ruby amp: q on values

[remmelt]

hello!

for my next project i'm building a ruby amp. i have a couple of questions:

i'm looking at the schem here: ruby amp.

1) in the bassman mod text, it says: "Replace the .047uF cap from the FET source pin". I see a .047 nF cap in the schematic. Which is the right value? With what should it be replaced for the bassman sound?

2) In the schematic and in the Perfboard layout, i see a 10 ohm resistor and 47nF capacitor going to ground. In the picture below the layout, it's gone AWOL. What happened? Do I not need them?

3) Do I need to worry about impedance of the speakers this amp connects to? I'm thinking about using the 8" 8ohm speaker that came in my Park G10. (Maybe some day I'll be rich and I can afford a nice Weber. One day.)

Thanks for your answers!

[Steben]

hello!

for my next project i'm building a ruby amp. i have a couple of questions:

i'm looking at the schem here: ruby amp.

1) in the bassman mod text, it says: "Replace the .047uF cap from the FET source pin". I see a .047 nF cap in the schematic. Which is the right value? With what should it be replaced for the bassman sound?

2) In the schematic and in the Perfboard layout, i see a 10 ohm resistor and 47nF capacitor going to ground. In the picture below the layout, it's gone AWOL. What happened? Do I not need them?

3) Do I need to worry about impedance of the speakers this amp connects to? I'm thinking about using the 8" 8ohm speaker that came in my Park G10. (Maybe some day I'll be rich and I can afford a nice Weber. One day.)

Thanks for your answers!

Is that an 8"?

[remmelt]

i just measured it, it's a little over 20cm. also, compared to my 12"es, it's WAY smaller. so my educated guess is, it's 8.

[B Tremblay]

1) in the bassman mod text, it says: "Replace the .047uF cap from the FET source pin". I see a .047 nF cap in the schematic. Which is the right value? With what should it be replaced for the bassman sound?

The complete sentence is "Replace the .047uF cap from the FET source pin to the volume pot with a 0.1uF."

2) In the schematic and in the Perfboard layout, i see a 10 ohm resistor and 47nF capacitor going to ground. In the picture below the layout, it's gone AWOL. What happened? Do I not need them?

The schematic and perf layout were updated after I built my prototype.  Some builders needed the 10R/47n network for stability.  I didn't, but added it to the schematic as a precaution.  I suspect that certain types of 386 need it more than others.

3) Do I need to worry about impedance of the speakers this amp connects to? I'm thinking about using the 8" 8ohm speaker that came in my Park G10. (Maybe some day I'll be rich and I can afford a nice Weber. One day.)

You can use a 4 or 8 ohm load with no problems.  I've never tried a 16 ohm load, but it may work well too.  Can anyone confirm this?

[remmelt]

1) in the bassman mod text, it says: "Replace the .047uF cap from the FET source pin". I see a .047 nF cap in the schematic. Which is the right value? With what should it be replaced for the bassman sound?

The complete sentence is "Replace the .047uF cap from the FET source pin to the volume pot with a 0.1uF."

sorry! i got that part. i was just looking at the values of that 47 uF cap: in the schematic it's a 47 NANO F, in the text, it says 47 MICRO F. which one is the right value?

[B Tremblay]

47nF is equivalent to 0.047uF.

Here's a helpful link for conversion:

http://www.diyguitarist.com/Misc/CapConversionChart.htm

[remmelt]

:oops: x 1000M.

[Toney]

Going to have a shot at the RUBY myself tomorrow.
It will be my first build here, so I am really looking foward to it. Going for the Bassman version too. Actually Remmelt, I puzzelled over the same point re. the photo so I am glad it's cleared up. I dont always ask such  questions because at this stage, I tend to assume I have missed something. :!:  
Do you intend to add an input for DC? If we do this must we also use a diode to guard against reversed polarity?

[remmelt]

the amp runs on a battery, so the V will be DC. did you mean a wall wart power supply? i never add the reverse polarity diode, but that's mainly because i haven't figured out what diodes do yet
i think i will be running the amp off a wall wart. i have one that switches voltages, that should be fun experimenting!

[Toney]

Yeah, a wall wart.
I'm gonna try to make two and give one to a bass player friend and if anyone can stuff up the polarity of a wall wart , my vague but talented buddy can. I think some protection is a good idea. Do you know if it is as simple as adding a diode that can handle 12v or is there some other components necessary?

[remmelt]

i think it's just the diode. i read a piece about that the other day but can't remember where!