Phase Linear 2000 PREAMPLIFIER SUPER UPGRADE AND REPAIR
- Thread starter GeorgeP
- Start date
I finally got done with cleaning and re-caping my unit, no mods yet but fully operational now, both channels working in stereo mode.
Started with a full circuit board wash as it was full of residue
I then replaced all caps and reconditioned pots and switches, including RCA connectors.
Also replaced the power cord with a 3 pronged to ground the chassis.
Thanks again to all for your help, it sounds and looks like new.
Started with a full circuit board wash as it was full of residue
I then replaced all caps and reconditioned pots and switches, including RCA connectors.
Also replaced the power cord with a 3 pronged to ground the chassis.
Thanks again to all for your help, it sounds and looks like new.
I've experimented with various ground schemes on the PL2000 using the ground lug on the IEC socket.
Using the QuantAsylum QA403 to measure noise, lowest noise is with no ground connection.
Kind of disappointing as I thought it would be cool to ground the entire system there. All components would be grounded through the cable shields.
Like Sniff says, they skipped grounding for a reason.
Using the QuantAsylum QA403 to measure noise, lowest noise is with no ground connection.
Kind of disappointing as I thought it would be cool to ground the entire system there. All components would be grounded through the cable shields.
Like Sniff says, they skipped grounding for a reason.
All 120V electrical appliances in the USA are IEC Class 1 (basic insulation), or Class II (double insulation) like a plastic 1/4" drill housing.*
Per the International Electrotechnical Commission (IEC), "A safety ground is required for all Class I devices."
This requirement did not exist when Bob Carver/Phase Linear Corp. was designing amplifiers. These amps, from the "vintage" era, only have a simple two-prong plug. In that case you would try one way in the socket, then try the other, and use the one that gives you the least amount of hum. Later, amplifiers would have a polarized plug with one blade wider than the other. The wide one is the neutral side, and the narrow is the hot.
Look at any modern amplifier and you will see a three-prong plug.
If your grounded audio component (which is Class I) is making more measurable noise when it is safely Grounded (you can use a Ground defeat plug to check) it is not because the noise is inside the audio component. The noise is coming from outside the audio component.
If the noise is enough to make a difference, say 0.02% higher, then you need to eliminate the source of noise because it is also affecting other audio components that may or may not be safety Grounded.
Worst case scenario is a faulty power supply or loose Ground in an appliance that will eventually shock you or start a fire.
Best case is a noisy fluorescent ballast that is getting ready to fail.
If you want to find the noise, connect your measuring equipment to the device under test (DUT). and systematically turn off all lights, unplug all appliances, disconnect anything with a cord, or turn off circuit breakers - one at a time to locate the source of the noise.
You will likely find one or more devices that have a Grounding issue. The only other possibility is a noisy Ground coming from the electric company; they will come to your location for free to determine the cause because they know the importance and safety of a good ground. Often the copper wire running down the nearby power pole into the Earth has been broken.
A quick note on Ground Loops. Do not break a ground loop by defeating a 3-prong plug. This is only one side of the Ground Loop. The other side of the Ground Loop is the interconnect cable. To properly break the Ground Loop, ensure the interconnect cables shield is not connected to the chassis of at least one device. This is a little harder to do than snipping off the Ground Pin on your electrical plug, but it will not kill you.
* Class I - where user protection from electric shock is achieved through a combination of insulation and a protective earthing/ground.
Class II - where user protection from electric shock is achieved through two levels of insulation (either double or reinforced), without the need for earthing.
Class III - where the input is connected to a safety extra-low voltage (SELV) circuit meaning no further protection, such as earthing, is required.
Per the International Electrotechnical Commission (IEC), "A safety ground is required for all Class I devices."
This requirement did not exist when Bob Carver/Phase Linear Corp. was designing amplifiers. These amps, from the "vintage" era, only have a simple two-prong plug. In that case you would try one way in the socket, then try the other, and use the one that gives you the least amount of hum. Later, amplifiers would have a polarized plug with one blade wider than the other. The wide one is the neutral side, and the narrow is the hot.
Look at any modern amplifier and you will see a three-prong plug.
If your grounded audio component (which is Class I) is making more measurable noise when it is safely Grounded (you can use a Ground defeat plug to check) it is not because the noise is inside the audio component. The noise is coming from outside the audio component.
If the noise is enough to make a difference, say 0.02% higher, then you need to eliminate the source of noise because it is also affecting other audio components that may or may not be safety Grounded.
Worst case scenario is a faulty power supply or loose Ground in an appliance that will eventually shock you or start a fire.
Best case is a noisy fluorescent ballast that is getting ready to fail.
If you want to find the noise, connect your measuring equipment to the device under test (DUT). and systematically turn off all lights, unplug all appliances, disconnect anything with a cord, or turn off circuit breakers - one at a time to locate the source of the noise.
You will likely find one or more devices that have a Grounding issue. The only other possibility is a noisy Ground coming from the electric company; they will come to your location for free to determine the cause because they know the importance and safety of a good ground. Often the copper wire running down the nearby power pole into the Earth has been broken.
A quick note on Ground Loops. Do not break a ground loop by defeating a 3-prong plug. This is only one side of the Ground Loop. The other side of the Ground Loop is the interconnect cable. To properly break the Ground Loop, ensure the interconnect cables shield is not connected to the chassis of at least one device. This is a little harder to do than snipping off the Ground Pin on your electrical plug, but it will not kill you.
* Class I - where user protection from electric shock is achieved through a combination of insulation and a protective earthing/ground.
Class II - where user protection from electric shock is achieved through two levels of insulation (either double or reinforced), without the need for earthing.
Class III - where the input is connected to a safety extra-low voltage (SELV) circuit meaning no further protection, such as earthing, is required.
A future experiment will be running a ground from the factory ground stud on the chassis to a dedicated ground rod. I've got the flat braid and rod in the ground about 6 ft deep using a slide hammer.
Just haven't had time to fire up the equipment and do the test. I doubt I'll see any change in the noise floor, but it's worth trying.
Just haven't had time to fire up the equipment and do the test. I doubt I'll see any change in the noise floor, but it's worth trying.
Use that as a station ground for yer HF rig. Mine is a 8’ rod, some 5/16 copper tube to run up to the transceiver and antenna tuner. I think my ground rod hits the water table…….
When powered by my inverter My C-1 was making noise until I hooked the chassis ground to the ground of the inverter…… the inverter probably need its own ground rod
When powered by my inverter My C-1 was making noise until I hooked the chassis ground to the ground of the inverter…… the inverter probably need its own ground rod
Well, I come from the computer server world and every appliance has a grounded chassis, for both noise and safety. UL regulations have changed in the last 30 years which would explain the lack of ground in older equipment.
Truth is that I acted based on experience rather than looking at the intended design. Now that you guys questioned it I will test with or without a ground for difference in noise levels as really that is the only drawback of connecting to earth ground.
Truth is that I acted based on experience rather than looking at the intended design. Now that you guys questioned it I will test with or without a ground for difference in noise levels as really that is the only drawback of connecting to earth ground.
I saw a slightly increased noise floor with a wire ran from the IEC ground lug to the left most circuit board grounding screw. I even went as far as removing the paint on the chassis where the "L" bracket sits against it.
Also perused schematics for other equipment and tried several variations of X and Y safety caps.
Lowest noise floor was with only a line and neutral connection.
But, this was seen on a piece of test equipment, a Real Time Spectrum Analyzer, and the noise would not be audible in the system.
One thing I haven't tried is one of those IEC modules with the 60 Hz noise filter and safety caps built into it.
Was working on a Symmetricom GPS receiver the other day, and it has one of those modules.
Also perused schematics for other equipment and tried several variations of X and Y safety caps.
Lowest noise floor was with only a line and neutral connection.
But, this was seen on a piece of test equipment, a Real Time Spectrum Analyzer, and the noise would not be audible in the system.
One thing I haven't tried is one of those IEC modules with the 60 Hz noise filter and safety caps built into it.
Was working on a Symmetricom GPS receiver the other day, and it has one of those modules.
I didn’t mention it but I do have a line filter coming into the external power supply. That feeds the meanwell SPS and that goes to the phono pre cabinet. It enters a WP designed filter specifically for the preamp and SPS and from there it feeds the power switch.
Also the filter board in the main cabinet is in a steel box as far as possible from the boards.
Where power and signal must cross it is at 90 degrees with as much gap as possible.
Input to the boards is extremely short run from input jacks.
I did my best to use every mechanical advantage to support the circuit that has immeasurably low noise and distortion so as to minimize any added noise.
Also the filter board in the main cabinet is in a steel box as far as possible from the boards.
Where power and signal must cross it is at 90 degrees with as much gap as possible.
Input to the boards is extremely short run from input jacks.
I did my best to use every mechanical advantage to support the circuit that has immeasurably low noise and distortion so as to minimize any added noise.
I am almost ready to order the new PCB for my version of the preamp. I decided that the newer OP-AMP OPA1612 is worth a try... its even better than the OPA-1602 as crazy as that sounds. Look at the spec sheet!! I attached it's data sheet. Same pinout, so why not? I printed the PCB on paper and pinned it on a foam carrier to check part placements. Pic attached. I can either use the AC to DC converter that will make no AC fields with coil windings, or the transformer it the far back corner. I had one error...the package size for the chip ordered was the really small one, much smaller that the SOIC-8, so I ordered the newer chip anyway in the extended temp range also. When that chip arrives, I place it on the paper PCB printed "one-to-one"
and see if all fits, then order the PCB from ExpressPCB.
If the design works out, maybe some out there may want to build one?? I also found a nice 1.75" high BUD chassis with RACK panel combo for $60 Bucks, will make a nice shielded home for this Preamp!
and see if all fits, then order the PCB from ExpressPCB. If the design works out, maybe some out there may want to build one?? I also found a nice 1.75" high BUD chassis with RACK panel combo for $60 Bucks, will make a nice shielded home for this Preamp!