Hi all.
I bought Philips FA960 MKII. After reconnection transformer from 220V to 240 V, recapping, changing voltage regulators in power supply, and putting some new resistors,everything sounds nice and clean, without any noise or hiss.This amp is the first one, what is completely quiet. You don´t even know, if it is turned on or off.
But one thing is very interesting.I measured idle current of STK 3102II (someone replaced the old one 3102 III).
Left side 2,3mV, right side 3,0mV.The manual says it should be 14mV (39mA).So I tried to put R-side very carefully to 6-7 mV while I was touching the cooler on the STK.It was getting too HOT very quickly.So I put it down immediately to 2,3mV like on the left-side. I have tried to adjust 3,6mV on both channels.STK got hotter and the sound has changed (in middle frequencies it was very nice and tight, but treble sounded much sharper....).
So now it is idling at 2,3mV. Amp is without distortion, just slightly warm and the heat sink with output transistors is nearly cold.
Maybe it is normal, that at 6mV it gets so hot, you can´t even touch the cooler of the STK.
.... But then you have to replace STK and all the caps around very often due the heat.
Could someone tell me, is so low idle current normal?
Thank you very much. Jan.
I bought Philips FA960 MKII. After reconnection transformer from 220V to 240 V, recapping, changing voltage regulators in power supply, and putting some new resistors,everything sounds nice and clean, without any noise or hiss.This amp is the first one, what is completely quiet. You don´t even know, if it is turned on or off.
But one thing is very interesting.I measured idle current of STK 3102II (someone replaced the old one 3102 III).
Left side 2,3mV, right side 3,0mV.The manual says it should be 14mV (39mA).So I tried to put R-side very carefully to 6-7 mV while I was touching the cooler on the STK.It was getting too HOT very quickly.So I put it down immediately to 2,3mV like on the left-side. I have tried to adjust 3,6mV on both channels.STK got hotter and the sound has changed (in middle frequencies it was very nice and tight, but treble sounded much sharper....).
So now it is idling at 2,3mV. Amp is without distortion, just slightly warm and the heat sink with output transistors is nearly cold.
Maybe it is normal, that at 6mV it gets so hot, you can´t even touch the cooler of the STK.
.... But then you have to replace STK and all the caps around very often due the heat.
Could someone tell me, is so low idle current normal?
Thank you very much. Jan.
Thank you David.
OK.But you know what is strange, when I adjusted the idle current to 1,4 mV, it plays very good.
I can put it up to 2mV, I think that´s the best sounding option.
And after that point the sound of treble is getting much "sharper".
So for me, if I put there 2mV, it would be a very nice sounding device.
And you are right, there are many fakes around.I think they do not have any RC compensations.
And only the way, how to know it, is to check inside the STK.
I have one more question:
If I let the idle current very low (1,4-2mV), could something get damaged over time (amp or speakers) or will the amp heat up more?
Thank you.
OK.But you know what is strange, when I adjusted the idle current to 1,4 mV, it plays very good.
I can put it up to 2mV, I think that´s the best sounding option.
And after that point the sound of treble is getting much "sharper".
So for me, if I put there 2mV, it would be a very nice sounding device.
And you are right, there are many fakes around.I think they do not have any RC compensations.
And only the way, how to know it, is to check inside the STK.
I have one more question:
If I let the idle current very low (1,4-2mV), could something get damaged over time (amp or speakers) or will the amp heat up more?
Thank you.
The STK3102 does not contain any compensation RCs.
If it is on the edge of oscillation, it might start off and blow the outputs and then the woofer
Low bias means lots of crossover distortion
Sorry I'm not David, but answer:
Temperature is not high(about 50-60 grad celc) because stk is VAS and work with small current of cascade, stk dissipation 2-3 Watt.
Why only 2 mV, this means middle current only 0.002/0.22=1 mA is very low. Normal is 50 mA on pair this not big power dissipation and normal level of distortion.
Temperature is not high(about 50-60 grad celc) because stk is VAS and work with small current of cascade, stk dissipation 2-3 Watt.
Why only 2 mV, this means middle current only 0.002/0.22=1 mA is very low. Normal is 50 mA on pair this not big power dissipation and normal level of distortion.
With small idle current you have big distortion. And small idle current not safe your STK. STK you was safe if your loudspeaker have normal impedance with minimum higher than 4 Ohm and you don't use your amplifier on big output power and if voltage in power net normal without big undervoltage and state of condencators in power supply in amplifier is good.
It’s strange, but according to the manual, the Luxman L-435 also needs to be set to a very low quiescent current of the output transistors of 24 mA per pair (emitter resistors 0.22 Ohm). Maybe that's enough. How many pairs of output transistors do you have in your Philips FA960 and which ones?
Yes. 8-16 Ohms.It is written right on the amp.
But look at this data (from the manual):
TECHNICAL DATA •
(Subject to alteration)
• Power output ace, to FTC
at 8 ohm load
(20-20,000 Hz, D .;; 0,03%): 100 W continuous sine wave
• Power output ace, to IEC
at 8 ohm load
(63-12,500 Hz, D .;; 0,3%): 115 W continuous sine wave
• IHF music power
at 8 ohm load: 120 W
at 4 ohm load : 225 W
at 2 ohm load: 280 W
• Harmonic distortion (1 kHz): 0.008%
• Intermodulation distortion: 0.03%
• Power bandwidth (- 3 dB): 10-30,000 Hz
• Frequency response: 40-20,000 Hz ± 0,5 dB
• SIN ratio: 106 dB (weighted)
• Channel separation (1 kHz): 75 dB
• Damping factor at 8 ohms: 180 x
• Input sensitivity:
Phono MC: 0,25 mV1100 ohm
Phono MM: 2,5 mV/47 kohm
Compact Disc: 150 mV/25 kohm
Tuner: 150 mV/25 kohm
TV1 I Aux 1: 150 mV125 kohm
Video 1I Aux 2: 150 mV125 kohm
Tape 1: 150 mV/25 kohm
Tape 2: 150 mV/25 kohm
• Outputs:
Tape: 150 mV/220 ohm
2 sets of speakers: 8 ohm
Headphones: 8-1000 ohm
• Tone control:
bass : + 10 dB to -10 dB at 100 Hz
treble: + 10 dB to -10 dB at 10 kHz
• Loudness : +6dBat100Hz, +4dBat10kHz
• Balance control: 0-50 dB
• Power requirements: 2 ,5A/120 V AC/60 Hz
But look at this data (from the manual):
TECHNICAL DATA •
(Subject to alteration)
• Power output ace, to FTC
at 8 ohm load
(20-20,000 Hz, D .;; 0,03%): 100 W continuous sine wave
• Power output ace, to IEC
at 8 ohm load
(63-12,500 Hz, D .;; 0,3%): 115 W continuous sine wave
• IHF music power
at 8 ohm load: 120 W
at 4 ohm load : 225 W
at 2 ohm load: 280 W
• Harmonic distortion (1 kHz): 0.008%
• Intermodulation distortion: 0.03%
• Power bandwidth (- 3 dB): 10-30,000 Hz
• Frequency response: 40-20,000 Hz ± 0,5 dB
• SIN ratio: 106 dB (weighted)
• Channel separation (1 kHz): 75 dB
• Damping factor at 8 ohms: 180 x
• Input sensitivity:
Phono MC: 0,25 mV1100 ohm
Phono MM: 2,5 mV/47 kohm
Compact Disc: 150 mV/25 kohm
Tuner: 150 mV/25 kohm
TV1 I Aux 1: 150 mV125 kohm
Video 1I Aux 2: 150 mV125 kohm
Tape 1: 150 mV/25 kohm
Tape 2: 150 mV/25 kohm
• Outputs:
Tape: 150 mV/220 ohm
2 sets of speakers: 8 ohm
Headphones: 8-1000 ohm
• Tone control:
bass : + 10 dB to -10 dB at 100 Hz
treble: + 10 dB to -10 dB at 10 kHz
• Loudness : +6dBat100Hz, +4dBat10kHz
• Balance control: 0-50 dB
• Power requirements: 2 ,5A/120 V AC/60 Hz