My First Phase Linear Restore- New Guy to the Forum

[laatsch55]

Used em on the Pig after I got em from you because I was swapping so much out at that time. They did good. After dismounting them they got looked over real close, couldn't see any damage and I got the pig real hot sometimes..

 

[mjstriker]

Had a chance today to do a recap on the 2000 series I. Essentially replaced all the lytics and the ceramic caps on the board. One question I have is regarding C42/43 which calls for 10uf/50V but the ones I pulled off were 0.47uf/50V. That is a pretty big difference. From the looks of the unit it doesn't look like anyone has been inside. I decided to replace caps with the same value (0.47uf). The preamp seemed to be working fairly well prior to the recap but now I am getting a significant hum when the amp is off/on and the preamp is on. Stuck a frequency probe and it appears to be 60hz at the speaker outputs. Otherwise the sound coming out sounds ok.

My question is could this be the cause of the hum? I looked over all my work and it seems adequate except the two caps I mentioned. The third pic has the two caps around the light wire that I am referring.

 

[mjstriker]

 

[Gepetto]

Had a chance today to do a recap on the 2000 series I. Essentially replaced all the lytics and the ceramic caps on the board. One question I have is regarding C42/43 which calls for 10uf/50V but the ones I pulled off were 0.47uf/50V. That is a pretty big difference. From the looks of the unit it doesn't look like anyone has been inside. I decided to replace caps with the same value (0.47uf). The preamp seemed to be working fairly well prior to the recap but now I am getting a significant hum when the amp is off/on and the preamp is on. Stuck a frequency probe and it appears to be 60hz at the speaker outputs. Otherwise the sound coming out sounds ok.

My question is could this be the cause of the hum? I looked over all my work and it seems adequate except the two caps I mentioned. The third pic has the two caps around the light wire that I am referring.

Didn't we fix this problem one time before... pretty sure we did and it has to do with the bleed resistor around the AC power switch.

 

[laatsch55]

Just like that.

 

[laatsch55]

Didn't we fix this problem one time before... pretty sure we did and it has to do with the bleed resistor around the AC power switch.

Yes we did Joe, but that was Calman 46's unit..

 

[mjstriker]

I saw that thread regarding the resistor but I wasn't sure if that had to do with him replacing the 4136 with the upgrade from brown dog. I will try disconnecting the resistor and see if that helps

Regarding the caps that are in there compared to what the schematic calls for, does it really matter or should I go for the 0.47uf or 10uf? I have both to try but that will have to wait till tomorrow

Thanks

 

[Gepetto]

Had a chance today to do a recap on the 2000 series I. Essentially replaced all the lytics and the ceramic caps on the board. One question I have is regarding C42/43 which calls for 10uf/50V but the ones I pulled off were 0.47uf/50V. That is a pretty big difference. From the looks of the unit it doesn't look like anyone has been inside. I decided to replace caps with the same value (0.47uf). The preamp seemed to be working fairly well prior to the recap but now I am getting a significant hum when the amp is off/on and the preamp is on. Stuck a frequency probe and it appears to be 60hz at the speaker outputs. Otherwise the sound coming out sounds ok.

My question is could this be the cause of the hum? I looked over all my work and it seems adequate except the two caps I mentioned. The third pic has the two caps around the light wire that I am referring.

Those caps should not be 0.47uF Mike. They should be 10uF as the schematic shows Your low frequency will suffer otherwise. I do not think that is your hum source.

You should take out R68, the 33K resistor across the power switch.

 

[Gepetto]

I saw that thread regarding the resistor but I wasn't sure if that had to do with him replacing the 4136 with the upgrade from brown dog. I will try disconnecting the resistor and see if that helps

Regarding the caps that are in there compared to what the schematic calls for, does it really matter or should I go for the 0.47uf or 10uf? I have both to try but that will have to wait till tomorrow

Thanks

It was Mike but that resistor does no good. Are you going to get rid of the 4136 op amps. Highly recommended that you do. They are not a good audio choice.

 

[laatsch55]

Mike the Brown Dog adapter with the mounted surface mount Burr-Browns are the way to go...

 

[mjstriker]

It was Mike but that resistor does no good. Are you going to get rid of the 4136 op amps. Highly recommended that you do. They are not a good audio choice.

I have the replacement just wanted to do the recap and make sure it went well before replacing the op amp

 

[laatsch55]

The 4739's are the sticking point. I have a couple of 2000's left and when we get time Joe said it would take a rework of the circuit design but they could be replaced. Everything I've tried results in an oscillation..

 

[mjstriker]

Couldn't resist (pun intended) so I ran out to the garage real quick and removed the resistor. Both the resistor and the ceramic have seen some heat previously so I replaced the ceramic also. Still getting the loud hum. Im looking at the schematic again and trying to figure out if the power/volume switch is wired correctly. The back of the switch has four points, two high and two low. The bottom has a white and black wire each. There is a jumper from the black wire to the upper left point which is then connected to the upper right point by the cap/resistor and has the yellow wire coming off.

 

[laatsch55]

Leave the ceramic and resistor off and see what happens...

 

[Gepetto]

Couldn't resist (pun intended) so I ran out to the garage real quick and removed the resistor. Both the resistor and the ceramic have seen some heat previously so I replaced the ceramic also. Still getting the loud hum. Im looking at the schematic again and trying to figure out if the power/volume switch is wired correctly. The back of the switch has four points, two high and two low. The bottom has a white and black wire each. There is a jumper from the black wire to the upper left point which is then connected to the upper right point by the cap/resistor and has the yellow wire coming off.

Do you have the stock 2 wire AC line cord on both amp and preamp?

 

[Gepetto]

Couldn't resist (pun intended) so I ran out to the garage real quick and removed the resistor. Both the resistor and the ceramic have seen some heat previously so I replaced the ceramic also. Still getting the loud hum. Im looking at the schematic again and trying to figure out if the power/volume switch is wired correctly. The back of the switch has four points, two high and two low. The bottom has a white and black wire each. There is a jumper from the black wire to the upper left point which is then connected to the upper right point by the cap/resistor and has the yellow wire coming off.

The problem we were fighting with Calman's preamp was that it was squealing into the amp when the pre was off and the amp was on. That was due to the bleedthrough from that resistor keeping the 2134 op amps just barely alive.

 

[laatsch55]

That's right...

 

[mjstriker]

I have the preamp hooked up to the 400 and both have stock 2 prong cord. I will take the cap off when I get a chance. I'll check to exactly when it starts to make noise. From what I can remember it doesn't start until both the preamp and amp are powered up.

 

[wattsabundant]

I have the preamp hooked up to the 400 and both have stock 2 prong cord. I will take the cap off when I get a chance. I'll check to exactly when it starts to make noise. From what I can remember it doesn't start until both the preamp and amp are powered up.

The switch is a 2 pole. One of the poles controls the preamp, the other controls the switched outlet. If there is a switching noise when the switch is turned on/off the standard fix is a .001uf/1kv ceramic disc around the contacts. I can't fathom a reason why that resistor is there unless it was supposed to be in series with the cap and the designer/draftsman got it wrong.

The unused opamps have their pins floating. That leaves them free to oscillate and impact the opamps that are used. It may not be a problem with 4739/4136, but any opamp that is substituted could oscillate. The usual fix is to tie the inverting input to the output and ground the non inverting input. The power supply also needs to be decoupled.

Every few years I look at the 2000 and think about converting the rear outputs to a sub woofer output. It would take some work but the unused opamps could be used as buffers and provide flexibility for the crossover design.

I don't know why nobody makes an adaptor board for the 4739. The chip was used in a lot of signal processors for pro audio.

 

[mjstriker]

So looking over my work I have now realized that I made a mistake when replacing C2 and C9 (rated at 22uf 10V) and substituted 2.2uf 35V in its place. Don't know if that could be causing the loud hum (which appears to be 60 Hz) but it obviously needs to be corrected. Was using a bad pdf of the service manual and was able to get my hands on a better resolution one and realized there was not dot between the 2's. Waiting for the parts to show up as the leads on the old parts are too short now to put back in

Hopefully this rectifies the situation and I can move forward cleaning this unit up. Still waiting to get some quality time with the 400 now seeing as I have pretty much all the parts and just need some time to start the tear down.