No more 60 Hz hum in a PL2000 preamp.

Wanted to go with WIMA film caps and I did try. Problem is they're very hard to fit on these old boards due to the square/rectangular shape and short leads. Also, many of them were out of stock.
So went with Panasonic ECW since they had good reviews, were in stock, and come with crimped leads that make installation easier
 

Attachments

  • PXL_20211003_171105177.jpg
    PXL_20211003_171105177.jpg
    3.4 MB · Views: 16
The pin vise is pointing to a CDE silver mica capacitor. Joe said to use these for the smaller values. He didn't say why, so I researched why. They are very expensive! The higher the value the higher the cost.
So, have to use electrolytic where a film would just be too large to fit, silver mica where it makes economic sense, and film everywhere else. No ceramic capacitors allowed on the board.
 

Attachments

  • PXL_20211003_192112333.jpg
    PXL_20211003_192112333.jpg
    1.5 MB · Views: 20
Yep, those little WIMA's are a bitch to get in there..
 

Attachments

  • 20211003_173555.jpg
    20211003_173555.jpg
    1.3 MB · Views: 22
laatsch55 said:
Yep, those little WIMA's are a bitch to get in there..
Click to expand...
Yeah, I got it down to pretty much all WIMA, but it bothered me that some of the leads were really angled. Then I started reading and Panasonic ECW seemed to be the best solution.
#2 was heavily oiled when I opened it up. Whatever they spayed on the pots didn't evaporate and left a oily mess. The pots fiber portion appears to be saturated to some depth on the outside with oil. One of the 10k tone controls snapped right off without any real force put on it. Most probably was already cracked, but the oil soak doesn't help. Most probably going to pull all the pots out of the test unit and use them here.
Note I installed the largest components first because there are no markings on the board. Those larger components provide a reference so the smaller components get installed correctly. If building a kit, normally the smaller components get installed first. That would take way too long here and induce errors.
 
Oil soaked clean thru or already cracked. Bummer. Oh well, the test unit has good pots.
 

Attachments

  • PXL_20211004_003940148.jpg
    PXL_20211004_003940148.jpg
    1.5 MB · Views: 17
I count (10) of those little ceramic capacitors on the original board. Are they all the same value? So, 10 silver mica caps for replacement? Which Mouser P/N did you select?
 
Mark L., I'm using 16 pcs of CDE silver mica on these builds. Probably easier to photo the numbers for you. The locations and quantity are written on the bags. Will write this all up in PDF eventually.
 

Attachments

  • PXL_20211004_015552813.jpg
    PXL_20211004_015552813.jpg
    2.1 MB · Views: 25
Mark L., It gets expensive. So if one wants to save, just use silver mica in the phono section, and films elsewhere. These will be with me until I'm gone so I decided to make the investment. Besides, I needed a preamp to match those magnificent WOPLs!
 
Joe makes very valid points about the quality of the original jacks. Wish there is a superb quality 90 degree replacement jack, but there isn't. I find originals adequate for my needs, particularly when servicing the unit. The first photo shows a good reason to keep the original jacks, and long wiring for the secondaries and power switch. No wiring was undone in the first photo.
The second photo shows my attempt to strengthen the rear edge of the board with a long length of solid copper ground wire I purchased at the local big box hardware store long ago. I don't remember the gauge, but it was the smallest gauge they sold off a spool. The "star ground" is the very right side screw hole by the transformer, the middle screw has no trace to it, the far left screw hole has the trace cut away from it with a sharp counter sink bit. That far left screw gets a nylon washer under the head.
 

Attachments

  • PXL_20211004_150254939.jpg
    PXL_20211004_150254939.jpg
    2.1 MB · Views: 27
  • PXL_20211004_152139677.jpg
    PXL_20211004_152139677.jpg
    3.5 MB · Views: 30
George S. said:
Joe makes very valid points about the quality of the original jacks. Wish there is a superb quality 90 degree replacement jack, but there isn't. I find originals adequate for my needs, particularly when servicing the unit. The first photo shows a good reason to keep the original jacks, and long wiring for the secondaries and power switch. No wiring was undone in the first photo.
The second photo shows my attempt to strengthen the rear edge of the board with a long length of solid copper ground wire I purchased at the local big box hardware store long ago. I don't remember the gauge, but it was the smallest gauge they sold off a spool. The "star ground" is the very right side screw hole by the transformer, the middle screw has no trace to it, the far left screw hole has the trace cut away from it with a sharp counter sink bit. That far left screw gets a nylon washer under the head.
Click to expand...

Is that strip along the length of those jacks fiberboard?

Don't know if it's adaptable in your case but I replaced their conterparts in a DH-101. The "cardboard" strips were broken in several places. I made an exact 1-1 drawing and with some fairly thin stainless steel, took it to a machine shop for precise cutting and hole drilling.

They fit perfectly and I loaded them with chassis mount insulated gold plated RCA jacks.

The entire jackpack of a DH-101 is made as cheap as cheap can be. The jacks themselves are really bad.
 
Nope, they are 90 degree phono jacks soldered directly to the circuit board. I like your idea though. In this case there just really isn't enough room to mount jacks on a intermediate plate. Very tight.
 

Attachments

  • PXL_20211004_174307492.jpg
    PXL_20211004_174307492.jpg
    2.8 MB · Views: 8
So I deviated from the test unit by using a 1 uF and 4.7 uF film in place of the two small electrolytics in the power supply area. Results were not good. Films are removed and electrolytics are in per the photo.
 

Attachments

  • PXL_20211004_172859777.jpg
    PXL_20211004_172859777.jpg
    1.9 MB · Views: 12
George S. said:
Nope, they are 90 degree phono jacks soldered directly to the circuit board. I like your idea though. In this case there just really isn't enough room to mount jacks on a intermediate plate. Very tight.
Click to expand...

Too bad, I thought it might be doable. Only seen inside a PL2000 once - a long time ago so I was guessing.
 
After swapping out those 2 film caps for electrolytics.
118 VAC line voltage today. Pulled the two 47 ohm voltage dropping resistors in series with the secondary and installed 25 ohm. B- rail is -13.3 VDC, B+ is +13.3. Joe says not to exceed 30 VDC total. Going to go with this for now on #1. Need to pull those film caps out of the #2 board.
A photo of the rear pcb stiffener from a different angle.
 

Attachments

  • PXL_20211004_201146013.jpg
    PXL_20211004_201146013.jpg
    3.1 MB · Views: 18
Been sitting here for a couple hours listening to #1. Listened to some digital Rush and Allman Bros.. Sounds super. Rush was right in my face, Allman Brothers I heard those big tall bongo type drums for the first time on one song I'm very familiar with. Channel separation and detail is unreal.
I'll get to #2 next weekend and will update if those jacks I ordered will work.
Takes a lot of work to completely rebuild one of these, but worth it. #1 in the system and the test unit on the speaker. Later.
 

Attachments

  • PXL_20211004_220637908.jpg
    PXL_20211004_220637908.jpg
    2.2 MB · Views: 9
George S. said:
Probably easier to photo the numbers for you.
Click to expand...
Thanks for this info.
Surprised that electrolytic caps in the PS section would give you better performance than film caps of the same capacity...

I found these beauties on ebay from Taiwan, not cheap; but what is these days? They are like Lee's but have the yellow metal:
https://www.ebay.com/itm/1pcs-Switchcraft-RCA-Gold-Plated-Female-Socket-Connector-NOS-/151725623932
They suit me for the "Output" and "Phono" jacks, everything else can stay OEM.

I like the rear stiffener, it accomplishes two things: 1 - It makes the back of the circuit board as stiff as a brick, and 2 - It keeps the two grounds at the same potential for the back area of the circuit board.

I saw your picture of the PL2000 in the "service" position to modify the RCA jacks. I will have to unsolder my secondary wires to make that move. But the more interesting thing is that my PL2000 does not have that metal plate behind the faceplate. My S/N is 7465, what is yours?
 
Last edited:
Mark L. , All 3 PL2000s I have are S2. The metal plate your talking about may be the transformer shield that is held in by two rear screws or the switch plate that holds the switches and is held in by the balance and reverb pot. The switch plate is 90 degree angled and is the filler for that cutout on the S2 faceplate.
As for the two film caps in the power supply. I think the reverb opamp became unstable and was creating distortion. Some thing wasn't right, and those two caps were the only difference between the two units.
Wish I knew more about electronics, but I don't. I could never have gotten these preamps to this level without the good people on this forum
 
Last edited:
George S. said:
Mark L. , All 3 PL2000s I have are S2. The metal plate your talking about may be the transformer shield that is held in by two rear screws or the switch plate that holds the switches and is held in by the balance and reverb pot. The switch plate is 90 degree angled and is the filler for that cutout on the S2 faceplate.
As for the two film caps in the power supply. I think the reverb opamp became unstable and was creating distortion. Some thing wasn't right, and those two caps were the only difference between the two units.
Wish I knew more about electronics, but I don't. I could never have gotten these preamps to this level without the good people on this forum
Click to expand...
What are the reference designators on those caps that were unhappy?
 
You must log in or register to reply here.
Back
Top