Pass F5 Turbo V2; one more build.

[surfatwork]

Updating the thread after a long while. Due to lack of time, I've passed on the kit to a FM, an electronics guy. Best of luck to him.

I finally started assembly. What are the FM's thoughts on the below chassis layout? (Dimensions in inches)

The first is a top view. All power components and wiring at the bottom of the chassis. I plan to cut the rectifier board and mount them on the two heatsinks on either side. I have not depicted the amp board in this pic.

The second is a side view of one heatsink. As you can see, the rectifier board is towards the front bottom, while the amp board is at the top of the heatsink. RCA in and speaker wiring will also remain at the top of the cabinet. The other side heatsink will be the same.

Also, if you notice in the top view, the cabinet bottom plate overlaps the heatsink fins at the bottom. Will this have a significant impact in air circulation and hence cooling? I plan this to ensure that the bottom plate provides robust support for the heavy heatsinks. The top plate will obviously not overlap.

 

[all4music]

if you notice in the top view, the cabinet bottom plate overlaps the heatsink fins at the bottom. Will this have a significant impact in air circulation and hence cooling? I plan this to ensure that the bottom plate provides robust support for the heavy heatsinks. The top plate will obviously not overlap.

how thick is your bottom plate?
IMO, that would for sure hinder the chimney effect and cooling efficiency of heat sinks. best bet would be use a L section or a thick square rod that runs across the chassis frame, over which you can mount your heat sinks and top/bottom plates. there are many examples of such build around.

 

[manniraj]

Power transformer should be ideally mounted near the front face plate to avoid any unnecessary AC noise getting transmitted to the input/outputs sources/wires. Looking at your layout I am presuming you are placing the transformer behind the back panel, so placing it right behind the front panel will be a good idea in my opinion.

 

[SanjeevM]

Consider keeping the Amp boards horizontal instead of vertical, as it will give you easier access for mounting the MOSFETs on the HS.

You may need a wider cabinet.

 

[jls001]

Consider keeping the Amp boards horizontal instead of vertical, as it will give you easier access for mounting the MOSFETs on the HS.

You may need a wider cabinet.

+1.

A common configuration is to have the rectifier boards on the floor and the amp boards stuck flat to the heat sinks.

And +1 to moving the toroidal towards front face plate.

 

[surfatwork]

Thanks for the input.

Power transformer should be ideally mounted near the front face plate to avoid any unnecessary AC noise getting transmitted to the input/outputs sources/wires. Looking at your layout I am presuming you are placing the transformer behind the back panel, so placing it right behind the front panel will be a good idea in my opinion.

My logic was as follows:
The trafo location was done based on the wire routing. Please see below pic.


This way the power wires can be as short as possible (my on/off switch is also on the back panel).
AC -> soft start -> Trafo -> rectifier boards -> filter board : the wiring is in one direction
the filter board orientation offers +/-32V DC just below the V+-0-V- pins on the amp board, keeping the DC powerline very short too.
The audio signals (line in and speakers) are at the top of the cabinet, separated by a good 6" atleast.

Consider keeping the Amp boards horizontal instead of vertical, as it will give you easier access for mounting the MOSFETs on the HS.

Amp board orientation: it is indeed horizontal i.e. not flat against the heatsink, but perpendicular to it.

 

[captrajesh]

The second is a side view of one heat sink. As you can see, the rectifier board is towards the front bottom, while the amp board is at the top of the heat sink. RCA in and speaker wiring will also remain at the top of the cabinet. The other side heat sink will be the same.

IMO, the maximum heat is produced by the MOSFETs. Hence it would make sense to put them in the centre of the heat sink for even distribution of heat in them for quicker stabilisation of heat. The transistors/ MUR Diodes on the rectifier boards do not heat up so much; so keeping individual smaller and lighter heat sinks for them should suffice I guess.

I leave the forum open for expert opinions.

Also, if you notice in the top view, the cabinet bottom plate overlaps the heat sink fins at the bottom. Will this have a significant impact in air circulation and hence cooling? I plan this to ensure that the bottom plate provides robust support for the heavy heat sinks. The top plate will obviously not overlap.

Passive cooling happens on account of convection in the heat sinks where, the air adjacent to the fins absorbs the heat and gets lighter in the process and rises up and dissipates. Cooler air present adjacent takes its place. This is a cyclic process Closing the back portion of heat sinks by mounting them partially over the bottom plate would definitely affect this cycle reducing the efficiency.

I've provided threaded holes on the top and bottom of the heat sinks for mounting the heat sinks onto them. If you think that this would be insufficient to maintain the structural integrity of the cabinet, you may consider reinforcing the joints by mounting additional 'L' shaped brackets especially to join the bottom plate to the heat sinks. (Same material preferable)

Edit: All4music seems to have beat me to it. Nevertheless, my 2 cents would remain.

 

[jls001]

The proposed location of the amp board would keep the heat generating power MOSFETs at one extreme edge of the heat sink. I feel placing them centrally would be best for heat distribution.

Also, if your amp board is going to be horizontally floating in the air, it would need some mechanical supports? to prop it up.

 

[surfatwork]

Thanks for moving it to a new thread.

IMO, the maximum heat is produced by the MOSFETs. Hence it would make sense to put them in the centre of the heat sink

The proposed location of the amp board would keep the heat generating power MOSFETs at one extreme edge of the heat sink. I feel placing them centrally would be best for heat distribution.

good point . Will mount the amp board upside down then and P1/P2 on the "wrong" side.

Will think a bit more about the cabinet and heat sinks. Not happy about just using 4/8 screws to maintain structural integrity of such a heavy thing.

Also, if your amp board is going to be horizontally floating in the air, it would need some mechanical supports? to prop it up.

plan to have a small ledge screwed to the heatsink (like a shelf support), to which the amp board will be bolted.

 

[saikatbiswas82]

Nice to see another world class amp in progress. Please follow this thread for ideas how to mount MOSFETs on HS.

http://www.diyaudio.com/forums/pass-labs/277850-f6-illustrated-build-guide.html

Please use biggest heatsinks that you could find. You may try 7-8 kg heatsink per channel. More the better. Because class A amps runs hot.... really hot.

My 2 paisa.

Sent from my ONEPLUS A3003 using Tapatalk

 

[surfatwork]

Please follow this thread for ideas how to mount MOSFETs on HS.

Thanks for the link. I did look at that guide. But I don't agree that mounting the MOSFETs at one end is good. Al is a very heat conductor and mounting it at one end only limits the amount of conducting surface in that direction....as Capt Rajesh pointed out.

ESP - Heatsink design and transistor mounting is a very good reference for heatsinks.htm, and he agrees with the above too.

 

[omishra]

I am around, just in case. But little delayed response.

 

[surfatwork]

been fairly tied up at work, bt managed to make some progress.

Filter boards


On the base plate with the heat sinks


A working PS!!! never been happier to see a bulb NOT glowing. Wiring is just for testing - will route it properly later.

 

[jls001]

Great progress :thumbsup:

 

[omishra]

Be careful about filter boards. There mounting holes have small clearance with current copper track on both sides of PCB. Please use mica washers from both the sides of PCB while putting screw/bolt through its mounting holes.

 

[surfatwork]

Be careful about filter boards. There mounting holes have small clearance with current copper track on both sides of PCB. Please use mica washers from both the sides of PCB while putting screw/bolt through its mounting holes.

Thks. Used nylon M3 screws and nylon spacers, running into m3 threads tapped into the base plate.

 

[surfatwork]

One side done.

 

[omishra]

One side done.

Don't connect those diodes on heatsink. At 50 drg Celsius it will conduct early that 0.5V. It would help thermal runaway. That's why we earlier builder installed PCBs parallel to heatsink. Either separate small heatsink or no heatsink. But away from main heat sources.

 

[surfatwork]

Don't connect those diodes on heatsink. At 50 drg Celsius it will conduct early that 0.5V. It would help thermal runaway. That's why we earlier builder installed PCBs parallel to heatsink. Either separate small heatsink or no heatsink. But away from main heat sources.

Removed!!!
Sincere thanks for saving my amp from an early grave!!

 

[surfatwork]

Wired the PS and routed the wires. Virtual ground to chassis Earth shows 10ohm, as expected, with no shorts, afaik.