My take on a discrete shunt voltage regulator - Page 4

Tham · 29th October 2009, 04:12 AM

Iko, will try to get the parts recommended in the schematics...have some irf3205 now and wonder they can be used.

ikoflexer · 29th October 2009, 04:21 AM

I experimented with the irf3205 before the irfbc40 and managed to fry a few of them when taking them to some extreme currents. They have higher input capacitance, which is not so desirable. Still, I don't think that you'd have problems getting them to work. At the moment my prototype v2 uses irfbc40 and works fine with them.

Tham · 29th October 2009, 04:26 AM

Iko, it will be low current shunts and I will put them in to try while sourcing for irfbc40. Will let you know how it goes when I built them

.

ikoflexer · 29th October 2009, 04:49 AM

Cool, looking forward to some action

HiFiNutNut · 06:48 AM

Having not had much time in the past a few days so it has been a bit slow.

I completed the build a couple of hours ago and have not heard it yet. No Bang, no smoke.

Mine is based on the earlier schematic in which all current sources were 2sk170 with the rest identical. This time the 2sk170 came from Spencer's batch.

For the Vref I had 27k resistors and 2k trimpot between gate and source of the 2sk170. I found this was good for only 17V plus unless I increase the trimpot to 5k. So I reduced the resistors to 20k and kept the 2k trimpot and the voltage available for adjustment started at 12V (2k on trimpot), which was good for me. Lowering the trimpot increases the voltage.

I have turned it on and off a couple of times.

The initial CCS current was set to very low with a 68k Vref resistor and a 2k trimpot set to about 1.2k in the CCS. The current was not measurable and the DMM showed 0mA. However, the voltage was regulated.

When I increased the current to 130mA a few minutes later the shunt heatsinks got very hot. I could not touch it for more than a fraction of a second. I guess it was hot enough to boil an egg. So I turned it off immediately. The heatsinks are rated at 7 degree W. For at most 2W power it got so hot therefore I thought it was definitely not right.

When cooled down I turned it back on and reduced the CCS current to 10mA. Then started to increase it. The CCS current drifted a lot. Eventually settled on above 100mA after 30mins. However, the heatsinks did not get hot this time, only warm.

Turned it on for the third time and had it run for 15mins now. Found the voltage to be very stable since turned on. It did not vary much at all. Maybe only 0.02V at most. The CCS started at 85mA only, and it is now at 93mA. Will it gradually increase to over 100mA? Time will tell.

So other than some shifts in CCS current things seem to be fine. I will turn it off and on one more time then connect it to the circuit and have a listen. It is promising as long as this thing does not oscillate.

Salas mentioned that he needed to solder to gate resistor right at the transistors to prevent oscillation in v1.1. In my PCB design I tried to do so. But the heatsinks are T03 type so the MOSFET legs are quite long. I have not soldered the resistor on the upper part of the leg so there can be a bit of inductance there. I will see if it oscillates. I don't have a scope so I can only judge by ear which is nearly impossible unless it gets the hash down to the audioband. Ikoflexer, I have seen some of your pictures previously and it seems that you soldered them point to point so you may not get oscillation. For me, it is a different story. Fingers crossed.

I suspect that the 2sk170 is not very stable with temporature.

HiFiNutNut · 29th October 2009, 06:44 AM

Another 15 minutes past the CCS current has increased to 105mA and 102mA. They were about 85mA when turned on. I will keep it on for another 30 minutes.

HiFiNutNut · 29th October 2009, 07:04 AM

Some minutes passed now. The CCS current did not increase but dropped to 102mA and 100mA.

By the way, in my PCB design the components are placed as far away from the hestsinks as possible. Since the heatsinks are only warm, they should not affect the temporature of the components. I still think the the 2sk170 is not very stable with temporature.

HiFiNutNut · 29th October 2009, 08:59 AM

I have now given it an hour listening. The voltage is stable. The heatsinks are just warm.

Sounds good. I have built 4 regulators in the past couple of months. They all sounded a bit different. Over all everyone I built was better than its previous one. Is there somebody who is going to publish a new regulator soon?

HiFiNutNut · 29th October 2009, 09:03 AM

I have a 10uF Nichicon Gold at the output. I got it from my old NAD541 CD player. Given it is a 10uF cap, it must have an ESR about / over 1R.

Since I basically like Rubycon ZL only, I am thinking about installing a 25uF/50V ZL there, which has an ESR 0.34R.

ikoflexer · 29th October 2009, 12:12 PM

Good job!

Indeed, as you noticed, the jfets are very sensitive to temperature variations; well known fact! Your circuit will probably boxed at some point, so the temperature will be more constant after warm up. Remember that if you have adequate heat sinks (read large) you can increase the current. My and others' experiments show correlation of higher current with better sound (lower output impedance). Of course this should be done with care, to avoid oscillation; I mean, at some point the circuit layout matters.

Again, well done and thanks for the report! When you got a chance, remember, we like pictures

It inspires us!

29th October 2009, 06:37 AM	#35
HiFiNutNut diyAudio Member Join Date: May 2004 Location: Sydney	Having not had much time in the past a few days so it has been a bit slow. I completed the build a couple of hours ago and have not heard it yet. No Bang, no smoke. Mine is based on the earlier schematic in which all current sources were 2sk170 with the rest identical. This time the 2sk170 came from Spencer's batch. For the Vref I had 27k resistors and 2k trimpot between gate and source of the 2sk170. I found this was good for only 17V plus unless I increase the trimpot to 5k. So I reduced the resistors to 20k and kept the 2k trimpot and the voltage available for adjustment started at 12V (2k on trimpot), which was good for me. Lowering the trimpot increases the voltage. I have turned it on and off a couple of times. The initial CCS current was set to very low with a 68k Vref resistor and a 2k trimpot set to about 1.2k in the CCS. The current was not measurable and the DMM showed 0mA. However, the voltage was regulated. When I increased the current to 130mA a few minutes later the shunt heatsinks got very hot. I could not touch it for more than a fraction of a second. I guess it was hot enough to boil an egg. So I turned it off immediately. The heatsinks are rated at 7 degree W. For at most 2W power it got so hot therefore I thought it was definitely not right. When cooled down I turned it back on and reduced the CCS current to 10mA. Then started to increase it. The CCS current drifted a lot. Eventually settled on above 100mA after 30mins. However, the heatsinks did not get hot this time, only warm. Turned it on for the third time and had it run for 15mins now. Found the voltage to be very stable since turned on. It did not vary much at all. Maybe only 0.02V at most. The CCS started at 85mA only, and it is now at 93mA. Will it gradually increase to over 100mA? Time will tell. So other than some shifts in CCS current things seem to be fine. I will turn it off and on one more time then connect it to the circuit and have a listen. It is promising as long as this thing does not oscillate. Salas mentioned that he needed to solder to gate resistor right at the transistors to prevent oscillation in v1.1. In my PCB design I tried to do so. But the heatsinks are T03 type so the MOSFET legs are quite long. I have not soldered the resistor on the upper part of the leg so there can be a bit of inductance there. I will see if it oscillates. I don't have a scope so I can only judge by ear which is nearly impossible unless it gets the hash down to the audioband. Ikoflexer, I have seen some of your pictures previously and it seems that you soldered them point to point so you may not get oscillation. For me, it is a different story. Fingers crossed. I suspect that the 2sk170 is not very stable with temporature. Last edited by HiFiNutNut; 29th October 2009 at 06:48 AM.

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29th October 2009, 04:12 AM	#31
Tham diyAudio Member Join Date: Jun 2006	Iko, will try to get the parts recommended in the schematics...have some irf3205 now and wonder they can be used.

29th October 2009, 04:21 AM	#32
ikoflexer diyAudio Moderator Join Date: May 2008 Location: Toronto	I experimented with the irf3205 before the irfbc40 and managed to fry a few of them when taking them to some extreme currents. They have higher input capacitance, which is not so desirable. Still, I don't think that you'd have problems getting them to work. At the moment my prototype v2 uses irfbc40 and works fine with them.

29th October 2009, 04:26 AM	#33
Tham diyAudio Member Join Date: Jun 2006	Iko, it will be low current shunts and I will put them in to try while sourcing for irfbc40. Will let you know how it goes when I built them .

29th October 2009, 04:49 AM	#34
ikoflexer diyAudio Moderator Join Date: May 2008 Location: Toronto	Cool, looking forward to some action

29th October 2009, 06:44 AM	#36
HiFiNutNut diyAudio Member Join Date: May 2004 Location: Sydney	Another 15 minutes past the CCS current has increased to 105mA and 102mA. They were about 85mA when turned on. I will keep it on for another 30 minutes.

29th October 2009, 07:04 AM	#37
HiFiNutNut diyAudio Member Join Date: May 2004 Location: Sydney	Some minutes passed now. The CCS current did not increase but dropped to 102mA and 100mA. By the way, in my PCB design the components are placed as far away from the hestsinks as possible. Since the heatsinks are only warm, they should not affect the temporature of the components. I still think the the 2sk170 is not very stable with temporature.

29th October 2009, 08:59 AM	#38
HiFiNutNut diyAudio Member Join Date: May 2004 Location: Sydney	I have now given it an hour listening. The voltage is stable. The heatsinks are just warm. Sounds good. I have built 4 regulators in the past couple of months. They all sounded a bit different. Over all everyone I built was better than its previous one. Is there somebody who is going to publish a new regulator soon?

29th October 2009, 09:03 AM	#39
HiFiNutNut diyAudio Member Join Date: May 2004 Location: Sydney	I have a 10uF Nichicon Gold at the output. I got it from my old NAD541 CD player. Given it is a 10uF cap, it must have an ESR about / over 1R. Since I basically like Rubycon ZL only, I am thinking about installing a 25uF/50V ZL there, which has an ESR 0.34R.

29th October 2009, 12:12 PM	#40
ikoflexer diyAudio Moderator Join Date: May 2008 Location: Toronto	Good job! Indeed, as you noticed, the jfets are very sensitive to temperature variations; well known fact! Your circuit will probably boxed at some point, so the temperature will be more constant after warm up. Remember that if you have adequate heat sinks (read large) you can increase the current. My and others' experiments show correlation of higher current with better sound (lower output impedance). Of course this should be done with care, to avoid oscillation; I mean, at some point the circuit layout matters. Again, well done and thanks for the report! When you got a chance, remember, we like pictures It inspires us!

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