Class-A calculations

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#23
500W ?

Multiply by 2 chanels, biamping, triamping or maybe a 5.1 system? 😀

PD: I get about 15ºC temperature increase [relative to outside] in my room with just a 1200W heater... [I'm planning a ZVS triac control to regulate it]
 
#24
Eva said:
500W ?

Multiply by 2 chanels, biamping, triamping or maybe a 5.1 system? 😀

PD: I get about 15ºC temperature increase [relative to outside] in my room with just a 1200W heater... [I'm planning a ZVS triac control to regulate it]
Click to expand...


Excellent, thats exactly what my basement needs.... its already 15-20F cooler than the rest of the house...

Talk about one solution fits all! :mischiev:
 
#26
I recently got 4 Altec 515's (16 ohm versions) and a 288-8k HF driver for my next project. 😎

Probably not up the alley of many, but they are hard to beat in Dynamics. Altec VOTS have been the backbone of many efficient systems for a while and still hold their own very well in my opinion.

Sorry for digressing from the thread. 😀
 
#27
OK guys how does this look?

Gentlemen,

I re-did my calculation sheet based on your inputs here is what I have for a theoretical 50 watt class-A amplifier. Let me know if these numbers look good.

Inputs
Number of output devices: 4 Pairs
Voltage rails (per rail): 41 volts DC
Emitter resistance (per device): 0.22 ohms
Bias voltage per Emmiter resistor: 100 mv
Speaker ohms 8 ohms

Results
Idle bias per device: 0.455 Amps
Total Amplifier bias (both rails) 3.64 Amps
Total Dissipation (per channel) 149.1 Watts
Class-A output: Peak 105.8 Watts peak
Class-A output: RMS 52.9 Watts RMS
Efficiency 35.48 %
Max class-AB RMS 85.09 Watts RMS

Makes sense now? :smash: :smash: :smash:
 
#28
Hi K-amps,

I think you made it.

As per your inputs:
Number of output devices: 4 Pairs
Voltage rails (per rail): 41 volts DC
Emitter resistance (per device): 0.22 ohms
Bias voltage per Emmiter resistor: 100 mv
Speaker ohms 8 ohms

You will get:
Idle bias per device: 0.455 Amps , yepp
Total Amplifier bias (both rails): Well, this is a question how
you define this wording. I would say:
4x0.455Amps=1.82Amps
This idle current is running from the positive rail through the
upper transistors, then through the lower transistors to the negative rail. From my side it does not make sense to add
the values of each rail, because pos. and neg supplies are not in parallel, but in series..... and in a single chanel you will also find no wire were you could measure this "double-value".
Total Dissipation (per channel) 149.1 Watts, yepp + some losses in the power supply and driver circuits and protection circuits...
Class-A output: Peak 105.8 Watts peak, yepp
Class-A output: RMS 52.9 Watts RMS, yepp
Efficiency 35.48 %, in a perfect world yes...
Max class-AB RMS 85.09 Watts RMS, may depend on saging of
your rails...

Have fun with this
Markus
 
#29
Thanks yet gain Markus, you have been patient and helpful.(As have Nelson, Millwood and Eva). 🙂

For this what rating trafo would you recommend (if the model has no thermal switch built in). I am guessing for a stereo amp, minimum would be a 600VA Toroid but 1kva would be better.

-K
 
#30
For home applications I would prefer the 600VA type,
because of the mechanical vibrations ==> noise!
I am running 2 pieces of 1kVA torroids in my old
monster (8x 150W@Ohms... parallelable & bridgeable up to
1.2kW@2 Ohms) and even after some semi professional vacuum
impregnation you can hear them, if no music is played.
I hate this :bawling:

If you can get it somewhere and have enough cash, then chose a completely vacuum potted type.
....might avoid some frustration.

Bye
Markus
 
#31
Vacuum Potted 😕

now thats a term I have not heard before. Is this like a Toroid encpsulated in sand within a metal can? or Plain Toroid but with Potting compound in the middle for fastening to a bolt?

A picture could help...

I am guessing that would rule out standard offerings from Plitron and that I would have to go with their mega-buck (US$500 plus) Low Noise Toroids for Solid state amps.... :dead:

-K
 
#33
For thermal protection you might use bi-metal
mains circuit breakers.
They are available in isolated versions with 6.3mm connectors
for various switching temperatures. Please keep you eye on
on a solid construction.

Or you can improve your speaker protection circuit.
Here you normaly turn on the speakers with some delay
and turn off, if DC comes from the amp.
You might sense the temperature of the trafo with a simple
PTC (low resistance below reference temperature, above this
reference temperature its resistances increases very much)
This way you might get a suitable signal, which you could integrate
into your turn off circuitry. If you are lucky, it works if you simply
put it into series with the coil of the relay (depends on resistance
of relay coil and chosen PTC). These PTC are cheap and available with vairous resistances and reference temperatures.

...hope this might help you....
 
#34
...no my monster is not class A...., not by far...!
....more close to a current dumping amplifier, but in
fact not a current dumoing type. Just a design with small idle current.
I wanted it in small size and useable without fans.
Fans only turned on when running at high levels....


Vacuum potted:
I have seen (somewhere ...?!!!???????) 😕
steel encapsulated types completely filled with some
compound.
The compound typically has to be filled under vacuum conditions,
otherwise the compound will not fill every hole.....
 
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