BF862 Preamp

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#261
juma said:
Obviously there's a ground loop that affects the -V supply. Chasing it is the only way to go - try different ground connections between DAC and preamp, dividing signal and power ground. When you find the solution analyze the ground path so that doesn't happen again 🙂

BTW, that heatsink on the shunt reg is really too small...
Click to expand...
I managed to get rid of the hum finally, but not with the trafos connected as in post #248 If I shared the negative supply winding with another supply anyhow I connected their grounds I got hum :scratch1:
Anyway, in the meantime I received my toroidal trafo ordered specifically for my application, so the preamp has separate windings and everything is OK now. Super silent, no hum, no noise and it sounds marvelous. I will try with BF862 and J310 in the following weeks.

p.s. It's a bit cumbersome that I need 1.3V from a 36V DC supply so I have do drop a lot of voltage. I use LM317 to pre-regulate to 15V DC then the shunt reg set to 5.5VDC then two LEDs in series to further drop to ~1.3V... life is hard 🙂

Thanks for your help!
 
#264
thanks you

Thanks JUMA and CHCYYONG
I have been using the basic version of the j310 with the cap multipier for the F5 and have thoroughly enjoyed the sound for the past few months.
I read your comments about the salas shunt reg and want to try first before moving on to BF862
regards
kp93300
 
#268
many thanks to all

juma said:
I suppose you are talking about this preamp (disregard the cap. multiplier). If that's so, you should know this too.

Answers:
1) C14 can be anything from 47uF to 470uF and C17 is "the bigger, the better" type.
2) Use good parts from reliable suppliers, but don't waste your money on "Le Boutique Audiophile" nonsense. The value of the coupling cap (C1 in preamp sch.) should be adjusted according to Zin of the following stage - 10uF will cover you down to 10k. Wima MKP 10 or Siemens stacked foil is what I use in that position.
c) yes, 24V AC will do the job. If you go higher than that Q11 will need a bigger heatsink.
Click to expand...

I completed the power supply as described above for the J310 and the sound quality is very good .The improvement is across the board as expected of a good power supply and never expect a single jfet to sound so good. .
I maintain the cap multiplier before the salas shunt .

Is the voltage output form the shunt determined by the zener D3? i am planning to build another shunt for my dac that requires 18 V dc.

Thanks to JUMA especially.

kp93300
 
#270
Cap multiplier for negative rail of the BF 862

Hi JUMA,
I am planning the power supply for the negative rail of the BF862 pre..

I refer to the cap multiplier in this schematic :

http://www.diyaudio.com/forums/attachments/pass-labs/180140-jfet-boz-j310-preamp.png

I want to seek clarification -----
I have to change Q1 to BC558 and reverse the polarity of c3, c5 and C2 ?

Is there a great advantage in building the cap multiplier before the salas shunt ?

regards
kp93300
 
#271
kp93300,
Q1 in cap. mult. can be any high hfe small signall BJT (i.e. BC558c) - take care about Pd.
Yes, cap polarities should be taken care off.
Not a great advantage, just some voltage to burn if your neg. rail has too many volts.
Good luck ! :up:
 
#273
Hi Juma,

npapp initiated a group buy in January, but it looks like he's gone away.

Do you (or anyone else) have any contact to him ?

I would like to set up and organize a new group by for that board, interest, any comments ?

If there is interest, can anyone send me the layout ?

regards Michael
 
#274
Thanks Juma for this preamp.. i was inspired to build my own so i made this layout and already sent it to pcb factory.. I expect to get the pcb this week and hopefully finished building it next weekend..

I'll compare it to my B1 preamp using my F5 amp.. thanks again.

An externally hosted image should be here but it was not working when we last tested it.
 
#279
cap values and BC 548, Bc 560

Hi Juma,
I am starting on the negative rail of the power supply for bf862.
I notice that C2, c11, c10,c19, c13and c16 are all 22Uf.
Can i substitute all these for 47 uF ?

Can i substitute BC 548c with BC 548B and BC 560 C with Bc 560 B.?

Thanking you in advance .

kp93300
 
#280
schematic

Hi JUMA,
Sorry I forgot to post the schematic in the previous mail.
I am following this schematic

kp93300
 

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