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 Line level stereo output on Model 1 Genesis (using op amps, not CXA1034)

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Grambo

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PostSubject: Line level stereo output on Model 1 Genesis (using op amps, not CXA1034)   Fri Mar 29, 2013 1:01 am

So, before frying my VA6 Model 1 Genesis yesterday (that's another story involving an unrelated mod) I was attempting a stereo line-out modification that uses the 2nd channel of the already on board LM358N op amp. The LM358 boasts a minuscule 0.02% THD as opposed to the CXA1034's 10%.

For the life of me, I can't figure out how exactly how they've wired the thing... pin 3 (Ch1 inverting input) appears to trace nowhere, while pin 5 (Ch2 non-inverting input) travels about a mile around the console visiting everywhere it can find. confused No matter how much I scratched my head, I couldn't seem to figure out how to get a decent output from the 2nd op amp channel.

So here's an abridged summary of what I had done to get my working results:
- Added another op amp (I used some quad channel one I had kicking around. I've ordered another LM358 for round 2.)
- Disconnected the right channel input from the original LM358 and hooked it up to the new op amp.
- Connected the non-inverting inputs of both op amps together.
- Connected both outputs up to RCAs.

Here's my (updated) schematic:


Last edited by Grambo on Mon Apr 29, 2013 1:10 am; edited 5 times in total
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Drakon
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PostSubject: Re: Line level stereo output on Model 1 Genesis (using op amps, not CXA1034)   Sun Apr 07, 2013 10:33 pm

Wow I missed this, checking the schematic. So the point of this is...to....amp it louder?
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Grambo

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PostSubject: Re: Line level stereo output on Model 1 Genesis (using op amps, not CXA1034)   Mon Apr 08, 2013 2:43 am

Levels will be probably quite similar, but the noise floor (the amp hiss that's more apparent at quiet volumes) will be most likely be reduced significantly.

I guess there's also the benefit of it being done "properly" as it'll be a consistant volume and leave the headphone circuit untouched.
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Grambo

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PostSubject: Re: Line level stereo output on Model 1 Genesis (using op amps, not CXA1034)   Fri Apr 26, 2013 7:15 pm

Update
Not sure what it is about the LM358, but the 2nd channel doesn't appear to work for me at all.
I just used the 1st channel on the op amp. I've adjusted my schematic accordingly.

Noise floor is super low now and headphone fader no longer adjusts the volume Smile
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PostSubject: Re: Line level stereo output on Model 1 Genesis (using op amps, not CXA1034)   Wed Jun 12, 2013 11:21 pm

Better than anything I can make.  All my experiments with opamps didn't sound right.
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PostSubject: Re: Line level stereo output on Model 1 Genesis (using op amps, not CXA1034)   Thu Jun 13, 2013 9:12 pm

Grambo wrote:
Update
Not sure what it is about the LM358, but the 2nd channel doesn't appear to work for me at all.
I just used the 1st channel on the op amp. I've adjusted my schematic accordingly.

Noise floor is super low now and headphone fader no longer adjusts the volume Smile














ive got to try your circuit, grambo.

 I cant say i like the ccam, although it is clear. i find the low volume level and slight hiss annoying. but a more powerful va5 or va6 would kick serious ass.

heres my ccam with the audio amp added and the volume slider hooked up. im happy to say the volume slider now works although the amp doesnt. It cuts out when i turn it up. These were taken before i moved the ccam board to
that empty spot with the ground plane.

Im also in the process of installing a .1uf cap and 20k dual input pot where the filter caps go, so i can tune the highs and lows.

" />

" />

btw, the ccam works awesome. Its just not loud enough. that was the purpouse of installing this 3w amplifier.

i think someone before made a comment that im dealing with a non-biased output and the amp is looking for a biased one or vice versa.

I didnt understand it. ive never run into an analog output that couldnt be amped, but it doesnt mean there isnt one.

how would i give the amp what it is looking for?
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