If a audio dual matched transistor pair is used at the i/p of a balanced amp and each half fed with the two differential phases of the i/p signal, will the alternate heating and cooling effects on each device cancel out due to their proximity.
can we assume that the two devices are close enough for this to occur ?
can anyone think of any drawbacks of such a scheme ?
would the cancelation cover all relevant frequencies ?
does anyone know about this kind of stuff ?
mike
can we assume that the two devices are close enough for this to occur ?
can anyone think of any drawbacks of such a scheme ?
would the cancelation cover all relevant frequencies ?
does anyone know about this kind of stuff ?
mike
Have you seen the following site (I happened on to it this morning). I think the author is a diyAudio member...
http://peufeu.free.fr/audio/memory/
JF
http://peufeu.free.fr/audio/memory/
JF
yes Iv'e read most of it twice !
However I don't think that this idea is covered there
If it works it is a very simple remedy in a balanced approach
However I don't think that this idea is covered there
If it works it is a very simple remedy in a balanced approach
Konnichiwa,
Absolutely not, UNLESS the transistor are on the same chip and the chip has a low thermal intertia. I think there are way too many if's and but's in this to rely too much on this.
As a rule, the higher the frequency the lower thermal distortion effects as the thremal inertia of the actual semiconductor chip becomes relevant and limits temperature changes.
Sayonara
mikelm said:
Absolutely not, UNLESS the transistor are on the same chip and the chip has a low thermal intertia. I think there are way too many if's and but's in this to rely too much on this.
mikelm said:
As a rule, the higher the frequency the lower thermal distortion effects as the thremal inertia of the actual semiconductor chip becomes relevant and limits temperature changes.
Sayonara
Re: Re: cancelling memory distortion ?
Not entirely. there are two "thermal effects" going on in a semiconductor component.
One is the steady state thermal heating. Let's say that you apply a constant sine wave, regardless of its frequency, the ohmic heating will reach an equilibrium after a period of time, and die temperature will stabilize at that point. the operating point of the component will, as such, shift depending on the signal. You will hear people talking about "thermal resistance / resistivity".
Another is the transient response of a device. the temperature of a device will go up and down with the signal, or being modulated by the signal. You will hear people talking about "thermal impedance" in those cases.
both effects are thermal-induced but its mechanism is slightly different.
Kuei Yang Wang said:
Not entirely. there are two "thermal effects" going on in a semiconductor component.
One is the steady state thermal heating. Let's say that you apply a constant sine wave, regardless of its frequency, the ohmic heating will reach an equilibrium after a period of time, and die temperature will stabilize at that point. the operating point of the component will, as such, shift depending on the signal. You will hear people talking about "thermal resistance / resistivity".
Another is the transient response of a device. the temperature of a device will go up and down with the signal, or being modulated by the signal. You will hear people talking about "thermal impedance" in those cases.
both effects are thermal-induced but its mechanism is slightly different.
Re: Re: cancelling memory distortion ?
I was thinking of the SSM2220P and SSM2210P with dual devices designed specifically for audio i/p
I was thinking that the two devices would be physically & thermally quite close.
does any one know what this inside of these things are like ?
Kuei Yang Wang said:
I was thinking of the SSM2220P and SSM2210P with dual devices designed specifically for audio i/p
I was thinking that the two devices would be physically & thermally quite close.
does any one know what this inside of these things are like ?
I don't know about these devices, but I do know that the similar LM394 dual consist of a chip of many (IIRC hundreds) of individual transistors, parallelled to form two transistors. The individual transistors are physically spread over the chip for two reasons:
1 averaging out the electrical characteristics for electrical matching;
2 idem for thermal matching.
This seems to be a standard technique, so I would expect (but don't know for sure) the SSM's to be similarly constructed.
Jan Didden
1 averaging out the electrical characteristics for electrical matching;
2 idem for thermal matching.
This seems to be a standard technique, so I would expect (but don't know for sure) the SSM's to be similarly constructed.
Jan Didden
This approach is standard in chip op amps, where the diff
transistors are made at the same spot, thus matching them,
and have the same temperature. Op amp performance
depends on such tricks, as the ability to select the components
on the chip is very limited.
transistors are made at the same spot, thus matching them,
and have the same temperature. Op amp performance
depends on such tricks, as the ability to select the components
on the chip is very limited.
Thanks, this sounds quite encouraging. I'll go ahead and do some experiments.
The only further question is one of max current
All these devices quote 20mA as the absolute max
and the max voltage is around 30V
I want to use a higher current perhaps 35mA in the cct I am thinking of but only 7 volts.
Given this very low voltage will a higher current damage the devices even though the power is far below the max
If this is the case, I do not understand why this would be.
or...Will I have to paralell them ?
Can anyone shed some light on this ?
The only further question is one of max current
All these devices quote 20mA as the absolute max
and the max voltage is around 30V
I want to use a higher current perhaps 35mA in the cct I am thinking of but only 7 volts.
Given this very low voltage will a higher current damage the devices even though the power is far below the max
If this is the case, I do not understand why this would be.
or...Will I have to paralell them ?
Can anyone shed some light on this ?
johnferrier said:
I've tried to modify the Balanced Line Stage with the suggestions depicted in that site and the result is great in terms of stage and darkness of the scene.
In some particulars the original design is better (armonics, warm) but they are quite negligible.
I'm building a second original-design BLS, so to make more in deep analysis.
Anyone else tried something similar?
Happy new year!
I have seen it done before where the two transistors are mounted right next to each other face to face.
Bu thermal coupling would help keep transistors balanced.
Both transistors would see same current anyway so there should be no imbalance.
even one of the members has in bottom sign that the junction temperature is not the case temperature...
Under same (thermal too) conditions:
Same parts sound different.
Different parts sound very very different.-) Or very very very different;-)))
Same parts sound different.
Different parts sound very very different.-) Or very very very different;-)))
I have been building amps for 40 years with LTP's and never heard a one that sounded bad or different. Sounds like snake oil to me.
Thermal tracking between bjts is best when on the SAME DIE and close.
A very desirable feature, it is too bad there is only a limited choice.
I wish I could have medium power bjt pairs on the same die. I only find no more than 100mA.
A very desirable feature, it is too bad there is only a limited choice.
I wish I could have medium power bjt pairs on the same die. I only find no more than 100mA.