😀 😀 😀
hello guys,
do you know of some ways to optimize the the VBE multiplier.
Does this thing affect sonic quality if not optimized, I mean
aside from thermal tracking?
what transistor parameters are involve or needed when designing an amp with VBE multipliers, becuase I think not all BJT's
are suitable for VBE multipliers.
I've got this amp here (pls. see the doc attachment).
Before finally arriving to that device (as VBE multiplier), BC546,
I've tried TIP41, although current and voltage tests were done.
The output was not that good, bass reproduction was sagging,
then Ive tried the D669, there was a little improvement,
until finally I arrived with BC546,
everything in the audio spectrum
was not compromised, bass was tight, the mids and highs were clear.
does these things affect:?
a) hfe
b) Ft
Or maybe the components around it.?
the real question here is, what if were building an amp with the different but the only available devices (for the VBE multiplier) around?
regards,
hienrich
😀 😀 😀
hello guys,
do you know of some ways to optimize the the VBE multiplier.
Does this thing affect sonic quality if not optimized, I mean
aside from thermal tracking?
what transistor parameters are involve or needed when designing an amp with VBE multipliers, becuase I think not all BJT's
are suitable for VBE multipliers.
I've got this amp here (pls. see the doc attachment).
Before finally arriving to that device (as VBE multiplier), BC546,
I've tried TIP41, although current and voltage tests were done.
The output was not that good, bass reproduction was sagging,
then Ive tried the D669, there was a little improvement,
until finally I arrived with BC546,
everything in the audio spectrum
was not compromised, bass was tight, the mids and highs were clear.
does these things affect:?
a) hfe
b) Ft
Or maybe the components around it.?
the real question here is, what if were building an amp with the different but the only available devices (for the VBE multiplier) around?
regards,
hienrich
😀 😀 😀
As I see it, the quality of a Vbe stage depends on the current through the stage and the gain of the used transistor.
To make the gain less important during transients, I use a capacitor in parallel with the Vbe stage. (collector-emitter).
The current through the Vbe multiplier is supplied (often) from the voltage gain stage. This also needs current enough to effectively drive the output stage(s).
The higher the gain of the Vbe transistor, the less current is needed to supply the base, which is needed to actually create the Vbe multiplying function.
Actually, with high value resistors, you could be in a situation where your Vbe-resistors do not provide a normal voltage divider, but a current source for the transistor. If you reach this point, you could be in trouble, as this current varies with the load (current) for the output stage.
For a given base current resistor set, the output impedance of the Vbe configuration (it's tendency to vary with current through it) is depending on the beta (gain) of the transistor.
I use BD139 (or is it the 140 which is NPN - can't remember) as Vbe stage, as it has reasonable gain, and has a hole for easy mounting on the heat sink.
Jennice
To make the gain less important during transients, I use a capacitor in parallel with the Vbe stage. (collector-emitter).
The current through the Vbe multiplier is supplied (often) from the voltage gain stage. This also needs current enough to effectively drive the output stage(s).
The higher the gain of the Vbe transistor, the less current is needed to supply the base, which is needed to actually create the Vbe multiplying function.
Actually, with high value resistors, you could be in a situation where your Vbe-resistors do not provide a normal voltage divider, but a current source for the transistor. If you reach this point, you could be in trouble, as this current varies with the load (current) for the output stage.
For a given base current resistor set, the output impedance of the Vbe configuration (it's tendency to vary with current through it) is depending on the beta (gain) of the transistor.
I use BD139 (or is it the 140 which is NPN - can't remember) as Vbe stage, as it has reasonable gain, and has a hole for easy mounting on the heat sink.
Jennice
hienrich !
Try to put a foil cap (1uF) paralell the 47uF, like Jennice told it.
I'am curious about the changes in the quality !
And what about series diodes as solution ?
Try to put a foil cap (1uF) paralell the 47uF, like Jennice told it.
I'am curious about the changes in the quality !
And what about series diodes as solution ?
Heinrich,
What is the current through the Vbe transistor and the voltage gain transistors?
Jennice
What is the current through the Vbe transistor and the voltage gain transistors?
Jennice
Using a Sziklai or Darlington pair instead of a single transistor decreases the Vbe multiplier's output impedance, reducing the variation in bias with current through it.
Hi,
Mr evil, what effect (better or worse) does the shiklai or darlington Vbe have on the sound quality?
Regards Andrew T.
Mr evil, what effect (better or worse) does the shiklai or darlington Vbe have on the sound quality?
Regards Andrew T.
hi sorry for the delay
hi guys,
Jennice: I think you've got the point, I was also thinking about this
after finalizing my amp.
as you could see in my schemes I'm using the BC546 which is the highest in gain and in Ft, (compared to TIP41 and D669) actually
there is an 11ma current across the voltage amp stage.
So far I didn't mount the VBE multiplier on the heatsinks! which it should be, but I'm using forced cooling fans against the heatsinks, which make me confident.
though without foil caps across (emmiter to collector),I just used
47uf electrolytic, and with the chosen VBE multiplier BC546 my best choice, the sonic output of this beast is very punchy and involving.
bass was very profound and dynamic even compared to the LEACH AMP which I've got one.
Cortez: if we are just near from each other I would enjoy listening
music with this newly built amp with you!!!!
😀 😀 😀
hey guys you might have some great sounding amps with you.
may you share their schemes.
I hope I could also post some pictures
regards,
hienrich
hi guys,
Jennice: I think you've got the point, I was also thinking about this
after finalizing my amp.
as you could see in my schemes I'm using the BC546 which is the highest in gain and in Ft, (compared to TIP41 and D669) actually
there is an 11ma current across the voltage amp stage.
So far I didn't mount the VBE multiplier on the heatsinks! which it should be, but I'm using forced cooling fans against the heatsinks, which make me confident.
though without foil caps across (emmiter to collector),I just used
47uf electrolytic, and with the chosen VBE multiplier BC546 my best choice, the sonic output of this beast is very punchy and involving.
bass was very profound and dynamic even compared to the LEACH AMP which I've got one.
Cortez: if we are just near from each other I would enjoy listening
music with this newly built amp with you!!!!
😀 😀 😀
hey guys you might have some great sounding amps with you.
may you share their schemes.
I hope I could also post some pictures
regards,
hienrich
Hi,
Hienrich the Vbe multi only monitors the output temperature in the darlington topology.
With shiklai, the Vbe must monitor the driver temp or predriver if using 3 deep cascade.
regards Andrew T.
Hienrich the Vbe multi only monitors the output temperature in the darlington topology.
With shiklai, the Vbe must monitor the driver temp or predriver if using 3 deep cascade.
regards Andrew T.
Andrew, Mr Evil was on about the actual Vbe multiplier being a Darlington or Sziklai. Your comment is correct if the output stage is Sziklai.
I should be
😀 😀 😀
andrewT,
hi, youre correct! but I'm using it the other way, a real contrast
to the "should be".
becuase I'm using fans for cooling the heatsinks, and I still have to redesign my PCB in order for the VBE multiplier to be closer and directly mounted to the heatsinks and the same time on the PCB.
regards,
hienrich
🙂 🙂 🙂
😀 😀 😀
andrewT,
hi, youre correct! but I'm using it the other way, a real contrast
to the "should be".
becuase I'm using fans for cooling the heatsinks, and I still have to redesign my PCB in order for the VBE multiplier to be closer and directly mounted to the heatsinks and the same time on the PCB.
regards,
hienrich
🙂 🙂 🙂
If you want something different, I have also seen a TL431 used as a vbe device, with a string of diode-connected transistors for thermal tracking. Look at the Stochino amplifier for an example 🙂
BTW you can get at least one TL431 for free from a dead PC PSU. I have a stack of them.
BTW you can get at least one TL431 for free from a dead PC PSU. I have a stack of them.
Here it is:
http://www.soton.ac.uk/~apm3/diyaudio/Stochino_circuit.jpg
I just tried this TL431 in my triple darlington amp SPICE sim (similar to the Leach Amp) and found it to be a bit tricky to control. Maybe a simple Darlington VBE would be best.
http://www.soton.ac.uk/~apm3/diyaudio/Stochino_circuit.jpg
I just tried this TL431 in my triple darlington amp SPICE sim (similar to the Leach Amp) and found it to be a bit tricky to control. Maybe a simple Darlington VBE would be best.
thanks I got it....
😀 😀 😀 😎 😎 😎
thanks Jaycee,
I got it I on to it now.
hienrich
offline........
😀 😀 😀 😎 😎 😎
thanks Jaycee,
I got it I on to it now.
hienrich
offline........
Heinrich,
When I sent my first reply, I didn't have time up open your schematic.
Therefore I didn't know that you were already using a capacitor. I am using a 100uF in mine, and it works well for me.
I don't see a need for the film too, as the frequencies are low. They're more relevant for HF problems, I think.
Who says your transistor needs to be on the PCB, and you need to redesign your PCB???
I have mine connected to the PCB with wires. Who cares - it's just a DC source with floating potential, so you won't have to worry about inductances in the wires and HF problems with the Vbe multiplier / thermal monitor.
Jennice
When I sent my first reply, I didn't have time up open your schematic.
Therefore I didn't know that you were already using a capacitor. I am using a 100uF in mine, and it works well for me.
I don't see a need for the film too, as the frequencies are low. They're more relevant for HF problems, I think.
Who says your transistor needs to be on the PCB, and you need to redesign your PCB???
I have mine connected to the PCB with wires. Who cares - it's just a DC source with floating potential, so you won't have to worry about inductances in the wires and HF problems with the Vbe multiplier / thermal monitor.
Jennice
Jennice said:
That bit. It's not just a DC source with floating potential because it's in the path of the VAS which is subject to AC and is sensitive to capacitance.
And who tells you thet one cannot have a DC source in an AC path? It just gives an offset.
I know the Vbe isn't an idea DC source with zero output impedance, but that's why the capacitor is placed on the PCB.
Jennice
I know the Vbe isn't an idea DC source with zero output impedance, but that's why the capacitor is placed on the PCB.
Jennice
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