The inductance of 0.1Ohm W/W resistors is so low as to be of virtually no relevance.
Even when you get to 0R47 the inductance is absolutely miniscule. If you read the threads on this topic, an 0R47 W/W will only have significant inductance at almost VHF frequencies.
The inductance of the PCB tracks and the speaker cables will be greater than that of the Emitter resitors.
Even when you get to 0R47 the inductance is absolutely miniscule. If you read the threads on this topic, an 0R47 W/W will only have significant inductance at almost VHF frequencies.
The inductance of the PCB tracks and the speaker cables will be greater than that of the Emitter resitors.
Re; non inductive resistors.
If you want to make your own there is an illustration on Geoff's site. Go to "other class-A amps"....Nelson-Jones......article (not schematic). At the end after the text pages Geoff has put various illustrations and there is a really neat DIY diagram of how to construct a non inductive resistor. Can't remember but you may need to consult the text section re; type of wire etc.
Fun for the purists.
On the other hand if you can't get the proper wire it has always struck me that if you parallel a lot of the appropriate value 1/4 watt (or less) resistors you can ensure both low inductance and a suitable power rating. Two reasons. (A) The smaller resistors will have an intrinsically lower inductance due to their size and (B) ever time you double the number you halve the inductance. It is not an elegant solution but it has been done before and should achieve an appropriate result.
Happy New year.
Jonathan
If you want to make your own there is an illustration on Geoff's site. Go to "other class-A amps"....Nelson-Jones......article (not schematic). At the end after the text pages Geoff has put various illustrations and there is a really neat DIY diagram of how to construct a non inductive resistor. Can't remember but you may need to consult the text section re; type of wire etc.
Fun for the purists.
On the other hand if you can't get the proper wire it has always struck me that if you parallel a lot of the appropriate value 1/4 watt (or less) resistors you can ensure both low inductance and a suitable power rating. Two reasons. (A) The smaller resistors will have an intrinsically lower inductance due to their size and (B) ever time you double the number you halve the inductance. It is not an elegant solution but it has been done before and should achieve an appropriate result.
Happy New year.
Jonathan
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Many thanks, Ashok, Mike, Andy & Jonathan for your replies.
This seems a very friendly thread, it's very refreshing when asking a question to get replies from people with more knowledge than myself who do not make me feel like an idiot for asking the question.
I'm certain that as I progress with this project there will be many things i am unsure of and it is very reassuring to know that help is at hand.
Once again, thanks.
Alan.
This seems a very friendly thread, it's very refreshing when asking a question to get replies from people with more knowledge than myself who do not make me feel like an idiot for asking the question.
I'm certain that as I progress with this project there will be many things i am unsure of and it is very reassuring to know that help is at hand.
Once again, thanks.
Alan.
Re; non inductive resistors.
Try Futaba MPC74, as used by Accuphase, amongst other top Japanese audio gear.
https://www.buerklin.com/default.asp?event=ShowArtikel(36E459)&l=d&jump=ArtNr_36E459
MPC Series RoHS ?FUKUSHIMA FUTABA ELECTRIC CO., LTD
Patrick
Try Futaba MPC74, as used by Accuphase, amongst other top Japanese audio gear.
https://www.buerklin.com/default.asp?event=ShowArtikel(36E459)&l=d&jump=ArtNr_36E459
MPC Series RoHS ?FUKUSHIMA FUTABA ELECTRIC CO., LTD
Patrick
Hi Alan,
Never thought about it before but this IS a friendly thread; you're right. Perhaps because class A has no discordant harmonics, ha ha......
On a tangential note I heard a guy on the radio recently who noted that orchestra conductors seemed, as a rule, to live long lives (I can't verify that statistically, it was just what he said). He went on to say that Sir Adrian Boult (1889-1983) agreed and he thought having a profession where your work was constantly surrounded by and making harmony was conducive to longevity. In a similar vein our organist at a small suburban church was a frustrated cathedral organist and I can remember him saying that he abandoned his dream of actually working in an Australian cathedral at a relatively early age. Not because he wasn't any good but for the simple reason that none of the incumbents had the good grace to die! So may be there is something in that. May even be a Doctoral thesis here exploring whether audio fanatics who have class A amp's live longer than those with class B!!!!!
On the other hand, Alan, if you do want some excitement check out the "Blowtorch" threads especially the early stuff before the Moderators started knocking heads together..........they are a willing mob over there......."high risk spectator sport" that thread.
Cheers, Jonathan
Never thought about it before but this IS a friendly thread; you're right. Perhaps because class A has no discordant harmonics, ha ha......
On a tangential note I heard a guy on the radio recently who noted that orchestra conductors seemed, as a rule, to live long lives (I can't verify that statistically, it was just what he said). He went on to say that Sir Adrian Boult (1889-1983) agreed and he thought having a profession where your work was constantly surrounded by and making harmony was conducive to longevity. In a similar vein our organist at a small suburban church was a frustrated cathedral organist and I can remember him saying that he abandoned his dream of actually working in an Australian cathedral at a relatively early age. Not because he wasn't any good but for the simple reason that none of the incumbents had the good grace to die! So may be there is something in that. May even be a Doctoral thesis here exploring whether audio fanatics who have class A amp's live longer than those with class B!!!!!
On the other hand, Alan, if you do want some excitement check out the "Blowtorch" threads especially the early stuff before the Moderators started knocking heads together..........they are a willing mob over there......."high risk spectator sport" that thread.
Cheers, Jonathan
Hello everyone, can I please have your comments and views on the following for my power supply.
This is for each channel:
300VA 18-0-18 transformer
2x 35A bridges
2x 100,000 micro farad ( one for +ve rail one for -ve rail )
2x 0.47 ohm 25 watt resistors
2x 10,000 micro farads.
I have not listed things like snubber caps and small value by-pass caps.
The capacitors I have already, will it be OK to use the 10,000 micro farad after the resistors in the C R C , are they of sufficient size? I have read that using too large a value will tend to make the bass seem slow, but I want to be sure that there will be no shortage of current available.
Any help would be greatly appreciated.
Thanks.
Alan
This is for each channel:
300VA 18-0-18 transformer
2x 35A bridges
2x 100,000 micro farad ( one for +ve rail one for -ve rail )
2x 0.47 ohm 25 watt resistors
2x 10,000 micro farads.
I have not listed things like snubber caps and small value by-pass caps.
The capacitors I have already, will it be OK to use the 10,000 micro farad after the resistors in the C R C , are they of sufficient size? I have read that using too large a value will tend to make the bass seem slow, but I want to be sure that there will be no shortage of current available.
Any help would be greatly appreciated.
Thanks.
Alan
A lot of poke for a 10W channel !
I would put the better quality caps after the R of the CRC. I suspect a listening test will sort this out.
Insert some local decoupling next to the output devices and maybe also at the front end.
I would put the better quality caps after the R of the CRC. I suspect a listening test will sort this out.
Insert some local decoupling next to the output devices and maybe also at the front end.
I agree about better quality caps closest to the amp but regarding the action of the rectifiers it is more logical to the 10,000 after the bridges, then R, then 100,000 next to the amps. This would mean that each current charging pulse through the rectifiers will be longer and less intense - but as andrew says listening will be the final judge of these theories.
That is the same sized transformer that I use. If I remember correctly, it was twice as large as I needed even considering running at higher current, but it was only marginally more expensive than the 180VA version.
Such large capacitors may not be necessary. There are disadvantages. Remember that a class A amp draws a more constant current than a class AB amp... less capacitance will still do a better job in the end. You'll just want to make sure it is enough to lower the supply ripple under load.
Such large capacitors may not be necessary. There are disadvantages. Remember that a class A amp draws a more constant current than a class AB amp... less capacitance will still do a better job in the end. You'll just want to make sure it is enough to lower the supply ripple under load.
but even done this way the ripple capacity of the first capacitor must be more than the ripple imposed on that capacitor at whatever frequency and temperature exists during operation. Ripple current is critical in CRC and CLC.
Hi, I have had a look at the ripple specs for the caps i have :
the 100,000 are rated at 19.2 A
the 10,000 are rated at 13 A
Alan
the 100,000 are rated at 19.2 A
the 10,000 are rated at 13 A
Alan
what does PsudII report for ripple current when you insert an appropriate continuous DC loading?
Hi everyone,
Andrew, sorry I do not understand your post 1853.
Advice please on R value in CRC circuit, I was going to use 0.47ohm as that seems to be a common figure but is there any reason I could not use a larger value eg. 1 ohm or even 2 ohm as my rail voltage is slightly high and I would like to drop it 2 or 3 volts. I have no problem dissapating the heat produced by the resistors.
Thanks
Alan.
Andrew, sorry I do not understand your post 1853.
Advice please on R value in CRC circuit, I was going to use 0.47ohm as that seems to be a common figure but is there any reason I could not use a larger value eg. 1 ohm or even 2 ohm as my rail voltage is slightly high and I would like to drop it 2 or 3 volts. I have no problem dissapating the heat produced by the resistors.
Thanks
Alan.
PsudII is free software that allows modeling of a PSU.
Have you downloaded your copy and installed it?
Have you downloaded your copy and installed it?
Provided you can get rid of the heat the increased value resistor will actually provide improved filtering.
Hi Alan,
This is an area I am not an expert on but I saw people talking about chokes/coils in PSUs and they weren't too uptight about values, not critical apparently. I'd have thought an aircored inductor of around 2mH could be arranged to have half an ohm (or more) resistance and you get some advantages.
But, as I say, this is not my long suite......
Regards to Somerset; born there early 60 yrs ago and was visiting last November.......did you know JLH lived in Taunton for many years?
Cheers, Jonathan
This is an area I am not an expert on but I saw people talking about chokes/coils in PSUs and they weren't too uptight about values, not critical apparently. I'd have thought an aircored inductor of around 2mH could be arranged to have half an ohm (or more) resistance and you get some advantages.
But, as I say, this is not my long suite......
Regards to Somerset; born there early 60 yrs ago and was visiting last November.......did you know JLH lived in Taunton for many years?
Cheers, Jonathan
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If you want more filtering, why not go the CLC route. You need to have more than 0.2 ohms to damp any tendency for ringing and temporary over voltage on turn on, so the 0.5ohm 2mH air coils Jonathon suggests would be just fine.
Also to avoid a tendency for ringing you should have the 10,000uF cap 1st and 100,000 after the chokes - otherwise it can ring a lot ( depending on values )
To gain the real benefit from this kind of filtering you really need a transformer with split secondaries tied together to form the earth only AFTER the chokes - this means you keep horrible diode switching noise isolated from the earth.
If you combine this with a 47ohm + 0.2uF cap in series across each secondary ( to eliminate HF / RF resonance when the diodes switch off ) it should sound as sweet as a nut 🙂
Personally I think a well implemented CLC PSU is about as good as it can get - especially for a class A amp.
I hope some of this helps
mike
Also to avoid a tendency for ringing you should have the 10,000uF cap 1st and 100,000 after the chokes - otherwise it can ring a lot ( depending on values )
To gain the real benefit from this kind of filtering you really need a transformer with split secondaries tied together to form the earth only AFTER the chokes - this means you keep horrible diode switching noise isolated from the earth.
If you combine this with a 47ohm + 0.2uF cap in series across each secondary ( to eliminate HF / RF resonance when the diodes switch off ) it should sound as sweet as a nut 🙂
Personally I think a well implemented CLC PSU is about as good as it can get - especially for a class A amp.
I hope some of this helps
mike
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Hi Jonathon,
long time . . . .
I'm just coming back to UK after a long time in USA, I wonder if I will ever get you hear your special JLH amps ?
cheers
mike
long time . . . .
I'm just coming back to UK after a long time in USA, I wonder if I will ever get you hear your special JLH amps ?
cheers
mike
p.s.
I should have mentioned that there should be chokes in both legs of each rail . . . so it would be 4 chokes total per amp ( assuming a separate PSU per amp )
I should have mentioned that there should be chokes in both legs of each rail . . . so it would be 4 chokes total per amp ( assuming a separate PSU per amp )
Hi, and thank you for all the replies, certainly a lot of food for thought.
Jonathan, Somerset returns your good wishes, I am also heading towards 60 ( next July )have seen a lot of changes to this lovely county over the years, most not for the better, I suspect thats the same everywhere.
Thanks again,
Alan
Jonathan, Somerset returns your good wishes, I am also heading towards 60 ( next July )have seen a lot of changes to this lovely county over the years, most not for the better, I suspect thats the same everywhere.
Thanks again,
Alan