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Old 16th January 2009, 09:55 PM   #1
Donovad is offline Donovad  United States
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Default 2 DIY "f" AMPs in Single Chassis

As I embark on my first DIY FirstWatt amp build, the F5, I had the idea that it might be possible to build two different "f" amps in the same chassis. The bulk of the cost in parts and most difficult to obtain for us DIY'ers seems to be the chassis and heatsinks. I've got a rather large aluminium enclosure with built-in sinks en route from the far east ( that will hopefully arrive in the next 30-90 days) that will have more than enough room for multiple boards and power supplies/transformers. Is it feasible to mount the Fets of say an F5 and an F1 on the same heatsink and not end up with a very temporary space heater ? I'm sure this idea has been thrown in and then out before but i couldnt find a reference to it. Opinions and ideas ?

Thanks everyone (and especially NP) for your time and efforts on the various F amp board groupbuys and build threads that make this type of communal audio possible.

Regards, Daniel.
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Old 16th January 2009, 10:24 PM   #2
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There's no reason why not, it's just a matter of having enough heat sink and PSU capacity. Calculating the amount of heat sink required needs to realize that you need more than just 2x the original heat sink size due to decreases in thermal efficiency.

Perhaps you could share more about your particular implementation you have in mind and the c/w rating of your heat sinks.

Edit: This assumes a common heat sink rather in multiple heat sinks used in a common chassis. example: 2 heat sinks per side for 4 amps rather than 1 heat sink per side for 4 amps.



-David
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Old 17th January 2009, 12:59 AM   #3
Donovad is offline Donovad  United States
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Default Diy F5/f1

David,
I was thinking of a combination like an f5/f1 that would share the same chassis and as much of the power supply as/if possible but could not be operated at the same time. Possibly 2 separate power switches or a rocker style switch that would alternate between the two topologies. I've tried to attach pictures of the chassis but they were sent to me as a word document and i cant seem to make it work. The heatsinks are 160mmx42mmx380mm each but i dont have a rating on them.

Regards, Daniel.

Edit: I should specify that there are 4 separate heatsinks. 2 pairs per side. The overall dimensions of each pair, per the manufacturers specs, is 160x42x380 mm per side.
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Old 17th January 2009, 01:26 AM   #4
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Its DIY, anything is possible!! This guy put F1/F2 in the same chassis. Based on his PS/heatsink, I don't think he ran both amps at the same time. The PS topology is the same, so that should be fine. A few three pole switches, just make sure power is going to the right place, and a main switch. You could feasibly run both amps at the same time; it sounds like you have enough heatsink. What size transformer/capacitance?
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Old 17th January 2009, 01:51 AM   #5
cfcubed is offline cfcubed  United States
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Hey, I AM that guy and yes, it only runs 1 bank at a time (F1 or F2).

I used little regs + good size relays (5A 4PDT for each channel) to handle the switching between banks... The idea was to use another of amb's nice ε24s to do the switching, but just used a mini switch (see my avatar).

Funny this would come up now... I originally did it to choose between F1 and F2. And I *think* I like F2 better in my environment. So, will be pulling the F1 banks & using them in a dedicated F1 build.

It's an injustice to have dormant F1 channels in a case
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Old 17th January 2009, 05:49 AM   #6
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This is a no brainer. I thought you wanted to run the 2 amps at the same time. I'd take the approach of have 2 switches. 1 Mains switch and a secondary toggle switch after the VDC PSU output to select which amps get the power. Assuming both amps have the same supply requirements. An F1/2/3/5 all do have the same PSU design.

-David
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Old 17th January 2009, 01:38 PM   #7
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You might want a switch for your inputs and outputs as well
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Old 17th January 2009, 04:02 PM   #8
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I was thinking of the same thing. I was looking at a full ranger and sub set up and I was going to test the amps in a similar fashion. I am building differential F1, F3, F4, and F5 boards soon and I was going to mount a switch or two to control two power supplies to help choose where their power would go. These days, I have decided to skip this idea and just use plugs for now to switch to different amps. I think I have come to the conclusion that for now I will "settle" on finishing an F1 and a pair of F4 monos for the full rangers and forget about the sub. The AN12's will give me enough bass in a cabinet, but I will eventually want to go OB and a sub. I will not need a switch yet because I will build the supplies for these.

In the future when I go OB and build subs, I will build the F3 and F5 to test with the F4. I was thinking of two SE F3 and F5 run as monos in a SE balanced type configuration and the F4 in balanced mono. These will be there for permanent use so I will never need to choose between which amp I will keep again. I will simply choose the one I want to listen to. I will want a remote controlled relay to switch power to these amps but I was not sure if I would need relays on the inputs/outputs as well, I was hoping power was enough. If I need to have relays on the inputs/outputs as well, it would not be that bad if I stay to one source(preamp). I would still need another couple of relay boards to switch that one source signal into four amps(F1, F3, F4, F5) and two balanced amp channels(L+/- andR+/-). The other simple sollution is a TRS or XLR plug board system like the pros used to use and some still do. I gues if you factor in the cost of the plugs an jacks, the relays are probably cheaper.

The dreaded cheapest way is to actually make up my mind and narrow it down to two amps. I am thinking F4 and a F3 or F5. I might want to keep the F1 as well, oh drat! I guess I will just have to build the amps and see what I can afford to do. If I have to choose between not having an F3 or F5 because the switches are going to cost as much as one of those amps, I will choose the amp. I may have to tin the wires and use a manual screw terminal board to switch them, but i will have the amps.

I will be watching to see what solutions come out of this thread.
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Old 17th January 2009, 05:28 PM   #9
cfcubed is offline cfcubed  United States
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Quote:
Originally posted by jupiterjune
You might want a switch for your inputs and outputs as well
I bet David meant that.... Note that I did full F1/F2 switching with 4 poles for each channel (4PDT)... And that's switching power & necessary inputs & outputs (see my thread).

Pretty cool being able to switch F1 / F2, one thing tho w/F2's caps there is a slight delay in its signal output while they charge. Not something you go switching back and forth very much BTW.

David - Did you mention those 10R 1W (or whatever) offset compensation resistors in the BoM of your GB? E.g. those emails I sent about them. May not need them but if you did would make for a disappointing completion to your build ($10 USD order for $2 parts?).
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Old 18th January 2009, 10:42 PM   #10
Donovad is offline Donovad  United States
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Default DIY F1/F5

Thanks for the input Gents.
Now that I see its been done before i feel encouraged that i can make it work. It's going to be slow developing though so please be patient with me. The enclosure is on a slow boat from China (literally) and I'm patiently putting together the other components from the various Group Buys (thanks David) and design threads. Still trying to sort out the transformer choices too not to mention the E Geddes multi-sub w/ Nathans project that occupies my workbench. Looking forward to putting these ideas and suggestions into a working amp. I'll update as soon as i have more.

Regards, Daniel.
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