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A Very Compact Hybrid Amp - Page 71

post #1051 of 2201
4/30/09 at 3:21pm
Quote:
Originally Posted by adamus View Post
how do crds work, in my simple mind it will limit the current is over 2ma, myvoltages suggest there is less than 2ma going through it..... bad science from me there!
http://www.centralsemi.com/PDFs/sele...t_is_a_cld.pdf
http://www.centralsemi.com/PDFs/prod...N5283-5314.pdf
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post #1052 of 2201
4/30/09 at 5:26pm
Ok, i just tried an 11k resistor in place of the CRD..... and no joy.

the servo must be doing the wrong thing. This suggests to me that the crd is ok.
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post #1053 of 2201
4/30/09 at 11:34pm
Thread Starter 
Adamus, I know that you have checked and checked, but maybe it's time for another set of eyes. There is simply something wrong in the components or board traces.

You voltage measurements on the opamp are:

1= 0
2=2.9
3=2.3
4=0
5=0
6=3.4
7=24
8=0

Pin 3 is the reference input and is the correct voltage. Pin 2 is the sample voltage from the plate divided down by the resistor ratio (1M/30k). It is more positive than pin 3. Since the opamp is inverting the output voltage of the opamp must go negative with respect to the reference. But the O/P, Pin 6, is at 3.4V.

It is almost as though the traces on your board are wired to make the opamp non-inverting. But, of course, this is impossible. So there has to be something else wrong. You say this is the right channel?

The only other possibility is that the opamp is oscillating in your particular setup. Do you have a scope?
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post #1054 of 2201
5/1/09 at 12:02am
Quote:
Originally Posted by smeggy View Post
Until I get more time, this $4.50 rat shack plastic box will have to do
It actually looks nice! And if it does the job, that's all that matters
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post #1055 of 2201
5/1/09 at 12:11am
I think it looks nice too. I think the opening for the tube could be a bit bigger, looks awful close to the plastic.
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post #1056 of 2201
5/1/09 at 1:35am
I may open the tube hole a little but it's a temporary housing. There is about 2mm all around the tube and the plastic doesn't seem bothered by the heat at all. I's been on for hours on end with no problem. It feels like it runs pretty cool considering. The metal cased one got really hot, this one, with much greater ventillation (1" hole in the back too) dissipates heat very quickly and the case only gets luke warm.

I was quite surprised at how well it allows cooling.
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post #1057 of 2201
5/1/09 at 3:08am
Quote:
Originally Posted by runeight View Post
Adamus, I know that you have checked and checked, but maybe it's time for another set of eyes. There is simply something wrong in the components or board traces.

You voltage measurements on the opamp are:

1= 0
2=2.9
3=2.3
4=0
5=0
6=3.4
7=24
8=0

Pin 3 is the reference input and is the correct voltage. Pin 2 is the sample voltage from the plate divided down by the resistor ratio (1M/30k). It is more positive than pin 3. Since the opamp is inverting the output voltage of the opamp must go negative with respect to the reference. But the O/P, Pin 6, is at 3.4V.

It is almost as though the traces on your board are wired to make the opamp non-inverting. But, of course, this is impossible. So there has to be something else wrong. You say this is the right channel?

The only other possibility is that the opamp is oscillating in your particular setup. Do you have a scope?
I do have a scope, wht shall i test (i.e. which pins with respect to what?).

I even traced the schematic for compentant values..... they are all fine. maybe this is a trace issue, but ohming out the circuit suggets its ok.

could a bad cap do this?

its the left channel by the way.
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post #1058 of 2201
5/1/09 at 3:25am
closeup of the suspect area
LL
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post #1059 of 2201
5/1/09 at 3:28am
Quote:
Originally Posted by adamus View Post
closeup of the suspect area
Man I hope you get it going soon.
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post #1060 of 2201
5/1/09 at 3:30am
Quote:
Originally Posted by olblueyez View Post
Man I hope you get it going soon.
i am in the lovely position of having the bijou to fall back on... not much stress with this one, and i am a bit of a weirdo and dont mind troubleshooting.
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post #1061 of 2201
5/1/09 at 3:34am
Quote:
Originally Posted by adamus View Post
closeup of the suspect area
Do you have a photo of the underside too? I'll compare it to one of mine and see if I can spot anything.
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post #1062 of 2201
5/1/09 at 3:34am
Quote:
Originally Posted by adamus View Post
i am in the lovely position of having the bijou to fall back on... not much stress with this one, and i am a bit of a weirdo and dont mind troubleshooting.
Good attitude! Somebody tell him how to fix this thing, its makin me nuts!
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post #1063 of 2201
5/1/09 at 3:36am
whatever is wrong does seem baffling, especially to people like me who don't understand how any of this stuff works anyway. Good that you enjoy troubleshooting. It's a shame you're forced to listen to that other sucky amp until this is fixed... I feel your pain

hehe

talking about Cavalli amps, my EHHA kit arrives tomorrow Yippee!!
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post #1064 of 2201
5/1/09 at 3:45am
underside, with the temporary 11k resistor in place.
LL
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post #1065 of 2201
5/1/09 at 6:33am
Thread Starter 
Quote:
Originally Posted by adamus View Post
I do have a scope, wht shall i test (i.e. which pins with respect to what?).

I even traced the schematic for compentant values..... they are all fine. maybe this is a trace issue, but ohming out the circuit suggets its ok.

could a bad cap do this?

its the left channel by the way.
Look at pins 2,3, and 6 for oscillation.
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