I had some help today to make the changes as described above.
Shunties
Changed R16 & R16A from 4R7 to 100R
Soldered 1nF (cheap Chinese) ceramic cap between B and C of Q11 & Q11A (BDXs).
Output is steady at 36V (Fluke 179: 4 digit steady) but I do see a few mV when I check with the scope (very high freq). This is both without load and with 470R resistors.
I have no idea what the output is supposed to be like, so assumed (for now) it is fine. I did not measure with a scope.
Pumpkins
I added 15k and 221k resistors as described above on the bottom of the pcb.
The voltage between TP0 and TP1 (or TP2) measured with inputs grounded still fluctuates (a few V up and down). I have attached some screenshots to show what I found.
Setup:
2 x Pumpkin pcb, each connected to its own Shunty
Inputs grounded
Pumpkins voltage supply steady +/-36V
Pumpkin A
Yellow traces (channel 1) = pos (or neg, can't remember) output ref. to output GND.
Pumpkin B
Pink traces (channel 3) = pos (or neg, can't remember) output ref. to output GND.
Question1.
Can I test the pumpkin on a +/- 30V lad power supply (30V max, so 36V impossible) to see if it makes a difference?
Question 2.
Can you suggest any measurements? I know from a previous test last week that it does play music, so I did not mess up completely 🙂
Shunties
Changed R16 & R16A from 4R7 to 100R
Soldered 1nF (cheap Chinese) ceramic cap between B and C of Q11 & Q11A (BDXs).
Output is steady at 36V (Fluke 179: 4 digit steady) but I do see a few mV when I check with the scope (very high freq). This is both without load and with 470R resistors.
I have no idea what the output is supposed to be like, so assumed (for now) it is fine. I did not measure with a scope.
Pumpkins
I added 15k and 221k resistors as described above on the bottom of the pcb.
The voltage between TP0 and TP1 (or TP2) measured with inputs grounded still fluctuates (a few V up and down). I have attached some screenshots to show what I found.
Setup:
2 x Pumpkin pcb, each connected to its own Shunty
Inputs grounded
Pumpkins voltage supply steady +/-36V
Pumpkin A
Yellow traces (channel 1) = pos (or neg, can't remember) output ref. to output GND.
Pumpkin B
Pink traces (channel 3) = pos (or neg, can't remember) output ref. to output GND.
Question1.
Can I test the pumpkin on a +/- 30V lad power supply (30V max, so 36V impossible) to see if it makes a difference?
Question 2.
Can you suggest any measurements? I know from a previous test last week that it does play music, so I did not mess up completely 🙂
Attachments
I believe you're good now to proceed with both Shunty and Pumpkin
residual HF weed you see on both you can ignore as environmental induced garbage
when you have Pumpkin boards in case, then it is what you get regarding offset stability - temperature equilibrium is what is needed
feel free to test Pumpkin with 30V rails, no problem there
residual HF weed you see on both you can ignore as environmental induced garbage
when you have Pumpkin boards in case, then it is what you get regarding offset stability - temperature equilibrium is what is needed
feel free to test Pumpkin with 30V rails, no problem there
I finally had a helper here today (my regular helper in abroad for a few months) to get back to the shunties and pumpkins.
I am having a wobbly rail again on one of the shunties, so it seems the previous changes did not cure it after all.
I thought I would forget about the pumpkins for a bit and try the pumpkins using my +/-30V bench psu. Current drawn was about 150mA per rail (which seemed about right).
Single ended input, neg input grounded, no music playing.
Before trying music I measured dc output and had around 50mV which seemed high. Switching my fluke to ac I found about 2V(not mV!) at 50Hz frequency. Obviously the lab/bench psu should give reasonably clean power and should not be the cause (I did not bother measuring the psu ripple, but at 150mA the 3A rated psu should be fine).
So, I think my pumpkin wiring is picking up a lot of noise.
Next steps:
Pumpkins
The setup in my shed is obviously very noisy. I will have to change the input and output wiring to shielded to try to get rid of some of this noise. Also, probably best to test in a metal enclosure as well.
Not sure if I can do this without my regular helper. If not I will get back to it when he returns.
Shunty
The problem rail needs sorting. The other 3 rails are solid but this one still wobbles around the 36V.
I'll recheck the changes I made, and see if I can measure any changes between the two shunties.
To be continued.
I am having a wobbly rail again on one of the shunties, so it seems the previous changes did not cure it after all.
I thought I would forget about the pumpkins for a bit and try the pumpkins using my +/-30V bench psu. Current drawn was about 150mA per rail (which seemed about right).
Single ended input, neg input grounded, no music playing.
Before trying music I measured dc output and had around 50mV which seemed high. Switching my fluke to ac I found about 2V(not mV!) at 50Hz frequency. Obviously the lab/bench psu should give reasonably clean power and should not be the cause (I did not bother measuring the psu ripple, but at 150mA the 3A rated psu should be fine).
So, I think my pumpkin wiring is picking up a lot of noise.
Next steps:
Pumpkins
The setup in my shed is obviously very noisy. I will have to change the input and output wiring to shielded to try to get rid of some of this noise. Also, probably best to test in a metal enclosure as well.
Not sure if I can do this without my regular helper. If not I will get back to it when he returns.
Shunty
The problem rail needs sorting. The other 3 rails are solid but this one still wobbles around the 36V.
I'll recheck the changes I made, and see if I can measure any changes between the two shunties.
To be continued.
