from my reading, it sounds like clipping has more to do with the power supply for the amp than any other factor. theoretically a well-matched power supply should all but eliminate the chance of clipping, if i understand correctly?
i've also always heard that speakers can generally handle being over-driven much better than amplifiers can handle being under-powered.
would it make sense to get the TDA8950, and use the potentiometers to keep the gain low enough that amp never pushes more watts than my speakers can handle? or you're thinking that the TDA8920 will already safely do that?
i have to keep reminding myself that these amps are rated for their RMS, and will always have a higher peak value
no point in buying a bigger amp and then never turning the input over half way. of course, i would rather just turn the gain down because the speakers are too loud at full volume, than have them too quiet even at full volume.
true enough. my sound experience is mostly in commercial 70volt systems: the only way to do zone volume control is a stepped attenuator in each zone. leaving the amp at 50-75% power all the time, and only turning the volume up or down with the attenuator.
thanks again
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Not really. Clipping occurs when the amp doesn't have enough amplitude range left to handle the highest peaks in your signal. That depends on the power supply voltage, not the quality of the power supply. You will always be able to drive the amp into clipping by using a high enough input signal, no matter what the power supply and voltage. Only way to avoid clipping is keeping the input signal below the clipping limit.
Depends on how you define "handle". Initially both produce distortion when driven too hard. Amps clip more abruptly - distortion goes up dramatically beyond clipping point. Speakers have a softer limit.
On the other hand, a badly overdriven amp produces a lot of distortion. A badly overdriven speaker gets permanently damaged.
The TDA8920 is more likely to sound bad before destroying the speaker - unless your speaker is 2-way or 3-way instead of a single driver. Tweeters are much more likely to burn out than woofers when faced with a lot of high frequency energy from a clipping amp.
Right.i have to keep reminding myself that these amps are rated for their RMS, and will always have a higher peak value
Again it all depends on how reliably you will know the maximum level of your source. If your sources are digital (ipod, computer) you will know the maximum level.
And the reason high-voltage systems are used is that they deal much better with the resistance of very long cable runs (and thus also higher-resistance potentiometers).
good evening,
i see.
so, the amp can run out of voltage to amplify the full-wave of the audio source, reguardless of what kind of speaker is attached to the output. i should remember that - largely - the part of the amp doing the amplifying is not directly connected to the speakers. the amplifing part of the circuit just sees an input and tries to multiply that until it runs out of power to do so. speakers are just on the other end to soak up the results.
that's a new perspective for me so a clipping amp will not actually be damaged by the process, excepting for some part over-heating? speakers on the other hand are the more vulnrable part of the equation, since they are receiving the output.
the speakers i plan to get, Fluance SV10S, are two way, with a crossover.
two additional questions, as long as you're helping me - is there any reason NOT to use a trimpot potentiometer for my gain control? i have searched a bit for "audio" grade trimpot, and not come up with much.
is there any reason TO use an attenuator instead of a potentiometer?
thank you for your continuing advice
i see.
so, the amp can run out of voltage to amplify the full-wave of the audio source, reguardless of what kind of speaker is attached to the output. i should remember that - largely - the part of the amp doing the amplifying is not directly connected to the speakers. the amplifing part of the circuit just sees an input and tries to multiply that until it runs out of power to do so. speakers are just on the other end to soak up the results.
that's a new perspective for me
so a clipping amp will not actually be damaged by the process, excepting for some part over-heating? speakers on the other hand are the more vulnrable part of the equation, since they are receiving the output. the speakers i plan to get, Fluance SV10S, are two way, with a crossover.
two additional questions, as long as you're helping me - is there any reason NOT to use a trimpot potentiometer for my gain control? i have searched a bit for "audio" grade trimpot, and not come up with much.
is there any reason TO use an attenuator instead of a potentiometer?
thank you for your continuing advice
Yes, the speaker is just a bunch of impedance to the amp.
Pretty much, yes. In a class D amp, you keep switching between positive and negative supply voltage very quickly. If there is no signal, the time ratio is 50/50, and it averages out to 0. When you try to go over the clipping limit, the pulse ratio becomes 100/0, and there is no way you can go beyond that.
Correct.
Mainly because they are electromecanical components that can be damaged from trying to move beyond the limits, and that need a voice coil that is light (and thus made of thin wire that burns if subjected to too much current).
Any normal trimpot will be fine.
No, not really. A passive attenuator is basically a potentiometer.
good evening,
thanks again for taking the time to answer so many questions from me. i feel like i'm learning alot, and making quick work of my lengthy list of questions.
while i have your ear, i have another blatantly non-thread-related question, if you care to share your opinion further :
i am planning on having multiple inputs; the standard "aux" input via RCA jacks, the eventual DAC, and possibly a bluetooth receiver (down the road). i have seen several threads recommending a pre-amp card for helping to normalize multiple inputs. presumably so you don't have to keep adjusting the gain when you switch sources.
of course, there is an opposite line of thought - people who feel it's best to add as few steps between source and speaker. they insist a simple good switch is enough to deal with multiple input sources. i've been looking at some nice ceramic rotary switches online.
the thing that absolutely nobody can agree on, is whether the switch should be MBB or BBM. with people arguing on both sides of the fence about the risk of unloading the impedence of the speaker from the amp causing damage (MMB), verses the speakers being fine to take the momentary surge in voltage from the amp dumping extra power into the speakers after being unloaded (BBM).
i guess that's a two-part question : switch VS pre-amp for multiple sources, and MMB vs BBM switch.
thanks again for taking the time to answer so many questions from me. i feel like i'm learning alot, and making quick work of my lengthy list of questions.
while i have your ear, i have another blatantly non-thread-related question, if you care to share your opinion further :
i am planning on having multiple inputs; the standard "aux" input via RCA jacks, the eventual DAC, and possibly a bluetooth receiver (down the road). i have seen several threads recommending a pre-amp card for helping to normalize multiple inputs. presumably so you don't have to keep adjusting the gain when you switch sources.
of course, there is an opposite line of thought - people who feel it's best to add as few steps between source and speaker. they insist a simple good switch is enough to deal with multiple input sources. i've been looking at some nice ceramic rotary switches online.
the thing that absolutely nobody can agree on, is whether the switch should be MBB or BBM. with people arguing on both sides of the fence about the risk of unloading the impedence of the speaker from the amp causing damage (MMB), verses the speakers being fine to take the momentary surge in voltage from the amp dumping extra power into the speakers after being unloaded (BBM).
i guess that's a two-part question : switch VS pre-amp for multiple sources, and MMB vs BBM switch.
No prob - my pleasure! We all have had to learn a lot...
There is actually 3 parts to that - switching between sources, normalizing levels, and actual amplifying (the "amp" part in "pre-amp"). The big question mark is your "aux" input - do you foresee ever having sources with a signal level so low that you actually need to amplify them before feeding them to the main amp? If not, you would be OK with a "passive pre-amp" (a contradiction of terms) - basically just a combination of a multi-way switch and resistor networks / trim pots to normalize the level of each input.
For any possible opinion, be it however crazy, there will be people supporting it. That doesn't mean it makes any sense.
See my signature
Between the artist and the recording, there are an unbelievable number of steps. A few more or less won't make a difference. And a switch is a switch, as long as the metal contacts aren't too corroded. Whatever possible differences are so tiny that any differences in source recording, speakers, your room and your ears will completely overwhelm them.
But you aren't switching the speakers, you are switching sources. BBM is the normal way of dealing with sources.
a quick ebay and amazon search only shows up incredibly expensive equipment, when i look for "passive pre-amp".
before i continue with my theory... is it acceptable to only switch the + feed on input signals? tying all - together as common?
if so, then you would just need a 6 pole, 3 position rotary switch, with a trimpot for each position.
simply adjust the trimpot for appropriate levels from each source.
if i did my pole count right.... basically switching + + for each source.
no phonograph low-level inputs... so i don't believe i will need any amplification.
i would like the ability to have outputs for 2 different sets of speakers.
would a regular MMB 4 pole 2 position switch work for speaker selection?
the transient connection of both sets of speakers, while the switch is being thrown, would only act as a 4ohm load for brief moment.
Shows you that the "less is more" theory is for people with more money than sense
As I said, a "passive pre" is basically just a combination of a multi-way switch and resistor networks / trim pots to normalize the level of each input. So easy to make.
If dealing with unbalanced conections (RCA), yes. Balanced connections (usually on XLR connectors, on pro gear) is another matter.
Yes.
Any reason to go for MMB instead of MBB?
the inputs will only be 1) from 3.5mm out on ipod or phone to RCA jacks on the receiver 2) DAC, which also outputs to RCA 3) bluetooth module - I think those output to a 3 pin plug of some kind.
I meant MBB
I figured better to momentarily provide a 4Ω load to the amp, during the switch throw, than removing all load.
thanks again for all your help. time for bed for me!
good afternoon,
back to the subject of gain control on input sources:
would resistors be a better option for gain control, instead of a potentiometer? it seems like a set value of a resistor might be an .... accoustically better option ... than a trimpot or a cheap potentiometer.
considering that the sources i intend to have (the DAC and the BlueTooth) will both be permenantly installed inside the amp, once i get the gain figured out it won't need to be adjusted again. no point in having moving parts where you can have solid-state instead.
have you ever seen a Resistor Network tied to a bank of DIP switches?
if you could get a good idea of the approximate amount of resistance you want to add, you could easilly add a 10-element Resistor Network and fine tune the amount of resistance for the input.
a DIP switch would make the job even easier... just use some loose resistors to find the right general Ωs need, and then add the Network and turn the DIPs on or off to dial in exactly the right value.
back to the subject of gain control on input sources:
would resistors be a better option for gain control, instead of a potentiometer? it seems like a set value of a resistor might be an .... accoustically better option ... than a trimpot or a cheap potentiometer.
considering that the sources i intend to have (the DAC and the BlueTooth) will both be permenantly installed inside the amp, once i get the gain figured out it won't need to be adjusted again. no point in having moving parts where you can have solid-state instead.
have you ever seen a Resistor Network tied to a bank of DIP switches?
if you could get a good idea of the approximate amount of resistance you want to add, you could easilly add a 10-element Resistor Network and fine tune the amount of resistance for the input.
a DIP switch would make the job even easier... just use some loose resistors to find the right general Ωs need, and then add the Network and turn the DIPs on or off to dial in exactly the right value.
Uh, why? Just because of "cheap"? A standard pot costs several $, a resistor $ 0.05...
Yes, lovely pieces of modern art.
Both rotary and DIP switches have the same issue as pots if you are concerned about "moving parts".
good afternoon,
show me a resistor that costs $0.10, and i will be very confident you have a very high quality resistor. show me a potentiometer that costs $5, and i won't trust it to be of very good build quality
i may be under the incorrect impression that potentiometers have a greater chance of introducing noise into the signal passing through them, due to my understanding that they are most often a coil of conductive material. i feel like voltage passing through a resistor will more certainly come out unchanged, other than reduced per the Ω rating of the resistor.
surely there must be a reason for people spending over $100 for the most fancy potentiometers for their amps. other than the obvious "a fool and his money are soon to part".
i also haven't seen many people talking about using trimpots in their home-made audio equipment. although they certainly are popular in every electrical device i've ever dealt with. are they the ugly child of the audio world? just as effective as a nice potentiometer, but since they aren't pretty and only cost a few cents, are ignored?
well, you are certainly technically correct that i am in error referring to a DIP switch as "solid-state". but i will argue that a DIP switch is a much different type of "moving part" than a potentiometer is...
i can get an IP67 rated DIP switch, that relies entirely on the kenetic force of "flipping" the switch, to seat a blade between two contacts. and then nothing moves. there's nothing internal that is spring-loaded or relying on contact-tension to maintain circuit continuity. no possibility* of dust or liquid intrusion... it's basically bullet-proof
compared to potentiometers that need a tensioning element of some kind to keep the wiping arm in contact with the coil.
*we know how saying those magic words work
as always, i am ready to be proven totally ignorant in how these things work. if a little $0.25 trimpot will do just as clean and reliable job as a resistor... it would certainly be an easier option
Uh, why? Just because of "cheap"? A standard pot costs several $, a resistor $ 0.05...
show me a resistor that costs $0.10, and i will be very confident you have a very high quality resistor. show me a potentiometer that costs $5, and i won't trust it to be of very good build quality
i may be under the incorrect impression that potentiometers have a greater chance of introducing noise into the signal passing through them, due to my understanding that they are most often a coil of conductive material. i feel like voltage passing through a resistor will more certainly come out unchanged, other than reduced per the Ω rating of the resistor.
surely there must be a reason for people spending over $100 for the most fancy potentiometers for their amps. other than the obvious "a fool and his money are soon to part".
i also haven't seen many people talking about using trimpots in their home-made audio equipment. although they certainly are popular in every electrical device i've ever dealt with. are they the ugly child of the audio world? just as effective as a nice potentiometer, but since they aren't pretty and only cost a few cents, are ignored?
well, you are certainly technically correct that i am in error referring to a DIP switch as "solid-state". but i will argue that a DIP switch is a much different type of "moving part" than a potentiometer is...
i can get an IP67 rated DIP switch, that relies entirely on the kenetic force of "flipping" the switch, to seat a blade between two contacts. and then nothing moves. there's nothing internal that is spring-loaded or relying on contact-tension to maintain circuit continuity. no possibility* of dust or liquid intrusion... it's basically bullet-proof
compared to potentiometers that need a tensioning element of some kind to keep the wiping arm in contact with the coil.
*we know how saying those magic words work
as always, i am ready to be proven totally ignorant in how these things work. if a little $0.25 trimpot will do just as clean and reliable job as a resistor... it would certainly be an easier option
Shows your high-power background.
High-power pots are indeed usually made from wire. Signal-level ones (ones not designed to deal with lots of power) are made from the same resistive carbon material as the $0.05 resistors.
Or $1500 for cables? $75000 for amps? Yes, it makes them feel better.
There is a reasonably easy and very reliable test - a controlled, double-blind ABX listening test. If people don't hear a difference, they don't hear a difference...
Pretty much, yes. When was the last time you managed to impress your neighbour (or even better, a pretty girl) with a "high-end" trimpot?
Sure. But it is just a question of degree.
The only situation where it will make a significant difference is if you have a lot of vibration and/or a lot of grease and water splashing around (or vaporized in the air), contaminating the swiper on the trimpot. You are OK as long as you don't mount your amp on the kitchen fan or washing machine.as always, i am ready to be proven totally ignorant in how these things work. if a little $0.25 trimpot will do just as clean and reliable job as a resistor... it would certainly be an easier option
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