DCP going south??

[roccus]

Actually 75mv on a stocker, a WOPL is less than 10..when checking offset there should be no amp input...nothing hooked to the RCA jacks. Have you replaced the 1237's??

Don't have the 1237's here yet they just got shipped out yesterday I think... these reading are with nothing connected to in or outputs except my DMM to the outputs.... when I first turn the amp on the mv's are a bit higher they seem to drop bit after 20 or 30 seconds to the readings I gave here....

So the next thing for me to do is wait for the 1237's and replace that?? It don't seem that would change my output DC voltage.........

Thanks guys for the help here

Edit... bias is good

 

[WOPL Sniffer]

Don't have the 1237's here yet they just got shipped out yesterday I think... these reading are with nothing connected to in or outputs except my DMM to the outputs.... when I first turn the amp on the mv's are a bit higher they seem to drop bit after 20 or 30 seconds to the readings I gave here....

So the next thing for me to do is wait for the 1237's and replace that?? It don't seem that would change my output DC voltage.........

Thanks guys for the help here

Edit... bias is good

I know the 700 DCP's are a piece of cake to remove and check DC offset, can you not do the same for the 400? if the DC offset is too high, it's too high. Verify with DCP out. It should eliminate the DCP instead of throwing parts at it.

 

[WOPL Sniffer]

If your Offset is that high, not sure why you are suspecting the DCP. Sounds like it's doing it's job.... Just MHO...

 

[marcok]

Here in this forum DCP protection is strongly recommended , but
I don't exactly understand the real advantages .
a ) most of preamps have a resistor and a cap at output stage ( 600 / 820 Ohm and 4,7 / 6,8 uF in series )
so no DC at the input of the Power Amp
b ) in case you have Pl 700 you can select normal / DC and so it' s possible to insert another protection .
I use normal position to drive Allison One with 3,15 amp fuses in series .
c ) in case you have Pl 400 you can simply insert ( if you want ) a 6,8 uF cap at the input .
In my case I have no problem to drive Infinity RSIII , because they have two big caps at the input .
This " strange crossover " creates a thump at power up , but it' s very easy to fix this issue , using
a 510 Ohm 5 W resistor connected between + and - of the speakers .
Look at the last page of PL service manual .
So are there other reasons to use DCP for domestic application ?
A curiosity : why PL 200 is equipped with DCP and 400 and 700 have no this circuit ?
Ciao
Marco

 

[roccus]

I know the 700 DCP's are a piece of cake to remove and check DC offset, can you not do the same for the 400? if the DC offset is too high, it's too high. Verify with DCP out. It should eliminate the DCP instead of throwing parts at it.

Pretty sure not hard just disconnect all wires from the DCP (it has phoenix connectors for the wires going to it) then just connect my meter straight off the output wires... will try to do it in a bit got my hands full today painting clapboard I replaced on house gonna rain tomorrow.....

But the point here is the DCP can raise or add DC output??

 

[WOPL Sniffer]

Here in this forum DCP protection is strongly recommended , but
I don't exactly understand the real advantages .
a ) most of preamps have a resistor and a cap at output stage ( 600 / 820 Ohm and 4,7 / 6,8 uF in series )
so no DC at the input of the Power Amp
b ) in case you have Pl 700 you can select normal / DC and so it' s possible to insert another protection .
I use normal position to drive Allison One with 3,15 amp fuses in series .
c ) in case you have Pl 400 you can simply insert ( if you want ) a 6,8 uF cap at the input .
In my case I have no problem to drive Infinity RSIII , because they have two big caps at the input .
This " strange crossover " creates a thump at power up , but it' s very easy to fix this issue , using
a 510 Ohm 5 W resistor connected between + and - of the speakers .
Look at the last page of PL service manual .
So are there other reasons to use DCP for domestic application ?
A curiosity : why PL 200 is equipped with DCP and 400 and 700 have no this circuit ?
Ciao
Marco

Yup, they're cool....

 

[WOPL Sniffer]

Pretty sure not hard just disconnect all wires from the DCP (it has phoenix connectors for the wires going to it) then just connect my meter straight off the output wires... will try to do it in a bit got my hands full today painting clapboard I replaced on house gonna rain tomorrow.....

But the point here is the DCP can raise or add DC output??

Not Likely (remotely possible but I doubt it), it sound like it is working.

 

[WOPL Sniffer]

Here in this forum DCP protection is strongly recommended , but
I don't exactly understand the real advantages .
a ) most of preamps have a resistor and a cap at output stage ( 600 / 820 Ohm and 4,7 / 6,8 uF in series )
so no DC at the input of the Power Amp
b ) in case you have Pl 700 you can select normal / DC and so it' s possible to insert another protection .
I use normal position to drive Allison One with 3,15 amp fuses in series .
c ) in case you have Pl 400 you can simply insert ( if you want ) a 6,8 uF cap at the input .
In my case I have no problem to drive Infinity RSIII , because they have two big caps at the input .
This " strange crossover " creates a thump at power up , but it' s very easy to fix this issue , using
a 510 Ohm 5 W resistor connected between + and - of the speakers .
Look at the last page of PL service manual .
So are there other reasons to use DCP for domestic application ?
A curiosity : why PL 200 is equipped with DCP and 400 and 700 have no this circuit ?
Ciao
Marco

It really has nothing to do with the PreAmp inputting DC, It has to do with maybe an output transistor shorting B+ or B- to the output.... or anything else in the amp sliding DC onto the output

 

[WOPL Sniffer]

Here in this forum DCP protection is strongly recommended , but
I don't exactly understand the real advantages .
a ) most of preamps have a resistor and a cap at output stage ( 600 / 820 Ohm and 4,7 / 6,8 uF in series )
so no DC at the input of the Power Amp
b ) in case you have Pl 700 you can select normal / DC and so it' s possible to insert another protection .
I use normal position to drive Allison One with 3,15 amp fuses in series .
c ) in case you have Pl 400 you can simply insert ( if you want ) a 6,8 uF cap at the input .
In my case I have no problem to drive Infinity RSIII , because they have two big caps at the input .
This " strange crossover " creates a thump at power up , but it' s very easy to fix this issue , using
a 510 Ohm 5 W resistor connected between + and - of the speakers .
Look at the last page of PL service manual .
So are there other reasons to use DCP for domestic application ?
A curiosity : why PL 200 is equipped with DCP and 400 and 700 have no this circuit ?
Ciao
Marco

Also, when WOPL'ing an amp (at least the 700's I do), the DC Switch is no longer connected.

 

[marcok]

It really has nothing to do with the PreAmp inputting DC, It has to do with maybe an output transistor shorting B+ or B- to the output.... or anything else in the amp sliding DC onto the output

It's O.K.
Infact I use two other fuses for Allison Ones , but I was not sure if it was sufficient .
Anyway I don't believe you can easily destroy the power transistors in a domestic application ,
but everything can happen ......
Probably it's easier that a short occurs in the two caps of power supply .
Is it correct ?
Ciao
Marco

 

[laatsch55]

Residential torture can get intense Marco, and even though On-Semi's QC is good, they don't test each individually. So a bad one could slip through, im not gonna risk 8k of corner horns on that. A 100.00 DCP takes all the risk out of it. Problems with Dons boards are rare and usually is a result of something besides the board causing the initial problem.

 

[marcok]

I think you're right , Lee .
" Glueing " woofers is not a good thing .
Ciao
Marco
PS: anyway sometimes I don't understand Bob Carver .
Why did he design PL 400 / PL 700 without DCP ?
And then he used DCP for the "baby " PL200 .!!!???

 

[WOPL Sniffer]

People's closets are FULL of 400's and 700's with blown outputs. Don't know what you are talking about that home use can't take out a transistor.... hmmmm

It CAN and will.

 

[laatsch55]

I think you're right , Lee .
" Glueing " woofers is not a good thing .
Ciao
Marco
PS: anyway sometimes I don't understand Bob Carver .
Why did he design PL 400 / PL 700 without DCP ?
And then he used DCP for the "baby " PL200 .!!!???

Had to.be some redeeming quality to the 200 and that was it. Simply a matter of money Marco, though I believe no speaker protection hurt the brand wayyyyyy bad in the long run...

 

[marcok]

People's closets are FULL of 400's and 700's with blown outputs. Don't know what you are talking about that home use can't take out a transistor.... hmmmm

It CAN and will.

For professional use ( PA ) you must consider these conditions .
- temperature range
- weather condition
- always full power
- transport
At home you must consider that some owners are worse than Attila .
For me at home the most common cause of failure is the human factor .
I think that if you pay attention and if you follow the manuals you have only to do normal maintenance .
( belts , caps , refoaming .etc )
This is my experience , with the exception of PL 4000 .
For this particular device you must replace all connector and.....
Now ,however , I have the doubt to introduce DCP .
Ciao
Marco

 

[WOPL Sniffer]

For professional use ( PA ) you must consider these conditions .
- temperature range
- weather condition
- always full power
- transport
At home you must consider that some owners are worse than Attila .
For me at home the most common cause of failure is the human factor .
I think that if you pay attention and if you follow the manuals you have only to do normal maintenance .
( belts , caps , refoaming .etc )
This is my experience , with the exception of PL 4000 .
For this particular device you must replace all connector and.....
Now ,however , I have the doubt to introduce DCP .
Ciao
Marco

It will come to light soon that there is no problem with the DCP

 

[roccus]

"a 510 Ohm 5 W resistor connected between + and - of the speakers"

What s the advantage to this?? is that not a short putting across + and - ?

 

[laatsch55]

That's ONLY for a certain type of speaker.....do not try that at home.....It's just a fancy Zoebel network.....there's one of those on all PL amps...

 

[roccus]

That's ONLY for a certain type of speaker.....do not try that at home.....It's just a fancy Zoebel network.....there's one of those on all PL amps...

I'm with you on this!! I think the DCP works well if everything is up to snuff but if something is out of whack like in my amp then it can be headache to deal with I don't see why I should already be having a problem everything is brand new....

 

[laatsch55]

I have ruined quite a few new stuff!! When an amp goes POP, SQUEAK< BANG from bad pre-amp, it's not the amps fault. Transients can cause hell....