ASR and the rise of the intelligent idiots

[r3xj0hn570n]

So BW of 100KHz plus is good?

OK, yes! Phase is hyper relevant. You can't restrict bandwidth without screwing up relative phase.

[Wonfor14]

I toyed with removing the cap for the low pass filter but I am not brave enough to try it. It's not bonfire night yet.

[Geoff.R.G]

So are we saying that wide out of ear shot BW on amps is needed ?
Please please say yes he he
So BW of 100KHz plus is good?
I do hope my bats enjoy TRex, well the seem to any how.

I wouldn’t want to suggest exactly how wide the bandwidth should be but rolling off around 20KHz is probably too early. Do we need to have bandwidth into the bottom of the RF? I don’t know but if filtering it out affects the AF probably best not to do so.

[Wonfor14]

I toyed with removing the cap for the low pass filter but I am not brave enough to try it. It's not bonfire night yet.

No bonfire please think climate warming thick CO2 think what the Doc would have done to you whoops

[Geoff.R.G]

I toyed with removing the cap for the low pass filter but I am not brave enough to try it. It's not bonfire night yet.

I find it interesting that you should consider that. There are plenty of filters in Hi-Fi circuits; CD players produce signals at low end radio frequencies but they aren't supposed to get beyond the DAC circuitry. Computers have clock frequencies in the 3GHz range but this isn't supposed to get out either. As I said earlier FM Stereo uses a 19KHz pilot tone, which has to be filtered out for the output, it also sets a practical upper audio frequency of 15KHz. Other frequencies will be present inside various devices and are also filtered out or otherwise prevented from reaching the output connectors. Tape recorders have a bias oscillator in the recording head drive circuit, usually well above the audio band but occasionally it is possible for it to beat with a VHF AM signal and allow the AF signal to be heard!

The choice of AF bandwidth for an amplifier is a balancing act between avoiding unwanted characteristics, such as distortions, and not amplifying what amount to noise signals at the higher end. Amplifying LF signals could result in the amplifier consuming more power, and running hotter, than might be the case if these frequencies were outside the bandwidth.

Are you sure you want to be messing with filtering Stu?

[Wonfor14]

I toyed with removing the cap for the low pass filter but I am not brave enough to try it. It's not bonfire night yet.

I find it interesting that you should consider that. There are plenty of filters in Hi-Fi circuits; CD players produce signals at low end radio frequencies but they aren't supposed to get beyond the DAC circuitry. Computers have clock frequencies in the 3GHz range but this isn't supposed to get out either. As I said earlier FM Stereo uses a 19KHz pilot tone, which has to be filtered out for the output, it also sets a practical upper audio frequency of 15KHz. Other frequencies will be present inside various devices and are also filtered out or otherwise prevented from reaching the output connectors. Tape recorders have a bias oscillator in the recording head drive circuit, usually well above the audio band but occasionally it is possible for it to beat with a VHF AM signal and allow the AF signal to be heard!

The choice of AF bandwidth for an amplifier is a balancing act between avoiding unwanted characteristics, such as distortions, and not amplifying what amount to noise signals at the higher end. Amplifying LF signals could result in the amplifier consuming more power, and running hotter, than might be the case if these frequencies were outside the bandwidth.

Are you sure you want to be messing with filtering Stu?

Hooray I hate digital lies and nasty PIC Micro Chip (should be fried) in kit as remote control is my pet hate, nasty noises and there offspring the dreaded harmonics.

[Geoff.R.G]

I toyed with removing the cap for the low pass filter but I am not brave enough to try it. It's not bonfire night yet.

I find it interesting that you should consider that. There are plenty of filters in Hi-Fi circuits; CD players produce signals at low end radio frequencies but they aren't supposed to get beyond the DAC circuitry. Computers have clock frequencies in the 3GHz range but this isn't supposed to get out either. As I said earlier FM Stereo uses a 19KHz pilot tone, which has to be filtered out for the output, it also sets a practical upper audio frequency of 15KHz. Other frequencies will be present inside various devices and are also filtered out or otherwise prevented from reaching the output connectors. Tape recorders have a bias oscillator in the recording head drive circuit, usually well above the audio band but occasionally it is possible for it to beat with a VHF AM signal and allow the AF signal to be heard!

The choice of AF bandwidth for an amplifier is a balancing act between avoiding unwanted characteristics, such as distortions, and not amplifying what amount to noise signals at the higher end. Amplifying LF signals could result in the amplifier consuming more power, and running hotter, than might be the case if these frequencies were outside the bandwidth.

Are you sure you want to be messing with filtering Stu?

Hooray I hate digital lies and nasty PIC Micro Chip (should be fried) in kit as remote control is my pet hate, nasty noises and there offspring the dreaded harmonics.

Colin, 50 years ago you could have built an amplifier with a wide bandwidth with little real fear of extraneous signals getting into the signal path. Today there is so much RF energy about that any wire that isn't protected in some way will pick some of it up and allow it into the signal path. Coupled to that RF energy is EM noise, from switched mode power supplies, Wi-Fi via mains extenders and mobile phones (better now than it was surprisingly). The only effective way to stop interference is, as you know, to put your Hi-Fi in a Faraday cage. Everyone else is fighting signals on their system that they don't want or need and they are, depending on the equipment, amplifying and re-radiating some of them.

My Hi-Fi, in the lounge, has a remote control for reasons of domestic harmony but the second system remote control is my right arm. I think I actually prefer the sound from the bedroom system, it is simpler. I know of no way to have a remote control system using the same power supply without something getting into the audio chain. Such a shame that we so readily sacrifice quality for convenience. I shall be cooking with real ingredients this evening.

[Wonfor14]

I thought better of in the end Geoff. I know RD pushed the low pass filter knee higher than most power amps (339kHz). I am sure he would have removed it if he could.

I love playing with filters Geoff. I love it even more when I can remove them. Moving my tweeter high pass from the speaker and doing it passively at line level with a lovely polystyrene cap was one of the most musically rewarding things I have done.

The other big one was bypassing a seven pole bessel filter in my CDP anologue output stage. After reading the dac chip data sheet I discovered that externally it only required a first order filter via a single polystyrene cap. I did what the data sheet suggested and wow, I much preferred the presentation. It was more detailed, organic and smoother sounding like a layer of artificial hash had green removed.

There have been other instances like removing dc blocking high pass caps where I am sure there is no dc prior to it. The musical window became clearer once more. It's quite an addictive pass time throwing things away and getting to the bare bones, The power amp low pass filter however is a step to far and one that is likely to end in disaster.

[Wonfor14]

I find it interesting that you should consider that. There are plenty of filters in Hi-Fi circuits; CD players produce signals at low end radio frequencies but they aren't supposed to get beyond the DAC circuitry. Computers have clock frequencies in the 3GHz range but this isn't supposed to get out either. As I said earlier FM Stereo uses a 19KHz pilot tone, which has to be filtered out for the output, it also sets a practical upper audio frequency of 15KHz. Other frequencies will be present inside various devices and are also filtered out or otherwise prevented from reaching the output connectors. Tape recorders have a bias oscillator in the recording head drive circuit, usually well above the audio band but occasionally it is possible for it to beat with a VHF AM signal and allow the AF signal to be heard!

The choice of AF bandwidth for an amplifier is a balancing act between avoiding unwanted characteristics, such as distortions, and not amplifying what amount to noise signals at the higher end. Amplifying LF signals could result in the amplifier consuming more power, and running hotter, than might be the case if these frequencies were outside the bandwidth.

Are you sure you want to be messing with filtering Stu?

Hooray I hate digital lies and nasty PIC Micro Chip (should be fried) in kit as remote control is my pet hate, nasty noises and there offspring the dreaded harmonics.

Colin, 50 years ago you could have built an amplifier with a wide bandwidth with little real fear of extraneous signals getting into the signal path. Today there is so much RF energy about that any wire that isn't protected in some way will pick some of it up and allow it into the signal path. Coupled to that RF energy is EM noise, from switched mode power supplies, Wi-Fi via mains extenders and mobile phones (better now than it was surprisingly). The only effective way to stop interference is, as you know, to put your Hi-Fi in a Faraday cage. Everyone else is fighting signals on their system that they don't want or need and they are, depending on the equipment, amplifying and re-radiating some of them.

My Hi-Fi, in the lounge, has a remote control for reasons of domestic harmony but the second system remote control is my right arm. I think I actually prefer the sound from the bedroom system, it is simpler. I know of no way to have a remote control system using the same power supply without something getting into the audio chain. Such a shame that we so readily sacrifice quality for convenience. I shall be cooking with real ingredients this evening.

How about a long stick to operate the hifi Geoff

[Geoff.R.G]

I thought better of in the end Geoff. I know RD pushed the low pass filter knee higher than most power amps (339kHz). I am sure he would have removed it if he could.

I love playing with filters Geoff. I love it even more when I can remove them. Moving my tweeter high pass from the speaker and doing it passively at line level with a lovely polystyrene cap was one of the most musically rewarding things I have done.

The other big one was bypassing a seven pole bessel filter in my CDP anologue output stage. After reading the dac chip data sheet I discovered that externally it only required a first order filter via a single polystyrene cap. I did what the data sheet suggested and wow, I much preferred the presentation. It was more detailed, organic and smoother sounding like a layer of artificial hash had green removed.

There have been other instances like removing dc blocking high pass caps where I am sure there is no dc prior to it. The musical window became clearer once more. It's quite an addictive pass time throwing things away and getting to the bare bones, The power amp low pass filter however is a step to far and one that is likely to end in disaster.

The trick is to determine which filters are necessary and which are not.