A guide to building the Pass F4 amplifier

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#2,985
I have another question - I have a heatsink 300x150x40. I have another heatsink 300x50x40. They would fit together vertically to make a larger heatsink 300x200x40. So how do I join them up to get good thermal transfer? Do I need a copper plate to join them or would aluminium be OK, like 300x70 or 300x100 e.g. 3mm or 4mm thick? And bolted together with thermal paste.
 
#2,989
My F4 didn't last long, fuse broke, changed and broke again, my skilled friend checked it out at my place and found out the diodes on a channel might be gone, it is still waiting to go to his workshop for restoration but at this point I am thinking to rework the filtering part.

Story being the guy who assembled it for me didn't want to use the DIY Audiostore boards, he said he would arrange that section and you can see the big caps which are connected with the other components with cable wiring and the rectifiers being underneath the thick aluminum plates in between the two caps boards.

On the back of the case you can see a relais underneath the skull shield and a small transformer to power the amp out as not to roast the switch (put it very simply, I don't really remember how this thing works), at this point I'd like to rework the filtering and rectifiers part of the amp with the UPS from the DIY Audiostore and wondering if with the actual layout (transformers in the middle) they would fit and then would also add the soft start board still if that fits and if it is not superfluous.

Please your suggestions are more than welcome, I'd order the boards the soonest as they take quite a while to ship off the US to here and in the meantime my guy should also start and work onto the BA-3 preamplifier which would squeeze all the gentle power off the F4 since my AR SP9 doesn't make justice to it.

Grazie mille for your attention

Giovanni


F4.jpeg
 
#2,990
I'd recommend asking your skilled friend to e-mail you the schematic and parts list they used for the existing system. You can post that here, and we can maybe help a bit better.

There may not be a need to re-do so much. It may be a good design with a small issue.

My :2c:
 
#2,991
best (easiest) recipe is using 35A or 50A metal case bridges (KBPC35 or KBPC50), firmly bolted to bottom of case, with some thermal paste in between and - as a must - having split washers under bridge screw nut
( I had dead bridge in amp built by someone else - bolt got loose from thermal cycling, without split washer ...... and bridge simply gone Dodo)

trick is simple - these bridges are enduring declared current only if cooled properly

example - in my T-Bed (chassis for prototype work) I have one 50A bridge, mounted on 120*120mm, 2mm thick Al plate; with regular Iq of 2*1A7 (to 2*1A8), bridge and plate are at least 55C

same conditions in regular amp, one bridge on bottom plate (scratch the paint!!), bridge is just warm
same conditions in regular amp, two bridges on bottom plate (scratch the paint!!), bridges are just warm

go figure ........
 
#2,992
ItsAllInMyHead said:
I'd recommend asking your skilled friend to e-mail you the schematic and parts list they used for the existing system. You can post that here, and we can maybe help a bit better.

There may not be a need to re-do so much. It may be a good design with a small issue.

My :2c:
Click to expand...
I don't want to rely on the builder any longer, just to say one you can tell how tidy the build is, very good looking actually but the white connection strips between the transformers, to say one, rather than using those things we call "fastons" on both ends has only the cable side crimped and then soldered on the connection strip, what's the point?
The diodes probably got too hot and the aluminum heatsinks don't dissipate enough so what my local skilled tech suggests is to change the diodes and add a proper heatsink on top of the aluminum plate to begin with, his other doubts are about the in the air cabling of the filter boards and the relais to switch the amp on which is the reason I though to add a soft start board since there should be enough room for it
 
#2,993
Giovanni1968 said:
My F4 didn't last long, fuse broke, changed and broke again, my skilled friend checked it out at my place and found out the diodes on a channel might be gone, it is still waiting to go to his workshop for restoration but at this point I am thinking to rework the filtering part.

Story being the guy who assembled it for me didn't want to use the DIY Audiostore boards, he said he would arrange that section and you can see the big caps which are connected with the other components with cable wiring and the rectifiers being underneath the thick aluminum plates in between the two caps boards.

On the back of the case you can see a relais underneath the skull shield and a small transformer to power the amp out as not to roast the switch (put it very simply, I don't really remember how this thing works), at this point I'd like to rework the filtering and rectifiers part of the amp with the UPS from the DIY Audiostore and wondering if with the actual layout (transformers in the middle) they would fit and then would also add the soft start board still if that fits and if it is not superfluous.

Please your suggestions are more than welcome, I'd order the boards the soonest as they take quite a while to ship off the US to here and in the meantime my guy should also start and work onto the BA-3 preamplifier which would squeeze all the gentle power off the F4 since my AR SP9 doesn't make justice to it.

Grazie mille for your attention

Giovanni


View attachment 1105332
Click to expand...
Let the guy do his bit, change those diodes for a better pair and heatsink properly with thermal goop ane tighten properly to 2 NM.

It’s a nice build. The stores PSU boards are not nescessarily going to get you a better amp. Gnd scheme had great room for improvement. In fact, as long as your F4 is quiet and nice when working, use what you have. Like Mighty sez, even he had diodes crap out on him. So it is not the end of the world.

Hugz and kissez,
Andy
 
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#2,994
Oh well, I know it's not the end of the world but since I have to be away from it for a while and also wait for the BA-3 tp be done I won't mind wait a little more as to not just fix it but also make it more reliable with a proper soft start instead of the transformer-relays, the PSU would only make it if they help prevent other issues, it will be my guy to tell me, once I have to get the soft start I would also get the PSUs to combine shipping.

Anyting else you would say being useful for reliability?

Also, if one wants to use it bridged is there any internal mod (with a switch for example) to achieve that?

Grazie
 
#2,995
just do what I wrote and implement big NTC * Cl60 class) in primary of each xformer


bridging demands nothing else than XLR jack at back plate, one hot going to one side, second hot going to other side, pin 1 hoing to both sides gnd input pad

output taken from two hots

read article, all explained
 
#2,996
Giovanni1968 said:
Oh well, I know it's not the end of the world but since I have to be away from it for a while and also wait for the BA-3 tp be done I won't mind wait a little more as to not just fix it but also make it more reliable with a proper soft start instead of the transformer-relays, the PSU would only make it if they help prevent other issues, it will be my guy to tell me, once I have to get the soft start I would also get the PSUs to combine shipping.

Anyting else you would say being useful for reliability?

Also, if one wants to use it bridged is there any internal mod (with a switch for example) to achieve that?

Grazie
Click to expand...
If you do what Mighty sez you’ll be fine. CL-60’s and replace and heatsink bridge rectifiers, both of them.

I have a finished BA-3 board fully working. Chime if interested.
 
#2,997
I didn‘t quite get the concept of that relay-thing, isn‘t that something like a softstart? Or does it just „ignite“ the real thing (switch triggers relay which triggers amp)?
The softstart would basically do the same as mZM‘s CL60, plus it then (after the start was made softly) goes out of the way… mo complicated (more parts, oh mighty! :devily: ).
Don’t know if this would save the diodes, I thought it was more to give the PSU a better and longer life with less stress

If you want to go really fancy, look out for mark Johnson’s superduper softstart thing…

Your amp looks gorgious BTW.
 
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