Tag: Salas Shunt HV regulator

Adjusting the shunt regulator

One of the problems I found when using the 4-65a SE amp was that my version of the Salas SSHV2 drifted significantly with temperature. This was due to the 01N100D characteristics (see extract from datasheet below). We can see that @ -1.5V VGS the temperature dependency is as much as 50mA/100°C. With the smaller heatsink I had before and the significant voltage drop given raw supply voltage levels this caused a problem:

01N100D temperature dependency
IXYS IXTP01N100D datasheet extract

I then reduced the input raw voltage level to 300V to ease the power dissipation across this FET. This was not sufficient so I proceeded to look at various things on the regulator as described below:

Change log

  1. Replaced M1 for DN2540. The DN2540 has a better temperature response. The voltage levels now allowed me safely use the DN2540 and no need for a 01N100D.
  2. Added bigger heatsinks for M1 and M3. Even 2.5W across M1 would need a bigger heatsink if we are looking to run the CCS as high as 90mA.
  3. Removed TP resistor to allow higher CCS current
  4. Set CCS current to 85mA
  5. Load will be now 30mA per channel (30mA each 46 driver valve)
  6. Set output votage to 270V

Image

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Testing the SSHV2

All tested well in the workbench. I used an external CCS set at 60mA and the output voltage stabilisation was rock solid at 270V. Temperature of the heat-sink was around 40-45°C after 30min of continuous use.

Back in the 4-65a SE Amp, the raw supply level at full load was 297V. The regulator played nicelly at 270V and the CCS current drifted only 5mA from 90mA down to 85mA after 2 hours of continuous play. The temperature of the CCS increased only to 47°C whereas the shunt FET got up to 54°C given the continuous 7W dissipated on it. I may try to reduce the CCS current a tad to ease here.

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The regulator is fitted back into the 4-65a SE amp

Played the amp for about 2 hours and slowly started to appreciate more and more the sweet sound of this beast. Bass has increased significantly in my systems and previously haven’t been able to extract the deep bass out of the SE amp through my Fostex FE167E full range drivers.

I’m really going to enjoy this amp for a while until I start looking at changes. Oh yes, many come to mind, but easy for now. Other projects are awaiting for a long time so far.

Ale