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Old 21st September 2008, 07:37 AM   #1
AndrewF is offline AndrewF  Australia
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Default Suitable tube pre-amp for Phase Linear 400?

I was given a Phase Linear 400 yesterday, would like to build a tube based pre-amp circuit to feed it. It is just for playing records in my apartment.

Somewhere I read the PL400 has 39k Ohm input impedance which may be problematic with tube circuits.

Could someone kindly recommend some designs for me to consider?

Or has someone already got a similar setup and could give some ideas.

Thankyou
Andrew
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Old 21st September 2008, 09:07 AM   #2
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Something with a transformer output or a cathode follower will work nicely. The Aikido board will do the job, or the Bottlehead Foreplay if you're looking for a complete kit.
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Old 21st September 2008, 09:42 AM   #3
poynton is offline poynton  United Kingdom
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Default Re: Suitable tube pre-amp for Phase Linear 400?

Quote:
Originally posted by AndrewF
I was given a Phase Linear 400 yesterday, ..........

OT.....Lucky guy !! Read the net about problems with this amp and take note before problems develop! (emitter resistors in the output stage for one thing)

There may be a few ideas on suitable tube pre-amps on the Chip Amps section

Andy
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Old 21st September 2008, 05:10 PM   #4
AndrewF is offline AndrewF  Australia
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Quote:
Originally posted by audiowize
Something with a transformer output or a cathode follower will work nicely. The Aikido board will do the job, or the Bottlehead Foreplay if you're looking for a complete kit.
Thankyou, the Aikido looks an easy build. Should have all the parts here.
I am a bit new at this, so one more question.

My TT is an Elac Miracord 40, with no phono pre-amp. Would I be able to connect Elac -> Aikido -> PL400 directly?
Or will I need a phono pre-amp between the Elac and the Miracord, something like a Shure M-65 ?

Thanks for your help!

OT - the PL400 has had an easy life in an elderly gent's living room, been in storage 20 years. The power caps have leaked, otherwise no obvious disasters but I won't know until the caps are replaced.
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Old 21st September 2008, 05:26 PM   #5
kevinkr is offline kevinkr  United States
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One that does not generate large dc transients during warm up or at power off.

Either transformer coupled or with an intelligently designed output muting circuit.

Plan on replacing all the capacitors, not just the ones in the PSU that have leaked. These amplifiers are quite unreliable and make sure that you get all of the service information required before you get started on its restoration. IMO One would have to ask whether or not it is even worthwhile given the dated design and fairly mediocre sound by today's standards. I'll admit they are very cool looking though..

Umm, replace the thermal grease and insulators on all of the output devices and the drivers.. (6 outputs, and 2 drivers per channel - age sometimes increases the thermal resistance of the grease used.)

You will need a phono stage, why not build a tube one? A Thorsten Loesch design or any number of other ones found here.
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Old 22nd September 2008, 01:53 AM   #6
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First things first.... before you use the Flame Linear rebuild it. The amp has aged since it was new so its better to be safe than sorry.

Any pre amp or line stage will work with the Flame Linear 400. Remember the basic rule and that is to turn the preamp or line stage on first and let it warm up. After it is stable then turn on the power amplifier. The second rule applies to turn off sequence and that is the power amplifier goes off first followed by the preamp or line stage.

I would also highly recommend the usage of a relay on the output of the Flame Linear 400 because it has no DC protection and a protection circuit is a heck of a lot cheaper than rebuilding a pair of speakers because the amplifier went to rail.
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