A guide to building the Pass F4 amplifier

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#2,846
Just when I thought [and still think] we've figured it out, I tested six new TL431As, all I have, and none test as working. I have 3 different transistor testers to run them thru.

We shall all have to wait a few days until a new order arrives.

Crazy...
 
#2,849
And peak atlas I have read don’t test all transistors correct either due to too low a current. Dunno if that’s the case here though (saw you tested your JFETs with that, or is my memory letting me down?).

You seem like a quick solderer. I would just take an unused A-version and drop it in. No need to test a new part, and the more doing, the more risk of failure, IME. Plus you prolly need a jug or something to verify a working TL anyways. Not worth it.
 
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#2,852
That's a good part and what I use in my build. I've offered a couple of times already in this thread, a couple in an envelope free of charge. The proper TL431 is critical to correct operation of the F4. It's a simple amp otherwise. And like any other amp, just demands proper and careful assembly and installation of the proper components, in the proper orientation where required. Don't overheat 3 legged creatures and critters, on and off with the solder operation. Just whats required for a proper solder joint and not more. Use flux during the solder operation for nice solder joints but clean it off with isopropyl alcohol and a small acid brush before powering the circuit. And wearing a grounded wrist strap for ESD protection during assembly and when handling any sensitive component isn't a bad idea either.
 
#2,853
andynor said:
And peak atlas I have read don’t test all transistors correct either due to too low a current. Dunno if that’s the case here though (saw you tested your JFETs with that, or is my memory letting me down?).

You seem like a quick solderer. I would just take an unused A-version and drop it in. No need to test a new part, and the more doing, the more risk of failure, IME. Plus you prolly need a jug or something to verify a working TL anyways. Not worth it.
Click to expand...


Good idea. I took the current one last night.

Let's see what happens
 
#2,854
Dennis Hui said:
Chip,

Ben asked you to measure the D2/R9 voltage and you got around 2.1V. This
suggests your TL431 is not regulating. One reason would be if the TL431 is current-starved.
If that turns out to be the case you may need to replace it with a lower
cathode current part, for example:

https://www.mouser.ca/ProductDetail...SrJuGrTrO3w==&countrycode=CA&currencycode=CAD
Click to expand...

Ben,

With a new TL341A in place, I get the same result from D2/R9 = 2.02 Vdc

I guess its on to the part you suggest.
 
#2,855
william2001 said:
That's a good part and what I use in my build. I've offered a couple of times already in this thread, a couple in an envelope free of charge. The proper TL431 is critical to correct operation of the F4. It's a simple amp otherwise. And like any other amp, just demands proper and careful assembly and installation of the proper components, in the proper orientation where required. Don't overheat 3 legged creatures and critters, on and off with the solder operation. Just whats required for a proper solder joint and not more. Use flux during the solder operation for nice solder joints but clean it off with isopropyl alcohol and a small acid brush before powering the circuit. And wearing a grounded wrist strap for ESD protection during assembly and when handling any sensitive component isn't a bad idea either.
Click to expand...

I just sent you a message with my address. Very much appreciate you sending me the part.

Chip
 
#2,857
Chip,

As far as I can tell the Vref measuring locations that I marked on the pcb looks correct. I just checked the pictures of the front and back of the board and the locations look good. The D2 location is connected to the TL431 anode pin and the R8 location is connected to the TL431 ref pin.

So if the soldering is good and the part is installed correctly, and you are not getting 2.5V, then I would assume that the part is faulty.

The other way of measuring is to use small clips to attach directly to the TL431 anode and ref pins and measure directly.

I had pointed to the marked locations on the board for ease of measurement.
 
#2,859
Are you sure you have the correct pins?
 

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