Dissipation about 260 mW, not storage. You only changed to 0805 R7,R10, R11 but not change R27, R30, R31, please change this and put new gerbers.
Sorry. I had to move things slightly to fit the other three.
If you are at a higher supply voltage, 3x18k is far too low, I aim for 1 mA in this diode bias chain, so 3 x 33k is more suitable for +/-55V.
If you are at a higher supply voltage, 3x18k is far too low, I aim for 1 mA in this diode bias chain, so 3 x 33k is more suitable for +/-55V.
It was never meant to be 2 mA and why I see photos of the original modules where these bias resistors have burnt.
So far as I can see (because Sanyo never published resistor values) the difference between the various variants of this module will be that resistor value for the supply voltage options.
The current in the LTPs and drivers is reasonably constant. Only this bias chain current varies with supply voltage
So far as I can see (because Sanyo never published resistor values) the difference between the various variants of this module will be that resistor value for the supply voltage options.
The current in the LTPs and drivers is reasonably constant. Only this bias chain current varies with supply voltage
[B]davidsrsb[/B], Let's say that my supply voltage is 116 V (2 x 56 V), then it turns out that Rbias = (116 - 2.2)/0.001 = 113.8 kOm. Why is the BIAS current 1 mA selected, and not 2 mA?
STK hybrids were designed when transistors had relatively high Cbe (capacitance between base and emitter).
They then went on with newer transistor dies that were cheaper to make that have lower Cbe.
After the amplifier gets past its manufacturers warranty the power rail decoupling capacitors begin to dry out and the thing goes off at RF and kills itself.
It is like putting new 2N3055s into an old amplifier. The old data sheets give a maximum Cbe and a minimum FT.
Those old data sheets never had any spec limits as long as the part can do what the old data sheet says with the same or less burden. If you find something with 2N3055 printed on it you might have an RF part that failed to meet the grade for its original purpose but still could handle audio. These would work but only if you add a capacitor from base to emitter very close to the lead-outs in most cases.
When designing these boards there would be some value in testing a lash up using video output transistors from old CRT TV sets and adding pads for capacitors between base and emitter of most of the transistors in the final design.
If you have an STK that is still good I would add at least two SMD non electrolytic capacitors of differing technologies in parallel with all electrolytic capacitors that are connected to the STK pins and fit them as close to the STK pins as you can.
I have in the past fixed things that never worked from new by adding SMD caps between power tracks under thru hole chips.
They then went on with newer transistor dies that were cheaper to make that have lower Cbe.
After the amplifier gets past its manufacturers warranty the power rail decoupling capacitors begin to dry out and the thing goes off at RF and kills itself.
It is like putting new 2N3055s into an old amplifier. The old data sheets give a maximum Cbe and a minimum FT.
Those old data sheets never had any spec limits as long as the part can do what the old data sheet says with the same or less burden. If you find something with 2N3055 printed on it you might have an RF part that failed to meet the grade for its original purpose but still could handle audio. These would work but only if you add a capacitor from base to emitter very close to the lead-outs in most cases.
When designing these boards there would be some value in testing a lash up using video output transistors from old CRT TV sets and adding pads for capacitors between base and emitter of most of the transistors in the final design.
If you have an STK that is still good I would add at least two SMD non electrolytic capacitors of differing technologies in parallel with all electrolytic capacitors that are connected to the STK pins and fit them as close to the STK pins as you can.
I have in the past fixed things that never worked from new by adding SMD caps between power tracks under thru hole chips.
If this is possible, could you explain it in more detail? I understand correctly that as a result of the loss of capacitor capacity, it is possible to obtain high-frequency oscillations, which lead to burnout of the output transistors. Based on the circuit specified in the service manual, the STK is very poorly shunt for power supply by two 4.7 uF 100V electrolytes. That is, it is not enough to replace faulty parts? It is necessary to check the electrolytic capacitors for the power supply of the amplifier and STK and additionally shunt them with ceramics for the power supply directly at the STK terminals.
I don’t want to use better and faster transistors than boules in the amplifier - I want to restore the amplifier using transistors of the same types as those installed from the factory. But I want to change the amplifier correction a little, lowering the loop gain and increasing the frequency of the first pole. I also want the amplifier to work reliably.
Transistors in the 1970s were made using an expensive process and were made obsolete by the beginning of the 1980s.
Those STKs were designed at about the time the old transistors were going obsolete.
The newer transistors are faster and much cheaper to make. They work fast enough to go right up to RF making them detect mobile phone signals and oscillate at RF.
A small capacitor from base to collector provides a little bit of negative feedback at RF and will allow the part to be used in an old audio circuit.
Those STKs were designed at about the time the old transistors were going obsolete.
The newer transistors are faster and much cheaper to make. They work fast enough to go right up to RF making them detect mobile phone signals and oscillate at RF.
A small capacitor from base to collector provides a little bit of negative feedback at RF and will allow the part to be used in an old audio circuit.
Refugee1
A capacitor between the base and emitter will negatively affect the speed and frequency properties of the amplifier. Maybe you are confusing it with small capacitors between the base and collector.I have a model of my Luxman in a microcap, I can share - it has a correction typical of an op-amp
In the original, the amplifier from the factory contains such capacitances at the base-collector junctions on 1 and two stage of the Darlington triple
I presume that you are talking about an output stage module. The driver module has no capacitors. These modules data back to long before SMD times. They were made using a chip on ceramic substrate with printed thin or thick film resistors. There was no easy way of adding a capacitor.
There were leadless ceramic capacitors available, but only in very low values.
I repaired the LUXMAN L 435 amplifier using the module you designed and tested it, tested it at an output power with a resistive load of 100 W at 8 Ohms at 20 kHz. I listened for several hours and my impressions of the sound of the amplifier are purely positive. The quiescent current is adjusted and remains excellent! If anyone needs a clone of STK3xxx on SMD developed by David on FR4, the second layer of foil of the board is preserved, then please contact me in a personal conversation or for advice.
I missed this post.
From the reported measured resistor values (They were never published), the current in the long tailed pair is about 2mA at the current source, 1mA in each side.
The current in the output buffer is about 6mA.
There is an ancient engineering rule of thumb that a bias should be not less than 10% so that transistor Hfe is not sensitive.
So we end up needing a bias of not less than 800uA, so I choose 1mA. If I went to 2mA there would be little change except a lot more heat in the bias chain. In the FR4 version this would be cooking the board. The choice of resistor value depends on the supply rails - which you must remember, are are not regulated.
That is implemention specific. In some cases it’s true and other cases it’s not but as you say it’s something to be mindful of none the less.
Hi, I just came across this, I have a Technics SU-C03, it uses the STK3062 (no II, III nor IV). Would this be a suitable replacement? I noticed you mention about having the bias resistors values according to the rail voltage, which in my case is +/- 41v. I guess it would mean that for my application I would need 41k of resistors instead of 54k?
Thanks for the responses!!
Thanks for the responses!!