John Curl's Blowtorch preamplifier part II - Page 3510 - diyAudio
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Old 15th February 2013, 01:54 AM   #35091
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Sorry, Esperado, that paper states the design 'rules' that I design by.
Everyone else, if you want to learn something important, please look at this paper.
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Old 15th February 2013, 02:21 AM   #35092
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by Esperado View Post
Virtual ground ? (Does not work so good because distortion.).
An other solution (don't know the word in English) is crossed feedback between the two sides.
There are several.... Master-Slave or dual Tracking regulator circuits are some that minimise differences between the + and - rail value.

Another is a simple way I introduced to audio is to put a large value C across the + to - supplies.

These means are not complex nor difficult to impliment and greatly reduces the circuit's need for extream PSRR's.

Thx-RNMarsh

Last edited by RNMarsh; 15th February 2013 at 02:41 AM.
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Old 15th February 2013, 02:30 AM   #35093
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Quote:
Originally Posted by RNMarsh View Post
Another is a simple way I introduced to audio is to put a large value C across the + to - supplies.
Nice simple idea. kind of virtual ground addition. Half the value of each rail caps, in order to get the same C for the 3 ?
Cap between + & - followed by simple stabilization of each stage, like emitter follower ?
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Last edited by Esperado; 15th February 2013 at 02:36 AM.
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Old 15th February 2013, 03:46 AM   #35094
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by Esperado View Post
Nice simple idea. kind of virtual ground addition. Half the value of each rail caps, in order to get the same C for the 3 ?
Cap between + & - followed by simple stabilization of each stage, like emitter follower ?
A value equal to the rail shunt caps works best. This is easy to do on line level circuits.

On a SIM of a power supply for a 250W power amplifier, two 10,000 mfd caps were bridged with another 10,000 mfd cap (2X voltage rating, of course) and when an 8 ohm load was switched across one rail or the other, the delta or rail voltage difference was minimal. A physical supply was made with same results. To do same with a high current tracking regulated power supply would be impractical in a consumer product.

When the delta is zero, there is no difference in rail voltages and therefore, no affect on the circuit and is as if the PSRR was very high. This allows Current feedback circuits to be more effective in audio circuits.


Thx- RNMarsh
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Old 15th February 2013, 04:39 AM   #35095
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Thanks, Richard. I wonder if we need C2 & C3 ?
And if it would be better the cap after the regulation ?
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File Type: jpg psu.jpg (33.4 KB, 175 views)
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Last edited by Esperado; 15th February 2013 at 04:50 AM.
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Old 15th February 2013, 05:17 AM   #35096
gpapag is offline gpapag  Greece
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Christophe
Richard means the cap at the output of the psu.

It works best when placed right at the load(s). A cap across +/- at each amplifying stage or each op amp IC

In practice, the capacitance of this C can be small (1/10th of the rail to ground caps or even less) since the unbalanced currents it has to deal with are small compared to the working rail currents.

George
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Old 15th February 2013, 05:35 AM   #35097
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Originally Posted by gpapag View Post
Richard means the cap at the output of the psu...OPA
I was thinking about a 2 channels power amp.
WIl try at each amp board rails. (Ça peut pas faire de mal :-)
I have pain to figure out the currents of such a configuration in dynamic mode, i don't know why.
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Last edited by Esperado; 15th February 2013 at 05:52 AM.
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Old 15th February 2013, 07:44 AM   #35098
RNMarsh is offline RNMarsh  United States
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Gpapag is correct: Place the cap where the amplifier needs it... at the output of the regulator. If no regulator -- as with a pwr amp output stage -- then place it across the rectifiers or the main filter caps.

With opamps, the value can be smaller of course as the dynamics on the +/- rails is smaller. But even so, a larger value with bypass works well.

Thx-RNMarsh

Note: Reason for using larger value --> besides cancelling D-M noise and transients on the rails, if one line went low, the bridging cap will discharge into that line to maintain the same level as before. Tendancy is to keep the + and - levels to be equal. The line may be drawn down but both rails will always be maintained at the same value.

Last edited by RNMarsh; 15th February 2013 at 07:57 AM.
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Old 15th February 2013, 08:13 AM   #35099
BV is offline BV  Slovakia
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Quote:
On a SIM of a power supply for a 250W power amplifier, two 10,000 mfd caps were bridged with another 10,000 mfd cap (2X voltage rating, of course) and when an 8 ohm load was switched across one rail or the other, the delta or rail voltage difference was minimal.
Would not be all improvements exactly the same, if You simply doubled value of existing capacitors, what is trivial?? And added bridging cap seems to dynamically push rail with lower loading to higher output voltage (adding ripple)..

Last edited by BV; 15th February 2013 at 08:29 AM.
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Old 15th February 2013, 12:57 PM   #35100
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As this is the Blowtorch thread, I might let you in on a design 'secret' that is in each of the power supply modules (up to 4) in the Blowtorch power supply.
We used 3 power caps as well, but we separated the single cap from the dual caps with a damped dual choke. This way, the input cap bears the majority of the input surge, and the 2 larger (in value) caps do most of the ground return.
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