Phase 400 rebuild

[Dchristie]

Hi Folks, I originally posted this request on AudloKarma and NavLinear suggested I might join this site for some additional help (thanks Navo). Basicaly, I had a PL 400 amp from 1978 through 1982 and it worked flawlessly for all 4 years. The amp had been out on the market for enough years to already start to have a reliability history and knowing this, I was very careful about not abusing it in any way. However, one day while cuing up the tone arm of my turntable at a moderate volume level, I heard a large bang and saw the amp's meters peg into the red and then saw all the bass drivers on my ADS speakers take a direct DC hit from the amp. I was able to get it repaired but quickly sold it to a band to use in their PA system. So, I was just one of many victims of the Phase Linear family and although I did like the way the amp sounded, I did not want to take any chances on another meltdown.

Anyways, I am revisiting my early stereo years and have started to have some fond memories of the 400 amp with regards to it's sound quality. Seeing that there are usually several for sale on ebay my questions for the Phase Linear experts are as follows:

1 - can the 400 amp be modified today so that it will avoid the meltdown problems that it had in the 70s ? I know that there are several mods out there (White Oak / etc) but I would like to know if the reliability problems inherent in the original design can truly be modified so they are no longer an issue.

2 - If the answer to question 1 above is yes, then can anyone recommend where a 400 can be sent for the restoration and modification? From other posts, it appears that several members on this Web Site are very knowledgeable about the 400 amp series and I have read differing opinions of some of the repair sites on the internet but I am truly looking for someone who might be willing to work with me if at all possible. Although I can handle a solder iron, this is a project that I would just like to send my amp to an expert to make all of the mods ( with fair compensation of course).

Sorry for the redundancy in bringing this up again, but I appreciate whatever assistance anyone can provide.

Thanks

 

[laatsch55]

A White Oaked Phase Linear, a WOPL, is simply one of the best amps on the planet when done. Frying your speakers was not an inherent design flaw, but a decision by bean counters to not have a DC protect circuit included. Any class AB amp can throw DC to the speaks if no protection circuits are involved. Modern TO-3 outputs are considerably more robust than in the past. There are a number of DC protect options out there but my favorite is Don Imlay's DC protect boards.
White Oak Joe's (member Gepetto here) redesign of the driver board and addition of backplane boards make them models of reliability. I have, several times, tested some of these amps to destruction. Still haven't actually destroyed one but have wounded several, and the lengths to which I had to go were ridiculous. There are several very capable amp builders here. Jerry and I do it quite regularly, I was hoping we would have more folks doing it by now for others, but that's not the case. A lot of people have built there own, maybe after that process the idea of charging someone for the hours involved would seem embarassing.
I have seen members here do dome incredible work, some better than mine, so I'm sure someone will take on your project. I would love to, but with the oilfield the way it is lately I don't have much time right now and am way over committed as it is....

 

[Gepetto]

Hi Folks, I originally posted this request on AudloKarma and NavLinear suggested I might join this site for some additional help (thanks Navo). Basicaly, I had a PL 400 amp from 1978 through 1982 and it worked flawlessly for all 4 years. The amp had been out on the market for enough years to already start to have a reliability history and knowing this, I was very careful about not abusing it in any way. However, one day while cuing up the tone arm of my turntable at a moderate volume level, I heard a large bang and saw the amp's meters peg into the red and then saw all the bass drivers on my ADS speakers take a direct DC hit from the amp. I was able to get it repaired but quickly sold it to a band to use in their PA system. So, I was just one of many victims of the Phase Linear family and although I did like the way the amp sounded, I did not want to take any chances on another meltdown.

Anyways, I am revisiting my early stereo years and have started to have some fond memories of the 400 amp with regards to it's sound quality. Seeing that there are usually several for sale on ebay my questions for the Phase Linear experts are as follows:

1 - can the 400 amp be modified today so that it will avoid the meltdown problems that it had in the 70s ? I know that there are several mods out there (White Oak / etc) but I would like to know if the reliability problems inherent in the original design can truly be modified so they are no longer an issue.

2 - If the answer to question 1 above is yes, then can anyone recommend where a 400 can be sent for the restoration and modification? From other posts, it appears that several members on this Web Site are very knowledgeable about the 400 amp series and I have read differing opinions of some of the repair sites on the internet but I am truly looking for someone who might be willing to work with me if at all possible. Although I can handle a solder iron, this is a project that I would just like to send my amp to an expert to make all of the mods ( with fair compensation of course).

Sorry for the redundancy in bringing this up again, but I appreciate whatever assistance anyone can provide.

Thanks

If you purchase one, make sure it is the 8 fin heat sink version. The early 4 fin versions are inconsistent in terms of what you might find inside so don't waste your time. The largest population built were with 8 fin so they are easy to find. There were 3 key design weaknesses that have been addressed in the redesigned electronics. Very rugged now.

 

[Northwinds]

Once you hear a WOPL, you realize you have something very special. Best amps I ever heard no hands down

Welcome to Phoenix!

 

[Nick Danger]

Welcome to the jungle, Dchristie! You are at the right place.

 

[Dchristie]

Thanks everyone for your replies.

So Lee and Joe, assuming the amp is currently functioning but stock only - no mods, what would you recommend modifying in a 400?

In other words, what would you update in the amp if it were your amp? ( I am considering anything that is a potential problem down the road even if it is currently functioning).

Thanks

Dean

 

[NavLinear]

Welcome Dean to Phoenix! It's pretty laid back here and there is a wealth of information regarding the Phase Linear amplifiers. Oh yeah - you get a welcome Nav babe too.

 

[BlazeES]

If TH had an awesome Talent Agent as good as you Nav ... hell, if they had one AT ALL ...

Welcome Dean to Phoenix! It's pretty laid back here and there is a wealth of information regarding the Phase Linear amplifiers. Oh yeah - you get a welcome Nav babe too.

 

[MarkWComer]

I made some long, drawn-out and boring videos of my PL400 upgrades- everything (DC protection, capacitors, control board and backplanes).

You can do everything yourself, the instructions are pretty clear, but you do have to pay attention to what you're doing and take your time with it.

If you're battling insomnia, have a look: https://www.youtube.com/user/Mark5W8Comer/videos

Keep a clear head...

 

[MarkWComer]

In other words, what would you update in the amp if it were your amp?

I think the majority of us would say to gut the thing- keep the case and transformer, but rebuild the entire sucker up from the input jacks all the way to the output plugs.

 

[Fishoz]

Oh boy!! Sounds like we're hooking another one! Welcome, welcome,welcome....

Nick Danger did the same to me as Nav did to you....pointed you in the right direction to here.

This is a great trip here. Bunch of great guys willing to help. Threads are constantly hijacked, usually someone flicking someone else, eventually gets back on track though. Share in the laughs and learn about one of the best amp rebuilds out there.

 

[laatsch55]

I think the majority of us would say to gut the thing- keep the case and transformer, but rebuild the entire sucker up from the input jacks all the way to the output plugs.

What he said.....cause I've heard a WOPL.....

 

[MarkWComer]

then saw all the bass drivers on my ADS speakers take a direct DC hit from the amp.

Which model of ADS speakers? I'm still using the L1290s that I bought back in 198(3? 4?)! Nice speakers!

 

[Gepetto]

What he said.....cause I've heard a WOPL.....

What he said. Nothing worth keeping inside except the meters, transformer, P straps, case. Everything else has a much better equivalent.

 

[Dchristie]

Thanks Mark, so can this ( WOPL 400 mod) be accomplished by someone with adequate soldering skills but minimal electrical circuit knowledge - I have built hafler amps from kits and repaired some of my own equipment when the defect was obvious but I do not have any formal electronics training. I am really a novice when it comes to circuit and parts knowledge but can follow directions and am OK at taking things apart and putting them back together. Of course I can tell the difference between a cap and a resistor, etc but do not claim to be intuitive to anything electrical. I also do not have any equipment to check values/etc other than a Circuitmate DM10 31/2 digit multimeter which I occasionally use to check L-pad resistance for my speaker projects. Thats about it!

Regarding my blown ADS speakers, they were 810s - the predecessors to your 1290s.

Thanks

Dean

QUOTE=MarkWComer;167342]I made some long, drawn-out and boring videos of my PL400 upgrades- everything (DC protection, capacitors, control board and backplanes).

You can do everything yourself, the instructions are pretty clear, but you do have to pay attention to what you're doing and take your time with it.

If you're battling insomnia, have a look: https://www.youtube.com/user/Mark5W8Comer/videos

Keep a clear head...
View attachment 22013 [/QUOTE]

 

[laatsch55]

A suggestion, have Gepetto send you the installation notes on the backplanes and driver board and see if you are intimidated or not......

 

[Dchristie]

Thanks Lee, good suggestion. I would like to see what is required to apply the WOPL mods. As I am adequate when it comes to the basic stuff, I have not been involved with any amp building or repairs ( other than Hafler 220 kits 30 + years ago).

Joe, would this be possible and if so, how do want to proceed?

Thanks

Dean

 

[Dchristie]

Hi Folks, OK, I bit the bullet and just bought a PL400 off of ebay and will order all of the White Oak parts this week. I will also order the DC protection board. My PL 400 is supposed to be in good shape so hopefully it will also be clean inside as well (no rusted areas/ etc). I watched all 7 or so of Marks' videos on his rebuild for the series 2 amp and although it certainly looks somewhat complicated, the most daunting task was the back plates and transistor replacement. The tolerances between the plates and chassis are very small and looks like it would be easy to cause a short. Also, Mark never covered the actual soldering of the transistor leads but I have been told that this is also critical as they do not handle too much heat. So, I think I will 1st change out the filter caps and add the DC protection just to get the amp safely running and use it for awhile. Probably order the assembled driver board and add it next and then the transistor updates last.

I also need to buy a variac (any suggestions would be welcomed as where to get one and what to look for) as well as how to construct the test light setup that Marks shows in his video (maybe Mark can steer me in the right direction to build such a test apparatus)?

Anyways, I am committed to this project now that I have bought the amp and I am looking forward to the rebuild although I have to admit that it is somewhat intimidating at this point since I have so little knowledge or understanding of all the circuit designs and certainly don't want to get into something that is over my head. I am absolutely certain that this is just the beginning of many future posts from me looking for help and advice from all of you and I do appreciate everyones' assistance and patience.

Best regards,

Dean

 

[NavLinear]

Hi Folks, OK, I bit the bullet and just bought a PL400 off of ebay and will order all of the White Oak parts this week. I will also order the DC protection board. My PL 400 is supposed to be in good shape so hopefully it will also be clean inside as well (no rusted areas/ etc). I watched all 7 or so of Marks' videos on his rebuild for the series 2 amp and although it certainly looks somewhat complicated, the most daunting task was the back plates and transistor replacement. The tolerances between the plates and chassis are very small and looks like it would be easy to cause a short. Also, Mark never covered the actual soldering of the transistor leads but I have been told that this is also critical as they do not handle too much heat. So, I think I will 1st change out the filter caps and add the DC protection just to get the amp safely running and use it for awhile. Probably order the assembled driver board and add it next and then the transistor updates last.

I also need to buy a variac (any suggestions would be welcomed as where to get one and what to look for) as well as how to construct the test light setup that Marks shows in his video (maybe Mark can steer me in the right direction to build such a test apparatus)?

Anyways, I am committed to this project now that I have bought the amp and I am looking forward to the rebuild although I have to admit that it is somewhat intimidating at this point since I have so little knowledge or understanding of all the circuit designs and certainly don't want to get into something that is over my head. I am absolutely certain that this is just the beginning of many future posts from me looking for help and advice from all of you and I do appreciate everyones' assistance and patience.

Best regards,

Dean

Cool Dean. This should be a fun build.

Joe's design of the backplane boards leave little to go wrong if you're careful. The backplanes incorporate standoffs that are soldered to the board and these provide the alignment of the board to the existing hole set in the chassis. Sockets are soldered to the board where the base and emitter legs of each transistor mate. This eliminates the need to solder the transistor legs to the board. A shoulder washer is installed into the chassis holes where the transistor legs penetrate the chassis providing electrical isolation between the transistor legs and the chassis so you won't need to worry about shorts there. The Bergquist Sil-pads provide electrical isolation between the chassis and the output transistors but they allow heat transfer so you really don't need to sweat this part of the installation. Make sure you don't over torque the transistors to the chassis as this can be a problem with the Sil-pads.

A variac is a nice piece of test equipment to have and eBay has some listed that are relatively inexpensive. A dim bulb tester is easy to build and can save your ass when testing so it is good to have one available for that initial turn on.

Show us some photos of your new amp when it arrives - this will be exciting.

Good luck!

 

[laatsch55]

Joe's design of the replacement goodies has taken the need to understand the circuit out of the equation for just assembling a WOPL. IF and when something goes wrong that may not be the case. But there is lots of competent help here...