You can still get ground loops, but they'll be harder to fix.
Let's say you have 20V DC power, then split it to +/- 10V DC and GND. This new GND will will be +10V relative to the old GND.
Then, if that 20V DC is powering something else, you don't want these two GNDs connected anyware, since that'll be a short circuit. In this case, 10V to GND.
You won't have that problem with one of those isolated DC-to-DC converters, or if you're rectifying an unused transformer secondary. But it was my understanding that the OP had limited space.
Let's say you have 20V DC power, then split it to +/- 10V DC and GND. This new GND will will be +10V relative to the old GND.
Then, if that 20V DC is powering something else, you don't want these two GNDs connected anyware, since that'll be a short circuit. In this case, 10V to GND.
You won't have that problem with one of those isolated DC-to-DC converters, or if you're rectifying an unused transformer secondary. But it was my understanding that the OP had limited space.
Attachments
2SC244 does it say? I didn't notice till today. That's not really packaging used now. I'm surprised to see something so physically large used there. I can see quite a few electrolytics placed directly in the signal path. Have you already swapped a few of them? I imagine you must of since the 70s.
need some last-time mod advice
Assembled PP4 Muffsy Phono Stage and the power supply and while ready to wire them found something alarming:
In the post 7 of this thread where wiring of the modded Muffsy PS is shown, the +41V DC supply wire goes directly into an electrolytic capacitor which is rated 35V DC. The ground wire goes into another 35V cap. Not good.
What I can do is to install a dropping resistor from 41 to 35 V or less, say 31V. This voltage should be fine for the PS.
Havard, what resistor ( wattage, value) would you recommend?
Assembled PP4 Muffsy Phono Stage and the power supply and while ready to wire them found something alarming:
In the post 7 of this thread where wiring of the modded Muffsy PS is shown, the +41V DC supply wire goes directly into an electrolytic capacitor which is rated 35V DC. The ground wire goes into another 35V cap. Not good.
What I can do is to install a dropping resistor from 41 to 35 V or less, say 31V. This voltage should be fine for the PS.
Havard, what resistor ( wattage, value) would you recommend?
How about using the Muffsy PSU with the +41V DC?
Skip all the stuff that I crossed out, and connect DC as shown. (Do not connect +/- 41V, only the +41V and GND.)
This will give you +/-15V DC output. Be careful to not connect the Muffsy PSU GND to the existing GND. That's easily done at the RCA connectors/through the chassis or similar.
What you really have here is the following:
Between 41V and GND on your DC power supply, you have two 35V capacitors. Each of them have a potential of 20.5V DC across. (The virtual GND is represented as the dotted line).
Not a case of "Not good", but in fact a healthy 42% to spare on each capacitor's voltage rating. No reason to panic, I stand by my suggestion. I have a setup like this that's been powered on for the best part of four years, still working.
EDIT:
Just remember the risk you have by doing so: DO NOT connect the 41V DC GND to the +/-15V DC virtual ground ANYWHERE. That could easily happen at e.g. the RCA input/output connectors, and you'll have a short circuit on your hands.
EDIT2: Also, you cannot just add a resistor to drop voltage. If you were to go that route, use a resistor divider or zener diodes to ground (from both the positive and negative voltages to virtual ground, which we've established isn't needed).
Between 41V and GND on your DC power supply, you have two 35V capacitors. Each of them have a potential of 20.5V DC across. (The virtual GND is represented as the dotted line).
Not a case of "Not good", but in fact a healthy 42% to spare on each capacitor's voltage rating. No reason to panic, I stand by my suggestion. I have a setup like this that's been powered on for the best part of four years, still working.
EDIT:
Just remember the risk you have by doing so: DO NOT connect the 41V DC GND to the +/-15V DC virtual ground ANYWHERE. That could easily happen at e.g. the RCA input/output connectors, and you'll have a short circuit on your hands.
EDIT2: Also, you cannot just add a resistor to drop voltage. If you were to go that route, use a resistor divider or zener diodes to ground (from both the positive and negative voltages to virtual ground, which we've established isn't needed).
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Just to be sure: "ground" that I connect to this power supply on a picture above is the chassis ground of the receiver. It is not the virtual ground.
What I was afraid of is that +41 V DC was measured against the receiver chassis ground so I'm getting 41V across TWO capacitors.
Double check everything tonight and fire her up.
What I was afraid of is that +41 V DC was measured against the receiver chassis ground so I'm getting 41V across TWO capacitors.
Double check everything tonight and fire her up.
Connected +41V and Ground as shown, and-everything worked! THe Power Supply gave + and - 15 V DC relative to its own ground.
Tested with DMM and the RCA phono input connectors and Muffsy phono preamp ground are not connected to +41V DC ground (=chassis ground).
Next step- Muffsy PP-4 connection and testing.
Tested with DMM and the RCA phono input connectors and Muffsy phono preamp ground are not connected to +41V DC ground (=chassis ground).
Next step- Muffsy PP-4 connection and testing.
So everything Muffsy was worked at the bench; however, things didn't go so well when I tried to use the turntable with the restored and assembled HK930.
When I use the turntable as source and increase or decrease volume - even if record is not playing - speaker's woofers move back and forward each time for a 1-1.5 centimeter or so with very low frequency sound. It's a lot for 6-inch woofers.
This did not happen if I use another source such as CD with HK 930, only with turntable. The Muffsy works since record plays and I can hear seemingly undistorted sound although with some hum which increases with the volume increase.
All the time the turntable ground wire is connected to the HK chassis; if I remove it, hum greatly increases and the woofer movement doesn't go away.
Sources other than turntable play well and woofers are not doing this.
What might be the reason for such woofer behavior.
The turntable input jacks ground is isolated from the HK930 ground (checked) and I BELIEVE same is true for the Muffsy output ground that goes to source selector.
When I use the turntable as source and increase or decrease volume - even if record is not playing - speaker's woofers move back and forward each time for a 1-1.5 centimeter or so with very low frequency sound. It's a lot for 6-inch woofers.
This did not happen if I use another source such as CD with HK 930, only with turntable. The Muffsy works since record plays and I can hear seemingly undistorted sound although with some hum which increases with the volume increase.
All the time the turntable ground wire is connected to the HK chassis; if I remove it, hum greatly increases and the woofer movement doesn't go away.
Sources other than turntable play well and woofers are not doing this.
What might be the reason for such woofer behavior.
The turntable input jacks ground is isolated from the HK930 ground (checked) and I BELIEVE same is true for the Muffsy output ground that goes to source selector.
Did some tests on the Muffsy/HK930 today.
Removing of all cables connecting the HK with sources including turntable didn't change anything.
Disconnecting of Muffsy power supply from Muffsy preamp PCB and disconnecting the turntable outputs completely eliminated woofers movement as well as hum. However, if turntable outputs were connected to HK930 with unpowered Muffsy strong hum appeared in speakers although no woofer movement was seen. Connecting of a turntable ground wire didn't help.
In the current setup Muffsy's ground and phono stage ground jacks are not connected with the HK930 ground while in the original phono stage they both were. This might be the reason for hum.
I wonder if using a DC to DC converter instead of Muffsy power supply and grounding Muffsy or turntable input ground jacks help to eliminate this hum.
Removing of all cables connecting the HK with sources including turntable didn't change anything.
Disconnecting of Muffsy power supply from Muffsy preamp PCB and disconnecting the turntable outputs completely eliminated woofers movement as well as hum. However, if turntable outputs were connected to HK930 with unpowered Muffsy strong hum appeared in speakers although no woofer movement was seen. Connecting of a turntable ground wire didn't help.
In the current setup Muffsy's ground and phono stage ground jacks are not connected with the HK930 ground while in the original phono stage they both were. This might be the reason for hum.
I wonder if using a DC to DC converter instead of Muffsy power supply and grounding Muffsy or turntable input ground jacks help to eliminate this hum.
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