Kevin's "I Want a Phase Linear 700 B White Oaked" thread

[soundude]

That puts a hole in the wallet!!!
Joe howd you do with the rain? I didnt get much, not like they were saying...I'm under you so you probably didnt get much since it came up from the south...

 

[mlucitt]

Lee, I asked Joe about a different value for R20 with the 2N5088s. One of mine is against the stops as well with the original 2N3403. I don't remember if the pot is sitting at minimum resistance or the full 5K Ohms. If it is at minimum maybe R19 (1K Ohms) could be replaced with a wire link, if it is maxed out maybe a 10K pot would work.

Thoughts?

 

[laatsch55]

I have had to play with R19 at times on some older 400's to get the pot to the .300 or so mark. I thinkl stock it's a 1K, but can be anyhere from 330to 1.5K.R19 is between the base of Q6 and the track of R20, not the wiper but the track.

It's acting as a current limiter in that instance so if you have too much go with a greater resistor value.

 

[mlucitt]

I'll try replacing Q6 first. If that won't let me get to the proper bias, I'll look at R19. The original boards (Serial #1-#3) have R19 as 470 Ohms, after Rev B of the BOM, R19 becomes 1K. On my PL 700B, the wiper (terminal 2) is turned all the way over to terminal 1 on the pot. I see that as picking off the maximum amount of resistance or 5K and that is not enough, so I will try a 1K or 1.5K resistor at R19. I'm only having an issue on the Left Channel, so it is probably the Q6 (OEM device).

Thanks,
Mark

 

[Gepetto]

John
We got a little under an inch of rain. Expected much more but it was much needed and we have been getting showers every day so seems like April finally arrived here.

 

[Gepetto]

Hi guys, some dialog on Q6.

The arrow on the schematic indicates the CCW rotation direction. When the pot is fully CCW it is at the 5K end of the pot so it puts 6K ohms across the Q6 base - emitter junction and this corresponds to the MINIMUM bias setting achievable.

Conversely when the pot is all the way CW, it is at the zero ohm end putting 1K across the Q6 base emitter junction.

Failure to achieve a low enough bias is generally associated with 2N3403 that is too low in beta and will not head toward saturation with low base current. I swap these tired 2N3403s out with a new 2N5088 which I know has good beta characteristics. If you do not want to swap out the 2N3403 device, then you can experiment with decreasing the value of R62 from 390 ohms to a smaller value (I would not recommend going below 150 ohms). This will provide Q6 with more base drive (through D6-D8 and then through R62).

I find that there are usually issues at the low end of the bias rather than the high end of the bias setting.

Hope this information is helpful to you.

 

[soundude]

Joe, i didn't get much rain here either, good thing didn't have to cut the lawn yet, YEH!!!

 

[Gepetto]

I think my first cutting is coming this weekend John. We have had a lot of showers and I dosed the lawn well with fertilizer and lime.

 

[laatsch55]

I've put it off for a week too long myself.
Joe, thanks for the tips on the bias. On the stock PL14 boards I have had some success messin with R19.

 

[Gepetto]

Yes R19 can work as well but you can end up with a zero ohm condition on the base emitter if you take R19 down to zero. No real harm done to Q6 but can produce unexpected results (and very non linear bias sensitivity) if the pot is turned all the way to the extreme low end.

Changing R62 is safer because of the 3 diodes remaining in the collector to base chain.

 

[laatsch55]

Damn Dude, that's just sweet!

 

[laatsch55]

Joe-----------you have not mentioned "Patricia", did I totally misunderstand your musical preference??

 

[Gepetto]

Sorry Lee, forgot to mention. I have listened to Patricia 3 times through now. Great CD, thanks very much for sending along. Some great covers on that album. Had heard great things about Patricia, now I have witnessed. She has a new fan.

 

[Gepetto]

Excellently mastered as well Lee, that makes all the difference in sound quality.

 

[laatsch55]

Yes it does, a very low noise live recording is hard to do I imagine.

 

[kevin]

OMG....... JUST GOT MY PL1000 FROM LEE.... DON'T EVEN KNOW WHERE TO START YALL..... ITS LIKE HE SENT NEW SPEAKERS WITH IT !!!!!! MY TWEETERS ARE ALIVE !!!! THE HIGH END JUST JUMPS OUT AND SLAPS YOUR FACE..... AND LOUD... I JUST THOUGHT IT WAS LOUD BEFORE !!!! WHEN I FIRST STARTED TURNING IT UP IT WAS GETTING REAL LOUD AND I LOOKED AND THE METERS WERE NOT EVEN MOVING.... LMAO... MAN.... I STILL GOT A BIG GRIN ON MY FACE AS IM WRITING THIS.... LEE.... AND EVERYONE INVOLVED... THANK YALL SO MUCH FOR WHAT YALL HAVE DONE FOR ME AND MY STEREO !!!!!!!!!!!!!! I JUST CAN NOT SAY ENOUGH.... ALL MY MUSIC IS NEW AGAIN CAUSE I AINT NEVER HEARD IT LIKE THIS......

 

[laatsch55]

Aw Kev, THAT"S WHY I DO THIS!!!!! Love hearing that shit!!!

 

[kevin]

DO WHAT ?????? This thing is so loud I can't even read !!!!! LMAO !!!!

 

[laatsch55]

Did you find the speaker plans and test results??

 

[kevin]

Its just unreal the things that I'm hearing that I have NEVER HEARD BEFORE !!!! What CLEAN CLEAN power !!! WOW !!!!