Wrong in more than one case.
Plastic watts are not equal to metal watts.
Maximum junction temperatures are different. It ususally takes 1.5X or even 2X as many plastic to be truely equal to the same part number in metal.
As regards cost.
Metal is less.
But what about those high performance boron-nitride filled insulators, and good non-inductive wirewound resistors?
Plastic is now a lot more expensive.
The best reason to use series connected outputs in this day and age:
http://www.signaltransfer.freeuk.com/Gfig11s.gif
Plastic watts are not equal to metal watts.
Maximum junction temperatures are different. It ususally takes 1.5X or even 2X as many plastic to be truely equal to the same part number in metal.
As regards cost.
Metal is less.
But what about those high performance boron-nitride filled insulators, and good non-inductive wirewound resistors?
Plastic is now a lot more expensive.
The best reason to use series connected outputs in this day and age:
http://www.signaltransfer.freeuk.com/Gfig11s.gif
Mikett,
If the Krell was better even after you have implemented all the tricks in the book ie regulation, independent supply, at a time when the Krell was not utilising most of these techinques then Leach's design may call for some improvement, if not complete reinnovation...
If the Krell was better even after you have implemented all the tricks in the book ie regulation, independent supply, at a time when the Krell was not utilising most of these techinques then Leach's design may call for some improvement, if not complete reinnovation...
A Leach PA amplifier, that'll be the day !
In my view TO3's are still the best for output stages, especially for high power applications and class A amplifiers.
If there were good TO3 devices today i would sure want them, and go for the extra labor of using L-brackets or exterior isolation covers, additional holes and precision hole drilling.
Fact is that fewer TO3's are produced, in time they'll probably dissapear completely.
The ones on the market now are almost antiques.
Like the 2955's and the 3055.
I still use them, and have a great deal of respect for those numbers.
Great for sub amplifiers or regulated power supplies, but in contemporary full range amplifiers those guys are obsolete.
I agree that the minimum ratio for plastic flatpacks will be 1.5.
With a slightly larger heatsink a number of 12 would probably be thermally equivalent to the 8 times TO3 version.
Given the total budget of a power amplifier i dont mind spending an extra 50 bucks on plastic fantastics.
Easier mounting of flatpacks may save some money, the actual difference could be $ 25 or less for the double channel amp.
Easier mounting and faster linear behavior of the outputs is more than worth the additional Dolares for me.
I still have a large number of different output devices, the ones i need i'll buy.
If Jens goes for separate power stage pcb's in both a flatpack as a TO3 version i would like a set of the TO3 pcb's too.
I'll build one with flatpacks and build an output stage on heatsinks with the TO3 version too for comparison.
My guess is that there have be several threads on the Leach amplifier and the Super Leach.
Argueing on a thread started for re-designing the Super Leach pcb on whether or not to re-design seems not relevant to the thread, in my view.
Especially not because a highly experienced pcb-designer offered to re-design the pcb layout to do us a favor, and a number of people here would like to build the amplifier with Jens's pcb's as the backbone.
Such an arguement will not draw other diy members to participate and make Jens's efforts more appreciated.
In my view, that is not a very kind thing to do !
If the question of re-designing the Super Leach is such a cruisade thing why not request BrianGT to ask Marshall Leach whether the man himself thinks making a different pcb and using other devices is a good thing, then take his word for it !
I would like professionally designed Super Leach pcb's by Jens Rasmussen, hopefully with his name and/or the Delta-Audio logo on it, and like to decide for myself which devices i'll use.
May the connection lines be of flowing curvature and the layout filled with extensive mass shielding lines, Amen.
Period !!!
In my view TO3's are still the best for output stages, especially for high power applications and class A amplifiers.
If there were good TO3 devices today i would sure want them, and go for the extra labor of using L-brackets or exterior isolation covers, additional holes and precision hole drilling.
Fact is that fewer TO3's are produced, in time they'll probably dissapear completely.
The ones on the market now are almost antiques.
Like the 2955's and the 3055.
I still use them, and have a great deal of respect for those numbers.
Great for sub amplifiers or regulated power supplies, but in contemporary full range amplifiers those guys are obsolete.
I agree that the minimum ratio for plastic flatpacks will be 1.5.
With a slightly larger heatsink a number of 12 would probably be thermally equivalent to the 8 times TO3 version.
Given the total budget of a power amplifier i dont mind spending an extra 50 bucks on plastic fantastics.
Easier mounting of flatpacks may save some money, the actual difference could be $ 25 or less for the double channel amp.
Easier mounting and faster linear behavior of the outputs is more than worth the additional Dolares for me.
I still have a large number of different output devices, the ones i need i'll buy.
If Jens goes for separate power stage pcb's in both a flatpack as a TO3 version i would like a set of the TO3 pcb's too.
I'll build one with flatpacks and build an output stage on heatsinks with the TO3 version too for comparison.
My guess is that there have be several threads on the Leach amplifier and the Super Leach.
Argueing on a thread started for re-designing the Super Leach pcb on whether or not to re-design seems not relevant to the thread, in my view.
Especially not because a highly experienced pcb-designer offered to re-design the pcb layout to do us a favor, and a number of people here would like to build the amplifier with Jens's pcb's as the backbone.
Such an arguement will not draw other diy members to participate and make Jens's efforts more appreciated.
In my view, that is not a very kind thing to do !
If the question of re-designing the Super Leach is such a cruisade thing why not request BrianGT to ask Marshall Leach whether the man himself thinks making a different pcb and using other devices is a good thing, then take his word for it !
I would like professionally designed Super Leach pcb's by Jens Rasmussen, hopefully with his name and/or the Delta-Audio logo on it, and like to decide for myself which devices i'll use.
May the connection lines be of flowing curvature and the layout filled with extensive mass shielding lines, Amen.
Period !!!
Mikett said:
I have been doing that since 1988, and will also do it on the Super Leach .
Simply, because it saves money too !
I know the feeling, Mike
Jacco,
So you are using a regulated discrete power supply for the driver stages and another for the power stages? Why is this cost effective when you need 4 traffos to do the job? I am not questioning its merits which I am sure is a superior design.
So you are using a regulated discrete power supply for the driver stages and another for the power stages? Why is this cost effective when you need 4 traffos to do the job? I am not questioning its merits which I am sure is a superior design.
The additional transformers are in series with the main toroids.
It saves a couple of volts, a small VA rating transformer costs next to nothing, especially when bought on the net.
Some time ago i bought 24 pcb mount transformers for a dollar the piece.
A few volts less saves with a big toroid transformer.
The driver stage does not need large caps, the added caps for the driver transformer save money on the power supply capacitors.
The Leach is a good example, a 60 Volt toroid is easier to get than a 65 Volt one here.
It is a lot cheaper because of the availability, and cheaper because i save 8 % on the VA rating.
MSRP of a Plitron/Amplimo 1000 VA toroid is around $ 200 overhere.
See: www.Amplimo.nl click : standaard reeks
8 % is a $ 16 save.
You can see on the Amplimo site that a 65 Volt model is not produced, that would be specially ordered, which COSTS !
For the caps 60 VAC means around 85 VDC. With 15 % extra for powersupply surge and an extra safety margin 100 Volt capacitor models will do.
With 65 VAC the capacitors needed would be 110 Volt minimum.
Then you are talking serious money.
A few 1000 uF/ 100 volt caps do not cost a great deal, small VA rating 3/4/5/6/9 volt block transformers i have crates of, only cost me 1 Dolares the piece.
I will call my Super Leach the Double Dutch Amp !
Makes sense ?
It saves a couple of volts, a small VA rating transformer costs next to nothing, especially when bought on the net.
Some time ago i bought 24 pcb mount transformers for a dollar the piece.
A few volts less saves with a big toroid transformer.
The driver stage does not need large caps, the added caps for the driver transformer save money on the power supply capacitors.
The Leach is a good example, a 60 Volt toroid is easier to get than a 65 Volt one here.
It is a lot cheaper because of the availability, and cheaper because i save 8 % on the VA rating.
MSRP of a Plitron/Amplimo 1000 VA toroid is around $ 200 overhere.
See: www.Amplimo.nl click : standaard reeks
8 % is a $ 16 save.
You can see on the Amplimo site that a 65 Volt model is not produced, that would be specially ordered, which COSTS !
For the caps 60 VAC means around 85 VDC. With 15 % extra for powersupply surge and an extra safety margin 100 Volt capacitor models will do.
With 65 VAC the capacitors needed would be 110 Volt minimum.
Then you are talking serious money.
A few 1000 uF/ 100 volt caps do not cost a great deal, small VA rating 3/4/5/6/9 volt block transformers i have crates of, only cost me 1 Dolares the piece.
I will call my Super Leach the Double Dutch Amp !
Makes sense ?
btw: i am talking 6 transformers, not 4 !
Per channel :
-1 regulated +/- powersupply for the front end gain stages
-1 regulated +/- powersupply for the driver stage
-1 large toroid for the output stage, that delivers voltage for the
two small transformers
With Mosfet amplifiers the driver stage needs to deliver quite a big current during transients for high slewrate numbers.
Splitting powersupplies for gain and driver stage is easy and has benefits.
A driver transformer and regulation saves a lot on the main transformer because:
- the additional voltage reserve between driver and power Mosfet
needed, see Pass comments.
- needed higher voltage to open up the Mosfets.
- plus the usual voltagedrop over the driver's source to emitter.
I have seen some freaks use 6 transformers per channel, even separate transformers for + and -
Elektor did a couple of designs with dual powersupplies for front end and power stage, i even think i got the idea for placing a small one in series with the toroid from them a long long time ago.
Of course Hybrids need dual supplies, i built a couple.
If you'd like i can name a number of companies that produced amplifiers that had multiple powersupplies per channel, and regulated ones.
Forgot the real nice one :
with totally separated multiple (regulated) powersupplies the main toroid can be turned off while the gain stage still has voltage and current.
As there is only a couple of millivolts going through these stages the electric bill does not suffer, plus the main caps have a longer lasting life.
But, the front end is constantly operating at its best, the moment the amp is switched on performance is 99 %.
A lot of amplifiers need to run for an hour to reach their top performance.
With class A amplifiers with stand-by switches it has been determined that the front end plays a heavy roll in settling time.
I built a set of class A mosfets amplifiers that could be switched completely off, with only front end running, with front end on and low bias, or in full class A.
I know a few people that turn their power amplifier on an hour before they are actually going to sit down and listen, that costs money every day.
SAVE people, SAVE. And then call yourself environmentally friendly !
Per channel :
-1 regulated +/- powersupply for the front end gain stages
-1 regulated +/- powersupply for the driver stage
-1 large toroid for the output stage, that delivers voltage for the
two small transformers
With Mosfet amplifiers the driver stage needs to deliver quite a big current during transients for high slewrate numbers.
Splitting powersupplies for gain and driver stage is easy and has benefits.
A driver transformer and regulation saves a lot on the main transformer because:
- the additional voltage reserve between driver and power Mosfet
needed, see Pass comments.
- needed higher voltage to open up the Mosfets.
- plus the usual voltagedrop over the driver's source to emitter.
I have seen some freaks use 6 transformers per channel, even separate transformers for + and -
Elektor did a couple of designs with dual powersupplies for front end and power stage, i even think i got the idea for placing a small one in series with the toroid from them a long long time ago.
Of course Hybrids need dual supplies, i built a couple.
If you'd like i can name a number of companies that produced amplifiers that had multiple powersupplies per channel, and regulated ones.
Forgot the real nice one :
with totally separated multiple (regulated) powersupplies the main toroid can be turned off while the gain stage still has voltage and current.
As there is only a couple of millivolts going through these stages the electric bill does not suffer, plus the main caps have a longer lasting life.
But, the front end is constantly operating at its best, the moment the amp is switched on performance is 99 %.
A lot of amplifiers need to run for an hour to reach their top performance.
With class A amplifiers with stand-by switches it has been determined that the front end plays a heavy roll in settling time.
I built a set of class A mosfets amplifiers that could be switched completely off, with only front end running, with front end on and low bias, or in full class A.
I know a few people that turn their power amplifier on an hour before they are actually going to sit down and listen, that costs money every day.
SAVE people, SAVE. And then call yourself environmentally friendly !
My god, when I thought that I was excessive by using two discrete PSU with own traffos...
Do you regulate using simple zeners or ?? please elaborate on that.
Do you regulate using simple zeners or ?? please elaborate on that.
I am in a typing mood
There is als a money issue when building regulated output stages.
I built the 'L'Amplificateur Fou Fou' by Hephaistos from the articles in the French L'Audiophile magazine.
Anyone know if they were ever translated to English ?
Also did the 100 watt class A mono block design of Norman Thagard in Audio magazine, somewhere in the 90s.
Both amplifiers had voltage regulation for the output stages.
Though additional parts are needed, with class A dissipation is a given thing anyway.
Spreading heat over several devices reduces the need for really expensive ones.
Same with heatsinks, a couple of small ones often cost less than one real piggy biggy.
Like with Mr Marshall reason for his double shotgun, if at the time higher voltage devices had been available they would have been costly.
So, regulation reduces the need for higher voltage output devices, that in some cases saves money.
Additionally, with regulation not only the output voltage is constant, also the max current can be limited.
That protects the output stage, saves money for protection gear, and gives the added advantage that no protection circuits can influence sonic quality.
A long time ago i spoke to someone who had built a class A amplifier with a regulated powersupply.
It could be switched to a high power class AB amplifier by bypassing the regulator stage.
Power on demand.
There is als a money issue when building regulated output stages.
I built the 'L'Amplificateur Fou Fou' by Hephaistos from the articles in the French L'Audiophile magazine.
Anyone know if they were ever translated to English ?
Also did the 100 watt class A mono block design of Norman Thagard in Audio magazine, somewhere in the 90s.
Both amplifiers had voltage regulation for the output stages.
Though additional parts are needed, with class A dissipation is a given thing anyway.
Spreading heat over several devices reduces the need for really expensive ones.
Same with heatsinks, a couple of small ones often cost less than one real piggy biggy.
Like with Mr Marshall reason for his double shotgun, if at the time higher voltage devices had been available they would have been costly.
So, regulation reduces the need for higher voltage output devices, that in some cases saves money.
Additionally, with regulation not only the output voltage is constant, also the max current can be limited.
That protects the output stage, saves money for protection gear, and gives the added advantage that no protection circuits can influence sonic quality.
A long time ago i spoke to someone who had built a class A amplifier with a regulated powersupply.
It could be switched to a high power class AB amplifier by bypassing the regulator stage.
Power on demand.
There are plenty of regulator circuits to be found on the web.
The French article i mentioned used Mosfets for the regulated output mounted on separate heatsinks, output devices were BJT's.
Same with Norman Thagard's design.
(you could ask N. Pass what he thought of the design, Mr Thagard had him take a look at it i believe
)
For gain and driver stages a discrete regulator is built out of transistors, caps, leds, and resistors, not that special but much nicer than plain zener diodes.
An easy way, of course, to build a regulator is just using an ic regulator beefed up with a power transistor, a cheap one like 2955/3055 can do a fine job.
Rod Elliot surely must have one on his ESP thing.
If anyone is interested in either Norm Thagard's articles or the Crazy Froggy amp, i can scan and post the stuff.
The French article i mentioned used Mosfets for the regulated output mounted on separate heatsinks, output devices were BJT's.
Same with Norman Thagard's design.
(you could ask N. Pass what he thought of the design, Mr Thagard had him take a look at it i believe
)For gain and driver stages a discrete regulator is built out of transistors, caps, leds, and resistors, not that special but much nicer than plain zener diodes.
An easy way, of course, to build a regulator is just using an ic regulator beefed up with a power transistor, a cheap one like 2955/3055 can do a fine job.
Rod Elliot surely must have one on his ESP thing.
If anyone is interested in either Norm Thagard's articles or the Crazy Froggy amp, i can scan and post the stuff.
While you all find out what direction the layout should take, I'll be working on my extended leach amp 😉
Please tell me what you agree on....
Now I have components that need soldering 🙂
\Jens
Please tell me what you agree on....
Now I have components that need soldering 🙂
\Jens
jacco vermeulen pontificates,
"Argueing on a thread started for re-designing the Super Leach pcb on whether or not to re-design seems not relevant to the thread, in my view.
Especially not because a highly experienced pcb-designer offered to re-design the pcb layout to do us a favor, and a number of people here would like to build the amplifier with Jens's pcb's as the backbone.
Such an arguement will not draw other diy members to participate and make Jens's efforts more appreciated.
In my view, that is not a very kind thing to do !"
Outside of proposing that plastic transistors be used for the output, where are the suggestions for "re-designing"this amplifier? Thus far claims about price, availability etc. have proved spurious.
jacco vermeulen claims "I can do a better single sided layout of the Leach with a modern pcb designing program in 2 hours." "but i am most certainly not going to.". The title of this thread is Leach Super Amp Pcb Re-Design. Where is there any discussion about re-design of the PCB BOARD? Most everyone can figure out how to attach wires or copper traces to the output devices, whatever their prejudice. Or is this about rearranging the deck chairs?
How about this?
Output devices with built in diodes. New! Modern! Plastic!
Everything to satisfy the petulant child.
BIPOLAR POWER TRANSISTORS
15A, 230V, 200W
Read all about it here:
http://www.onsemi.com/pub/Collateral/NJL3281D.PDF
Quoted from Damon Hill on another thread.
"I could see a redesign of the Leach amplifier boards that
would further reduce wiring to just the power and
output leads; careful placement of the board with a
PCB mounted RCA connector and a slightly larger hole
in the chassis could eliminate wiring for the input as well.
Having to mount those bias diodes was always a minor
annoyance."
Now here is an idea many folks would get behind that might actually constitute re-design.
Or is this just a mutual appreciation society?
Prosit
"Argueing on a thread started for re-designing the Super Leach pcb on whether or not to re-design seems not relevant to the thread, in my view.
Especially not because a highly experienced pcb-designer offered to re-design the pcb layout to do us a favor, and a number of people here would like to build the amplifier with Jens's pcb's as the backbone.
Such an arguement will not draw other diy members to participate and make Jens's efforts more appreciated.
In my view, that is not a very kind thing to do !"
Outside of proposing that plastic transistors be used for the output, where are the suggestions for "re-designing"this amplifier? Thus far claims about price, availability etc. have proved spurious.
jacco vermeulen claims "I can do a better single sided layout of the Leach with a modern pcb designing program in 2 hours." "but i am most certainly not going to.". The title of this thread is Leach Super Amp Pcb Re-Design. Where is there any discussion about re-design of the PCB BOARD? Most everyone can figure out how to attach wires or copper traces to the output devices, whatever their prejudice. Or is this about rearranging the deck chairs?
How about this?
Output devices with built in diodes. New! Modern! Plastic!
Everything to satisfy the petulant child.
BIPOLAR POWER TRANSISTORS
15A, 230V, 200W
Read all about it here:
http://www.onsemi.com/pub/Collateral/NJL3281D.PDF
Quoted from Damon Hill on another thread.
"I could see a redesign of the Leach amplifier boards that
would further reduce wiring to just the power and
output leads; careful placement of the board with a
PCB mounted RCA connector and a slightly larger hole
in the chassis could eliminate wiring for the input as well.
Having to mount those bias diodes was always a minor
annoyance."
Now here is an idea many folks would get behind that might actually constitute re-design.
Or is this just a mutual appreciation society?
Prosit
The comment that someone have constructed the leach super amp and found that “KRELL's beast was a tad better” did not surprise me. KRELL uses the same output transistors as the leach, but much more of them at a much higher class A bias. Personally class A at these power levels is just not practical for me.
One option I would like to see on the board would be a transformer coupled input for balanced inputs. Those small high quality signal transformers cost as much as the main power transformer. Does anyone have a recommendation on a transformer that would suit this purpose (I mean part number not just manufacture)?
However I’m building the leach amp not the leach super amp, so I probably have no right to comment on this.
Don’t forget that the NJL3281D has the lowest SOA of all the output bjt’s onsemi makes that we have discussed as yet. It’s really an MJL3281A.
Leve
One option I would like to see on the board would be a transformer coupled input for balanced inputs. Those small high quality signal transformers cost as much as the main power transformer. Does anyone have a recommendation on a transformer that would suit this purpose (I mean part number not just manufacture)?
However I’m building the leach amp not the leach super amp, so I probably have no right to comment on this.
Don’t forget that the NJL3281D has the lowest SOA of all the output bjt’s onsemi makes that we have discussed as yet. It’s really an MJL3281A.
Leve
Suggestions so far :
- Through holed.
- Double sided front end pcb.
- Double sided or single sided power stage pcb.
- Extra holes for attaching a brass powerline bar on the output
pcb.
- Standard connector scheme.
- No hardwired output devices.
- Extra space for larger or additional components.
- Symmetrical layout.
- Use of compact 0.5w metal film resistors (0.2" spacing).
- Minimize the size of the (front end) pcb.
- 2oz copper boards.
- Silk screen.
- pc power connectors or other connectors.
- A single board with perforations between power/driver/output
areas.
- Four hole mounting for all the small transistors.
- Three plastic for every two metal outputs (minimum).
- Separate powerlines for the gain and driver stages, wire link.
Jens showed his other Leach board yesterday.
The board reveals :
- extensive mass areas.
- All traces have a nice width.
- Smooth trace cornering.
All the things the original Super Leach pcb does not have.
It also shows that Jens has the experience to make a layout better than we( I ) can, even better than a lot of pro product boards.
In my view that is the absolute best there is, without going over the top.
I suppose Jens will design the Super Leach board in a similar manner.
Meaning, we need not make suggestions on improvements of the Leach layout that will be business as usual for Jens.
- Through holed.
- Double sided front end pcb.
- Double sided or single sided power stage pcb.
- Extra holes for attaching a brass powerline bar on the output
pcb.
- Standard connector scheme.
- No hardwired output devices.
- Extra space for larger or additional components.
- Symmetrical layout.
- Use of compact 0.5w metal film resistors (0.2" spacing).
- Minimize the size of the (front end) pcb.
- 2oz copper boards.
- Silk screen.
- pc power connectors or other connectors.
- A single board with perforations between power/driver/output
areas.
- Four hole mounting for all the small transistors.
- Three plastic for every two metal outputs (minimum).
- Separate powerlines for the gain and driver stages, wire link.
Jens showed his other Leach board yesterday.
The board reveals :
- extensive mass areas.
- All traces have a nice width.
- Smooth trace cornering.
All the things the original Super Leach pcb does not have.
It also shows that Jens has the experience to make a layout better than we( I ) can, even better than a lot of pro product boards.
In my view that is the absolute best there is, without going over the top.
I suppose Jens will design the Super Leach board in a similar manner.
Meaning, we need not make suggestions on improvements of the Leach layout that will be business as usual for Jens.
On the heatsinks :
An amplifier like the Super Leach will require quite a bit a cooling.
The classic approach for determining the heatsink factor is to calculate maximum dissipation at the lowest impedance the design dictates.
Driven full at a low impedance the power supply voltage will go as deep as nominal AC level.
At 60 VAC nominal the regular AC voltage can be 10 % higher.
Maximum load for the output devices is at 1/2 phase, 33 Volts.
At a normal minimum design load of 4 Ohms the maximum dissipation will be Square(33) / 4 = 272 watts.
That is a heap of heat, if the amplifier would be required to drive serious low impedance loads full power the heat calculation would be even worse.
Divided by 12 is 22.67 watts per device ( the Plastic)
At 100 degress max over ambient total thermal factor would be:
100 / 22.67 ~ 4.40
Cjc = 0.70 for the MJL's , for a TO247 thermal resistance from the case to the heatsink is around 0.50.
Which leaves: 4.40 - 0.70 - 0.50 = 3.20 for the heatsink.
Divided by 12 is 0.27 for 1 Heatsink or 2 times 0.55 for dual side mounting.
And that would be the bare minimum in my view, cause at that load the heatsink temperature would be (272 *0.27) + 25 degrees ambient ~ 100 Celsius / 222 F ( Ouch)
Acceptable because at livingroom conditions the actual load will be around 40 % of the calculated one (pink noise).
At 40 % the dissipation is 109 watts per channel, at 0.27 heatsink temperature will be 55 C /136 F max.
An amplifier like the Super Leach will require quite a bit a cooling.
The classic approach for determining the heatsink factor is to calculate maximum dissipation at the lowest impedance the design dictates.
Driven full at a low impedance the power supply voltage will go as deep as nominal AC level.
At 60 VAC nominal the regular AC voltage can be 10 % higher.
Maximum load for the output devices is at 1/2 phase, 33 Volts.
At a normal minimum design load of 4 Ohms the maximum dissipation will be Square(33) / 4 = 272 watts.
That is a heap of heat, if the amplifier would be required to drive serious low impedance loads full power the heat calculation would be even worse.
Divided by 12 is 22.67 watts per device ( the Plastic)
At 100 degress max over ambient total thermal factor would be:
100 / 22.67 ~ 4.40
Cjc = 0.70 for the MJL's , for a TO247 thermal resistance from the case to the heatsink is around 0.50.
Which leaves: 4.40 - 0.70 - 0.50 = 3.20 for the heatsink.
Divided by 12 is 0.27 for 1 Heatsink or 2 times 0.55 for dual side mounting.
And that would be the bare minimum in my view, cause at that load the heatsink temperature would be (272 *0.27) + 25 degrees ambient ~ 100 Celsius / 222 F ( Ouch)
Acceptable because at livingroom conditions the actual load will be around 40 % of the calculated one (pink noise).
At 40 % the dissipation is 109 watts per channel, at 0.27 heatsink temperature will be 55 C /136 F max.
With added output devices output will be slightly higher than the TO3 configuration, at lower impedance loads the difference will increase.
BJT's may not have an Rds, the resistors in emitter or source lines cause a voltage drop that increases with lower impedances.
Use 6 pairs of plastic instead of 4 pairs of TO3's and less voltage will be lost in the output stage resulting in higher output.
It may even have a slight effect on Zout.
Another added bonus of using more output devices is that with devices from the same lot multiple parallel devices will cancel out eachothers deviations from the average.
The more devices the less the deviation.
As there is no Cgs the driver looks at, like with Mosfets, paralleling multiple BJT's does not have that many drawbacks.
There is a company here in Holland that builds amplifiers which have a huge number of low power output devices, they claim benefits.
btw:
the Double Barrel concept can have the added advantage
of additional stability besides the division of voltage between two devices.
Stacking output devices need not be a downside, the criteria for building a high power amplifier are steeper than for a low power version.
Stacking them causes a voltage drop of less than 1 volt, for regular use of the amplifier that is of little importance in my view.
BJT's may not have an Rds, the resistors in emitter or source lines cause a voltage drop that increases with lower impedances.
Use 6 pairs of plastic instead of 4 pairs of TO3's and less voltage will be lost in the output stage resulting in higher output.
It may even have a slight effect on Zout.
Another added bonus of using more output devices is that with devices from the same lot multiple parallel devices will cancel out eachothers deviations from the average.
The more devices the less the deviation.
As there is no Cgs the driver looks at, like with Mosfets, paralleling multiple BJT's does not have that many drawbacks.
There is a company here in Holland that builds amplifiers which have a huge number of low power output devices, they claim benefits.
btw:
the Double Barrel concept can have the added advantage
of additional stability besides the division of voltage between two devices.
Stacking output devices need not be a downside, the criteria for building a high power amplifier are steeper than for a low power version.
Stacking them causes a voltage drop of less than 1 volt, for regular use of the amplifier that is of little importance in my view.
Just a little comment on the plastic devices:
I gathered that the ones considered are the MJL1302(a) and MJL3281.
Maybe some of you know that these are OnSemi and Motorola production remakes of the Toshiba 2SA1302 and 2SC3281.
The original Toshiba models were produced for many years, have been used in quite a number of mega dollar amplifiers, at the same time when the MJ15*** series were regular build components in models from Threshold, Krell, even Mark Levinson i think to recall.
Recently i aquired the schematic for the Threshold SA4/e.
In time i will build the SA4/e and use the original MJ1502* devices
because i wanted that amp badly in the production years and could not afford it.
I want the original SA4/e despite being able to choose output devices that are far superior to the original ones.
The MJL1302 and MJL3281 have a slightly inferior SOA than the 2SA1302 and 2SC3281.
Here the latter can still be bought, not fakes.
Still, the MJL models do 30 mHz, 15 amps continuous and deliver 30 amps in peaks.
Maybe plastic, but with a die that is quite nice for a power transistor.
And considering what i had to pay for Toshiba 1302/3281 15 years ago also affordable.
I gathered that the ones considered are the MJL1302(a) and MJL3281.
Maybe some of you know that these are OnSemi and Motorola production remakes of the Toshiba 2SA1302 and 2SC3281.
The original Toshiba models were produced for many years, have been used in quite a number of mega dollar amplifiers, at the same time when the MJ15*** series were regular build components in models from Threshold, Krell, even Mark Levinson i think to recall.
Recently i aquired the schematic for the Threshold SA4/e.
In time i will build the SA4/e and use the original MJ1502* devices
because i wanted that amp badly in the production years and could not afford it.
I want the original SA4/e despite being able to choose output devices that are far superior to the original ones.
The MJL1302 and MJL3281 have a slightly inferior SOA than the 2SA1302 and 2SC3281.
Here the latter can still be bought, not fakes.
Still, the MJL models do 30 mHz, 15 amps continuous and deliver 30 amps in peaks.
Maybe plastic, but with a die that is quite nice for a power transistor.
And considering what i had to pay for Toshiba 1302/3281 15 years ago also affordable.
JensRasmussen,
"While you all find out what direction the layout should take, I'll be working on my extended leach amp"
King jacco vermeulen has decreed the direction. We will all now dutifully follow. Sorry folks, no real re-design, just moving the deck chairs around.
Prosit
"While you all find out what direction the layout should take, I'll be working on my extended leach amp"
King jacco vermeulen has decreed the direction. We will all now dutifully follow. Sorry folks, no real re-design, just moving the deck chairs around.
Prosit
I would like to see (and make) a re-design….
I would like newer transistors.
I would like a new PCB layout
I will probably make a layout and post it here, no matter what the outcome of the ongoing discussion might be.
🙂
\Jens
I would like newer transistors.
I would like a new PCB layout
I will probably make a layout and post it here, no matter what the outcome of the ongoing discussion might be.
🙂
\Jens
Not really sure what else we could change without completely throwing out the original circuit design.
Ace: What else do you think should be updated so we aren;t just "rearrainging deck chairs"?
Ace: What else do you think should be updated so we aren;t just "rearrainging deck chairs"?
- Status
- Not open for further replies.