PL2000 Series 2

George S.

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#1
So when I upgraded my speakers to JBL L150s I noticed my right channel had slightly less gain than the left. I swapped everything around and finally narrowed it down to the preamp after swapping in a Marantz 3200 from the garage system. Tore the 2000 apart last weekend and ordered parts and also finding a broken solder pad. I've had this unit for probably 30 years, getting it I think from a pawn shop outside Ft. Bragg NC. Five years ago I recapped it, but it really needed a total rebuild. So I started this morning, all new or NOS silicon, all new caps, and all new 1% resistors. And I had some of the good wire left over from amp builds so why not use it. I'm thinking I'll get it finished and back in the system tomorrow. And yes, rebuilt it wearing a Magnivisor for magnification and checked components against the service manual through out rebuild and after. Many of the resistors were of slightly different values than the schematic and like resistors varied quite a bit from each other, debatable if replacing them will make a audible difference, but i don't want to go back into the unit in the future. And, I'm sticking with the stock opamps. PXL_20201122_235859034.jpg PXL_20201123_001225048.jpg PXL_20201123_001328814.jpg
 

mlucitt

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#6
The channels will remain unbalanced until... you remove that Allen socket screw and washer on the switch circuit board.
Seriously, I had a preamp with a dual potentiometer volume control and one wiper showed more resistance than the other in all positions. Easy check. I didn't know if I could 'clock' one against the other, so I just replaced it. Problem solved.
 

George S.

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#7
So I installed the Switchcraft RCAs with fiber washers on the chassis, but was unhappy with them. Did not like the grounding scheme, and the chassis output holes were closer together than the input holes, forcing me to file a flat on each fiber washer outside edge to get them to seat correctly and not overlap, My original RCAs were in good shape with no broken plastic so I cleaned and reinstalled them. I like the pcb mount RCAs much better on this preamp. So completed reassembly, checked everything over once more, put power to it, and blew the fuse. So it's got to be a noob mistake right? Looking at it I found it right away. I put the 4136 opamp in backwards, DUH! So, replaced it with a extra, along with the fuse, and fired it up. Worked great, until I pressed the Ambience button, then real bad hum. So back to the bench, replaced Q1, a TIS97, and opamp 4739. Powered it up, and Oh Man, success! What a difference! Now I know that before, the sound was "thin", can't really describe it any better that. The 2000 is dead silent with no hum or static, yet, oh how she sings, so much better. I played the FLAC file Moody Blues Days of Future Past, just amazing. So, was it worth the trouble? Oh yes, definitely! PXL_20201123_180925573.jpg PXL_20201123_180954164.jpg PXL_20201123_200034608.jpg PXL_20201123_200325009.jpg
 

George S.

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#9
The channels will remain unbalanced until... you remove that Allen socket screw and washer on the switch circuit board.
Seriously, I had a preamp with a dual potentiometer volume control and one wiper showed more resistance than the other in all positions. Easy check. I didn't know if I could 'clock' one against the other, so I just replaced it. Problem solved.
Yes, or use the balence control. With the 2000, it was just time to bite the bullet and rebuild it. Think it was built in 78 or 9. Sheesh, I'm getting old
 

George S.

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#10
My man cave is the garage, ask the wife. Since I put the big Samsung curved screen up, the room is hers. And never leave the TV audio out set to optical going to the DAC, that's a no no. Don't you know the TV has perfectly good speakers, why route it to the stereo?
 

George S.

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#11
So I've now had quite a few hours listening to the preamp, and what a difference. If your old preamp hasn't been upgraded to modern components, go for it, it makes such a difference. Do it yourself or pay one of the builders to do it. There is such a difference I need to rerun REW to reintegrate the subs and the mains on this 2.2 biamp system. Me being just a hobbyist and knowing just enough to screw things up, I ordered the cap kit from that seller on the Bay with the Blackwood address. Selecting caps confuses the hell out of me. The resistors were easy, just took a couple hours making a list using the manual and looking at the board. Go for it, it's so worthwhile! Now, only thing to do is open it back up next weekend, and replace every last bit of original wire with silver plated teflon insulated wire. Then it's finished. PXL_20201126_134741688.jpg
 

Wheel-right

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#12
Eve
So I've now had quite a few hours listening to the preamp, and what a difference. If your old preamp hasn't been upgraded to modern components, go for it, it makes such a difference. Do it yourself or pay one of the builders to do it. There is such a difference I need to rerun REW to reintegrate the subs and the mains on this 2.2 biamp system. Me being just a hobbyist and knowing just enough to screw things up, I ordered the cap kit from that seller on the Bay with the Blackwood address. Selecting caps confuses the hell out of me. The resistors were easy, just took a couple hours making a list using the manual and looking at the board. Go for it, it's so worthwhile! Now, only thing to do is open it back up next weekend, and replace every last bit of original wire with silver plated teflon insulated wire. Then it's finished. View attachment 46045
Even though I'm using a Kenwood Basic C-1 in my set-up my PL 2000II still sits front and center because it's just darn good looking.
 

George S.

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#13
Eve

Even though I'm using a Kenwood Basic C-1 in my set-up my PL 2000II still sits front and center because it's just darn good looking.
Yes, so cool looking. Yes, it's a dinosaur and there are much better preamps out there. Yes, I don't care, I like the looks and simplicity of the PL2000.
 

George S.

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#14
So finally getting the preamp finished. Today I did Joe and Lee's ground mod from the DChristie thread, and getting the last of the original wiring replaced with quality mil-spec wire. Been putting off rewiring the balance pot because it's slightly off in the center position, verified it on the scope and ohm meter. Since I can't find a good replacement right now, I'll reinstall it clocked to about 2 o'clock and live with it until I find a replacement.
 

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George S.

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#15
Photo of the now insulated ground screw that's furthest from the transformer. Took a 3/8" sharp drill bit and countersunk the hole slightly with aim being to cut that trace out around the hole so the screw can't ground. Then installed screw with a #6 nylon washer. It is no longer a ground screw.
 

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George S.

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#17
Thanks go to you all! Think I'm done with it other than finding a high quality balance pot.
All new film caps.
All new 1% metal film resistors.
Joe's DC protect film cap mod.
Joe's secondary voltage reduction mod.
Joe's grounding mod.
Joe's LED mod.
Mark , Joe, and Lee's Opa 2134 Browndog mod.
New mil-spec wiring.
Feet.
IEC socket.
It sure sounds good. Now playing Dire Straits FLAC files. Biggest improvement I think was Browndog Opa 2134 in the Phono section. Big improvement!
Tomorrow I'm going to pull 1 of 2 Optimus MPA-250 amps out of the garage system and some big Pioneer CS speakers to see how the rear channels work. Want to test the reverb as I have same Browndog in that circuit.
 
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George S.

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#19
Yup, can't remember the opamp designators on the schematic right now, but a dual Opa 2134 as the main one up front center, and single Opa 2134 for the phono and another single for the front/rear speaker circuit. Reverb circuit with two channels is interesting, turn reverb all way up and normal reverb on the music, but vocals really echo. Turn it down and it seems to work properly across the spectrum. Going to test rear speakers tomorrow with a Optimus MPA-250 amp and big Pioneers. I checked phono and aux input I use for digital over and over on the scope and REW real time spectrum analyzer. Everything looked good and sounds excellent.
 

George S.

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#20
I never liked the stock reverb, but I like it now. Listening to digital Dire Straits it seems to expand the sound stage. I have it turned 1/2 way up, very impressive. Going to turn it down some.
 
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