Phase Linear 400 - Part 1 - Circuit Theory & Evaluation

[@xraytonyb]

One thing I forgot to mention in the video; Do not try to bring one of these amplifiers up on a variac. It is better to use a dim bulb tester with a 100-150 watt bulb. This should minimize the chance of the amp going into LF oscillation.

[@jeditoto3441]

@@ameldaquirk3965 Interesting points - had never considered these points. My approach has always been with the variac. Bulb only when I plug into 240V. But after Tony's video - seems it is more subtle than that ....

[@andymouse]

@@ameldaquirk3965 Yes it's good for shorts ! but if you have too smaller bulb you will be fooled into thinking you have a problem when in fact you don't it's just the quiescent power your seeing.

[@KeritechElectronics]

@@andymouse yeah, always match your bulb with the device's power rating.

[@andymouse]

@@KeritechElectronics And be aware :)

[@peanutbutterjellyjam2179]

When I was a young DJ, I had a rackful of these. Good old days.❤

[@thermionic1234567]

Lights musta seriously dimmed when you turned them all on!

[@brotherspock8180]

Fondly remembered as Flame Linears 🔥

[@deviantmultimedia9497]

Phase Linear 400 circuit analysis by XRTB- the video I've been waiting for. These are EXCELLENT sounding amplifiers. Probably unrivaled imo. A friend of mine who's not with us anymore used to do sound installs for some pretty serious clientele. He had a busted PL400 MK II that used to belong to Dr Dre. He said one of the channels was out and that Dre would nuke a pair of NS10's with the 400 at the end of nearly every session. He benched it when the channel went out and then ended up moving his operations to a more clandestine underground studio for which my friend designed a custom playback system. Needless to say Dre didn't want the PL anymore so that's how I got it. I ended up designing a new preamp board for it because at the time White Oak Audio didn't make replacements for the series II. I didn't really want to "upgrade" it anyway. I wanted it to be as close as possible to the original but use modern, readily available components and a more robust two-sided PTH substrate because the transistors are all unobtainium and those zener resistors totally barbecue the flimsy one-sided boards. That also gave me a whole additional PCB side to use if I needed to but I didn't. I opted to rout the signal & power on one side of the board just like the original. Rather than using the other side as a ground layer, I mindfully routed ground on the same side as everything else and flooded the whole reverse side with copper. Then I flooded the negative space of circuit side with copper and stitched the two copper pours together with vias. This creates shielding around the traces but more importantly it provides welcomed parasitic capacitance right up against those signal traces. The reactance is nowhere near the realm of anything audible but it's enough to offer HF oscillations a more attractive path than that of the signal, as this guard layer is to be connected directly to the chassis-not signal ground. Under the zeners I isolated a little copper island and tied it to the pads for on-board heat-sinking. Like Tony, I decided to replace the op amp but I went with the TLE2071. Tony is the GOD OF VINTAGE CONSUMER AMPLIFIERS. I've been waiting for the day he gets a Phase Linear on his bench. Looking forward to this whole series.

[@mackfisher4487]

"More schematic thing," Love your use of it schematic to explain the operation of the component on your bench.

[@Sunnbobb]

I love this video on several levels. I have restored several of these, and I went through several pots of coffee pondering the LF Osc until I discovered I wasn't feeding it enough current. Looking forward to more vids! Thanks.

[@billsmith5166]

These were the dream of we young audiophiles in the 70s. Even the name sounded good.

[@bryanmcwhirter9945]

I have a "400" loved it! have to recap it before I fire it up, havnt ran it in 15 years, untouched as of now, looking forward to your series. Thankyou!

[@ancienttech4636]

I rebuilt many PLs throughout the 70s. The main design flaws were a not-so-responsive protection circuit design coupled with a preamp design that had a faster slew rate than the output stage itself. If any kind of oscillation presented itself within or at the input or driver stages, the outputs would not be able to follow it, increasing the current load on the DTA410 drivers which now drove into a lower impedance at the output transistors. The feedback loop would become unstable and since the rails could supply nearly limitless current, catastrophic destruction would ensue. 💥💣

[@peterlarkin762]

Really enjoyed this. Nothing wrong with quasi complimentary designs - it's all in the implementation! I made a 'Circlophone' amp (designed by Elvee) years ago - very fast and dynamic with epic bass. I also have a Carver TFM-35 class-g with 5 pairs of parallel outputs... Carver preferred lower idle currents but made up for this by minimising crossover distortion using parallel outputs. When done right it has that 'class A' sound without all the heat.

[@gamerpaddy]

bob's stuff is allways fascinating to work on and see how it works

[@michaelpelley2815]

Back in 1979 I purchased my first stereo at our local hi-fi shop which was a Pioneer SA-6500 II integrated amplifier, Pioneer HPM-30 speakers and a Panasonic SL-H401 direct driver turntable (I still have the turntable - I wanted a Technics but it was outside my budget). Two things I remember so well: 1) the smell of the owner's pipe tobacco and 2) in the back of the store with the "high end" gear the Phase Linear power and pre-amps including the 400 and 700. Those were WAY outside my budget.

[@robertduvall7392]

Phase Linear started in a bay in back of and below the Tradewell store in Edmonds, WA - where I lived. When Carver built the building in Lynnwood just seven miles to the east, all of my high school friends worked there to get the discounts on the equipment. Most of my friends got their speakers from Speaker Lab in the university district by the University of Washington. Speaker Lab sold kits, and everyone was building their own. When you think about it - that much innovation in such a small area for stereo buffs was nirvana, no matter how hot the equipment got. I was known for blowing up tube guitar amps - no big deal. Just a little goofy history on very, very early Phase Linear.

[@briansilcox5720]

This is a remarkably simple looking design. My first rebuild was a contemporary Dynaco Stereo 400, (Fantasia boards) with large protection circuit, and it’s amazing how to me the contrast in simplicity here. Great topic!

[@HansFormerlyTraffer]

The guys where I lived inherited a phase 400 from a band that went out of business in 1974. We had quite the sound system for our "home stereo"

[@windward2818]

I recently completed my troubleshooting isolated variable 10A AC power supply with some features you might be interested in as compared to the unit on your bench. This is actually the third troubleshooting AC power supply I have either built from the ground up or modified from off-the-shelf. 1) I replaced current limiting bulbs (I don't like the inrush or glass or burning out) with automatically cooled power resistor 220 ohm 600W on a heatsink for equipment with a dead short, switched in and out of the circuit with a make before break switch. 2) I use floating ground duplex receptacles (one 15A and the other 20A GFCI) instead of single floating round receptacles on the output of the variac which is after the isolation transformer. Mainly for the better construction available and floating ground but also to support more insertion cycles. The high quality orange floating ground (ground not connected to mounting straps) hospital or industrial grade receptacles are very well made with large power screws and large wiping blade connection surfaces. The GFCI can be used as a crude AC leakage detector (around 6 mA max) when used as a tied neutral ground at the output of the isolation transformer. I have a switch to enable or disable the protective earth connection on the GFCI and to un-isolated ground on the 15A receptacle. I have a separate Hioki AC current leakage clamp meter I used for equipment outgoing final test, but the GFCI is a good quick test before moving over to the calibration bench (traditionally different than the troubleshooting bench). 3) I have three AC circuit breakers in parallel (1A, 3A, 10A, only one used at a time) as a equipment fuse saver. They are trip free hydraulic/magnetic Airpax marine type AC CBs (also UL1077 type would work) where you can choose the current trip profile (called delay curves by Airpax) to trip before a slow blow fuse of a similar rating. 4) For the large isolation transformer and variac (magnetic devices) I have a time delay in-rush power resistor based current limiter circuit to supply the magnetization current before enabling the output. This is needed on large isolation transformers. More stuff: I do all of my troubleshooting with isolated test gear: A Fluke DMM and Scopemeter. For calibration I use a different AC power supply (pure sinewave) and a Picoscope with high voltage differential probes to take data incase I need to include the data in a report.

[@rb89509]

Bob Carver was before his time. I had a couple M400a's I ran bridged back in the 80's.

[@miguelangelmontenegro9939]

Hi ! I have one 400 MK II like a new one ! And never have any problem . Ever being carefully with the speakers terminals... The power rms is 210 per Chanel. The early 700 with needle vu meters was used Live ! , by ELP, Emerson Lake Palmer, for the stage sound , and studio. The Crowns too. Cheers from Buenos Aires Argentina

[@justinmijnbuis]

Very much looking forward to this series evolving.

[@stevea3007]

My 400 series one was unstable at turn-on. I went ahead and rebuilt the whole thing with White Oak boards and the speaker protection relay kit. Probably not your style, but it's a nice upgrade.

[@williamsquires3070]

Hi Tony. The “back-and-forth” Cylon Eye/K.I.T.T. “display” are called, “Larson Scanners” after Glen Larson, the producer of Battlestar Galactica and Knight Rider. At least that’s what I heard. Whether it’s true or not, I don’t know. 😊

[@andymouse]

It's true.

[@KeritechElectronics]

A lovely amp with some cool and well thought out design - after taking off the panel, it's all so easy to work on. I love it. Point-to-point wired output transistors are a nice touch, I'm not sure about the reliability of the sockets though.

[@mcgjohn22]

These amps were quite the thing when they came out. amazing amount of power from a relatively small form factor.

[@stevefoster2700]

I had a similar issue with a dim bulb fooling me into thinking I still had problems with a Sansui 771. I'm watching this series as I have an Adcom GFA-555 II that I need to bench test. No speaker protect, no volume pot. Looks good on the test equipment so far...just quite a bit of power to run straight into speakers. Makes me nervous :)

[@mitkothemacedonian]

A 100n ceramic cap across the +and - supplies of the opamp directly at the pins under the board and a 10k resistor from the opamp output pin 6 to ground could solve the thump at turn-on if that thump was caused by the opamp.

[@peterlarkin762]

That's a good solution. I always prefer adding a speaker output protection board with delayed relay trigger. Mitigates any turn on/off thumps and possible speaker damage if your amp goes thermonuclear.

[@paulb4661]

Speaker fuses also contribute to overall THD figure, their resistance will vary in response to temperature rise, caused by conducting high currents, hence exhibit some hysteresis. Bob Cordell investigates it thoroughly in his bible on amplifiers. Relays and ultra low Rds on mos-fet switches offer an advantage in that respect and, of course, the reaction time.

[@andymouse]

Are you saying that you can 'Hear' a fuse ? or determine what value or if one is present from audio ?

[@paulb4661]

@@andymouse I'm saying precisely what I've said, presented the reasoning behind the observation and cited the source, for those wishing to quantify the detriment. Whether it's audible, I do not know and wouldn't think so, considering a complex set of non-linearities accompanying every amplifier, whether it's measurable, it certainly looks like it, but since I'm unlikely to end up with an AudioPrecision analyzer in my workshop any time soon, I often rely on studies conducted by accomplished engineers. I suppose a valid argument on the influence of the output stage "driving" the protection circuit in parallel with the load can also be made.

[@bazzaar1869]

I believe the LF oscillation you are seeing is ONLY due to the dim bulb being used. If you had genuine line voltage at 100v, or 90v or whatever, because of the low source resistance of power lines you would be fine with no oscillation, but restricted in output power. The dim bulb adds resistance in line with the power source and the voltage will then vary with the power whereas just a low voltage would be constant with varying power. Its like the bulb turns the amp into a relaxation oscillator. That also means you wont see any LF oscillations with a variac, at least not a decent one with good regulation and low source impedance. Dim bulb is only of real utility for determining catastrophic failure, it is not good for running devices at reduced voltage.

[@Silent-Lucidity]

That was classic! Hook them up to your CVs, and now it's a party!! Lol!

[@dannyfreitas2120]

i have all 3, i have the d 500 that you need two people go carry in. the 1000 watt every time you turn on lt would dim all the light in house . the transformer is inside the case its taking. .most space inside. there was 20 car dome lights in inside the cross over.in the speakers when you crank it up. all those lights in series with the speaker lit up show bright like a christmas tree .

[@TrevorsBench]

Add some PS bypass filtering, esp around those op-amps. It can't hurt and only can help

[@douglashoff95]

We serviced a lot of 700's as well as the 400. We always used the original Delco manufactured output transistors (PL909) as others created more troubles.

[@marka1986]

Even in the mid 80s those were rare. Had used mj15024 for the npn and mj15025 for the pnp. Saved the remaining good xpl transistors and was able to keep some amps original.

[@brucebuckeye]

Oh those Oak Island boards are real treasure! 😂

[@NovaluxStereophonic]

Sometimes wirewound resistors are made in the old carbon comp looking style package. I have been fooled by this before on Audio Research amplifiers. May be worth cracking one open to see.

[@ancienttech4636]

@@NovaluxStereophonic Generally, the wire wound guys have imperfect surfaces, whereas the Allen-Bradley carbon comp stuff had a very smooth shell.

[@NovaluxStereophonic]

@@ancienttech4636 I have seen them both ways.

[@EdwardLehman]

Presently own the Phase Linear 5100 Series Two Tuner and a 3000 Series Two Preamp! Had the 400 amp shown but it blew up years ago!

[@thefreestylefrEaK]

I had my 400 II bench tested and it produced 270 watts a side at 8 ohms.

[@g.fortin3228]

Another interesting one here Tony ! I'm being very careful with my two incan dim bulbs geez where do i get a replacement these days !?!

[@marka1986]

40w appliance bulbs. Also some specialty places online may sell traffic light bulbs. Those were around 100 watts and long life. See if you can go to a small hardware store that's been around for years. There might be some old stock.

[@g.fortin3228]

@@marka1986 excelent ideas thank you.. i could use multiple 40's if need be..love the hw store idea. no big box LoL.. those got wiped out of incans a long time back

[@stevenholquin2127]

Looks 👀 Like The Great Bob Carver Just Retired and Is Gonna Enjoy His Retirement Life and Golden Years Thank Bob For The Phase Linear 400 and 700

[@alvinsilcott2036]

@alvinsilcott2036 0 seconds ago the original op Amp used in the phase linear amps were a LF351..wouldnt the "upgrade" to modern day op-amps with much larger bandwidths ...higher slew rates & near infinite input impedances amount to instabilities (parasitic oscillations) partially due to the absence of decoupling/bypass capacitors thru out the amplifier ??

[@michaelnorth3666]

Good replacement for TLO71 is analogue devices AD711.

[@peterlarkin762]

Thanks for this, I gave up looking for Analog devices opa amps a few years ago when there was no stock. Definitely going to try some. How do they compare to OPA 2134?

[@mistermac56]

The TL082 is fine. It has lower input bias current than the TL072. Other than that, the specs for two parts are pretty much identical, other than the TL082 being a bit noisier, but isn't a show stopper. The TI OPA2134PA (originally Burr Brown) is a more modern replacement and what I use instead of the TL072 or TL082.

[@peterlarkin762]

2134 is hard to beat if you want a jfet input. They seem to be the only decent sounding opamp that's readily available, although prices keep going up!

[@mitkothemacedonian]

In this case opa134, since the amp uses two single opamps.

[@alvinsilcott2036]

the original op Amp used in the phase linear amps were a LF351..wouldnt the "upgrade" to modern day opamps with much larger bandwidths ...higher slew rates & near infinite input impedances amount instabilities (parasitic oscillations) partialy due to the absence of decoupling/bypass capacitors thru out the amplifier ??

[@gregnewberry4813]

Oh yea... What is that cute little scope you have there?

[@karllangeveld6449]

Hi Tony, Great video, again! At 16:20: I doubt if the extra collector resistance will make any difference, since it is in the collector circuit. The collector will work as kind of a current source. It would make a difference if it was in the emitter circuit. Does that make sense?

[@peanutbutterjellyjam2179]

@9:33: So, audiophiles are validated in their desire for audiophile fuses?😶

[@bobbauvian7700]

I remember one time after I thought, I repaired a pcb, I connected it to a current limiting light. it lid then it when out. I figured pcb was repaired. next I connected it straight to the wall. then it just blowup

[@andymouse]

Blimey ! there have been a lot of awesome channels caught out by forgetting what the dim bulb does. Dim bulbs show you a dead short and protect your amp. Just because the bulb is lit doesn't automatically mean there's a problem, what wattage is your bulb ?....great vid ...cheers.

[@jimfarrell4635]

Yep. Can be confusing for noobs like me. Trying to fix a Sansui power amp. Dim bulbs - 2x100w - were bright, and I tracked down shorted output transistors and replaced em. This time dim bulbs came on bright but almost immediately faded to maybe 25% brightness. I swithered but eventually decided to try the amp off the dim bulb and bam went a fuse and it took out two of the new output transformers. I guess it's a question of experience and matching the bulbs to the current draw of the device. Happily today, after weeks on the bench, I switched it on and not a flicker from the 100w bulbs, but I'm going to switch them out for 60w bulbs just to be sure.

[@andymouse]

@@jimfarrell4635 :)

[@jeditoto3441]

looking forward to the 700 - I have one lying around here that needs fixing.... Thanks for those great video. I wonder if these videos can be used for AI model training... just image what would do to the repair world....

[@Dutch-linux]

the meters behavior is called flying spot

[@angelomorello4116]

Hi Tony love your. Can you please do a demo on how to alter wiring on a vintage receiver to add a powered subwoofer. thanks

[@thefreestylefrEaK]

Why? You can already do it with vintage receivers. I'll bet you're in Brazil.

[@angelomorello4116]

@@thefreestylefrEaK No.

[@2packs4sure]

I actually called it,, the bulb wasn't giving it enough juice.... And I'm never right.. lol

[@andymouse]

Ive seen two Audio channels on youtube suddenly realise its their dim bulb set up thats causing the problems. When I asked what was the bulb wattage I didn't get an answer. So may you be right every time Sir !

[@joetaylor5078]

Please consider replacing the Q106, Q206 (40412) transistor in place of something that is more economical to find if needed.

[@gregnewberry4813]

Great videoTony. When checking DC offset should the speakers be connected or not? Seems to be some controversy about this in some of the audio forums. Thanks!

[@jimfarrell4635]

I'm new at this but always measure without a speaker load, assuming that if there is very high dc offset on the outputs you run the risk of destroying the drivers if the speakers are connected when you measure. You could use a dummy load safely, I guess. I also don't have anything plugged in to the inputs. I could be talking nonsense, though.

[@stevenholquin2127]

There is a Extremely Rare 700-B Black Face Touring Amp Show Case One of Those

[@Bamafpv]

@xraytonyb Study the newer carver "magnetic field power amp designee" and its triac throttled power supply. You will think its A work of art. 😁

[@petertimp5416]

Thanks

[@SchindlerJr1]

Phase Linear 400 - Junk Amps My Model 400 blew up on me after a few months of normal use; these things were unstable.!. I bought 3 Cheapo "250 Watt - American Audio" Amps about 20 years ago, and all three of them still work fine..

[@thefreestylefrEaK]

I've had my 400 II since 1982. Never needed a repair.

[@ukw4472]

Is this an Italian unit?

[@bradfordclemens5422]

@@ukw4472 If it is, make sure you lubricate contact points with olive oil. Not only will this make a good solid connection if you use a heavy virgin blend but, a heavy oil will absorb unwanted distortion.

[@thefreestylefrEaK]

Are you for real?

[@ukw4472]

@@thefreestylefrEaK not anymore :) for some reason I thought it was an Italian device

[@ukw4472]

@@bradfordclemens5422 Phase Lunar :)

[@chucksurgeonertribute2113]

It was old school before class d amplifiers.

[@NICK-uy3nl]

I read the reliability of Phase Linear amps is not the best due to simplistic design and lack of protection circuits, designed for outright power with little regard for much else !

[@thefreestylefrEaK]

Do you believe everything you read on the internet?

[@garygranato9164]

"if your all good little boys and girls........" theres no girls that watch this channel !! this channel is literally 'man cave tv' :)

[@jeditoto3441]

You are probably right - but I hope you are wrong 😀. I was surprised when my 15y daughter asked to install an old marantz 1120, SABA speakers (really superb btw) and a vintage record player ( Barthe roto fluid from the 70's - built like tank) - maybe one day she repair stuff too....

[@garygranato9164]

@@jeditoto3441 i stand corrected :) hope she enjoys the hobby

[@jesiscott6048]

And a female electronic tech here, also doing Vintage repair as a hobby. So "if you're all good B&G" is quite accurate, as Tony nearly always is.

[@666kty3]

Phase linear stuff is junk. Total waste of time repairing it.

[@jeditoto3441]

it seems this reputation is mainly because the early models place the bias transistor on the driver board and not the heat sink - can not track temperature - later models fixed that - but reputation was made... would like to know what Tony might say about that - and what the group here says....

[@marka1986]

Am curious to see what can be improved. As original though, it seems these were easy to have fail. Especially when used as a public address or any other stage use. If used for home stereo, it did somewhat better.

[@666kty3]

@@marka1986 Nobody used theseon stage or for a PA. They were turds trying to steal some market share from the big boys, only cheapskates bought these.

[@bradfordclemens5422]

What is your opinion regarding a Krell KSA 300s from about 1993?

[@666kty3]

@@bradfordclemens5422 Inefficient heat soaked class a junk. Im an electronics engineer and anyone...who is a serious audiophile will know tube amps are the only true path to sonic perfection....based on human anatomy and hearing function. Even second order harmonics are what tickle your stirrup, hammer, and anvil bones in your ear just right.....something solid state amps will never produce as copiously.

[@jdmccorful]

Will follow with interest. Thanks for your time.