470r potentiometer vs a 470k

[estch71]

I'm building the Amtron UK854 fuzz and it calls for a 470R linear potentiometer.  I have a 500K lin that I can lower with a resister across lugs 1 and 3 but, is the fact that it's K going to make that much difference?

[GGBB]

I'm building the Amtron UK854 fuzz and it calls for a 470R linear potentiometer.  I have a 500K lin that I can lower with a resister across lugs 1 and 3 but, is the fact that it's K going to make that much difference?

K stands for kilo - so that's 500000 ohms whereas 470R means 470 ohms.

[estch71]

Thanks for the reply.  Since I don't have one at the moment, can I use a 470R resistor in place of it? 

[GGBB]

Thanks for the reply.  Since I don't have one at the moment, can I use a 470R resistor in place of it?  

If it's being used as a variable resistor yes.  If it's being used as a divider no.

EDIT: Actually, even as a variable resistor maybe not.  Do you have a link to the schematic?

[XXISouthpaw]

Well considering there's 469,530 ohms of a difference I highly doubt they'll work in the circuit sufficiently. Nip down to your local electronics store or grab some online, they cost about £1/$1.50 ~ a piece.

[estch71]

Here's the link.  It's not allowing me to embed it in the post.

http://tagboardeffects.blogspot.com/2013/01/amtron-uk854-fuzz-box.html

[estch71]

Hopefully I have this right.  If I take a B5k pot and place a 6.8M resisitor across lugs 1 and 3, I should have a .404 or a 404R pot.

[GGBB]

That's a standard fuzz control which is a divider.  You can replace it with 470R resistor but you have to wire it so that you have full fuzz all the time (many fuzz users typically run them that way anyway).  Place the 470R between the Fuzz1 and Fuzz3 rows, and move the 100uF cap anode connection from Fuzz2 to Fuzz3.

Hopefully I have this right.  If I take a B5k pot and place a 6.8M resisitor across lugs 1 and 3, I should have a .404 or a 404R pot.

You could do that, and you'll get the biasing of the transistor about right (there'll be a little more gain), but the fuzz control won't work the same.  You can't do any damage so you could try it and see of you like it.

[estch71]

the resistor method worked.  Amazing little unit.  Thanks so much for the help.  I'll post some pics once I get this housed.

[duck_arse]

If I take a B5k pot and place a 6.8M resisitor across lugs 1 and 3, I should have a .404 or a 404R pot.

6.8M is 6,800,000 Ohms. it would effectively look like an open circuit to the 5,000 Ohm pot.

6k8 across the 5k will reduce to a bit more than half the pots' original value. or just use a 1k B pot. there are thousands of posts about getting this control to work without bunching at one end and wot value to use.

[Hemmel]

Very small thread hijack for a small question :

The layout shows a 1N5817 diode for polarity protection. Could any 1N4001(or 4003, 4005, etc) work as well ? Why specifically a 1N5817 ?

[duck_arse]

1n5817 is a schottky, no? schottky, and I hope I'm spellink it right, has a lower forward voltage drop than a silicon power diode, so you lose less of your precious 9V.

[Hemmel]

Ok. But ... really ? 1N400x would have around 0.7V forward drop where the schottky would have 0.45V.
Do I really need the quarter-volt ? Will it really make a difference ?

I'm just asking because I have plenty of 1N400x at home but I don't think I have any schottkys (plural = schottkies ?)

[GGBB]

Ok. But ... really ? 1N400x would have around 0.7V forward drop where the schottky would have 0.45V.
Do I really need the quarter-volt ? Will it really make a difference ?

I'm just asking because I have plenty of 1N400x at home but I don't think I have any schottkys (plural = schottkies ?)

The actual voltage drop is proportional to the amount of current.  In typical stompboxes, a 5817 will drop about 0.2V on a 9V power source (I just measured one on the weekend and got exactly 0.2V) versus 0.7 for the 4001.  Whether or not a half volt difference matters is entirely dependent on the circuit itself.  In this one, the transistor biases are fixed by the resistor values so they depend on the input voltage and the diode drop.  The circuit will work with a 4001, but will sound a little different than with a 5817, just as it would over the lifespan of a battery or with a power supply that is not exactly 9.0V.  In the case of fuzzes, 1/2 volt is not insignificant.  Even variations in the biasing resistors' values will change the sound a little.  So try it, you might like it.

[Hemmel]

So try it, you might like it.

I will ! Thanks for the info.
I'll actually socket the diode and try out those I have to see which one has the lowest drop (I read germanium diodes also have a low voltage drop). Then when I get the schottkys I'll just swap it.

[GGBB]

So try it, you might like it.

I will ! Thanks for the info.
I'll actually socket the diode and try out those I have to see which one has the lowest drop (I read germanium diodes also have a low voltage drop). Then when I get the schottkys I'll just swap it.

I recently tested a whole bunch of diodes including 1N34A germanium and several different Schottkys and regular silicons.  The 1N34A was quite low but not as low as the 1N5817 which was the lowest by about a 0.1V margin or more over all the others.  But it will depend on current draw - I tested at about 5mA.

[estch71]

The layout shows a 1N5817 diode for polarity protection. Could any 1N4001(or 4003, 4005, etc) work as well ? Why specifically a 1N5817 ?
Posted on: Today at 10:15:03 AM Posted by: duck_arse

I used a 4001 and things seem to be fine, although I'm sure I'm missing a bit of the tone due to the 10k trimmer, 470R resistor and the diode I'm using.  This thing is seriously gainy though.  Great sound.  It also works amazingly with a SHO boost first in line.