Rob DeFries
Active Member
There's a 3090 SM on Hifiengine. Difficult to read with broken up schematic. But it'll show you the servo is an input on Q315B.
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Onkyo Super Servo Cable - Tech minded people THIS IS FOR YOU!
- Thread starter DrDarkFish
- Start date
Rob, I need your advice. I build 2 shorting plug with 470ohm resistor and and put into the left and right jack of the servo loop. The servo connection light is on when I turned on the preamp, but when I turned on the power amp, loud distortions heard. Shall I just put rca cap on the L/R of the servo loop.
Thanks
Rob DeFries
Active Member
If it works without the short plugs it'll work.
But why use a 470 ohm resistor in the plug? The diagram shows clearly that the live pin comes from the outer (ground) layer of the signal cable (which is connected to the ground of the power amp) and minus comes from ground poweramp too.
I don't see any 470 ohms....
Look closely at the diagram. The signal is on the middle pin of both plugs, lika any normal cable. The outer layer, minus signal, ground, whatever you wanna call it, is connected from the power amp side to the middle pin of the plug that goes into the servo connection.
And the ground of that plug connects to the ground of the power amp. Ground plus ground is ..... Just make a connection between the plus and ground and with that plug you'll put the inverted amp to ground. Doing nothing...... as it is drawn in the manual.
Am I wrong than I'll have no clue whatsoever what the servo is doing.
But why use a 470 ohm resistor in the plug? The diagram shows clearly that the live pin comes from the outer (ground) layer of the signal cable (which is connected to the ground of the power amp) and minus comes from ground poweramp too.
I don't see any 470 ohms....
Look closely at the diagram. The signal is on the middle pin of both plugs, lika any normal cable. The outer layer, minus signal, ground, whatever you wanna call it, is connected from the power amp side to the middle pin of the plug that goes into the servo connection.
And the ground of that plug connects to the ground of the power amp. Ground plus ground is ..... Just make a connection between the plus and ground and with that plug you'll put the inverted amp to ground. Doing nothing...... as it is drawn in the manual.
Am I wrong than I'll have no clue whatsoever what the servo is doing.
Ok, I am just seeing this. I have an Onkyo M5090 Amp and P3090 pre. Ever since I bought these (used) I had a hum in the right Chanel not matter how I grounded them.
I don't have this servo cable.
Just used normal RCA cables in the slot that says "Output 2" on the pre-amp. And left the 4 RCA (Servo) outlets in "Output 1" on the pre-amp vacant (NO cables).
Would that be causing the hum ?
Also can you explain (In Plain English) what do you mean by using a short RCA cable on R and Left servo? There are 4 RCA connects for the servo cable....where would you plug the short RCA cable? And it is 1 or 2 ?
Also if you ever opened the Pre-amp there are 6 circuits for this Servo thing, they are housed under smoky plastic covers. So there is circuitry for this, it is not just plugs in the back.
Would appreciate the info.
Thanks.
I don't have this servo cable.
Just used normal RCA cables in the slot that says "Output 2" on the pre-amp. And left the 4 RCA (Servo) outlets in "Output 1" on the pre-amp vacant (NO cables).
Would that be causing the hum ?
Also can you explain (In Plain English) what do you mean by using a short RCA cable on R and Left servo? There are 4 RCA connects for the servo cable....where would you plug the short RCA cable? And it is 1 or 2 ?
Also if you ever opened the Pre-amp there are 6 circuits for this Servo thing, they are housed under smoky plastic covers. So there is circuitry for this, it is not just plugs in the back.
Would appreciate the info.
Thanks.
Ok....
(THIS THREAD APPEALS TO THE TECH MINDED-NOT JUST THOSE FAMILIAR WITH ONKYO PRODUCTS)
There is one or two threads out there where people have tried to get to the bottom of this mystery. It doesn't appear to be resolved. It isn't rocket science...
I'm determined to work this out..:yes:
How the hell do we make an 'Onkyo Super Servo Cable'???
I just bought myself an Onkyo Integra M-509 Power and P-309 pre.. which have the capacity to use one of these mystery cables.. It simply allows you to connect your preamp to your power amp in a "better way"- at least by early 80s standards.
For those of you who dont know what these cables are, I have attached two photos (among other attachments) of what they look like. They simply look like an RCA cable that has 4 plugs on one end and two plus a grounding wire on the other..
According to Onkyo propaganda:
"In a normal RCA the grounding for both L and R channels is common. Therefore due to cable impendance and pin terminal contact resistance, the right channel signal will tend to flow back through the left channel ground lead and visa versa. The Super servo cable completely eliminates the left/right mutual interference"
I found a diagram in an manual for a Onkyo M-506 amp which explains what's going on. I have attached this to my post. The diagram appears to show how ONE channel operates.
From what I can tell: out of the preamp there are two outputs per channel, one labled 'Signal' and the other called 'Servo Sensor' this comes together as ONE input to the poweramp.I don't know how esle to interpret this diagram, it seems right to me.
The signal terminal is the positive terminal.. The centre pin carries the signal and conncects to the centre pin on the input of the poweramp. There is a grounding wire that is attached to the outercasing of the (+) plug on the preamp end that also attaches to the outercasing of the input on the power amp but also follows on to the a grounding horsehoe.
The superservo cable is the negative cable, it is connected to the centre pin on the preamp BUT connects to the outercasing of the input to the power amp.
I assume that both grounding wires for the left and right channels come together after being attached to their respective channel plug outercasings and form one grounding wire..
What are your thoughts? Any help would be greatly appreciated
Cheers,
Fish
Perhaps a stupid question: I assume the 2 RCA (Red) plugs would plug into one Chanel on the back of the pre-amp & the other 2 White RCA plugs would go into the other Chanel, thus the 4 RCA cables would be Horizontal (Not Vertical) on the back of the Pre-amp ?
Thanks.