Hello! I got a Kenwood KA-400 solid state amplifier and I found some problems on it, I wonder if someone here knows about this problem and how to fix it 
I have the schematics for this amp which helped me a lot, I have one channel working now but with a strange sound comming out, it's like when you record something in the sound recorder of windows using a low frecuency, or when you unplug an amp and keep earing the sound but with lower quality until it dissapear.. :s I believe it could for any dried capacitor, but I'm not sure 
And for the other channel, I can't use it because it causes the protective circuit (HA12002) to open the output, I measured the output and there's around 12 vdc coming out from that channel =/
any help with this?
I have the schematics for this amp which helped me a lot, I have one channel working now but with a strange sound comming out, it's like when you record something in the sound recorder of windows using a low frecuency, or when you unplug an amp and keep earing the sound but with lower quality until it dissapear.. :s I believe it could for any dried capacitor, but I'm not sure And for the other channel, I can't use it because it causes the protective circuit (HA12002) to open the output, I measured the output and there's around 12 vdc coming out from that channel =/
any help with this?
oh, I'll check that! thank you
and you can get the schematic from here:
KENWOOD_KA-100_Amplifier.zip
and you can get the schematic from here:
KENWOOD_KA-100_Amplifier.zip
Hi gecko,
The tone controls are part of the feedback network. They use the gain of the amplifier stage to function, so you are not going to find your problem there.
What makes you think the problem is with the tone controls? What transistor did you change? There is a protection circuit, so you should not have had any sound with a 12 VDC offset.
Have a look at C101, C102 and D18, D19. D18 and D19 are zener diodes to stabilize the supply for the tail currents for the diff pairs. C101 and C102 help decouple this supply for noise.
-Chris
The tone controls are part of the feedback network. They use the gain of the amplifier stage to function, so you are not going to find your problem there.
What makes you think the problem is with the tone controls? What transistor did you change? There is a protection circuit, so you should not have had any sound with a 12 VDC offset.
Have a look at C101, C102 and D18, D19. D18 and D19 are zener diodes to stabilize the supply for the tail currents for the diff pairs. C101 and C102 help decouple this supply for noise.
-Chris
Thanks Anatech, I'm checking those right now
I got sound in one channel because I opened the circuit just after the Pin of the HA12002 so it couldn't detect those 12v coming out from the faulty transistor , the transistor I changed was the driver 2sc1735 from the channel that was not working.
I was not really sure why it could be from the tone control, I just wanted to take that circuit aside just to make sure, but if you say that it couldn't be from there so I'll believe you
I got sound in one channel because I opened the circuit just after the Pin of the HA12002 so it couldn't detect those 12v coming out from the faulty transistor
, the transistor I changed was the driver 2sc1735 from the channel that was not working. I was not really sure why it could be from the tone control, I just wanted to take that circuit aside just to make sure, but if you say that it couldn't be from there so I'll believe you
Hi gecko,
Find R55 and R56. They are white, three legged parts near the heatsink. Measure (in mV) across the outside two terminals. These are 0.47 ohm each, two in series. Therefore your mV reading is close to the actual current in mA. Be careful not to short anything with the leads. Let the unit sit and settle down before taking a reading.
-Chris
Find R55 and R56. They are white, three legged parts near the heatsink. Measure (in mV) across the outside two terminals. These are 0.47 ohm each, two in series. Therefore your mV reading is close to the actual current in mA. Be careful not to short anything with the leads. Let the unit sit and settle down before taking a reading.
-Chris
Hi gecko,
That explains it. You have no bias current flowing. The schematic does not indicate a bias level adjustment figure. VR5 and VR6 adjust the bias current. I have a feeling something else is wrong, you should have some current flowing even if it's wrong.
Measure the voltage across D1 and D2, they should be mounted on the heatsink. These are temperature sensing (compound) diodes. Also check Q11 and Q12.
-Chris
That explains it. You have no bias current flowing. The schematic does not indicate a bias level adjustment figure. VR5 and VR6 adjust the bias current. I have a feeling something else is wrong, you should have some current flowing even if it's wrong.
Measure the voltage across D1 and D2, they should be mounted on the heatsink. These are temperature sensing (compound) diodes. Also check Q11 and Q12.
-Chris
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