| Buhl |
Hello
Having assembled my god knows what number gainclone, I find it to behave strange - that is I have 25 volts on the output og leg no.3 - I have double, triple and quadruple checked everything.
Both channels behave this way.
Any suggestions ?- blown chips ? anything ?
Cheers !
Buhl - who's getting more grey hair than I should..... |
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| Leolabs |
| Single supply or dual supply??? |
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| Nuuk |
Buhl, I have also got quite a few successfully completed GC's under my belt but I started making a paralelled LM3875 and found that I had 25 volts on the output (37 volt rails). I separated both sections and found that they also both have 25 votls on the output.
I have been over this amp I don't know how many times and cannot find anything wrong so I too would welcome any suggestions! :xeye: |
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| Buhl |
Dual supply, 18-0-18 vac supply, 25 volts rectrified - one rec. bridge / channel - 25volt caps (mabye cutting it close, but they are good so i would like to use them.
Cheers !
Buhl |
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| Nuuk |
| So you are getting the full voltage on the output and I am getting 25 volts from 37 volt rails! Even more mysterious! ;) |
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| Buhl |
| exactly - 25 volts in and 25 volts out - nice equation..... |
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| Nordic |
| Which at least in theory = a dead short... oh well glad to see I'm not the only one in chipamp hell this weekend. At the rate I'm loosing hair graying is not going to be a big problem... |
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| Shigeko |
| I've heard you can have that problem if you dont have a 47k Resistor to ground behind your dc filter Capacitor at the input. And I had the problem because the negative Input was connected to the wrong side of the 20k negative feedback Resistor... |
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| Buhl |
Yehaa !
Thanx for helping me turn the magnifying glass in the rigth direction - I had looked only at the amp board again and again, and found no errors, turns out I had forgot to attact signal ground to star ground with a lead from the volume pot, hence no resistor from signal input to ground....works like a charm now !
By the way, the Elna Cerafine caps i use in the PSU(1000uF/25V) is a lot better than the "standard" panasonic FC caps to my ears - with the pana caps the highs got a little sharp og edgy, now they are detailed and not straining to listen to - well worth their relativly low price I think.
Thank you!
Cheers !
Hans |
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| CarlosT |
| When everyone talk about DC rail voltage, is that measured between the V+ and PGN+ and not V+ and V-? |
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| Buhl |
That can be understood in two ways I think - I think of it as the voltage of the positive supply, that is between + and 0 - but the negative side will have the same value (should have).
So when I say 25 volts, you "could" say that the total supply is 50 volts(measured over + and -), but I think that most people will say that a 25-0-25 volt DC supply is a 25 volt supply.
Cheers !
Hans |
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