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View Full Version : Phase Linear D-500 DC Protect (and other questions)



jshupe
03-09-2014, 06:39 PM
I have two Phase Linear D-500 amps that have been sitting in storage for the last decade or so. I'm going to be pulling them out, cleaning them up, recapping them, and hopefully putting them back into service.

I've read online about the "flame linear" issue with 400 and 700 amps since they don't have DC protect and can inadvertently send 70+V DC directly to the speakers. I can't find any information about this on the D-500s, except for one post where someone mentions that they do have DC protection on the outputs.

Should I be looking at adding DC protect to this AMP? Even if it has it, does it work adequately enough to trust? I bought a few UPC1237 ICs to experiment with but realize now that I may not need them.

I'm going to be using one amp to drive my mains (2x Pi 4 w/ B&C DE250 and JBL 2226H) and the other to drive my subs (2x Pi 3 w/ Eminence LAB12). I have two PL-4000 II preamps, but don't plan on using them. Instead, I plan to use a Yamaha RX-A830 w/ pre-outs because this is going to double as a home theater.

A couple other questions:


Any suggestions for caps since I'm recapping?
I know a lot of people where recommend White Oak, but they don't seem to have anything for the D-500s. Does anyone know if the PL14_20 is used in the D-500? If so, is it worth replacing?

laatsch55
03-09-2014, 06:43 PM
I believe the D-500's had the PL-36 driver board. They had DC protect. Pop the hood and post some pics, I believe the WO board could drive the d-500 but I'll leave that question for Joe.

Northwinds
03-09-2014, 06:43 PM
Welcome aboard! I'd love to stumble across a D-500!

jshupe
03-09-2014, 06:45 PM
I believe the D-500's had the PL-36 driver board. They had DC protect. Pop the hood and post some pics

I will as soon as I get them! They're at my dad's house still - about five hours away. I might make the trek this week to get them. He's the original owner from when he bought them in 1982, I believe.

laatsch55
03-09-2014, 06:46 PM
And welcome to Phoenix, you've come to the right place. We've been waiting for someone with a D-500 to see what could be done with them...

jshupe
03-09-2014, 06:53 PM
And welcome to Phoenix, you've come to the right place. We've been waiting for someone with a D-500 to see what could be done with them...

I've read they're quite rare.

If they do have the PL-36 driver boards in them, it seems like the White Oak RevD will work according to http://forums.phxaudiotape.com/showthread.php/3689-PL14_20-Revision-D-Control-Board-Assembly-now-available

So was the issue on the 400/700's that they didn't have DC protect, or that it was faulty?

laatsch55
03-09-2014, 06:56 PM
Some 700 Ser II's with the PL36 dtiver board have been converted with excellent results. like I said , there were none around to play with. The D-500 is not rare, but darn sure not as many of those were built as say like the 700B.

jshupe
03-09-2014, 06:58 PM
Welcome aboard! I'd love to stumble across a D-500!


Thanks! My dad was generous enough to give me two of them, along with two PL-4000 II preamps (one non-working) and a Sansui XR-Q7 TT. I just have to make a ten hour round trip to pick them up.

laatsch55
03-09-2014, 07:13 PM
That's a ten hour trip I would gladly make, save a few hours to visit the old man too, I bet he misses his son....

laatsch55
03-09-2014, 07:14 PM
As you can see jshupe we pull no punches around here, hope you can deal with that, we're a pretty real bunch, but loyal and fair as hell..

jshupe
03-09-2014, 07:23 PM
That's a ten hour trip I would gladly make, save a few hours to visit the old man too, I bet he misses his son....

My wife and I are talking about driving up and spending a few days there this week. We head up there at least 3-4 times a year and stay a few nights each time.

NavLinear
03-09-2014, 07:39 PM
Welcome JS to Phoenix. Those D-500s will be cool to see. Does anyone know approximately how many were made?

The 400s and 700s did not have DC protection on the outputs - the recommendation was to fuse the positive output but speaker coils would generally go before the fuse.

laatsch55
03-09-2014, 10:10 PM
Your a good son.......

jshupe
03-10-2014, 04:41 PM
Going to be heading home with these guys tomorrow.

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laatsch55
03-10-2014, 04:46 PM
That's a boat load of power there lad...

laatsch55
03-10-2014, 04:47 PM
What neck of woods are you in?

jshupe
03-10-2014, 09:17 PM
What neck of woods are you in?

I live in Austin, Texas. Visiting my parents in the NE TX today.

laatsch55
03-10-2014, 09:26 PM
I was born in Harlingen, yep a fella can drive all day and not get outta Texas...

jshupe
03-11-2014, 05:12 PM
I believe the D-500's had the PL-36 driver board. They had DC protect. Pop the hood and post some pics, I believe the WO board could drive the d-500 but I'll leave that question for Joe.

I emailed WOA this morning asking about it, but haven't heard back yet. If anybody has any information about this, please let me know. We ended up staying another day so I haven't been able to test the amps or pull any parts for better photos yet.

From what I've read about WOA, they significantly reduce noise and improve response. A few people have commented on increased power output, but I don't see how the WOA would accomplish this. Can you explain if that is true?

I plan on replacing the power caps on each amp with higher capacity units, installing WOA boards, and potentially replacing -all- output transistors if any of them have issues. Are there any other things that I should consider doing assuming that the amps work fine from the start?

Edit: Also, I have two PL-4000 II pre-amps I'm not going to use. I may be putting them on Ebay or something to recoup some of the D-500 rebuild costs. Any idea if there is even demand for them?

laatsch55
03-11-2014, 06:06 PM
How are your tech skills? You feel comfortable inside that monster? If you do , Joe with White Oak Audio posts here as Gepetto. He's seen your thread. He does not post immediately, probably because he's evaluating your question of converting the D-500's to a White Oak driver board.

On the subject of White Oak conversions of 400's and 700's I can say unequivicolly that a White Oaked amp is better in every regard than the factory version, quieter, better crosstalk, signal to noise ratio, better response(way better), better distortion specs, and yes more power--due to the slight gain in Joe's design, and better output transistors than used back in the day. I've had some 700's test in the 500-525 watt per channel range but that was mainly due to a hot transformer design. And you are correct in questioning that as power is usually a result of rail voltage , but a more subltle factor is how you use that power. When a PL is White Oaked (here we call em WOPL"s for White Oaked Phase Linears) it will stand toe to toe with almost anything made today or ever for pure, clean audio power. I've done it, heard it and have heard the testaments of others in the before and after catagories. I guess the proof is in the fact that after all the conversions I've done I've NEVER had someone say BS and that they wanted their amp UNCONVERTED. Joe's choice of components is the best he can get and the board design and manufacture takes a back seat to nothing, in Joe's day job he is a very well respected world class electrical engineer, and thermal, and power, and mechanical.... he does not do anything halfway nor does he rest on his laurels, he's always striving for better. And yes I sing Joe's praises because you won't hear it from him, he's just that kinda guy. I feel extremely lucky that Joe's hobby is audio and all that expertise is at our disposal...
The 4000Ser II's should fare better that the Ser I's for damn sure. The earlier model is not known for reliability..

laatsch55
03-11-2014, 06:17 PM
BTW, Joe and I just finisned a "build off" on his new backplane boards for the 700B's. I'll link the threads. Peruse those builds to see how one of these critters can look on the inside. Joe is a very meticulous feller, his might look a wee bit better than mine, but mine will still be quieter....and I say that with a bit of braggadoccio, as the final analyzer measurements have not been taken yet....



http://forums.phxaudiotape.com/showthread.php/4747-What-We-ve-All-Been-Waiting-For-700-BP-boards!!!!!!!!!

http://forums.phxaudiotape.com/showthread.php/4772-Russ-Phase-Linear-700B-Going-Fully-Comp!!!!!!!/page37

I started both threads but he featured his in the first one. When reviewing his keep in mind he's very, very good at what he does....

laatsch55
03-11-2014, 06:20 PM
Are your outputs MJ15024's and MJ15025's?

jshupe
03-11-2014, 06:27 PM
How are your tech skills? You feel comfortable inside that monster?

I dabble in this stuff, but have an expert on hand to make sure I don't do anything stupid.

laatsch55
03-11-2014, 06:30 PM
Excellent..me too...

jshupe
03-11-2014, 07:02 PM
Are your outputs MJ15024's and MJ15025's?

Motorola TP9054 and RCA 66546.

I was also told that both of these amps were built/modified by an engineer named Leroy Weber in the early 80's. I have no idea what was changed, but they were supposedly configured for increased output over stock.

According to http://home.earthlink.net/~dimlay/sitebuildercontent/sitebuilderfiles/outputs.pdf, the TP9054 is the MJ15024. The 66546 is the same as the RCA 410. On both amps, the 9054 and the 66546 positioning is the same, so I doubt they were haphazardly mismatched during repairs.

I did find something concerning when looking over these: the power fuse on one of the amps has been removed and is internally fused rather than the replaceable fuse on the outside. If anybody has the main fuse assembly, I'd be interested!

I grabbed the serial numbers for fun: 1158 and 2548.

laatsch55
03-11-2014, 07:51 PM
The 66546 are RCA-410's, the TP9054's are rebadged Mj15024's. So you have a quasi-complementary D-500. The fuseholder is a standerd AGX available from any electronics supplier.. I see no reason a WO board won't work, but like I said we'll se what Joe comes up with.
The 410's are drivers and the 9054's are outputs. Do they work?

jshupe
03-11-2014, 09:07 PM
I'm still not home, but I pulled the covers off while these were sitting in the trunk of my car to take some better photos of the boards. I found that one amp has been repaired and/or modified in the past. See photos:

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laatsch55
03-11-2014, 09:33 PM
Well, the board does not mount the same, so there may be some problems there.

jshupe
03-12-2014, 06:29 PM
I made it home today and was able to power up both amps on a Variac. I didn't test any audio input or output, but noted the following:

Amp1: Hi-Freq lit up, Power button does not work (but amp defaults to on)
Amp2: Hi-Temp lit up, Impedence button does not work

Amp1 & 2: smoke coming from right side of driver board!

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I'm going to work on recapping everything before continuing testing.

jshupe
03-12-2014, 06:32 PM
Schematic from the original owner's manual (attached)

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laatsch55
03-12-2014, 06:51 PM
Have you identified the component from whence the smoke escaped??

jshupe
03-12-2014, 07:07 PM
Have you identified the component from whence the smoke escaped??

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R101, I think.

Skratch
03-12-2014, 07:07 PM
I made it home today and was able to power up both amps on a Variac. I didn't test any audio input or output, but noted the following:

Amp1: Hi-Freq lit up, Power button does not work (but amp defaults to on)
Amp2: Hi-Temp lit up, Impedence button does not work

Amp1 & 2: smoke coming from right side of driver board!

12575
12578
12579
12580
12581
12582
12584

I'm going to work on recapping everything before continuing testing.
It looks like someone worked on these before, I thinks it is time for them to see a doctor? The drivers are in the wrong position

laatsch55
03-12-2014, 07:09 PM
7.5K 5 watt?

laatsch55
03-12-2014, 07:12 PM
It looks like someone worked on these before, I thinks it is time for them to see a doctor? The drivers are in the wrong position

These are nothing like the 400's or 700's Mark. I believe they're in the correct position..

jshupe
03-12-2014, 07:17 PM
7.5K 5 watt?

3K. I'm about to remove the D101 and test it.

Here is another photo I forgot to take earlier; the output and driver transistors:

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Skratch
03-12-2014, 07:24 PM
These are nothing like the 400's or 700's Mark. I believe they're in the correct position..

Never too old to learn

laatsch55
03-12-2014, 07:25 PM
Amen Mark. Got a service manual comin myself so I appear I will know what I am talking about..

laatsch55
03-12-2014, 07:27 PM
1 driver and 8 outputs......that sound familiar Mark?

laatsch55
03-12-2014, 07:32 PM
From where that resistor is located it's part of the low voltage supply. Check EVERY semiconductor on that board. For that to smoke you probably have a predriver smoked, one of the MM4003's or 40327. Check the 40412v's also..

jshupe
03-12-2014, 07:34 PM
Another suspect component:

Photos from amp1 and amp2 - same damage to both.

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laatsch55
03-12-2014, 07:37 PM
All op-amps are suspect in that amp, if you do anything get some good sockets and solder themm in place so swapping op-ampps is easy. There are some more modern choices for the 4558.

laatsch55
03-12-2014, 07:39 PM
What damage are you referring to?

jshupe
03-12-2014, 08:10 PM
What damage are you referring to?

It looks to have heat damage, but I suppose that doesn't necessarily mean failure. What opamps are recommended nowdays?

laatsch55
03-12-2014, 08:19 PM
TLE2072...Burr Brown OPA2134

jshupe
03-12-2014, 09:44 PM
BTW, the D-500 uses the PL-32 driver board.

jshupe
03-13-2014, 05:42 PM
The 4558s do seem to have failed on both amps. When I pulled them, the 15v rails stabilized (previously all over the place and causing the 3k 5w resistors to run scalding hot) and Hi-Freq lights went off.

I went ahead and took an inventory of all caps and opamps, and ordered new+extras from Mouser. I also ordered some new resistors to replace some select ones that look to have run hot for a while. When the order comes in I'm going to recap everything and replace the opamps. I am going to go the socket route and ordered 4558s for testing as well as OPA2134 to use in the final product once I'm confident they won't be quickly destroyed.

I'm looking at PS cap replacement but haven't made a decision yet. Each amp currently uses 2x 125v 13000uf caps and I'm looking at 160v, 20000uf+ replacements, but they're expensive.

All the LEDs work great!

I'm still trying to figure out why one amp is permanently on. The power switch itself hasn't failed, but I can't find the issue. Hoping I'll run across it when recapping anything. Any thoughts? The impedance switch on the other amp doesn't work, but I haven't even taken a look at it.

None of the fuses for the output transistors blow, so that seems like a good sign.

laatsch55
03-13-2014, 08:12 PM
One of those 3 big relays controls the input power. The other 2 are DC protect and hi/low rain voltage. That amp senses what kind of load it's hooked to and if the load is too low in ohms it will switch in the lower rail voltage to save itself.Hiz/lowZ switch accomplishes this..

laatsch55
03-13-2014, 08:13 PM
Have you checked the size of the new PS caps, those new ones are probably much taller..

jshupe
03-13-2014, 08:15 PM
Have you checked the size of the new PS caps, those new ones are probably much taller..

That's been my search criteria on mouser. I can find some with close to the same capacity as these, but they're almost half as tall...

laatsch55
03-13-2014, 08:16 PM
FWIW, it may not be the op-amps that are faulty but what they control, when bringing the amp back up, use your variac and I've found if the variac is used in series with a DBT your chances of not hurting parts is much better. A variac will limit voltage but not current and current is usually what kills an amp...

laatsch55
03-13-2014, 08:18 PM
That's been my search criteria on mouser. I can find some with close to the same capacity as these, but they're almost half as tall...

Well that's not near as bad as TOO tall....

jshupe
03-14-2014, 01:28 AM
This isn't mine, but I bid on it for a while until I gave up at over $1200.

http://www.ebay.com/itm/Phase-Linear-Dual-500-with-rare-wood-kit-/321347747135?pt=LH_DefaultDomain_0&hash=item4ad1d17d3f

laatsch55
03-14-2014, 09:04 AM
IIRC that guy has a dozen of those..