy.[/QUOTE]

Originally Posted by NYCOne

Moving right along...

Originally Posted by NYCOne

Now I'm trying to decide on rail voltage. I have a 22v transformer I'll try for testing (~30V rails), but that doesn't get me any real change from the stock F5. What are the limits for rail voltage folks have encountered in the cascoded F5? I was hoping to use 2 outputs on each side of PP circuit and bias a bit higher than the stock F5.

Hey, I'm going to use 2 Pair of the Tosh parts with higer bias also but, somewhat like Patrick has done, I'm going down to 20V rails as I'm actually driving 2 ohm (nominal)speakers. I don't think I'll go the cascode route on this one though.
30V rails should get you close to 50WRMS out! That's not enough?
I have to say though that N.P. has pointed out there are subtleties in this design that can be lost by changing things to much. I really can't tell you if 30V rails or cacoding will be that much of a change or not but, those little develish subtle details are why the original version is so good.

Originally Posted by NYCOne

Thanks

Thanks, I suppose I need to go find my dictionary Hugh?

[Bksabath]

NYOcone

Dear friend I can only say that I know how you feell

100 % agree with you

I was part of that club but soon found that it was a weri wrong place where to be.

As you I am new to power amplifiers and it all atarted with same question.

Apart from a few all you sems to get is go and read this and that or just plain cucus that sems to change as the wind blow.

I beter report this as maybe somebody get ofended and get me in the sin bin.

Cascode lets see Papa say bipolar and no problem with that

But dont forghet to chek out Erno Borbelli (sorry is spelled wrong).

There was a published design on the F5 tread worth looking at.

As you I wil push the boundaries trriple balanced 28V rails

As said before I am new to this so I can't suggest that your traffos be alright

But Papa said they are a bit thogher than the manufacturer told as

I posted recently on the F5 tread that I am looking for speaker protection

The speakers I have are 4 ohms nominal.

Anything I can do just let me know

PM maybe?

Don't get worked up and get building you not the only one....

[Zen Mod]

there are at least 4 cascoded F5 schematic posted , all of them pretty much similar .....

dunno - I think that AR2 even tried this one

I didn't , but I can't see why it shouldn't work

( full blast voltage version really needs few values/parts endurance confirmation)

[Bksabath]

Hi Zen

Tanks for the reashuring words if you say you can't see why it shuld not work I will take the liberty to translate that as it will.

Not by any chance that you will tell us what tose pats may be.

It would be really appreciated.

Many tanks in advance.

[NYCOne]

I laid out the PCB exactly following your cascode recommendation (attached). I have BC546 and BC556 doing the cascode (awaiting BC550 and BC560 - though I don't know if the noise is an issue) as well as standing in for the Zetex parts. The only change I am making is I am planning to use a 220uF 50V Panasonic electrolytic cap (I don't have a 10uF cap around at the moment).

I'm not sure I follow the "caps to ground" - I have the caps where your diagram suggests. I can change this if I misinterpreted your figure.
Regarding rail voltage - how high do you think sensible?

Thanks again

(Edit) I think I understand - use the bipolars as outputs, right?

Originally Posted by Nelson Pass

The trick in cascoding the F5 would be to use some nice
bipolar devices and see to it that their Bases see a low
impedance at high frequencies. Nice big caps to ground
would do it.

[NYCOne]

I understand your points, but disagree on some.

The issue I have with the "Balanced" thread is one of exclusion. Certainly no one wants to be an unlimited free resource, but it often takes no effort to answer real questions when compared to obfuscating an answer in the name of being an expert.

When someone asks you "What time is it?" you can either answer "10:30" or start explaining how the earth orbits around its axis and what a solar day is. One is fast, accurate, and serves the intended purpose; the other is intellectual snobbery.

Originally Posted by flg

Hey, sounds like you still are...

Wowa, why do you say it worked against you? This is a forum with all the typical give and take, social, technical, high level, low level, etc. etc... You admit your new and I sense some desire to learn or you would not still be here. No one person is in control of anything here, not even N.P. himself. Starting a thread does not mean you will get what you want, or the thread will even continue on the tract you intended. It just means you are part of the group and contributing. Even by only asking questions. Do you realize how many people could have had the same questions but couldn't, wouldn't, or didn't ask? Now we ar all getting the benifit of you starting this thread.
There is a wealth of information here about F5. Both in the Balanced question and the original thread. I realize you can spend weeks reading the 1000 odd posts in the original but it's worth it.
As far as the private club Yes it does appear that Patrick and the "developement team" have taken over. But, that was a direction other participants thought was interesting and I don't think that is so bad or even OT. Patrick is a very intelegent, highly educated individual who works in the very high tech world along with being a decerning audiophile and participant like you and me. And I believe, one of those experts. Trouble is, he dosent want to become the center of attention, answering questions and helping the hundreds of poeple who see the value in what he has done but can't quite do it themselves. He has generously offerd to organize, develope, design etc. etc. a system that will undoubtedly be a most worthwhile project that everyone can likely achieve success with. He seems to be running it like a project at work but, that's Patrick I guess. It's not the most comfortable but, I see the value in what he's doing. There has been much discussion about some parts of the project and the why's and how's already. There is much more to come when it is ready to publish as he would say. It's not a private club, it's a developement period focused on a permutation of the F5 for the forum to enjoy.

[ashaw]

I happen to be a member of that "private club" and I can say that it is not as exciting as you think it is. All of the schematics are either public relatively straight forward or could be dangerous in the current state. We are just not very fast and are working on our own. There is just not that much to see.

Alexis Shaw