Phase Linear 2000 troubleshooting

[laatsch55]

Well then ...get those 4739'S outta there and get the sockets in and ready ..

 

[Coldsmoke]

Well then ...get those 4739'S outta there and get the sockets in and ready ..

Hope so, but the fact that I get very clean scope traces is very troubling...

 

[laatsch55]

Why??

 

[Gepetto]

Nope, it definetly comes from the 2000 ...

Seems that I recall that this preamp relies on some screw connections from the board to the chassis to establish a ground for the chassis. Are all the board screws in place? Have you replaced C40 and C41? This pre just uses bulk unregulated voltages, no multistage regulators such as other preamps have. This preamp relies on the PSRR of the OP amps for hum and noise rejection. Not a great plan for a preamp.

Make sure the center tap of the transformer secondary is well connected.

You have hum on all inputs or just on some? Do you have AC safety ground connections on any components in your system that might be causing ground loops?

 

[Gepetto]

Well then ...get those 4739'S outta there and get the sockets in and ready ..

4739s are only in the phono stage Lee. If Florian is getting hum on all inputs, that is not the issue.

 

[laatsch55]

In the tone controls too Joe..

 

[Gepetto]

In the tone controls too Joe..

That is the rear channel out Lee, not the tone controls. The bulk of the pre is RC4136 based except the phono stage input amp and the rear channel (ambience) outputs.

 

[Coldsmoke]

Seems that I recall that this preamp relies on some screw connections from the board to the chassis to establish a ground for the chassis. Are all the board screws in place? Have you replaced C40 and C41? This pre just uses bulk unregulated voltages, no multistage regulators such as other preamps have. This preamp relies on the PSRR of the OP amps for hum and noise rejection. Not a great plan for a preamp.

Make sure the center tap of the transformer secondary is well connected.

You have hum on all inputs or just on some? Do you have AC safety ground connections on any components in your system that might be causing ground loops?

Hello Joe,
I actually noticed the chassis ground through the screw and it is in place.
C40 and C 41 have been replaced
The center of the secondary of the transformer is connected
And finally, yes, I have hum on all my inputs and no source is conected to earth

 

[Coldsmoke]

My mistake, I can't locate 40 et 41 that are resistors to me. But all the electrochimical caps have been replaced.

 

[Coldsmoke]

Why??

Because I would have thought seeing the hum thing on the scope...???

 

[laatsch55]

With a spectrum analyzer yes...you would have to tune the scope to the hum frequency to find it......

 

[Coldsmoke]

With a spectrum analyzer yes...you would have to tune the scope to the hum frequency to find it......

Mmmm I get it....

 

[gadget73]

Not really. If its a hum, its usually going to be line frequency or double line frequency, so 50 or 100 hz in your part of the world. If that is clean on the scope and you get a nice flat line out of it, it shouldn't be humming. It really does sound more like grounding issues than some actual fault within the unit. Open grounds will make for a 50 hz hum.

 

[Gepetto]

Because I would have thought seeing the hum thing on the scope...???

have you (carefully)scoped it when the 2 components are connected together?

 

[Coldsmoke]

Not really. If its a hum, its usually going to be line frequency or double line frequency, so 50 or 100 hz in your part of the world. If that is clean on the scope and you get a nice flat line out of it, it shouldn't be humming. It really does sound more like grounding issues than some actual fault within the unit. Open grounds will make for a 50 hz hum.

Mmm. That was my first idea, the thing is that I scoped it only from 1000 HZ and above, I guess that if the hum is at a (much) lower frequency I maybe can't see it on my shit** scope ....?

I'll give it a try tomorrow morning.

 

[Coldsmoke]

have you (carefully)scoped it when the 2 components are connected together?

Joe, I haven't had the idea to scope one one of the too output while the other is connected to the amp. Is it what you suggest?

 

[Gepetto]

Joe, I haven't had the idea to scope one one of the too output while the other is connected to the amp. Is it what you suggest?

that is what I am suggesting

 

[gadget73]

Mmm. That was my first idea, the thing is that I scoped it only from 1000 HZ and above, I guess that if the hum is at a (much) lower frequency I maybe can't see it on my shit** scope ....?

I'll give it a try tomorrow morning.

Anything will read 50 hz unless you have a high pass filter or something on it. Might have to wind the sweep speed down a bit so it shows up decently though. Try somewhere between 2 and 10 ms/div. If its a CRT type, you'll probably be seeing flicker as it retraces. You may also need to turn down the volts/div adjustment to read it.

 

[Gepetto]

Anything will read 50 hz unless you have a high pass filter or something on it. Might have to wind the sweep speed down a bit so it shows up decently though. Try somewhere between 2 and 10 ms/div. If its a CRT type, you'll probably be seeing flicker as it retraces. You may also need to turn down the volts/div adjustment to read it.

set your trigger source to Line and you see it

 

[MarkWComer]

Preamp capacitors

Cracked open my 4000 to look it over. Since I'm going to Capacitor Hut to buy some stuff for other phono projects, decided to recap the preamp. In another thread I expressed my agony with these suckers, but came to the realization that some caps are audio grade, as are on the White Oak driver board. When should I worry about this?

I'm figuring that the power section (1000µ/50v x2, 47µ/35v x2, and 50µ/35v x3) really don't need "audio grade" caps since they deal mainly with the power to the unit, not really a signal path component.

I'm dealing with the PL 40 board on the bottom (it says "UDDER MUDDER" on it!) for now, will deal with the correlator and tone circuits later. I do notice some low level electron hiss, and expect that it's either related to capacitor or resistor value drift that comes with age.

Opinions, anyone?

I also see that some of the ICs in my 4000 are the same mentioned in this thread- looks like some of the edges of the epoxy are chipped. Hmmm... Suspicious...