Preamp ideas for F5

[stein2]

Originally posted by Zen Mod



J310 will work there ...... as a charm

for both Juma & stein - easy and cheap in Su - Elementa

under 10E/100pcs

So, what you say is this would suit F5 as preamp but instead of 2SK170, have to use J310?

[Zen Mod]

Originally posted by juma


I never tried them, but looking at datasheet for Vishay J310 I see Vgs(off)= -2 to -5 V and gm=8mS, so it looks more like BF245 than K170, right ?
But if you had good experience with J310, it's surely worth a try

170V on steroids , in fact

min 8mS,max 20mS


it's good enough for

[juma]

After few months of experimenting here is the circuit that sounds best to me - it's the same topology as the first one in this thread but with BJTs in output and higher Id through JFETs (6ma).
It takes the +/- 24V from F5 (they are both in the same case - F5 as integrated amp) and preamp's OUT is connected directly to F5's input.
I used the PCB from the post #3 of this thread but with some diferent components and values.

[juma]

This is the preamp:

[estman]

Juma,
excellent work. How about MosFet output transistors instead of BJT with lower Source resistors ?

[juma]

Thanks, estman.
Yes, the MOSFETs could be an option if higher output current is wanted. For driving F5, this preamp sounds better with BJTs. I tried IRF610 and IRF9610 - some smaller MOSFETs, like ZVP3306 and ZVN3306 might sound different but they are unobtainable to me.

[estman]

Originally posted by juma
I tried IRF610 and IRF9610 - some smaller MOSFETs, like ZVP3306 and ZVN3306 might sound different but they are unobtainable to me.

Hi juma,
no...no, I thought to use only AUDIO mosfets - Toshiba 2sj313/2sk3013 for higher output current and for lower current (F5) Hitachi 2sj76/2sk213.
I have too many 2sj313Y - can send to you for Christmas if you PM me with your data.
Unfortunately I have no adverse part - you must have possibility to get it yourself !

[juma]

Those are also unobtanium

[juma]

estman, YGM

[apassgear]

Hi Juma,

Why should you need an input cap?

Wouldn't a bit of load at the input be enough?

Cheers,