Is this box good for small A class amp ?

Bubba Zanetti · 13th December 2005, 03:29 AM

I've got luckily for free two cast Al enclosures : they are std 19" rack width and I think 2U height, with cooling fins on the rear, all sides are 4mm thick.

Can I use one of these for small A class amp like JLH amp or similar or I need something with larger cooling area ?

cowanrg · 13th December 2005, 03:49 AM

they look cool, but where would you put transformer, caps, and circuit boards?

amplifierguru · 13th December 2005, 04:40 AM

Hi Bubba Zanetti,

Yes it looks (through the darkness) to be 3.5" height. Looking at the size of those fins it would possibly be at least 0.3C/W, and good enough for an 'efficient' 40-50W Class A. I would be raising it off the surface on platform feet for better convection. Use one per channel - monoblocks.

Of course you could put a stereo 150W/channel Class AB in each.

Cheers,
Greg

Bubba Zanetti · 13th December 2005, 06:00 PM

First, tnx all for fast reply,

Yes, space for transformer almost doesn't exist there, even for very slim toriodal , but I've got 2 PSU boxes like this:

On right side of PSU is some old 400VA transformer to get the
approx. size of box - my idea is to remove old PCB's from this box and put transformer , greatz, PCB's and two spare Sprague capacitors as power supply for my future amp - so I can have separate power supply.

Then in other cast box will be placed only amp pcb with output transistors.

On PSU box there are 3 heatsinks as can been seen, 2 per sides and one on back - are they suitable for semiconductors on regulated power supply for example, 2x15 W JLH amp ?

I'm not sure if there can be some problems with hum and ground loops when using power supply in separate housing - what wiring schematic do you suggest in that case to minimize problems?

Maybe on upper pic isn't shown very clear, but there is in fact enough space for pretty large pcb's there - here are old boards that are still placed inside:

Top of the box:

Btw. all boxes on pics are from old cell phone station rack - I had part time job at local telecom this summer and they were throwing away massive amounts of different receivers, RF amps, PSU's - I kindly asked if I can take something home for my project and they kindly gave hundred kilo's of nice boxes and heatsinks

amplifierguru · 14th December 2005, 02:32 AM

Hi bubba,

I cannot see that you would not have the room for even a 300VA (local are 105D x 55H mm) transformer. If you use multiple smaller PS caps (like my PS 12 x 4,700uF is only 55D x 100W x 40H mm).

Just replace the faceplate and all the c*** attached to it. A 40W Class A should only need a 150W traffo. Remember also that there are only really diode spikes to concern with on Class A so it's very forgiving of close encounters. Probably half the reason for the smoother perceived sound.

Cheers,
Greg

13th December 2005, 03:29 AM	#1
Bubba Zanetti diyAudio Member Join Date: Jun 2005 Location: Rijeka, Croatia	Is this box good for small A class amp ? I've got luckily for free two cast Al enclosures : they are std 19" rack width and I think 2U height, with cooling fins on the rear, all sides are 4mm thick. Can I use one of these for small A class amp like JLH amp or similar or I need something with larger cooling area ?

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13th December 2005, 03:49 AM	#2
cowanrg diyAudio Member Join Date: Apr 2002 Location: Lafayette, CO	they look cool, but where would you put transformer, caps, and circuit boards?

13th December 2005, 04:40 AM	#3
amplifierguru Account Disabled Join Date: Aug 2004 Location: Earth	Hi Bubba Zanetti, Yes it looks (through the darkness) to be 3.5" height. Looking at the size of those fins it would possibly be at least 0.3C/W, and good enough for an 'efficient' 40-50W Class A. I would be raising it off the surface on platform feet for better convection. Use one per channel - monoblocks. Of course you could put a stereo 150W/channel Class AB in each. Cheers, Greg

13th December 2005, 06:00 PM	#4
Bubba Zanetti diyAudio Member Join Date: Jun 2005 Location: Rijeka, Croatia	First, tnx all for fast reply, Yes, space for transformer almost doesn't exist there, even for very slim toriodal , but I've got 2 PSU boxes like this: On right side of PSU is some old 400VA transformer to get the approx. size of box - my idea is to remove old PCB's from this box and put transformer , greatz, PCB's and two spare Sprague capacitors as power supply for my future amp - so I can have separate power supply. Then in other cast box will be placed only amp pcb with output transistors. On PSU box there are 3 heatsinks as can been seen, 2 per sides and one on back - are they suitable for semiconductors on regulated power supply for example, 2x15 W JLH amp ? I'm not sure if there can be some problems with hum and ground loops when using power supply in separate housing - what wiring schematic do you suggest in that case to minimize problems? Maybe on upper pic isn't shown very clear, but there is in fact enough space for pretty large pcb's there - here are old boards that are still placed inside: Top of the box: Btw. all boxes on pics are from old cell phone station rack - I had part time job at local telecom this summer and they were throwing away massive amounts of different receivers, RF amps, PSU's - I kindly asked if I can take something home for my project and they kindly gave hundred kilo's of nice boxes and heatsinks

14th December 2005, 02:32 AM	#5
amplifierguru Account Disabled Join Date: Aug 2004 Location: Earth	Hi bubba, I cannot see that you would not have the room for even a 300VA (local are 105D x 55H mm) transformer. If you use multiple smaller PS caps (like my PS 12 x 4,700uF is only 55D x 100W x 40H mm). Just replace the faceplate and all the c*** attached to it. A 40W Class A should only need a 150W traffo. Remember also that there are only really diode spikes to concern with on Class A so it's very forgiving of close encounters. Probably half the reason for the smoother perceived sound. Cheers, Greg