Guide to fix up a Cmoy 2

[kross 0]

i am also using the rechargebles when i am home until i acquired a power supply recently. from my experience, using AA rechargeables (i used 8 AA 1.5V rechargebles) really last longer than using only one 9V battery.

[squalle 0]

i am also using the rechargebles when i am home until i acquired a power supply recently. from my experience, using AA rechargeables (i used 8 AA 1.5V rechargebles) really last longer than using only one 9V battery.

a few things here:

 

1. rechargables, especially Ni based batteries are not rated at 1.5v. they're 1.2v and will spend most of their operating time in the vicinity of that voltage level

 

2. of course it will last a lot longer. 9v rechargables are most probably like 170mAh, whereas AAs highest at the moment are 2500mAh rated. so using AAs can last more than 10 times longer

 

well, making regulated power supply is not a big feat. rather simple. dont even need to get watever TREAD board. p-t-p soldering would do very nice result and it only consists of very little components

[siriuz 0]

oops! slipped my mind

forgot that rechargeables are 1.2v instead of 1.5

haha sorry

[arc_sine_squared 0]

I just received my caps today, but I ordered the wrong ones.

I got .01uf instead of 1.0uf

 

Will these work, why or why not, and what difference will the sound be?

(bass, no bass, thin, etc.?)

 

I read we change r2 and r6 for more gain, up to about a 20k resistor. Could I put a linear trimmer pod here to have adjustable gain?

 

What about changing the bass, treble, etc. like a built in EQ. What resistor would I need to be adjustable to have a little control over the bass and treble, or is this possible?

 

thank you

[squalle 0]

thin bass as it's like 100 times smaller, then let's calculate

 

fc = 1/(2pi*RC)

fc = cut off freq

pi = 3.14

R= depend on wat's the input resistance u put, if you follow as prescribed, it would be 10k ohm.

C = 0.01uF (u replaces the symbol of mu)

 

so the result would be 1592Hz

and that cut off doesnt mean it goes straight, but it's already at -3dB

so yah, ur bass will suffer a lot

 

for bass boost you can add on, but not on that board, rather tight spacing.

treble boost never heard ppl wanting that, but yeah, can be done too

 

for adjustable gain, I suggest you small trimpot, then you can fit it there easily. dont get those large ones (with the handle bar or something, but the ones that you've gotta use a jeweller's screwdrive to turn)

 

I suggest you build the amp first before going to EQ-ing the sound

and, for the adjustable gain, maybe you can just plug in straight away rather than desoldering the resistors later on

[1bit 0]

one thing to note about adjusting gain with trimpots, you'll need two trimpots for both right and left channel

when you set them you need to match their resistances properly with a multimeter to avoid volume imbalance between the right and left channel

 

so practically not a very good idea imho

[arc_sine_squared 0]

thin bass as it's like 100 times smaller, then let's calculate

 

fc = 1/(2pi*RC)

fc = cut off freq

pi = 3.14

R= depend on wat's the input resistance u put, if you follow as prescribed, it would be 10k ohm.

C = 0.01uF (u replaces the symbol of mu)

 

so the result would be 1592Hz

and that cut off doesnt mean it goes straight, but it's already at -3dB

so yah, ur bass will suffer a lot

 

for bass boost you can add on, but not on that board, rather tight spacing. 

treble boost never heard ppl wanting that, but yeah, can be done too

 

for adjustable gain, I suggest you small trimpot, then you can fit it there easily.  dont get those large ones (with the handle bar or something, but the ones that you've gotta use a jeweller's screwdrive to turn)

 

I suggest you build the amp first before going to EQ-ing the sound

and, for the adjustable gain, maybe you can just plug in straight away rather than desoldering the resistors later on

Thank you for the very detailed help and formula.

 

Which R are we talking about in the fc = 1/(2pi*RC)

R2 and R6 again?

 

As far as low end, I guess the rule 20hz to 20khz is typical hearing, what is reasonable for an amp, maybe in the hundreds or so (100-300hz) or can we get down to double digits?

 

I understand about having two trimmers and the mix it could cause once adjusting. What about adding a dual linear pot instead? That would solve the potential problem of having different values.

 

I built one amp already and it was...okay, but not great. So Im looking to beef it up a little. My desoldering skills are terrible, so I'm building a new one from scratch.

[arc_sine_squared 0]

Okay, I'm not having any luck with the math. You said the answer is 1590Hz

 

I don't know if it's an order of operation or if all values need to be equivalent or something? .01uF of 1 Farad and 10K ohms?

 

For 10K, I plugged in 10,000 to my TI-89 and used .01 (10 -6) for the caps I currently have and I'm getting a value result with a decimal off six places (1,000,000)

 

What the heck??

 

[arc_sine_squared 0]

Got it!

 

1 / (2pi*10000 * .00000001) since .01uF is .00000001 of a farad.

 

 

[siriuz 0]

1uF = .000001 F

 

edit: ah , a minute too slow

Edited January 6, 2006 by siriuz

[arc_sine_squared 0]

I see we are using the resistor value of 10k for the math, but which R is this? Or in this case, which R's

[1bit 0]

 

the resistors in question are R8 and R4

 

the input caps and these resistors make two high pass filters, one for each channel

 

i think you can also bring down the cutoff frequency by increasing the resistance for R8 and R4, but it might reduce signal/noise ratio

 

[arc_sine_squared 0]

Sorry if this has been said a thousand times before...

 

So really we only need to be concerned with C1 and C2 in order to drop or lower the cutoff (by adding a 2.0uf - 3.0uf cap) --- Thinking about the cost of metal film polypros in a 5mm spacing, and I see they cost about US$2 each, but if we only need two and not five that's a bonus.

 

So can we use something generic like a 100nF for the others? Any negative repercussions to this thinking?

[jasonhanjk 0]

The C3 to C5 you can use 100nF ceramic cap.

[1bit 0]

 

So really we only need to be concerned with C1 and C2 in order to drop or lower the cutoff

 

well i'm not absolutely sure about this so please do correct me if i'm wrong

 

i think you can still play with R4 and R8 too

i guess the snr won't really matter, i think you can raise them to 100k and won't hear any noise

(fyi, pimeta uses 1 Mohm resistors for the input filter)

that would make your finding caps easier

 

btw are you in singapore?

you can get small sized (low voltage) 1uF to 4uF polyester caps easily at koba in people's park centre level 3

polypropylene caps would be harder to find though