Crown Amp DC300A - One channel distirted, other good.

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

In the current operating setup area, get access to things is difficult. Personally, I can't remember ever feeling heat coming out of the amp area although I can't say that I listen at extreme volume levels so I am not sure that the amp is pushed at any time. Will see how it goes. I am enjoying listening to "plain stereo" again.

[petehall347]

Re: Crown Amp DC300A - One channel distirted, other good.

main heatsink should be warm . if you set bias to spec you will just have to see how it goes .

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

Couple of hours running with the "big" jbl sovereigns at moderate volume... not sure my ears or "heart" (fear of blowing things up) can take much higher. Might be psychological, but the sound seems brighter and maybe a bit clearer than in the distant past (its been a while and my ears aren't getting any younger). Hopefully, things will hold up for while so I can move onto a "lost speed revox reel to reel"... :-(.... :-)

Thanks for the continued guidance along the way, it has help get me headed in good directions.

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

So user error comes into play. I needed to get of "auto" mode and go to selected range. Once on a "3 decimal range", I can measure voltages across each .33 resistor. They range from 6 mv to zero although zero is probably not "true" as it flickers from 1mv (smallest measureable increment).

Based on your earlier comment ("there should be some small voltage ... 4mv..."), it would appear that some are seeing such a thing. IF true, it would appear that there is some differences across the outputs.

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

yes you are right. There is a "path" by the first driver thru a 180 ohm resistor to the output.... but IF that path was used as the "only source", I think that the resistor would be "cooked" as it is only a 1/4 watt resistor. I will check what kind of voltage I see going on them.

On the meter side of things, maybe the meter has an issue measuring voltage on very low resistance components / wiring such that the "leakage current" going into the "high impedance" measuring component (for voltage measurement) has some sort of "restriction" on how it handles it. I see a momentary voltage of a 30-40 mv flash on the screen and then it moves to zero.

[petehall347]

Re: Crown Amp DC300A - One channel distirted, other good.

good question . i do not know the answer .all i know is some drivers are capable . i need to look at the schem again to see how the signal gets through but there are usually something like 100 ohm resistors between the drivers emitters connecting to the centre line . .

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

ok... so then you are saying that in a nominal 8 ohm load (speaker), with 8 volts, the system might only be needing 1 amp which could be supplied by just the pre-driver.
But if the outputs are not on, how is that current finding it way to thru the "non-turned on" outputs without significant distortion?

[petehall347]

Re: Crown Amp DC300A - One channel distirted, other good.

from what i find they are 1 amp or thereabouts

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

sorry, not sure that I understand. you are saying at the low power needed for the small speakers that I am running, they might be the only thing operating and that the slight temperature is just that. When the "big boys speakers" are connected, then things will fall apart. :-( I haven't found a spec for the rca 61061 yet but some one indicates that 2n3440 can be used so I will try that info. not sure what I am actually looking for.

[petehall347]

Re: Crown Amp DC300A - One channel distirted, other good.

look up the specs ..they might be in tolerance running small speakers . i dont have schem open here and my pc is too busy recovering a hard drive . just browsing the net is painful slow

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

could be just the driver transistors powering the speakers . see if they are hot to touch

I "touched" them with a thermal reader... all 4 are running about 28-30C. The opamp is running about 40C. Most other components are seeing 25-27C.

I think they are OK and just doing their normal job... hopefully.

[petehall347]

Re: Crown Amp DC300A - One channel distirted, other good.

could be just the driver transistors powering the speakers . see if they are hot to touch

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

that's an interesting question. I am going by my scope of 1khz input 200-300mv p-p that shows up as 1-2v pp at the speaker outputs. Seems rather meek. :-) Maybe I am not recalling the numbers correctly. I will have to double check. The rail voltages are there as that is always the first thing that I check (+/- ~60).

edit: just checked, .4v p-p input to the main board results in 8+v p-p at the speaker terminal.... so possibly with a 2v p-p input would result maybe in 40 v p-p. "lightly speaking" into possibly a 8ohm @ 1khz (speaker impedance response might be less), 200 "watts" average...maybe given the "grossness" of my "thumb calculation" (forgetting about the 1/2 factor for "AC")

[petehall347]

Re: Crown Amp DC300A - One channel distirted, other good.

i am wondering if the outputs are working . there should be over 600 mv at their bases and rail voltages at the collectors .

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

not that I can detect but then again, I am currently only running it into little speakers.

[petehall347]

Re: Crown Amp DC300A - One channel distirted, other good.

does the main heatsink get warm ?

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

three decimal points shows nothing although during the initial connection of the probe, the meter shows a 10's of mv but they disappear shortly thereafter. Perhaps the meter can't see such low voltages. Having said that, in areas of the main board, it has measured 10's of mv. so I am don't know. I will let it be for now. I am getting pretty good at "cracking it open" so if need be, I will go back in at a later time... maybe. Hope to enjoy some of my JBL sovereign II again. :-)

[petehall347]

Re: Crown Amp DC300A - One channel distirted, other good.

there should be current flowing . it will be in the low mv . could be 5mv or more likely about 10 or 20mv .

[budwich]

Re: Crown Amp DC300A - One channel distirted, other good.

that's the strange thing. I never see any voltage across those .33 resistors on either the positive or negative legs of the outputs. It doesn't matter whether I have no input or constant 1khz input, or measuring AC or DC voltage. Perhaps a meter problem although other voltage measurements seem good / accurate.

[petehall347]

Re: Crown Amp DC300A - One channel distirted, other good.

one thing i do check is voltages across each output transistor emitter resistor to see how the current is being shared .