Hi,
hope someone could give me clue, what’s the cause of hum and buzz in my system.
Situation is as follows:
Sony TA-F5000 integrated amp with 3 prong IEC detachable cord
Connection via RCA cables from Sony pre-outs to inputs of two Marantz MA-22 mono blocks
2x Marantz MA-22s with 2 prong non-detachable power cords
Power connection to high quality power strip which itself is connected to one grounded wall outlet
Speakers connected to Marantz MA-22s
This set up has very audible and disturbing buzz from loudspeakers, spectrum shows peaks every 50Hz starting from 50Hz to kHz region with largest energy peak at 150Hz.
I tried to narrow down the problem, the findings so far:
- Volume, balance, bass and treble attenuators on Sony doesn’t affect the buzz in volume or frequency at all
- Switching the inputs or disconnecting all inputs Sony - same hum
- Plugging all devices to separate dedicated wall outlets, turning power plugs in outlets in different combinations -> still same hum
- Using different RCA cables, cheap or solid, or turning RCA plugs for better contact -> same hum
- Disconnect RCA cables from Marantz - no hum
- Shorten Marantz RCA inputs - no hum
- Shorten Marantz RCA inputs with 120 ohm resistor - no hum
- Connect portable battery powered player to Marantz - no hum
- Connect speakers or headphones to Sony - no hum
So what is this? No hum with portable battery powered player indicates a potential ground loop, but the only connection to the real ground is via Sony 3 prong plug, so it might be amp internal loop. Both amps are unmodified and otherwise untouched, power cords are original, RCA posts are original, ground screws in the amps tightened, as far as a can tell. Marantz's bias is OK according to service manual at 50mV, very little DC offset of 20MV is present at loudspeaker terminals.
Could it be some dried out electrolytics in one of the amps? Or is it some badly implemented grounding in one of the amps?
Attached are schematics of both amps.
Help and ideas are greatly appreciated!
Cheers
Daniel
hope someone could give me clue, what’s the cause of hum and buzz in my system.
Situation is as follows:
Sony TA-F5000 integrated amp with 3 prong IEC detachable cord
Connection via RCA cables from Sony pre-outs to inputs of two Marantz MA-22 mono blocks
2x Marantz MA-22s with 2 prong non-detachable power cords
Power connection to high quality power strip which itself is connected to one grounded wall outlet
Speakers connected to Marantz MA-22s
This set up has very audible and disturbing buzz from loudspeakers, spectrum shows peaks every 50Hz starting from 50Hz to kHz region with largest energy peak at 150Hz.
I tried to narrow down the problem, the findings so far:
- Volume, balance, bass and treble attenuators on Sony doesn’t affect the buzz in volume or frequency at all
- Switching the inputs or disconnecting all inputs Sony - same hum
- Plugging all devices to separate dedicated wall outlets, turning power plugs in outlets in different combinations -> still same hum
- Using different RCA cables, cheap or solid, or turning RCA plugs for better contact -> same hum
- Disconnect RCA cables from Marantz - no hum
- Shorten Marantz RCA inputs - no hum
- Shorten Marantz RCA inputs with 120 ohm resistor - no hum
- Connect portable battery powered player to Marantz - no hum
- Connect speakers or headphones to Sony - no hum
So what is this? No hum with portable battery powered player indicates a potential ground loop, but the only connection to the real ground is via Sony 3 prong plug, so it might be amp internal loop. Both amps are unmodified and otherwise untouched, power cords are original, RCA posts are original, ground screws in the amps tightened, as far as a can tell. Marantz's bias is OK according to service manual at 50mV, very little DC offset of 20MV is present at loudspeaker terminals.
Could it be some dried out electrolytics in one of the amps? Or is it some badly implemented grounding in one of the amps?
Attached are schematics of both amps.
Help and ideas are greatly appreciated!
Cheers
Daniel
Attachments
A most peculiar case. The Sony does not appear to be using the IEC earth pin at all, so what's getting you has to be all transformer leakage currents.
I would suggest:
1. Experiment with mains power plug orientation (if possible) until a multimeter indiciates a minimum of AC voltage between all 3.
2. Check for a possible bad ground connection to the TA-F5000 pre-out board (e.g. resistance between pre-out RCA and speaker (-)).This may indicate a ribbon cable issue or hairline fracture somewhere.
I would suggest:
1. Experiment with mains power plug orientation (if possible) until a multimeter indiciates a minimum of AC voltage between all 3.
2. Check for a possible bad ground connection to the TA-F5000 pre-out board (e.g. resistance between pre-out RCA and speaker (-)).This may indicate a ribbon cable issue or hairline fracture somewhere.
As noticed by #2, in the drawing of the Sony the (middle) earth pin of the IEC is not connected to the chassis. So why a three pin IEC? Check that for a possible drawing error.
Does (one of the) Marantz start to hum if a RCA cable of some length is connected to it's input but NOT connected to anything (open end)?
Same to connect an open end RCA cable to the pre out of the Sony: hum audiable?
Connect only one Marantz to the Sony: hum?
Connect both Marantz's inputs together with a (mono) RCA: hum?
To me it seems the (one of the) RCA's (unbalanced!) are picking up net-related noise, indicating a loose grounding somewhere. The cable itself may be fine, but the joint of the chassis connecter (one of the many used) can be broke.
Connect a parallel single wire from RCA shield to the other RCA shield (pre to main): hum?
Connect a single wire between the input RCA's of the Marantz's.
Does (one of the) Marantz start to hum if a RCA cable of some length is connected to it's input but NOT connected to anything (open end)?
Same to connect an open end RCA cable to the pre out of the Sony: hum audiable?
Connect only one Marantz to the Sony: hum?
Connect both Marantz's inputs together with a (mono) RCA: hum?
To me it seems the (one of the) RCA's (unbalanced!) are picking up net-related noise, indicating a loose grounding somewhere. The cable itself may be fine, but the joint of the chassis connecter (one of the many used) can be broke.
Connect a parallel single wire from RCA shield to the other RCA shield (pre to main): hum?
Connect a single wire between the input RCA's of the Marantz's.
Great catch, many thanks! Sony is floating ground as well, seeing 3 prong plug I blindly assumed it was grounded, but you're right, it is floating as well. And it has double box symbol indicating it is floating in the backside as well. I checked for schematic error and the pin is really not connected, so schematic is correct.
I also checked the grounding of pre out board and it seems to be solid (see markings in attached foto), all 0R resistance:
- pre out RCA ground shields (red mark) to speaker minus (green mark) - 0R
- pre out RCA ground shields (red mark) to pre out board grounding point (yellow mark) - 0R
- pre out board grounding point (yellow mark, black wires) to both main board connection points - 0R
- pre out board ground connection (blue marking, brown wire) to input board grounding point - 0R
As the grounding seems solid, the cause are probably transformer leakage currents between the amps.
Let me experiment with plug orientations and see what it brings!
Attachments
"As noticed by #2, in the drawing of the Sony the (middle) earth pin of the IEC is not connected to the chassis. So why a three pin IEC? Check that for a possible drawing error."
It would probably remain another mystery why Sony decided to use 3 prong cable for the EU version of the amp, as the amp seems to be designed for floating ground, Japan and US versions use 2 prong plugs.
"Does (one of the) Marantz start to hum if a RCA cable of some length is connected to it's input but NOT connected to anything (open end)?"
Yes, depending on the length and position of connected cable it does.
"Same to connect an open end RCA cable to the pre out of the Sony: hum audiable?"
With speakers connected to Sony and open end RCA connected to Sony pre-outs there is no hum.
"Connect only one Marantz to the Sony: hum?
Yes
"Connect both Marantz's inputs together with a (mono) RCA: hum?"
Could you please elaborate on this, I am not quite following... You mean input to input?
"Connect a parallel single wire from RCA shield to the other RCA shield (pre to main): hum?"
You mean like have amps connected by RCA and add additional RCA shield to the other RCA shield cable? I already did something similar by connecting the ground terminals (both connected to closure)
"Connect a single wire between the input RCA's of the Marantz's."
Without ground connection? Is this safe?
It would probably remain another mystery why Sony decided to use 3 prong cable for the EU version of the amp, as the amp seems to be designed for floating ground, Japan and US versions use 2 prong plugs.
"Does (one of the) Marantz start to hum if a RCA cable of some length is connected to it's input but NOT connected to anything (open end)?"
Yes, depending on the length and position of connected cable it does.
"Same to connect an open end RCA cable to the pre out of the Sony: hum audiable?"
With speakers connected to Sony and open end RCA connected to Sony pre-outs there is no hum.
"Connect only one Marantz to the Sony: hum?
Yes
"Connect both Marantz's inputs together with a (mono) RCA: hum?"
Could you please elaborate on this, I am not quite following... You mean input to input?
"Connect a parallel single wire from RCA shield to the other RCA shield (pre to main): hum?"
You mean like have amps connected by RCA and add additional RCA shield to the other RCA shield cable? I already did something similar by connecting the ground terminals (both connected to closure)
"Connect a single wire between the input RCA's of the Marantz's."
Without ground connection? Is this safe?
I measured the AC between the amps using 2 different methods. First directly ground terminal to ground terminal. Second using the method outlined in "HUM & BUZZ IN UNBALANCED INTERCONNECT SYSTEMS" white paper by Bill Whitlock ground terminal to wall outlet safety earth pin via 1k resistor and 0.1uF cap.
https://www.jensen-transformers.com/wp-content/uploads/2014/08/an004.pdf
Here are the values:
Method 1 ground pin Sony to ground pin Marantz, no RCA, no loudspeakers
- All power plugs at 0°
-- Amps off
Sony to Marantz left 33.7mV
Sony to Marantz right 33,7mV
-- Amps on
Sony to Marantz left 49,5mV
Sony to Marantz right 48,6mV
- All power plugs at 180°
-- Amps off
Sony to Marantz left 33.5mV
Sony to Marantz right 34mV
-- Amps on
Sony to Marantz left 48,3mV
Sony to Marantz right 48,4mV
- Sony Plug at 0°, Marantz plugs at 180°
-- Amps off
Sony to Marantz left 35,0mV
Sony to Marantz right 35,0mV
-- Amps on
Sony to Marantz left 43,5mV
Sony to Marantz right 44,0mV
So while the third orientation has 4-5mV less AC, there is for me no perceived difference in hum from the speakers in all three orientations, the defirence might be just too small.
Then I measured the AC using the method from white paper Figure 3:
Sony
Plug at 0°, Amp off 1mV, Amp on 33mV
Plug at 180°, Amp off 39mV, Amp on 5,5mV
Marantz left
Plug at 0°, Amp off 33mV, Amp on 18mV
Plug at 180°, Amp off 1mV, Amp on 14mV
Marantz right
Plug at 0°, Amp off 32mV, Amp on 17mV
Plug at 180°, Amp off 0mV, Amp on 14mV
So while there are difference in AC indicated by both methods, it is too small to be perceived as improvement.
Do I need a ground isolator or is there any thing else what I can do to improve the situation?
Looking at the schematics of the Marantz Pre-amps from the same era like SC-22 and SC-80 I noticed they use transformers at the pre-outs. Probably to solve exactly this issue.
https://www.jensen-transformers.com/wp-content/uploads/2014/08/an004.pdf
Here are the values:
Method 1 ground pin Sony to ground pin Marantz, no RCA, no loudspeakers
- All power plugs at 0°
-- Amps off
Sony to Marantz left 33.7mV
Sony to Marantz right 33,7mV
-- Amps on
Sony to Marantz left 49,5mV
Sony to Marantz right 48,6mV
- All power plugs at 180°
-- Amps off
Sony to Marantz left 33.5mV
Sony to Marantz right 34mV
-- Amps on
Sony to Marantz left 48,3mV
Sony to Marantz right 48,4mV
- Sony Plug at 0°, Marantz plugs at 180°
-- Amps off
Sony to Marantz left 35,0mV
Sony to Marantz right 35,0mV
-- Amps on
Sony to Marantz left 43,5mV
Sony to Marantz right 44,0mV
So while the third orientation has 4-5mV less AC, there is for me no perceived difference in hum from the speakers in all three orientations, the defirence might be just too small.
Then I measured the AC using the method from white paper Figure 3:
Sony
Plug at 0°, Amp off 1mV, Amp on 33mV
Plug at 180°, Amp off 39mV, Amp on 5,5mV
Marantz left
Plug at 0°, Amp off 33mV, Amp on 18mV
Plug at 180°, Amp off 1mV, Amp on 14mV
Marantz right
Plug at 0°, Amp off 32mV, Amp on 17mV
Plug at 180°, Amp off 0mV, Amp on 14mV
So while there are difference in AC indicated by both methods, it is too small to be perceived as improvement.
Do I need a ground isolator or is there any thing else what I can do to improve the situation?
Looking at the schematics of the Marantz Pre-amps from the same era like SC-22 and SC-80 I noticed they use transformers at the pre-outs. Probably to solve exactly this issue.