Hi all,
i like to build me a pass A3 amp, but i have so many questions, i did buy some nice pcb's.
And i have some stuff lying around what i like to use if it's suitable for the amplifier, so i can keep the cost down for the build.
First starting out with the supply i have a 500va with 2x18v ac out, and a 500va with 2x24v ac out, can i use them and which is better to use with the A3 amp, i believe the original power supply to have is a 2x20v ac out.
Next i did see that in my schematic diagram i did get from the seller of the pcb's i did see that they use the bc550c, and i did see in the Aleph 3 Service Manual that they did use the mpsa18 so i did saw that they did have lower distortion and more hfe so i did order them.
Than i have some new mosfets lying around, again in the original Aleph 3 Service Manual they did use the irf244 i do not have them, i have the irfp250 that are used in my clone A3 schematic diagram and i have the irfp260 also, what must i do, buy the irf244 or go for the irfp250 or the irfp260 what i already have.
I believe the irfp260 has the lowest resistance, does the resistance matter or not in a amp, oke so where i have to look for in a mosfet for a amplifier, what is important to look for.
So next i have some new Panasonic caps lying around, the FR version, so fast and a long life span, they are just the value i need 220Uf, can i use them or do i need real audio caps for this amp.
I did build a Hood 1969 amp before so normal u set the middle voltage with a pot and the bias with a pot, i do not see them with this design, so i am sure that they are resistors that do that job, but i do not now which resistors i have to change, but i think i need to change them with i higher or lower voltage on the rails.
please understand i am a beginner at this, so please do not judge me for not knowing, i did build so many other things, but only ones i did build a small amplifier, and i did like the sound of that Hood 1969 with the toshiba 2sc5200 in it, i did build that amp for in my jukebox diy project.
And yes i do like nice music, who doesn't, so i do build my own speakers, but this amp is the next step up, building your own amp, so i need help to do it.
And i hope i get it here.
O yea i did hear a few years ago a original Pass Amp, i can not remember what type of Pass amp that was but i did like it, i did not forget the nice sound, i hope my Pass clone amp will get the same sound, or near to the original sound, but for the real thing i do not have the money so that's why i go this way of building my own Pass clone amp and hope for the best.
i ad my schematic diagram i did get from the seller of the PCB's
i like to build me a pass A3 amp, but i have so many questions, i did buy some nice pcb's.
And i have some stuff lying around what i like to use if it's suitable for the amplifier, so i can keep the cost down for the build.
First starting out with the supply i have a 500va with 2x18v ac out, and a 500va with 2x24v ac out, can i use them and which is better to use with the A3 amp, i believe the original power supply to have is a 2x20v ac out.
Next i did see that in my schematic diagram i did get from the seller of the pcb's i did see that they use the bc550c, and i did see in the Aleph 3 Service Manual that they did use the mpsa18 so i did saw that they did have lower distortion and more hfe so i did order them.
Than i have some new mosfets lying around, again in the original Aleph 3 Service Manual they did use the irf244 i do not have them, i have the irfp250 that are used in my clone A3 schematic diagram and i have the irfp260 also, what must i do, buy the irf244 or go for the irfp250 or the irfp260 what i already have.
I believe the irfp260 has the lowest resistance, does the resistance matter or not in a amp, oke so where i have to look for in a mosfet for a amplifier, what is important to look for.
So next i have some new Panasonic caps lying around, the FR version, so fast and a long life span, they are just the value i need 220Uf, can i use them or do i need real audio caps for this amp.
I did build a Hood 1969 amp before so normal u set the middle voltage with a pot and the bias with a pot, i do not see them with this design, so i am sure that they are resistors that do that job, but i do not now which resistors i have to change, but i think i need to change them with i higher or lower voltage on the rails.
please understand i am a beginner at this, so please do not judge me for not knowing, i did build so many other things, but only ones i did build a small amplifier, and i did like the sound of that Hood 1969 with the toshiba 2sc5200 in it, i did build that amp for in my jukebox diy project.
And yes i do like nice music, who doesn't, so i do build my own speakers, but this amp is the next step up, building your own amp, so i need help to do it.
And i hope i get it here.
O yea i did hear a few years ago a original Pass Amp, i can not remember what type of Pass amp that was but i did like it, i did not forget the nice sound, i hope my Pass clone amp will get the same sound, or near to the original sound, but for the real thing i do not have the money so that's why i go this way of building my own Pass clone amp and hope for the best.
i ad my schematic diagram i did get from the seller of the PCB's
Attachments
I probably would just go with 2x18 just to keep the dissipation a bit lower
since you have 2 pairs of mosfets. If you use 2x24 you should also
increase the bias current to take advantage of the extra voltage, so again
more heat.
Be careful with changing MPSA18 for BC550 since they have different pinouts.
Not a big problem since you can just flip the mpsa18 around, but it is
something you need to be aware of.
For mosfets, most people here use IRFP240. Each pair of mosfets should
be matched by Vgs to avoid one mosfet running much hotter then the other.
The input devices should be Vgs matched at around 10mA to minimize
dc offset. The bias of the amp is determined by part values.
The dc offset can be trimmed by adjusting R28 (the 390R resistor). You
might even consider temporarily installing a trimmer there and replace it
with a fixed resistor once you know which resistance value minimizes
the dc offset.
Panasonic is fine (the original probably had Panasonic FC). Mr. Pass
had some comments on the Aleph a few years ago:
https://www.diyaudio.com/forums/pass-labs/267857-aleph-design- reloaded.html#post4184920
Your R8 (10k) is probably too high; consider going to 3.3k to keep the zener
happy.
For the input transistors you might use something like FQP3P20 which is
easy to find.
since you have 2 pairs of mosfets. If you use 2x24 you should also
increase the bias current to take advantage of the extra voltage, so again
more heat.
Be careful with changing MPSA18 for BC550 since they have different pinouts.
Not a big problem since you can just flip the mpsa18 around, but it is
something you need to be aware of.
For mosfets, most people here use IRFP240. Each pair of mosfets should
be matched by Vgs to avoid one mosfet running much hotter then the other.
The input devices should be Vgs matched at around 10mA to minimize
dc offset. The bias of the amp is determined by part values.
The dc offset can be trimmed by adjusting R28 (the 390R resistor). You
might even consider temporarily installing a trimmer there and replace it
with a fixed resistor once you know which resistance value minimizes
the dc offset.
Panasonic is fine (the original probably had Panasonic FC). Mr. Pass
had some comments on the Aleph a few years ago:
https://www.diyaudio.com/forums/pass-labs/267857-aleph-design- reloaded.html#post4184920
Your R8 (10k) is probably too high; consider going to 3.3k to keep the zener
happy.
For the input transistors you might use something like FQP3P20 which is
easy to find.
Last edited:
read Babelfish J thread for some details about OS arrangement
in short - use just one pair of IRFP150, avoiding matching, with care of source resistor values, to accommodate that arrangement
keep dissipation up to 40-45W per device, with Keratherm or Alumina pads, and you're good
for FE, Dennis pointed you to right place
in short - use just one pair of IRFP150, avoiding matching, with care of source resistor values, to accommodate that arrangement
keep dissipation up to 40-45W per device, with Keratherm or Alumina pads, and you're good
for FE, Dennis pointed you to right place
first of all thanks for the reply to you 2, Dennis ur info did help a lot about Mr Pass, i did see there that many things are different to my design, i think my design is a Aleph 5 with only a few things different, also the ballance input is not in the Aleph 3 design.
yes i will go with the 2x18v power supply, the mpsa18 i did see that it has a different pinout, but thx for pointing it out, you never now, everyone can make a mistake.
And yes in my schematic diagram the R8 is 10k and i think that's a higher voltage design, i see that in the schematic diagram of the Aleph 5, Mr Pass did say that it needs to be 3,3k so i will use that, thx for pointing that out to me, also R3 and R13 are different values, i think that my bias or not?
I can also see that R9 is 1k in the Aleph 3 2015 schematic diagram with my diagram its 1,5 k.
And R29 is 150R and in the Aleph 3 2015 schematic diagram its 100R, so many things are different and i have to look what i do with them, i think i go for the Aleph 3 2015 design, i think the newer the design how more up to date everything is.
you say for the input go with the FQP3P20 and not the IRF9610 wy are they better, Mr Pass did say about a Toshiba mosfet, i have to look which type i did forget it, i have to read it all but i did not get to it.
Oke Zen mod also thanks for the reply, and that IRFP150 has a very low Rds and its cheap, but i think i use the IRFP250, i have more than 30 of them so i think i use them if they can do the job, i have also the IRFP260 but not so much i think about 12 of them.
And i now how to match mosfets so that is not a problem, and i like mica and paste its cheaper and also good, and also that Keratherm i can not get here so far if i now.
so again thx and i post here the process i make and the troubles i get underway in to the build, and i have to say i have 4 PCB's, i did buy more than i did now, yea i need the read better before i buy 😀
yes i will go with the 2x18v power supply, the mpsa18 i did see that it has a different pinout, but thx for pointing it out, you never now, everyone can make a mistake.
And yes in my schematic diagram the R8 is 10k and i think that's a higher voltage design, i see that in the schematic diagram of the Aleph 5, Mr Pass did say that it needs to be 3,3k so i will use that, thx for pointing that out to me, also R3 and R13 are different values, i think that my bias or not?
I can also see that R9 is 1k in the Aleph 3 2015 schematic diagram with my diagram its 1,5 k.
And R29 is 150R and in the Aleph 3 2015 schematic diagram its 100R, so many things are different and i have to look what i do with them, i think i go for the Aleph 3 2015 design, i think the newer the design how more up to date everything is.
you say for the input go with the FQP3P20 and not the IRF9610 wy are they better, Mr Pass did say about a Toshiba mosfet, i have to look which type i did forget it, i have to read it all but i did not get to it.
Oke Zen mod also thanks for the reply, and that IRFP150 has a very low Rds and its cheap, but i think i use the IRFP250, i have more than 30 of them so i think i use them if they can do the job, i have also the IRFP260 but not so much i think about 12 of them.
And i now how to match mosfets so that is not a problem, and i like mica and paste its cheaper and also good, and also that Keratherm i can not get here so far if i now.
so again thx and i post here the process i make and the troubles i get underway in to the build, and i have to say i have 4 PCB's, i did buy more than i did now, yea i need the read better before i buy 😀
Attachments
Hello again,
i have a question, in my schematic diagram i did get from the seller of the PCB's there's a C2 over Q4 the BC550, i can not find it in any schematic that a have of all the Pass Aleph's, did they have a problem of oscillating of some sort or something else, my question why is it there?
Why why why, please someone now, can you explain it to me, i try to learn something with this build.
i have a question, in my schematic diagram i did get from the seller of the PCB's there's a C2 over Q4 the BC550, i can not find it in any schematic that a have of all the Pass Aleph's, did they have a problem of oscillating of some sort or something else, my question why is it there?
Why why why, please someone now, can you explain it to me, i try to learn something with this build.
Attachments
reminds me of some ebay clone schematics
someone was wisea$$, not first and not last time
when you're in doubt, just look at original Papa's schematic and don't bother why someone else did different
someone was wisea$$, not first and not last time
when you're in doubt, just look at original Papa's schematic and don't bother why someone else did different