[Chadly]

I'm planning the building of the Grado RA-1 replica that I'm going to do. Rubins schematic is great but it doesn't show where to put in the switch and LED. Please look at my version and tell me if I did it right? The colors are my additions. I put the original unchanged schematic on the left.

Thanks,
Chad

Also, I got R1 as 10k from the CMOY schem. Should I use 20k because the RA-1 uses 2 9v's?

 

[rickcr42]

the switch is incorrect . You need to switch both polarities simultaneously so you have to purchase a DPDT (double pole/double throw) switch.

Also , try to obtain a low current LED then do the math according to the actual LED , though 10-2K should be OK.

Standard LEDS can draw more current than the entire amp and drain your batteries in short order

Rickeraptor

 

[Chadly]

Thanks, how do I do the math according to my LEDs?

Can I get away without using that kind of switch? How does the CMOY get away without it?

Thanks, you have been an invaluable rescource

Chad

 

[rickcr42]

the Chu Moy Pocket Amp uses a single 9 volt battery with an artificial ground to generate the dual polarities . You are using two discrete voltages ,+ 9 V /-9V and a "common" whichbecomes the ground point.
So each "rail" must be switched or the unswitched polarity will continue to drain causing one side to have low voltage .

Ohms law for the LED . If you have a package look on the back for the formula . Otherwise if web shopping the info will be on the site . Not a critical value , you just don't want to blow the part up.
Actually add a pot to a nominal value and dial in the brightness level allthe time.

 

[Chadly]

I guess I don't know as much about this as I thought I did.

How do I go about wiring up the "common?"

What is a rail?

I know my questions are getting tiresome, i'm sorry. I'm actually just generating more questions by asking these questions. Things are strarting to clear up though.

Does radioshack sell a good DPDT switch? I hope so, I've already placed my order with digi-key.

Thanks a bunch,
Chad

 

[rickcr42]

your questions are NOT tiresome. I enjoy helping out newguys . Only way we get the nextgeneration of DIYers is if the new have a good experience building .

OK ,to work

The "common" is the point where the plus of battery A and the negative of batteryB tie together . It is where all of your ground connections go . Every single one .You leave one out and something just will not work as all voltages need to reference to a ground in order to complete the circuit

A "rail" is just a term used to describe the power supply voltage point . so the +rail is the + of the battery and the - rail is the - of the battery

Radio Shack has several good DPDT switches . Go for the minature on with the flattened lever . Always had good luck with it .

Rick

 

[Chadly]

Thanks a bunch. All is clear for now........

 

[rickcr42]

good luck chad , if using the original op-amp actually sounds pretty good with grados . Good power.
And you gotta love the clean and simple layout.

KISS (KEEP IT SIMPLE STUPID)

Rickasaurus rex