[and now for something completely different part 3]

On 5/16/2023 at 3:24 PM, Pars said:

Just an FYI, the diyaudio store has Toshiba matched quads and octets of J74/K170. Octet is US $90 or $100 depending upon IDSS. These are BL devices.

Good luck on the tube input, and if that is what you really want, I'd agree; go for it. I'm sure Dukei will be much help here.

 

Thanks for the heads up! Thoughts on which LDSS value might be most appropriate? 6-8 or 8-11ma?

[and now for something completely different part 3]

On 4/26/2023 at 8:20 PM, Pars said:

Yeah, that could work, though I'm not sure why everyone breaks taps? Are you tapping by hand or using a drill? By hand, do a couple of turns, back out 1/2 turn or so, continue, rinse and repeat. I've never broken a tap, even on blind holes with a bottoming tap.

 

This is very helpful advice. I will also add, that I broke a ton of taps until I realized....

1. I was using the wrong size drill bit. M3 requires a 2.5mm bit. Not a SAE drill bit that is close.

2. Impatient, and just kept pushing (spiral fluted taps help if you are in a rush like me)

3. Buying junk taps on amazon

[goldenreference low voltage power supply]

9 hours ago, audiostar said:

If you want to use the trimpots, you need to recalculate the 1M resistors depending on selected output voltage. Like for 15V, one of them per side would need to be 473k, so 1M is too hight for 20V output.

Thanks a million - this makes perfect sense and I understand.

[goldenreference low voltage power supply]

4 hours ago, jamesmking said:

The output voltage is set by two resistors R8/R7 and R10/R9 (see schematic below).

the trim pots make only very small adjustments - a few mV for those who want spot on voltages - there is a trade-off between adjustment range and temperature stability.

If you want more adjustment range decrease the value of R24,R23,R18,R17. 810K instead of 1M for each gives about + and - 20mV adjustment range.

If you want reasonably accurate voltages AND lower temperature drift you can use 0.1% resistors for R8,R7,R10 and R9 with low temperature coefficients (stock resistors are usually about 100ppm, 0.1% are usually around 25ppm) and omit the 1M ohm resistors and trim pot.

 

I thought about making this value change (I did read every page of this thread- seems like one other person had the same issue, but just decided to live with it).
 

I’m not seeing any change in voltage at all even 1mv, which leads me to worry I have an actual issue. I am not measuring with a load, maybe that’s part of it? I’m at a loss - it’s a simple part of the circuit. Maybe there really isn’t enough range to see on my meter un loaded. 

Will do more testing, any suggestions appreciated.
 

[goldenreference low voltage power supply]

So I built a set and they work! I am however not seeing any adjustment with the 100k trim pots. Same for two boards and the positive and negative side of each. I've checked my work (and orientation), and all seems ok. I could just leave them (they run stable at +/-20v as expected) but i'd like to understand why i'm not seeing any adjustment. Looking at the circuit it seems pretty simple... I know I am probably missing something obvious.