GB for Salas Folded Simplistic Phono PCB

[cmiu007]

quick question about R3x and R6x values based on Q2,3,5x IDSS values

it the build guide, the following values are mentioned:
normal; R3x=9.1K ;R6x=22R
high; R3x=6.2K ; R6x=33R

in the KIT (from the first page of the thread:
normal: R3x=9.1K ;R6x=33.2R
high; R3x=6.2K ; R6x=27.4R

which values should I choose for "normal"?

thank you

 

[Salas]

If your Q2x are 3-4mA IDSS use the 27.4R. If around 5mA IDSS use the 33.2R. If you delta button your DMM while having your probes shorted first, and then remeasure, they are probably 27R & 33R components. I would suggest you use the R3x 9.1k anyway and if this gives you a bit more max range it should still be within the control of VR2x

 

[AndrewT]

274 and 332 are standard E48, E96 & E192 values
I think he is quoting from the documentation, not from measurements of his components.

But a 1% resistor supplied as a 27r could be between 26r73 and 27r27 and 33r could be between 32r67 and 33r33

 

[Salas]

I though of E24 but you never know what goodies Tea-Bag Mike digs in the vast US stockists. Sometimes he goes for very good ppm primarily which is not a bad thing

 

[AndrewT]

27r1 is an E192 that fits inside the 1% tolerance of a 27r

27r4 is outside 1% tolerance, unless it happens to be a lower value, rather than the higher value component.

 

[Salas]

There is also the unknown DMM tolerance + last digit uncertainty spec which maybe tricks us that the components are coming from a more detailed range. Those are fine there anyway since the Q2x IDSS chance and its degeneration for keeping its dissipation lower is an approximation

 

[AndrewT]

I suspect that many of our builds would work with ±10% resistor values.
It's rare that we actually need very tight tolerances for resistors.

But we do need to learn how to use what few instruments we have at our disposal.
Just reading the DMM digits is not always reliable.

 

[Salas]

It depends on each circuit's nature. In this phono for instance which has no loop feedback the tight selection and matching weight falls on the shoulders of JFETS & LEDS to have good channel gain agreement but for its RIAA filter portion falls on the shoulders of film capacitors and resistors again

 

[cmiu007]

indeed, I was talking only based on documentation.

actual the resistors are 27r34 and 27r23 (delta vs short probes)

thanks for clarifications

 

[buzzforb]

Salas, firing up a simplsitic based on documentation on page 1. Not sure if there are revisions. On one channel, Jfet ccs Q2x and Q3x are functioning properly, the Q1x is passing appropriate current, but i have no adjustablity on shunt regulator. Q6x is dropping full rail voltage. Does this mean it is cooked or is there an issue with its reference? I always forget how Q4x and Q6x intereact.

 

[Salas]

Check Q4x Q6x BJT & MOSFET are not bad. Recheck Q3x & Q5x JFETs

 

[buzzforb]

measuring R3x, i get 36V and it is adjustable, so the Vref seems to be intact, including Q3x. How do i check Q5x, Q4x, and Q6x?

 

[Salas]

Ohmic RDS, Vbe, VGS

 

[buzzforb]

looks like Jfet is good. BJt and Mosfet are not.

 

[Salas]

I had once a zapped MOSFET incident in a bib which is alike reg. It took the BJT along. Maybe static killed it, because it did it on the get go and did not repeat with new semis.

 

[buzzforb]

It's a mystery to me. All I did was transfer it into a new case and one reg went down. I seem to live Murphy's Law

 

[Salas]

Was working before and you just handled the build and then boom smells static again

 

[buzzforb]

Thanks for the help

 

[Salas]

It may happen with MOSFETS if not wearing grounded wristband but not all the time. I am playing with them on breadboards grabbing them by the pins many times, but that one time it was dead just after assembled. Alright, DIY fun assembly standard, its not for NASA use anyway

 

[buzzforb]

You saying I am unprofessional?