About make an audio power amplifier.

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spec said:
I did say check. Also TO220. There is also another bigger plastic pak (can't remember and too lazy to look it up) too. No big deal- just a thought
Click to expand...
But there is too much space between 2 output transistors as your can see, even enough space for fat guy like 2SC2922/2SA1216.
 
Nikolai Petrenko said:
It is just the mounting method, of course the heatsink will be raise up vertically for best air flow.
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That will be OK, and what you have shown will be fine for an audio amplifier, but to get the optimum performance, it is best to mount the transistor in the middle of the heat sink and to have a free flow of air around the heatsink, both sides.

It is also better to mount the transistor in the center of the heatsink rather than the edge. If you do need to mount the transistors on the edge of the heatsink they should be mounted on the bottom of the vertical heat sink.

Remember that the case of the VBE amplifier transistor must be mounted in contact with the case one of one of the output transistors.

It is also better to mount the audio amplifier PCB at 90 deg to the heatsink to avoid heating the board and possibly introducing distortion. As a general rule, always allow access to all parts of your circuitry. With your present layout you cannot access the bottom of the PCCT board.

There is a saying in electronics: 'Any part of a circuit, never mind how simple, that cannot be accessed will always be the most troublesome'. God has his little jokes.

You did ask

spec
 
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spec said:
PCCT
Click to expand...
PCCT???
If I mount like the shown, I cannot access the board without unscrewing the output transistors?
 
Thermal heatsink is critical when class AB output stages lose up to 50% power at swings of Vcc/2 for low hotspot rise.
This is another reason your design is less capable than the Leach Design which uses two parallel output stages. I recall the Crown DC200 used 8 parallel output Q's. So heat spreading to multiple devices is critical for cooler operation.

This excellent Nakamichi design, above, which I Just found on web using your transistor part numbers, does what I just wrote.
 
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Nikolai Petrenko said:
Mounting board and transistor in this way, well?View attachment 100037
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Heatsink should have vertical fins and long for best convection air flow, otherwise use a quiet 35 mm fan to get a plenum of air moving at least 1m/s , volume of air like 10 CFM can be small and quiet if low RPM.

BUT air Speed is most important, so for convection , heat rises , make use of free air rising to cut thermal resistance in half and with ducted tiny fan , 10x better.

If heatsink is under board and horizontal , you just made it at least 2x hotter temp rise on Transistor Case.

Study commercial Power Amp layouts for heatsink. Fan can be avoided to prevent dust, but requires understanding of how heat rises and airspeed, with vortex and vents below and above to create chimney effect. Otherwise, use more parallel devices to spread heat.
 
Tony Stewart said:
View attachment 100042
This excellent Nakamichi design, above, which I Just found on web using your transistor part numbers, does what I just wrote.
Click to expand...

There are many reasons this Japanese design is superior to other designs. It has only 4 gain stages, yet many transistors to with cascode , current limit and constant current front end with feedback. This results in least phase shift and most power gain*bandwidth product with ample current sharing.. Small emitter power R's with tight tolerances compensate for wide variations in Rbe , so they share current equally. Essential pots control Null Dc out and null crossover distortion.

There are many more details you should study to have an Amp that will last 60 years or more
 
PCct is spec's way of abbreviating printed circuit assembly or PCA.

study the best layouts of the best designs and then make notes. read, read more. Study Nakamichi design , cap quality, layout, design details. When U understand it better, you will know what to do. Do it right the first time.

Every design detail has a reason. Service, Reliability, low noise, shortest path, best conductors,good shielding, (red perimeter), smallest size for max heat dissipation and lowest Trise of hottest spot. At full power, nothing should burn your finger. It should look logical and pleasing to the eye.
 
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Tony Stewart said:
This is another reason your design is less capable than the Leach Design which uses two parallel output stages. I recall the Crown DC200 used 8 parallel output Q's. So heat spreading to multiple devices is critical for cooler operation.
Click to expand...
Sorry, I am a poor man, my money still for speakers, not only can concern on output transistors.
Yes, I am going to make a thermal controlled fan speed for better thermal protection, it is also available to control speed by hand. If the fan can't cold down heatsink in some condictions, the mission is for thermal fuse..........
Tony Stewart said:
If heatsink is under board and horizontal , you just made it at least 2x hotter temp rise on Transistor Case.
Click to expand...
The pic I have shown only tell the mounting method, of course I never fool enough to turn my amp into a toast.
I have known about this way since I have learn about thermal and airflow. This way is much more benefit than using more output transistors in parallel.
 
I once designed a rack mounted enclosure for Lucent / Avaya 1U high (47mm) with 180W 48V OEM (Lambda or Power One )SMPS enclosed. You can buy this rack off EBAY for $25. (obsolete) if still avail. (Definity Power over ethernet) I learn how to make a spoiler air intake to create turbulence then attach thermistor to transformer hotspot with epoxy and use LM317 + Q + pot + RC network to make automatic temperature speed control. The trick I learned better than any PC box is small aperture duct over hotspots with high air speed >1m/s with turbulent flow is better than laminar flow over hotspots, rather than flow way over top of the tall parts to remove heat and resulted in only 15'C rise at max load loss, pushing air horizontally within 1cm above the hot parts and out exbaust grill. Usually fan never operate until it reached 45'C at high ambient and full power.
We then made 1000 units. per month.

Check EBAY for obsolete AVAYA racks.
 
e.g. good quality 48V need two. modify to make common ground bipolar out to make 200W+ PSU for power Amp
Add plenum duct and 35mm fans or put into rack. terminal posts for AC in. chassis ground, normally output floating.

4 avail.

**broken link removed**

shop around. make vs buy ?.
 
Yes screwmount to your heatsink blocks access to PCA bottom.

With test vias on top, that should not hamper testability but certainly repairability if parts on bottom.

If only 1 sided board, with Cu on bottom, then design no good with heat sink under. If Cu on top only, delaminated tracks can occur easily if not careful with removing solder befor parts, so no good either, but possible for 1st attempt proto.

Why not study good layouts and build it right first time or buy surplus, garage sale

What's your budget and priorities?
https://www.tonepublications.com/old-school/nakamichi-pa-7-amplifier/attachment/3-126/
 
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