I have tried a loop back, I'm familiar with REW for speaker measurements but not tried this
My subs are DSP controlled and these have a 34Hz PEQ and low pass at 40Hz. My gain loop is in this case
lowered Mv to DAC>naim 32.5>DSP>power amp. the db chain is -15db through the pre at 'normal' volume levels, -10db through the dsp for all apart from LFE the +37db via the BPSP500, int this case I think the BLK1000's are circa 30+db gain (maybe high 30's ?)
Not sure what this tells me !
My subs are DSP controlled and these have a 34Hz PEQ and low pass at 40Hz. My gain loop is in this case
lowered Mv to DAC>naim 32.5>DSP>power amp. the db chain is -15db through the pre at 'normal' volume levels, -10db through the dsp for all apart from LFE the +37db via the BPSP500, int this case I think the BLK1000's are circa 30+db gain (maybe high 30's ?)
Not sure what this tells me !
Do the loop back test using only your soundcard. Connect the output of the soundcard to its input and run your test.
When you test a device, such as your amplifier, then the actual result would be the difference between your device test measurement and the loopback test result.
When you test a device, such as your amplifier, then the actual result would be the difference between your device test measurement and the loopback test result.
Toroidal transformers are touted as no having radiate magnetic field which is true to a point. There are field due to switching currents in the diodes in a bridge rectifier block and these induce radiated fields. One could specify a copper strap around the toroid to contain this. H noise can arise through capacitive coupling between the primary and secondary windings so if one wants to eliminate this there needs to be a shield between these windings. One trick I have tried is to fit ferrite inductor is series to each transformer feeding the bridge rectifier this was possible in my application as the resistance in the inductors reduced the rectified voltage to a satisfactory level. I had a custom - made toroid which delivered more voltage than I needed. With this approach I did not need to invoke the expense of having my toroid unwound to allow a shield between the primary and secondary winding as the inductors flattened the shape of the peaks in rectification.
For the rest I was guided by an article by a contributor to this website - Earth points. Any ac in a length of wire will have some resistance and one place not to earth a signal is at the junction between the supply capacitors in a T junction with an arm to the metal case. The true earth is somewhere outsize of a house where this will go to true earth through a metal stake into the ground.as a cardinal rule the dirty earth leads should go to ground without passing through any length of signal wire to earth. Some other useful strategies are to twist output and transformer wires together to cancel/shield differences and reduce intrusion in the vicinity of radiated effects - these could pollute the general environment. in the equipment. This idea can also be applied to the input signal wiring which can go to signal earth at the input connector via a small value resistor. Any ac drop across this will result in a lower ac voltage in line with a linear element i.e. the resistor.
For the rest I was guided by an article by a contributor to this website - Earth points. Any ac in a length of wire will have some resistance and one place not to earth a signal is at the junction between the supply capacitors in a T junction with an arm to the metal case. The true earth is somewhere outsize of a house where this will go to true earth through a metal stake into the ground.as a cardinal rule the dirty earth leads should go to ground without passing through any length of signal wire to earth. Some other useful strategies are to twist output and transformer wires together to cancel/shield differences and reduce intrusion in the vicinity of radiated effects - these could pollute the general environment. in the equipment. This idea can also be applied to the input signal wiring which can go to signal earth at the input connector via a small value resistor. Any ac drop across this will result in a lower ac voltage in line with a linear element i.e. the resistor.
Thanks, I did get a chance to look at this but wasn’t sure about connections as my Mac is USB C for all intents so I assume I’d need to buy some usb c to RCA connectors. Not sure if a MacBook Pro will have a suitable sound card ?
Andrew, thanks I am very confused with this all I get is my MacBook speaker. if I link the USB C to USB C I cant seem to choose any suitable in and out settings
Does your soundcard have an output and an input? It should do. You want to connect the output of each channel to its corresponding input and then look at the display. Note carefully you have to use the line level inputs and outputs. Some sound cards have mic inputs - that won’t work properly.
Have you got a photo of your soundcard?
Have you got a photo of your soundcard?
Andrew, hi
I can't seem to find anything on my soundcard it's internal to a 2020 MacBook Pro, seems the MacBook just senses what connections are in place and displays them. When I connect two USB Cs together and try and assign in and out I dont seem to be able to do it !
I might try apple support they can be quite helpful
Next on my long journey is to see if I can measure some voltages. and see if I can find the time to experiment with the oscilloscope. I do think it's down to perhaps the construction and layout. It's so frustrating that the 500 is as quiet as a mouse. This isn't loud but it's a slippery slope if I use an amp that has a small amount of noise coming through it's frustrating enough with projector noise, a small amount of video processor fan noise (I have managed this with additional heatsinks with additional copper and acoustic fan in the case), minor mechanical transformer hum and as we know anything on it's own can be small enough to be ignored but add them up and it's cumulative
I can't seem to find anything on my soundcard it's internal to a 2020 MacBook Pro, seems the MacBook just senses what connections are in place and displays them. When I connect two USB Cs together and try and assign in and out I dont seem to be able to do it !
I might try apple support they can be quite helpful
Next on my long journey is to see if I can measure some voltages. and see if I can find the time to experiment with the oscilloscope. I do think it's down to perhaps the construction and layout. It's so frustrating that the 500 is as quiet as a mouse. This isn't loud but it's a slippery slope if I use an amp that has a small amount of noise coming through it's frustrating enough with projector noise, a small amount of video processor fan noise (I have managed this with additional heatsinks with additional copper and acoustic fan in the case), minor mechanical transformer hum and as we know anything on it's own can be small enough to be ignored but add them up and it's cumulative
I tried with my serial number and model this was the bets In could get !
Integrated Audio:
Integrated Audio:
- MacBook Pro computers, including the 2019 models, utilize integrated audio circuitry on the motherboard. This means the audio processing is part of the system's overall design, rather than a separate, removable "soundcard" in the traditional PC sense.
- Apple focuses on delivering high-quality audio output and input through its integrated audio solutions.
Looking at the relay circuit for the signal, I can see it's not a great design as pointed out the 7W resistor gets to 90+ degrees and drops 59V to get to 24V before the 7812 drops it to 12V
Look like the 500 uses a separate transformer tap to avoid this, interestingly it uses a similar voltage drop on the pre section
I wonder if the relay part if the circuit is responsible for some of the noise ?
MF 1000
BPSP 500
Look like the 500 uses a separate transformer tap to avoid this, interestingly it uses a similar voltage drop on the pre section
I wonder if the relay part if the circuit is responsible for some of the noise ?
MF 1000
BPSP 500
Here’s what I got re the soundcard:-
So it seems your MacBook does not accept line level inputs - it’s optimised for mic level inputs - so a few mV. If this is the case, it would explain some of the readings you were getting. I unfortunately assumed you were using an external sound card. The other issue you are likely to have here is the computer will automatically adjust the input gain, so getting realistic absolute reference readings will be nigh on impossible. Ideally what you want for audio work is an external USB sound card with isolated USB.
So it seems your MacBook does not accept line level inputs - it’s optimised for mic level inputs - so a few mV. If this is the case, it would explain some of the readings you were getting. I unfortunately assumed you were using an external sound card. The other issue you are likely to have here is the computer will automatically adjust the input gain, so getting realistic absolute reference readings will be nigh on impossible. Ideally what you want for audio work is an external USB sound card with isolated USB.
It's an older laptop now, bought 2020 still seems 'new' to me !
No matter perhaps the delta between the 500 and 1000 readings are still relevant
No matter perhaps the delta between the 500 and 1000 readings are still relevant
Thinking about the power supply for the signal relay, I could use this to provide the 12V, with no regulation it shows 12.8V when powering the fan
This has a thermal switch on the power in so I can rewire again to have power in and put the thermal switch on the power out to the fan and use the 12V to feed in to the sywitch circuit
its a 3VA, 9v-9v https://www.rapidonline.com/blore-bowron-a4003-pcb-transformer-230v-3va-9v-9v-88-5326
The fan is 0.6W, looks like the Ne555 perhaps 15Ma at 12V so the supply looks adequate, relay states 400mw
A few ideas and questions
This has a thermal switch on the power in so I can rewire again to have power in and put the thermal switch on the power out to the fan and use the 12V to feed in to the sywitch circuit
its a 3VA, 9v-9v https://www.rapidonline.com/blore-bowron-a4003-pcb-transformer-230v-3va-9v-9v-88-5326
The fan is 0.6W, looks like the Ne555 perhaps 15Ma at 12V so the supply looks adequate, relay states 400mw
A few ideas and questions
- should I wire in another rectifier and use the spare secondary winding and cap ?
- Is it worth adding another cap to GND, I fitted a 2,200uf out of the rectifier if I use the two supplies in parallel
- Any other comments ?
No idea what this circuit is doing with a 47k link to the signal, this isn't on the 500, just the 555 timer circuit and a thermal switch
That circuit turns off the relay if there's either +ve or -ve DC on the amp output.
Any voltage generated by cap current through the impedance from blue to green is 'seen' by the signal 0v at yellow.
You could try cutting the trace above the text 'MOSFET' and wiring yellow directly to green. So green is a proper star earth.
Thanks, so I could remove to see if that might be adding noise, just lift the connection to and from ?
I don't think that output relay circuit will be adding significant noise.
You could remove it, but it would be annoying if you then blew up a speaker while probing around.
Are you simply expecting too much from this amp?
It's go a continuously running mains fan.
That suggests it's more PA than HiFi.
A bit of low level hum and a fan going around are completely acceptable when you've got an audience of even 30 people just breathing.
The way it's laid out, with the PSU caps in the middle suggests to me it was always a compromise?
It might be interesting to separate the amp and PSU.
You could remove it, but it would be annoying if you then blew up a speaker while probing around.
Are you simply expecting too much from this amp?
It's go a continuously running mains fan.
That suggests it's more PA than HiFi.
A bit of low level hum and a fan going around are completely acceptable when you've got an audience of even 30 people just breathing.
The way it's laid out, with the PSU caps in the middle suggests to me it was always a compromise?
It might be interesting to separate the amp and PSU.
Briz, hi
Sorry the thread is now 200 posts !
A quick summary of the journey and thinking
Initially a loud buzz like a GND earth problem with a few changes predominantly reducing RFI with the 0.1uF can from input RCA to chassis. So that problem is now solved the next and continued journey is general noise which whilst at a relatively low Level is too loud for me - just audible at the seating position. If the driven unit was not an 18" sub you would say 'hiss'
I've removed the fan and wired in a temperature driven 12v unit which is quiet and only comes on when needed (I have yet to see it come on with out a hot air gun checking)
My benchmark is an existing sub amp no longer made a BK BPSP500, the MF1000 amp with noise is essentially the same power unit found in the 500 but with twice as many transistors, output caps. Looking through the circuits the power amp part is nearly identical and hence the reason to pursue getting it as quiet the BPSP 500 also uses a filter board and pre-amp
So far I have rewired the GND layout with help from Andrew, Jean (when he's not too distressed at my lack of expertise 🙂 ), Bill and a few others. Ive replaced all small caps added some more in a few places and swapped out the majority of the carbon resistors which has helped as well
I have tried a few cheap pre-amps in front of the MF1000 and this does add more noise but I do want to run analogue volume and not use the DSP for this and I dont think the DSP that feeds the subs is ideal direct.
So I am determined to see if I can get closer to what does seem to be the same power amplifier with noise. I will try removing the 47k fuse, the speaker is a 1,500W RMS 18" sub so pretty tolerant and there is no DC on the output
I have yet to try replacing the main caps 10,000uf 100V they measure in spec and relatively expense as an experiment
Sorry the thread is now 200 posts !
A quick summary of the journey and thinking
Initially a loud buzz like a GND earth problem with a few changes predominantly reducing RFI with the 0.1uF can from input RCA to chassis. So that problem is now solved the next and continued journey is general noise which whilst at a relatively low Level is too loud for me - just audible at the seating position. If the driven unit was not an 18" sub you would say 'hiss'
I've removed the fan and wired in a temperature driven 12v unit which is quiet and only comes on when needed (I have yet to see it come on with out a hot air gun checking)
My benchmark is an existing sub amp no longer made a BK BPSP500, the MF1000 amp with noise is essentially the same power unit found in the 500 but with twice as many transistors, output caps. Looking through the circuits the power amp part is nearly identical and hence the reason to pursue getting it as quiet the BPSP 500 also uses a filter board and pre-amp
So far I have rewired the GND layout with help from Andrew, Jean (when he's not too distressed at my lack of expertise 🙂 ), Bill and a few others. Ive replaced all small caps added some more in a few places and swapped out the majority of the carbon resistors which has helped as well
I have tried a few cheap pre-amps in front of the MF1000 and this does add more noise but I do want to run analogue volume and not use the DSP for this and I dont think the DSP that feeds the subs is ideal direct.
So I am determined to see if I can get closer to what does seem to be the same power amplifier with noise. I will try removing the 47k fuse, the speaker is a 1,500W RMS 18" sub so pretty tolerant and there is no DC on the output
I have yet to try replacing the main caps 10,000uf 100V they measure in spec and relatively expense as an experiment