Continuing the Aikido story.....
I managed to get my B+ down to 260VDC, but removing the 1.5uF cap.
This now means that I am running a 125-0-125 transformer from both ends to give 250V, going into a diode bridge, into a 10H choke; 60uF cap; 10H choke; 60uF cap. My outlet gives 123VAC.
So, I have a couple of questions:
1. Is 123VAC too much for a Hammond transformer rated for 115V? I am using the 269AX.
2. Can my chokes handle being used for a choke input filter? They are Hammond 193G rated for 150mA. I am drawing around 24mA from the circuit.
If I modelled this in PSUDII, what would I look for to see if the chokes can handle being in a choke input filter?
As far as the pesky hum, all I can say is that it's all quiet on the sn front. I lifted the ground by another 10 ohms to 20 ohm. If I put my ear to the speaker, I can hear a little bit of 60Hz, and may end-up with a 30 ohm ground lift.
Regards,
Charlie
I managed to get my B+ down to 260VDC, but removing the 1.5uF cap.
This now means that I am running a 125-0-125 transformer from both ends to give 250V, going into a diode bridge, into a 10H choke; 60uF cap; 10H choke; 60uF cap. My outlet gives 123VAC.
So, I have a couple of questions:
1. Is 123VAC too much for a Hammond transformer rated for 115V? I am using the 269AX.
2. Can my chokes handle being used for a choke input filter? They are Hammond 193G rated for 150mA. I am drawing around 24mA from the circuit.
If I modelled this in PSUDII, what would I look for to see if the chokes can handle being in a choke input filter?
As far as the pesky hum, all I can say is that it's all quiet on the sn front. I lifted the ground by another 10 ohms to 20 ohm. If I put my ear to the speaker, I can hear a little bit of 60Hz, and may end-up with a 30 ohm ground lift.
Regards,
Charlie
If possible use more capacitance, youve got a really really high q filter cascade there. You may see large spikes at start up. The chokes are waay overrated for their duty, a lower current higher inductance model would be more typical. These chokes are wasted here, put them in a power amp. Id use a 159M choke 15H 256DCR and follow it with both caps for 120uF, with a bleeder if need be.
True choke input should give <225V DC (<240V given higher mains here) output. If 24ma is not enough draw to make the system act as choke input, you can add a bleeder resistor. If you must stay with the current chokes, use both in series for 20H and follow them with the 120uF, it should act as intended. If theres noise; youve most likely got a grounding issue, it should give output more than clean enough.
True choke input should give <225V DC (<240V given higher mains here) output. If 24ma is not enough draw to make the system act as choke input, you can add a bleeder resistor. If you must stay with the current chokes, use both in series for 20H and follow them with the 120uF, it should act as intended. If theres noise; youve most likely got a grounding issue, it should give output more than clean enough.
With a solid state rectifier, always use a snubber cap (.05-.22, 1KV or more) or an MOV across the input - the inductor will kick back a voltage s[pike on turn-off, which can take out a rectifier sooner or later. With cap input, you have to consider peak current, with choke input, it's peak voltage.
Great comments and advice. At least for the present, I'll continue with the PSU laid out as it is, I suppose that I could go in search of some low value caps (less than 1uF) to place before the first choke.
I should certainly use a snubber, but where exactly should this be placed? Should I put it in the same position as I would the cap for a cap-input filter? Or should I put it over the on-off switch?
Finally, I opened up my solid-state power amp (AKSA 55N) to remind myself of the grounding work that I did when I made it. The star-earth is connected via a single ground cable to the chassis near the IEC inlet. I may redo this with some beefier cable, and redo the earth bolt.
So....if I am still getting some hum, which I do (in part because of a semi-lifted ground-loop, as well as poor tubes), would I be likely to gain anything (or lose hum) by adding a ground-lift resistor/cap network (say 20 ohms) to my power amp??
Thanks,
Charlie
I should certainly use a snubber, but where exactly should this be placed? Should I put it in the same position as I would the cap for a cap-input filter? Or should I put it over the on-off switch?
Finally, I opened up my solid-state power amp (AKSA 55N) to remind myself of the grounding work that I did when I made it. The star-earth is connected via a single ground cable to the chassis near the IEC inlet. I may redo this with some beefier cable, and redo the earth bolt.
So....if I am still getting some hum, which I do (in part because of a semi-lifted ground-loop, as well as poor tubes), would I be likely to gain anything (or lose hum) by adding a ground-lift resistor/cap network (say 20 ohms) to my power amp??
Thanks,
Charlie
Put the cap from input to ground - it's to protect the rectifier from the reverse voltage if current is suddenly interrupted (as it is every time it's switched off...).
As for hum... if you're lifting the SAFETY ground, a pair of back-to-back 25A diodes (use a bridge) will lift if and maintain a safe path for short circuits.
As for hum... if you're lifting the SAFETY ground, a pair of back-to-back 25A diodes (use a bridge) will lift if and maintain a safe path for short circuits.
Tom,
Please could you be real specific about the location of the cap. Is it at the switch? I doubt it. Is it across the output of the bridge rectifier? Oh....I already take the +ve output of the bridge rectifier through a schottky prior to entering the first choke.
As for the ground lift, I have implemented the following circuit:
http://sound.westhost.com/earthing.htm
Thanks,
Charlie
Please could you be real specific about the location of the cap. Is it at the switch? I doubt it. Is it across the output of the bridge rectifier? Oh....I already take the +ve output of the bridge rectifier through a schottky prior to entering the first choke.
As for the ground lift, I have implemented the following circuit:
http://sound.westhost.com/earthing.htm
Thanks,
Charlie
Tom,
Excuse my ignorance, but how is the choke input to ground different than in parallel with the choke??
Are you saying that I should connect it from choke input directly to the IEC ground, or star-ground on the PCB?
This is how things are set-up right now:
transformer; diode bridge recitifer; schottky; choke; cap; choke; cap with B+ to the B+ pad on the Broskie PCB. For the GND of the PSU (ie. the other side of the final cap) it goes to the GND pad on the Broskie board. A wire from the GND pad of the Broskie board then runs through the 20 ohm resistor/cap/bridge network to chassis GND; chassis GND to IEC Earth.
The same predicament of what GND is (for me at least) applies to the voltage divider that I use to reference the AC heaters to 1/4 B+. Voltage comes into the divider from the final cap (B+ lug) and goes to ground on the final cap (the non-B+ lug). I have wondered what would happen if I took the voltage divider between this cap and PCB GND, or even to the chassis gnd.
It would be easier for me to draw this wouldn't it?
Charlie
Excuse my ignorance, but how is the choke input to ground different than in parallel with the choke??
Are you saying that I should connect it from choke input directly to the IEC ground, or star-ground on the PCB?
This is how things are set-up right now:
transformer; diode bridge recitifer; schottky; choke; cap; choke; cap with B+ to the B+ pad on the Broskie PCB. For the GND of the PSU (ie. the other side of the final cap) it goes to the GND pad on the Broskie board. A wire from the GND pad of the Broskie board then runs through the 20 ohm resistor/cap/bridge network to chassis GND; chassis GND to IEC Earth.
The same predicament of what GND is (for me at least) applies to the voltage divider that I use to reference the AC heaters to 1/4 B+. Voltage comes into the divider from the final cap (B+ lug) and goes to ground on the final cap (the non-B+ lug). I have wondered what would happen if I took the voltage divider between this cap and PCB GND, or even to the chassis gnd.
It would be easier for me to draw this wouldn't it?
Charlie
Diggin
Charlie,
What is the purpose of this R/C/B? network?
Why didn't you just run GND Pad to chassis earth?
Is this the "safety" ground I've read about?
Another newbie question, I am using a seperate transformer for 12.6 heater supply, with the B+ bias of 1/4 to 1/2 B+ should the caps in the HS be rated for the 12.6V (30V caps) or 12.6 + 65V (100V minimum)?
I realize the HS is ~12.6 as relative to itself, and not chassis GND (earth) but does the Cap value pertain to the overall Voltage?
One more Q if you please....
Is the B+bias to heater wire tied directly to the (-) of the heater on the PCB? or am I totally lost????
Thanks as always for your time Charlie.
I think your questions were great! I must be learning something.
Ron
A wire from the GND pad of the Broskie board then runs through the 20 ohm resistor/cap/bridge network to chassis GND;
Charlie,
What is the purpose of this R/C/B? network?
Why didn't you just run GND Pad to chassis earth?
Is this the "safety" ground I've read about?
Another newbie question, I am using a seperate transformer for 12.6 heater supply, with the B+ bias of 1/4 to 1/2 B+ should the caps in the HS be rated for the 12.6V (30V caps) or 12.6 + 65V (100V minimum)?
I realize the HS is ~12.6 as relative to itself, and not chassis GND (earth) but does the Cap value pertain to the overall Voltage?
One more Q if you please....
Is the B+bias to heater wire tied directly to the (-) of the heater on the PCB? or am I totally lost????
Thanks as always for your time Charlie.
I think your questions were great! I must be learning something.
Ron
cbutterworth said:
A wire from the GND pad of the Broskie board then runs through the 20 ohm resistor/cap/bridge network to chassis GND;
Diggin' up the past
Charlie,
What is the purpose of this R/C/B? network? A wire from the GND pad of the Broskie board then runs through the 20 ohm resistor/cap/bridge network to chassis GND;
Why didn't you just run GND Pad to chassis earth?
Is this the "safety" ground I've read about?
Another newbie question, I am using a seperate transformer for 12.6 heater supply, with the 1/4B+ bias, should the caps in the HS be rated for the 12.6V (30V caps) or 12.6 + 65V (100V minimum)?
I realize the HS is ~12.6 as relative to itself, and not chassis GND (earth) but does the Cap value pertain to the overall Voltage?
I've read that a MOV across the + and GND at the Power switch will help prevent turn on/off thump? Any experience with this?
One more Q if you please....
Is the B+bias to heater wire tied directly to the (-) of the heater on the PCB? or am I totally lost????
Thanks as always for your time Charlie.
I think your questions were great! I must be learning something.
Ron
Charlie,
What is the purpose of this R/C/B? network? A wire from the GND pad of the Broskie board then runs through the 20 ohm resistor/cap/bridge network to chassis GND;
Why didn't you just run GND Pad to chassis earth?
Is this the "safety" ground I've read about?
Another newbie question, I am using a seperate transformer for 12.6 heater supply, with the 1/4B+ bias, should the caps in the HS be rated for the 12.6V (30V caps) or 12.6 + 65V (100V minimum)?
I realize the HS is ~12.6 as relative to itself, and not chassis GND (earth) but does the Cap value pertain to the overall Voltage?
I've read that a MOV across the + and GND at the Power switch will help prevent turn on/off thump? Any experience with this?
One more Q if you please....
Is the B+bias to heater wire tied directly to the (-) of the heater on the PCB? or am I totally lost????
Thanks as always for your time Charlie.
I think your questions were great! I must be learning something.
Ron
cbutterworth said:
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