B1 Buffer Preamp

Jump to Latest
#301
lineup said:


Lineup - now waiting for the investigations and findings that Mr Pass will do in B2
Click to expand...


Me 2 🙂

I already started messing around with what may become known as B2 😉

Ok, not exactly that, but...

I started with high-pass part of the circuit, because this is what I need for my Open baffle speakers. For the moment, no notch filter, only a 12 db/oct high-pass. I set it up at 80 Hz. (I've experimented with a broad range of frequencies, and between 80-100 Hz seems to work best). The C and R values are calculated using Rod Elliot's ESP calculator: http://sound.westhost.com/project81.htm
The high -pass circuit is very similar to the block that he is using in Project 81, except that the op-amp is replaced by Papa's Jfet buffer. Well, almost. The exception being the current source; since I don't have enough 2Sk170's handy (can't buy them locally), I have purchased some BF245C ones. (Thanks Choky) However, I have to use it with the resistor to set a proper current...
Also, I'll use a split supply, +-9 v for the moment (I am using two 9 V batteries), but If I use regulators, I may most probably use +-12 v (7812 and 7912 Ic regs).

Work in progres...If I am lucky, I may get it done over the weekend...
Will post pics...

P.s. Ot question for Papa: What alignment did you use for you 12 Db/oct high pass? You mentioned somewhere that you had to increase the Q of high-pass to get smoother response?...

Regards,

Vix
 
#304
Originally posted by Zen Mod
just in case - look at Shunty schm for CCS with BF245C
----
measure first Idss of your 170 (at 9V)
then tweak that resistor for BF
Click to expand...

I use plenty of BF245 for current sources (Not for real yet. But in Simulation)

Having a supply of BF245A, BF245B & the mentioned BF245C is well worth it for a JFET designer.
- BF245A at currents of like 1-3 mA
- BF245B at currents of like 4-5 mA
- BF245C at currents of >5 mA

These BF245 are good bargain and fairly low cost
compared to 'waste' 2SK170 and other Super priced JFET for the CCS job (costant current sources)

So, I say to anyone, follow Zen Mod good advice
.. and get yourself some home supply of BF245
to assist your other JFETs in circuit.


Lineup
 
#306
DVBjunky said:
Hi ZenMod,

so if i want to use the B1 in my Aleph J then your schmatic will work with these regulators?

Regulator LM317

Mini-Regulator
Click to expand...


in both cases max input voltage is pretty close to voltage you have in Aleph J - just look at 25V markings on electrolyt caps on both regs you linked to.

anyway - bigger problem is that you can't use any of these for minus leg , because GND is already established on your main cap bank in A J .

if you made AJ , and you can make B1 , then you can make any adequate regs ........ either 317/337 , 7812/7912 or discrete zener followers ........ with pair of two small bjt darlingtons .

hehe - you can even make simple shunt regs with two darlingtons ...... just look somewhere in few Treshold NS10 threads for schematic
 
#307
KSTR said:
No no, it's 13 Euros (US$20, today ;-) for a bag of 25pcs.
And they have 2SJ74 for EUR10, 10pcs., too.
Click to expand...


MRupp said:


The text is obviously in German: the price is per lot of 25 pieces, plus shipment, so 0,67 euro or roughly 1 $ per JFET. I think that is not too bad, especially considering this is a well know local supplier and you still get the original and not any fakes, plus they have J74BL as well.

Click to expand...

Patience please I'm a novice: I know that for Q100/101 etc I need 2SK170BL's (or alternatives) - do I also need 2SJ74's and J74BL's ?
 
#310
DVBjunky said:
Hi ZenMod,

so if i want to use the B1 in my Aleph J then your schmatic will work with these regulators?

Regulator LM317

Mini-Regulator
Click to expand...


here it is - sweet & simple

use any smaller darlingtons , with Pd from 25W up
 

Attachments

  • chokys_darlington.jpg
    chokys_darlington.jpg
    27.1 KB · Views: 3,775
#313
Hi,

I need a bit help with setting Idss...

First, I measured Idss on 170's, using 9 v battery and tying Source to Gate. One of them was 9.4 mA and the other one was 10 mA.
So, I decided that I should tweak the BF245C resistor to give me around 9mA (It was putting put 14.2 mA without resistor). But, here is the problem: I started with 2.2 K between Source and Gate, and got only 1.5 mA. So I decreased the reistor until I got 9 mA. Resistor value was 110 ohms! (2x220 in parallel). It this Ok? :scratch:

Thanks
 
#314
Vix said:
Hi,

I need a bit help with setting Idss...

First, I measured Idss on 170's, using 9 v battery and tying Source to Gate. One of them was 9.4 mA and the other one was 10 mA.
So, I decided that I should tweak the BF245C resistor to give me around 9mA (It was putting put 14.2 mA without resistor). But, here is the problem: I started with 2.2 K between Source and Gate, and got only 1.5 mA. So I decreased the reistor until I got 9 mA. Resistor value was 110 ohms! (2x220 in parallel). It this Ok? :scratch:

Thanks
Click to expand...


why you have doubts in your own measures ?
maybe I mixed thing or two when I told you to start with 2k2 :rofl:

then that CCS string in my case was really for 1~2mA , not 5 :clown:
 
#316
#317
You must log in or register to reply here.
Top Bottom