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Topic: homebrew variable load buffer |
J.D.White
From:
Lafayette, Louisiana
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Posted 24 Nov 2017 2:23 pm |
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If you do a search for Tilman Preamp or Fetzer Valve (runoffgroove.com) - a number of layouts will show up & could easily be modified for this FET based circuit.
There's also a freeware program called DIY Layout Creator (Windows/Linux/MacOS). It allows you to do layouts (pcb, perfboard, veroboard,...) It's simple to use & how-to videos on youtube. |
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Scott Duckworth
From:
Etowah, TN Western Foothills of the Smokies
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Posted 24 Nov 2017 2:40 pm
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OK, I edited the schematic, it's in the original post I did.
_________________
Amateur Radio Operator NA4IT (Extra)
http://www.qsl.net/na4it
I may, in fact, be nuts. However, I am screwed onto the right bolt... Jesus! |
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Dave Hepworth
From:
West Yorkshire, UK
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Posted 5 Dec 2017 8:06 am
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Hi again folks,
With regard to this circuit can ask a question .
How will the circuit run using 2 X 2.7 M ohm resistors instead of the 2.2 M ohm ones as per schematic values.I am finding it hard to get 2.2 M values and I have a couple of 2.7M ones.
Thanks for looking .
Regards Dave |
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Chris Reesor
From:
British Columbia, Canada
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Posted 5 Dec 2017 12:58 pm
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Dave, 2.7 meg should be fine for that bias voltage divider in this circuit.
_________________
Excel Superb U12, MIJ Squier tele, modified Deluxe Reverb RI, Cube 80XL, self built acoustics & mandolins |
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Dave Hepworth
From:
West Yorkshire, UK
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Posted 5 Dec 2017 4:13 pm
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| Thanks Chris. |
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Dave Hepworth
From:
West Yorkshire, UK
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Posted 7 Dec 2017 11:00 am
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Hi Folks ,
Yet another question!
The 500 k pot ...is it a variable resistor in this schematic or just a normal potentiometer ?
Where does the 47 K resistor go relative to the pot lugs? I realise one end goes to ground which makes me think it is not a variable resistor .Can you explain please.I have built the rest of the circuit and now need to wire the pot up.
Thanks for looking Dave |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 7 Dec 2017 4:33 pm
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Yes, it is a variable resistor. You'll likely want fully clockwise to be 500k and counter-clockwise to be zero. Then the fixed resistor in series sets the minimum z.
You can put the fixed resistor on either side of the pot (variable resistor). Doesn't matter.
B |
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Mark Fowler
From:
Minnesota, USA
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Posted 7 Dec 2017 6:00 pm
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| That 47k resistor is a limiter resistor so the 500kA pot doesn't go lower then 47k ccw. |
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Dave Hepworth
From:
West Yorkshire, UK
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Posted 8 Dec 2017 9:19 am
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Hi Brad and Mark,
Thanks for the help .So I take it that the 47k goes like this.....
1) one end to ground
2) the other end to one of the 2 lugs used as an in and out of the pot.
Regards Dave. |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 8 Dec 2017 1:30 pm
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The resistor can go between ground and the CCW lug on the pot.
Then the center (wiper) lug goes to the input signal.
It's also a good idea to also tie the CW lug to the center lug. It's a variable resistor and even if the pot gets dirty, there will always be the 500k load present no matter what.
B |
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Mark Fowler
From:
Minnesota, USA
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Posted 9 Dec 2017 8:07 am
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Perhaps something like this.
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Dave Hepworth
From:
West Yorkshire, UK
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Posted 9 Dec 2017 11:23 am
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Thanks Brad thanks Mark .Can now finish off the project !
Regards Dave |
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Tony Glassman
From:
The Great Northwest
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Posted 9 Dec 2017 5:13 pm
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bOb, SGF seems faster since the change-over. Thanks for all that you do  |
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Terry Lovett
From:
Texas, USA
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Posted 3 Jan 2018 12:20 pm
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Hello Guys,
I really like the drawing Scott included on this Steel Buffer project. The reverse current battery protection is a plus, especially if no mechanical safeguard is built in place to prevent battery or polarity reversal. I always hate changing out batteries and using a standard diode really shortens the battery life. There are a couple of options that are quite useful: you could use a Schottky diode with a much lower forward voltage drop or even better would be to place a P-channel MOSFET parallel with the original diode and reference its gate back to the ground (neg) side. This would have a minimum voltage drop on the circuit and clamps shut with a reversal. MOSFET's have a very low resistance from Drain to Source. See: TI Application Report SLVA139, 2003
_________________
"Things can work,but not as well as they might if your thinking had been better" - J. Williams, MIT |
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Alan Muir
From:
Colorado, USA
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Posted 18 Jan 2021 3:02 pm
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One of my Covid hobbies is learning about electronics. I bought a breadboard and the parts to try this circuit. Thanks for all of your efforts and input on this. I worked from the schematic and experienced a big volume loss across the range of the pot. I added the jumper across the lugs as in the napkin diagram and it works better but I don't understand why. Can somebody enlighten me? Thanks.
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