F5X -- the EUVL Approach - The Build Thread

Please check also the line of the alternative Caddock source resistors. I thin one or the resistors number is not correct.


But I wanted to ask you another question: I am selecting the JFets. In the BOM 6.6 and 7.2 Idss are indicated, but this does not match with the formula you posted in the F5 thread. Or you are using a different value for Yfs.

Additionally, how close should the match be? It's not so easy to find BL at that Idss, we may want to look on GR with high Idss.

D.


Quoting:
Idss (2SJ74) = Id * (1 + Rs*Yfs)
where Id = Idss of the 2SK170 in this case; Rs =5.1R; Yfs = 0.033 S for 2SJ74 at that bias range

Some sample calculations:
2SK170=7mA
6mA(1+5.1*0.033)=6.0mA(1.1683)=7.01mA for 2SJ74
6.5mA(1+5.1*0.033)=6.5mA(1.1683)=7.59mA for 2SJ74
 
I have mailed Dave about the mistakes but he has not read my mail yet.

> In the BOM 6.6 and 7.2 Idss are indicated, but this does not match with the formula you posted in the F5 thread.

The formula is an approximation assuming Yfs is constant.
But Yfs varies both with Idss and actual Id.
You can put in the entire full JFET model equation to calculate if you wish to be more exact.

> Or you are using a different value for Yfs.

These are also only typical figures. Real FETs have different values.

> Additionally, how close should the match be?

I have also published a table listing various values of Idss for both FETs.
The easiest way to match, if you have many JFETs, is to actually use a 5R1 degen resistor, gate to Gnd and measured degenerated Id for the J74s.

How well match depends on how much even harmonic cancellation you want between top and bottom halves.
It also depends on how well match the MOSFETs Vgs at 2A are.
In practice you want as good cancellation as you can get from top to bottom, and let the left / right take care of what is left.
This is the advantage of the balanced F5 and has been discussed multiple times in more detail elsewhere.

It is much easier to get left-right match then N-P match.
So don't go too extreme on this.


Patrick
 
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> In the latest schematic of the F5, I think our R12, R13, R30, R31 was 22k, instead of 10k.

It is because the standard F5 use 24V rails instead of 16V.
You can go to the original NP article on F5 to dig out the maths how to calculate this.
My original protos has 10k, so I stick to that.

> Did we do any thought on this ?

Of course. Nothing are left to chances.

> I know, it's a minor thing.

We try to be correct, as many people are copying, and consequences of mistakes are costly, for you and for us.


Patrick
 
How to measure J74 has already been described in the 3-point match document.
But here is it again :

PSU 0V to -13V (or -16V, does not matter so much). Important is negative supply for P-FETs.
Gate of J74 connected to 0V (via an optional 100R resistor).
5R1 connected between 0V and J74 source.
J74 Drain connected to -Vs.

Measure current Id.

If still not clear then post a schematics and I shall let you know if correct.


Patrick
 
Patrick,

Business demands seem to keep my responsiveness here slow. My sincere apologies.

I will check all of the questions posted and update the BOM with corrections or clarifications where needed.

Information for measuring JFETs is here. The chart with details for selecting various JFET Idss values and the corresponding degen and drain resistors is here.

I'll post the bias article for those who need it already here ASAP.



Dave
 
I started today mounting the amplifier, and probably this are a dumb questions:

-K1530/J201 (close to unobtainium) or K3497/618 (I have the GB set)?.

-Cascode or not? (16V supply)

-Optional Protection Circuit or not? (Main amplifier board)

-CRC or regulated?.

-Anybody have the R45, R46 for sale? (SUSUMU 5R1 OHM 0805 SMD 1%), the minimum in Mouser are 5000 units

Probably this questions had a answer in the multiple threads, but I'm very doubtful. I'm sorry in advance.

Cheers
 
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Joined 2009
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> K1530/J201 (close to unobtainium)
In a week or so I will be posting good news with respect to the unobtaniun. Please follow this thread.

> K3497/618 (I have the GB set)?.
These are for the regulated supply. In the works. Keep.

> Cascode or not? (16V supply)
Not. Benefit not fully tested at this moment. In the works.

> Optional Protection Circuit or not? (Main amplifier board)
Your call I guess......

> CRC or regulated?.
CRC until the new regulated supply has been fully tested.

> Anybody have the R45, R46 for sale? (SUSUMU 5R1 OHM 0805 SMD 1%), the minimum in Mouser are 5000 units
Ask ashaw. There is a GB for small components and I believe this is one of them.
 
> K1530/J201 (close to unobtainium)

You will be catered for by 3 gentlemen who have taken on this enormous task of procuring 1000 FETs and matching them by curve tracing at 16V 2A 60°C.
Just count the hours, say 10 minutes a FET.

> K3497/618 (I have the GB set)?.

Keep them for now. The first tester who tried both prefers K1530/J201 in the amp.

> Cascode or not? (16V supply)

If you have to have an answer today then cascode.
But since you can add it in later easily, I would build standard to start with.
Why spoil your joy with experimenting progressively ?

:)

> Optional Protection Circuit or not? (Main amplifier board)

If you ask me definitely.
I have expensive speakers.

> CRC or regulated?.

CRC until the new regulated supply has been fully tested, as Nic said.

The first tester also preferred Regulator.
But he is going to build it all in the case and report later.
How late depends on his workload. But the regulator sinks are expensive.

Again since this can be upgraded later without too much work, why not start with CRC first ?

> Anybody have the R45, R46 for sale? (SUSUMU 5R1 OHM 0805 SMD 1%), the minimum in Mouser are 5000 units

Not true.
You can get 1 piece also :

DK #RL12S5.1FCT-ND 0.29 Euro a piece.



Patrick
 
May I suggest you post at the GB thread with your measurement of all 8 resistors, plus details of the equipment and method used.

This issue is a GB issue which is best sorted out at the GB thread.
It probably will have a better chance also of drawing the attention of the right people who can resolve this.


Patrick