Power supply specifications
Hi Juma,
i assembled the negative rail and has a voltage of -4.75 V dc at the output. Is this acceptable?
I like the power supply very much and made another one for my dac that requires 18V dc. The dc after rectification is only 22V and after the salas shunt i have a 18.8 V . There is only 3.2 V difference .
Can this shunt work well ?Sorry, I do not have a scope to tell.
Thank you in advance .
kp93300
Hi Juma,
i assembled the negative rail and has a voltage of -4.75 V dc at the output. Is this acceptable?
I like the power supply very much and made another one for my dac that requires 18V dc. The dc after rectification is only 22V and after the salas shunt i have a 18.8 V . There is only 3.2 V difference .
Can this shunt work well ?Sorry, I do not have a scope to tell.
Thank you in advance .
kp93300
I received a request for version of this preamp that uses 2sk170BL (Idss about 9mA). Right now k170 is easy to get and BF862 is a SMD component (not convenient for old hands and eyes 
), so here is the schematic.
The gain is a bit higher (9 dB) and the PSU is a bit different (be exact with input DC voltages +28V and -8V).
), so here is the schematic.The gain is a bit higher (9 dB) and the PSU is a bit different (be exact with input DC voltages +28V and -8V).
Attachments
Wheat flour is a basic part of the recipe anyway and spicy coconut flour was left out unsubstituted.
It looks like we don't have an analogy with this preamp ...
Wow, thanks I think I will try this. Do the sk170 jfets need to be matched?
Are you saying this needs its own power supply, or is it fed off the existing one?
Russellc
If you are talking about gain stage from post #286 it's just one JFET per channel, but both channels should be same.
It needs -3.3V and +24V (both very, very clean, the neg. rail especially).
Gain stage is designed to use 2sk170BL with Idss about 9mA (8-10mA). Voltage of neg. PSU is chosen for amount of gain we aim for and Idss of JFET at hand. That determines the Rs and Rd too. I always aim for Id between 70% and 90% of Idss.
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yes, this is the one...I see only one fet, I was getting confused, that question concerns the BF862 preamps SK170s. sorry.
The one shown for the Preamp the thread concerns (BF 862) appears to be perfect for it? Post# 283
Russellc
PSU shown in post #283 is something that I use lately. I like it very much. You can use whatever PSU you like providing that voltages are right and noise is low.
The surface mount JFETs can be placed on the Radio Shack prototyping boards a la:
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Of course. I even didn't have much trouble to solder the leads on, but many people find handling this part difficult.
An externally hosted image should be here but it was not working when we last tested it.
The radio hack breadboard solution shown by jackinnj looks like a no-brainer. No doubt one could find better quality proto-boards (epoxy-glass with decent copper thickness and some plating on the pads) with similar characteristics (E-pay?). The big sticking point with me for these BF862 parts has been some sort of jig that would allow me to sort for Vgs vs Id without losing my mind. There are several Far East Ebay sellers offering a "clamshell" type" 6-pin SOT-23 socket for a logic device programmer of some sort. The price is about half of what a clamshell socket generally sells for in these parts, and a 6-pin SOT-23 socket fits the standard 3-pin part just fine. I ponied up and got one of them - the fit and finish is not quite as nice as the domestic product, but it still works just fine. Expect some BF862 projects from me some time down the line (but not right now, please).
Juma, I got my BF862's today. All I could do was laugh. Anybody who works with those little things regularly should be commended. Oh Yeah, I got 30, but i don't think that was enough.
Piece of cake...
This one was a bit tougher, i used just a simple 15W Weller soldering iron...