PSU
My apologies on the schematic, the second Caps should be in parallel.
From this http://www.diyaudio.com/forums/showthread.php?s=&threadid=3748&pagenumber=42 the thermistors will act as an R.
This thread explains that the choke supply is really a cLCRLCR.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=26223&perpage=15&highlight=&pagenumber=2
I have talked to mikelm about this, though to finalise I really have to simulate it. The likelyhood is that I will order the parts and experiment as a diyer should. Estimating 18V x 0.9 supply for (axe-1.xls)
Voltage 16.2 V
Bias 8 A
Ac current gain 50%
Number of fets 12
Peak current 8 A
Power 8 Ohms (RMS) 50 W
Power 4 Ohms (RMS) 101 W
Power 2 Ohms (RMS) 64 W
Dissipation for one channel 259 W
Dissipation per fet 22 W
In discussion with D3 yesterday he recommended mounting the Fets on a copper bar (50mm x 12mm x 250mm) to spread the heat with the 50 x 250 face against the heatsink. Any comments?
BP how did the exams go?
Simon
My apologies on the schematic, the second Caps should be in parallel.
From this http://www.diyaudio.com/forums/showthread.php?s=&threadid=3748&pagenumber=42 the thermistors will act as an R.
This thread explains that the choke supply is really a cLCRLCR.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=26223&perpage=15&highlight=&pagenumber=2
I have talked to mikelm about this, though to finalise I really have to simulate it. The likelyhood is that I will order the parts and experiment as a diyer should. Estimating 18V x 0.9 supply for (axe-1.xls)
Voltage 16.2 V
Bias 8 A
Ac current gain 50%
Number of fets 12
Peak current 8 A
Power 8 Ohms (RMS) 50 W
Power 4 Ohms (RMS) 101 W
Power 2 Ohms (RMS) 64 W
Dissipation for one channel 259 W
Dissipation per fet 22 W
In discussion with D3 yesterday he recommended mounting the Fets on a copper bar (50mm x 12mm x 250mm) to spread the heat with the 50 x 250 face against the heatsink. Any comments?
BP how did the exams go?
Simon
Trafos
D3, the box of 3 trafos was waiting for me in the hall when I got home last night. Apparantly, the lady across the road (who had them dropped off with her) and my Missus could barely lift the box between them!!
Thanks very much for sorting it wall out. It's about time I got the soldering iron out again!!
Cheers
Jon
D3, the box of 3 trafos was waiting for me in the hall when I got home last night. Apparantly, the lady across the road (who had them dropped off with her) and my Missus could barely lift the box between them!!
Thanks very much for sorting it wall out. It's about time I got the soldering iron out again!!
Cheers
Jon
Hi, the exams weren't so great in the end (my own fault admitedly, but hopeufly I should still be here next year and be let loose on an audio amplifier design project for about 40% of next years mark).
As far as what you are saying goes (I think), what people are meaning when they say CLC is realy CLRC is simply that the inductors are not perfect and will has some series resistance to go allong with it, and so you will get a voltage drop. As far as increasing this artificialy using the thermistors goes, I have no idea how this will effect things in any gret deatail (lots of nasty maths in there somewhere) but it will mean you get a larger voltage drop in your supply to igve you your lower output voltage, and as they will have a higher on resistance it will give you a bit of soft start type effect. It is however a bit of a belt and braces aproach to the supply, but I'm sure it should give fairly decent results even if it does cost significantly more than simply using fixed resistors to get the desired voltage drops.
Also, as far as using the copper bar as a heatspreader, this could be decent idea depending on your heatsink base thickness and what you put between the trasistor, copper and heatsink. The best thing that you could do would be mount the transistors all on individual lumps of copper using only heat transfer compoud, and then an insulating kapton sheet between the copper and heatsinks so that this doesn't go live (although it may be trickey to fix the copper to the heatsink without any electrical conection being formed). However, I believe in most case you would still gain some benifit by using an insulator between the chip and copper then using the thermal paste between the copper and heatsink. Once again though this is one of those things where I personaly would question the worth of the extra expense, as the transistors are only dissipating about 25W a piece into a heatsink with a good thick base. So, when you compare this to a CPU for example, where you are looking at ower 100W from one device which is smaller in size than a TO-247 case it doesn't seem to bad (and they have only recently started to recomend copper heat spreaders, and were quite happy with plain aluminium up until about 80W).
Anyway, that's enough of a rant for now, so I'll be off to do some work (or something) now.
As far as what you are saying goes (I think), what people are meaning when they say CLC is realy CLRC is simply that the inductors are not perfect and will has some series resistance to go allong with it, and so you will get a voltage drop. As far as increasing this artificialy using the thermistors goes, I have no idea how this will effect things in any gret deatail (lots of nasty maths in there somewhere) but it will mean you get a larger voltage drop in your supply to igve you your lower output voltage, and as they will have a higher on resistance it will give you a bit of soft start type effect. It is however a bit of a belt and braces aproach to the supply, but I'm sure it should give fairly decent results even if it does cost significantly more than simply using fixed resistors to get the desired voltage drops.
Also, as far as using the copper bar as a heatspreader, this could be decent idea depending on your heatsink base thickness and what you put between the trasistor, copper and heatsink. The best thing that you could do would be mount the transistors all on individual lumps of copper using only heat transfer compoud, and then an insulating kapton sheet between the copper and heatsinks so that this doesn't go live (although it may be trickey to fix the copper to the heatsink without any electrical conection being formed). However, I believe in most case you would still gain some benifit by using an insulator between the chip and copper then using the thermal paste between the copper and heatsink. Once again though this is one of those things where I personaly would question the worth of the extra expense, as the transistors are only dissipating about 25W a piece into a heatsink with a good thick base. So, when you compare this to a CPU for example, where you are looking at ower 100W from one device which is smaller in size than a TO-247 case it doesn't seem to bad (and they have only recently started to recomend copper heat spreaders, and were quite happy with plain aluminium up until about 80W).
Anyway, that's enough of a rant for now, so I'll be off to do some work (or something) now.
copper bus bar
The idea .......... is to get as much heat out of the fet as possible....this is done by fixing fets directly to copper ...using a smear of grease............this means that the bus bar is ....live....so you use a length of silpad between bus bar and heatsink..........(the stuff that is used for cpu heatsinks..........) .... this gives good thermal conduction. The copper bus bar also assists in dissapaiting heat evenly accross sink...avoiding hot spots.
According to some sources......using a bus bar in this way can .......improve thermal transfer by 200%.
I think that the heat calcs. in the spread sheets are not conservative.....there is alot of heat in these amps......the trafo, amp circuit board, rectifier and resistors..........will also pump out a reasonable mount of heat.....probably 50-70w......right in the core of the amp.........so dissapating heat will be a big issue for all of us...........
I have had a price of £6+vat for a 250mm length of copper bus bar 12mm x 50mm in section....
I don't know about others but I want reliability...........
The idea .......... is to get as much heat out of the fet as possible....this is done by fixing fets directly to copper ...using a smear of grease............this means that the bus bar is ....live....so you use a length of silpad between bus bar and heatsink..........(the stuff that is used for cpu heatsinks..........) .... this gives good thermal conduction. The copper bus bar also assists in dissapaiting heat evenly accross sink...avoiding hot spots.
According to some sources......using a bus bar in this way can .......improve thermal transfer by 200%.
I think that the heat calcs. in the spread sheets are not conservative.....there is alot of heat in these amps......the trafo, amp circuit board, rectifier and resistors..........will also pump out a reasonable mount of heat.....probably 50-70w......right in the core of the amp.........so dissapating heat will be a big issue for all of us...........
I have had a price of £6+vat for a 250mm length of copper bus bar 12mm x 50mm in section....
I don't know about others but I want reliability...........
Hi D3
I have received my trafos and they are heavy...
Though It looks like the firm could not understand my name, adress etc. None of them was correct the only correct information was the zip code of my city all the rest information was only partial correct....thumbs up to the postman that found me with that information
Martin
I have received my trafos and they are heavy...
Though It looks like the firm could not understand my name, adress etc. None of them was correct the only correct information was the zip code of my city all the rest information was only partial correct....thumbs up to the postman that found me with that information
Martin
Traffo...
I am really sorry about ..... that ......... do you wan't me to talk to Air Link.............
My Traffos were tightly packed in and had tightly packed poly chips separating traffo's ........... they appear fine...
I have Sineras Traffo's here and they were packed well.....
I am really angry that your goods were damaged....have they been opened by customs????
I am really sorry about ..... that ......... do you wan't me to talk to Air Link.............
My Traffos were tightly packed in and had tightly packed poly chips separating traffo's ........... they appear fine...
I have Sineras Traffo's here and they were packed well.....
I am really angry that your goods were damaged....have they been opened by customs????
Richard, did you ever hear back from the people you snet off to about the possible component orders? As I'm ittching to try and get the order in soon so so I can have some more tys to play with, so would like to get it sent off in the next week or so, so I have all the bits here when I finish my work for the term (finaly) in a couple of weeks time.
Parts
Right I started compiling a list..........not just the spreadsheet.....but
4 X resistor etc.
However, ...........I got stuck with the caps.........what voltage should I go for???? say I am running @ 20v rail voltage.....what swings of voltage are seen by the caps??????
Also the bias resistors............what if my rail voltages end up higher despite my CRCRC ps.......will they be defunct..........or will it not matter too much.......ie I will either draw a touch more current....or less.....
either way I need some advice. THLaudio were interested in quoting........provided the list was symplified. Yep I don't mind.....I would go for it ........... but probably in about 3 weeks time....
I thought it would be a good idea to build the ps first......measure the voltages underload..........and then order...
Right I started compiling a list..........not just the spreadsheet.....but
4 X resistor etc.
However, ...........I got stuck with the caps.........what voltage should I go for???? say I am running @ 20v rail voltage.....what swings of voltage are seen by the caps??????
Also the bias resistors............what if my rail voltages end up higher despite my CRCRC ps.......will they be defunct..........or will it not matter too much.......ie I will either draw a touch more current....or less.....
either way I need some advice. THLaudio were interested in quoting........provided the list was symplified. Yep I don't mind.....I would go for it ........... but probably in about 3 weeks time....
I thought it would be a good idea to build the ps first......measure the voltages underload..........and then order...
Well, the two supply decouplying electrolytics on the board should be rated at least as high as your rail voltage, so if you have 20v rails, then a 25V cap would be the minimum I would go for. I haven't got the schematic about right now, but for the other ones, if you think about it the worst case would be the voltage from +rail to -rail accross it, so potentialy higher ratting than the local decoupling caps but you might be able t o get away with using a lower voltage)
Heatsinks
Worked has again slowed on the Aleph, not that it really took off!
I am under orders to finish the garden ready for my daughters Birthday party.
At last I have a quote for a heatsink. I did not join in the Conrad buy as they do not dissipate enough heat.
For my 250W heat output per channel I was aiming for a child friendly max of 40C ie 18C rise on ambient ie 0.07K/W for two sides or 0.14K/W each heatsink. This will aso give me the option to increase the voltage at a later date for more power if necessary, just by changing the transformer and adding more fets.
Looking at something like 400mm F-B, 80m fins, 300mm high.
Quote is from ablcomponents 196AB (no reply through heatsinks online)at £95 each (+vat I think).
Still waiting for Fischer SK159's via www.dau-components.co.uk
and alutronic PR256/300/SE via www.jaytec.co.uk. Others I might try for a quote are seifert's KL272 and seem-semrac CO2782P.
Any further on a group buy for passives?
Simon
Worked has again slowed on the Aleph, not that it really took off!
I am under orders to finish the garden ready for my daughters Birthday party.
At last I have a quote for a heatsink. I did not join in the Conrad buy as they do not dissipate enough heat.
For my 250W heat output per channel I was aiming for a child friendly max of 40C ie 18C rise on ambient ie 0.07K/W for two sides or 0.14K/W each heatsink. This will aso give me the option to increase the voltage at a later date for more power if necessary, just by changing the transformer and adding more fets.
Looking at something like 400mm F-B, 80m fins, 300mm high.
Quote is from ablcomponents 196AB (no reply through heatsinks online)at £95 each (+vat I think).
Still waiting for Fischer SK159's via www.dau-components.co.uk
and alutronic PR256/300/SE via www.jaytec.co.uk. Others I might try for a quote are seifert's KL272 and seem-semrac CO2782P.
Any further on a group buy for passives?
Simon
I've been stuck in the lab this week with project work, but my last deadline is this Saturday night (what is it with cambridge and saturday deadlines?) so I will hopefuly get some free time next week and start looking at this a bit more.
As far as I know though I will be placing an order for the parts in the list that I posted a while back, and as there are no real price breaks on most of the parts (appart from some of the FETs from digikey) the benifit realy will come from the lower shipping costs from the states. So, if people don't want the same values it should be quite easy to accomodate your wishes in the order, so long as I get a compleet list of everything you want if you do want to share the shipping costs out a bit.
Andrew.
As far as I know though I will be placing an order for the parts in the list that I posted a while back, and as there are no real price breaks on most of the parts (appart from some of the FETs from digikey) the benifit realy will come from the lower shipping costs from the states. So, if people don't want the same values it should be quite easy to accomodate your wishes in the order, so long as I get a compleet list of everything you want if you do want to share the shipping costs out a bit.
Andrew.
Hi, the file is in post 443 just a page or so back. It cantains mainly decent quality parts, but nothing outrageous, no 0.1% resistors or blackgates (if a few of us get the same sorts of values for the resistors, I have a meter wich is accurate to about 0.05% that I can match them into pairs on if people want) as I can't justify spending the extra money on them right now. However, saying that, I don't think there will be too many places where there will be much of a problem with the parts in the list.
Hi guys
I could join a parts group buy if you like if im not too late. I need some IRF9610s to match as well.
What options on the PCB are you planning to use (if you are looking at the schematic in pdf format, cant remember where it was from now, probably the wiki). ie D1a or D1b or Q12a etc.
also what parts do we need to change if we are going to increase power that the circuit works at?
If we want more amps we should be changing R5/R40 and R2//R3 and R42//R43, is that all?
As most of us are using the 18-0-18V xformers from the group buy we are probably looking at approx +-20V rails after BR and CRCRC. Are there any other changes needed to work at this voltage??
Speak to Y'all later
Mark
I could join a parts group buy if you like if im not too late. I need some IRF9610s to match as well.
What options on the PCB are you planning to use (if you are looking at the schematic in pdf format, cant remember where it was from now, probably the wiki). ie D1a or D1b or Q12a etc.
also what parts do we need to change if we are going to increase power that the circuit works at?
If we want more amps we should be changing R5/R40 and R2//R3 and R42//R43, is that all?
As most of us are using the 18-0-18V xformers from the group buy we are probably looking at approx +-20V rails after BR and CRCRC. Are there any other changes needed to work at this voltage??
Speak to Y'all later
Mark
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