Hi Everyone,
Wow you guys are on the ball! Yes, the review and Nelson's write up now appear on Enjoy the Music.com. i spread them between the two magazines as it will come built/assembled (Review Magazine) and as a kit (new DIY Magazine). Links were posted on this thread, though to keep it simple:
Review Of Assembled Unit:
http://www.enjoythemusic.com/magazine/equipment/0708/first_watt_b1_preamplifier.htm
Nelson Pass' Write Up For DIY Magazine:
http://www.enjoythemusic.com/diy/0708/first_watt_b1_preamplifier.htm
BTW: i am STILL HIRING writers for the DIY Magazine. And YES you WILL be paid for your efforts. If interested, e-mail me at Rochlin AT EnjoyTheMusic DOT com with the subject being all caps DIY WRITER INQUIRY.
Many thanks and my hopes are to spread the word of the joys in DIY, s my first 'day job' was working for Heathkit Electronics many years ago
Thanks again and as always, in the end what really matters is that you...
Wow you guys are on the ball! Yes, the review and Nelson's write up now appear on Enjoy the Music.com. i spread them between the two magazines as it will come built/assembled (Review Magazine) and as a kit (new DIY Magazine). Links were posted on this thread, though to keep it simple:
Review Of Assembled Unit:
http://www.enjoythemusic.com/magazine/equipment/0708/first_watt_b1_preamplifier.htm
Nelson Pass' Write Up For DIY Magazine:
http://www.enjoythemusic.com/diy/0708/first_watt_b1_preamplifier.htm
BTW: i am STILL HIRING writers for the DIY Magazine. And YES you WILL be paid for your efforts. If interested, e-mail me at Rochlin AT EnjoyTheMusic DOT com with the subject being all caps DIY WRITER INQUIRY.
Many thanks and my hopes are to spread the word of the joys in DIY, s my first 'day job' was working for Heathkit Electronics many years ago
Thanks again and as always, in the end what really matters is that you...
vdi_nenna said:
Hi!
IMHO i am not so sure about that recommendation. I would chose a Idss for the current sink that is a few mAmps lower so that the upper one is running a bit under its Idss, this to avoid gate current. Since Nelson is using a coupling cap there is no need to worry about a few mV DC on the output.
BR,
Anders
bappe said:
Or use source resistors on both devices, as is usually done with this topology. That way you can take quite a lot of input voltage before the PN junction becomes forward biased even with low impedance loads. Borbely recommends 22 Ohms, if I remember correctly. In my buffer I use 10 Ohms as John Curl recommended. Actually, I am curious why Nelson doesn't use any source resistors.
I also do not have any series output resistor, but perhaps a smallish one, like 50 or 100 Ohms, would be good considering the RFI discussions in the Blowtorch thread. I also use dual 18 V supplies so there is no need for an output cap if matching the JFETs. I think the DC offset was under 2 mV on both channels when I last measured.
Having enough series resistance between input and gate so one doesn't exceed the max gate current of 10 mA with highest possible/probable input voltage if the junction is forward biased by accidentily shorting the output might be a good idea.
BTW Nelson, I used the spare hole for a LED instead of a switch on my buffer.
Thanks for the response/explanation/conjecture guys. I ended up buying some matched from tech-diy. Then the mail came today. I got a notice that a package from China is sitting in the post office for me. I had given up on them, but as Murphy would have it.. this package has matched 2sk170's in it. Ordered the rest of my parts and a tiny regulated wall wart from DigiKey today. Will use the two 50k pots I have hooked into my ChipAmp for the B1 and should be in business to use this to drive my drive my ChipAmp and F5 soon
Loved the new chipamp I built so I am sure to fall over when I hear the F5
Loved the new chipamp I built so I am sure to fall over when I hear the F5
Hi,
I was wondering if it would be more convenient to use a dual power supply, +-9 v . This is because it seems easier to 'transform " this buffer into a first or a second order active crossover if it uses a dual PSU.
If so, R2, R3, R103, R203, D1, C2 and C3 would be removed. A resistor would be attached from the gate of Q100 (Q200) to ground, and, if you want to make a 1st order high pass filter, C100 (C200) could be scaled down for a specific frequency. For a second order high pass filter, I would add another resistor going from the source of Q100 (Q200), then to the front of C100 (C200), plus one more cap...(you know the topology of the second order high pass filter).
Please let me know if this idea doesn't work...
Regards,
Vix
I was wondering if it would be more convenient to use a dual power supply, +-9 v . This is because it seems easier to 'transform " this buffer into a first or a second order active crossover if it uses a dual PSU.
If so, R2, R3, R103, R203, D1, C2 and C3 would be removed. A resistor would be attached from the gate of Q100 (Q200) to ground, and, if you want to make a 1st order high pass filter, C100 (C200) could be scaled down for a specific frequency. For a second order high pass filter, I would add another resistor going from the source of Q100 (Q200), then to the front of C100 (C200), plus one more cap...(you know the topology of the second order high pass filter).
Please let me know if this idea doesn't work...
Regards,
Vix
Following previous discussions on diyaudio I think this is not strictly true. You can forward bias this particular JFET to between +0.2 and +0.3. Volts, depending on chip temperature, before you see any significant gate currents, and running the JFET at full IDSS appears to be about optimal.
third small blue colour capacitor
Hi friends,
I just look into internal photos of B1 ( attached on enjoythemusic web site - review ) and I see third small ( blue colour ) capacitor laying between both channels in the middle of the PCB. His two traces coming directly into direction of both 2SK170 transistors on right channel. One leg of this small one connect probably GATE in first transistor and SOURCE in other one. I don`t see such small capacitor on attached circuit diagram !
Hi friends,
I just look into internal photos of B1 ( attached on enjoythemusic web site - review ) and I see third small ( blue colour ) capacitor laying between both channels in the middle of the PCB. His two traces coming directly into direction of both 2SK170 transistors on right channel. One leg of this small one connect probably GATE in first transistor and SOURCE in other one. I don`t see such small capacitor on attached circuit diagram !
Do not judge a book by it's cover.
The B1 schematic does contain 3 of the Beyschlag MKP416 caps.
Although the 1uF value only comes in 15mm lead spacing, it's safe to assume it has it's leads soldered to pads at the bottom and not at the top.
The one you see is a ground trace, the gate of the bottom JFET connects to it, as does bypass cap C3 of the voltage divider.
Which makes the second trace the one that supplies the 9Vdc to the gates of both input JFETs through the 1M resistors, and why the 2 traces run between both channels.
The B1 schematic does contain 3 of the Beyschlag MKP416 caps.
Although the 1uF value only comes in 15mm lead spacing, it's safe to assume it has it's leads soldered to pads at the bottom and not at the top.
The one you see is a ground trace, the gate of the bottom JFET connects to it, as does bypass cap C3 of the voltage divider.
Which makes the second trace the one that supplies the 9Vdc to the gates of both input JFETs through the 1M resistors, and why the 2 traces run between both channels.
Jacco is right: most probably the loonely blue cap in the middle of the borad is C3. Good idea to place it closer to the Jfet: it lowers the impedance of the tracks.
It looks like Nelson uses (at least in pictured unit) some BC polyester (mylar) caps for C3, C100 and C200 even if in the article he suggested some BC polypropylene ones for C100 and C200 (according to the Digikey part number).
The latter are grey instead of blue and much bigger (15 mm leads spacing instead of 5 mm).
I don't think the polypro caps are soldered underneath.
It looks like Nelson uses (at least in pictured unit) some BC polyester (mylar) caps for C3, C100 and C200 even if in the article he suggested some BC polypropylene ones for C100 and C200 (according to the Digikey part number).
The latter are grey instead of blue and much bigger (15 mm leads spacing instead of 5 mm).
I don't think the polypro caps are soldered underneath.
