F5(25W) help with parts and design

[captJackSparrow]

F5 Turbo V2 help with parts and design

Thank you all who responded and helped me with ideas and valuable information.

So i am going for F5(25W), since its class A i don't want more watts if i am not going to use those extra watts. I'll be using some of the hardware that can be used with F5 turbo in case need arises.

Need feedback here
1. Transformer : F5 needs 300-500VA and F5 Turbo 600-800VA,
i can get 500-800VA locally but which transformer should i go for, what output should i look for that will work with both F5 and F5T?
http://www.toroidal.com/toroidal-transformers2

 

[Zen Mod]

for standard F5 power range (25W/8R) , you need xformer with two separate 18Vac secondaries

for Turbo - look in article

separate econdaries are intended for 2 bridge per xformer arrangement , which is sort of better than 1 bridge/center tap approach , which is sensitive to unequal load on secondary halves

when purchasing , give a note that xformer is intended for A class amp , loaded constantly with 160VA (in case of one xformer/PSU for both channels )

 

[captJackSparrow]

thankyou Zen

F5 its 18V(2 separate secondaries)
For F5Turbo its 24V(2 separate secondaries)

Can i use 600VA 24V(2 separate secondaries) and use regulation to output 18V?

 

[Zen Mod]

no need for regulation , just use higher rails

start with F5T schematic without diodes in parallel to source resistors (that needs exact Iq , so plenty in sum) , use higher rails , crank Iq according to heatsinks

 

[mbrennwa]

thankyou Zen

F5 its 18V(2 separate secondaries)
For F5Turbo its 24V(2 separate secondaries)

Can i use 600VA 24V(2 separate secondaries) and use regulation to output 18V?

Yes, you can reduce the rail voltage by inserting a voltage regulator. But a voltage regulator will dissipate a lot of power / heat in this position, isn't really necessary (or useful), and may be waste of money; I wouldn't go that route. Use a transformer with the proper specs instead.

 

[Zen Mod]

or , if you are taking custom xformer , ask for secondary taps on 18Vac (with full at 24Vac)

 

[captJackSparrow]

custom with two secondary sounds a better idea.

Thank you

 

[Zen Mod]

and nothing new under the sun

some Japanese amps (mainly with sort of STK IC in OS) had at back selector for 4/8 load - nothing else than selector for secondary voltage tap - full (8R load) or lower one (4R load)

 

[captJackSparrow]

For JFET/MOSFET can anyone please recommend alternative which are easily available on mouser/digikey having same characteristics as toshiba components that use to be available

2SJ108

2SK370

IRFP240

IRFP9240

 

[Zen Mod]

for JFets ,see in Diyaudio store (LSK , B range) , or member spencer for original Toshiba (2SJ74BL/2SK170BL)

regarding IRFP , there is no need for alternative

 

[captJackSparrow]

F5 Turbo V2

Hi,

I am building F5 Turbo V2

1. What wire gauge should i use for all internal wiring(Transformer is 800VA/2X24V secondary)?
2. In F5 Turbo illustration thread what is that red wire called(connected from board input to RCA Jack), can i use any ordinary cable(pair)?
3. How much copper thickness on double sided clad board?

 

[captJackSparrow]

JFET Matching

Hi,

I have 2sk170 BL in range from 9mA - 10mA (closest ones have .2mA difference )
2sj74bl in range 6.5mA - 10mA (closest ones have roughly around .5mA difference)

what i have got from forums is match 2 of each type and then see that 2SK170 is 1mA higher than 2sj74bl, is that correct?

also seeing that difference is around .2 to .5 mA between each type should i start searching for another source for closely matched pair of it will do fine?

Thankyou

 

[AndrewT]

The F5 uses singleton N & P jFETs.
They don't need N:N, nor P matching.

You can select similar Idss between the two stereo channels. But since the two channels don't talk to each other a few tenths of a mA diff in Idss makes no difference.

The Pchannel is reported differently as having a lower transconductance and a higher transconductance than the Nchannel.
That difference in transconductance will affect what Idss you choose for the upper and lower input devices.
Ideally the circuit will perform better if the transconductances and the operating currents match between the upper and lower halves.
Just try similar Idss and test/listen.

 

[captJackSparrow]

The F5 uses singleton N & P jFETs.
They don't need N:N, nor P matching.

You can select similar Idss between the two stereo channels. But since the two channels don't talk to each other a few tenths of a mA diff in Idss makes no difference.

The Pchannel is reported differently as having a lower transconductance and a higher transconductance than the Nchannel.
That difference in transconductance will affect what Idss you choose for the upper and lower input devices.
Ideally the circuit will perform better if the transconductances and the operating currents match between the upper and lower halves.
Just try similar Idss and test/listen.

My apology i should have mentiomed, its for F5 Turbo V2

 

[AndrewT]

you're in the wrong Thread.
this one is titled F5 (25W) help.