[ProFingerSk8er]

hi, finally summer's here..... im finally going to build a pocket amp

i went through the part list at http://www.tangentsoft.net/audio/cmo...arts.html#gain and the image

but something seems weird....here's my part list..

220 ìF 35V electrolytic capacitor, radial leads x2 C1/C2*
0.1 ìF 50-plus volt full-size film cap** x2 C1*
10 KÙ 1/4W metal film resistor x1 R1*
4.7/4.75 KÙ 1/4W metal film resistor x2 R2/R3*
100 KÙ 1/4W metal film resistor x2 R2*
1 KÙ 1/4W metal film resistor, gain 11 x2 R3*
10 KÙ 1/4W metal film resistor x2 R4
Dual op-amp OPA2132PA x1 OPA
Power indicator LED, 1.8V, 1-5 mA, 3mm x?
Stereo mini jack (3.5mm) x2 IN/OUT
Alt. volume knob (aluminum silver) x1
Power switch (mini SPDT* toggle) x1

this list seems a little weird, according to the image, there should be 3 R2s, 3 R3s, 2 R4s, and 2 R5s....but on tutorial's partlist there are many R2/R3s....so how do i kno how many of which parts to order?

also, on the list it listed "Alt. 1/4W metal film resistor assortment - R1-R5" isnt R5 required? and what does it mean by R1-R5?...and they only have part number for RadioShack, is that the only place that sells this resistor?

thank you for all your help, if possible, can you show me the exact partlist you used to built your cMoy? only extra parts im going to add to my amp are only the on/off switch and the volume nub...

thank you soo much for your help, any help would be great

brandon

 

[bralack42]

The way I look at the resistor names is to break the cmoy into two parts, the power and the amplification stages. Actually, I rename the R2/R3 next to the caps to Rpower when I think about it, and the LED resistor to RLED, because it seems more logical to me.

R5 isn't required unless something's wrong. All's I know is I haven't had to use it yet. Just be sure to jumper it if you don't.

Here's what I used for my first Cmoy:

1@ NKK SPST toggle switch
2@ 10K resistors for R4
2@ 4.75K resistors for R2/R3 in the power section.
2@ 4.75K resistors for the R3's near the opamp (sets gain to 3.1)
2@ 100K for R2 in the amp section.
1@ 332 resistor for R1 (RLED)
2@ 220uF electrolytics for the power section's C1/C2.
1@ OPA2132PA
2@ Switchcraft 3.5mm in/out jacks
a DIP-8 socket to mount the opamp
2@ 0.1uF metal film box cap for C1.
a green 3mm green panel mount LED.
a Panasonic 10K pot.

 

[stereth]

The amp has two parts, with overlapping part designations. You have your power supply caps (the electrolytics) and virtual ground resistors (R2 and R3 at the top of that pic). In the amp part, you have C1 and R1 through R5 for each channel.

By the way, I would highly recommend using a railsplitter for your virtual ground. The part is TLE2426, it costs about $1.50, and it physically fits in the place of R2 and R3 in the power supply. (It replaces those two resistors.) I built the power supply in the Headwize design paper, the same as a cmoy power supply but with a railsplitter instead of resistors, and 330uF caps instead of 220uF ones. Bigger caps supposedly give more bass.

If you're doing an online order, don't worry about the Radio Shack resistors. It's a metal film assortment that has all the values you need. But at Mouser or Digikey or wherever online, you can get all the values, in better components, for cheaper than Radio Shack.

R5 is recommended for low-impedence headphones. It reduces background hiss. Just get a couple extra resistors, 47, 100 ohms, and see how much you need.

 

[ProFingerSk8er]

thanks for the input guys....
bralack42, thanks for your list, since im only going to use this amp to imcrease the output of my minidisc player, i dont think i need any speical designs/parts...ill just fellow tangentsoft.com's design, but thanks for clearing up my questions...

bralack42, im going to use this amp with my eggos and v6, which are all very east to drive, so i guess i would need a R5 huh?
so you are suggesting 47, 100 ohms?...... ill be ordering my parts off digikey.com, and 4.75K res only comes with pack of 5 (for my R2/R3) so i will have 3 extra, im guessing i can use those for R5?
here are the details:
Resistance In Ohms 4.75K
Power 1/4W
Tolerance ±1%
Lead Style Axial
Packaging Bulk
Other Names 4.75KX
4.75KXBK
4K75 MF-1/4W-B 1%
MF-25-B-4.75K
MFR-25FBF 4K75

thanks again for your help, if there are anything to look out for, please be kind and let me kno.
brandon

 

[PeterR]

Quote:

4.75K res only comes with pack of 5 (for my R2/R3) so i will have 3 extra, im guessing i can use those for R5?

4k8 is too high. A lot. Like Stereth said, 47-100 Ohms, if at all. Don't loose sleep over 3 leftover resistors, they're cheap and one day you'll need them for something else anyway.

Love those smilies...

 

[bralack42]

About R5, I'm really not sure, as I've never used it. Using my Koss KSC-35's and Sony V7506's, I've never heard any hiss or anything to warrent putting a resistor there. Although CMoy, in the original article, says, to try a 50 ohm resistor, and then increase to 100 ohms. If I remember correctly, I remember reading somewhere that the more ohms are at R5, the less control the opamp has over the headphones, but you'll haveta ask someone who knows more than I if that's correct.

Good luck, building amps is so fun, though listening to the end product is the best!

 

[ProFingerSk8er]

thanks for all the help guys, this would be a fun project, im going to order the parts tonight.
cant wait

 

[ProFingerSk8er]

just place my order at digikey.com, i cant wait untill those parts comes in

does anyone has any idea how fast do they ship out items?

omg..i seriously cant wait

 

[Sol_Zhen]

Good luck!

Post pics when you're done.

*just waned to try a new smiley*

 

[bralack42]

I find Digikey to be much, much faster than Mouser. I ordered a shipment on Wednesday, it was sent out in the afternoon that day, and it arrived on my doorsetep just this night (2 days later). Of course, Wisconsin is pretty close to Minnesota, where I think their warehouse is. I love Digikey, except for that $25 minimum order. Now if only they started selling Vishay Dale resistors, ALPS pots, and those Wima caps, life'd be good!

 

[ProFingerSk8er]

thankx for sharing bralack42, now i kno im safe with digikey and can just sit back and relax (not really

the wait is killing me)
till the day i starting building my amp

 

[RacerX]

Best of luck. This is a great project and Tangent's tutorial makes it all a bit easier.

 

[ProFingerSk8er]

hi again guys, just one more question...

my parts list is as fellowing:

will i need 2 9v batteries? or will one do...if i can hook up 2, will i notice difference in sound?
thanks once again

 

[ProFingerSk8er]

anyone?

 

[bralack42]

Well, I would say two batteries would be better than one, because batteries lose voltage toward the end of their lives. If you have two batteries, it you could run them lower before the total output volts would drop below the minimum needed by the opamp. I personally would use two batteries if possible.

Also, from the parts list, did you include a resistor for the LED?