Difficult situation. You have to let us know the cartridge you are having so to estimate the gain needed and maybe give you new resistor values for 3 close pairs you maybe have around a more specific IDSS. Like 5.5-6mA or 4.5-5mA. So state the cartridge and 3 reasonable pairs you can work with.
i have selected 3 pairs all of them in 5.8-6.2 ma idss (1. 5.91 , 5.91 2. 5.93 , 5.89 3. 6.24 , 6.17 )
i don`t know the manufacturer of the cartridge but it is an mm with 2-2.5 mv output
i don`t know the manufacturer of the cartridge but it is an mm with 2-2.5 mv output
i have replaced the pair with high idss 6.24 , 6.17 with another one that has 5.60 , 5.59 ma idss .so i have :
1. 5.53 5.56
2. 5.60 5.59
3. 5.91 5.91
4. 5.93 5.89
i have replaced the pair with biggest idss so i could get the pairs in 5.5-6ma idss range
1. 5.53 5.56
2. 5.60 5.59
3. 5.91 5.91
4. 5.93 5.89
i have replaced the pair with biggest idss so i could get the pairs in 5.5-6ma idss range
Sorry I have come in late in this thread. What method did you use to measure Idss. Do you have cct? I have made three Le Pacific style phono preamps in the last four weeks. I'm about to do another and have a bunch of FETs. I would like to match them.
all you need to match jfets are a multimeter and a 9v battery.more you can find here Transistor matching
Will look later what I can do for you with those in the same circuit of the PDF. Will post to let you know.
Use 24V PSU and the HiMC-MM circuit values of the PDF. Keep R2 33R, make R7 2K2. Use your pairs 1,2,3 for Q1,Q2,Q3 between channels. That will give 41dB gain.
The Boozhoundlabs Le Pacific kit comes with matched jFETs, I believe, because the voltage drop across each similar positioned jFET is the same.
What are the dissipations of the two mosFETs during normal operation?
What are the expected Tc & Tj of these mosFETs during normal operation?
What are the dissipations of the mosFETs during worst case fault conditions?
Will the mosFETs survive during fault conditions?
The fact that the second mosFET runs a bit hotter is of virtually no consequence, if you don't know what is happening.
What are the expected Tc & Tj of these mosFETs during normal operation?
What are the dissipations of the mosFETs during worst case fault conditions?
Will the mosFETs survive during fault conditions?
The fact that the second mosFET runs a bit hotter is of virtually no consequence, if you don't know what is happening.
Each phono channel draws around 30mA. If you run at 45V B+ I guess its normal there is considerable dissipation from the shunt Mosfets for those heatsinks in the picture burning the excess. IRFP TO-247s are dogs to say the truth, very reliable, but it will be prudent to lower the CCS a bit to ensure no failures in the long run especially when it will be boxed up.
Hi AndrewT.
All are working perfect but I am going to use the heatsink and the case you can see on photos. If there is no insufficient cooling may reduce a little the total current per channel.
Attachments
Nice old radio, it's very similar like I heard when I was 4 years old (Telefunken tubed)🙂
Don't forget to insulate the Mosfets when you will use the case for sinking.
P.S. Auricaps without flying leads? New issue, or suspect?
TO-247s just need insulation pads, no nylon screws. Maybe you refer to some chassis screws you miss.
