"The Wire AMP" Class A/AB Power Amplifier based on the LME49830 with Lateral Mosfets - Page 214 - diyAudio
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Old 8th April 2013, 09:32 PM   #2131
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Wow... that's a lot of amps & a lot of heat to disperse under high biasing. Reading a few articles about regulated supply design & demands from various sources online, it came across that most aim at a providing constant current draw of 1/3 peak (or RMS) and let the Caps deal with the peak load.

However, the better way looks to have the supply being able to provide 100% peak or more, and having the Caps largely for smoothing!?

I could do with getting some proper books on the subject.


DPS-600, I understood that it could provide 6A constant draw, but had 13A short term in my head. Mine are mounted on a single aluminium sheet 250mm x 250mm x 3mm and will be raised 10mm off the chassis base.

I've been looking at supply needs as a precaution against my mishandling of the DPS-600 units I have, plus for other projects.
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Old 12th April 2013, 11:27 PM   #2132
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Question Amp's Mute Function

More Questions:

I know there was a discussion about audible on/off thumps etc. during power-up/down... In case of a minor incident, will having the LME muted during these stages stop anything being passed through to the speaker?

Currently the Mute Function goes into Play Mode as the LME's Vcc (55V on mine) reaches 12V(?). Reading the datasheet, I've seen the max Imute, and that it says Vmute can be powered from Vcc but no mention of a max V... Within the amp's mute circuit would it be possible to change Z1 from 12V to say 39V or 43V, so that switching to/from Play Mode occurs once the rails are much higher?

Obviously, the values of R38 & R53 would need to change in conjunction with Z1's Vz to keep near the current Imute value... Would C75 also need changing to accommodate the higher V's?

This on top of a simple switch, when I want to mute play back.
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Last edited by BuildMeSomething; 12th April 2013 at 11:31 PM.
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Old 14th April 2013, 01:27 AM   #2133
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Quote:
Originally Posted by BuildMeSomething View Post
More Questions:

I know there was a discussion about audible on/off thumps etc. during power-up/down... In case of a minor incident, will having the LME muted during these stages stop anything being passed through to the speaker?

Currently the Mute Function goes into Play Mode as the LME's Vcc (55V on mine) reaches 12V(?). Reading the datasheet, I've seen the max Imute, and that it says Vmute can be powered from Vcc but no mention of a max V... Within the amp's mute circuit would it be possible to change Z1 from 12V to say 39V or 43V, so that switching to/from Play Mode occurs once the rails are much higher?

Obviously, the values of R38 & R53 would need to change in conjunction with Z1's Vz to keep near the current Imute value... Would C75 also need changing to accommodate the higher V's?

This on top of a simple switch, when I want to mute play back.
Hi Paul,

I don't think the mute in the LME chip will fix all of these cases that produce spurious noises during power off. I found some of the posts where this was discussed previously and here is a few of the ones that I think clarified the issues:

Quote:
Originally Posted by opc View Post
That is true... I should clarify that the LF thumps only occur during a hard power down (loss of power from a power outage or direct un-plug). If you use the correct shutdown pin on the DPS600 then there are no transients on start-up or shutdown.

Cheers,
Owen
And this might give you some more food for thought on options for the mute circuit.


Quote:
Originally Posted by opc View Post
You don't need the zener if you calculate the resistor value properly:

IMUTE = (VMUTE VBE) / (1kΩ +RM) where VBE ≅ 0.7V

The problem lies in the fact that the calculated resistance only really works with one supply voltage (over a reasonable range) and needs to be adjusted as per the above formula for different supply voltage.

Using the zener simplifies this as you can use any rail voltage you want and the current into the mute pin is always the same.

If you were designing this into a product with a set rail voltage, it would be cheaper and easier to simply calculate the right resistance and omit the zener.

Cheers,
Owen
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Old 14th April 2013, 04:36 AM   #2134
Oland is offline Oland  Russian Federation
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Simple "A",Full description can send ,from journal "audioXpress" 7/11
A 100-Watt Class-A
Power Amplifier
A 100-Watt Class-A .jpg
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Old 14th April 2013, 10:43 AM   #2135
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@ hochopeper: Yep, those are some of the post that I was thinking of and had read. Shows that full Vcc can be used for Vmute, though from TI's reference docs a lower Vmute looks to be a preference.

One TI doc (snaa057a) for a proposed +/- 72V unregulated power supply for the LME49810/11/30, uses a similar mute circuit to opc's design, but sets Vmute at 3.9V and 'Play Mode' switching at 54.9V using two zeners.

Interesting paragraph from the doc:
Quote:
5.3 Power Up/Down Mute Control

The Mute function of the audio amplifier input stage IC is used for a completely quiet turn on and turn off. The amplifier is held in Mute mode until the voltage supplies are nearly stable and also goes into Mute mode once the supplies have collapsed below a determined voltage. With 40,000μF of supply reservoir capacitance per rail the amplifier can continue operation for some time after the mains power has been removed. The mute control circuit removes the drive signal for a quicker turn off well before the supplies have collapsed down below the minimal operating voltages. The amplifier will turn off quietly and smoothly without any undesired noise.
Just trying to think of simple options as a just in case, doesn't take away from the need to correctly shut down the amp & supplies.

Paul
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Old 14th April 2013, 12:09 PM   #2136
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Hi All,
I read some comments just now (I have not seen activity or listening tests with the DPS-600 in this thread for a long time).
Some Info: All DPS-600 in this GB (i know used in class AB), and then were tested with a load of 2x360mA (360mA per rail), during the on / off and temperature produced. (this means, 720mA at 55V, seen from the side of the power-unit).
All had no spike while turn on / off.
With this constant load, mounting vertically to the DPS-600 on an aluminum base 180x40x3mm with an ambient temperature of 28 , the temperature is balanced at 44 , 16 delta heat is not bad for this type of smps I remember does not use a pwm.
-----------------------------------------------------
Many DPS-600 at + /-68V (not in this GB), allow you to get on with mosfet amps, 400w @ 4R without problems.
I do not agree to try and measure the smps, with constant resistive loads to see at full power. I accept this for only a few investigations
We use to active load (instrument similar to fast mosfet amplifier, driven by pattern from the PC, so you can see the exact behavior and many parameters, ideal when it works as an amplifier.

Regards
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Old 14th April 2013, 12:25 PM   #2137
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Quote:
Originally Posted by AP2 View Post
Some Info: All DPS-600 in this GB (i know used in class AB), and then were tested with a load of 2x360mA (360mA per rail), during the on / off and temperature produced. (this means, 720mA at 55V, seen from the side of the power-unit).
All had no spike while turn on / off.
With this constant load, mounting vertically to the DPS-600 on an aluminum base 180x40x3mm with an ambient temperature of 28 , the temperature is balanced at 44 , 16 delta heat is not bad for this type of smps I remember
Thanks for this description and temp measurement data Roberto!

Was there any thermal interface material between DPS-600 and the alu base?
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Old 14th April 2013, 12:45 PM   #2138
AP2 is offline AP2  Italy
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Quote:
Originally Posted by hochopeper View Post
Thanks for this description and temp measurement data Roberto!

Was there any thermal interface material between DPS-600 and the alu base?
No, but surface is well flat. fixed well with 2x4MA.
this alluminum rectangle, we use with both dps-600/500 in the laboratory.
For mute on wire amp, a good solution can be a window comparator on vcc rail. if<(vcc-30%) then switch. is better add a costant=1Sec. just in case of unregulated power supply.

Last edited by AP2; 14th April 2013 at 12:52 PM.
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Old 14th May 2013, 09:43 PM   #2139
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I have just installed my boards into the old carcass of my monoblock amps. I just "tacked" in the power connections etc for the moment because I will build a new chassis for the amps and use them with DPS 500 power supplies I have ordered from AP. They work but I have the mother of all hums, likely ground loop induced which I will need to play with to fix.

In relation to that, where are people grounding their amps to the chassis? I have run a ground wire from the high current power ground input to chassis. Another alternative would be from the centre of the off board filter caps. I might need to experiment with lifting the board from chassis ground with a low ohm resistor too. Time to get out the clip leads.

Finally thanks to Owen for all the hardwork, and the great boards.

Rob.

Last edited by Robert F; 14th May 2013 at 09:52 PM.
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Old 15th May 2013, 03:00 PM   #2140
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Robert F View Post
.......... I might need to experiment with lifting the board from chassis ground with a low ohm resistor too..........
No No No !!!
the connection from Main Audio Ground to Chassis may have to pass Fault Current if something really serious goes wrong with your mains powered equipment.
A resistor used for this connection potentially kills any one who touches any other component connected to that "lifted ground" amplifier.
This is a DEATH TRAP.

Do not ever put a resistor in a Fault Current escape route.
Read all the many Threads here, or go to ESP and read about it there.
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