Yes, 2.8Aac into a 4r0 (resistive) load is equivalent to 32W average power.
This requires a maximum current of 4Apk into that same 4r0 load. i.e 4Apk from both supply rails alternately.
A 4ohm speaker can demand approximately three times the current of the nominal resistive load. So expect to design for 12Apk to drive your 4ohm speaker.
No National chipamp can meet this current demand. The highest current output chipamp (lm3886) is limited by specification to between 7A and something unspecified over 11.5A when the chipamp is cold.
I do not recommend a low sensitivity 4ohm speaker as the load for any chipamp. They cannot pass the transient current required for good quality sound at the louder SPLs.
Either, stick to medium sensitivity 8ohm speakers, or go discrete.
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Hi Andrew, That would require an impedance of 2.3 Ohms.... Whilst I will concur than an impedance measurement of my MTM's when I put a zobel on them did have dips in the impedance curve almost that low, it is only at certain frequencies below and above the resonant freq of the box, and not across the entire freq spectrum...
The chances are the music source is not going to be exclusively in the freq range which just so happens to coincide with the minimum impedance of the speaker. Yes it is possible that there may be times when something might demand more current than the chip can deliver, but what are those chances..
ColdCathode, one thing is definite about chipamps.. When they are overdriven their clipping is not pleasant. If you have an impeadance curve of your speakers that may give you a better idea as to whether you would have a problem or not
Tony.
The chances are the music source is not going to be exclusively in the freq range which just so happens to coincide with the minimum impedance of the speaker. Yes it is possible that there may be times when something might demand more current than the chip can deliver, but what are those chances..
ColdCathode, one thing is definite about chipamps.. When they are overdriven their clipping is not pleasant. If you have an impeadance curve of your speakers that may give you a better idea as to whether you would have a problem or not
Tony.
Any amount of watts along with a 4 ohm load and any amount of voltage will create either space heater or a lot of clipping. I have certainly done both with LM3886TF. The fortunate aspect of the 4 ohm load is less clipping.
There are several ways to cool it off, but there is only one with the extremely powerful dynamics necessary for a bass woofer amp to keep pace with a tube amp.
You need the PA100 design from National Semiconductor's AN1192.pdf and you can slightly alter the value of R-Out (page 8) to cool off the amp.
You also need an Antec transformer.
Here's some tolerances:
From 20 0 20 vac To 28 0 28 vac with a 20+ amper capacity bridge rectifier. -OR- From 20+20 vac To 28+28 vac with a pair of 10+ amper capacity bridge rectifiers.
From 3.5 ampers to 7 ampers transformer tolerance.
VA. . . the total transformer voltage multiplied by its amperage tolerance. Example 24+24vac * 4 ampers = 192VA, and that is a recommendable figure to use for a dual mono or monobloc. About 6a is good for stereo.
And, have a look at page 8. http://www.national.com/an/AN/AN-1192.pdf <click link
AndrewT may tell you that a larger size capacitance figure for the NFB cap will make for better quality bass. That is true. As a starting point, use a made-for-audio-power small canister Nichicon or Panasonic 220uF electrolytic // 22nf polyester.
For Pa100 bass amp use inexpensive 1% metal film resistors throughout. If you happen to want a "resistor trick" then the resistor that is in series to the NFB cap may be 1/2w carbon 1% matched by ohmmeter.
Smaller caps for power at the amplifier board tend to make for less heat. For example 470uF//100nF or 220uF//220uF//100nF per each rail, per each chip. In this case, you'll need fairly short length power supply cables.
The sidenote in the CarlosFM power supply indicates a polyester capacitor (250v, sized from 2uF to 4.7uF) reaching from V+ to V- and whatever else that may do, it also makes the amp run cooler.
For power, look up the CarlosFM power supply as that can be helpful to a bass amp. See also Decibel Dungeon.
Use LM3886TF--the TF is conveniently pre-insulated. This is helpful to avoid voltage output upon the heatsink. For the "TF" Plastic to Metal thermal interface, it can be optimized with the filler properties of metallic thermal paste.
With the parallel amp, PA100, it is important that exactly the same signal goes into both chips. It is also important that DC offset for both is exactly the same (hopefully zero).
There are several ways to cool it off, but there is only one with the extremely powerful dynamics necessary for a bass woofer amp to keep pace with a tube amp.
You need the PA100 design from National Semiconductor's AN1192.pdf and you can slightly alter the value of R-Out (page 8) to cool off the amp.
You also need an Antec transformer.
Here's some tolerances:
From 20 0 20 vac To 28 0 28 vac with a 20+ amper capacity bridge rectifier. -OR- From 20+20 vac To 28+28 vac with a pair of 10+ amper capacity bridge rectifiers.
From 3.5 ampers to 7 ampers transformer tolerance.
VA. . . the total transformer voltage multiplied by its amperage tolerance. Example 24+24vac * 4 ampers = 192VA, and that is a recommendable figure to use for a dual mono or monobloc. About 6a is good for stereo.
And, have a look at page 8.
http://www.national.com/an/AN/AN-1192.pdf <click linkAndrewT may tell you that a larger size capacitance figure for the NFB cap will make for better quality bass. That is true. As a starting point, use a made-for-audio-power small canister Nichicon or Panasonic 220uF electrolytic // 22nf polyester.
For Pa100 bass amp use inexpensive 1% metal film resistors throughout. If you happen to want a "resistor trick" then the resistor that is in series to the NFB cap may be 1/2w carbon 1% matched by ohmmeter.
Smaller caps for power at the amplifier board tend to make for less heat. For example 470uF//100nF or 220uF//220uF//100nF per each rail, per each chip. In this case, you'll need fairly short length power supply cables.
The sidenote in the CarlosFM power supply indicates a polyester capacitor (250v, sized from 2uF to 4.7uF) reaching from V+ to V- and whatever else that may do, it also makes the amp run cooler.
For power, look up the CarlosFM power supply as that can be helpful to a bass amp. See also Decibel Dungeon.
Use LM3886TF--the TF is conveniently pre-insulated. This is helpful to avoid voltage output upon the heatsink. For the "TF" Plastic to Metal thermal interface, it can be optimized with the filler properties of metallic thermal paste.
With the parallel amp, PA100, it is important that exactly the same signal goes into both chips. It is also important that DC offset for both is exactly the same (hopefully zero).
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OK,
Now all of you have me more confused than ever. Let me try to explain EXACTLY what I am looking for and what I am NOT looking for also.
A: I do NOT need 100Watts, therefore I don't think that I need a parallel chip configuration.
B: ALL I need to understand is why the power supply for 40 Watts into an 8 ohm load needs to be so high? Using the math in the LM3886 datasheet indicates a supply voltage of 18V and 4.5Amps by my calc that is 81 WATTS so the amp is 50% efficient?
C: Assuming all I want is 20 Watts into an 8 ohm load what do I do?
Now all of you have me more confused than ever. Let me try to explain EXACTLY what I am looking for and what I am NOT looking for also.
A: I do NOT need 100Watts, therefore I don't think that I need a parallel chip configuration.
B: ALL I need to understand is why the power supply for 40 Watts into an 8 ohm load needs to be so high? Using the math in the LM3886 datasheet indicates a supply voltage of 18V and 4.5Amps by my calc that is 81 WATTS so the amp is 50% efficient?
C: Assuming all I want is 20 Watts into an 8 ohm load what do I do?
That all sounds quite logical if you were amplifying DC. However, you don't want to amplify DC.
You want to amplify AC, as in audio.
It is dynamic.
In order for a clean 20 watts of bass from a chipamp, you need to factor in dynamic headroom versus speaker efficiency. To keep up with your tube amp is beyond the capacity of the 200 watt amplifier listed in the AN1192 document.
You can cover up the ringing cries of anguish from a too small transformer if you use a capacitive multiplier circuit or a regulator in the power supply. Transformers ring like a bell, and the smaller the transformer, the higher the pitch. . . directly into the audio band. Its not all about amperage. Don't you want pretty bass?
Your power supply would be cheaper if your transformer is larger.
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B. 4 ohms is nominal, most drivers are lower at some point and also present a reactive load that is different from a 4 ohm resistor. Some posters just wanted to make sure you had anticipated the worst case scenarios. Also, don't forget the difference between DC and RMS power - that's where the other 50% is hidden.
C. LM3886, preferably the TF insulated version. Very overkill, but we like overkill. 18-24vac, 50-100 VA transformer. 4-10,000uF or so of caps. Just my suggestion.
I've built dozens of chipamps, both bugsplat and PCB. I've moved on to tube amps, but still use chipamps where I think they're practical. My Home Theater uses 15 chipamps (5 channels, two woofers and one tweeter each) with an active crossover. Too expensive and power consuming to do practically with tubes and my relatively low effiency speakers.
C. LM3886, preferably the TF insulated version. Very overkill, but we like overkill. 18-24vac, 50-100 VA transformer. 4-10,000uF or so of caps. Just my suggestion.
I've built dozens of chipamps, both bugsplat and PCB. I've moved on to tube amps, but still use chipamps where I think they're practical. My Home Theater uses 15 chipamps (5 channels, two woofers and one tweeter each) with an active crossover. Too expensive and power consuming to do practically with tubes and my relatively low effiency speakers.
The worst case scenario, which was already illustrated, is this: Low resource power circuit makes retail subwoofer sound.
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OK,
NOW I've got it!
Pardon my thickheadedness, my surplus transformers were just stuck in my head! I will certainly source a new transformer.
Thank you all for your help!
Just a couple more questions and I will start ordering a few parts.
1: Why do most designs call for such little PS capacitance? Is there any down fall to MONGO capacitors? Should I consider "overkill" on the transformer side rather than capacitance?
2: I will design for an 8 ohm load and increase the sensitivity of the woofers I am looking for. I also think designing everything around 50W with plenty of headroom in the powersupply, but limit the gain to give me about 35 watts should keep me in a lower distortion area away from clipping?
3: Can someone explain the basic way this type of amp works? I am guessing that the incoming signal Voltage is amplified by the gain and the resultant voltage thru the load R determines the Amperage? thus the Power?
So 1 volts in X Gain of 18 = 18Volts out 18 volts thru 8 ohms is 20Watts?
4: This is where the power dissipation comes in? I need to be sure that the excess voltage can be bled off by heat dissipation?
NOW I've got it!
Pardon my thickheadedness, my surplus transformers were just stuck in my head! I will certainly source a new transformer.
Thank you all for your help!
Just a couple more questions and I will start ordering a few parts.
1: Why do most designs call for such little PS capacitance? Is there any down fall to MONGO capacitors? Should I consider "overkill" on the transformer side rather than capacitance?
2: I will design for an 8 ohm load and increase the sensitivity of the woofers I am looking for. I also think designing everything around 50W with plenty of headroom in the powersupply, but limit the gain to give me about 35 watts should keep me in a lower distortion area away from clipping?
3: Can someone explain the basic way this type of amp works? I am guessing that the incoming signal Voltage is amplified by the gain and the resultant voltage thru the load R determines the Amperage? thus the Power?
So 1 volts in X Gain of 18 = 18Volts out 18 volts thru 8 ohms is 20Watts?
4: This is where the power dissipation comes in? I need to be sure that the excess voltage can be bled off by heat dissipation?
Most designs are "gainclone" as in a copy of 47 labs.
Other designs are "chipamp" as in a more traditional design. The chipamp, specifically the CarlosFM chipamp will make your bass.
Yes with the large transformer. Its not all about the amperage. Its about the pitch to which the transformer will ring. All transformers ring during use and the concept is like a bell--also very much like a woofer.
The power supply concept is first cousin to a speaker crossover. Use transformer from 4 to 7 ampers capacity so that it is thick enough for the job.
Good ideas, but implementation is almost backwards, and here's why:
Remember that you have a highly dynamic tube amp on mids and treble.
In order to keep up, the chipamp will require significant voltage. In order for dynamics the bass amp will require significant gain (can be the chipamp itself or a smaller opamp helper). The other way to say this is: You must have headroom.
Solid state needs more than double the headroom of vacuum tube, in relation to the loudspeaker's typical 3db efficiency rule--yes, scads more power it takes. . .
With solid state, there is a pre-clipping. At this point, although the clipping is not yet or barely audible, heat output has increased. Shortchanging the solid state amplifier on voltage so that it can't do its job will increase the heat output, because almost all noise increases the heat output with solid state.
The minimum transformer for your project is this: Stancor / White-Rodgers - P-8566 - Allied Electronics 20-0-20 (40vct) EI core transformer as requested.
An externally hosted image should be here but it was not working when we last tested it.
I'd love to suggest 26 0 26 (52vct or 26+26) as a minimum although the facts wouldn't support that statement. The facts, as tested in practice, are really:
18 0 18 (36vct or 18+18 ) is insufficient.
20 0 20 (40vct) will do.
Unlike vacuum tubes, chipamps are solid state where headroom is neither graceful, nor automatic.
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It is an opamp (Operational Amplifier) chip.
It is a larger size opamp.
It isn't unity stable, and, as such, this type may do a mids or treble lift, which is not exactly relaxing, but its excellent for clear bass harmonic support in this bass amp project. The functional gain range is from 3 (inverting mode) to 48 (non-inverting mode). A plausible centerpoint tolerance is 25.
Think of it as a really big size opamp headphone amplifier project. Headphone amplifier projects with non-unity-stable opamps, non-inverting configuration, and split-rails power, will match schematics. . . because LM3886TF is an op amp.
To discover in practice, with a live demo, on how this amplifier works, try a headphone amplifier project.
Daniel,
Those transformers would be just about what I am looking for.
That was where I was headed with a supply of about 36 volts.
Gain of about 16 (I will have a little over 2V PtoP clean signal from my ALL TUBE preamp/crossover)
Load will be 8 ohms and I will look for drivers with a decently flat impedance curve (that fit in my budget)
I am drawing it up and will post at some point for people to check.
Thanks for all the help I think I am on my way now.
Those transformers would be just about what I am looking for.
That was where I was headed with a supply of about 36 volts.
Gain of about 16 (I will have a little over 2V PtoP clean signal from my ALL TUBE preamp/crossover)
Load will be 8 ohms and I will look for drivers with a decently flat impedance curve (that fit in my budget)
I am drawing it up and will post at some point for people to check.
Thanks for all the help I think I am on my way now.
Oh, you're welcome.
While you're sourcing parts. . .
Drop the gain on noise with a simple trick:
1/4w metal film for nfb
1/2w carbon for its partner
1/4w metal film for input load
1/2w carbon for its partner
*exploits the all band performance of metal film pitted against the hf failure mode of big carbon within each voltage divider, thus dropping the gain on hf noise.
The NFB cap is half the size of the local power caps that are also positioned directly at the amplifier:
If your power caps are a pair of 470uF//100nF then your NFB cap is 220uF//47nF.
The NFB cap is a good helper for both dynamics and speaker protection.
Panasonic FC 50v caps have good characteristics for bass amp use.
Noise removal trick (when works, amp runs cooler):
A made-for-power 4.7uF 250v electrolytic for V+ to V- use, is a good resource to have as a noise filter. You may or may not need this part, but its only a few cents (cheaper shipping to have it ride along with other parts).
A prosound favorite:
A Nichicon ES for the input cap--they promise loud clean bass to the prosound people in their advertising, and they do deliver. A substitute is a polypropylene power type or audio type--one that's not made for tweeter use.
Useful for bass amp:
The MUR860's although quite noisy and confusing to wire, may also be helpful in the necessary amount of dynamics. I'd suggest to use them in this bass amp project. That Stancor 40vct will need only 4 of those MUR860's.
Caps that recharge quickly:
A pair of 10,000uF 50v Panasonic TS-U with canister size 35mm x 30mm, at the power supply board, can also be helpful to bass dynamics.
Slight omission from the manual:
The zobel at the amplifier's output on the diagram is helpful to good bass. Because its resistor value looks inappropriate (too much load), we can tell that it is to be a high ESR capacitor and a stout resistor--This is: A cheap polyester dip cap and an economical 3w or a 5w resistor.
These are the specific parts for the output zobel (RC) of 2.7 ohms + 100nF illustrated on Page 6 of LM3886.pdf from National Semiconductor.
The values are reliant on specific parts (especially a polyester dip cap), else the amp could overheat and/or sound terrible and/or blacken the resistor. The little green 100nF mylar (polyester) dip caps at the local Radio Shack will be perfect for output zobel.
http://www.national.com/ds/LM/LM3886.pdf
Speaker protection plus extra Low bass:
According to the folks at the parts express forum, an capacitive load may be helpful to bass dynamics. This depends on the speaker driver. The spot to hook it up is also illustrated on page 6. The tolerance is actually 4700uF to 1500uF. I've used 3300uF for a test and there were indeed more powerful low pitches coming forth from the speaker as well as a reduction in unproductive cone movement (much less flopping, much more bass). Its so easy to test and see if it works for you. Mine is this: Cornell-Dubilier - LP332M050C5P3 - Allied Electronics and, in practice, it has survived long term use with grace.
This component also provides significant speaker protection just in case the LM3886TF's output transistors wear out someday. When that happens, your amplifier can continue uninterrupted service if it has the protection of the output capacitor on page 6. http://www.national.com/ds/LM/LM3886.pdf
Although output caps are a controversial topic, you'll want to protect this speaker, especially after you hear it. . .
Speaker drivers? These may be worth a look: Parts-Express.com:*Dayton RS270S-8 10" Reference Shielded Woofer 8 Ohm | rs270s-8 10" woofer midbass shielded woofer dayton audio dayton loudspeaker reference reference series RS aluminum reference-22008 cone shielded phase plug RS270 reference DARSW because the tonality is gorgeous on bass. For dampening, I have a guesswork figure of: Thick 2.6mH and a plastic 20uF (ballpark figures). This is in addition to (not instead of) your active components. That 20uF (or so) goes soldered directly across to the woofer's connections to maximize the electronic dampening.
Good grounding--search AndrewT's grounding methods--will also increase bass dynamics.
A good bass amp sounds shouty if run full band; however, you can see the advantage of having sufficient harmonics present in order to make nice clear bass tones. LM3886TF fits this description nicely.
That's all I've got.
It was nice working with you. I'd love to know how your project turns out.
Your project is awesome and has inspired me. Thank you.
While you're sourcing parts. . .
Drop the gain on noise with a simple trick:
1/4w metal film for nfb
1/2w carbon for its partner
1/4w metal film for input load
1/2w carbon for its partner
*exploits the all band performance of metal film pitted against the hf failure mode of big carbon within each voltage divider, thus dropping the gain on hf noise.
The NFB cap is half the size of the local power caps that are also positioned directly at the amplifier:
If your power caps are a pair of 470uF//100nF then your NFB cap is 220uF//47nF.
The NFB cap is a good helper for both dynamics and speaker protection.
Panasonic FC 50v caps have good characteristics for bass amp use.
Noise removal trick (when works, amp runs cooler):
A made-for-power 4.7uF 250v electrolytic for V+ to V- use, is a good resource to have as a noise filter. You may or may not need this part, but its only a few cents (cheaper shipping to have it ride along with other parts).
A prosound favorite:
A Nichicon ES for the input cap--they promise loud clean bass to the prosound people in their advertising, and they do deliver. A substitute is a polypropylene power type or audio type--one that's not made for tweeter use.
Useful for bass amp:
The MUR860's although quite noisy and confusing to wire, may also be helpful in the necessary amount of dynamics. I'd suggest to use them in this bass amp project. That Stancor 40vct will need only 4 of those MUR860's.
Caps that recharge quickly:
A pair of 10,000uF 50v Panasonic TS-U with canister size 35mm x 30mm, at the power supply board, can also be helpful to bass dynamics.
Slight omission from the manual:
The zobel at the amplifier's output on the diagram is helpful to good bass. Because its resistor value looks inappropriate (too much load), we can tell that it is to be a high ESR capacitor and a stout resistor--This is: A cheap polyester dip cap and an economical 3w or a 5w resistor.
These are the specific parts for the output zobel (RC) of 2.7 ohms + 100nF illustrated on Page 6 of LM3886.pdf from National Semiconductor.
The values are reliant on specific parts (especially a polyester dip cap), else the amp could overheat and/or sound terrible and/or blacken the resistor. The little green 100nF mylar (polyester) dip caps at the local Radio Shack will be perfect for output zobel.
http://www.national.com/ds/LM/LM3886.pdf
Speaker protection plus extra Low bass:
According to the folks at the parts express forum, an capacitive load may be helpful to bass dynamics. This depends on the speaker driver. The spot to hook it up is also illustrated on page 6. The tolerance is actually 4700uF to 1500uF. I've used 3300uF for a test and there were indeed more powerful low pitches coming forth from the speaker as well as a reduction in unproductive cone movement (much less flopping, much more bass). Its so easy to test and see if it works for you. Mine is this: Cornell-Dubilier - LP332M050C5P3 - Allied Electronics and, in practice, it has survived long term use with grace.
This component also provides significant speaker protection just in case the LM3886TF's output transistors wear out someday. When that happens, your amplifier can continue uninterrupted service if it has the protection of the output capacitor on page 6. http://www.national.com/ds/LM/LM3886.pdf
Although output caps are a controversial topic, you'll want to protect this speaker, especially after you hear it. . .
Speaker drivers? These may be worth a look: Parts-Express.com:*Dayton RS270S-8 10" Reference Shielded Woofer 8 Ohm | rs270s-8 10" woofer midbass shielded woofer dayton audio dayton loudspeaker reference reference series RS aluminum reference-22008 cone shielded phase plug RS270 reference DARSW because the tonality is gorgeous on bass. For dampening, I have a guesswork figure of: Thick 2.6mH and a plastic 20uF (ballpark figures). This is in addition to (not instead of) your active components. That 20uF (or so) goes soldered directly across to the woofer's connections to maximize the electronic dampening.
Good grounding--search AndrewT's grounding methods--will also increase bass dynamics.
A good bass amp sounds shouty if run full band; however, you can see the advantage of having sufficient harmonics present in order to make nice clear bass tones. LM3886TF fits this description nicely.
That's all I've got.
It was nice working with you. I'd love to know how your project turns out.
Your project is awesome and has inspired me. Thank you.
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Can you explain how the noise is lowered by using this resistor combination? Why don't you use metal for all?
Why the hell do you need harmonics in an amplifier? I thought the point is not to have any.
Dropping the gain on HF is appropriate for a subwoofer amplifier. Possibly, your simulator will show all resistors as absolutely perfect. In practice, this isn't the case.
An example:
Divider at the inverting input is 10k 1/4w metal film and 220R 1/2w carbon.
(For decreased gain, I think that the owner may be substituting 680R instead of the 220R.)
Divider at non-inverting input is 10k 1/4w metal film and 220R 1/2w carbon.
The effect is slight.
The purpose is for greater efficiency within the audio band.
Bass as a sine wave is inefficient. The point: On LM3886TF just let it play cleanly, without any sort of "relax" voicings. For a dedicated bass amp, clarity will do what sheer power cannot.
There wasn't much power available anyway, because the owner didn't want power. However, this 25 watt chip based subwoofer amplifier must keep up with a vacuum tube "music amplifier" with large dynamics.
With no other recourse to make the design work, I cheated, at the last minute, with the component list. You caught me.
The selections promote dynamics. That, a bigger charge, increases output. At this time, I didn't have LM3886TF's readily available, so I tried this with LM1875 scaled to 25 watts. With no preamp, mine has high gain (10k metal film with 220R carbon), because it also has computer source. The performance is significant. The LM3886TF will be more durable for bass amp; and, that will be important for longevity.
The owner may increase or reduce the capacitance value of the NFB cap to adjust low bass versus mid bass contour for personal taste. That should be most effective at some point after he has set up the gain for his system.
For a further increase in efficiency, the speaker output zobel (RC) may use a smaller capacitor value. The range is 220nF to 3.3nF, any of which are polyester/mylar film unless the resistor value is changed.
National Semiconductor's 2.7R would be an inappropriate load if coupled to a polypropylene capacitor. There is another case where simulation software can error, if it showed the same results for both polyester and polypropylene capacitors at the speaker output zobel (RC).
The resistor value range is from 2R to 3.3R for polyester or from 3.3R to 15R for polypropylene, depending on the internal resistance of the capacitor.
Components have great internal variance that can affect application.
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I don't use simulators, just build, test, measure and listen. I still don't get it: why carbon is better than metal? If you really want to get rid of HF noise, you put a capacitor between inverting and non-inverting inputs of the chip and/or a low pas fillter at the input. Those resistors have nothing to do with efficiency.
As for the second point: nobody cares if the bass wave is efficient or not, from a HiFi amp you expect it to be reproduced as it is, nothing to add, nothing to subtract from it. If I'm the only one who thinks like this, then I'm probably on the wrong forums. The Zobel has also nothing to do with efficiency. The amplifier sees the load as a resistor which varies along frequency and the Zobel cell corrects this to make it more linear.
Ah, the simulator doesn't know about dielectric properties, you must me the one to define them. A capacitor must me modelled as a combination of R, L and C. But you probably know this already. You need to make sure you use these in your simulations.
As for the second point: nobody cares if the bass wave is efficient or not, from a HiFi amp you expect it to be reproduced as it is, nothing to add, nothing to subtract from it. If I'm the only one who thinks like this, then I'm probably on the wrong forums. The Zobel has also nothing to do with efficiency. The amplifier sees the load as a resistor which varies along frequency and the Zobel cell corrects this to make it more linear.
Ah, the simulator doesn't know about dielectric properties, you must me the one to define them. A capacitor must me modelled as a combination of R, L and C. But you probably know this already. You need to make sure you use these in your simulations.
Resistors in subwoofer amps:
Carbon isn't better than metal, except at isolating (use to carry audio)--Metal isn't better than carbon, except at radio/HF (use for the opposite role as carbon). This applies nicely to subwoofer amps. It may or may not give a full-band amp a decreased treble. . . but the project isn't a full band amp.
You're right about the caps.
Specialty bass amp of 25 watts:
Hi-fi or not, a 25w subwoofer amp needs efficiency. At 25w, big efforts with an EQ would run the amp out of resources, and that cannot work at all (no fidelity whatsoever). Instead, the little amp must be very good at making bass all on its own--With so little resources, that's the only option (except for increasing the amp's power).
Output Zobel:
It is a load. A 25w subwoofer amp is a limited resource; therefore, you use as much Zobel as needed. . . and not one bit more. The amp has more important loads to drive, which are its speakers.
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