looking at it from the top
these particular units are in a fanned enclosure -- they run warm -- you can see that I use a PC-style power connector and, if memory serves correctly, the power traces are 0.040" (the Digital Camera is on the fritz so I just placed the unit on my flatbed scanner -- ergo the poor resolution.)
these particular units are in a fanned enclosure -- they run warm -- you can see that I use a PC-style power connector and, if memory serves correctly, the power traces are 0.040" (the Digital Camera is on the fritz so I just placed the unit on my flatbed scanner -- ergo the poor resolution.)
Attachments
Re: looking at it from the top
You should be able to turn up the scanners rez in the software to get a larger picture with much higher rez than any digi-cam.
dave
jackinnj said:
You should be able to turn up the scanners rez in the software to get a larger picture with much higher rez than any digi-cam.
dave
Inverting amp
The inverting version of the amp would be voltage shunt feedback. In this mode the common mode voltage is much lower than in the case of the voltage series feedback ( normal noninverting scheme) . So an amp with noticeable amounts of distortion with high common mode voltage will fare better and often sound better with voltage shunt feedback ( inverting scheme). In non operational type amps with substantially lower open loop gain than 100,000 or so , this may be more noticeable.
Has anyone tried both schemes with modern day audio amp chips ?
The inverting version of the amp would be voltage shunt feedback. In this mode the common mode voltage is much lower than in the case of the voltage series feedback ( normal noninverting scheme) . So an amp with noticeable amounts of distortion with high common mode voltage will fare better and often sound better with voltage shunt feedback ( inverting scheme). In non operational type amps with substantially lower open loop gain than 100,000 or so , this may be more noticeable.
Has anyone tried both schemes with modern day audio amp chips ?
Just to give credit where it's due. The entire LM3876 article on the circuit Jean used is at Rod Elliotts site
http://sound.westhost.com/project19.htm
http://sound.westhost.com/project19.htm
what power supply do you guys use for this? I was gonna get a 40v transformer but i dont know how many amps is good. anyone care to help.
STMicro Link
I saw a link to this on the SingleChip Amp section of EZBoard -- a calculator for audio amp design from the folks at ST Micro
http://us.st.com/stonline/products/support/designin/audio.htm
I saw a link to this on the SingleChip Amp section of EZBoard -- a calculator for audio amp design from the folks at ST Micro
http://us.st.com/stonline/products/support/designin/audio.htm
thermal resistance of fully insulated package?
Got a couple of 3886TF, i.e. fully insulated. Checked this data sheet as well as 3875. They give theta_JA at 1 K/W, without reference to the type of case. I just can't believe regular and insulated package have the same heat resistance.
Eric
Got a couple of 3886TF, i.e. fully insulated. Checked this data sheet as well as 3875. They give theta_JA at 1 K/W, without reference to the type of case. I just can't believe regular and insulated package have the same heat resistance.
Eric
The graphs in the datasheet will tell you how much power is dissipated by the chip for given power output, voltage rails, and speaker impedance. Calculate the power by adding output power to chip power. Double this to get a VA rating for the transformer.syko82 said:
A 40v transformer will give you about 56 volts DC at low output power.
better based on what?
Is the 3886 really better that the 3876? Based on what?
Sonically the concensus is that the 3875 sound way better.
And talking about power. in my experience, when you use any of them, the real limiting factor is power dissipation. With such a small pakqge, heat is a problem.
Unless you do some hard cooling with fans or something better.
cheers
Ric
Is the 3886 really better that the 3876? Based on what?
Sonically the concensus is that the 3875 sound way better.
And talking about power. in my experience, when you use any of them, the real limiting factor is power dissipation. With such a small pakqge, heat is a problem.
Unless you do some hard cooling with fans or something better.
cheers
Ric
On the other hand, why would the 3875 sound better? How many people have compared the two directly and have come to this conlusion? Myths get started very quickly in this community.
Looking at the disto plots in the data sheets, I'd say the 3886 is slightly better.
Eric
Looking at the disto plots in the data sheets, I'd say the 3886 is slightly better.
Eric
LM3875 - High-Performance 56W Audio Power Amplifier
*LM3876 - with mute
35V { 56W ~ 0.1% THD ~ 8 Ohm
{ 100W peak
11 pin
http://www.national.com/pf/LM/LM3875.html
____________________________________________________
LM3886 - High-Performance 68W Audio Power Amplifier with Mute
35V { 68W ~ 0.1% THD ~ 8 Ohm
{ 135W peak
28V { 60W ~ 0.1% THD ~ 4 Ohm
11 pin
http://www.national.com/pf/LM/LM3886.html
____________________________________________________
LM4651 - 170W Class D Audio Amplifier
22V { 75W ~ 1% THD ~ 8 Ohm
{ 90W ~ 10% THD ~ 8 Ohm
{ 125W ~ 1% THD ~ 4 Ohm
{ 155W ~ 10% THD ~ 4 Ohm
{ 135W ~ MAX POWER ~ 1% THD ~ 4 Ohm
{ 170W ~ MAX POWER ~ 10% THD ~ 4 OHM
http://www.national.com/pf/LM/LM4651.html
*LM3876 - with mute
35V { 56W ~ 0.1% THD ~ 8 Ohm
{ 100W peak
11 pin
http://www.national.com/pf/LM/LM3875.html
____________________________________________________
LM3886 - High-Performance 68W Audio Power Amplifier with Mute
35V { 68W ~ 0.1% THD ~ 8 Ohm
{ 135W peak
28V { 60W ~ 0.1% THD ~ 4 Ohm
11 pin
http://www.national.com/pf/LM/LM3886.html
____________________________________________________
LM4651 - 170W Class D Audio Amplifier
22V { 75W ~ 1% THD ~ 8 Ohm
{ 90W ~ 10% THD ~ 8 Ohm
{ 125W ~ 1% THD ~ 4 Ohm
{ 155W ~ 10% THD ~ 4 Ohm
{ 135W ~ MAX POWER ~ 1% THD ~ 4 Ohm
{ 170W ~ MAX POWER ~ 10% THD ~ 4 OHM
http://www.national.com/pf/LM/LM4651.html
data sheets do not tell the SOUND
Something I'd like to add to this conversation:
There's no point in comparing the sound of an amplifier based on the specs ALONE. Amps that measure better that others not always sound better.And that is a fact.
To be fair, lots of silly audio miths circulate around, but bear in mind that sometimes an "improved" version of a chip sounds worst than the old one that "upgrades". In this case could be the mute circuit added or a slight change in the topology, I do not know for sure.
But to say that a chip is "better" that other based on a spec of a few more watts , without taking in consideration that both chips sharre the same disipation limit that is critical even for the "smaller" one is not seeing the complete picture, in my opinion.
cheers
Ric
Something I'd like to add to this conversation:
There's no point in comparing the sound of an amplifier based on the specs ALONE. Amps that measure better that others not always sound better.And that is a fact.
To be fair, lots of silly audio miths circulate around, but bear in mind that sometimes an "improved" version of a chip sounds worst than the old one that "upgrades". In this case could be the mute circuit added or a slight change in the topology, I do not know for sure.
But to say that a chip is "better" that other based on a spec of a few more watts , without taking in consideration that both chips sharre the same disipation limit that is critical even for the "smaller" one is not seeing the complete picture, in my opinion.
cheers
Ric
- Status
- Not open for further replies.