3U Mini. I had my son draw up a back panel, and we just got it back from SendCutSend
Hi, thermistor question.
My essentials kit came with three of the mid-size EPCOS 10 Ohm NTC thermistors (Digikey PN 495-76260-ND) and one bigger green SCK 108. I have the V1R1 board which uses four thermistors as rail filters, one as a circuit ground to earth ground isolator, and I'll need another on the primary to stall the inrush.
I have a quad of Amphenol CL-60 thermistors (Digikey PN KC006L-ND). Can I use these in place of the EPCOS in the rail fliter position? Both parts are 10 Ohm and rated 5A, but it's not clear from the spec sheets if their rate of change of resistance, or steady-state hot resistance (180mOhms for the Amphenol part, none given for the EPCOS), is the same, or if this matters in this applications.
I know I can just ask the shop for more, I'm trying to be efficient.
My essentials kit came with three of the mid-size EPCOS 10 Ohm NTC thermistors (Digikey PN 495-76260-ND) and one bigger green SCK 108. I have the V1R1 board which uses four thermistors as rail filters, one as a circuit ground to earth ground isolator, and I'll need another on the primary to stall the inrush.
I have a quad of Amphenol CL-60 thermistors (Digikey PN KC006L-ND). Can I use these in place of the EPCOS in the rail fliter position? Both parts are 10 Ohm and rated 5A, but it's not clear from the spec sheets if their rate of change of resistance, or steady-state hot resistance (180mOhms for the Amphenol part, none given for the EPCOS), is the same, or if this matters in this applications.
I know I can just ask the shop for more, I'm trying to be efficient.
Hi Anand,
Could you please tell me the spec of the smaller thermistors on the PSU board, I have not seen an updated BOM yet.
Thanks
Eric
Eric,
First of all, I don’t have a kit and I don’t plan on getting one (I’ll be building my own F5m with existing F5 boards).
Member ranshdow just posted the Digikey part number for the TDK thermistors used on the supply board (these are the original ones I believe). There are charts and graphs on the pdf datasheet with that link. You can see how low the resistance once fully biased. There are also 5 ohm NTC resistors which are rated for higher currents.
The steady state resistance once the amp is fully biased does matter since too much resistance will render a bigger voltage drop and hence lower rail voltage and of course lower power output. So the small TDK/Epcos ones supplied should be the right ones.
Posts 1133 and onwards have some good discussions.
Best,
Anand.
First of all, I don’t have a kit and I don’t plan on getting one (I’ll be building my own F5m with existing F5 boards).
Member ranshdow just posted the Digikey part number for the TDK thermistors used on the supply board (these are the original ones I believe). There are charts and graphs on the pdf datasheet with that link. You can see how low the resistance once fully biased. There are also 5 ohm NTC resistors which are rated for higher currents.
The steady state resistance once the amp is fully biased does matter since too much resistance will render a bigger voltage drop and hence lower rail voltage and of course lower power output. So the small TDK/Epcos ones supplied should be the right ones.
Posts 1133 and onwards have some good discussions.
Best,
Anand.
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Vinay,
So if I understand correctly, you were able to get one F5m Essentials kit? So you have the amplifier PCBs, power supply PCB, MOSFETs, and the JFETs (2 x 2SK170, 2 x 2SJ74) already in hand?
The bigger heat sinks with longer fins - these will work fine too; what is the thickness of the baseplate for these units?
FWIW, in post #1,367 , @WBS mentioned that, with regard to the updated kit to be released later in the month, "Thermistors will be Ametherm 10 Ω 8A 22mm". That was then followed that up in post #1,377 with "The new completion kit will include 6, 5 for the PSU and 1 for the AC line."
I took this to mean that this part will be used for all 6, but I could be wrong. Clarification welcome.
I will say, for diyAudio projects in general, a column or set of footnotes in the BOM that includes the parameters of interest for the more critical parts like this, and why certain values were chosen, would be helpful, and cut down on the number of repeat questions. "Such and such value is critical, this value can fall between X and Y, this value doesn't matter at all," etc.
(I know the default answer here is "if you don't already understand, then just buy the kit when it's in stock", but 1) I find just buying the kit all the time allows a person to sleepwalk through a build without learning anything, and 2) I plan on using bigger caps, and so the 4700uF would be surplus to my reqs).
I took this to mean that this part will be used for all 6, but I could be wrong. Clarification welcome.
I will say, for diyAudio projects in general, a column or set of footnotes in the BOM that includes the parameters of interest for the more critical parts like this, and why certain values were chosen, would be helpful, and cut down on the number of repeat questions. "Such and such value is critical, this value can fall between X and Y, this value doesn't matter at all," etc.
(I know the default answer here is "if you don't already understand, then just buy the kit when it's in stock", but 1) I find just buying the kit all the time allows a person to sleepwalk through a build without learning anything, and 2) I plan on using bigger caps, and so the 4700uF would be surplus to my reqs).
Regarding the thermistors:
I was intrigued by the change up from the standard CRC designs we've seen from Mr. Pass and thought it over repeatedly, always arriving at the same conclusion. The thermistors were a clever means of shaving the cost somewhat. That idea fit nicely with the reduced capacitance as well as NP having directly stated on multiple occasions that cheaper, simpler projects encourage more people to build amps. Just look at the success of the ACA and spinoffs. I also thought that any performance advantages I may be missing would have been pointed out by the considerable brain-trust here.
I bought a few of the epcos therms in the 4R7- 7.5A version to play with but hadn't pulled them out of the bag until today. I've been running f5m channels with an Antek 4218 - 64,400uF per rail CRC instead.
So, seeing the questions raised again, I placed a parallel pair of CL60's between the PS and one channel, with a parallel pair of Epcos 4.7R between the PS and the other channel. Both biased to 1.3A.
After several minutes with everything fairly settled, I measured a voltage drop of ~ 1.6V across the CL60's and ~ 0.85V across the Epcos.
I repeated the experiment with a single device per side and as one might expect, with twice the current and twice the resistance, the results appeared to be on track to match the first run... but with considerably higher temps.
My knowledge is limited and I wouldn't be terribly surprised to hear of advantages that haven't occurred to me but my curiosity is satisfied for the time being.
I was intrigued by the change up from the standard CRC designs we've seen from Mr. Pass and thought it over repeatedly, always arriving at the same conclusion. The thermistors were a clever means of shaving the cost somewhat. That idea fit nicely with the reduced capacitance as well as NP having directly stated on multiple occasions that cheaper, simpler projects encourage more people to build amps. Just look at the success of the ACA and spinoffs. I also thought that any performance advantages I may be missing would have been pointed out by the considerable brain-trust here.
I bought a few of the epcos therms in the 4R7- 7.5A version to play with but hadn't pulled them out of the bag until today. I've been running f5m channels with an Antek 4218 - 64,400uF per rail CRC instead.
So, seeing the questions raised again, I placed a parallel pair of CL60's between the PS and one channel, with a parallel pair of Epcos 4.7R between the PS and the other channel. Both biased to 1.3A.
After several minutes with everything fairly settled, I measured a voltage drop of ~ 1.6V across the CL60's and ~ 0.85V across the Epcos.
I repeated the experiment with a single device per side and as one might expect, with twice the current and twice the resistance, the results appeared to be on track to match the first run... but with considerably higher temps.
My knowledge is limited and I wouldn't be terribly surprised to hear of advantages that haven't occurred to me but my curiosity is satisfied for the time being.