Preamp ideas for F5

[buzzforb]

Juma, thinking about your bf862 pre and was wanderin what kind of spread you get with you fet matching. I woul dlike to drop them in my DCB1, but at anything more than about 10mA, i hav eto woory about heat and need degeneration, correct.

[juma]

Buzz, I bought 500 pcs. batch from Mouser and 90% of them are in 13-14 mA range. The rest is 1-2 mA higher or lower.
Since I don't like gate current, degeneration is mandatory (5-10R). I use them with Id of about 10mA at Vds of about 10V so heat is not a problem. Actually I didn't have a single failed BF862 with Pd of 150mW - for more you'd probably have to cool them. A small area of copper at the Gate is enough to keep them coll enough.

[woodturner-fran]

Didn't read all the thread, but a 6sn7 aikido sounds great with the F5.

[chchyong89]

Using juma's post 53rd schematic to draw a buffer with input selectors. Hope he don't mind The size is 56 X 85 mm.

I am curious that should I put each 0.1uF on the voltage rail near to the buffer? Or just one unit 0.1uF on the PSU is enough. 78L05 regulator feeding G6K-2P-5VDC relay with 1n4001, I doubting will this work nicely?

PS:
I am using SK-13D07 slider for selecting input. I wonder if the connections correct compare to datasheet

[TzeYang]

^do you really need the input buffer? ;p The 2sk170 input has high enough input impedance.

[reytnz]

Hi fellow Diyer's

need a little help from my friends'

I have been using my F5 for quite some time now using a SONY digital processor as preamp. Sounds very good I'm happy with the set-up. but would like to try the sound of the TUBE , for cheap. Just to have a taste of what the buzz is all about, I bought a 2nd hand Little dot MK III pre /headphone amp .which is nice using it as a headphone amp. I have measure the DC offset of the tube amp and it's in mV so I think it's fine to connect it to F5 just to quickly check. I was happy I like what I'm hearing.

The next listening session, very eagerly, I turned everything ON, CD player, Tube pre and F5 in that order, I forgot that I need to let the Tube pre to warm-up first and stabilized. DISASTER... in a split second my Fostex BLH speaker fried really good!! cone is stuck and voice coil open circuit. Whaaa!!! Can anybody in the cummunity help me with my problem? I like this tube pre and F5 combination but don't know if it's alright / or a SIN to put a coupling cap infront of F5? what value? Any help is appreciated.

Thank,

Reytnz

[Itsmee]

Originally Posted by reytnz

don't know if it's alright / or a SIN to put a coupling cap infront of F5? what value? Any help is appreciated.

Thank,

Reytnz

Use a good quality 1uF capacitor, and connect a 1M resistor from the cap input to ground.

[juma]

Originally Posted by reytnz

....my Fostex BLH speaker fried ....
... a SIN to put a coupling cap infront of F5? ...

This is what you wrote.
Read it again and you tell us what's a sin and what's a good thing to do?

[Tea-Bag]

That bites, maybe it's a sign to also look for new speakers.

[juma]

Another idea for a nice preamp suitable to drive F5 (post #55 and onwards) :
If You Don't Have a SIT, Fake It...
When used to drive F5, C4can be 1uF and R9=1Meg. For C3 (10uF) I successfully used SMD (0603) COG cap.