Guys I'm really sorry i didn't update this, i got side tracked building my new workshop. Anyway I did complete my F5 and it come out very very nicely indeed here are a few pictures of the build getting completed and test run on my little old mission m71i bookshelfs in the kitchen. its now been moved into the workshop, next step is to build a nice pair of efficient diy Speakers (currently driving Kef's in the workshop) and then build a preamp so i can connect my dab to it.
to be honest im really impressed with the amount of grunt its got even though none of the speakers i have run it with are particularly efficient. i dont see any point in turning it into an f5 turbo as i can achieve uncomfortable volumes with a good strong source.
working out the layout
marking up and cutting out the back panel. (note dont do this in the living room when the wife is home!)
back panel finished
picture of the final internal layout
biased up lovely both sides, i think matching all the components for both boards really helped make this much easier. both channels are setup at 0.59 volts with the bias as close as i can get to 0v (seems to float around +/-0.3 milivolts has anyone got it any better?) heatsinks are both the same temp +/- 0.5 degC which kinda makes me think i did a reasonable job of screwing it together. it runs at about 42degC in a 22deg room which is about as hot as the uk gets lol.
little picture of it rigged up in the kitchen, had a good week of testing before i was happy to shift it to the workshop to replace the ropey old cambridge audio A5 that i got for free as it was broken (couple of blown caps).
Final result I'm very happy with it, its very precise and clean even more than i thought it would be. It may just be me but the more i use it the better it seems to get. if im ultra ultra critical it does have a very very quite hum but i can only hear it if i put my ear right next to the speaker and stop breathing. i was going to play about with the grounding slightly to see if i could get rid of it completely but i am so happy listening to it i haven't found the time to bother.
to be honest im really impressed with the amount of grunt its got even though none of the speakers i have run it with are particularly efficient. i dont see any point in turning it into an f5 turbo as i can achieve uncomfortable volumes with a good strong source.
working out the layout
marking up and cutting out the back panel. (note dont do this in the living room when the wife is home!)
back panel finished
picture of the final internal layout
biased up lovely both sides, i think matching all the components for both boards really helped make this much easier. both channels are setup at 0.59 volts with the bias as close as i can get to 0v (seems to float around +/-0.3 milivolts has anyone got it any better?) heatsinks are both the same temp +/- 0.5 degC which kinda makes me think i did a reasonable job of screwing it together. it runs at about 42degC in a 22deg room which is about as hot as the uk gets lol.
little picture of it rigged up in the kitchen, had a good week of testing before i was happy to shift it to the workshop to replace the ropey old cambridge audio A5 that i got for free as it was broken (couple of blown caps).
Final result I'm very happy with it, its very precise and clean even more than i thought it would be. It may just be me but the more i use it the better it seems to get. if im ultra ultra critical it does have a very very quite hum but i can only hear it if i put my ear right next to the speaker and stop breathing. i was going to play about with the grounding slightly to see if i could get rid of it completely but i am so happy listening to it i haven't found the time to bother.
agreed. it would be fab to hear other peoples efforts. posting up here inspired me to open my f5 up and hunt the last tiny bit of noise out of it.
after several hours of experimenting with all sorts of grounding i managed to find the issue.
it had absolutely nothing to do with the grounding. of all the things i went through it was the most simple issue in the world but but something so easily overlooked!
the power switch! pulled it apart to find a duff/marginal contact. put a new switch in and problem went immediately, i now have no audible noise even with my ear millimetres away from the speaker.
while i had it open i checked the bias. spot on hardly any drift and still under a milivolt.
I'm writing this as i listen to Mike Oldfield Tubular Bells with the hairs on my neck raised, i really love this amp thanks Nelson your dedication to the DIY cause has allowed me to build something that i can come home from work to and completely de-stress.
after several hours of experimenting with all sorts of grounding i managed to find the issue.
it had absolutely nothing to do with the grounding. of all the things i went through it was the most simple issue in the world but but something so easily overlooked!
the power switch! pulled it apart to find a duff/marginal contact. put a new switch in and problem went immediately, i now have no audible noise even with my ear millimetres away from the speaker.
while i had it open i checked the bias. spot on hardly any drift and still under a milivolt.
I'm writing this as i listen to Mike Oldfield Tubular Bells with the hairs on my neck raised, i really love this amp thanks Nelson your dedication to the DIY cause has allowed me to build something that i can come home from work to and completely de-stress.
Hi Ash, good to see it's finished!
Thanks,
Alex.
- did you use r47 or r68 source resistors? If it's r47 i.e. you have ~1.25A through each FET then 42C seems a bit low... Did you measure the FET temp?
Thanks,
Alex.
I use 3PD05300 HS from modushop (it's a 210mm high rather than 165mm as in Ash's case). It's listed there as a 0.20C/W.
With 1.25A (and 23.7V rail) it gives me ~50C, which is ~32C above my ambient.
If a smaller HS stays cooler under similar wattage, I guess FET to HS interface might be optimised.
With 1.25A (and 23.7V rail) it gives me ~50C, which is ~32C above my ambient.
If a smaller HS stays cooler under similar wattage, I guess FET to HS interface might be optimised.
I think it should get to about 20C above T Amb with 0.31C/W...
With 0.20C/W you should be at plus 12C.
I'm planning to build the std F5 with the 4U, is it enough?
It could be listed as 0.31C/W. Or 0.20C/W. Or 0.15C/W - you choose.
However, they forgot to mention at what Trise it has been measured.
Look at some well established HS makers sites - for instance Heatsinks: 1000 Series - 1500HS | Birmingham Aluminium Ltd
- they rate same size HS as 0.343C/W, stating clearly that "Results given are for black anodised heatsinks based on a temperature rise of 60°c above ambient". No way it would achieve the same efficiency at 20°c above ambient. I bet it would be closer to 0.4-0.5 C/W end.
Having said that, it's not the end of the world. I saw a few examples of using modushop cases (even with 3U HS) for F5 implementation, including excellent 6L6 guidance that inspired me to build one. I guess they all still work. After all, the bias can be trimmed appropriately.
What I want to find out - why my results are so different. I wish I had 40°c on my HS after an hour of work.
However, they forgot to mention at what Trise it has been measured.
Look at some well established HS makers sites - for instance Heatsinks: 1000 Series - 1500HS | Birmingham Aluminium Ltd
- they rate same size HS as 0.343C/W, stating clearly that "Results given are for black anodised heatsinks based on a temperature rise of 60°c above ambient". No way it would achieve the same efficiency at 20°c above ambient. I bet it would be closer to 0.4-0.5 C/W end.
Having said that, it's not the end of the world. I saw a few examples of using modushop cases (even with 3U HS) for F5 implementation, including excellent 6L6 guidance that inspired me to build one. I guess they all still work. After all, the bias can be trimmed appropriately.
What I want to find out - why my results are so different. I wish I had 40°c on my HS after an hour of work.
60C above ambient is typical for several heatsink manufacturers in Europe.
In contrast to e.g. Conrad in Australia, who uses a delta-T of 80C as standard.
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