The Phoenix: Jer rebuilt WOPL 500

[Northwinds]

Zip, no movement of the needle at all

Ok, I am bushed, this can sit until tomorrow I guess. Get some sleep Jer, I will be up all night reading about muting transistors. From what I have been able to garner, they keep an amp from distorting the signal? I mainly see references to them in CD players??? Popped the top of the preamp and EVERYTHING still looks cherry new

 

[laatsch55]

I wish we could get him to stick a finger on Q5 to see how hot it's getting....

 

[laatsch55]

Most pre's are cap coupled on the output, keeps DC from going out...

 

[Northwinds]

Something to note, I was going to lay down for a few with some ZZ Top on....

Volume is all the way down but when I get next to the speaker, I hear a hum and can actually here the CD playing, right speaker less of a hum but I can hear the CD

This is not right, I should hear nothing at all hmmmm.... that preamp signal has to be pretty hot for that to happen eh? The hum I am clueless about, that sounds like a bad thing

Anyway, tomorrow is another day

 

[laatsch55]

While ya had your meter out , measure the output of your pre, both AC and DC...

 

[Northwinds]

I wish we could get him to stick a finger on Q5 to see how hot it's getting....

I'd gladly volunteer your finger Lee, you probably have more experiece with getting fried occasionally. I would want to learn from the best and it may take a couple times watching you so as to learn NOT to touch Q5

I love this board

 

[laatsch55]

I can do 120 standing on my head eating ice cream. Found out yesterday I can still take a good jolt of 480 and keep going. I have built up a nice resistance....

 

[jbeckva]

Most pre's are cap coupled on the output, keeps DC from going out...

Yah.. that's my point too.... If'n it wasn't then it'd be a prime suspect here... But looks like we can discount the idea of any DC offset goings-on since Ron's measured that already.

Hum, Ron??? Aw geeze.... I'm so cursed...

 

[laatsch55]

That was measured at the amp outputs though....

 

[jbeckva]

That was measured at the amp outputs though....

Well sure! but the 400's fully DC coupled, right? So if we had some offset going in, at idle we'd have it coming out.. that's my thought. But unless those caps in the skeezer I posted are shorted, that's not happening anyway.

I think having set the bias on that puppy to 410 might not have been a good idear. Ron we're going to need to get ya to dial that back a bit. But you might need a meter that has a 1V range to set it accurately or close enough, thereabouts.

 

[Gepetto]

Well sure! but the 400's fully DC coupled, right? So if we had some offset going in, at idle we'd have it coming out.. that's my thought. But unless those caps in the skeezer I posted are shorted, that's not happening anyway.

I think having set the bias on that puppy to 410 might not have been a good idear. Ron we're going to need to get ya to dial that back a bit. But you might need a meter that has a 1V range to set it accurately or close enough, thereabouts.

No it is not fully DC coupled Jer. The purpose of C6 is to reject DC amplification. That shows in the many response plots that Lee has posted. A Crown DC-300 (I have sometimes have used one of mine as a power supply) will amplify DC just as well as a signal but not a PL400 or PL700.

 

[laatsch55]

With C6 at 470UF what's the cutoff freq??

 

[Gepetto]

With C6 at 470UF what's the cutoff freq??

Hi Lee
The -3dB point is about 1.25 Hz.

 

[laatsch55]

And the 100UF from the factory?

 

[Phase Linear Phanatic]

Yah.. that's my point too.... If'n it wasn't then it'd be a prime suspect here... But looks like we can discount the idea of any DC offset goings-on since Ron's measured that already.

Hum, Ron??? Aw geeze.... I'm so cursed...

Heeeeeey? To WHAT project, doth thou elude to?

 

[Northwinds]

Just woke up, had the amp running all night and it's cool as a cucumber but this was at a low listening volume obviously or the wife would have booted me out to the motorhome LOL. So what could cause me to hear the CD playing when the volume on the preamp is all the way down

The hum I hear is very similiar to that of an ungrounded TT but so low you can't hear it unless your ear is to the speaker. If you crank a TT like that (from experience in the past with a bad phono ground), it will start to feedback, this does not and I don't hear the hum while music is playing

 

[Gepetto]

And the 100UF from the factory?

6 Hz

 

[Northwinds]

Been up surfing the net looking for other people who have this same issue. I have run across quite a few references to the Carver preamps being too hot. One even mentioned that Carver showed a mod that by changing a few resistors, you could change the preamp gain to less output (-3dB -6dB). This is more looking like an issue with my preamp then the amp itself (just surmising as it seems funny that Carver preamps are always mentioned in reference to this problem). Guy described the same thing with his C1 preamp... still hearing the CD play faintly with the volume all the way down

 

[laatsch55]

Thanks Joe, that would explain that.

 

[Northwinds]

Made it all day without tripping the speaker protections. Will be looking for another preamp I think until I figure out what's going on for sure. I notice that no one has really addressed the preamp output level of the Carver???