-5 volts?

[DaveC]

Hello.. I've built a little Guitar effects circuit, Its basic
configuration is as follows Input -> LM741(variable Gain) -> ADC -> PIC
-> DAC(MAX5354) -> output. I used a voltage divider to impose a 2.5 volt
DC offset on the analog input of the OPAMP so I could get a clear reading
as the signal swings in either direction.

It all works fine, except that the 2.5volt offset is still on the output.
Due more to the DAC then the above mentioned. Any way. I wish to power
the whole thing of a regular 9 or 12 volt DC wall wart. So I need -5
volts to pull the signal down again (removing the DC offset.

Are they called charge pumps.? somthing? At the moment I only have the 5v
digital supply and ground.

Thanks.

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

 

[DaveC]

"Richard Webb" <webby@REMOVEMErichardwebb-online.co.uk> wrote in
news:-IWdnWaAQ_bDfZbfRVn-iA@pipex.net:

"DaveC" <bobason456@hotmail.com> wrote in message
news:Xns95F9F07046803ohirohotmailcom@38.119.85.36...
Hello.. I've built a little Guitar effects circuit, Its basic
configuration is as follows Input -> LM741(variable Gain) -> ADC -
PIC -> DAC(MAX5354) -> output. I used a voltage divider to impose a
2.5 volt DC offset on the analog input of the OPAMP so I could get a
clear reading as the signal swings in either direction.

It all works fine, except that the 2.5volt offset is still on the
output. Due more to the DAC then the above mentioned. Any way. I wish
to power the whole thing of a regular 9 or 12 volt DC wall wart. So I
need -5 volts to pull the signal down again (removing the DC offset.

Are they called charge pumps.? somthing? At the moment I only have
the 5v digital supply and ground.

Thanks.

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet
News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World!
120,000+
Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption
=----

If I'm correct all you want to do is remove the DC offset from the
output of the DAC.

A capacitor passes AC but blocks DC.

Putting a sensibly sized cap in series with the output of your circuit
will only allow the AC components of your signal to pass and block the
DC component.

Its hard to tell from your description but it sounds like you might be
trying to impose a 2.5v DC offset onto your input directly which could
be feeding back to your guitar. No idea if this will affect your
guitar or not. Use a capacitor in series with the input and after the
cap place a resistor to ground, this will form a high pass filter. Set
the break frequency nice and low (20Hz ish).

As for the power, why not use a regular 9v wall wart and regulate it
with something simple like a 7805?

Hope this helps,
Rich.

Thanks.. The cap worked. I'm only in my first year as electronic degree
so forgive me

What is the use of positive and negative voltage on many opamp circuits
I've seen then?

DaveC

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

 

[Jamie]

Chris Carlen wrote:

DaveC wrote:

Hello.. I've built a little Guitar effects circuit, Its basic
configuration is as follows Input -> LM741(variable Gain)


:-D

LM741, I love it!

Consider a more modern general purpose OP-amp like TL081,2,4.
Rail-to-rail opamps are really cool, but expensive. Avoid if not
needed. Spend a lot of time reading various op-amp datasheets to
understand the specifications, and read "The Art of Electronics" a bunch
of times.

he said effects amp, maybe the effects he is getting from the 741 is
what he wants!