Transient speed. . . as in h2 vs h3 and bass speed resolution. . . makes a lot of sense. Less puuuushing a boom with consequently more pretty bass rumbles, would seem possible to run cooler.
But, there's no problem. Brian has used the centerline tolerance that just happens to agree with my rather mysterious heat management observation. . . so the potential problem is absent.
Let's just keep it simple and say that "room for the screwdriver" is a very, very good thing.
But, there's no problem. Brian has used the centerline tolerance that just happens to agree with my rather mysterious heat management observation. . . so the potential problem is absent.
Let's just keep it simple and say that "room for the screwdriver" is a very, very good thing.
danielwritesbac said:
The "transient speed" of any decent cap should be much faster than any audio waveform. The basic equation i=C(dv/dt) is what governs the amount of current that a capacitor can source or sink. The lower the load impedance is the larger the amount of current that will flow through the capacitor, and the larger the voltage drop that will occur across the capacitor. This is the reason that larger capacitors can provide better bass performance - higher capacitance values can supply more current with less voltage sag. But larger capacitors also tend to have higher inductance, which is governed by the other basic equation V=L(di/dt). This is more or less trivial for class ab amps, but it has more of an effect in class d amps where the output transistors are switched on and off very rapidly.
danielwritesbac said:
Ironically, the 220uF 35V cap I chose coincides with the value that works for your amps. I'd be willing to bet that different values of caps will work equally as well with my board. We'll see soon enough since I've ordered some boards earlier today.
BWRX said:
Hey bud, sorry about the elipses, but I nearly fell off my chair when I read that part.
I've tried and tried to think up an explanation, but, couldn't do it. My apologies.
Instead, here is my selection method for that part:
Too big for more bass adds noise in proportion to the additional bass, including problems of slow bass resolution, problems with general speaker compatibility--in which case the approach can backfire and become bass shy due to insufficient impact.
If just the right size. . . well you get hifi.
Likewise, too small can make an "extra generous" upper midrange, like the chipamp.com kit. One amplifier like that in my collection is more than sufficient.
I like amplifiers best described by what they don't sound like--no extra bass, no extra mids, no extra details, no distracting extras whatsoever. Does that make sense?
Again, I apologise that I couldn't come up with a better response on the topic of the caps onboard with the amplifier. Well, I just wish I could have given an explanation, but the three comparisons above is all I can do.
And, I can't name the optimum part to use--that will vary by application. I didn't say to use only 220uF, but what I did say is that its a great place to start because its the centerpoint of a range that's likely for hifi results. There's probably still going to be a hunt because many other factors (probably all) will affect the outcome of which part is optimal.
Some of that is fun. I hope the boards arrive soon.
BWRX said:
Perhaps that statement was a little too general. You need to look at the power supply and amp as a whole and not just focus on the electrolytic caps closest to the chip. Since all chip amps use feedback, they will try correct the output voltage to match the input voltage regardless of power supply fluctuations. Even so, that doesn't mean that we don't want good stiff supply voltages. If an amp has a very stiff power supply then it will be able to supply a lot of current without any droop in voltage.
Consider an amp that does not have feedback. Any power supply ripple or sagging will affect the output voltage. When asked to deliver large amounts of current the supply rails will sag the most. What this looks like on a frequency response plot is a low end that starts to roll off.
A heads-up. A great resource (mentioned above) is going away.
A very much ideal driver for this lm1875 project, is currently on a clearance sale. Its 92db, 6-1/2 inches woofer, and it works in boxes from 0.5 cubic feet ported (or sealed) to 1 cubic foot ported (or sealed). Normally, its $43, but on closeout special its $26.
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=264-852
It can enable your LM1875 projects to hit home theatre volume levels.
Another option, also using this driver, is http://www.partsexpress.com/projectshowcase/indexn.cfm?project=MagnaCumLaude without about 98db efficiency, good for popular music.
That is easily driven by a single LM1875, although it makes a wonderful tri-amp or quad-amp project.
Hey Brian, I guess some of us are going to find out just how much that little amp can do.
A very much ideal driver for this lm1875 project, is currently on a clearance sale. Its 92db, 6-1/2 inches woofer, and it works in boxes from 0.5 cubic feet ported (or sealed) to 1 cubic foot ported (or sealed). Normally, its $43, but on closeout special its $26.
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=264-852
It can enable your LM1875 projects to hit home theatre volume levels.
Another option, also using this driver, is http://www.partsexpress.com/projectshowcase/indexn.cfm?project=MagnaCumLaude without about 98db efficiency, good for popular music.
That is easily driven by a single LM1875, although it makes a wonderful tri-amp or quad-amp project.
Hey Brian, I guess some of us are going to find out just how much that little amp can do.
Check the math?
Here's some thoughts on the potential of the LM1875
According to the LM1875.pdf from National Semiconductor, and if I read the graphs right. . .
The LM1875 tops out at 42 watts, which it cannot pass because of its size--the heat won't go into the heatsink fast enough.
And a slight break for some collected empiric data. . .
The LM1875 is frequently enjoyed at voltages less than 16vdc or more than 25vdc.
Using it. . .
Okay, so, the recommendable transformer is a 36vct/18vds (18vac rectifies to about 26v rails, sometimes 27v rails).
Back to the PDF. . .
Since we shouldn't increase the voltage, we can increase the load, as long as we never pass the 42w barrier. Okay, if I read the charts right, that's a 6 ohm load.
Applying it. . .
The little 92db driver mentioned above, can make 6 ohm MTM's (two woofers per speaker) with a laid-back midrange (helpful to chipamps).
This would be 1 pair of drivers per each lm1875.
To make 12 ohms for each driver, add a 4 ohm resistor to the + terminal of each driver. There are two drivers, so that means two resistors (1 resistor per each driver).
This would be paralleled to make 6 ohms.
I believe the crossover to be one 0.5mh with one 16uf, second order.
And, I'm guessing that's about 94db, of hifi, at the very first watt.
Given the LM1875's abilities to make 39 watts on a 6 ohm load. . . and typically overstated specs that actually means 32 watts of music (with 39w of heat). . ., that's a whopping 110 db per each lm1875 (113db stereo), if I did the math right.
Did I do the math right?
If so, it seems that this system would outperform most high-power systems. It also seems like the laws of physics are on vacation, so can somebody check the figures? Thanks!!
Here's some thoughts on the potential of the LM1875
According to the LM1875.pdf from National Semiconductor, and if I read the graphs right. . .
The LM1875 tops out at 42 watts, which it cannot pass because of its size--the heat won't go into the heatsink fast enough.
And a slight break for some collected empiric data. . .
The LM1875 is frequently enjoyed at voltages less than 16vdc or more than 25vdc.
Using it. . .
Okay, so, the recommendable transformer is a 36vct/18vds (18vac rectifies to about 26v rails, sometimes 27v rails).
Back to the PDF. . .
Since we shouldn't increase the voltage, we can increase the load, as long as we never pass the 42w barrier. Okay, if I read the charts right, that's a 6 ohm load.
Applying it. . .
The little 92db driver mentioned above, can make 6 ohm MTM's (two woofers per speaker) with a laid-back midrange (helpful to chipamps).
This would be 1 pair of drivers per each lm1875.
To make 12 ohms for each driver, add a 4 ohm resistor to the + terminal of each driver. There are two drivers, so that means two resistors (1 resistor per each driver).
This would be paralleled to make 6 ohms.
I believe the crossover to be one 0.5mh with one 16uf, second order.
And, I'm guessing that's about 94db, of hifi, at the very first watt.
Given the LM1875's abilities to make 39 watts on a 6 ohm load. . . and typically overstated specs that actually means 32 watts of music (with 39w of heat). . ., that's a whopping 110 db per each lm1875 (113db stereo), if I did the math right.
Did I do the math right?
If so, it seems that this system would outperform most high-power systems. It also seems like the laws of physics are on vacation, so can somebody check the figures? Thanks!!
gfiandy said:
It looks funny, doesn't it.
Well, in practice, the 92db driver with the 4 ohm resistor does still play noticably louder than an 89db driver that has no resistor.
Here's what's happening.
Viewed by itself, the 4r does decrease the loudness, but mostly at the mids.
I think that this approximately compensates for the boost of the cap in the crossover. So, it doesn't require the masking and power loss of an RC (zobel). Is it break-even? I don't know. But, there's no masking. Power,
Two of eight ohm speakers, each one having a 4 ohm resistor on their + terminal, still comes out like a single 6 ohm speaker, so I think that the LM1875 amplifier doesn't lose any power.
Well, I got very loud hi-fi out of LM1875, without stressing it out. But, I think that my figures must be off a bit.
My goal here is setting up the very dynamic amplifier with a very dynamic speaker. I think that this is helpful to modern recordings. The amp is unsuited to continuous high spl, but it can deliver a big wallop on dynamics, especially with efficient speakers. Maybe its a bit more like a live performance?
EDIT: I keep wanting to give the little amp a big "push" and this is my "most seemly" idea yet. Of course, from 1 to 2 cubic feet (either size sealed or ported), is almost a floor stander. But, its still a nice compact size, sort of like my cousin's speakers over at Devore Fidelity. Well, there is a slight difference in price. Oh, but the tweeter crossover can just be a 1.5uF cap (that's a guess) and an Lpad, so research time is more like 8 minutes (no cap in the voice band--the easy way).
Hi,
to get 110db/m from a 92db/W/m driver, one would need 63W delivered to the driver.
If the feed also has a resistor in the line then the power wasted in the resistor must be added to find the total power required from the amplifier.
Of course, this assumes there are no losses in the cables nor in the crossover.
Then, one would have to consider the effect the series resistance will have on the speaker Q and design the box accordingly.
to get 110db/m from a 92db/W/m driver, one would need 63W delivered to the driver.
If the feed also has a resistor in the line then the power wasted in the resistor must be added to find the total power required from the amplifier.
Of course, this assumes there are no losses in the cables nor in the crossover.
no.
Then, one would have to consider the effect the series resistance will have on the speaker Q and design the box accordingly.
Hi,
Here is my pennies worth, I am a bit dopey at the moment as I am off work unwell so I may have made mistakes.
The Zoble network (assuming it is a 10R and 100nF to GND) dissipate very little power in the audio band. As for masking the sound this is a subjective thing and I find it depends on the type of capacitor, resistor and the the return path you use for the ground currents.
However 4R in series with the load will dissipate 1/3 of the power in the region where the drive unit is about 8R. (Agreed it will be much less arround the bass region where the drive uinit starts to resonate)
If you apply 1W in the mid range, 1/3W is lost in 4R 1/3W is dissipated in each of the drive units. This means the output of each drive unit will be down by approx 9.5dB (20*log(1/3)) but because there is two of them, then assuming perfect summation you get +6dB so the output level will be 92 - 3.5 approx 88.5dB. If the drive units in fact dip to arround 6R then the situation is much worse. The capacitor in the crossover does not make up for the loss it just increases the reactive load on the system (reducing the impedance further) drawing more power from the amplifer so for your nominal 1W in you don't get any more output.
Also you will have lost alot of control over the drive unit as it is being driven from such a high impedance, tending to cause an under damped response in the driver. Meaning the driver will tend to flap a bit creating harmonics much like the sound you get from Tube amps. This will also affect the frequency reponse tending to cause a lift a low frequencies. This does mean that it will sound louder than an 89dB speaker especially in the bass region.
This is in effect the reverse of conjugate loading as it will tend to amplify the effects of the speaker impedance changes.
However in the end if you like it, that is all that really counts, but I would just turn the rails down a bit and take the 4R resistors out or use another amplifer if you want more power.
Regards,
Andrew
Here is my pennies worth, I am a bit dopey at the moment as I am off work unwell so I may have made mistakes.
The Zoble network (assuming it is a 10R and 100nF to GND) dissipate very little power in the audio band. As for masking the sound this is a subjective thing and I find it depends on the type of capacitor, resistor and the the return path you use for the ground currents.
However 4R in series with the load will dissipate 1/3 of the power in the region where the drive unit is about 8R. (Agreed it will be much less arround the bass region where the drive uinit starts to resonate)
If you apply 1W in the mid range, 1/3W is lost in 4R 1/3W is dissipated in each of the drive units. This means the output of each drive unit will be down by approx 9.5dB (20*log(1/3)) but because there is two of them, then assuming perfect summation you get +6dB so the output level will be 92 - 3.5 approx 88.5dB. If the drive units in fact dip to arround 6R then the situation is much worse. The capacitor in the crossover does not make up for the loss it just increases the reactive load on the system (reducing the impedance further) drawing more power from the amplifer so for your nominal 1W in you don't get any more output.
Also you will have lost alot of control over the drive unit as it is being driven from such a high impedance, tending to cause an under damped response in the driver. Meaning the driver will tend to flap a bit creating harmonics much like the sound you get from Tube amps. This will also affect the frequency reponse tending to cause a lift a low frequencies. This does mean that it will sound louder than an 89dB speaker especially in the bass region.
This is in effect the reverse of conjugate loading as it will tend to amplify the effects of the speaker impedance changes.
However in the end if you like it, that is all that really counts, but I would just turn the rails down a bit and take the 4R resistors out or use another amplifer if you want more power.
Regards,
Andrew
Re: Re: Check the math?
EDIT: I just received notes over email. There is an error. The application with LM1875, the little efficient hifi driver, and the resistor, results in a sealed box application--with resistor it can't do ported.
Brian,
Compare 86db speakers at 128w for 107db (stereo 110db).
So, an LM1875 system as in teamed with 93db (or so) speakers can, indeed, outperform an average high power system.
I did say "average" and I did say "system" as an amplifier makes no sound until you add a speaker.
EDIT2: I'm sorry that those specifics weren't mentioned.
I think that this table below illustrates what happens if we use efficiency *somewhere* in the 90's decibel efficiency range. . .
Attempt at possibly the correct figures here:
One driver, 12R with resistor, maybe 90db.
MTM, 6R, 93db.
1w, 93db
2w, 96db
4w, 99db
8w, 102db
16w, 105db
32w, 108db
Stereo (2 lm1875, 4 drivers) 111db.
Other ways it outperforms the average hi power system:
1). Non-peakish response means no zobel required in the speaker's crossover (no masking). I wasn't talking about amp zobel.
2). High crosspoint avoids tweeter capacitor in the voice band (no noises at the ear's most senstive frequencies).
3). A more dynamic presentation, from both amplifier and speaker (system) is potentially more helpful to modern recordings.
For #3 compare the awful noise of modern CD source with a high power 128w amplifier pushing a stubborn speaker in contrast to the beauty of the LM1875 on an efficient speaker. I think there's no contest whatsoever.
In a nutshell, your amplifier, if given some good, efficient speakers, can, as a system, present high-end audio, at force, and it can do it on a small budget.
The speaker that I was talking about (above posts) is like the amplifier in that its small, its cute, its affordable, its easy, its hi-fi, and its loud.
I said "hi-fi" and this, to me, means that we're going to be specific on applications. Well, choose any efficient fidelity speaker. EDIT3: I was just trying to get the conversation started on whole system application for the LM1875 amps.
Your designs are great, and the SMD approach is very interesting. This upgrade to the well-loved little amplifier is why the post has more than 4600 views.
gfiandy,
Yes, that makes perfect sense. I had tested this in a sealed box, and without the need for a zobel on the woofer and with the LM1875's talents at driver command, it made quite the presentation, clear, lovely, and it shook the house.
The amplifier's zobel has remained in-place. I wasn't discussing it. Sorry for the confusion. Your writing with the flu is better than my writing on any day.
I knew my math was outta-wack because the little system didn't blow out the windows. Maybe next week?
BWRX said:
EDIT: I just received notes over email. There is an error. The application with LM1875, the little efficient hifi driver, and the resistor, results in a sealed box application--with resistor it can't do ported.
Brian,
Compare 86db speakers at 128w for 107db (stereo 110db).
So, an LM1875 system as in teamed with 93db (or so) speakers can, indeed, outperform an average high power system.
I did say "average" and I did say "system" as an amplifier makes no sound until you add a speaker.
EDIT2: I'm sorry that those specifics weren't mentioned.
I think that this table below illustrates what happens if we use efficiency *somewhere* in the 90's decibel efficiency range. . .
Attempt at possibly the correct figures here:
One driver, 12R with resistor, maybe 90db.
MTM, 6R, 93db.
1w, 93db
2w, 96db
4w, 99db
8w, 102db
16w, 105db
32w, 108db
Stereo (2 lm1875, 4 drivers) 111db.
Other ways it outperforms the average hi power system:
1). Non-peakish response means no zobel required in the speaker's crossover (no masking). I wasn't talking about amp zobel.
2). High crosspoint avoids tweeter capacitor in the voice band (no noises at the ear's most senstive frequencies).
3). A more dynamic presentation, from both amplifier and speaker (system) is potentially more helpful to modern recordings.
For #3 compare the awful noise of modern CD source with a high power 128w amplifier pushing a stubborn speaker in contrast to the beauty of the LM1875 on an efficient speaker. I think there's no contest whatsoever.
In a nutshell, your amplifier, if given some good, efficient speakers, can, as a system, present high-end audio, at force, and it can do it on a small budget.
The speaker that I was talking about (above posts) is like the amplifier in that its small, its cute, its affordable, its easy, its hi-fi, and its loud.
I said "hi-fi" and this, to me, means that we're going to be specific on applications. Well, choose any efficient fidelity speaker. EDIT3: I was just trying to get the conversation started on whole system application for the LM1875 amps.
Your designs are great, and the SMD approach is very interesting. This upgrade to the well-loved little amplifier is why the post has more than 4600 views.
gfiandy,
Yes, that makes perfect sense. I had tested this in a sealed box, and without the need for a zobel on the woofer and with the LM1875's talents at driver command, it made quite the presentation, clear, lovely, and it shook the house.
The amplifier's zobel has remained in-place. I wasn't discussing it. Sorry for the confusion. Your writing with the flu is better than my writing on any day.
I knew my math was outta-wack because the little system didn't blow out the windows. Maybe next week?
Tiny PCB
Well, this (photo) is as small as I could get a PCB on hole-thru components. There were lots of notes about possible sizes of SMD, and I just couldn't figure it which of those were actually available for purchase.
Its one layer. Is the 2" size is okay for having 7 caps and 7 resistors? I'd like to shrink that down to about a postage stamp and then cram a preamp on there too.
Its the first time I used software to make a PCB, so is this board okay?
Well, this (photo) is as small as I could get a PCB on hole-thru components. There were lots of notes about possible sizes of SMD, and I just couldn't figure it which of those were actually available for purchase.
Its one layer. Is the 2" size is okay for having 7 caps and 7 resistors? I'd like to shrink that down to about a postage stamp and then cram a preamp on there too.
Its the first time I used software to make a PCB, so is this board okay?
Attachments
Daniel,
For resistors, either 1206 (typically 1/4W) or 0805's (typically 1/10W) are readily available from the typical suspects. For caps, the sizes vary greatly, so I would find the part I wanted to use and use the appropriate size. Of all places, Wikipedia seems to have a good chart of common surface mount part sizes, so you might want to glance over that before you start figuring out what parts to use. You can also meander through the Digikey or Mouser catalogs to see what people are selling if you get stuck.
It looks like you are using the ExpressPCB software, which is TERRIBLE!!! I would highly recommend searching for an alternative. Eagle is pretty commonly used by forum members, but I personally like DipTrace since the libraries are much easier to manage IMHO. Each has their own quirks, but each also has a free version, so no loss to install both and see which strikes you. If you have any CAD background, then you should be able to jump into either pretty easily. If not, then the learning curve will be steeper, but each also has a pretty good tutorial and decent help files, so you should be able to get up to speed a little more quickly.
For resistors, either 1206 (typically 1/4W) or 0805's (typically 1/10W) are readily available from the typical suspects. For caps, the sizes vary greatly, so I would find the part I wanted to use and use the appropriate size. Of all places, Wikipedia seems to have a good chart of common surface mount part sizes, so you might want to glance over that before you start figuring out what parts to use. You can also meander through the Digikey or Mouser catalogs to see what people are selling if you get stuck.
It looks like you are using the ExpressPCB software, which is TERRIBLE!!! I would highly recommend searching for an alternative. Eagle is pretty commonly used by forum members, but I personally like DipTrace since the libraries are much easier to manage IMHO. Each has their own quirks, but each also has a free version, so no loss to install both and see which strikes you. If you have any CAD background, then you should be able to jump into either pretty easily. If not, then the learning curve will be steeper, but each also has a pretty good tutorial and decent help files, so you should be able to get up to speed a little more quickly.
danielwritesbac said:A heads-up. A great resource (mentioned above) is going away.
A very much ideal driver for this lm1875 project, is currently on a clearance sale. Its 92db, 6-1/2 inches woofer, and it works in boxes from 0.5 cubic feet ported (or sealed) to 1 cubic foot ported (or sealed). Normally, its $43, but on closeout special its $26.
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=264-852
It can enable your LM1875 projects to hit home theatre volume levels.
Another option, also using this driver, is http://www.partsexpress.com/projectshowcase/indexn.cfm?project=MagnaCumLaude without about 98db efficiency, good for popular music.
That is easily driven by a single LM1875, although it makes a wonderful tri-amp or quad-amp project.
Hey Brian, I guess some of us are going to find out just how much that little amp can do.
Be careful with this driver--Its impedance curve takes a big ride up the ladder after 1000HZ!!!Always a reason for half price items!!
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