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A possible approach to adding a silent start/shutdown to the ACA
A possible approach to adding a silent start/shutdown to the ACA
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Old 10th December 2018, 06:30 PM   #81
Mooly is offline Mooly  United Kingdom
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A possible approach to adding a silent start/shutdown to the ACA
Bias... as in the midpoint adjustment setting.

The midpoint voltage should rise and fall at the same rate for both amps and if it does then that means no difference in voltage exists between the two separate amplifier outputs. In practice that probably wont happen due to tolerances in caps and the semiconductors. Hopefully it will be fairly quiet though.
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Old 10th December 2018, 08:33 PM   #82
xrk971 is offline xrk971  United States
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A possible approach to adding a silent start/shutdown to the ACA
One way that I prevent turn on thump in almost any amplifier is to use a cap multiplier with a slow ramp up of output voltage. So in addition to providing ripple reduction of the power supply, it never has thump for turn on or off.

Pretty simple circuit (replace IRF610 with IRFP240 for higher currents) - this is design I got from Juma. I use this in almost all of my single rail amps now.

Click the image to open in full size.
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Old 26th December 2018, 08:00 PM   #83
anotherJoachim is offline anotherJoachim  Germany
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first of all, it's christmas time and i am a non electrician, so please be patient
I am just working on a ACA
Not the original one, but another one, also described here which has an old style PSU with a LM1084 voltage regulator.
Having no pops and also the advance of a cap multiplier makes me curious.
The situation is now that i have a bridge rectifier followed by the regulator.
First thing on the PCB is a 4700F cap
Can i just plug off the rectifier and pull in that little circuit before the regulator?
I suppose that would be what i can handle with my limited skills

Can i 'recycle' the 4700F cap on the regulator as C7 of the cap multiplier?
Best without screwing up the cap multiplier or the regulator
I have downloaded the Juma sheme and tried to mark what i think to do (see pic)



thanks Joachim
Attached Images
File Type: jpg cap-multi.jpg (36.6 KB, 114 views)

Last edited by anotherJoachim; 26th December 2018 at 08:04 PM.
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Old 26th December 2018, 08:26 PM   #84
Mooly is offline Mooly  United Kingdom
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A possible approach to adding a silent start/shutdown to the ACA
I can't quite follow what you are trying to do in particular 'plugging off the bridge rectifier'.

For a conventional power supply you need in order from left to right, the bridge rectifier and suitable reservoir cap (47,000uF in your diagram which seems a bit big tbh). Then you could add the cap multiplier and following that your original regulator.

You need to ensure the regulator still has enough voltage to work with once the multiplier is added.
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Old 27th December 2018, 08:19 AM   #85
anotherJoachim is offline anotherJoachim  Germany
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Quote:
Originally Posted by Mooly View Post
I can't quite follow what you are trying to do
that's because i am trying to explain things i do not know about in an language i did not speak

Quote:
in particular 'plugging off the bridge rectifier'.
the regulator and the ACA are both on the same PCB.
The rectifier is mounted on the case.
What i want to ask is where the right place for the cap multiplier is.
Between the regulator and the ACA or before the regulator.
The later one would be easy to handle.
Now i know. I will try to build that thing.

Of course C1 is way to big, it was only thought as an example.
I will read thte article i have stolen the pic from
Thanks for the advice with the voltage

reagrds Joachim



For a conventional power supply you need in order from left to right, the bridge rectifier and suitable reservoir cap (47,000uF in your diagram which seems a bit big tbh). Then you could add the cap multiplier and following that your original regulator.

You need to ensure the regulator still has enough voltage to work with once the multiplier is added.[/QUOTE]
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Old 27th December 2018, 08:28 AM   #86
Mooly is offline Mooly  United Kingdom
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A possible approach to adding a silent start/shutdown to the ACA
A cap multiplier added after a regulator will totally negate the final 'voltage regulation' of the regulator.

In other words the final voltage from the multiplier will vary with current drawn from the supply due to the finite impedance of the multiplier. That may or may not matter to you in this application.

Adding the multiplier before the regulator allows for increased ripple reduction (a good thing).

(Also remember that most voltage regulators like the LM1084 should not work into to large a capacitive load, 47 uF to 100uF is usually all that is required)
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Old 27th December 2018, 02:44 PM   #87
Mark Johnson is offline Mark Johnson  United States
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A possible approach to adding a silent start/shutdown to the ACA
Which is exactly the mistake Teddy Pardo made in the SuperTeddy Regulator. He connected the VR first ("upstream") and the CM second ("downstream") Oops!

Here is a link: SuperTeddyReg | DIY | TeddyPardo
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Old 28th December 2018, 01:42 PM   #88
anotherJoachim is offline anotherJoachim  Germany
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thanks a lot for all the informations.
Voltage will be the problem
Looks like i need other toroids.
Maybe i should first test the ACA like it is.

regards Joachim
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Old 28th December 2018, 02:41 PM   #89
Mooly is offline Mooly  United Kingdom
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A possible approach to adding a silent start/shutdown to the ACA
The recommended SMPS + ACA really is the best option for a current hungry Class A design. No mains related ripple and minimum noise/hash. Linear regulators and cap multipliers are hugely inefficient under these operating conditions.

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