Le Monstre vs. Parallel JLH class A?

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#41
Yes,

I do have access to these parts, and I'm in Dallas, TX right next to Mouser electronics and various other surplus shops.

The issue in mainly that I have a vision for what these are supposed to look ike finished and I get very carried away in trying to follow the game plan closely once it is stuck in my head. It is probably a very limiting factor in my DIY projects, but we all have our vices.😉

Hopefully, I can get a few pictures going once I get the angle iron on these sinks and they start coming together.

Thank you,

Blair
 
#42
The guide is perfectly correct but I fear you are being misled over the nature of single ended amplifiers. It requires greater voltage but less current to attain a certain power into an 8R load but less voltage and higher current to give that same power into a 4R load (ohms law). Notice that the variant running at 2.8A gives 32W into 4R but will voltage clip to limit power to 16W into an 8R load whereas the variant running at a slightly lower 2.7A gives the proportionately lower 30W into 4R BUT it has 33 Volt rails so it can swing enough output volts to sustain 60W into an 8R load, quite the opposite of what have assumed😉
But I can see how you got there!
The version giving 60W into 8R would dissipate 178.2W per channel but the first version, capable of the same power (roughly) into 4R would only dissipate 100.8W per channel. Getting rid of the heat is always a major problem in class A amps :gnasher:
 
#43
I see.

Thank you very much, and based on your experience, what rail voltage would you run based off the chart? Would you aim for the 25v rails @ 3.2A Quiescent? It seems to be the middle of the road and happiest across the spectrum.

Thank you again for your assistance. Their is no cost difference associated with the transformers. They cost are in vA, so a 500vA tranny cost the same amount regardless of secondary voltage. 500vA is sufficient for each monoblock I would assume.

Blair
 
#44
jez said:
The version giving 60W into 8R would dissipate 178.2W per channel but the first version, capable of the same power (roughly) into 4R would only dissipate 100.8W per channel. Getting rid of the heat is always a major problem in class A amps :gnasher:
Click to expand...


When you say 178.2W, are you referring to peaks. 60W continuous with 178.2W peaks? Sorry for my ignorance.

I hope my heatsinks are sufficient. I do not know the heat transfer figures, but they are fairly large at 11.5" X 4.5" X 1.25" The base plate is 3/8" thick also which helps.

Thanks,

Blair
 
#45
no. continuous at all times no matter what the volume is set at, for each channel!!!!! serious heat.
You have to decide for yourself what power you want. With this type of amp you can have either lots of power into low impedance load or lots into high(er) but not both, unless you have ridicules resources to plough into it anyway!
Do you really need so much power? many assume that they need much more then is actually the case. many a time I have shocked listeners by showing that the loud volumes they are listening to are only averaging 1 Watt or so😱
 
#46
if you really must have more power into lower impedance loads (sure?) then the Hiraga design will do this as it is true push pull without current sources in the output stage. Don't know how it sounds as have not heard it.. good reputation though.
good luck and i'm sure you will have fun with this project whichever route you choose....🙂
 
#47
I Agree with what Jez is saying for the same voltage rails that is.

When you are talking about the speakers you are using do you have some specs on them or what model they are perhpas we can help you with the power requirements...

-Dan
 
#48
jez said:
if you really must have more power into lower impedance loads (sure?) then the Hiraga design will do this as it is true push pull without current sources in the output stage. Don't know how it sounds as have not heard it.. good reputation though.
good luck and i'm sure you will have fun with this project whichever route you choose....🙂
Click to expand...

I'm hoping to have fun🙂

The reason I chose 50W as a benchmark is because I have owned about two dozen amplifiers in the past three years including the LM3886 designs, SE KT88 amplifiers, PP triode strapped 6550 amplifiers, PP KT88 amplifiers, etc... You get the point. I built all of them. I am experienced in building amps, but never a scratch build SS amplifier. I agree that 10W is more than substantial in most cases. I'm leaning towards a bit more because my speakers are typically a little lower sensitivity. I cannot give brand references for my speakers because there is not a commercial product in the house minus the CD player which is of little consequence here😉

Here is the impedance plot for my current speaker project if this helps at all. (Attached)

As you can see, this is not an easy load. Nothing that will kill most of my tube amps, but I'm not familiar with SS gear which is why I'm turning to you guys for assistance. I think the design I would prefer would be lots of power into low impedance loads. I cannot remember the last time one of my speakers had a 8 ohm nom. impedance.

That being said, this should indicate that I would want a low rail voltage with higher quiescent current right? Like the one in the chart with 56W into 4 ohms using 23v rails and 3.7A quiescent current???😕

I just need to make sure I buy the correct transformers. The rest I'm fairly confident in assembling even though that statement is probably foot in mouth at its best.

Thank you,

Blair
 

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#49
danieljw said:
I Agree with what Jez is saying for the same voltage rails that is.

When you are talking about the speakers you are using do you have some specs on them or what model they are perhpas we can help you with the power requirements...

-Dan
Click to expand...

Hey Dan,

See the attachment in the above post for the impedance plot on my speakers. They are about 87db efficient. I think I'm confusing everyone by using the word dissipation vs output power. I realize the transistors are on all the time and dissipate the same amount of heat regardless.

If I go with 23v (3.7A quiescent current) regulated rails on the high power JLH, will the amplifier not out out 56W into 4 ohms before clipping and 28W into 8 ohms before clipping?😕

Thank you,

Blair
 
#52
I highly recommend fan cooling. Without fans the heatsinks will need to be HUGE. Using fans will reduce the size (and cost) of the heatsinks by maybe x5 or so. Use bigger fans than seems appropriate and then run them at reduced voltage. This keeps things fairly quite.😉
 
#55
I'm feeling a little gun shy over these plans...

It's easy for me to egg you on with that 370W (dissipation) design, but I don't have to build it... seems an awful lot of heat to me and very easy to under-estimate the challenges even with prior amplifier building experience.

I might sound a bit negative about all this, but it seems that people who build these kind of amplifiers either over-design with lots of margin on the thermal management (and usually end up relieved because the thing still runs a lot hotter than the calculations show) or they start smaller, with lower power dissipation and discover what's good and what's not so good.

My Class A ambitions are still in the experimental stage. Just cranking up the bias on my Class AB DIY amp surprised me by how darn hot it got without a lot of current flowing - real HOT !

Lower voltages help reduce total power dissipation - but they're not friendly for low distortion.

I'm impressed what you guys are able to build, I'm looking forward to cooking up some heatsinks myself (appropriate expression eh ?)
 
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#60
Here are a few pictures for reference of my heatsinks. This is one rail of one monoblock, so there are four sets like this. I know it will get hot, but I do plan to make the majority of the enclosure out of perforated steel or aluminum and use fans as suggested. C'mon, it's just Texas. Average summer ambient temp - 102 degrees fahrenheit 😎

Blair
 

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