Balanced F5 question

NYCOne

Member
2010-07-13 6:27 pm
I've asked a few times in the main F5 thread, but I didn't have a schematic. I put together a rough sketch of my question on the attachment.

Briefly, I have a standard F5 set of parts, and I'm interested in whether two boards can easily be converted to one balanced channel. I've seen Patrick's balanced F5 schematic, but he uses the Toshiba outputs, I have the IRFs.

Can the attached setup work without substitution of a lot of resistor values, or is the effort more complex?

I'd appreciate any input, as modeling circuits is well beyond my abilities.
 

Attachments

  • Potential Balanced F5.pdf
    192.9 KB · Views: 1,807
Oh Sh..., Oh dear, is allowed.
I noticed that I had misread your partially inverted pdf. I intended to come back with an "oops" and ask you to explain what was happening to the two sides of the inputs.
But, I forgot. Sorry!

If the left side is restored to non-inverted, then the two new links get twisted to form the X, that is part of this balanced arrangement.
If you draw that part with the X and with both sides non-inverted, how does your proposal compare to the other examples of balanced topologies? I think there are about 4 ways to make this balanced work.
 
The balance topology is basically correct.
As shown, it delivers its full power for a 15 ohm load.
If you have a lower load impedance, then you are not using the rail voltage to the full, and you could have used with more current.

This is why the circuit I published has 16V rails and 2A bias.

But it will work.
And I suggest you ground the intersection of the "X" to start with, trim everything properly, before you float the X for final trimming.


Good luck,
Patrick

PS This balanced circuit requires a balanced input signal.

.
 
......And I suggest you ground the intersection of the "X" to start with, trim everything properly, before you float the X for final trimming.
is this your recommended setting up procedure?

Ground the X and set up the amp resistors/currents.
Then unground the X and trim to final currents/offsets?

If ungrounding shows up an error, can we read the errors to work out where they are coming from and make circuit adjustments to correct the circuit errors, eg. change the value of a source resistor rather than simply trim out an offset.
 
Last edited:

bobodioulasso

Member
2008-05-02 12:06 am
Balanced F5 new question

Is it reasonable to power a balanced F5 using a single supply?
As the ground in F5 concerns the input only, i mean there is no decoupling cap, and as i am the happy owner of several 25v beautiful german potted transformers (from shuro)
I contemplate to do so.
Though, as i will risk expensive matched 2sk 1530/ sj201 and i have no spare, i would prefer to be shure first.
 

Attachments

  • F5X.JPG
    F5X.JPG
    16.4 KB · Views: 1,755
Yes, the advantage of a balanced circuit is that it draws near constant current from the PSU even when drying heavy load. I would not do it any other way (than supplying the two halves with one PSU and one Cap, as you have drawn).

BTW Schuro Tx are not really the best you can get. And single point matched k1530/J201 are not that expensive (about 100 Euros for 8).

But to make full advantage of the balanced circuit, you should consider :

1) dropping voltage to 20V or below and increasing bias current to at least 2A per FET (and watch dissipation max 32W per FET);
2) implementing the 5R degeneration trick on the J74 if you use Toshiba MOSFETs;
3) dropping the MOSFET source resistor value to 0R22;
4) using the Xed version of the balanced circuit.

Nothing new, all published before over the F5 thread.


Patrick
 
Last edited:
Thanks, Patrick, for your fast reply.

I have been following the F5 thread since the begining and ( i believe) I am aware of your recommendations.

1) dropping voltage to 20V or below and increasing bias current to at least 2A per FET (and watch dissipation max 32W per FET);

I think you mean per rail.
As i will be using single 25v Ac transformers ( paralleled windings), i will get about 33v DC rail to rail, which corresponds to your schematic.

BTW Schuro Tx are not really the best you can get.

:( Are they so bad? They seem to be silent nevertheless. They are screened too. What is their issue? Regulation?
 
Last edited:
Schuro is OK for the price, but they are not using oversized cores for the rating, which is what you want to do for Class A.

We took the plunge and bought a few Piltrons recently.
They are really very well made. Whether they are worth the money is up to you.

Otherwise we use the same supplier as Peter Daniels.
Not perfect (mistakes with wiring now and then), not cheap, but amongst the top 3 we have tried.

And for real audio use, you should not encapsulate with porting compound.

For the balanced F5, you consume 130W. So 500VA minimum.
We use 650VA for ours, per channel that is.


Patrick
 
Last edited:
OK, I have a soft spot today.

For those of you who want to build the balanced (Xed) F5 using my circuit (i.e. Toshiba MOSFETs), here is a one-time offer.

If you can :

1) get approval from Nelson for a PCB offer from the DIYA forum;

2) convince the moderators of the forum to take care of the sourcing and sales of the "EUVL Xed-F5" PCB,
in the same fashion as the other single ended F5 Design;

3) find someone who can convert my design from Autocad to Gerber;

4) find someone to volunteer to build the first proto based on the PCB offered
(to debug and to take over answering questions for the building process later),

then you can get that person in (3) to contact me so that I can give him instructions of how to layout the PCB as per my current design, plus component placements and bill of material, etc.

The following preconditions apply :

a) Sales only through DIYA, and profits donated to the forum.
b) I retain the rights to the layout.
So the Gerber files are only known to me and the DIYA forum.

When you are ready, send me a PM. ;)


Good luck and happy building,
Patrick


PS This balanced circuit requires a balanced input signal.
 
Last edited:
We took the plunge and bought a few Piltrons recently.
They are really very well made. Whether they are worth the money is up to you.

I think Plitron = Amplimo in Europe. Please correct me if I'm wrong.
I do have an 800VA Amplimo trafo. They're not cheap (far from) but mine looks and feels beefier than most 1000VA ones I've seen from random suppliers.

As for your offer, I really hope it goes through!
Unfortunately the only help I can offer is to cross my fingers and commit to buy the boards once they become available.
 
Last edited: