Phase Linear 2000 Pre-Amp Rebuild

Yes I use LDOs all the time. That is what they are designed for.
 
Or instead use LM317/337 and use 2 adjustment resistors to get +/-14 V instead of +/-15V. The op amp will not care about 14V. It will care about >18V

The problem you may face with many new LDOs is that many are only offered in SMT packages which are usable but more of a challenge to implement than the older 3 pin through hole technology parts. The LM317/337 are old school 3 pin regulators that are easy to apply and not very fussy. Many of the newer LDOs also are for low voltage input only since many/most new electronic applications have moved to low voltage operation driven largely by battery powered applications.
 
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I did my 3300 power supply on perf board. Perry has a power supply board he did. It's not small but it serves the purpose. You can always go the way of the zener power supply used in the 400II. I'd add some caps across the zeners. This is the last time Im going to say use 7812's and be done with it.
 
Watts, I hear you about the +/-12. About the TO92 package, on Mouser it looks like they can only supply 100mA. I may be reading datasheet wrong but assuming I'm not, is 100mA enough?
 
punchback said:
Watts, I hear you about the +/-12. About the TO92 package, on Mouser it looks like they can only supply 100mA. I may be reading datasheet wrong but assuming I'm not, is 100mA enough?
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There are plenty of TO-220 options available.
 
After getting some parts, I'm getting started on the +/- 12 Volt Power Supply that will power the new op-amps. I found a schematic on the internet and ordered parts accordingly. I ordered ST Micro L7812CV and 7912 for the regulators. After ordering the parts based on the schematic I found that the data sheet for the L78/7912CV showed a test circuit with a 2.2K uF cap right before the regulator. Based on the schematic I had bought 1K caps for inbetween the bridge and the regulator. Should I be concerned about having a smaller capacitor?

I attached the output of the PL2000 transformer to the +/- PS and powered up using a DBT to make sure it produced the correct voltage (and no smoke;)) before installing the regulators. I got positive and negative voltage where I expected it. The positive was 23.50 VDC and the negative was -23.55.

IMG_20200524_143228_1[1].jpgIMG_20200524_142425[1].jpg
 
I measured the unloaded output of the transformer and it's 17.8 VAC. I think the capacitors being just 25 volts may be a bit on the low side seeing that I'm getting 23.5 volts. Maybe new 2.2k uF 50 volt capacitors are in order?? The schematic I mentioned was based on a 15 vac transformer.
 
It seems odd that I'm getting +/- 23.5 volts out of essentially the same circuit. When the 2000 was fully assembled I got 18.85 volts. The 23.5 come from an unloaded circuit and my PS has 1k uF filters as opposed to 470uF. Would the unloaded circuit or higher filter capacitance explain the higher voltage?
 
I don't suppose you measured the ripple voltage on the caps the first time. What you describe is capacitors that are failing and have high ripple.
 
Without a load the filter caps will charge to the peak voltage of the transformer output minus the voltage drop across the diode, which in your case should be about (17.8vac x 1.4) - 0.7 = 24.2 vdc. Pretty close to what you are measuring. Looks good to me. There will be next to no ripple without a load as the only ripple would be due to the leakage of the caps.
 
And I agree that caps with a 25 wvdc rating are inadequate. 35 volts would be ok, 50 volt caps would be better.
 
BlueCrab said:
Without a load the filter caps will charge to the peak voltage of the transformer output minus the voltage drop across the diode, which in your case should be about (17.8vac x 1.4) - 0.7 = 24.2 vdc. Pretty close to what you are measuring. Looks good to me. There will be next to no ripple without a load as the only ripple would be due to the leakage of the caps.
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My mistake. I was assuming this was the voltage on the 2000 board and the original caps had been changed out.
 
I'm getting some 2.2K 50V caps tomorrow. I'm also going to try +/-15 volt regulators sine I've apparently got enough bulk DC to power them.

Per the service manual the 2000 is supposed to have +/- 17 VDC. I'm not sure how they were getting the with a 117/24V CT transformer. Correct me if I'm wrong but wouldn't you get half of the 24V on each side of the center tap? That gives 12 x 1.414 - 1.4 = 15.57 VDC? I was getting 18.85 VDC before I disassembled it.
 
I wondered about this earlier, this is a good time to bring it up. My PL2000 Service Manual shows a diagram of a Zener diode and a 2.2K ohm series resistor on the output of the power supply, and it is identified as Q2, a TIS 97 transistor. The PL2000 Series Two drawing corrects the schematic by showing a diagram of a TIS 97 transistor with the Collector not connected (NC) and the series resistor is not labeled. Of course, one half of the TIS 97 does act as a diode. Is this the 34V (+/- 17V) regulator that PL envisioned? Would a 5W Zener diode such as 1N5364B (33V) work? Or even better two 5W 17V Zener diodes like the 1N5354B across the positive output and negative output to ground?
 
wattsabundant said:
Was it really common to have 110 VAC 40 yeras ago? I've never seen anything specified for 110 in the U.S. 117 and 120 yes. 9 out of 10 electricians "hook it up to 110". Was that just something that was handed down?
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I have several antique generators from the early/mid 1940’s which are rated as 110v output. The “hook it up to 110” May be a hold over from those days but obviously well before PL’s days. They use reverse current relays in the DC section as aliens hadn’t crashed yet allowing the reverse engineering of semi conductors...
 
Hi everyone it’s been a while. This project has been on the backburner for some time. I’ve been following the DChristie's PL 2000 thread and will use the knowledge gained to make my final assembly better. I was also wondering why there was the break in the ground plane back near the RCA’s. I will also join the planes in the middle and isolate the screw on the transformer side.

I got my +/- 12volt power supply made and mounted. I tested it w/o the pcb attached by attaching resisters across the voltage and ground, I found it craps out at about a max of 120mA. I’m guessing that’s all that the small transformer can give. Hopefully that will be enough power to run thing properly. Initially I tested with the pcb attached but w/o the Brown Dog 4739 and eBay 4136 adapter boards installed. Once I saw that the correct voltage was on the right pins, I installed the adapters. Everything was good except that the adapter for the phono input didn’t have the +/- 12 volts I expected. I found that the voltage drops across two 680ohm resistors R7 & R14. The resulting voltages going to the NE5532 opamp is +7.49 and -7.38. Any ideas on why PL did this? Are those resisters and the capacitors hanging off of pins 7 and 14 some sort of filter or were they just going for a lower voltage? Assuming they were just going for a lower voltage what would the sweet spot be for the NE5532? The recommended voltage is +/-5 – 15 volts. On the clip the voltages are before and after the 680 ohm resister.

PL2000 Phono PS.png
 
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