Ruby Bassman Mod

[Ofek Deitch]

Hi everybody!

I wanna go to the store soon and buy the parts required for building this amp + the bassman mod, which I've heard is much better than without the mod.

my question is if I wrote down all the parts needed, according to the scheme bellow:


Resistors:
• 1x 1.5M Resistor
• 1x 3.9K Resistor
• 1x 10R Resistor
• 1x 2.2K Resistor

Caps:
• 1x 47nF Capacitor
• 1x 100nF Capacitor
• 1x 220pF Capacitor
• 1x 0.1uF Capacitor

Electrolytic Caps:
• 1x 100uF Electrolytic Capacitor
• 1x 220uF Electrolytic Capacitor

Transistors:
• 1x MPF102 Transistor

ICs:
• 1x JRC386D IC

Pots:
• 1x A10K Pot (Log)


Also, I was wondering if the Volume pot is supposed to be a Log or a Lin pot?

Thanks!
Ofek Deitch

[Bill Mountain]

Well...in the schematic the pot is listed as linear.  So, I would go with that.

[Ofek Deitch]

"Volume controls are different. The human ear does not respond linearly to loudness. It responds to the logarithm of loudness. That means that for a sound to seem twice as loud, it has to be almost ten times the actual change in air pressure. For us to have a control pot that seems to make a linear change in loudness per unit of rotation, the control must compensate for the human ear's oddity and supply ever-increasing amounts of signal per unit rotation."

So according to that, shouldn't I use a log pot, to get a sort of linear effect when turning the volume up?
Thanks again!

[PRR]

If the _POT_ is listed "linear", you buy a linear pot.

> shouldn't I use a log pot, to get a sort of linear effect

That's a complicated question. In this case, the '386 loads the pot away from true linear. But the main thing about an Audio Taper pot is that you can turn WAY down without having to twitch around in the 0-1 zone of the dial. In the case of guitar to a '386, there is no likely situation where you'd want to turn WAY down. Mostly you will work this pretty near wide-open. The designer's pot-spec, "linear", seems likely to be suitable and is your first choice until test shows you really do want WAY-down operation.

[Ofek Deitch]

Okay thank a lot!
Now I kind of under stand, so I'll just get a linear pot...

[Ofek Deitch]

I've got another stupid question which was probably answered here before more than a few times:
If I want to install a GREEN led instead of the ordinary red one, which resistor should I get?

Also, I am not sure how to wire the ON\OF switch...
Is the wiring of the switch below (of the Noisy Cricket) is suitable to the Ruby?




THANKS!!

[DavenPaget]

A green is the same as red . For a SPDT just use the two outer lugs . Of course the switch wiring is suitable !

[jdanner722]

Hi all,

I've just finished up my Ruby amp with a Bassman mod. I would now like to add an on/off switch though I'm not exactly sure how. I have a rotary switch that I'd like to use but all I have is a two pole, six position switch I picked up. First, can I modify this switch for simple on/off functionality and secondly how can I incorporate out into the schematic? Thank you in advance for your help!

J.

[PRR]

> two pole, six position switch I picked up. can I modify this switch for simple on/off functionality

One pole one throw is just 1/12th of a 2 pole 6 throw.

It probably has 2 lugs near the middle and 12 lugs around the rim. Wire to one of the middle and one nearby one of the rim. One of your 6 positions is ON.

Goes right where the ON/OFF is in the above sketch.

If you peer in the side you may be able to see what-hits-what.

Some many-pole rotaries have a stop-pin which may be moved from position 6 to position 5 or 4 or even 2, so you don't have all the useless positions. Cheap ones may not.

[jdanner722]

Thanks for the fast reply! After disassembling the rotary switch I decided to give up on trying to change the settings. It looks like our may have been a cheap one so I replaced it with a toggle as it was outlined above with no problems. Thanks again!