Questions regarding building the CMoy

[kenshinz 0]

Eh... as in can I connect the (-) on 1st batt to the ground, and (+) on 2nd batt to ground, instead of connecting them together 1st, then use another wire to connect them to ground

[tropicalrips 0]

jason

yes i connect (+) of batt 1 & (-) of batt 2 to ground

i also tried the one battery layout both had the same problem (hissing)

but i solved that now by using the same resistor value for R3 (op-amp audio output) & R2 which is the op-amp's own ground i think

 

everything was ok liao, i tested it with the volume pot and it works, no more hissing

 

then i finish the case and put everything in...turn on the power...hear only silence... it went dead, going to do another board tonight, i think i re-soldered the first one too many times, but it did live for abt 20mins

[jtfoo 0]

I guess that the voltage of your batt1 and batt2 are different(usually the case), thus giving out uneven positive and negative volatge. That's why it's better to at least use matched resistors to divide the voltage.

[tropicalrips 0]

done up new board...still no sound...

i think the op-amp is KAPUT

 

anyway to test the amp? i hear a split second of audio when i switch it on then its gone, total silenca again

 

i measure the (+) to ground at 7.8v and the (-) to gound is 1.2v this is not normal right?

 

went back to the 2 batt layout and it works, but something very funny, i pull out one of the 9v and it still works is it normal, it works with (+ 9v) to ground and (- 9v) to the cap

 

now i'm lost liao i hav double check all the resistors and they r correct, so can't figure out why it worked the first time

 

i manage to to get it to work with 1 batt (very soft volume) just now using 1k as voltage divider, the other 4 around the op-amp is 4.7k, 2 10k as R4 based on Kenshinz drawing

 

Edited November 1, 2003 by tropicalrips

[jtfoo 0]

i measure the (+) to ground at 7.8v and the (-) to gound is 1.2v this is not normal right?

 

THis is bad. For 9V, should roughly be +-4.5V. Varies within 10% still acceptable.

 

went back to the 2 batt layout and it works, but something very funny, i pull out one of the 9v and it still works  is it normal, it works with (+ 9v) to ground and (- 9v) to the cap

 

Very weird. I think your wiring is wrong already.. Can post a good closeup picture on your wiring?

[ckng 0]

done up new board...still no sound...

i think the op-amp is KAPUT

 

anyway to test the amp? i hear a split second of audio when i switch it on then its gone, total silenca again

 

i measure the (+) to ground at 7.8v and the (-) to gound is 1.2v this is not normal right?

 

went back to the 2 batt layout and it works, but something very funny, i pull out one of the 9v and it still works is it normal, it works with (+ 9v) to ground and (- 9v) to the cap

 

now i'm lost liao i hav double check all the resistors and they r correct, so can't figure out why it worked the first time

 

i manage to to get it to work with 1 batt (very soft volume) just now using 1k as voltage divider, the other 4 around the op-amp is 4.7k, 2 10k as R4 based on Kenshinz drawing

 

You can build a circuit to test the op-amp. Tangent's site has full instructions.

 

http://www.tangentsoft.net/audio/opamp-tester.html

 

Regards

CK

 

[tropicalrips 0]

i think if i build a test board it would make me more blur i hav trace my wiring base on the pic on tangent's test site everything looks ok, all my in & outs r in the correct place, the ground is also correct, but i'm still not 100% sure abt the values of the resistors to use, the list is confusing...

 

what should the voltage divider resistors be? & also the (+a,-a) & (+b,- around the op-amp, the only resistor i'm sure is the R4 which is 10k

[ckng 0]

Can you post a pic of the under side as well?

 

Regards

CK

[kenshinz 0]

From the tangent site, the voltage divider resistors should be 4.7K

BTW, what type of wires are you using ? The ones I got(AWG 30) keeps breaking apart, think they're too thin, and inflexible

[tropicalrips 0]

i'm using 3.5mm electrical wires for the jumpering, strip away the insulation and just use the copper wire, they fit nicely into the board

[jtfoo 0]

It seems you're using 5% carbon resistors, brown color. Your next upgrade you can try using the 1% metal film type, which is blue color. Your voltage dividers resistor appear to be correct, both 4.7K.

 

From the picture can't tell much.. Maybe take a picture showing how your battery is connected to the board..

[tropicalrips 0]

thanks Jtfoo, what abt the resistors around the op-amp? i'm using 100k, is it correct?

 

the voltage side i'm quite sure its correct, + on the left - on the right, following the caps, both the caps and the dividers r connected to ground as well

 

with the 4.7k dividers, i get very soft volume, almost none, tried it with 1k, volume increase, can i use 0.5k ?

 

there is also a voltage difference between the left & right side, 2v & 7v on the other, is the op-amp causing this?

[tropicalrips 0]

here is pic of the under side, don't know if this can help

[tropicalrips 0]

here is a better pic of the front

the jumpers are following the pics on Tangent's site

Edited November 2, 2003 by tropicalrips

[jtfoo 0]

Couldn't see the color band on the other resistors. Sorry, can't tell is the layout is ok, though it looks about right.