My cell phone's RTA analyzer through a 1/8 jack headset microphone is picking up the frequency at 2k-5k and strongest at about 4k. The noise is sort of white-ish. This amp has a low pass crossover which cannot be switched off.
Since this amp is a sub-only amp I guess that noise isnt such a problem for subs in a trunk but its the worst unnatural noise I've heard to date; even worse than (remember) my PPI PC275 playing FM radio broadcast through the Miniamp. That problem was never solved btw.
If you dont have it already, look for the free RTA analyzer on the Android market. Its 20 band and for free its pretty neet.
Since this amp is a sub-only amp I guess that noise isnt such a problem for subs in a trunk but its the worst unnatural noise I've heard to date; even worse than (remember) my PPI PC275 playing FM radio broadcast through the Miniamp. That problem was never solved btw.
If you dont have it already, look for the free RTA analyzer on the Android market. Its 20 band and for free its pretty neet.
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Whether referencing amp ground or secondary center tap; From the powersupply to the output half; the noise seems to originate from this precise location; the leftern transformer coil, mark at approximately 8-o'clock. This transformer's landing point seems to be where the noise is starting. By comparison, the transformer on the right does not have any signs of this noise.
I think this tells me the noise is being produced after the power supply and well before the audio / opamp section.
I think this tells me the noise is being produced after the power supply and well before the audio / opamp section.
The high frequency noise you originally posted is normal and inaudible. In some amps with unsynchronized audio/power supply oscillators, noise is normal (hifonics amps, as one example). I can't say whether this noise is normal because I've never worked on one of these amps.
Did you determine why the preamp power supply voltages were uneven?
Is the small power supply working properly?
Do you have a frequency counter?
Did you determine why the preamp power supply voltages were uneven?
Is the small power supply working properly?
Do you have a frequency counter?
The transformers in this amp don't have 'normal' secondaries. One leg is connected to the secondary ground and the other is connected to the rectifiers. If you're checking for noise on one transformer's leg that's grounded and the other one's leg that's driving the rectifiers, the difference will be 100+v.
I found the voltage to be +-9vDC when referencing secondary tap. From amp ground its -7.5, +10.5. I think that that is OK if 9v is enough.
You mean my Pyramid 10A model PS-15KX? I think its ok. There is no noise coming from it with it disconnected from the amp. Connected to the amp theres is a +-15mv ripple. I have another 5A power supply and it does the same thing. IF I place a large cap across the output of the supply and the ripple reduces by %20 percent but does not go away; The sound output from the test speaker doesnt change.
I dont have a frequency counter... By the google images they dont look too hard to make.
Not sure either. To me this amp is for sub-only as it has a crossover that cannot be turned off. Its not the best of amps by any means.
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I agree to that, but I found it odd that the leg of the transformer to the right doesnt have the same noise on the same leg. Between the two transformer legs I measure 0 ohms and low voltage, but the noise is only on one of the legs of the left transistor from what I can scope. I cant tell if the 100v sides have noise.
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The small power supply near the large transformers in the amp. You were concerned about the low voltage. I don't think 9v is so low that it would cause any problems but I think it should be a bit higher. Check the waveform on the tabs of the two FETs driving the small transformer. It should be a full duty cycle square wave.
You 'buy' a multimeter with a frequency counter, unless you have lots of spare time.
You 'buy' a multimeter with a frequency counter, unless you have lots of spare time.
I'll scope that area, however those are 50n06 fets and likely not powering the opamps.
In this photo, the opamps are far left. Just up from the green square board are two silver surface mount caps. Just behind (to the right) of the caps are two KIA7909/7809 transistors. The 3rd leg of these transistors have the +-9v and 0 ohms to the + and - power pins of the opamps depending on which transistor and pin tested through.
Come to think of it, I just noticed this amp has just about 2 of everything. Two power supplies, two TL494s, Twice the failure potential... Yet only a single output for mono subwoofer amp.
Two seperate but internally connected power terminals (including 2 remote turn-on terminals)
In this photo, the opamps are far left. Just up from the green square board are two silver surface mount caps. Just behind (to the right) of the caps are two KIA7909/7809 transistors. The 3rd leg of these transistors have the +-9v and 0 ohms to the + and - power pins of the opamps depending on which transistor and pin tested through.
Come to think of it, I just noticed this amp has just about 2 of everything. Two power supplies, two TL494s, Twice the failure potential... Yet only a single output for mono subwoofer amp.
Two seperate but internally connected power terminals (including 2 remote turn-on terminals)
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On the KIA7909 and KIA7809 referencing center ground:
KIA7909
Pin 1: 0.000vDC
Pin 2: -14.67vDC
Pin 3: -9.20vDC
KIA7809
Pin 1: 14.02vDC
Pin 2: 0.000vDC
Pin 3: 9.20vDC
With the scope set to AC coupling, there is no clear defined waveform; just the noise as I posted. Unless if I set the scope to 20mv/div and 5uS, then a waveform can be observed.
"Zoomed in" at 20mV/Div
KIA7909
Pin 1: 0.000vDC
Pin 2: -14.67vDC
Pin 3: -9.20vDC
KIA7809
Pin 1: 14.02vDC
Pin 2: 0.000vDC
Pin 3: 9.20vDC
With the scope set to AC coupling, there is no clear defined waveform; just the noise as I posted. Unless if I set the scope to 20mv/div and 5uS, then a waveform can be observed.
"Zoomed in" at 20mV/Div
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ok. It appears I may have isolated the area in which the noise is originalted from.
Scope set to .2v/Div, and time set to 20 uS
Referencing center tap, the positive speaker terminal looks like this:
Im not sure what this control does exactly; something to do with phase... but is I set the 'Master' switch to Slave (Selectable from 180 - 0 - SLAVE), the slave setting shows this on the scope, and the test speaker's noise gets distinctly louder. I verified the finction of both the LP crossover and the sub-sonic filter to be working in this amp.
If I touch the ~9 of so resistors due north of the opAmps while the Master switch is set to anything but slave, the output is laced with terrible static and noise. If I touch these resistors with the master switch set to SLAVE; well, lets just say I almost burnt out one of my test speakers:
I'll poke around this area for while...
Scope set to .2v/Div, and time set to 20 uS
Referencing center tap, the positive speaker terminal looks like this:
Im not sure what this control does exactly; something to do with phase... but is I set the 'Master' switch to Slave (Selectable from 180 - 0 - SLAVE), the slave setting shows this on the scope, and the test speaker's noise gets distinctly louder. I verified the finction of both the LP crossover and the sub-sonic filter to be working in this amp.
If I touch the ~9 of so resistors due north of the opAmps while the Master switch is set to anything but slave, the output is laced with terrible static and noise. If I touch these resistors with the master switch set to SLAVE; well, lets just say I almost burnt out one of my test speakers:
I'll poke around this area for while...
I kind of lost track of what I was searching for in that area, so I picked up something somewhere else in the amp. i thought this diode (w/ green) was installed backwards under what looked like a previous repair, so I pulled it off the PCB. After I realized that it was actually installed correctly, but this may not have been theright diode to begin with. Also this area of the board seems to have been previously repaired, and it looks like some things may not be right or belonging. Approximately 10 surface mount resistors, a few caps, and ~1 transistor were disturbed or replaced in this area.
If you look at R88, its actually a cap on top of a resistor
If you look at R88, its actually a cap on top of a resistor
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