-5 volts?
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-5 volts?

 
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DaveC
Guest
Posted: Thu Feb 10, 2005 4:41 pm    Post subject: -5 volts? Reply with quote
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.

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martin griffith
Guest
Posted: Thu Feb 10, 2005 9:58 pm    Post subject: Re: -5 volts? Reply with quote
On 10 Feb 2005 04:41:20 -0600, in sci.electronics.design DaveC
<bobason456@hotmail.com> wrote:

Quote:
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 =----


"At the moment I only have the 5v digital supply and ground."

First thing....
from http://www.national.com/pf/LM/LM741.html
it sez the minimum supply rail is 10V, so select another opamp,
preferably with good rail to rail specifications




martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.
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Richard Webb
Guest
Posted: Fri Feb 11, 2005 4:30 am    Post subject: Re: -5 volts? Reply with quote
"DaveC" <bobason456@hotmail.com> wrote in message
news:Xns95F9F07046803ohirohotmailcom@38.119.85.36...
Quote:
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
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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.

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SCADA
Guest
Posted: Fri Feb 11, 2005 5:31 am    Post subject: Re: -5 volts? Reply with quote
"DaveC" <bobason456@hotmail.com> wrote in message
news:Xns95F9F07046803ohirohotmailcom@38.119.85.36...
Quote:
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==----
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Newsgroups
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Have a look at the LMC7660...
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DaveC
Guest
Posted: Fri Feb 11, 2005 6:11 am    Post subject: Re: -5 volts? Reply with quote
"Richard Webb" <webby@REMOVEMErichardwebb-online.co.uk> wrote in
news:-IWdnWaAQ_bDfZbfRVn-iA@pipex.net:

Quote:

"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

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Mook Johnson
Guest
Posted: Fri Feb 11, 2005 6:57 pm    Post subject: Re: -5 volts? Reply with quote
Quote:
"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



This allows for DC coupling (direct to the opamp output) without a coupling
cap. This is useful when cascading stages so you don't have to worry about
all those AC coupled stages rolling off you low frequency gains (bass).

As a guitar guy, you might want to look into Tubes. I'm in a project with a
musician friend of mine and even though he will admit that solid state get
much better specifictions and cleaner sound, tuba amps are more desirable
because they become part of the musical instrument. Tube distortion due to
signal overdrive (hitting the string hard) is more pleasing to the ear and
make the guitar sound fuller rather than raspy. I'll admit that he is
correct in that as I have heard teh difference for myself. not saying that
solid state cant be made to mimick the shound of a tube, but tube amps are
pretty much the norm for musicians I know.

This is NOT the Hi-Fi tube amp vs Solid State discussion/arguement and
please lets not open that can of worms. :)

good luck
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Fred Bloggs
Guest
Posted: Fri Feb 11, 2005 8:29 pm    Post subject: Re: -5 volts? Reply with quote
Quote:
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.

It is not necessary to invert for your slight loading, a simple power
supply split will suffice-use figure 10 in the MAX5354 datasheet and run
the input and output 741's off this:

View in a fixed-width font such as Courier.



78L05
+-------+
+-------------+---+---|IN OUT|---+-(+)5V
| | | | | |
| | | | | |
| | 680 | GND | ===
| | | +-------+ 1u
| | | | |
(+)---+ | | | |
| +-------+-------+----+-->
| | | |
12v === 1n5231B| | ---
1u ---/ === ///
| // \ 1u
(-)---+ | --- |
| | | |
| | | |
| | | |
| | | |
+-------------+-----------+-------+-(-)5V
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Chris Carlen
Guest
Posted: Fri Feb 11, 2005 10:26 pm    Post subject: Re: -5 volts? Reply with quote
DaveC wrote:
Quote:
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.

You should stick with higher slew rates to provide enough full power
bandwidth (not the same as small signal bandwidth, which is the front
page spec given in datasheets). For an interesting extra homework
problem, determine the slew rate r needed from an op-amp to avoid
distortion for a desired signal output of frequency f, and peak amplitude A.

For audio, there are some really cool op-amps that aren't expensive:

OPA134, OPA2134, etc.
NE5532

From TI. Go to TI's web site, register, and they will send you samples
overnight (yes, to students as well) You can get about 4 each of at
least two part numbers per order.

Here's a neat article:

http://www.edn.com/article/CA200380.html



Good day!

--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
crcarle@sandia.gov -- NOTE: Remove "BOGUS" from email address to reply.
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Jamie
Guest
Posted: Sat Feb 12, 2005 3:16 am    Post subject: Re: -5 volts? Reply with quote
Chris Carlen wrote:

Quote:
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! :)
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