 |
Search Sci.Electronics.Basics |
|
|
|
|
|
|
 |
|
|
Sci.Electronics.Basics -> LM1875 on a single supply
There are 13 messages in this thread.
You are currently looking at messages 1 to 13.
|
|
|
I was reading the datasheet for the LM1875
http://www.national.com/ds.cgi/LM/LM1875.pdf
and I noticed that they do have a schematic for a single supply (as
opposed to a +/- supply).
If running on a single supply, does the chip amplifer consume
significant power during quiet tracks?
Would this be pretty much the same as running the amplifier in Class A
mode (vs. Class AB)?
I'm trying to figure out if I really need a +/- power supply, or if I
can just go with a single supply (easier to build).
Thanks,
Michael
|
|
|
|
Author: Don BoweyDate: 14:48 01-07-08
|
|
On 7/1/08 11:30 AM, in article
a1662fad-e0d7-4306-9e20-195abb1e7311@c19g2000prf.googlegroups.com,
"mrdarrett@gmail.com" <mrdarrett@gmail.com> wrote:
> I was reading the datasheet for the LM1875
> http://www.national.com/ds.cgi/LM/LM1875.pdf
>
> and I noticed that they do have a schematic for a single supply (as
> opposed to a +/- supply).
>
> If running on a single supply, does the chip amplifer consume
> significant power during quiet tracks?
>
> Would this be pretty much the same as running the amplifier in Class A
> mode (vs. Class AB)?
>
> I'm trying to figure out if I really need a +/- power supply, or if I
> can just go with a single supply (easier to build).
>
> Thanks,
>
> Michael
The datasheet does have a "Typical Single Supply Operation" schematic.
Have another look.
|
|
|
|
|
|
On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
> On 7/1/08 11:30 AM, in article
> a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,
>
>
>
> "mrdarr...@gmail.com" <mrdarr...@gmail.com> wrote:
> > I was reading the datasheet for the LM1875
> >http://www.national.com/ds.cgi/LM/LM1875.pdf
>
> > and I noticed that they do have a schematic for a single supply (as
> > opposed to a +/- supply).
>
> > If running on a single supply, does the chip amplifer consume
> > significant power during quiet tracks?
>
> > Would this be pretty much the same as running the amplifier in Class A
> > mode (vs. Class AB)?
>
> > I'm trying to figure out if I really need a +/- power supply, or if I
> > can just go with a single supply (easier to build).
>
> > Thanks,
>
> > Michael
>
> The datasheet does have a "Typical Single Supply Operation" schematic.
> Have another look.
Yes, that's what I said. There is a schematic. It's on Page 2.
(amused grin)
Michael
|
|
|
|
Author: Don BoweyDate: 15:06 01-07-08
|
|
On 7/1/08 11:48 AM, in article C48FCA1C.BCF88%dbowey@comcast.net, "Don
Bowey" <dbowey@comcast.net> wrote:
> On 7/1/08 11:30 AM, in article
> a1662fad-e0d7-4306-9e20-195abb1e7311@c19g2000prf.googlegroups.com,
> "mrdarrett@gmail.com" <mrdarrett@gmail.com> wrote:
>
>> I was reading the datasheet for the LM1875
>> http://www.national.com/ds.cgi/LM/LM1875.pdf
>>
>> and I noticed that they do have a schematic for a single supply (as
>> opposed to a +/- supply).
>>
>> If running on a single supply, does the chip amplifer consume
>> significant power during quiet tracks?
>>
>> Would this be pretty much the same as running the amplifier in Class A
>> mode (vs. Class AB)?
>>
>> I'm trying to figure out if I really need a +/- power supply, or if I
>> can just go with a single supply (easier to build).
>>
>> Thanks,
>>
>> Michael
>
> The datasheet does have a "Typical Single Supply Operation" schematic.
> Have another look.
>
>
Oops! I misread your post.
You shouldn't have any problem with a single supply, but be sure to follow
the guidelines on heat sinking. It appears the amp operates in Class B and
will idle at about 6W of heat dissipation.
|
|
|
|
Author: John FieldsDate: 15:15 01-07-08
|
|
On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarrett@gmail.com wrote:
>On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
>> On 7/1/08 11:30 AM, in article
>> a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,
>>
>>
>>
>> "mrdarr...@gmail.com" <mrdarr...@gmail.com> wrote:
>> > I was reading the datasheet for the LM1875
>> >http://www.national.com/ds.cgi/LM/LM1875.pdf
>>
>> > and I noticed that they do have a schematic for a single supply (as
>> > opposed to a +/- supply).
>>
>> > If running on a single supply, does the chip amplifer consume
>> > significant power during quiet tracks?
>>
>> > Would this be pretty much the same as running the amplifier in Class A
>> > mode (vs. Class AB)?
>>
>> > I'm trying to figure out if I really need a +/- power supply, or if I
>> > can just go with a single supply (easier to build).
>>
>> > Thanks,
>>
>> > Michael
>>
>> The datasheet does have a "Typical Single Supply Operation"
schematic.
>> Have another look.
>
>
>Yes, that's what I said. There is a schematic. It's on Page 2.
>(amused grin)
---
Look at "Supply Current" on page 2 and read: "Power Dissipation and
Heat Sinking" on page 6.
JF
|
|
|
|
|
|
On Jul 1, 12:15 pm, John Fields <jfie...@austininstruments.com> wrote:
> On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
> >On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
> >> On 7/1/08 11:30 AM, in article
> >> a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,
>
> >> "mrdarr...@gmail.com" <mrdarr...@gmail.com> wrote:
> >> > I was reading the datasheet for the LM1875
> >> >http://www.national.com/ds.cgi/LM/LM1875.pdf
>
> >> > and I noticed that they do have a schematic for a single supply (as
> >> > opposed to a +/- supply).
>
> >> > If running on a single supply, does the chip amplifer consume
> >> > significant power during quiet tracks?
>
> >> > Would this be pretty much the same as running the amplifier in Class
A
> >> > mode (vs. Class AB)?
>
> >> > I'm trying to figure out if I really need a +/- power supply, or if I
> >> > can just go with a single supply (easier to build).
>
> >> > Thanks,
>
> >> > Michael
>
> >> The datasheet does have a "Typical Single Supply Operation"
schematic.
> >> Have another look.
>
> >Yes, that's what I said. There is a schematic. It's on Page 2.
> >(amused grin)
>
> ---
> Look at "Supply Current" on page 2 and read: "Power Dissipation and
> Heat Sinking" on page 6.
>
> JF
Ah, so apparently the chip does not use more power with a single
supply than with a +/- supply.
Is there any reason why I should NOT use a single supply with this
chip?
Thanks,
Michael
|
|
|
|
Author: John FieldsDate: 18:07 01-07-08
|
|
On Tue, 1 Jul 2008 13:30:05 -0700 (PDT), mrdarrett@gmail.com wrote:
>On Jul 1, 12:15 pm, John Fields <jfie...@austininstruments.com> wrote:
>> On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
>> >On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
>> >> On 7/1/08 11:30 AM, in article
>> >> a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,
>>
>> >> "mrdarr...@gmail.com" <mrdarr...@gmail.com> wrote:
>> >> > I was reading the datasheet for the LM1875
>> >> >http://www.national.com/ds.cgi/LM/LM1875.pdf
>>
>> >> > and I noticed that they do have a schematic for a single supply
(as
>> >> > opposed to a +/- supply).
>>
>> >> > If running on a single supply, does the chip amplifer consume
>> >> > significant power during quiet tracks?
>>
>> >> > Would this be pretty much the same as running the amplifier in
Class A
>> >> > mode (vs. Class AB)?
>>
>> >> > I'm trying to figure out if I really need a +/- power supply, or
if I
>> >> > can just go with a single supply (easier to build).
>>
>> >> > Thanks,
>>
>> >> > Michael
>>
>> >> The datasheet does have a "Typical Single Supply Operation"
schematic.
>> >> Have another look.
>>
>> >Yes, that's what I said. There is a schematic. It's on Page 2.
>> >(amused grin)
>>
>> ---
>> Look at "Supply Current" on page 2 and read: "Power Dissipation
and
>> Heat Sinking" on page 6.
>>
>> JF
>
>
>
>Ah, so apparently the chip does not use more power with a single
>supply than with a +/- supply.
>
>Is there any reason why I should NOT use a single supply with this
>chip?
---
I don't think so, but try it and see if it works the way you want it
to. If it does you've saved a supply, but if it doesn't it's only
cost you a handful of discretes.
JF
|
|
|
|
|
|
On Jul 1, 3:07 pm, John Fields <jfie...@austininstruments.com> wrote:
> On Tue, 1 Jul 2008 13:30:05 -0700 (PDT), mrdarr...@gmail.com wrote:
> >On Jul 1, 12:15 pm, John Fields <jfie...@austininstruments.com> wrote:
> >> On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
> >> >On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
> >> >> On 7/1/08 11:30 AM, in article
> >> >>
a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,
>
> >> >> "mrdarr...@gmail.com" <mrdarr...@gmail.com>
wrote:
> >> >> > I was reading the datasheet for the LM1875
> >> >> >http://www.national.com/ds.cgi/LM/LM1875.pdf
>
> >> >> > and I noticed that they do have a schematic for a single
supply (as
> >> >> > opposed to a +/- supply).
>
> >> >> > If running on a single supply, does the chip amplifer
consume
> >> >> > significant power during quiet tracks?
>
> >> >> > Would this be pretty much the same as running the amplifier
in Class A
> >> >> > mode (vs. Class AB)?
>
> >> >> > I'm trying to figure out if I really need a +/- power
supply, or if I
> >> >> > can just go with a single supply (easier to build).
>
> >> >> > Thanks,
>
> >> >> > Michael
>
> >> >> The datasheet does have a "Typical Single Supply
Operation" schematic.
> >> >> Have another look.
>
> >> >Yes, that's what I said. There is a schematic. It's on Page 2.
> >> >(amused grin)
>
> >> ---
> >> Look at "Supply Current" on page 2 and read: "Power
Dissipation and
> >> Heat Sinking" on page 6.
>
> >> JF
>
> >Ah, so apparently the chip does not use more power with a single
> >supply than with a +/- supply.
>
> >Is there any reason why I should NOT use a single supply with this
> >chip?
>
> ---
> I don't think so, but try it and see if it works the way you want it
> to. If it does you've saved a supply, but if it doesn't it's only
> cost you a handful of discretes.
>
> JF
Good point. Thanks.
Michael
|
|
|
|
Author: Dan CobyDate: 18:46 01-07-08
|
|
<mrdarrett@gmail.com> wrote in message
news:1e6e5d05-ed46-4ff7-a246-35a18c841cd1@i18g2000prn.googlegroups.com...
> On Jul 1, 3:07 pm, John Fields <jfie...@austininstruments.com> wrote:
>> On Tue, 1 Jul 2008 13:30:05 -0700 (PDT), mrdarr...@gmail.com wrote:
>> >On Jul 1, 12:15 pm, John Fields <jfie...@austininstruments.com>
wrote:
>> >> On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
>> >> >On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
>> >> >> On 7/1/08 11:30 AM, in article
>> >> >>
a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,
>>
>> >> >> "mrdarr...@gmail.com" <mrdarr...@gmail.com>
wrote:
>> >> >> > I was reading the datasheet for the LM1875
>> >> >> >http://www.national.com/ds.cgi/LM/LM1875.pdf
>>
>> >> >> > and I noticed that they do have a schematic for a single
supply (as
>> >> >> > opposed to a +/- supply).
>>
>> >> >> > If running on a single supply, does the chip amplifer
consume
>> >> >> > significant power during quiet tracks?
>>
>> >> >> > Would this be pretty much the same as running the
amplifier in Class A
>> >> >> > mode (vs. Class AB)?
>>
>> >> >> > I'm trying to figure out if I really need a +/- power
supply, or if I
>> >> >> > can just go with a single supply (easier to build).
>>
>> >> >> > Thanks,
>>
>> >> >> > Michael
>>
>> >> >> The datasheet does have a "Typical Single Supply
Operation" schematic.
>> >> >> Have another look.
>>
>> >> >Yes, that's what I said. There is a schematic. It's on Page 2.
>> >> >(amused grin)
>>
>> >> ---
>> >> Look at "Supply Current" on page 2 and read: "Power
Dissipation and
>> >> Heat Sinking" on page 6.
>>
>> >> JF
>>
>> >Ah, so apparently the chip does not use more power with a single
>> >supply than with a +/- supply.
>>
>> >Is there any reason why I should NOT use a single supply with this
>> >chip?
>>
>> ---
>> I don't think so, but try it and see if it works the way you want it
>> to. If it does you've saved a supply, but if it doesn't it's only
>> cost you a handful of discretes.
>>
>> JF
>
>
> Good point. Thanks.
>
> Michael
I would like to point out that the single supply schematic has a 2200 uF
capacitor in series with the output speaker. In theory, with an ideal
capacitor, this is going to give an 18 Hz cutoff frequency into a 4 ohm
speaker (36 Hz into 8 ohms). A real capacitor will have some internal
resistance. This is going to give a higher cutoff frequency.
|
|
|
|
Author: Paul E. SchoenDate: 02:43 02-07-08
|
|
<mrdarrett@gmail.com> wrote in message
news:a1662fad-e0d7-4306-9e20-195abb1e7311@c19g2000prf.googlegroups.com...
>I was reading the datasheet for the LM1875
> http://www.national.com/ds.cgi/LM/LM1875.pdf
>
> and I noticed that they do have a schematic for a single supply (as
> opposed to a +/- supply).
>
> If running on a single supply, does the chip amplifer consume
> significant power during quiet tracks?
>
> Would this be pretty much the same as running the amplifier in Class A
> mode (vs. Class AB)?
>
> I'm trying to figure out if I really need a +/- power supply, or if I
> can just go with a single supply (easier to build).
>
> Thanks,
>
> Michael
Since the LM1875 is inexpensive, you might try using two of them on a
single supply, and putting the speaker between the outputs. You would have
to make one amp inverting and the other non-inverting, but you will get
twice the output voltage and save the capacitors. A single 24 volt supply
will then give +/- 24 volts, or about 17 VRMS, to an 8 ohm speaker, or 36
watts. There are lots of 24 VDC supplies available. The downside of this
approach is making sure the DC level of both amps are equal and about 1/2
the supply.
If you check SemiElectric's eBay store you will find PC boards and kits for
the LM3875, as well as other single and dual amplifier ICs:
http://search.stores.ebay.com/semielectric_audio-amp_W0QQfciZQ2d1QQfclZ3QQfsnZsemielectr
icQQfsooZ2QQfsopZ3QQfsubZ0QQsaselZ650588702QQsofpZ0
His LM3875s are about $6.50 each. They are larger (56 watts vs 20 watts),
but seem to be otherwise quite similar. Most of the additional IC pins are
NCs, for heat sinking and mechanical mounting, I suppose. They are only
$5.90 each from DigiKey, and the LM1875 is $3.28. Wow: 10 to 15 cents per
watt!
Paul
|
|
|
|
|
|
On Jul 1, 11:43 pm, "Paul E. Schoen" <pst...@smart.net> wrote:
> <mrdarr...@gmail.com> wrote in message
>
> news:a1662fad-e0d7-4306-9e20-195abb1e7311@c19g2000prf.googlegroups.com...
>
>
>
> >I was reading the datasheet for the LM1875
> >http://www.national.com/ds.cgi/LM/LM1875.pdf
>
> > and I noticed that they do have a schematic for a single supply (as
> > opposed to a +/- supply).
>
> > If running on a single supply, does the chip amplifer consume
> > significant power during quiet tracks?
>
> > Would this be pretty much the same as running the amplifier in Class A
> > mode (vs. Class AB)?
>
> > I'm trying to figure out if I really need a +/- power supply, or if I
> > can just go with a single supply (easier to build).
>
> > Thanks,
>
> > Michael
>
> Since the LM1875 is inexpensive, you might try using two of them on a
> single supply, and putting the speaker between the outputs. You would have
> to make one amp inverting and the other non-inverting, but you will get
> twice the output voltage and save the capacitors. A single 24 volt supply
> will then give +/- 24 volts, or about 17 VRMS, to an 8 ohm speaker, or 36
> watts. There are lots of 24 VDC supplies available. The downside of this
> approach is making sure the DC level of both amps are equal and about 1/2
> the supply.
>
> If you check SemiElectric's eBay store you will find PC boards and kits for
> the LM3875, as well as other single and dual amplifier ICs:
>
> http://search.stores.ebay.com/semielectric_audio-amp_W0QQfciZQ2d1QQfc...
>
> His LM3875s are about $6.50 each. They are larger (56 watts vs 20 watts),
> but seem to be otherwise quite similar. Most of the additional IC pins are
> NCs, for heat sinking and mechanical mounting, I suppose. They are only
> $5.90 each from DigiKey, and the LM1875 is $3.28. Wow: 10 to 15 cents per
> watt!
>
> Paul
That's a good idea. Thanks.
Michael
|
|
|
|
Author: Jasen BettsDate: 06:47 10-07-08
|
|
On 2008-07-01, Dan Coby <adcoby@earthlink.net> wrote:
> I would like to point out that the single supply schematic has a 2200 uF
> capacitor in series with the output speaker. In theory, with an ideal
> capacitor, this is going to give an 18 Hz cutoff frequency into a 4 ohm
> speaker (36 Hz into 8 ohms). A real capacitor will have some internal
> resistance. This is going to give a higher cutoff frequency.
Higher? I would have thunk lower.
Bye.
Jasen
|
|
|
|
Author: Dan CobyDate: 17:39 10-07-08
|
|
"Jasen Betts" <jasen@xnet.co.nz> wrote in message
news:g54pbg$435$6@gonzo...
> On 2008-07-01, Dan Coby <adcoby@earthlink.net> wrote:
>
>> I would like to point out that the single supply schematic has a 2200 uF
>> capacitor in series with the output speaker. In theory, with an ideal
>> capacitor, this is going to give an 18 Hz cutoff frequency into a 4 ohm
>> speaker (36 Hz into 8 ohms). A real capacitor will have some internal
>> resistance. This is going to give a higher cutoff frequency.
>
> Higher? I would have thunk lower.
Yes. My mistake, the series resistance of the capacitor is going to move the
break frequency lower. However the series resistance of the capacitor is going
to cut the overall gain of the circuit since it will form a voltage divider with the
speaker impedance.
|
|
|
|
1 |
|
|
|
|
Contact | Electronic Portal
|
|
|
