DCP going south??

A few months ago, I was installing new components in a Toshiba preamp that had an op amp in the phono stage. Several were suggested including OPA2134. Being the obsessive compulsive sort that I am, I read to death opinions about op amps. Somewhere I came across something that said because an OPA2134 was JFET, they could oscillate in some circuits in some gear. Although I bought a couple, I never tried them. I stuck in an NE5532 and since it worked and seemed to sound better than what it replaced, I left it alone.
 
WOPL Sniffer said:
It's a big learning curve doing these amps. I learned some hard lessons. Iffn it weren't for the crazy goombahs here that helped me through my mistakes, Id still be employed... Crap, that didn't come out right.. LOL
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lol... yea I'm learning to my background was mostly old simple 50's tube amp type stuff and the crazies here can't make me crazy I already am but damn this is driving me crazy :banghead::banghead:
 
62vauxhall said:
A few months ago, I was installing new components in a Toshiba preamp that had an op amp in the phono stage. Several were suggested including OPA2134. Being the obsessive compulsive sort that I am, I read to death opinions about op amps. Somewhere I came across something that said because an OPA2134 was JFET, they could oscillate in some circuits in some gear. Although I bought a couple, I never tried them. I stuck in an NE5532 and since it worked and seemed to sound better than what it replaced, I left it alone.
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In this application the 2134 has been used very successfully after I did the mod with them and saw things go boom I posted on the carver site where the info from on this mod someone posted there may be a chance the supplier I got the 2134's from may have a bad batch..... guess you could say I most likely confirmed that 3 of the 6 2134's I bought were faulty... think when I get the c-1 back if it is all working good I will weld the covers on it to keep my fingers out of it lol
 
See I set my meter to mv and I get mv reading in this case (point) .548 mv dc

fl_zps1kuzovqp.jpg
 
laatsch55 said:
Except bias, ya don't want just a third of a millivolt for bias....
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My mistake that is volt not mv I am resetting bias now
I now have .3501 V dc on the right channel and left channel is now .3503 V dc
 
roccus said:
Here is offset with DCP removed
Right .585 mv dc ( this went up from when DCP was in and is pretty jumpy compared to left)
Left .038 mv dc

Looks to me like something may be going on in that right channel??
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So, there is no issue with your offset. It's less than 1 millivolt.
 
roccus said:
Want to record my readings here before I disconnect DCP next I will take the DCP out of the loop and and see what offset is

Offset
Right .125 mv dc
Left .065 mv dc

Bias
Right .3447 mv dc
Left . 3486 mv dc (the bias seems to have dropped just a tad since break in)

Rail volts
84.02 vdc

DCP pins
J1-1 .082 mv dc
J1-2 not used
J1-3 .001 mv dc, 0.27 ohms

J2-1 .296 mv dc
J2-2 not used
J3-3 .006 mv dc, .31 ohms

J3-1 83.46 v dv
J3-2 .0002 v dc, .51 ohms
J3-3 61.50 v ac
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Your bias was recorded WRONG. You said now it's .344 VOLTS which is near perfect
 
Maybe you should have Lee test it. Since the readings are fine, it needs to be run up and monitored without your speakers. By applying a signal and monitoring the output with a scope, we can tell what's up. Or, with the DCP out, crank it.... (don't do that)
 
Yep, drive it with no load while hooked up to check for ac, see where it clips, then switch meter to DC AFTER bringing it BELOW clip, see what ya got then....
 
laatsch55 said:
Yep, drive it with no load while hooked up to check for ac, see where it clips, then switch meter to DC AFTER bringing it BELOW clip, see what ya got then....
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Hi Lee when you say drive it no load does that mean connect preamp for input but no speakers?
 
laatsch55 said:
Well, I was hoping you had a signal generator....
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All I have is a DMM, an oscope and an app to send signals from my laptop but it wont put any voltage out... anyone here have a signal generator they will part with??
 
OK, well, best thing to do now is wait until the 1237 shows up, get it swapped in and hook the DCP back up. Then see if it keeps tripping. IF that happens, search for a signal generator program you can burn a steady state signal to a CD,. then burn a CD and pop it in your CD player. IIRC, there are some burnable signal sources that will have different frequencies for a pre-determined period of time.
I haven't used one but when I was sniffing out signal sources i stumbled across one somewhere. I don't remember which one it was....
 
laatsch55 said:
OK, well, best thing to do now is wait until the 1237 shows up, get it swapped in and hook the DCP back up. Then see if it keeps tripping. IF that happens, search for a signal generator program you can burn a steady state signal to a CD,. then burn a CD and pop it in your CD player. IIRC, there are some burnable signal sources that will have different frequencies for a pre-determined period of time.
I haven't used one but when I was sniffing out signal sources i stumbled across one somewhere. I don't remember which one it was....
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I need a signal generator not an audio generator correct?
 
Yep, you need to be able to burn a 200hz tone and a 1khz tone....
 
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