redesign of leach amp pcb for integrated TO-247 output devices

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#41
Jens:

For the inrush current, you can try to use thermistors, as used in the Pass Labs Aleph design. Look at the service manuals at:
http://www.passlabs.com/aleph.htm
Look at the power supply implementation with the thermistor.

The ones used are the Keystone CL-60 10 ohm thermistor.

The specs are here:
http://www.thermometrics.com/assets/images/cl.pdf


fcel:
I just unpacked the box with my boards. They are mostly soldiered, and I will finish them up tonight. My chassis is still in the school lab, and I looked at it yesterday. I am hoping to progress on it this friday.

--
Brian
 
#43
The inrush current is a combination of A+B. The high magnetizing inductance of the transformer core requires a higher instantaneous current to build the flux density inside the core and....the charging of empty filter caps. When the caps are empty, it looks like a short circuit until they are charged to a higher level. To reduce the amount of inrush current the initial current path is limited in some way usually with a large power resistor so that you are dictating the maximum current allowed to inrush then after a brief moment when the filter caps are charged and the flux is built within the core of the transformer the limiting resistor is switched out with a relay. I have a two channel Leach SuperAmp with a 1500VA toroid and two 55k uF capacitors. When I turn this thing on it draws a huge amount of current. The amount of inrush current can be limited by turning the unit on at exactly the peak of the line voltage (good luck trying this one). The inrush current is at a maximum when going through the zero-crossing because the current is highest at that point. If a large power supply is turned on like yours or mine without any inrush limiting close to this zero crossing it will trip your house breaker. My home and other homes I have tried it on which have tripped are 120V / 15 lines. It is a good idea to use inrush protection because it is inconvenient to have to reset the breaker every time you want to listen to audio....Good luck

BeanZ
 
#44
Startup thing

Hi again,

Right, this is my plan.

Two relays.

The first to turn on the mains, but running through 2 resistors, the second relay is turned on when the voltage on the caps is 1/3 up and thereby shorting the resistors making the startup complete.

Would that ever work ?

\Jens 🙂
 
#46
Startup

Hi Brian

The reason for the first relay is simpel:

My preamp has two control outputs. The first is a power on signal that I'll use for just that, and the second is acitvated when muted.

I'll use them both so the amp will be controlled by the preamp.

\Jens
 
#48
Freq response.

I found the error :headbash:

The standing current in the output was too low resulting in a bad high freq. response.

Now it's flat to about 40 kHz 🙂

On monday I'll get the school's workshop to make four small signal PCB's, and hopefully they will all work.

Also working on the control cuircuit for the amp :scratch:

\Jens
 
#49
Supply board

Today I made the sypplyboard.... There will be a bank of 6 * 10000µF 80V caps pr. channel. In all 240 mF.

I also have 20000µF on each outputboard. I hope it will be enough to make a decent railquality.

I'll post pics later 🙂

\Jens :xfingers:
 
#51
I have my boards mostly populated, and will match my input transistors, zeners and test the boards. Pictures are at: http://brian.darg.net/leachpcb

--
Brian
 

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#59
Listening to ½ an amp

Hi

Great to hear your amp is working Brian, how much are the boards ?

I now have two of four PCB's fully populated ad playing....sweet 🙂

I'll post pic's later.

There are no problems, and the sound is great (I'm problably biased but newer the less it's great)

\Jens
 
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