Yeah I checked that site.
The problem you know with heatsinks is that you dont get linear thermal resistance with heatsink size.
I mean if you buy a double size heatsink it doesnt have half thermal res.
It gets bigger and bigger and very expensive.
The worst is you can´t find very big heatsinks in the normal stores. A 0.6 K/W is usually the biggest they have.
So if you are looking for 0.08 its a little hard.
If you get a lot of them then the construction becomes hard.
The problem you know with heatsinks is that you dont get linear thermal resistance with heatsink size.
I mean if you buy a double size heatsink it doesnt have half thermal res.
It gets bigger and bigger and very expensive.
The worst is you can´t find very big heatsinks in the normal stores. A 0.6 K/W is usually the biggest they have.
So if you are looking for 0.08 its a little hard.
If you get a lot of them then the construction becomes hard.
Re: Looks like Fischer part numbers
ALL:
Have anybody tried the LEDs instead of zeners in current cource of input transistors? I suppose this change should lower the noise. I am not sure if it is important in power amp.
Second: What is the point of using LED between base and emitor in current mirror ( some recommended to use it).
ALL:
Have anybody tried the LEDs instead of zeners in current cource of input transistors? I suppose this change should lower the noise. I am not sure if it is important in power amp.
Second: What is the point of using LED between base and emitor in current mirror ( some recommended to use it).
The LED is a diode too, like the zener. So we take advantage of the leds voltage and current that under certain conditions stays consant.
the advantage is that it has very low noise. the disadvantage is that the voltage across a LED is low around 3-5 volts. I have seen it in very good transistor circuits maybe it works in some FET circuits too but I don´t know to which you are reffering too.
the advantage is that it has very low noise. the disadvantage is that the voltage across a LED is low around 3-5 volts. I have seen it in very good transistor circuits maybe it works in some FET circuits too but I don´t know to which you are reffering too.
Hi guys,
I have a question ( as usually).
What is the point of using using the resistor in the source of the output MOSFETs (IRFP...)? I suppose it should limit the current of the transistor ( any kind of protection or to increase the stability?). Is it worth of changing the value? - in my case. I am going to drive low impedance ( 4ohm).
And the same question for the output resistors between speaker and MOSFETs. The lower impedance ( the higher current), the lower values?
As for the LED diods - using LEDs instead of zener diode in current source to lower the noise?
I have a question ( as usually).
What is the point of using using the resistor in the source of the output MOSFETs (IRFP...)? I suppose it should limit the current of the transistor ( any kind of protection or to increase the stability?). Is it worth of changing the value? - in my case. I am going to drive low impedance ( 4ohm).
And the same question for the output resistors between speaker and MOSFETs. The lower impedance ( the higher current), the lower values?
As for the LED diods - using LEDs instead of zener diode in current source to lower the noise?
Koy,
The voltage drop across a LED is not enough to turn on a mosfet, you will have to stack several. I think it is easier to use a zener and place a small capacitor across it to get rid of any zener noise.
Do not get rid of the resistor's inline with the speaker output, the current source gets it's reference from the voltage drop across these resistors. The amplifier should drive 4ohm loads ok.If you need more drive capability you have increase the bias and adjust the current limiting.
Jam
[Edited by jam on 05-31-2001 at 12:10 AM]
The voltage drop across a LED is not enough to turn on a mosfet, you will have to stack several. I think it is easier to use a zener and place a small capacitor across it to get rid of any zener noise.
Do not get rid of the resistor's inline with the speaker output, the current source gets it's reference from the voltage drop across these resistors. The amplifier should drive 4ohm loads ok.If you need more drive capability you have increase the bias and adjust the current limiting.
Jam
[Edited by jam on 05-31-2001 at 12:10 AM]
A-40 Subs
I noticed there was some discussion earlier about substitutes for the A40 transistors. Nelson Pass has a letter in the new AudioXpress concerning this; it is also posted at http://www.passlabs.com./tech.htm
With the substitute parts, and bare PCBs apparently still available from the AudioXpress store (link below), this looks like a very buildable project again.
http://www.audioxpress.com/bksprods/index.htm
I noticed there was some discussion earlier about substitutes for the A40 transistors. Nelson Pass has a letter in the new AudioXpress concerning this; it is also posted at http://www.passlabs.com./tech.htm
With the substitute parts, and bare PCBs apparently still available from the AudioXpress store (link below), this looks like a very buildable project again.
http://www.audioxpress.com/bksprods/index.htm
Hi guys!!!, there is something about
these Alephs that always make me wonder...
I presume most of you have read the patent
about the dynamic current source.
Well, whenever I simulate the Alephs (Microsim,
evaluation program) it seems like
the ratio for the gain resistors doesn't make
sense and it never kicks in like a
dynamic current source unless you really
make a small value the rsistor that
goes to the BJT that controls the current FET...
Do you know what is the modulation percentage
for the dynamic current source,
let say for the Aleph 3?
Drakonis...
(Hope this is not a basic question...)
these Alephs that always make me wonder...
I presume most of you have read the patent
about the dynamic current source.
Well, whenever I simulate the Alephs (Microsim,
evaluation program) it seems like
the ratio for the gain resistors doesn't make
sense and it never kicks in like a
dynamic current source unless you really
make a small value the rsistor that
goes to the BJT that controls the current FET...
Do you know what is the modulation percentage
for the dynamic current source,
let say for the Aleph 3?
Drakonis...
(Hope this is not a basic question...)
Hi there.
paulb:
It looks like the A40-PCB from AudioXpress is for the original partlist, and not the new one, but don't give up, since I've been working on a new layout, using the PCB-mounted TIP-142/147 powerBJT's, thus eliminating the need for wirering between the them and the PCB, not to forget all the drilling for the TO-3's.
Status is that I'm still waiting for the powerBJT's from my supplier, and untill I get them, I can't test the layout :-(
paulb:
It looks like the A40-PCB from AudioXpress is for the original partlist, and not the new one, but don't give up, since I've been working on a new layout, using the PCB-mounted TIP-142/147 powerBJT's, thus eliminating the need for wirering between the them and the PCB, not to forget all the drilling for the TO-3's.
Status is that I'm still waiting for the powerBJT's from my supplier, and untill I get them, I can't test the layout :-(
Pass DIY Addict
Joined 2000
Paid Member
A40 parts
Thanks for the info. I've decided to start with a DoZ amp because I have the PCBs available (I was going to make a headphone amp with them) - as per my post in another thread.
I may end up building a lower-power version (limited by an existing power supply) of the A40 sometime later. I kind of like the idea of being able to try out different amps, so I'm making my power supply and amp as modular and configurable as possible.
Thanks for the info. I've decided to start with a DoZ amp because I have the PCBs available (I was going to make a headphone amp with them) - as per my post in another thread.
I may end up building a lower-power version (limited by an existing power supply) of the A40 sometime later. I kind of like the idea of being able to try out different amps, so I'm making my power supply and amp as modular and configurable as possible.
A-40
Guys,
I can't understand the facination with the A-40 after all these years. Don't get me wrong it is a great amplifier, I must have built five or six of them but the A-75, Zen's and Aleph's are far superior amplifiers.
Maybe nostalgia rules but for those who are building the amplifier I suggest running the front end off its own bridge rectifier and supply capacitors (2000uf is enough) and you will notice an improvement.
Jam
Guys,
I can't understand the facination with the A-40 after all these years. Don't get me wrong it is a great amplifier, I must have built five or six of them but the A-75, Zen's and Aleph's are far superior amplifiers.
Maybe nostalgia rules but for those who are building the amplifier I suggest running the front end off its own bridge rectifier and supply capacitors (2000uf is enough) and you will notice an improvement.
Jam
JAM
I totally agree with You in using a double power-supply, and I've also thrown in a couple of electrolytic caps on the PCB for the front-end.
C2 and C3 was originally tantalium caps, wich I've changed into electrolytic caps, for wich low-ESR caps are prefered. Sanyo makes some very fine OSCON caps, available from i.e. Farnell, try them ;-)
I totally agree with You in using a double power-supply, and I've also thrown in a couple of electrolytic caps on the PCB for the front-end.
C2 and C3 was originally tantalium caps, wich I've changed into electrolytic caps, for wich low-ESR caps are prefered. Sanyo makes some very fine OSCON caps, available from i.e. Farnell, try them ;-)
interesstign
idea to make a separate ps for the front end...how big traffo like 20Va should be plenty?...2000µF isnt that a lite on the light side but the current sorce only need above 9,1V to work? am i right?.... then you could give it some hefty capacitance......(im working on aleoph 4 monoblocks right now)
/micke
idea to make a separate ps for the front end...how big traffo like 20Va should be plenty?...2000µF isnt that a lite on the light side but the current sorce only need above 9,1V to work? am i right?.... then you could give it some hefty capacitance......(im working on aleoph 4 monoblocks right now)
/micke
A-40
Hoffmeyer,
I have not tried the os-cons but I got excellent results with black gates.
In the last A-40 I built I went one step further and replaced the differential transistors with fets, which allowed me to get rid of one of the caps and have low offset.
Regulated supplies can help, but the biggest improvement comes from isolating the front end from the main supply. This could be done in the simplest form with two diodes and two caps and tap this off the main supply, or add a second bridge across the secondary of the transformer, followed by some caps.
Jam
P.S. I suppose one day I should build an all mosfet version of the A-40.
[Edited by jam on 06-27-2001 at 08:33 AM]
Hoffmeyer,
I have not tried the os-cons but I got excellent results with black gates.
In the last A-40 I built I went one step further and replaced the differential transistors with fets, which allowed me to get rid of one of the caps and have low offset.
Regulated supplies can help, but the biggest improvement comes from isolating the front end from the main supply. This could be done in the simplest form with two diodes and two caps and tap this off the main supply, or add a second bridge across the secondary of the transformer, followed by some caps.
Jam
P.S. I suppose one day I should build an all mosfet version of the A-40.
[Edited by jam on 06-27-2001 at 08:33 AM]
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