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Old 17th February 2003, 06:31 PM   #1
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Default Lowering Supply voltage of a Toroid

Is this possible? How so? I think I have come to a conclusion on my lack of bass. I am running 35V rails on my gainclone, and my speaker dips down to about 4.5 ohms at 35 Hz, which could force the gainclone into not operating as it should in this reigon.

-Paul
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Old 17th February 2003, 06:58 PM   #2
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Ummm...can you please restate the question?

Tim
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Old 17th February 2003, 07:01 PM   #3
UrSv is offline UrSv  Sweden
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Wouldn't that be only when driven that hard? With a lower rail voltage wouldn't be closer to clipping and the nasty artifacts of all the protection circuitry reacting.

I have however never understood why the graph in the datasheet is interpreted the way it is although it may seem reasonable. I just think of it as the limits versus rail voltages for continuous use. When rails are lower you can supply maximum rail dependant power into lower loads. That however for me does not say much but maybe I am slow. I just see the higher rails as the possibility to supply the maximum power intermittently into higher loads and still pretty good. I will run my GCs with 35 V rails.

I would seek the solution elsewhere before lowering the rails. Bass shy would not be the result IMHO if you were limiting the way the graph suggests. Unacceptable sound would be.
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Old 17th February 2003, 07:17 PM   #4
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Default Re: Lowering Supply voltage of a Toroid

Quote:
Originally posted by PaulHilgeman
Is this possible? How so? I think I have come to a conclusion on my lack of bass. I am running 35V rails on my gainclone, and my speaker dips down to about 4.5 ohms at 35 Hz, which could force the gainclone into not operating as it should in this reigon.

-Paul
Hi Paul,

the use of a series choke, resistor or thermistor between the bridge rectifier and the smoothing capacitors will lower the voltage a little and also decrease ripple. However, I don't think this will be enough in your case. You could unwind a few turns from the secondaries of the transformers. This is possible with a standard E-I transformer and may be possible in the case of toroids as well. Peter Daniel, I think, has mentioned this a few times and may be able to give practical details.

If you don't want to go to all this trouble then new transformers with lower secondary voltages ( 24-0-24 V seems to be recommended for gainclones ) may be a more convenient solution.

James
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Old 17th February 2003, 07:19 PM   #5
UrSv is offline UrSv  Sweden
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Default Re: Re: Lowering Supply voltage of a Toroid

Quote:
Originally posted by nemestra


Hi Paul,

the use of a series choke, resistor or thermistor between the bridge rectifier and the smoothing capacitors will lower the voltage a little and also decrease ripple. However, I don't think this will be enough in your case. You could unwind a few turns from the secondaries of the transformers. This is possible with a standard E-I transformer and may be possible in the case of toroids as well. Peter Daniel, I think, has mentioned this a few times and may be able to give practical details.

If you don't want to go to all this trouble then new transformers with lower secondary voltages ( 24-0-24 V seems to be recommended for gainclones ) may be a more convenient solution.

James
Choke, resistor or thermistor would not be recommended for this amp as that would cause severe dynamic compression IMHO. Actually it seems he is running 24 V secondaries already. 18 V would be the key to safe graph areas giving some 23-24 VDC at load.
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Old 17th February 2003, 07:27 PM   #6
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Default Re: Lowering Supply voltage of a Toroid

Quote:
Originally posted by UrSv


Choke, resistor or thermistor would not be recommended for this amp as that would cause severe dynamic compression IMHO.
If the filter capacitance was increased from the 1000 - 4700 uF range commonly used for gainclones up to a more 'normal' 10000 - 20000uF value then all of the above should work fine.


Quote:
Originally posted by UrSv


Actually it seems he is running 24 V secondaries already. 18 V would be the key to safe graph areas giving some 23-24 VDC at load.
Agreed.

James
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Old 17th February 2003, 07:32 PM   #7
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Dear UrSv
I don't know which chip you are using, but what i have seen in application notes of National and Thomson may hold true for all monolithic power ICs.
These ICs are tracking their power consumption and their Safe Operation Area by close monitoring the "junction temperature", that is point(s) inside the chip. Some are using global temperature and some point temperature tracking.
If the load is 4 Ohms, the internal power consumption rises high , so internal temp rises high very fast (at a rate that does not reflect to the temp of the heatsink), so internal temp. monitoring activates safety mechanisms, which in most cases are either cliping the peaks or are lowering the drive of output devices. This may form a mechanism of reduced bass at high levels with 4 Ohms (low frq has longer period, thus more time for activation). The chip manufacturers claim the onset of safety mechanisms activation at much lower power output than the nominal specified(approx at 1/2-2/3 depending on the signal form).
So for 4 Ohm load, they recomend lower supply voltage (+/_28V Volts, against +/_ 37V for 8 Ohm) if maximum output is to be acheived.
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George
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Old 17th February 2003, 07:33 PM   #8
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OK, sounds good, I am indeed running 25V secondaries. I will not pursue this option anymore, as the power supply (at least the transformer part of it seems fine).

I will try to increase the capacitence, and see where that takes me.

-Paul
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Old 17th February 2003, 07:45 PM   #9
Elkaid is offline Elkaid  Canada
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If you wish to lower voltage of your secondaries, here's an easy tip.

Add a winding connected in serie with your secondary.
This way, you can increase or decrease voltage simply by changing the number of winding around your toroid.

Do this twice... once for each of your secondaries

If you want to increase voltage, connect your winding on one the the secondary wire and vice-versa if you wish to lower voltage.

Hope this helps !
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Old 17th February 2003, 09:07 PM   #10
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Default Re: Lowering Supply voltage of a Toroid

Quote:
Originally posted by PaulHilgeman
Is this possible? How so? I think I have come to a conclusion on my lack of bass. I am running 35V rails on my gainclone, and my speaker dips down to about 4.5 ohms at 35 Hz, which could force the gainclone into not operating as it should in this reigon.
Paul, can you give any explaination of how your idea has accured? What things control the bass reproduction?
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