TPR for HackerNap
- Thread starter timH
- Start date
martin clark
pinko bodger
1. If fitting the zener diode in place of R3 does it particularly matter what value R4 is?
You want to get a least 5mA or so through a zener for lowest noise/dynamic impedance, so for 1.25v say 240ohm (its low precision - 220 -270R fine). At higher voltages though you must check the resulting disspation in the zener. Calculate current x zener rating is nowhere near the zener's rated power disspation. 0.005A x 60v = 300mW (0.3W) - so you need 1 or 1.3w zeners, and they will run warm.
2. 75v 33uF tants are pretty expensive. Can I get away with 10uF?
I'd just use good-quality electrolytics and not worry about it. 100v and 33or 47uF are quite compact parts with comparable ESR. You must use the reverse-bias protection diodes around any 3-pin reg at these sort of voltages and capacities (the stored energy at turn-off can kill the reg if the supply rail falls faster than the load side of the regulator - especially I've found the negative versions, LM337, very sensitive to this)
You want to get a least 5mA or so through a zener for lowest noise/dynamic impedance, so for 1.25v say 240ohm (its low precision - 220 -270R fine). At higher voltages though you must check the resulting disspation in the zener. Calculate current x zener rating is nowhere near the zener's rated power disspation. 0.005A x 60v = 300mW (0.3W) - so you need 1 or 1.3w zeners, and they will run warm.
2. 75v 33uF tants are pretty expensive. Can I get away with 10uF?
I'd just use good-quality electrolytics and not worry about it. 100v and 33or 47uF are quite compact parts with comparable ESR. You must use the reverse-bias protection diodes around any 3-pin reg at these sort of voltages and capacities (the stored energy at turn-off can kill the reg if the supply rail falls faster than the load side of the regulator - especially I've found the negative versions, LM337, very sensitive to this)
Here's my HackerNAP with super-regs on the front-end.
Toroid is circa 400VA from a Harman Kardon power amp, with two sets of 44-35-0-35-44 windings. Front-end regs are modified Sulzer regs (PCBs from ebay), op amps are OPA551 with 56V zeners to limit the supply voltage, rectifiers are FR155. Regs are set at circa +/- 50V. Output stage supply is 6800uF -> inductor -> 6800uF//10000uF giving around +/- 47V output. 56uF feedback cap and ERO 2.2uF MKT1813 for the front-end supply rails. I'm just finishing it off but the regs and the front-end of the NAP boards works fine, hopefully you get the idea:
http://img842.imageshack.us/img842/5073/gjhf.jpg
Toroid is circa 400VA from a Harman Kardon power amp, with two sets of 44-35-0-35-44 windings. Front-end regs are modified Sulzer regs (PCBs from ebay), op amps are OPA551 with 56V zeners to limit the supply voltage, rectifiers are FR155. Regs are set at circa +/- 50V. Output stage supply is 6800uF -> inductor -> 6800uF//10000uF giving around +/- 47V output. 56uF feedback cap and ERO 2.2uF MKT1813 for the front-end supply rails. I'm just finishing it off but the regs and the front-end of the NAP boards works fine, hopefully you get the idea:
http://img842.imageshack.us/img842/5073/gjhf.jpg
Well the 60v zeners arrived so I made up the TPR on stripboard with LM1086, 100r for R1, 3r3 for R2, IN5371B 60v zener for R3 and 220r for R4
It all works ok with around 70v in I'm getting around 66.3v out. This seems a bit strange to me. With the 60v zener I thought I should be getting 60 + 1.25v out. Do I need to adjust any of the resistor values? Ultimately it doesn't matter because 66v into the HackerNap front end is fine. I'm just curious.
It all works ok with around 70v in I'm getting around 66.3v out. This seems a bit strange to me. With the 60v zener I thought I should be getting 60 + 1.25v out. Do I need to adjust any of the resistor values? Ultimately it doesn't matter because 66v into the HackerNap front end is fine. I'm just curious.
john.luckins
pfm Member
Tim,
Even with a 5% zener tolerance the voltage should be no more than about 64.3 volts. The TPR feeds a consistent 12.5mA into the load, set by the 100R of course, and you might want to increase that resistor to something like 220R to give the voltage setting regulator something to do, i.e. regulate, depending upon the load current drawn. If you have one per front end channel then that might be the reason for the higher than expected voltage.
John
Even with a 5% zener tolerance the voltage should be no more than about 64.3 volts. The TPR feeds a consistent 12.5mA into the load, set by the 100R of course, and you might want to increase that resistor to something like 220R to give the voltage setting regulator something to do, i.e. regulate, depending upon the load current drawn. If you have one per front end channel then that might be the reason for the higher than expected voltage.
John
Suffolk Tony
Aim low, achieve your goals, avoid disappointment.
OK, so I've built up my two Fetlington boards & want to install them. Is there some way I can test them before fitting them please?
Agreed, try disconnecting the output stage transformer from the output stage hackercap. This will stop the caps from charging, and will ensure you're only powering the low-current front-end circuitry.
You could also just disconnect the output stage hackercap from the hackernap, but the disadvantage of this approach is that the hackercap charges up, which leads to sparks when you connect it back to the amplifer PCB. If you're using the resistor/LED combo on your output stage hackercap this shouldn't be a problem because the caps will slowly drain and will be safe to connect to the hackernap once the LEDs go out.
Easier just to disconnect the trafo!
You could also just disconnect the output stage hackercap from the hackernap, but the disadvantage of this approach is that the hackercap charges up, which leads to sparks when you connect it back to the amplifer PCB. If you're using the resistor/LED combo on your output stage hackercap this shouldn't be a problem because the caps will slowly drain and will be safe to connect to the hackernap once the LEDs go out.
Easier just to disconnect the trafo!
Suffolk Tony
Aim low, achieve your goals, avoid disappointment.
OK, thanks guys, that seems sensible. I was going to just go ahead yesterday & install the fetlingtons from the top, than at the last minute I thought I'd double-check them... Lucky I did as I'd soldered the BC550Cs in the wrong place! In my defence my eyesight's not too good at the moment.
john.luckins
pfm Member
The difference is in the value of Idss (drain current) when the gate and source are at the same voltage. As the drain current in this application doesn't come anywhere near that value the difference between these two types is unimportant. Lower current Idss (Vgs=0v) is probably better value/cheaper.
John
John