bias and offset adjustments

T-wrecks

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#1
Ok so I have a series 1, 8 fin, 400 with revE pl14_20 which has a very slight channel imbalance im trying to iron out. I thought maybe adjusting the bias and offset may help. I cannot find any of the document I had when I installed the board though, and cant locate them on the internet. Can anyone steer me in the right direction? thank you ;)
 

laatsch55

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#3
Is the channel imbalance something you can hear or are you going by the meter response??
 

laatsch55

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#4
Bias is adjustable, offset isn't...neither will make a "balance" problem better...,
 

T-wrecks

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#5
Is the channel imbalance something you can hear or are you going by the meter response??
I could hear a channel imbalance for awhile. Turns out most was due to my preamplifier. Still felt like a good idea to check bias though. I don't think the meters are accurate enough to trust.
 

T-wrecks

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more to the story

ok so there is more to this, the right channel has always given me fits. Today while auditioning my new Phase Linear 3000 preamp (more on that in a different thread maybe) the right channel has intermittent high frequency distortion and noise. After a bit of this, the right channel completely cuts out. Im convinced at this point that something is amiss with my right channel of my amp. :scratch: (eventually the channel came back)
 
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oldphaser

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ok so there is more to this, the right channel has always given me fits. Today while auditioning my new Phase Linear 3000 preamp (more on that in a different thread maybe) the right channel has intermittent high frequency distortion and noise. After a bit of this, the right channel completely cuts out. Im convinced at this point that something is amiss with my right channel of my amp. :scratch: (eventually the channel came back)

Where do I begin? Let's see...

Phase Linear 3000:

There were several versions of the Phase Linear 3000 preamp. The 3000's were notorious for problems with the clear-see through top relays. Early 3000's had (13) relays. Eventually many of them had (6) or (7) of the relays replaced with the Aromat HB2E-DC24V yellow topped nitrogen gas filled sealed relays with gold contacts. A little later on all (13) relays were HB2E-DC24V's. Then Phase Linear added an additional (14th) relay in the tape loop to prevent oscillations.

The 3000's also had problems with the micro-switches... even a few megohms of resistance (caused by dirty contacts) would cause false-triggering of the CMOS IC's and in turn the relays. In which case the input selector switches would not always engage or disengage when depressing the button. In other words, more than (1) switch would be engaged as indicated by the illumination of more than 1 LED. Using an appropriate cleaner/lubricant sprayed into the switch and exercising the switch should solve this problem.

The 3000's power switches also had a high failure rate.

After all the problems noted above have been addressed you should have a good preamp.



Have you tried swapping your cables to see if the problem moves from one channel to the other?




Phase Linear 400 Amplifier:

Do you still have the original Switchcraft 3501FR RCA input jacks on your Phase Linear 400?

If so, I would suggest also checking the RCA jacks out. In order to do this; find a RCA patch cable you are willing to sacrifice. Bend the (4) petals back so that only the center pin is exposed. (NOTE: The nominal diameter should be close to .125"). Now use the RCA jack like an inspector would use a GO-NO Go plug gage and insert it into the jack on the back of your amplifier. There should be some resistance when you plug it into the female input on the RCA jack. I have found that approximately 60% or so of all the old Phase Linear amps have at least (1) loose input jack. Unfortunately, the Phase Linear service manuals do not discuss this (nor any other manufacturer I have seen who utilizes chassis mount RCA jacks).
NOTE: This has not been a problem with PC board mount style RCA jacks.

If your jack(s) are loose.....

WARNING: Be sure to wear safety goggles.
1.) Examine the opposite end of the jack and locate the solder tab (this will be the view as taken from inside the amplifier). Note the orientation of the solder tab.
2.) On the other end of the jack locate the area directly across (180 degrees) from the solder tab.
3.) Using a small flat-bladed jeweler's screwdriver and wedge it between the formed jack and the insulating material.
4.) Reform the jack by bending it back slightly with the jeweler's screwdriver.

See attached photos.

I hope this information is of some help.

Ed
 

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T-wrecks

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#17
3000

IMG_1913[1].jpg
Good morning! Check this out. This is my inside of my 3000 lol, best to start another thread about this turd. Yes my input RCA on my 400 are original. And this has occurred to me also. While I had music playing yesterday I leaned the amp up so that it was resting on its cooling fins. I slid a thick paperback book underneath the transformer and unscrewed the bottom cover of the amp. Very carefully I poked the input wires with a plastic utensil to see if they were intermittent. They seemed ok. I also just tried your go/no go gauge and still seemed ok. Also I don't think that would create distortion. I have swapped cables bunches of times. Its definitely the right channel.
 

oldphaser

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#18
View attachment 31552
Good morning! Check this out. This is my inside of my 3000 lol, best to start another thread about this turd. Yes my input RCA on my 400 are original. And this has occurred to me also. While I had music playing yesterday I leaned the amp up so that it was resting on its cooling fins. I slid a thick paperback book underneath the transformer and unscrewed the bottom cover of the amp. Very carefully I poked the input wires with a plastic utensil to see if they were intermittent. They seemed ok. I also just tried your go/no go gauge and still seemed ok. Also I don't think that would create distortion. I have swapped cables bunches of times. Its definitely the right channel.

Oh that 3000 looks terrible with all those original relays!
The 3000 relay issues are one of the reasons I began to hate replacing parts on double-sided pc boards with through hole plating.

For replacement relays, perform a search on ebay using "HB2E-DC24V".


Ed
 
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T-wrecks

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Oh that 3000 looks terrible with all those original relays!
The 3000 relay issues are one of the reasons I began to hate replacing parts on double-sided pc boards with through hole plating.

For replacement relays, perform a search on ebay using "HB2E-DC24V".


Ed
the terrible part is the relay with the ridiculous flying leads that has been glued to the circuit board!
 
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