How to avoid the BANG on Phase Linear amp 400 Series Two

[Abascal]

A bottle to the sea sent from France.

I inherited from my late uncle back in 2002 a complete stereo system made of :


Phase Linear amplifier 400 Series Two (repaired already twice : fuses and change of transistors bank)
Phase Linear preamplifier 3000 Series Two
Phase Linear tuner 5000 Series Two
Phase Linear noise reduction 1000 Series Two (not in use anymore)


And a venerable pair of Acoustic Research AR10pi speakers which are not longer in good condition and require either another repair (woofers suspension in tatters and one medium
speaker very noisy). The option is to repair the speakers (the repair specilaist asks for the equivalent of about 200usd) or to swap them by a newer pair of second hand speakers.

The initial question was about which speakers could well replace the Acoustic Research AR10pi if I were to not repair them ? It looks like I will go for the woofers repair as i cannot imagine what equivalent speakers I could buy for 150€ (200usd).

Hence this thread now about adding the magic board. Lee kindly wrote to me a PM stating that there is a 95.00 dollar DC Protect board that allows to avoid the Bang that occurs every time the amp is ON-ed or OFF-ed. What else does this board do ? Any impact on improving the sound under normal usage ?
I can solder and follow directions. So her I am, available to take advice. Pascal

 

[laatsch55]

Well sir, glad to see you post about it. We LOVE off cover inside hudies of the subject equip,ment!!


#1-- Does it power up without blowing fuses??
#2-- If it does what is the DC offset on the speaker out posts?
#3-- If DC offset is under 75 millivolts DC, what is the bias reading?

#4--- if none of the above makes any sense, we need to understand what you do comprehend to find some common ground.

#5 Do you have a digital or analog multimeter, and or oscilloscope?

 

[laatsch55]

The White Oak driver board simply pulls the PL topology kicking and screaming onto the 21st century.



Pascal , is this discussion going through a translator program, If so I'll tone down the regional colloquilisms..

 

[Abascal]

Well sir, glad to see you post about it. We LOVE off cover inside hudies of the subject equip,ment!!


#1-- Does it power up without blowing fuses??
#2-- If it does what is the DC offset on the speaker out posts?
#3-- If DC offset is under 75 millivolts DC, what is the bias reading?

#4--- if none of the above makes any sense, we need to understand what you do comprehend to find some common ground.

#5 Do you have a digital or analog multimeter, and or oscilloscope?

I hope I don't need a translator of any sort ! However "hudies" definitely requires some translation as I did not find it neither in the harrap's dictionary nor in the Chambers English dictionnary, not even on internet. Must indeed be a regional expression.

so :
#1 : yes , it works normally. It has always made a bang when powered up, and same as well when turned off
#2 no idea. I did not measure it and btw how do you measure it ?
#3 see above
#4 I was told by the repair engineer that the bang was not important. Same comment from the guy who repaired the AR10pi the fist time I had to redo the woofers suspension. No impact also on the speakers. To be clear, the 400 Series Two does not require any repair at this moment. It works, but makes a big noise when ONed. It always did that. Isn't a characteristic of Phase Linear ?
#5 I have a power indicator which is made of red horizontal LEDs, not view meters à la Accuphase
it is the one corresponding to the second row of pictures as shown on: http://www.phaselinearhistory.stereomanuals.com/400seriesamp.htm

 

[laatsch55]

Pascal, I'm sorry. Ihave a bad habit of posting without proofreading. "hudies" is supposed to be "nudies". Just a pic of the insides.

The turn on/off thump was a PL design deficiency. Joe's new driver board eliminates this ENTIRELY, HOWEVER it will not protect your speakers should an output ":Short". 90% of power amps will do the same thing but most were built with DC protect a part of their design. Don's DC protect board does exactly what it is supposed to do. It also requires no drilling or other modifications to your amp. Is your Series II 400 quasi or fully comp?? A pic of the output stage will tell us.

 

[laatsch55]

DC offset is measured by putting meter positive on + post and meter negative on - post. Meter on mv scale in DC.

 

[laatsch55]

#5 was refering to test equipment. A volt/ohm meter and an oscilloscope.

 

[laatsch55]

To check bias, positive meter lead on the base bus bar, negative lead on the common emitter tie point. If youll notice in the pic, the smaller 10 ohm resistor(Brown-black-black-slver) is also tied to these points. That is known as r38 on the positive side and R39 on the negative drive side. So when they say "Measure voltage drrop accross R38,39" that is what is meant by this. Have your meter set on mv scale in DC. Ideal is 380mv, range can be from 200-400mv.

 

[laatsch55]

Pascal-----this may help also----http://forums.phxaudiotape.com/show...ar-400-Series-II-Quasi-Comp?highlight=Imlay's

 

[NavLinear]

Here is some additional insight into the turn on and turn off thump.

http://forums.phxaudiotape.com/show...-latch-up-tendency-in-Phase-Linear-Amplifiers

By adding the two diodes as explained by Joe (Gepetto) the thump you're hearing is eliminated.

 

[laatsch55]

Nav, the 1N4148 diodes alone do not eliminate turnon/off thump. If youll notice on Q5 in the latest iteration, turn off voltage now collapses through the collector of Q5 to ground. Which now results in a quiet fade to b;lack.

 

[Abascal]

Pascal, I'm sorry. Ihave a bad habit of posting without proofreading. "hudies" is supposed to be "nudies". Just a pic of the insides.

The turn on/off thump was a PL design deficiency. Joe's new driver board eliminates this ENTIRELY, HOWEVER it will not protect your speakers should an output ":Short". 90% of power amps will do the same thing but most were built with DC protect a part of their design. Don's DC protect board does exactly what it is a to do. It also requires no drilling or other modifications to your amp. Is your Series II 400 quasi or fully comp?? A pic of the output stage will tell us.

Sorry for #5, my misunderstanding. Yes I do have a volt/ohm meter. But:

it's gonna take time to take a picture as the amp is with my Brother in law at about 90 miles from where I live. He is supposed to bring the speakers for repair to my place (i'm the one who is going to take them to the repair center). I will ask him to bring the amp together with him. I'll take pictures then and will reconnect to this post.

thanks very much for all the explanations. Very usefull.

 

[laatsch55]

We try Pascal, sometimes we even help. Pascal is a measure of pressure correct??

 

[NavLinear]

Nav, the 1N4148 diodes alone do not eliminate turnon/off thump. If youll notice on Q5 in the latest iteration, turn off voltage now collapses through the collector of Q5 to ground. Which now results in a quiet fade to b;lack.

My memory fails me here - is this on Joe's new controller board or is there another modification for the original board?

BTW - USPS tracking number 9405503699300200613221 for a small goodie package coming your way.

 

[Gepetto]

My memory fails me here - is this on Joe's new controller board or is there another modification for the original board?

BTW - USPS tracking number 9405503699300200613221 for a small goodie package coming your way.

Lee is correct here. The magic is in the power supply circuitry on the White Oak board which eliminates the design issues on the original board that caused the turn on and off thump that was never fixed in any generation of the PL400 or 700. The back to back diodes on C6 is to correct a random latch up problem on the early PL boards, not the turn on/off thump.

 

[NavLinear]

Lee is correct here. The magic is in the power supply circuitry on the White Oak board which eliminates the design issues on the original board that caused the turn on and off thump that was never fixed in any generation of the PL400 or 700. The back to back diodes on C6 is to correct a random latch up problem on the early PL boards, not the turn on/off thump.

Thanks for clarifing that Joe and Lee. When I read your post on how to fix the latch up issue I assumed that if the latch up was fixed that this would eliminate the thump. I been bitten by the assume bug again.

 

[laatsch55]

But your so cute when that happens....

 

[laatsch55]

A FaboNav goody box??????????

 

[NavLinear]

It should be at your door step tomorrow. FYI - both types of cable are 20 AWG. Have I sent you any solder sleeves?

 

[laatsch55]

Like Christmas again. That shielded, twisted pair you sent is neat stuff biut does not solder well at all. Gotta use rosin and lots of heat to get it to stick. I had used some for the DC protect AC feed.Tucked in very nice along the bottom with the low signal stuff with no inductance to the signal path. What's your take on it??