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Juma's Easy-Peasy Capacitance Multiplier
Juma's Easy-Peasy Capacitance Multiplier
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Old 5th April 2018, 04:06 AM   #471
kking85743 is offline kking85743
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Quote:
Originally Posted by jameshillj View Post
You could easily just attach them to the main heatsinks towards the back beside the power amp boards and this allows for shorter cables too - could lift the audio input signal wires well above the re-located CMx to avoid any possible 'noise' transfer

The heat generated by the C-Mx is basically 'VxI' so this is about 4.5v (volts across the fet) x 1.5A (guessing the current thru the ACA) = approx 7watts and on the main heatsink, this won't make much difference but will keep the fet much cooler

That 'switcher supply' makes the assembly very simple
To make room on the main heat-sinks, I would have to rearrange (ie re-drill) the holes). For me, this isn't a big issue, as I have the MOSFETs on short wires, so I'd probably move the ACA boards to the baseplate and mount just the heat generators to the heat-sink.

Based on basic heat generated (and current leaving the circuit to go thru the speaker instead of the amplifying device), I'd split the heat sink about 1/6 for the CapMult device, 1/2 for the constant current device and the remaining 1/3 for the amplifying device. When the music is quiet, the amp device will be a little warmer, but the louder you play it, the better off it will be (heat wise). 8)
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Old 5th April 2018, 04:09 AM   #472
kking85743 is offline kking85743
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Originally Posted by xrk971 View Post
Or even bend the legs on IRFp240 90 degrees and mount underhung with thermal contact to the steel bottom panel. It’s probably enough for 5-7w dissipation.

I don’t recall ACA having on board rail smoothing cap, big one is output coupler. So leave the one in the cap Mx board. Mounting on 2U heatsink is adding probably 7w too much heat load as that one is at about the limit of 35w already (~1.5amp x 24v). I have 4U and it has about 75w limit.
These devices are already underhung (the individual heat sinks are 2.5" tall!!), but I have plenty of heat capacity, as I got the 300mm deep case, not the stock 200mm deep one. That and I'm only adding about 20% over existing load (which is spread over 50% more heatsink, so I should be fine). Fins are presently running about 43C at the root and noticeably cooler at the tips.

Last edited by kking85743; 5th April 2018 at 04:22 AM.
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Old 5th April 2018, 04:20 AM   #473
kking85743 is offline kking85743
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Originally Posted by xrk971 View Post
If you just need to have ripple control the best are the IRFP240 9240 from value standpoint. They are designed for this type of power regulation and handle up to 20amps when heatsinked properly. If you want more current by the IRFP250/9250 - basically double current. If you can look for lower Vgs MOSFETs you have lower dropout voltage.
This leads nicely into a question I had. The voltage drop seems to be a little over the Vth/Vgs for the 250 (4v). There are other fairly heavy duty devices (Infineon IRL2703pbf, as an example) which has a 1v Vth/Vgs, which would be easier on the power supply (crank it to a fraction over 25v instead of 28.5), as well as dissipate about 1/4 the heat.

Since we're scraping off only tens of mV at about 1.5A, a whole volt seems like it is a ton margin. The only situation where the lower margin could be a problem is if there was a big bass hit and a sudden surge of current was needed. However, based on how the ACA is built (constant current source), that shouldn't ever happen.

Does anyone have any thoughts or words of wisdom regarding looking for a lower Vth/Vgs part to help reduce heat?
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Old 8th April 2018, 04:32 PM   #474
maouna is offline maouna  Greece
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Does any of the following STP55NF06,STP60NF06,IRFS630 have lower voltage drop across cap multiplier? I will use the cap multiplier in powering preamps.At the moment i am using IRF610.
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Old 8th April 2018, 05:14 PM   #475
szpunk is offline szpunk  China
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Quote:
Originally Posted by jameshillj View Post
The Cap multiplier circuit is a voltage follower filter that reduces ripple, output impedance, etc but goes up/down according to current demand of the application and the supply design.

By adding that Zenner to the base of the transistor (1N5862, 28volt, 5 watts?!) you've fixed the voltage of the output of the pass transistor (IRL510x) so it has been converted to a simple regulator and the voltage across the pass transistor and the incoming transformer/diode supply has to be increased to allow for dips in supply created by current variations.

Then you have added another C-R-C with 2 x 0.47R in series that defeats all the best properties of the follower/regulator but consumes lots of components - it may even sound okay but why do it this way in the first place

Yes donovas,
Adding a bypass will slightly improve C9 but is dependent on the particular properties of that C9 - usually, you'd increase the whole C-Mx by using better base voltage control, some feedback mechanism, etc, etc but it isn't then a simple Cap multiplier circuit

There are plenty of more highly developed Cap multiplier filters around to investigate both low and high current use - have a look at the K-multiplier site for some good explanations about filter operating techniques.
Thanks for you input. Too many things to learn especially English.
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Old 29th April 2018, 05:02 PM   #476
donovas is offline donovas  South Korea
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how do you think the latfets will fare in this circuit?
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