You could use the VFET chassis as a monoblock: put the SIT on one heatsink and the CCS FET on the other. Then you can really crank it up to over 2 amps bias. In fact, with 50V supplies, there is not enough bias available with respect to the dissipation on one sink. So, monoblock would make sense. Or, you could deploy a choke and cut out the CCS dissipation. Of course, performance is probably not as great as yhe CCS but won’t be bad either.
If used as Mono block chassis the heat transfer via the thick front panel which cover the ends will help transfer heat to the other heat sink.
Thermal paste can be used to enhance the heat transfer (then other heat sink will not be pure "waste"). But if CCS FET is placed a one sink and e.g., SIT on the other it will of course be the best solution. Some designs like the "Lazy Bush" have one PCB for CCS and another for the SIT/Mosfet. Then a longer wire needs to connect the two PCBs. If design can handle that it will be a perfect situation.
Thermal paste can be used to enhance the heat transfer (then other heat sink will not be pure "waste"). But if CCS FET is placed a one sink and e.g., SIT on the other it will of course be the best solution. Some designs like the "Lazy Bush" have one PCB for CCS and another for the SIT/Mosfet. Then a longer wire needs to connect the two PCBs. If design can handle that it will be a perfect situation.
From the "Burning Amp 2022 – Simple DIY SIT Power Amplifiers" document, I see two design that I wanted to build. First the Common Source Mode/Constant current (CS/CC) and second the Common Drain Mode/MUFF (CD/MUFF). The CS/CC bias at 1.8A but the CD/MUFF seem to bias at 3A.
So from what I understand, one chassis will be good for all the CS designs but not for all the CD which will needed two (perhaps even then not enough) ?
Looking at Papa’s Sony design, there is 36V x 1.6A bias. So, you have 57W to burn on one side. The CCS FFET takes half the voltage, so at a 50V supply, and monoblock assumption, you can crank the bias to 57/25 = 2.3A. Now do your own math for the various designs.
If the SIT / CCS Mosfet is mounted directly on the heatsink the heat transfer is probably a bit better than if mounted via a bracket.
Also, a SIT like THF-51 and the large SOT 227 devices may have a bit better heat transfer than the TO-3's. My goal is approx 3A bias, 60V as mono blocks where both heatsinks are used. I will measure how hot the devices get and take decision from that.
I placed the VFET bracket pr. spec which is not 100% optimal regarding heat transfer (some extra space needed for other frontend cards). I know that other mounted the bracket more optimal regarding heat transfer. The back of the heatsinks on my VFET amp is not near as hot as the front. So, I am optimistic about 3A bias / 60V. Time will show......
Also, a SIT like THF-51 and the large SOT 227 devices may have a bit better heat transfer than the TO-3's. My goal is approx 3A bias, 60V as mono blocks where both heatsinks are used. I will measure how hot the devices get and take decision from that.
I placed the VFET bracket pr. spec which is not 100% optimal regarding heat transfer (some extra space needed for other frontend cards). I know that other mounted the bracket more optimal regarding heat transfer. The back of the heatsinks on my VFET amp is not near as hot as the front. So, I am optimistic about 3A bias / 60V. Time will show......
So the CD/MUFF with 180W to dissipate is too much for that case. Thank you all for your explanation (from a newbie who is still impress with his ACA and B1korg preamp). Regards.
it's covered in details in https://www.diyaudio.com/community/...-pt-2-n-channel-assembly-by-mighty-zm.385977/
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I have deleted myself from the list as I need chassis with more heat dissipation for the SIT SE mono block build.
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I have deleted myself from the list as I need chassis with more heat dissipation for the SIT SE mono block build.
To me the Deluxe 5U Chassis seems the only viable option if you stay with Modushop.
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What about the new look/design Modushop made for this forum. Where this limited production only?
I remember there was a specific thread about these very nice chassis.
I have the 5U for my M2X mono blocks (runs very cool). A shame to scratch it and only use the chassis 🙂
Yes!
It is a "closed story" now?
I will re-read thread tonight.
I assume one of these can handle the power of ZM's "Lazy Bush"?
Nothing is a closed story, as per the VFET chassis if there is enough interest we may produce more
I'll let someone more experienced than me answer the last question 🙂
I'll let someone more experienced than me answer the last question 🙂
You have two options for the SIT amps:
a) monoblock operation. Each chassis can do 100+W, which is more than enough.
b) substitute CCS FET for choke and cut dissipation in half, i.e., 90W, then use single chassis.
After re-thinking I think it was this thread:
https://www.diyaudio.com/community/threads/new-monoblock-chassis-sets-from-modushop.381702/
Are those available?
Yes of course this is always available since this chassis is a standard product https://modushop.biz/site/index.php?route=product/category&path=324
I’ve had a change of heart. I decided that I will be using the Mini Disspante cases I already purchased during Modushop’s summer sale for any additional explorations into the various VFET/SIT amps I’m interested in building with my round 3 OS kits.
derekr 3
ranshdow 1
OtisCampbell 1
Kannan_s 1
Winyl 2
Eddie18 - 1
claudio52 - 1
ARGOS - 2
CritterSoft - 1
derekr 3
ranshdow 1
OtisCampbell 1
Kannan_s 1
Winyl 2
Eddie18 - 1
claudio52 - 1
ARGOS - 2
CritterSoft - 1