Chopper vs. clasic PSU for audio.

Status
Not open for further replies.
V

vlad777

Member
I dont know why they use clasic 50-60 Hz
iron core transformers for audio.
When the amplifier is at max volume
and playing bass the only thing standing
betwen your speaker and transformer is
the bridge and capacitor(s).Now as big
as capacitors can get they can newer filter
out 100 Hz noise voltage at max volume.
So your bass gets distorted.
A two phaze chopper at a few tents of KHz
whith a good filter would do much better.
After all the cd audio that we so much
apreciate is 44 KHz digital signal
that is filtered out.
 
Sorry, but you're talking nonsense - 50/60Hz supplies are fine for audio use, and all the very best audio systems use them, no distorted bass, no noise.

There are a small number of systems that use switchmode PSU's, particularly PA ones - my Behringer PA does, but it's for size and weight, nothing else.
 
**broken link removed**
Go to the video under this link. Here is an explanation of how the quality of the power line effects audio. Under heavy load (loud audio) there is much ripple on the main power supply. The point where the amplifier clips (distorts) changes at a 100/120hz rate. Heavy base loads cause the clipping point to change. This also causes the power line to sag down.

I agree that the power line problems to speaker output is small. PS Audio sold 40,000 of the power plant premiers.
 
I respect your opinion Nigel but when amp is playing lets say 50Hz
you cant tell me that at max power/volume the signal is not a (litle)
bit distorted.
Anyway havent you noticed that when you turn the volume to more than
85% only high pitch tones are louder no matter what equiliser settings are.
 
You are not supposed to overdrive an amplifier so its output is clipping like crazy unless you are blasting a very distorted electric guitar.
A half-decent amplifier has extremely low distortion up to the output where it begins to clip which is at its rated power. Maybe your speaker is distorting.
The half-decent amplifier has very good rejection of hum and noise from its power supply also up to the output where it begins to clip.

If you are deaf and cannot hear clipping distortion then use an amplifier with a clipping indicator.

The position of the volume control does not reliably tell you the output power of an amplifier. It depends on the input level of the signal source and on the gain of the amplifier. Maybe the amplifier begins to clip when the volume control is turned up higher than 20% or maybe the amplifier never clips and is not loud enough when the volume control is at maximum.
 
vlad777 said:
I respect your opinion Nigel but when amp is playing lets say 50Hz
you cant tell me that at max power/volume the signal is not a (litle)
bit distorted.
Click to expand...

How would you know?, it's so loud that any possible distortion would be much too low to hear.

But in any case, decent quality amps specify their distortion and power figures over their full range - with 0.05% at low bass frequencies being commonplace - hardly a 'little distorted' even.

Anyway havent you noticed that when you turn the volume to more than
85% only high pitch tones are louder no matter what equiliser settings are.
Click to expand...

No, it sounds like you're ussng a cheap amp and cheap speakers.
 
I think he has the bass frequencies boosted very much and when he turns up the volume control way too high then the bass is severely clipped and does not get any louder but the lower level high freqhencies are amplified more.

If he likes clipping distortion without it being modulated by hum from the power supply then he should use a "fuzz" circuit instead of causing his amplifier to clip.
 
Nigel Goodwin said:
How would you know?
Click to expand...
I know you know this Nigel, this is for the benefit of vlad777.

Simple, connect the output to an oscilloscope and look at the waveform for clipping.

This isn't conclusive though, it might be the speakers which are clipping, in which case you need to connect a mic' and pre-amplifier to the oscilloscope to look at the waveform produced by the speakers.
 
Hero999 said:
Simple, connect the output to an oscilloscope and look at the waveform for clipping.
Click to expand...

As soon as I buy an osciloscope I will most certainly but I will be less interested in clipping
and I will look for the hum from the power supply .

(As I suggested in my original post.)
 
Last edited:
Don't you understand that amplifiers reject hum from the power supply very well unless their output is clipping?
When the output is clipping then it is saturated to the positive and negative supply voltages that have lots of ripple voltage. Then the ripple voltage is connected directly to the speaker.

If you keep the volume turned down low enough to avoid clipping then you will not hear hum and not hear the high frequencies louder than the distorted bass. If you hear hum with the volume turned down so that there is no clipping then you have a different problem like poor shielding of the input cable.
 
If the power supply was designed properly the ripple will still be below your hearing threshold in regards to is background noise level.
Thats what the big capacitors do in the power supply, they filter out that hum. In a good amplifier power supply that ripple should still be very small in comparison to the rail voltages themselves. Likely under 5% at maximum power draw unless you have a a bad power supply design, a bad capacitor, or are running speakers that are far below the amplifiers designed impedance ratings. Such as running a 2 - 4 ohm speakers on a 8 ohm rated amplifier.

The other possibility is that the line hum is being superimposed in a preamp stage due to a bad ground system or simply bad design and is getting amplified by the main amplifier stages so that you hear it when ever there is a high power load on the system.
Bad grounding is notorious for adding background noises or all kinds and in line powered stuff the 50 - 60 cycle line hum is usually the most obvious noise that is first recognized.
 
A ripple of 5% on a 50V supply is 2.5V which will be quite loud through an 8R speaker.

A properly designed amplifier should have a high enough ripple rejection ratio to reduce even a 5V ripple to an inaudible level.
 
But the OP hears hum and distortion when the volume is turned up high. So the output is a square-wave with the speaker connected directly to the humming rails. He thinks he should be able to turn the volume control up to 100% and the amplifier should majically keep its output from clipping.
 
A ripple of 5% on a 50V supply is 2.5V which will be quite loud through an 8R speaker.
Click to expand...

True but how much louder is that signal that the 50 volts is producing?

2.5/8 = .3125 amps or about .78 watts.
25/8 = 3.125 amps or about 78 watts which is 100 times more energy.
 
I think the amplifier has very poor quality and its main filter capacitor value is much too low so the ripple might be 25% or more at clipping, not 5%.
 
audioguru said:
He thinks he should be able to turn the volume control up to 100% and the amplifier should majically keep its output from clipping.
Click to expand...
I admit I dont have much practice but you are not feeling me people.
When amp is outputing sine wawe signal just milivolts bellow clipping
(that is when amplitude of signal is equal to transformer amplitude)
at a frequencey of 50 Hz with caps of 4700 uF with amplitude of 40V
on 4 ohm speaker that gives efetive current of 7.07A .
If you now calculate hum voltage based on that current it gives
7.5 V .
(Uh=Il*t/C ; Uh=7.07*0.01/0.0094)

This is 7.5/80*100 = 9.4 % hum voltage.

A chopper supply should not have this problem.
 
You cannot compare a mains transformer powered amplifier to a battery powered chopper power to an amplifier.

The chopper power supply powered from the mains will have exactly the same ripple as a normal power supply without the chopper.
 
Do not forget that the voltage on chopper psu caps is 220/110*sqrt(2) which is much higher than needed.
Now chopper has wide range of voltage above needed to bring down to meet the reqirements.

Edit: But yes it has lower value of caps.
 
Last edited:
If your running a 4700 Uf capacitor on a amplifier with a 50 volt rail thats most of your problem.

I have a old technics home theater unit that was rated for 50 watts per channel at 8 ohms and it used 8700 uf capacitors on both sides of the rails that only ran at around 40 volts.

I have seen some commercial application amplifiers rated at around 250 watts RMS per channel built with multiple capacitors adding up to well over 40K+ uf on each side of the power supply rails.
 

Decent amplifiers don't either. The power supply rejection ratio (PSRR) is high enough to take care of this. If it's not, get a decently designed amplifier.
 
Status
Not open for further replies.

Similar threads

B
  • Question
Emerson Model AA25990L PSU for HP Designjet510
Replies
3
Views
2K
Tony Stewart
S
  • Question
audio input line problem
Replies
16
Views
897
SentinelAeon
S
  • Question
Used vs New Multimeters
Replies
19
Views
2K
ZipZapOuch
M
  • Question
PSU "Schematic" help me understand AC/DC Bridge Rectifiers, Proper Grounding, and Series AC Connections
Replies
8
Views
1K
Tony Stewart
V
  • Question
How to convert stereo audio signal into mono out for mono amplifier
Replies
16
Views
3K
audioguru
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…