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Old 25th May 2020, 07:32 AM   #1331
prasi is offline prasi  India
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Quote:
Originally Posted by Harry3 View Post
or a 10Volt 5W zener in series with a 12V fan. However some fans might not start up if they don't get 12V on start up.
Something like this?
100W Ultimate Fidelity Amplifier
I do not know where it was posted originally, so quoting the Apex thread.
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Old 25th May 2020, 11:05 AM   #1332
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by fab View Post
...as Harry3 indicates read post 880 regarding 4 or 8 speakers
Dealing with the transition of class A to class B is one thing. Of course I like to keep it in class A for most of the time. My speakers are "amplifier friendly", so I am not too much concerned about the "4 Ohm vs 8 Ohm" issue (although I do understand this point). I also think that the "XYZ Ohm" rating method is almost useless in most situations, because it's usually more important if the impedance curve is smooth or has sharp peaks.

The other thing is that I want to bias the output devices such that they are operating in a more linear range. That's why I want to crank up the bias current. Looking at the Exicon curves, the linearity of the LatFETs is best between 2-6 A. That's why I thought to set the bias higher than suggested in the manual.
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Old 25th May 2020, 07:16 PM   #1333
mbrennwa is offline mbrennwa  Switzerland
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Originally Posted by nfsgame View Post
Click the image to open in full size.
I like those test point pins. Where did you get them? Do you maybe have a Mouser part number?
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Old 26th May 2020, 04:49 AM   #1334
zman01 is offline zman01  Bangladesh
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mbrennwa,

Not sure, but after zooming looks like individual pins from break-away 2.54mm straight pin male header - something like Mouser part # 54102-T10-08 (example of an 8 pin header).

Another option used by diyAudio member Vunce for his build:

5002 Keystone Electronics | Mouser

Pics of Vunce's PCB:

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Last edited by zman01; 26th May 2020 at 04:56 AM.
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Old 26th May 2020, 09:14 AM   #1335
manniraj is offline manniraj  India
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I have used the same breakaway 2.54mm pins from the the long strip. Works perfectly fine and we can leave them on the boards after the setup as well. Can be helpful later and should be careful with the wiring not touching them during running any open wires. Otherwise test points are the best highlighted feature of Fab's boards, very very useful for the build process

Thanks
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Old 29th May 2020, 06:30 AM   #1336
mbrennwa is offline mbrennwa  Switzerland
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My USSA-5 will not have the power transistors and the NTC soldered to the PCB. I will use extension leads for the connection, because the PCB will not be on the heatsinks. I was wondering how to fix the NTC to the heatsink, and found this:

NTCALUG01A472H Vishay | Mouser Schweiz

Anything wrong with using this part instead of the one listed in the BOM/manual?
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Old 29th May 2020, 06:47 PM   #1337
nfsgame is offline nfsgame
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Someone earlier in this thread tried them and that resulted in bad behavior...
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Old 29th May 2020, 10:50 PM   #1338
fab is offline fab  Canada
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Quote:
Originally Posted by mbrennwa View Post
My USSA-5 will not have the power transistors and the NTC soldered to the PCB. I will use extension leads for the connection, because the PCB will not be on the heatsinks. I was wondering how to fix the NTC to the heatsink, and found this:

NTCALUG01A472H Vishay | Mouser Schweiz

Anything wrong with using this part instead of the one listed in the BOM/manual?
Hi
The BOM part has B parameter 3950K which is different from the ones you selected (3984K).
Electrical Isolation is absolutely required between chassis and thermistor.

As for extension leads with output transistors I am worried for possible oscillation.... at least gate resistor must be absolutely mounted on the transistor itself. Ensure to use an oscilloscope to check for oscillation.
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Last edited by fab; 29th May 2020 at 10:55 PM.
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Old 30th May 2020, 07:46 AM   #1339
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by nfsgame View Post
Someone earlier in this thread tried them and that resulted in bad behavior...
I found this post. Hower, I couldn't find any problem reports reltated to this. Can you explain / point me to the problem?

Quote:
Originally Posted by fab View Post
Hi
The BOM part has B parameter 3950K which is different from the ones you selected (3984K).
That's a 1% difference. Also take a look at this comparison between the Vishay/lug NTC and the BOM NTC. I don't see any difference at all. What am I missing?

Quote:
Originally Posted by fab View Post
As for extension leads with output transistors I am worried for possible oscillation.... at least gate resistor must be absolutely mounted on the transistor itself. Ensure to use an oscilloscope to check for oscillation.
Yes, I am very well aware of this. I have done it in a few builds now, and I never ran into problems as long as the gate stopper was installed directly at the FET pins.

However, I just thought of something else that might be an issue in my situation. How important is thermal tacking between the power FETs? The reason I am asking is that I am planning to build my USSA-5 using an "Aleph" chassis, see here. There will be one power FET and one driver FET per heatsink to share the heat across the four sides of the chassis. The heatsinks will have some thermal contact with each other, but it's not like if the the power FETs would be mounted next to each other on the same heatsink. Also, the drivers would be distributed across the four heatsinks in the same way as the power FETs. So, here are a few questions related to this:
  • How important is thermal tracking between the power FETs?
  • How important is thermal tracking between the driver FETs?
  • How important is thermal tracking between drivers and power FETs?
  • What would be the best compromise for the pairing of the driver and power FETs on each heatsink? Positive power FET and positive driver on the same heatsink (and negative + negative on other heatsink)? Or positive power FET and negative driver on the same heatsink (and negative + positive on other heatsink)?
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Last edited by mbrennwa; 30th May 2020 at 07:51 AM. Reason: fixed wrong link
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Old 30th May 2020, 01:32 PM   #1340
fab is offline fab  Canada
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Hi
For the thermistor characteristics, I just pointed out that it was a different temperature curve . If you have checked that from 25C to about 65C it has only 1% difference than it should be ok.

“ How important is thermal tracking between the power FETs?” Important
“How important is thermal tracking between the driver FETs?“ Important
“How important is thermal tracking between drivers and power FETs?“ Important
“What would be the best compromise for the pairing of the driver and power FETs on each heatsink? Positive power FET and positive driver on the same heatsink (and negative + negative on other heatsink)? “Yes
“Or positive power FET and negative driver on the same heatsink (and negative + positive on other heatsink)?” no.

There are 2 thermistors, one for each polarity of the symmetrical circuit. Thus, as long as the heatsink location where is installed each thermistor for one channel (left or right) is the same then you should have the same temperature. Have in mind that P1 and P2 will be adjusted to center DC offset once the temperature has stabilized. However, temperature dissipation for positive and negative polarity should be the same. Some tweaking for that can also be done by moving one the thermistor closer to the output FET (a few millimeters for example) where is the max heatsink temperature. This way you can balance. It is easier with original part using the leads to move the thermistor on the heatsink location.
Drivers should be as close to the output transistors than it is meant if they were on the pcb.

As the distance on heatsink of each thermistor to the driver and output they should be the same as for the pcb.

As for the extension leads please ensure you have minimum length possible and I would sure check with a scope for the 10KHz square wave shape..

If you can show a sketch of your planned inside amplifier arrangements that would be great since it was never tried before for this amplifier. Thus you are really a FAB (Fearless Amplifier Builder)

Fab
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Last edited by fab; 30th May 2020 at 01:45 PM.
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