quite a number of the jFETs in a DCB1 and in many of the Salas style shunt regulators do not need to be high gm, low pinch off voltage types.
Many of the very cheap and very available lower gm with higher pinch off are very suitable.
Some of the Salas regulators have a Vbe across the jFET. This one jFET must be a low pinch off type.
I have used bf244 a & b grades and have posted details in many replies/advices.
Many of the very cheap and very available lower gm with higher pinch off are very suitable.
Some of the Salas regulators have a Vbe across the jFET. This one jFET must be a low pinch off type.
I have used bf244 a & b grades and have posted details in many replies/advices.
I can recall that I have read some of your replies somewhere before.
Yet, I need some time to find them out.
Anyway, your information is very useful.
I look up several datasheets this morning and I found that BF245B seems to be a good alternative to 2SK170BL. It has very low noise figure and low input capacitance.
Also, 2N5457 has similar specification except that its Idss is widely spread, i.e. 1mA ~ 5mA. For 2N5458, Idss range from 2mA ~ 9mA. It may be used for the SSLV where strict matching of Idss is not crucial. It is really dirt cheap!
If you will end up to some candidates let me know before you build so to check the phase margin of the total circuit.
Which four of the 2SK170 has to be matched? Are these the ones near the output relay at the center of the PCB?
Just want to make sure I understand this correctly. So the LED must be matched so that the sum of the voltage drop of each group is the same?
So I will group the LEDs as follow (measurement in Volts):
For the 3 LED rows:
Group 1A: 1.947+1.947+1.949 = 5.843
Group 1B: 1.947+1.948+1.947 = 5.843
For the 5 LED rows:
Group 2A: 1.952+1.955+1.956+1.957+1.959 = 9.779
Group 2B: 1.952+1.955+1.956+1.957+1.959 = 9.779
Do I group this correctly?
Thank you!
So I will group the LEDs as follow (measurement in Volts):
For the 3 LED rows:
Group 1A: 1.947+1.947+1.949 = 5.843
Group 1B: 1.947+1.948+1.947 = 5.843
For the 5 LED rows:
Group 2A: 1.952+1.955+1.956+1.957+1.959 = 9.779
Group 2B: 1.952+1.955+1.956+1.957+1.959 = 9.779
Do I group this correctly?
Thank you!
Yes, but do you have options for settling 2A,B lower near 9.4V? That would be nearer 10V when 0.6Vbe is added from the BJTs. Not that is anything too important subjectively.
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Salas,
I've got all of my parts for a DCB1 hot-rod build with a Lightspeed attenuator, likely driven by one of the MV-04 remote control kits from e-bay (the cool part is that it will stay out of the signal path!). The last element to plan is a chassis configuration. I'm trying to gauge the necessary level of heat sinking capacity. It looks like the power supply for the big MOSFETs is 10v, so if I run at 600mA, the mosfets will dissipate 6w each? So, close to 25w total dissipation at 600mA?
Am I approaching this the right way?
Thanks,
Eric
I've got all of my parts for a DCB1 hot-rod build with a Lightspeed attenuator, likely driven by one of the MV-04 remote control kits from e-bay (the cool part is that it will stay out of the signal path!). The last element to plan is a chassis configuration. I'm trying to gauge the necessary level of heat sinking capacity. It looks like the power supply for the big MOSFETs is 10v, so if I run at 600mA, the mosfets will dissipate 6w each? So, close to 25w total dissipation at 600mA?
Am I approaching this the right way?
Thanks,
Eric
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About to order parts for my new Mez pcb 🙂
Post 717 has a new BOM, Thanks for that. Salas, are there any other updates you see needed in that? Is that BOM just for stock....no hotrodding?
The LED p/n for Mouser I found in the "DC Coupled B1 Shunt PSU V4.3.pdf" links to yellow but from what I read, red is preferable....Would yellow suffice?
Post 717 has a new BOM, Thanks for that. Salas, are there any other updates you see needed in that? Is that BOM just for stock....no hotrodding?
The LED p/n for Mouser I found in the "DC Coupled B1 Shunt PSU V4.3.pdf" links to yellow but from what I read, red is preferable....Would yellow suffice?
A Mez can't take heavy hot rod anyway, that BOM is for low current Mez. Specifically the 4x68R and the DO-41 rectifiers. Yellow or red they are both low noise and near for voltage drop. Its usual that red has a bit lower drop. You can change to 4X27R while mounting the Mosfets to the box floor with insulating silpads. Or clip sinked individually making no other contact. You can also choose for yourself the 220K & 220R types referred as Takman Carbon between many boutique resistors alternatives. Still a low ppm Dale type would be at least equal.
Thanks Salas. I plan to go stock for now with 4x68R and sinks on the 240/9240. I have seen posts hotrodding this pcb and I know there is plenty of caution given.....would it handle 2x10R 6.5w and add cpu or amp heatsinks to the 240/9240 ?
They don't get that hot with 10R for going CPU sinks. 5C/W for each one would be plenty. Mount the MUR120 diodes upright in that situation. Its the way they dissipate to air best.
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Hmmm... I am planning to build my Mezmerize board hot-rod style as well. I presume that if I mount high-current diodes off board with a sink, mount the bias set resistors off board, double up the PS caps, and sink the power mosfets that I'd be fine taking the bias up to 800-1000mA?
Is there any other design constraint with the remainder of the board that makes this not a good idea?
Is there any other design constraint with the remainder of the board that makes this not a good idea?
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With 0.8-1A you will not need sinking on TO-220 rectifier diodes and you will avoid the elongated leads inductance. Keep strays to a minimum in general.
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