Preamp ideas for F5

[juma]

Originally posted by stein2

....
Edit: So, one question about this one: http://www.diyaudio.com/forums/attac...amp=1221762706
Do I have to match the SK170 to pairs for this... ?

Matching is always nice in LTP, although not mandatory. At least take care that both JFETs belong to same Idss group (BL, V or GR). I used V flavour, but if you choose JFETs with lower Idss, you'll have to adjust CCS' output current, as well as drain and source resistors.
In fact you'll have to recalculate it all over again
Ok, tell me what JFETs you have (Idss) and I'll do it for you

[stein2]

Originally posted by juma



Matching is always nice in LTP, although not mandatory. At least take care that both JFETs belong to same Idss group (BL, V or GR). I used V flavour, but if you choose JFETs with lower Idss, you'll have to adjust CCS' output current, as well as drain and source resistors.
In fact you'll have to recalculate it all over again
Ok, tell me what JFETs you have (Idss) and I'll do it for you

Thanks for being kind and nice, but you can't help me much around it because I don't have other 2SK170 than the two in the F5

Locally, none of the shops that sell this stuff (Elementa, Lunar etc) don't even have them listed, have to order from Farnell, wait a month or at least two weeks (best case) and somehow I hate to wait for weeks for parts that cost next to nothing. That is why I keep being stupid and have to beg for change... I prefer buying on the spot, have the money, want my stuff...

[juma]

Maybe this one, with BF245C:

http://www.diyaudio.com/forums/showt...57#post1572057

http://www.diyaudio.com/forums/attac...amp=1217283456

you'll be surprised

[dodo]

How about this one
feedback resistors 750R and 2k21 gain 12dB

[stein2]

Originally posted by dodo
How about this one
feedback resistors 750R and 2k21 gain 12dB

And make an order for 100 of each 170/74... (that would reduce the waiting time per fet...

[coloradosound]

Originally posted by dodo
How about this one
feedback resistors 750R and 2k21 gain 12dB

Like a variation of the Denon DAP-5500 Unity Gain Interface
Buffer stage with voltage gain input stage!

[twitchie]

Originally posted by juma
Bored by a rainy day I decided to try JFET-CCS-BOSOZ (schematics in attachment) as a preamp for F5. Yes, it has 1k Zout, but that's without significance when driving F5 (100k Zin).

2SK170 are of V type (12mA Idss). CCS gives 20mA. Gain is 6dB (2V/V).
+/- 18V PS is made from F5's PS by means of 7818 and 7918.
Output cap is 1uF MKP + 100nFMKS and it doesn't leave any imprint that I'm aware of.

Preamp is very neutral, nothing is changed in music presentation compared to F5 without preamp, signal is just amplified to level that drives F5 to full power.

I don't know if I like this preamp more than previous one, it's in nuances, so it will take more listening to make a decision. Anyway, circuit is simple, parts are easily obtainable, topology is nice, F5 is light load, it's simple enough to make it p2p, and this preamp sounds better than its' cousin with MOSFETs - what more could a man want to give it a try ?

Will BL grade work here or just become another Choky and Oly Fuse Killer?

[juma]

Originally posted by twitchie

Will BL grade work here...

Yes, it will work. But...
Let's say you have JFETs with Idss=8mA. You'd want CCS to supply 12 mA, so R5 should be 56 R. R8 and R3 should be 1k5. R1 and R2 will determine the gain, higher R => lower gain. You can read a lot about it in Mr. Pass' articles (BOSOZ and such) with difference that he used MOSFETs (enhanced mode devices) but you can also find a lot of readings about JFETs on E. Borbely's site.

[Zen Mod]

Originally posted by juma


Yes, it will work. But...
Let's say you have JFETs with Idss=8mA. You'd want CCS to supply 12 mA, so R5 should be 56 R. R8 and R3 should be 1k5. R1 and R2 will determine the gain, higher R => lower gain. You can read a lot about it in Mr. Pass' articles (BOSOZ and such) with difference that he used MOSFETs (enhanced mode devices) but you can also find a lot of readings about JFETs on E. Borbely's site.

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

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

under 10E/100pcs

[juma]

Originally posted by Zen Mod


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

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