[weibby]

Picked this up a local electronic store.
Tried to google for ideas, but seems that even the website lite8.com don't have this model anymore.

Tot of going dual mono set up but i haven't the clue for 130P, 5P and 104 is.
No BOM so have to go back to the guy again to ask him whats the parts.

Thought might run it by you guys for any inputs.

 

[Nisbeth]

130p = 130pF cap (mica or ceramic)
5p = 5pF cap (mica or ceramic)
104 = 100nF polyester:
Gain = 1+R2/R4 (11 with the values in the schematic)

/U.

EDIT: It's R2/R4, not R2/R1. Also, what are the p/n for the output IC's.
EDIT2: The dual Opamp (IC3) can be any quality dual opamp. Check the supply voltage of the model that you are using as 18V is a bit high for many of the popular audio types.

 

[jcx]

on 1st sight looks like a problematic circuit schematic - op amps don't like being paralleled this way

maybe it is meant to be used with either the dual op amp position stuffed or the 2 singles, not both

in which case you have a large choice of op amps - espically if you change the supply V and gain appropriately

headphone impedance, sensitivity should influence your choices

130p, 5p are likely Caps of those values, 104 probably 100KOhm power supply drain resistors - not really needed at this low voltage


it would be nice to know if the schematic and board are the same, maybe the revision was for the 104 resistors

 

[Nisbeth]

Quote:

Originally Posted by jcx /img/forum/go_quote.gif 130p, 5p are likely Caps of those values, 104 probably 100KOhm power supply drain resistors - not really needed at this low voltage it would be nice to know if the schematic and board are the same, maybe the revision was for the 104 resistors

Look at C7/C8 on the schematic.

/U.

 

[weibby]

Do i need to jump the dual opamp set up if i were to use dual mono?

 

[Nisbeth]

No.

/U.

 

[weibby]

cool

One last question, what kinda opamp can I use?
The usual fan fare of opa2227/LM4562 etc? Or will be it be different.

Do i have to go 18V or can drop down to a lower voltage setting?

 

[jcx]

Quote:

Originally Posted by Nisbeth /img/forum/go_quote.gif Look at C7/C8 on the schematic. /U.

you're right - the mix of reference designators and values is a mess when you need to look for square box bigger than pads vs smaller for C vs R


I wouldn't go for very fast op amps with the feedback nodes so spread out

op amp and power supply choice depend on what's available and the headphones you intend to use (hint: tell us what headphones you intend to use with this amp)

 

[weibby]

basically its for IEMs and low impedence headphones.

32 - 60 ohms.

I like OPA 2227/2107 and AD823a

 

[jcx]

for iem most op amps will give enough drive, probably down to their min operating V spec

for full size 32 Ohm Grados, or worse the AKG K701, you need much more current than general purpose op amps can provide

Grado's RA-1 amp is said to use the JRC4556 wich claims up to 80 mA output - one of the higher output current PDIP op amps

 

[weibby]

I can do a DIP socket for all 3 opamp slots to try out the different opamp
but if i hope i don't burn the opamp if i put in 18 v.

 

[jcx]

for Low Z cans +/-12 V supply should work most of the time (there are really low sensitivity headphone that are exceptions)

a amp for sensitive iem could use 1/2 that Vsupply - check the op amp datasheets for Vsuppy_min