Hi.
I just bought my first used tube amps. A few tube resistors are burnt so I have those coming next week. I found that the speaker terminal ground on one mono block has zero resistance to ground while the other mono block speaker terminal ground has 10ohm to ground. Inside the speaker ground goes though a resistor with a yellow component running in parallel. What is this and what is the function and shall I have zero ohm to ground or 10 ohm?
I just bought my first used tube amps. A few tube resistors are burnt so I have those coming next week. I found that the speaker terminal ground on one mono block has zero resistance to ground while the other mono block speaker terminal ground has 10ohm to ground. Inside the speaker ground goes though a resistor with a yellow component running in parallel. What is this and what is the function and shall I have zero ohm to ground or 10 ohm?
Attachments
There is several "ground" in tube amplifier.
The main ground is the amplifier's "reference" point, which is usually the input signal "negative" point (and usually the main B+ negative point).
The "chassis" ground is the amplifier metal parts grounding point.
The "safety" ground is the mains safety ground wire connecting point.
In you picture, the amplifier ground is tied to chassis ground to 10R//10nF, which is very correct solution.
The mains safety ground tied to chassis ground, which is OK.
The output transformers secondary "cold" points (as loudspeaker "black" lug) tied to amplifier ground, which is also OK.
What's the problem?
The main ground is the amplifier's "reference" point, which is usually the input signal "negative" point (and usually the main B+ negative point).
The "chassis" ground is the amplifier metal parts grounding point.
The "safety" ground is the mains safety ground wire connecting point.
In you picture, the amplifier ground is tied to chassis ground to 10R//10nF, which is very correct solution.
The mains safety ground tied to chassis ground, which is OK.
The output transformers secondary "cold" points (as loudspeaker "black" lug) tied to amplifier ground, which is also OK.
What's the problem?
The "correct" is the first.... but if the output transformer secondary "negative" is connected to the "ground" via any -low- resistance, nothing would go wrong.
The important thing is connect the OPT secondary to definite -low- voltage potential.
BTW check the wiring of both mono block. In the #1 post the wiring is correct.
The important thing is connect the OPT secondary to definite -low- voltage potential.
BTW check the wiring of both mono block. In the #1 post the wiring is correct.
Morning. I have measured the two monoblocks and it looks like below. I guess B is some how wired incorrectly. True? Is it correct is that in and out signal ground shall sit 10 ohm from chassis ground like mono A?
Thanks for any help.
Mono Block A
Thanks for any help.
Mono Block A
- Speaker Ground
- Has two wires
- One to chassis ground via 10R/10nF
- One from Output Transformer
- Has two wires
- Measurements
- Speaker Ground to chassis = 10ohm
- Speaker Ground to RCA ground = zero ohm
- RCA Ground to chassis = 10 ohm
- Disconnecting/lifting 10R/10nF ground cable
- Measurements
- Speaker Ground to chassis = no connection
- Speaker Ground to RCA ground = zero ohm
- RCA Ground to chassis = no connection
- Measurements
- Speaker Ground
- Has two wires
- One to chassis ground via 10R/10nF cable
- One from Output Transformer
- Has two wires
- Measurements
- Speaker Ground to chassis = zero ohm
- Speaker Ground to RCA ground = zero ohm
- RCA Ground to chassis = zero ohm
- Disconnecting/lifting 10R/10nF ground
- Measurements
- Speaker Ground to chassis = zero ohm
- Speaker Ground to RCA ground = zero ohm
- RCA Ground to chassis = zero ohm
- Measurements
- Disconnecting Output Transformer cable from speaker ground
- Measurements
- Output Transformer Speaker Ground to chassis = no connection
- Measurements
Attachments
Thanks. Just found a thin ground wire that goes from the capacitor bank to the through hole nut of the metallic XLR /RCA input switch. This thin ground wire is both on amp A and B but on A it did not ground. When I tightened the switch nut it is now grounded. So both amps are now like Amp B.
Thanks!
- Speaker Ground to chassis = zero ohm
- Speaker Ground to RCA ground = zero ohm
- RCA Ground to chassis = zero ohm
Thanks!
I suggest the #11 solution.
The 10R//100nF act as hum-loop block network.
If the previous source (phono, preamp, DAC etc.) and this power amp connected together with interconnect, sometimes ground loop be formed (via mains safety earth, if both devices is "earthed"), and audible hum may presents.
This loop can be interrupt with ground-lift switch, which can separate the device "ground" and safety earth/metal part of device (which are ALWAYS connected together metallically).
The hum-loop block network works like ground-lift switch, so if you shorting it, acts as shorted switch, which is unbreakable.
Sometimes, the hum-loop block network is unnecessary (no hum), but if you changes sources, the hum may occur.
Not a viable assumption to solder/desolder wire if hum is audible.
The 10R//100nF act as hum-loop block network.
If the previous source (phono, preamp, DAC etc.) and this power amp connected together with interconnect, sometimes ground loop be formed (via mains safety earth, if both devices is "earthed"), and audible hum may presents.
This loop can be interrupt with ground-lift switch, which can separate the device "ground" and safety earth/metal part of device (which are ALWAYS connected together metallically).
The hum-loop block network works like ground-lift switch, so if you shorting it, acts as shorted switch, which is unbreakable.
Sometimes, the hum-loop block network is unnecessary (no hum), but if you changes sources, the hum may occur.
Not a viable assumption to solder/desolder wire if hum is audible.