TDA2003 odd size cap

[Fenris]

hi there

im currently working on a voice modulator with sound to light and have made a change to the original amplifier.
the front end of the voice mod uses an LM358 to amplify the input from an electret mic and a 7555 IC /
M74HC4066 combination 'chops' the signal so it sounds like a robot. the original output amplifier was an LM386
feeding an 8ohm speaker. what i have done is remove the latter and replace it with a TDA2003 amplifier which
can have 2ohm, 4ohm or 8ohm speaker attached with a corresponding level of output wattage depending what
speaker you use. i have based my PCB layout on a datasheet circuit so there wont be a problem with layout
induced audio problems but it has a capacitor with the following rating 8n2. my problem is no one seems to
stock this size ( i have looked under 8200pF as well) what would be a suitable replacement and would i have
to change any other components within the amp? i attach a pic of said circuit. the red line indicates where
the amp has replaced the original LM386 circuit.

Regards

Fenris

 

[ericgibbs]

hi,

Googled 'buy 8n2 capacitor"

**broken link removed**

**broken link removed**

 

[Hero999]

Don't use the LM358, use a reall audio IC like the TL072.

You should be able to use a 10nF capacitor instead, especially if you increased R15 to 120R.

 

[Fenris]

thanks for the heads up added that site to my favorites.

also noted the value alternatives cheers.

the main reason im using the 358 is that the circuit is
not my design and the layout was already done so i dont
have to worry about 'correct layout'. also it would call
for a total redesign and im just not clever enough. the
output amp was easy because it was at a defined point
(the end) of the circuit. the 358 however is integrated
around the 4066. so im guessing the 358 first stage
amplifies the mic into the 4066 which 'chops' the input
then its passed on to the second stage of the 358 where
it is further amplified then goes to the power amp. heres a
pic of the original circuit for your interest. i have built this
as is on vero board as the original kit is no longer available
it worked very well. the point of upping the output amp is
so the person using it cant be heard above the amped out
put when inside their mark III travel machine.....small clue
there

regards

Fenris

 

[kchriste]

The TL072 is a drop in, pin compatible, replacement for the LM358. If you have a LM358 on hand go ahead and use it since the robot voice isn't supposed to be HiFi anyway. But if you are ordering the parts, get some TL072s instead for future projects as most places will give you a discount if you order 10 or more.

 

[Fenris]

hi there

well if its pin for pin compatible i
shall make note of it as a suitable
replacement. ill get one just to try
and see what the difference is.
thanks again.

regards

Dave

 

[audioguru]

The LM358 has noise (hissss), crossover distortion and poor high frequency audio response. The TL072 is low noise, low distortion and wide bandwidth.
They cost almost the same.

 

[Fenris]

ok i'll definately have a look thanks.
whilst im here , im trying to run my simulated
circuit to see if the preamp and the audio amp
are compatible. as in; is the preamp putting
out enough signal for the TDA2003 circuit
posted above to work with. problem is that
the software doesn't have an actual component
of the TDA2003 so im using a virtual opamp
from the list. could be its not what i need as
it has less output showing on the virtual osci'
than whats being inputed which seems to be up to
100mV tops. to get a reading on the speaker out
put i have to change the range from 50mV/Div for the
LM358 to 1mV/Div for the speaker to get a reading of
far less in the region of 200uV, again it could be the
component isnt anything like a TDA type amp.
and i cant fathom the data sheet of the
lm 358 to see what the output is; same for what
the data sheet says for the required input of the
TDA, so could anyone just tell me if the meeting
of the pair is ok. circuit runs on 12V DC with a
electret mic.

Regards

Fenris

 

[audioguru]

The TDA2003 and the LM386 are power amplifiers. The current in an 8 ohm speaker has a peak of 625mA when at full output with a 12V supply.
The max output current from a little LM358 opamp is only about 30mA.

Your TDA2003 circuit has a voltage gain of 100. So if the input is 35mV RMS then the output will be at max.

 

[Fenris]

thanks for that. it was my only last worry
that there would not be enough juice from
the 358 to work properly with the TDA. so
it looks like im ok, touch wood.

regards

Fenris

 

[tblo163]

8n2 capacitor

I might be a bit late ,but I`ve only just seen you post.I`ve been rearching for a 8n2 for ages,none of my local suppliers have them.Luckily I found an exellent site,called Capacitor uF - nF - pF Conversion Chart & downloaded their Capacitor Coversion chart.Looking under 8.2nF it equalls 0.0082uF MFD.or 8200pF MMFD.The next cap up the chart was .01uF so I INSTALLED it & the amp works perfect.I`m new to this forum,and it looks pretty interesting.Regards Terry.