My First Phase Linear Restore- New Guy to the Forum

[mjstriker]

Nice work mike!!! Glad the 2000 works..

I really enjoyed working on the unit. I was surprised on how night and day the difference in sound is. Makes me eager to get the 400 done and hear what they sound one together powering the CV D9's

 

[mjstriker]

Speaking of the D9's, I just recently recapped the crossovers in both units minus the 100uf nonpolar. I ordered a 100uf 50v and installed it one speaker but was blowing the fuse. I reLized it was supposed to be 100v. The 100uf 100v bipolar showed up a couple days ago and I installed it in one speaker. I also switched polarity of the tweeter and high mid as some say it sounded better. I am still blowing the fuse at higher levels.

My question is, is there a difference between bipolar and nonpolar? That really is the only change I made to the one speaker that is blowing the fuse except for switching the polarity. From what I have read there isn't a difference between the two but I figured then why have two different names.

Gonna put the old cap back in tomorrow to test the theory

 

[Northwinds]

Definitely nice clean work Mike! Glad you got your preamp working ok!

 

[mjstriker]

So I had some time today to really sit and listen to the preamp. It sounds great but after about two hours of play time. I get a really loud hum in the left channel that slowly takes over the right channel. If I turn the unit off and then on the hum goes away but comes back again after about another 2 hours. Checked it all over and my solder connections are sound. It seems to me like a capacitor is slowly building charge and creating this loud hum and when I turn it off/on it discharges and everything sounds fine again. Would I be correct in making that assumption? Maybe I have a bad cap somewhere that doesn't look bad?

 

[laatsch55]

60hz hum?? Man, 2 hours is a long time for something to manifest itself like that. Beins ir affects both channels sounds like a power supply issue. Did you swap the Brown dogs out? Sounds like something could be an issue with them. This is the same unit with the selection switch issue?? Next time bypass the switch when this happens to eliminate that.

 

[laatsch55]

On the D9 crosses, if a polar is in place of a non-polar, you should have that nice filler paper all over the place after a big "POP". If it was installed wrong of course....Haven't seen any polar caps in crosses , but haven't seen a lot of crosses either...

 

[mjstriker]

Been out of town for a while. Had a few minutes today to look over the unit again. The input switch seems to be working fine now. It goes to the correct input and plays without noticeable issue

Stuck the multimeter on the unit and the dc offset is all over the place and really high. Looked at the service manual and it talks about the tone control switch being the issue. I do notice now the tone control switch makes a pop when pushed in or out and makes the offset go haywire.

I started checking voltages beginning with the documented +\- 17 at b+\-. I was measuring roughly 17.4 on both. I did notice I have significant voltage going into the back to back electrolytics prior to going to output

I looked over the unit and all caps are oriented correctly and I don't seen any cold solder joints. As it stands now I have to look at the schematic more closely to determine what kind of voltages I can expect at other test points.

Anothet possibility is the tone control switch is bad as the manual states but that would involve taking off the metal cover as there isn't any external evidence of being broken.

Lastly I do have the faceplate and two bottom covers off. Also the tone control board isn't mounted at this time. Don't see how that would affect anything but I do not know for sure

 

[laatsch55]

DC ofset on the output of the pre amp?? Not good. The caps are there to prevent that. Check upstream of the output caps to see if it's there before the caps...

 

[laatsch55]

Got the 400 done???

 

[mjstriker]

Got the 400 done???

Unfortunately haven't been able to do much of anything the past week and a half with work and other stuff. Need to buy a drill bit to round put a couple of the output mounting holes then I can move forward.

Voltage is there before the back to back caps. I checked some points further upstream but do not know what is appropriate or not. Unfortunately, have to spend the day at the inlaws so that puts a damper on garage work

 

[mjstriker]

What is weird is that the unit sounds fine until about 2 hours then there is audible distortion but the music is still heard.

 

[laatsch55]

Hookay...

 

[mjstriker]

Tinkered around a little more with the preamp. Measured the B+/B- off the the main caps and I am running around +/-19V. Tracing it back to the IC AMP (Now with brown dog adapter) I get the same voltage at pins 7 and 11 so that checks out well. I also get voltage out of pins 4 and 12 and from what I gather isn't supposed to happen. The voltage initially starts around 900mV and slowly increases until I turn the unit off and it starts all over. This voltage is also the same at the tone control switch and connects to most the tone controls so it is difficult to trace where the leakage may be happening

I checked the other IC AMPs and all the pins are 0V except B+/-. So at this point I am thinking I should probably remove the new IC AMP and re-install the old one to see if it rectifies the voltage issue. The only other thing I can think of is maybe a cold solder joint somewhere I can't see or one of the WIMA caps I installed is bad or possibly the wrong value (I triple check everything).

Do you think I am heading in the right direction with swapping out the IC AMP

 

[laatsch55]

Yes, that's te first thing I would do. You could have possibly harmed it by having the selector switch F&^%$ up...

 

[Gepetto]

Tinkered around a little more with the preamp. Measured the B+/B- off the the main caps and I am running around +/-19V. Tracing it back to the IC AMP (Now with brown dog adapter) I get the same voltage at pins 7 and 11 so that checks out well. I also get voltage out of pins 4 and 12 and from what I gather isn't supposed to happen. The voltage initially starts around 900mV and slowly increases until I turn the unit off and it starts all over. This voltage is also the same at the tone control switch and connects to most the tone controls so it is difficult to trace where the leakage may be happening

I checked the other IC AMPs and all the pins are 0V except B+/-. So at this point I am thinking I should probably remove the new IC AMP and re-install the old one to see if it rectifies the voltage issue. The only other thing I can think of is maybe a cold solder joint somewhere I can't see or one of the WIMA caps I installed is bad or possibly the wrong value (I triple check everything).

Do you think I am heading in the right direction with swapping out the IC AMP

What are you running on the brown dogs? If you are running OPA2134 op amps in them you CANNOT run +/-19V into the power pins on them. Look at the other thread with Jer and his pre.

 

[mjstriker]

I am running the OPA2134 so that probably narrows down my problem as I am having similar experiences with the popping while pushing in the defeat control. Looked at the specs and it operates at +/-15V so I am well above with it being 19. The question now is which OP AMP can I use. I see in that thread he used LME49860 and that has better specs to handle the higher voltage. Trying to figure out which one I can/can't use is a little out of my league.

Right now about to go look through my old parts bin to find the original and put it back in to test.

 

[Gepetto]

I am running the OPA2134 so that probably narrows down my problem as I am having similar experiences with the popping while pushing in the defeat control. Looked at the specs and it operates at +/-15V so I am well above with it being 19. The question now is which OP AMP can I use. I see in that thread he used LME49860 and that has better specs to handle the higher voltage. Trying to figure out which one I can/can't use is a little out of my league.

Right now about to go look through my old parts bin to find the original and put it back in to test.

Recommend lowering your voltage to as close to +/-15 as possible. Just about all op amps are specified for +/-18V absolute maximum. Typical design operating voltage for op amps has always been +/-15.

 

[Gepetto]

Recommend lowering your voltage to as close to +/-15 as possible. Just about all op amps are specified for +/-18V absolute maximum. Typical design operating voltage for op amps has always been +/-15.

I don't think Phase Linear got the memo

 

[laatsch55]

Ya THINK?? No shit Mr. Joe, but why has my other applications of the Brown-Dogs worked. They are touted as a direct drop in replacement for the 4136's.....ponderous, very ponderous..

 

[Gepetto]

Ya THINK?? No shit Mr. Joe, but why has my other applications of the Brown-Dogs worked. They are touted as a direct drop in replacement for the 4739's.....ponderous, very ponderous..

They are Lee as long as you observe the absolute max of the OP AMPs involved. The RC4136 had a special variant (suffix on part) that allow the absolute max to go up to +/-22V.

Totally unnecessary in a preamp.+/-15V would do just fine.