In this post I use the term 'ground' loosely! My Tokin build is progressing well but I've come across a design consideration that's caused me to pause and give it some thought. As seen in the diagram (One of Randy's drawings) below all of my mosfet or vfet, whether they be bipolar or unipolar power supplies, have always been referenced to chassis ground through a thermistor. If I connect the drain of my THF-51S to the chassis without an insulator or the screw of the drain wire attaches to the heatsink the THF-51S will be reference to the chassis by two routes. One through the power supply thermistor and one directly.
An issue?
Regards,
Dan
An issue?
Regards,
Dan
There are two grounds:
1.chassis/safety ground - connected to the AC power ground
2. audio ground - connected to the DC power supply ground
The audio ground is separated from the chassis ground by the thermistor. The thermistor is connected between the DC power supply output ground and the chassis/safety ground.
You will need to electrically isolate the SIT drain and its connection wire from the heat sink and chassis.
You may delete the isolation if you delete the thermistor and connect the audio ground directly to the chassis/safety ground. However you may hear noise from the amplifier output. I have connected preamplifier audio ground directly to chassis/safety ground with no issue though.
1.chassis/safety ground - connected to the AC power ground
2. audio ground - connected to the DC power supply ground
The audio ground is separated from the chassis ground by the thermistor. The thermistor is connected between the DC power supply output ground and the chassis/safety ground.
You will need to electrically isolate the SIT drain and its connection wire from the heat sink and chassis.
You may delete the isolation if you delete the thermistor and connect the audio ground directly to the chassis/safety ground. However you may hear noise from the amplifier output. I have connected preamplifier audio ground directly to chassis/safety ground with no issue though.
When using a thermistor (or a 10 Ohm resistor + diode bridge) to make the audio ground connection, I have found it beneficial to connect 0.1 uF in parallel for each channel. Preferably film type. The capacitor shorts higher frequency ground noise to chassis gnd.
Ben
I have recently upgraded my 45W Mu follower to the 70W version and intend to move from SMPS to linear PS using your CLC design. I had some PS boards made some time ago and was wondering whether you could send me the Gerbers for the rectifier/snubber boards please?
I have acquired two 625VA transformers with dual 30V secondaries which should provide more than sufficient voltage and current for the amps. The unloaded AC voltage is around 69V with the secondaries connected in series. DC output after rectifiers (before CLC) is around 63V unloaded. Based on what you and others have stated you are getting using dual 30V secondaries in series, I had expected it to be roughly between about 86 and 97V, that is, 1.25 and 1.41 times the AC input voltage.
Any thoughts on why this might be so?
Thanks.
I have recently upgraded my 45W Mu follower to the 70W version and intend to move from SMPS to linear PS using your CLC design. I had some PS boards made some time ago and was wondering whether you could send me the Gerbers for the rectifier/snubber boards please?
I have acquired two 625VA transformers with dual 30V secondaries which should provide more than sufficient voltage and current for the amps. The unloaded AC voltage is around 69V with the secondaries connected in series. DC output after rectifiers (before CLC) is around 63V unloaded. Based on what you and others have stated you are getting using dual 30V secondaries in series, I had expected it to be roughly between about 86 and 97V, that is, 1.25 and 1.41 times the AC input voltage.
Any thoughts on why this might be so?
Thanks.
Your post reminds me of the Mark's work posted here. Measuring the "ESL" inductance of electrolytic caps (at 10 MHz!)
And Mike's use of film caps bypassing electrolytics in his F5mX power supply. F5mX - A 50w bridged F5m... Sort of...
Regards,
Dan
Hi rolotube, your low voltage is due to no capacitors after the rectifier. The voltage should be higher after the CLC filter.
I will send you the files for the boards.
I will send you the files for the boards.
Thanks Ben.
I should have mentioned that I had not connected the CLC components before measuring DC voltage at the rectifier. I’ll complete the PS and check again.
Cheers.
I should have mentioned that I had not connected the CLC components before measuring DC voltage at the rectifier. I’ll complete the PS and check again.
Cheers.
While waiting for my first PCBs and other parts to arrive I've had more time to nose around and do some reading. I found an alternative design that peaked my interest (only because I have a surplus of film caps in my spare parts bin). With little else to do for the moment I'm pondering a mild redesign that uses film/foil polypropylene caps and maybe some vishay power film resistors.
Regards,
Dan
Regards,
Dan
Absolute Audio Labs SIT-A15 power amp
That amplifier may or may not be a mu follower follower. It is hard to tell just by looking at the built amplifier.
It's diy so you are free to choose what ever capacitors that you desire. In my amps, I have metallized polypropylene capacitors at the input and also at the output in conjunction with electrolytics. They are DC filter caps from Digikey or Mouser though, not "audiophile" film and foil caps.
As for Vishay power resistors, I don't know whether you would hear a difference.
I even have low cost no name resistors in my amps and preamps. I buy them locally when I need them when between Digikey orders.
I generally use regular grade components in my amplifiers as I think the circuit and Tokin SITs are the main contributors to the sound. 🤓
It's diy so you are free to choose what ever capacitors that you desire. In my amps, I have metallized polypropylene capacitors at the input and also at the output in conjunction with electrolytics. They are DC filter caps from Digikey or Mouser though, not "audiophile" film and foil caps.
As for Vishay power resistors, I don't know whether you would hear a difference.
I even have low cost no name resistors in my amps and preamps. I buy them locally when I need them when between Digikey orders.
I generally use regular grade components in my amplifiers as I think the circuit and Tokin SITs are the main contributors to the sound. 🤓
I agree 100%. Topology and active devices first. I always use film capacitors, usually polypropylene if I have DC blockers and such. And bypassing electrolytic capacitors with PP is a low hanging fruit. For resistors I just go for normal 1%. But I have some Borbely amplifiers with tantalum resistors from back in the day. I did that, but doubt I can hear it. And they were expensive. (It is allowed to disagree though.)