Phase Linear Amplifiers, design

[SirPaulGerman]

I got a Phase Linear 200 for free, it works fine, sounds good.
The build quality must be good because still working fine, not bad for a 45 years amp, very relaxing amp and more than enough power for my system.

However there seem to be a bias against phase linear amps in the audio community
I am on the fence about a restoration, can you guys review the service manual, and make some comments about the design ?
Is the 200 a good amp in the end ?

thanks for your help

Phase Linear 200 Stereo Power Amplifier Manual | HiFi Engine

www.hifiengine.com

 

[Gorgonzola]

I have no specific recommendation. I'll only say that the Phase Linear 400 I used for years was a horrible, horrible sounding amp -- very harsh and glassy sound in the top end but, at the same time, opaque to musical detail.

 

[fpitas]

Many called them Blaze Linear. I doubt because they were hot property. But with no schematic, it's real tough to review anything.

I'd consider it a labor of love, at the very least. And as pos notes, it may take your speakers when it goes.

 

[pos]

Beware, these amps have an history of blowing speakers attached to them when failing.

 

[SirPaulGerman]

Here is the service manual with the schematic, can someone comment on the design and output transistors ?

 

[fpitas]

Here is the service manual with the schematic, can someone comment on the design and output transistors ?

The design is pretty conventional, BUT... no output Zobel. Usually that's 0.1uf in series with 10 ohms to ground, followed by a series coil with a resistor across it
(see here under Amplifier Instability:
http://education.lenardaudio.com/en/12_amps_3.html)
to isolate the output stages from cable capacity. That might account for why they suddenly decide to explode.

 

[SirPaulGerman]

The design is pretty conventional, BUT... no output Zobel. Usually that's 0.1uf in series with 10 ohms to ground, followed by a series coil with a resistor across it
(see here under Amplifier Instability:
http://education.lenardaudio.com/en/12_amps_3.html)
to isolate the output stages from cable capacity. That might account for why they suddenly decide to explode.

thanks, that what I wanted to know, so just move on to another vintage amp ?

 

[fpitas]

thanks, that what I wanted to know, so just move on to another vintage amp ?

If you insist on vintage, yes.

 

[SirPaulGerman]

How you guys fell about BGW 250D power amp ?

http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/BGW%20250%20Series%20Prof.%20Power%20Amplifiers%20(brochure).pdf

 

[fpitas]

How you guys fell about BGW 250D power amp ?

http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/BGW%20250%20Series%20Prof.%20Power%20Amplifiers%20(brochure).pdf

Looks pretty, but once again I'd need the schematic to even guess.

 

[SirPaulGerman]

Is a professional amp, distortion is a bit high, but after restoration it will last forever

Can you also type what class of amp is it ?

 

[fpitas]

Is a professional amp, distortion is a bit high, but after restoration it will last forever

Can you also type what class of amp is it ?

Class AB, almost certainly. Very conventional again, although plenty of output devices. Which is good.

 

[levimax]

thanks, that what I wanted to know, so just move on to another vintage amp ?

Not all amps have a Zobel network nor do they need one. The fact that this amp is still working after all these years proves that. Phase Linear had a name that rhymed with Flame Linear but from what I have read they are no more or less likely to have problems. I don't think there would be big advantage to another vintage amp. If you were going to keep it I would check the voltage at the test points from the service manual and adjust the bias. If the voltages are off or it won't bias properly then you need to investigate and repair if voltage and bias are in spec I would just enjoy it.

 

[fpitas]

Not all amps have a Zobel network nor do they need one.

Well, I respectfully disagree

Perhaps this one was never presented with the right tuned line load that got it upset. But in production, I'd be very worried about followers driving a capacitive line, especially with variations in ft and device capacitance.

 

[restorer-john]

The design is pretty conventional, BUT... no output Zobel. Usually that's 0.1uf in series with 10 ohms to ground, followed by a series coil with a resistor across it

 

[DVDdoug]

I am on the fence about a restoration, .

"If it ain't broke, don't fix it."

And it would probably cost more than replacing it with a modern equivalent. The cost of "power" has come down a LOT.

very relaxing amp

I have no idea what that means in scientific-engineering terminology.

There are ONLY 3 important audio-quality characteristics - Noise, distortion, and frequency response. Beond that we can talk about power, gain, features, appearance, etc.

very harsh and glassy sound in the top end but, at the same time, opaque to musical detail.

Again, no idea what that really means. It seems to imply distortion but that would have to be measured and/or verified in a blind listening test.

Something I learned recently (from a Dan Clark video) is that distortion is often described as "more detailed" so maybe less detail means less distortion! Let's just see a distortion measurement,... If we are talking about distortion....

This kind of audiophile terminology is useless...

However there seem to be a bias against phase linear amps in the audio community.

The "audiophile community" is mostly nuts! If they had vacuum tubes they'd probably love it!!! This site is one of the more scientific exceptions.

I don't remember Phase Linear having a bad reputation "back in the day." From what I remember they just had way more power than almost everything else, and the theory was that you needed the headroom to prevent clipping on the peaks. Probably untrue for most listeners...

 

[SirPaulGerman]

I have no idea what that means in scientific-engineering terminology.


Again, no idea what that really means. It seems to imply distortion but that would have to be measured and/or verified in a blind listening test.

Something I learned recently (from a Dan Clark video) is that distortion is often described as "more detailed" so maybe less detail means less distortion! Let's just see a distortion measurement,... If we are talking about distortion....

This kind of audiophile terminology is useless...

The "audiophile community" is mostly nuts! If they had vacuum tubes they'd probably love it!!! This site is one of the more scientific exceptions.

I don't remember Phase Linear having a bad reputation "back in the day." From what I remember they just had way more power than almost everything else, and the theory was that you needed the headroom to prevent clipping on the peaks. Probably untrue for most listeners...

What do you make of the design of the Phase linear ?

 

[SirPaulGerman]

View attachment 241523View attachment 241525

What do you mean by that ?

 

[levimax]

Well, I respectfully disagree

Perhaps this one was never presented with the right tuned line load that got it upset. But in production, I'd be very worried about followers driving a capacitive line, especially with variations in ft and device capacitance.

I agree that amps need to take into account stability in their output section and a zobel is the most common but not the only way ... I didn't even look at the schematic but it looks like it does have a zobel. If I have a point it is that amps from this era were pretty robust and the fact that they are still around and working proves the point. It is entirely possible the amp is still working within spec and doesn't need any restoration but this needs to be checked out.

 

[levimax]

What do you mean by that ?

He is showing that it does have a Zobel netwok