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grado ra1 pcb layout

post #1 of 7
Thread Starter 
I have used search option but i can not find answare
i have allready made cmoy and nowi i am willing to make this little amp for my grado sr80i.
question is , is there any pcb layout for grado rs1 ?
Edited by kefalo81 - 9/8/13 at 5:58pm
post #2 of 7

If you have really searched than you know why one can not talk freely about the mahogany cmoy 'round these parts. 


Well, not the mahogany cmoy in specific, but clone amps in general. 


The Mahogany cmoy is a cmoy with very specific part requirements. 

For what it costs to build it is quite nice. 

post #3 of 7
Thread Starter 

Edited by kefalo81 - 9/9/13 at 12:56am
post #4 of 7
Thread Starter 

have yout tried it ?

generaly i see that in power section missing three resistors in comparison wiht cmoy .

specificli it is 10k Ohm resistor for led and two 4.7k ohm resistors 

led is missing too !

in amp section everything is same exepct the fact that i cant see potenciometar!

whan i saying evererything is same i am thinking on components schedule not values.


for all these what i sead i have used two schematic



original  cmoy 


and schematic for ra1 from these thread 




post 7

post #5 of 7

The Mahogany Cmoy needs a specific op amp to work. Most of what people describe as the "sound of an op amp" is really the interesting and occasionally unpredictable ways in which op amps fail to drive headphones. Please don't tell anyone in the cmoy thread that I told you this, they don't like to hear it. The way the JRC4556 op amp fails just works well with Grado headphones. 


Now, this specific op amp has BJT inputs which have high(ish) input offset currents. Accordingly the resistors around the op amp must be selected to balance these currents. These values can be adjusted (I would try for lower gain) if you know how. Tangent has a great article - working with cranky op amps that tells you how. 


In order to *really* balance input offset currents you **must** have input caps. The value of these caps can also be tweaked, and 4.7uf is on the large side . 1-2uf is plenty (check against the part values you use....) and this opens the door to higher quality input caps or a physically smaller layout and perhaps both! 


The board layout is exactly the same as a conventional Cmoy, except that you should follow the 2x9V battery supply instead of using the resistor based rail splitter.

post #6 of 7




post #7 of 7

Ooh, I never said if I tried it... 

I built a balanced mahogany cmoy a few years back. 

It sounds great with pink-driver RS-1. 

With the HP2 it does not sound as good as the Melos, but that kind of goes without saying. 

Edited by nikongod - 9/9/13 at 5:47pm
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