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Capacitor multiplier supply for ALEPH 3
Capacitor multiplier supply for ALEPH 3
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Old 16th April 2001, 06:52 PM   #1
hifi is offline hifi  Sweden
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hello, Im currently building an aleph 3 (the aleph 5 run to hot om my heatsinks) and im curios about building i supply with a capacitor multiplyer. but in not certain of how the circuit operates i only know that it uses the "miller" effect. It should be quite ideal when the aleph is a class A amp and draws a constant current.


I have found an article :http://www.sound.au.com/project15.htm
witch is quite informing. but i need a supply that can handle +-25V and about 2A. and im not sure that TIP3055 and TIP2955 can handle that?.... and i wonder can you "overkill" the circuit with a to high multiple ratio ? and will i need a soft start for this kind of a circuit as i would for a real 1F-2F cap?. it belive TIP3055/BD139 in an darlington config will result in an hfe of about 3500 that times 470 is a quite nice capasitance....1,5F

and can i change the "real" output and input cap to 22 000F variants (got a good stock of them) ?...the original uses a 4700 and an 1000 cap for that.


/micke
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Old 16th April 2001, 08:41 PM   #2
Geoff is offline Geoff  United Kingdom
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Micke

The Aleph does not draw a constant current from the power supply. The current in the supply rails, under load, will vary from near zero to twice the quiescent current (see my postings in other threads, Zen v Trimodal and A75 Mono).

The capacitor multiplier circuit will work well in your application, though use a complementary rather than darlington arrangement (ie a pnp pass device in the +ve supply and an npn in the -ve supply). This will reduce the voltage drop across the multiplier.

There should be no problems using your 22000uF capacitors on both the input and output of the circuit (though see the following re pass transistor). The initial diode peak current will be little worse than that due to the 22000uF input capacitor.

Regarding the pass transistors, the TIP2955/3055 should be adequate if you are using separate supplies for each channel since the maximum current draw will be 4A (assuming an Iq of 2A) and the voltage drop across the transistor will be about 3V. However, I would strongly recommend something a little more robust, preferably in a case with a better thermal characteristic. This will definitely be neccessary if you are using only a single supply for two amps.

Geoff
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Old 16th April 2001, 09:39 PM   #3
hifi is offline hifi  Sweden
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I will use separate multiplyer for each channel, but would there be any benefit in increasing the multiplying cap for larger capacitance say like from 1,5F(470) to 3F(940F)?

/micke

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Old 16th April 2001, 10:01 PM   #4
hifi is offline hifi  Sweden
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but if i skipp the darlington arrangement it would result in a rather low multiple factor say TIP2955 att about hfe 25-70 with bd139 in a darlington arrangement it will be
160x25=4000 thats a rather hefty difference.

/micke

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Old 16th April 2001, 10:05 PM   #5
Geoff is offline Geoff  United Kingdom
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Micke

If you are using the 'basic' capacitance multiplier in the ESP Audio Pages Project, increasing the base capacitance form 470uF to 1000uF will reduce the rms ripple voltage from about 2.5mV to about 1.25mV at a 4A current draw and with your 22000uF capacitors on the input and output. However, if you are using the 'improved' version with the additional filtering, my simulations show that increasing the base capacitance will actually cause the rms ripple to increase from about 350uV to 400uV.

The 'improved' version of the multiplier circuit needs more careful 'tuning' so as to get the full benefits of the additional filtering. Increasing the capacitance sizes without altering the associated resistances does not necessarily give any improvement in smoothing.

Hope this helps.

Geoff
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Old 16th April 2001, 10:29 PM   #6
Geoff is offline Geoff  United Kingdom
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Micke

Your second query was posted whilst I was replying to your first one, hence the separate replies.

You are going to need both pnp and npn pass transistors whichever arrangement you use. The only difference is the supply rail in which they are used. Anyway, I'm not sure there is a problem as the data sheets I have for the TIP2955/TIP3055 show very similar hFEs for these two devices. If you are concerned about the total gain, use drivers and/or pass transistors with a higher hFE, eg MJE15029/MJE15031 drivers and MJL3281A/MJL1302A power transistors (these are only examples, there are many other altenatives).

You could also use MOSFETs as the pass transistors. These could be the same type as the ones in your Aleph output stage (particularly if you have some left over after matching). Some people prefer to keep to the same device in both the output stage and any regulator or similar feeding the amp.

Geoff.
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Old 16th April 2001, 11:18 PM   #7
hifi is offline hifi  Sweden
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Well i wouldnt know how to redesign the circuit for Mosfet:s but yes i got quite a good stock of them left.
Is it hard to remake the multiplier with mosfets? would it impeed operation?...


yes i know i will need both NPN and PNP devices but i have made the layout for the circuit using the darlington config but i havnt etched it so it is easily reconfigurable.



/micke
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Old 17th April 2001, 01:04 AM   #8
Geoff is offline Geoff  United Kingdom
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Micke

Reply by email, shortly.

Geoff
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Old 17th April 2001, 09:57 PM   #9
Asen is offline Asen  Bulgaria
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Default PSU

I have just one question here.
Why Nelson himself doesn't use regulated PSU in the Aleph series? It's cheeper, with lower noice... All looks fine at first glance. I have bitter experience with regulated supplies for OPamps. I tried to make some upgrades on my CD player. The result was that I put my previous configuration back. I think that sometimes "just caps" is the better solution.

[Edited by Asen on 04-17-2001 at 04:02 PM]
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Old 17th April 2001, 10:47 PM   #10
Geoff is offline Geoff  United Kingdom
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Asen

We're not talking about regulators here, merely a way of achieving a high effective capacitance without the cost and bulk of very large capacitors.

Geoff
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