Agree , I tried upwards of 10hz , DC voltage was pretty high and tripped the protection too . I suppose one possible solution might be filtering ultra low freq at the line level .
DC coupled meant to cover wide range of freq , but seems to be its enemy too!
DC coupled meant to cover wide range of freq , but seems to be its enemy too!
Hi there,
I had a look at the photos, the amp seems to be microprocessor controlled. The soft start/inrush current control utilises high power large dissipation resistors and optocouplers, most likely... -> it is quite possible that this causes the issues you are experiencing. The fact that you were sent a different control board confirms my suspicion.
The amp does not appear to be a DC-coupled design - I see two white Mundorf film in oil capacitors that are probably used to AC-couple the audio signal at some point....they might be the bypass-capacitors connected in parallel with a large capacitance output capacitors... I suppose it would be quite easy to determine if they are used at the input, or as bypass capacitors at the output. Maybe you can take a close-up high-res photo of that section?
Maybe they loaded the outputs with small value capacitors??? Who knows what they did in there...
The bottom line is that you have a faulty amplifier. The issue is most likely related to that large DIL chip that looks like a microprocessor.... and to that soft start section... The optocouplers can sometimes get damaged, but only slightly, which could also be the root cause. Is the amplifier still under warranty? If not, try to obtain the circuit diagram and then come back here, we might be able to help further.
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DC coupling is calling for problems. Claims of correlated sound enhancements are audiofool voodoo.
Each audio-amp should be fitted with an appropriate hi-pass filterung sub audio frequencies.
just my 2c.
Obviously the protection triggers at +-0.7V DC. To prevent this from false triggering, its lowpass filter must be set to a lower frequency corner.
Each audio-amp should be fitted with an appropriate hi-pass filterung sub audio frequencies.
just my 2c.
Obviously the protection triggers at +-0.7V DC. To prevent this from false triggering, its lowpass filter must be set to a lower frequency corner.
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The issue could be in the feedback loop as well... maybe the gain of the amplifier is constant across the full range, starting from 0 Hz (from DC)...
I suppose having the DC-coupled amp should not necessarily require that the gain at DC is not unity. There is no reason not to attenuate the gain as we approach 0 Hz frequencies.
I suppose having the DC-coupled amp should not necessarily require that the gain at DC is not unity. There is no reason not to attenuate the gain as we approach 0 Hz frequencies.
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Thanks extreme boky for taking time to analyse the circuit .
Will take some detailed photos once I open up the amp to replace the control board .
Will take some detailed photos once I open up the amp to replace the control board .
Please tell me you are joking 🙂
It is more realistic to reverse engineer that part of the circuit from good photos. There will be a cap shunting AC in front of the DC detector and it's value, together with a resistor will set the lowest frequency that gets detected as DC. There will also be a resistor divider to set the level. Both can be adjusted. But most likely the replacement control board will solve the issue.
Amp appears to be constructed extremely well. Same as Kinki's preamps. Unbelievable construction quality for the price.
Haha , yea it's quite unlikely they will provide schematics .
Agree , the amp is very well made , built like a tank , sounds great too , hopefully the new board not just an increase of the threshold but they do something smart to prevent false detection
Agree , the amp is very well made , built like a tank , sounds great too , hopefully the new board not just an increase of the threshold but they do something smart to prevent false detection
Still waiting for the new control board to come, got bored and took some photos of the current internals , the middle section is the control board(which I’ll be getting) , left right sections are the amplification boards.
Kinki ex m7 - Google Photos
Will take a photo of the new control board once I receive it .
Stay tuned
The STC15W404S is a microcontroller with onboard flash. They'll be sending you a new controller board with different code loaded, most likely.
The LM324 is a quad OP that is most likely used as a comparator for protection purposes.
So, when the DC is detected, does the amp disconnect the output to the speakers, OR the whole amp shuts down?? Tell me what happens exactly, step by step (does the speaker output recover, and then the protection kicks in again, and this goes on and on...? OR the amp shuts down and then you have to manually turn it ON?) I'm asking because the amp seems to have both of these protections implemented... the mains voltage surge protection and the bypass relay, as well as speaker protection on each AMP PCB. It also looks like that uPC chip controls the speakers directly; however, there are relays on the AMP PCB as well...
What are the power modes: only ON/OFF, or ON/StandBy/OFF?
The LM324 is a quad OP that is most likely used as a comparator for protection purposes.
So, when the DC is detected, does the amp disconnect the output to the speakers, OR the whole amp shuts down?? Tell me what happens exactly, step by step (does the speaker output recover, and then the protection kicks in again, and this goes on and on...? OR the amp shuts down and then you have to manually turn it ON?) I'm asking because the amp seems to have both of these protections implemented... the mains voltage surge protection and the bypass relay, as well as speaker protection on each AMP PCB. It also looks like that uPC chip controls the speakers directly; however, there are relays on the AMP PCB as well...
What are the power modes: only ON/OFF, or ON/StandBy/OFF?
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Hi Extreme_Boky ,
thanks for the quick reply !
the amp goes to a faulted state , not entirely turned off , it shows "faulted" on the front panel LCD display. Then i need to press the button on the front to return it to operational state.
It does not recover itself without pressing that button.
i also noticed it has a "DC test" chip next to the STC15W404S .
thanks for the quick reply !
the amp goes to a faulted state , not entirely turned off , it shows "faulted" on the front panel LCD display. Then i need to press the button on the front to return it to operational state.
It does not recover itself without pressing that button.
i also noticed it has a "DC test" chip next to the STC15W404S .
I suppose the new controller board should fix your issue. The board may have a new code for the uPC IC loaded, or it may have changes done to resistors/capacitors surrounding that quad OP, or both... The large resistors handle raw mains... so make sure it's all nice and safe before you start replacing the card.
thank you and thanks for the reminder! hope so! will do a comparison and see what changed.
Got the new board today , playing the same low frequency track at louder volumes seems to work fine .
quickly testing it, the threshold seems to be set at 1.4vdc now.
comparing the board , the most obvious one is that they have added a resistor on the back of the board near the OP amp.
on the front , not much has changed , except they have change the larger resistors to dale resistors
note:the one sitting on the white foam is the new board.
Kinki ex m7 - Google Photos
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Seems like the change was done in "hardware" -> the voltage divider only, around that quad OP. At least that's what is visible.
Are you sending the old board back?
Are you sending the old board back?