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Old 10th July 2014, 08:13 PM   #11
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Whaleman.

Twist the wires to the power switch tightly.

jn
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Old 11th July 2014, 12:47 AM   #12
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Quote:
Originally Posted by vzaichenko View Post
Hi Waleman, couple of overall comments...

Second op amp does not make sense. You've set the first stage gain to 1.5, second one - 10, so total gain = 15. You can get exactly the same 15, putting 150K resistor instead of 15K at the first op amp and removing the second one. Less active (and passive) elements - less distortion - better sound. I mean, it's fine to use more elements when there is some purpose for it, but not in this particular case.

I would use regulated supply for a line amp - simple 7809 / 7909 regulator chips (cost nothing, don't require any additional parts) will dramatically improve supply quality.

Wiring needs complete redesign. In such builds I usually use shielded co-axial cables for internal signal connections. You also need to pay attention to grounding scheme - there is a lot of material here on this matter.

Attached is just an example of my 7-channel filter build - dead silent when idle.

Hope this helps

Cheers,
Valery
Thanks folks, I knew I could count on you alls' help and advise. Problem solved!

Valery, you had the answer and I had thought about doing this earlier, but I wanted to see if I could make a go of the two op amps, but no luck, so back to single op amp pre with the 150K feedback resistors Valery suggests, success! You will see them in the pic, they are Dale 1% precision metal film. Other components are Ohmite carbon film input resistors (more organic sound, to my ears at least), Elna Silmic II capacitors, Nichicon power caps, Radio Shack bread board, Comscope Category 6 Teflon wire, etc. The power transformer came from a donor Teac VCR.

Sound is extremely quiet, no hum, buzz, hiss. Look at the specs on this op amp, they are quite good. Gain is very generous and I need it to drive a 5 watt SE EL84 tube amp, so it is up to the task now. For tonight it drives my Gainclone power amp in the pics along with a home brewed DAC. Sound is very pleasing, analogish, and quiet. I used the same op amp at the DAC with a 100K feedback resistor. Single op amp, very analog sounding, try it.

I will update the schematic and upload for someone to try it and consider you all's (moschfet) tips on wiring for the next box, this one is dead quiet and my speakers will reveal any noise no matter how faint.

Thanks again, pics of the unit in action, very pleasing.
Attached Images
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File Type: jpg DSC00008.jpg (244.2 KB, 130 views)
File Type: jpg DSC00001.JPG (819.6 KB, 136 views)
File Type: jpg DSC00002.jpg (215.1 KB, 133 views)
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Last edited by whaleman; 11th July 2014 at 12:52 AM.
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Old 11th July 2014, 03:23 AM   #13
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Cool
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Old 11th July 2014, 03:37 AM   #14
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Why do you need a gain of 176? That's mic preamp gain. I run a gain of 200 (46 dB) for my AKG condenser mics. I can't imagine what line level device needs that kind of gain.

What are you trying to do?

G
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Old 11th July 2014, 04:28 AM   #15
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Quote:
Originally Posted by stratus46 View Post
Why do you need a gain of 176? That's mic preamp gain. I run a gain of 200 (46 dB) for my AKG condenser mics. I can't imagine what line level device needs that kind of gain.

What are you trying to do?

G
How did you calculate 176? It's just 15 in fact.

Cheers,
Valery
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Old 11th July 2014, 08:34 AM   #16
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Originally Posted by vzaichenko View Post
How did you calculate 176? It's just 15 in fact.

Cheers,
Valery
Brain fade. The original post 1 drawing was 15x10 -- 150 but the brain fade was inverting vs non inverting - 16x11. Then in post 7 gain was backed off to 15 - a bit high for my taste but in the ballpark.

For line level I prefer more headroom and would go to the edge on the power supplies - whatever the manufacturer says for max - split 15 to 17 Volt rails for the LME49720. I'd likely run the gain between 2 and 5.

G
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Old 11th July 2014, 10:15 AM   #17
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Quote:
Originally Posted by stratus46 View Post
Brain fade. The original post 1 drawing was 15x10 -- 150 but the brain fade was inverting vs non inverting - 16x11. Then in post 7 gain was backed off to 15 - a bit high for my taste but in the ballpark.

For line level I prefer more headroom and would go to the edge on the power supplies - whatever the manufacturer says for max - split 15 to 17 Volt rails for the LME49720. I'd likely run the gain between 2 and 5.

G
I agree - I would also go for higher rails
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Old 11th July 2014, 10:33 AM   #18
AndrewT is offline AndrewT  Scotland
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I can see that each input has a twisted pair.
I can also see that all the RCA Barrels/Returns are interconnected.
That interconnection then goes off to somewhere else.

That then includes an enormous set (multiple) of BIG LOOP AREAs.
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Old 11th July 2014, 10:38 AM   #19
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by stratus46 View Post
Why do you need a gain of 176? That's mic preamp gain. I run a gain of 200 (46 dB) for my AKG condenser mics. I can't imagine what line level device needs that kind of gain.

What are you trying to do?

G
Quote:
Originally Posted by vzaichenko View Post
How did you calculate 176? It's just 15 in fact.

Cheers,
Valery
Quote:
Originally Posted by stratus46 View Post
Brain fade. The original post 1 drawing was 15x10 -- 150 but the brain fade was inverting vs non inverting - 16x11. Then in post 7 gain was backed off to 15 - a bit high for my taste but in the ballpark.

For line level I prefer more headroom and would go to the edge on the power supplies - whatever the manufacturer says for max - split 15 to 17 Volt rails for the LME49720. I'd likely run the gain between 2 and 5.

G
The first stage is 1.5times
The second stage is 10times
The total is 15times (+23.5dB)
That is enormous for a line level gain stage.

Many builders manage with 1times and a few have a requirement for 2times and/or 4times.

I have suggested that a no gain Buffer be augmented with a switchable 2x and 4x for very low line level signals. Giving +0db, +6dB or +12dB as the three options.

What is the gain and/or sensitivity of the amplifier?
What is the sensitivity of the speaker?
These two parameters determine the gain required to reach absolute maximum signal input to the amplifier.
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Last edited by AndrewT; 11th July 2014 at 10:43 AM.
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Old 11th July 2014, 10:41 AM   #20
AndrewT is offline AndrewT  Scotland
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The big capacitors at the back panel has long lengths of single wire.
These should be twisted with the other half of the signal wiring.
You have used twisted pairs a lot. Continue with this for EVERY set of Flow and Return Pairs.
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